THE
STANDARDIZATION
AND
INTERPRETATION
OF
SUBMAXIMAL
AND
MAXIMAL
TESTS OF
WORKING
CAPACITY
Henry L. Taylor, Ph.D., Yang Wang, M.D., Loring RoweIl,* Ph.D.,
and Gunnar Blomqvist,t M.D.
The Laboratory of Physiological Hygiene and the Department of Medicine, The University of Minnesota
WORK RATE IA*ZCRME
* PRESENT ADDRESS: The Department of Medicine University of Washington Medical School, Seattle, Washington.
fPRESENT ADDRESS: The Department of Medicine, Karolinska Institutet at Serafimerlasarettet,
Stock-holm, Sweden.
PEDIATRICS, October, Part II, 1963
703
I
T is generally agreed by work physiolo-gists that the capacity to perform longcontinued physical work in a temperate
en-vironment is related to the capacity of the
cardiovascular respiratory system to deliver oxygen to the muscles (the maximal oxygen
intake).1’2’3 Since under carefully standard-ized conditions in selected homogeneous
groups the pulse rate at submaximal levels of work is systematically related to the
maximal oxygen intake,4’5 it follows that the
capacity to perform physical work can be estimated from study of the pulse rate at
Ftc. 1. Schematic representation of pulse-rate!
work-rate curves in sedentary (upper curves) and
well-conditioned (lower curves) college men. The
figures on the abscissa are actual 02 intakes in
liters per minute. The rate of work could be
sub-stituted. The pulse rate response to a standard task (in this case requiring 2 liters of 02 per minute)
is illustrated by the dotted lines on the left. Work-ing to a specific pulse rate (in this case 180 beats per minute) and measuring the work required to
produce this pulse rate is illustrated by the dotted lines on the right.
submaximal work levels. Work physiologists have employed for this purpose, the re-sponse of the pulse rate to a standard task6’7 or have measured the amount of
work required to elevate the pulse rate to predetermined pulse levels.8’9 Work
physi-ologists have been preoccupied with the
estimation of the capacity to do physical work. But it should not be overlooked that
the maximal oxygen intake, considered to be the most effective measure of the
capac-ity to perform aerobic work is also, in the absence of pulmonary pathology, directly related to cardiac capacity. This procedure has been used for this purpose by a number
of investigators interested in several aspects of cardiovascular performance. Age,
val-vular heart disease,12,13 congestive failure,14 repair of damaged valves’s and a variety of
debilitating conditions have been examined
in this way.
Pulse Rate Tests
PART I
For the purposes of this discussion, it is
useful to examine initially the basic rela-tionships that are to be discussed here. Fig-ure 1 is a schematic representation of the
relationship between the rate of work and the pulse rate in an ambient temperature
of 75 to 80#{176}F.Two types of individuals are represented, i.e., the athlete and the seden-tary male in the third decade of life.
The well conditioned man has a lower pulse rate at rest and at all levels of work.
Ftc. 2. The pulse-rate/02-consumption relationship
of one Bantu working in cool conditions and in hot humid conditions after acclimatization. Multiple determiations made it possible to provide the
standard errors of estimate shown on the graph (re-produced by permission from paper of Williams,
et at.”).
load the pulse rate levels off and does not change with increasing load of work. The well conditioned individual then can push himself to much higher work loads. Under
these conditions, both men reach their maximal pulse rate before a maximal work load is attained.
In the case of the investigator who elects
to study the response to a standard task, figure one illustrates the generally ac-cepted fact that a.) the well conditioned man will have a lower pulse rate at work,
and b.) the ability to discriminate between
individuals will be greater at higher work loads. On the other hand, figure one also shows that the quantity of work which pro-duces a given pulse rate level will be larger in the well conditioned individual than in the sedentary subject and this is the basis of the procedures used by Wahlund8 and
Balke.9
It might appear that the two methods are
essentially redundant. But in practice it is
impossible to predict the difference in the
actual amount of work represented by a
difference in work pulse rate response to a
standard task in two individuals. This is true because the slope of the work-rate
/pulse-rate curve is different for each in-dividual. Figure one is based in part on data obtained from the same group before
and after training. Accordingly if actual work capacity of an individual patient is
desired the procedures of Wahlund or Balke are the methods of choice.
It should be clearly understood that the procedure employed by Wahlund specifies
that the subject should be put through
in-creasing work loads until the work pulse
rate reaches 170 beats a minute. Balke has
used 180 beats a minute as a cut off point but he also pays attention to changes in
blood pressure, particularly a narrowing pulse pressure, and in some instances
changes in ventilation.
It has been recognized, for many years, that, over a wide range of submaximal pulse rates or submaximal work loads, there is a
large number of physiological conditions which will alter the work pulse rate.
Ac-cordingly, if one is interested in work ca-pacity, rigid standardization is necessary if the results of the procedure are to be interpreted in terms of work capacity.
Among those physiological and experi-mental errors which in general tend to dis-place the pulse-rate/work-rate curve to the left resulting in an underestimation of work
capacity, one can mention temperature, meals, time of day, fatigue, the mechanical efficiency of work (skill) associated with the work task, and the test protocol itself which
will have effects and consequences which the investigator should not overlook. Fi-nally, there are problems of stress and
emotion which have not been entirely worked out.
ENVIRONMENTAL TEMPERATURES.
Work-ing in a hot environment will move the pulse-rate/work-rate curve to the left. This effect is demonstrated in Figure 2 taken from the work of Williams, et al.17 It is clear that
maximal work levels but that the maximal
pulse rate was not altered. This means that it is possible to set the criteria of work performed (i.e., pulse rate) at any level on
the curve up to maximal and if one meas-ures the work performed at the point at which the maximal pulse is attained (or at any lower level), the work performance will be underestimated unless one is interested
only in work performance under the par-ticular heat load employed. The data of Williams, et al.’ were worked out on 3 Bantus who were well acclimatized to heat.
Rowell and his collaboratorsl8 studied men who were unacclimatized to high tempera-tures and showed that the same phenomena
existed but that in the unacclimatized men the maximal pulse rate was reached at a lower level of work and that the oxygen intake in liters/mm can increase as much as 2 liters of oxygen with no change in the
maximal pulse rate. In men of this type the maximal pulse did not change as the result of exposure to high temperature. It was
further shown that work in 65#{176}Ftempera-ture displaced the curve to the right from that found in ambient temperatures of 78#{176}F.
Since there are large differences between individuals in the cardiovascular response to warm or hot temperatures, it can be suggested that pulse rate differences ob-tained in really cool environments, i.e.
60-65#{176}Fwill result in discrimination of differ-ences between individuals in which inter-fering effects of heat dissipation will be
minimized.
EFFECTS OF AN 8 Houn Siuvr OF HARD PHYSICAL WoRK AND Viconous ATHLETIC EXERCISE. Careful investigation19 carried on at the site of lumbering operations demon-strated that when workers in the lumber industry engaged in 8 hours of hard physi-cal work in the forest a change in the pulse rate response to a standardized task on the
bicycle ergometer occurred between going to work in the morning and returning from work in the afternoon. Four levels of
oxy-gen consumption were tested. In an ex-treme case, the pulse rate rose from 102 beats per minute at 1.5 liters of 02
con-sumption before breakfast to 152 before dinner. In all cases the pulse rate/work rate
curve was displaced to the left. The maxi-mal oxygen intake was not studied. It was
found that a walk of 7 kilometers did not produce a displacement but that a walk of
15 kilometers did. The author did not
clarify the question of time or rate of work vs total work in this study. There is reason to believe that if an individual spends 8 hours in the upright posture, the pulse rate/ work rate curve will be displaced to the left.
EFFECTS OF MEALS. The effect of meals on the circulation at rest has been
exten-sively tu92’ and it is well known that meals increase the pulse rate and the
cardiac output. Systematic work on the
effects of meals on the work pulse rate is not common. Lundgre& has published the effects of a breakfast on the work pulse rate
of his lumberjacks. At an 02 consumption of one liter a minute the pulse rate differ-ence was found to be 18 beats per minute. Unpublished results from the Laboratory of
Physiological Hygiene show that at an oxy-gen intake of 2 liters per minute, a 1000
calorie meal increases the work pulse rate from 132 to 144 beats per minute (mean of 12 men) and that this effect has not disap-peared completely at the end of one hour and a half. Information on the effects of
meals on work pulse rates produced by a wide range of work loads and by different size meals is lacking so that it is not
pos-sible to extrapolate this information to max-imal or near maximal pulse rates.
Loss OF SLEEP. It is interesting that
fatigue induced by lack of sleep has no effect on the work pulse rate. During the
second world war, the staff of the Labora-tory of Physiological Hygiene investigated the effects of loss of sleep on performance.22
Twelve conscientious objectors were kept from sleeping for 62 hours. The men had
been walking for one hour a day on the treadmill at 10% and 3.5 m/h before the ex-periment started. This activity was broken down into 4 15-minute periods evenly
TABLE I
SIrrING AND STANDING PulsE RATES
Data from Brouha and Heath, l943.
APPREHENSION
PULSE RATES
One Suhjec/
/6o
/5O
/3O
‘J
/z i 4. 6
Periods of
F/r5/ Day Condition iS Extremes % above 100
Medical Exam
Siting 73 48-105 2.4
Standing 82 54-182 12.4
Before run
Sitting 90 55-136 26.4
Standing 123 85-165 93.7
men took part in psychological tests, were
allowed to sit in chairs, watch television, etc. No change occurred in the work pulse rate or 02 consumption.
Tii TYPE OF WORK TASK AND THE
ME-CHANICAL Emaiic. Submaximal work
tests are currently being carried out most frequently with the use of the treadmill or the bicycle ergometer. Under ideal circum-stances, one would like to choose a work
task which all subjects could perform with the same degree of skill, thus imposing the same work load on each individual. In-dividual differences in skill result in
meas-urable differences in mechanical efficiency. This is particularly true of running (Dill,
et
al.23). But walking is another matter as the difference between individuals in cc of02 intake per kilogram of body weight is small. The standard deviation of the differ-ences attributed to individuals is 4% of the
mean at an oxygen intake of approximately 2 liters.24 Several repetitions of this proce-dure over a period of time result in either no change in oxygen intake2 or in a
de-crease of less than 5 per cent.25 In areas where bicycles are used by a large fraction of the population the difference between individuals in the 02 requirement adjusted for weight is small.28 But it is not clear that
this will be so in areas where bicycle riding
is not popular. Furthermore, ample
evi-dence exists that repeated bouts of work on the bicycle can result in a substantial
change in mechanical efficiency.27
EFFECTS OF EMOTION. All physiologists who employ submaximal work tests make
the tacit but unstated assumption that the
stress of work overrides any effect of emo-tion on the behavior of the work and/or re-covery pulse.
Evidence that this may be the case was presented by Brouha and Heath28 who com-pared the variability of the resting pulse rate in young men during a medical
ex-amination with the variability found in the resting pulse rate of the same men just
prior to undertaking the Harvard Fitness Test, i.e., running to exhaustion at 7 miles per hour on 8.6% grade on the motor driven
treadmill. The authors then present evi-dence that the recovery pulse after
exhaust-ing exercise is quite stable. While one can express some reservations about this par-ticular presentation it is a fact that work
and recovery pulse rates are stable and do not show the kind of variability that the prework rates do. Indeed, the work pulse
rate may be lower than the prework rate. In 1944 in connection with studies of physical activity and diet, Civilian Public Service made available 8 men who volun-teered for service as guinea pigs. These men
arrived at the Laboratory by bus about
8:00 A.M. one morning without breakfast. They were taken directly to the locker room
EFFECT OF
ON WOR/
Averc9e. 7-5u4ec/s
I 3 4 c 6
We1,4in9
5econd zJav
Fic. 3. The unusual response of the work pulse
rate in one subject compared to the expected per
formance of 7 men tested at the same time. All
men walked for 6 periods of 10 minutes separated
by a 10 minute rest period in the morning without
breakfast in an ambient temperature of 78#{176}F. dur-ing each of the first two days of exposure to tread-mill walking. (Original data from the Laboratory
TABLE II
WORK PULSE RATES OF ATHLETES AND NON-ATHLETES BEFORE AND AFrER SYSTEMATIC PROCEDURAL ADAPTATION. PUlSE RATES COUNTED AFFER A 5 MINUTE WALK ON A MOTOR
DRIVEN TREADMILL AT 3.5 M/H ON A 10% GRADE
Non-Athletes Athletes
.
Sublect First After AJAZP.
.
Sublect First Tri
After Adapt.
R.M. 179 175 -4 Fi 151 123 28*
C.H. 154 147 -7 J,J 139 116
J.H. 151 142 -9 Gi 142 130 -1
H.J. 147 153 +6 C.B. 137 137 +2
J.G. 190 181 -9 C.P. 121 121 0
D.A. 160 145 D.H.
R.R.
128 137
125 138
-3 +1
Mean 163.5 157.2 -6.3 136.4 127.1 -9.3
* Standard error of measurement 6.8 beats/minute.
Asterisk indicates a decrement >2 standard errors.
and told to put on shorts, T-shirts and sneakers. The men were then assigned the task of walking on the treadmill at 3.5 m/h on a 10 per cent grade for 6 10-minute
pe-nods before lunch. The treadmill was large enough so that 4 men could walk on it at a time and by giving everyone a 10 minute rest it was possible to have a man getting
off and another man getting on every two minutes. Everything went well until at the end of the third period when one of the
men stumbled as he got off the mill. The observer caught him by the arm and he did
not fall. It is not known what kind of emo-tion he experienced but there is no ques-tion that whatever it was it affected his pulse rate. The results presented in
Fig-ure 3 show that his work pulse rate rose from 130 beats a minute to the neighbor-hood of 160 beats a minute. Three repeti-tions of the 10 minute walk dmd not change
the pulse rate to any marked degree. The work schedule was repeated the next morn-ing, the subjects working without
break-fast as on the first day. Again, the man who had stumbled had a pulse rate above 150
but this time on successive trials his pulse became lower until on the 5th repetition the
pulse rate again reached 130 beats per min-ute.
This experience which illustrates what
can happen to the work pulse rate when
certain kids of emotion arise was, of course, an accident. The emotion which was cre-ated by the situation was unknown and would be difficult to reproduce. So it was
necessary to set up a different type of ex-periment to examine the matter further.
The usual maneuver employed by a physiologist when he is faced with a
rest-less or excited subject that he wishes to
study under controlled conditions is to re-peat the experiment on several successive
days until excitement is replaced by bore-dom and measurements on successive days
give repeatable results. At this point the effects of emotion, whatever the emotion was, are assumed to have been dissipated.
It was then decided to study athletes and non-athletes in a systematic way to see whether emotional effects could be demon-strated in athletes or non-athletes by this method. The men were recruited and brought into the laboratory as “experi-mental subjects.” They were then told that
they would be required to run on a grade which would elicit a maximal oxygen in-take and that this would be a severe test of their capacity to perform exhausting work.
A preliminary warm up task was carried out by having the subjects walk at 3.5 m/h on a 10% grade for 15 minutes. This
708
TABLE III
EFFECTS OF CATHETER PROCEDURES ON PULSE RATES DURING WORK BEFORE AND AFrER A
CONDITION-ING PROGRAM IN A GROUP OF 7 YOUNG MEN
Conditions
Pulse rates at 02 intakes of
Max. 1.0
Liter/mm Liter/mm
Before
normal 113 168 198.7
catheter 114 170 195.5
After
normal 98 137 187.5
catheter 105 146 187.5
change on successive days. The results in 7 athletes and 6 non-athletes are presented in
Table II. When men walk every day on the treadmill under controlled environ-mental conditions (T = 78 ± 2#{176}F)which were the conditions employed here, the
standard error of measurement in a test retest situation is 6.8 beats per minute.29 By
this criteria, 2 of the athletes and 1 non-athlete had changes that were larger than
2 standard deviations. A third athlete had a change that was just short of 2 standard deviations. It appears likely that the situa-tion was a greater challenge to the athletes
than to the non-athletes. None of the thir-teen men studied had significant positive
pulse rate increments with repeated ob-servations. The effects of increased skill in walking on the motor driven treadmill are
small compared with the results reported here. As mentioned above the effects of repeated bouts of treadmill walking at 3.5 m/h on a 10 per cent grade are either not measurable or less than 5 per cent. A 5 per cent decrease in oxygen consumption at the general level of 2 liters a minute will produce a change in pulse rate of 3.0 to 3.5 beats per minute. It is evident that the
initial contact with a work test can result in significant increases in submaximal work
pulse rate. Furthermore, there is no reliable method of recognizing these effects except by the time consuming one of repeating the procedure.
Direct evidence on the effects of
emo-tion on the maximal pulse rate is generally lacking in the literature but recent experi-ence with the use of venous and arterial
catheters during both submaximal and max-imal work throws some light on this
ques-tion.
Measurements of pulse rate and 02 con-sumption were made in seven clinically
normal young men at 4 levels of submaxi-mal work, i.e., at 3.0 rn/h on a zero per cent
grade and at 3.5 m.p.h. on grades of 5, 7.5 and 10 per cent and in addition a work level was used which had been demon-strated to elicit a maximal oxygen
consump-lion. The pulse rates in submaximal work were linearly related to oxygen
consump-tion so that it was possible to interpolate the values of the pulse rate at 1 L. and 2 L.
of 02 consumption per minute. Compari-Sons with and without catheters were made before and after an intensive conditioning program that lasted for 3 months. The re-sults are presented in Table III.
It is gratifying to note that on the initial
occasion that in spite of the fact that work
was performed with a catheter in the su-perior vena cava and another one in the brachial artery there was virtually no dif-ference between the pulse rates obtained
under carefully controlled conditions with-out catheters and those with catheters. However, a somewhat different result was obtained at the end of the period of physical
conditioning. Under these conditions, the pulse rates with the catheter were sub-stantially higher than those under standard-ized conditions. It is of real interest that the maximal pulse rate was not affected by this procedure.
The maximal pulse rate then appears to be less sensitive to the stress of working with venous and arterial catheters in place than the submaximal pulse rates. It is clear
that the submaxirnal pulse rate-work rate relationship as illustrated in figure one can be displaced to the left without an im-portant change in the maximal pulse rate. This is the same kind of situation discussed
fol-lows that physiological responses produced
by stress (emotion?) can arise where if one wishes to measure the work necessary to increase the work pulse to a given level, the estimate of the work capacity will be
low. It is not known whether the condi-tioning process made the pulse rate more sensitive to stress such as that imposed by the catheters or whether the repetition of the procedure somehow created an
emo-tional situation which was reflected in the change in pulse rate.
The use of a specific cut-off or end point
based on pulse rates in work capacity tests such as those of Wahiund or Balke would make it impossible to identify emotional effects by any other means than repetition on successive days. It might be possible to argue by analogy, with the experience
ob-tained in high temperature, that if in a
specific individual the pulse rate end point was ignored and a further increase in load was examined, a further increase in oxygen
consumption would follow with only a small increase in pulse rate. In the presence of adequate control of other factors, there would be a reasonable justification for
sug-gesting that factors other than those con-trolled had produced an unusual increase in pulse rate and if the subject showed
signs of being tense, etc., it would be likely that emotion and/or stress of some kind was responsible.
Finally, the reader should recognize that most of the data reported above are based on either intermittent work loading or re-sponse to a standard task. Most of the
pulse-rate/work-rate curves reported by Balke and his collaborators fail to show the plateau phenomenon that Wyndham
or Rowell, et al.18 have observed. It is true, however, that this has not been tested in
Balke’s procedure as carefully as one might like.
PART II
The Oxygen Consumption
1. SUBMAXIMAL WORK. It is generally
agreed that the oxygen consumption during submaximal work on a bicycle ergometer or
a motor driven treadmill can be predicted with reasonable accuracy if the weight of
the subject is known and the rate of work is known and maintained constant in the
case of the bicycle ergometer, and grade and speed are known in the case of motor-driven 21, 26 Oxygen consumption
can be predicted on the motor-driven
tread-mill regardless of whether the investigator uses a procedure which calls for intermit-tent use of a standardized time of work
with adequate rest periods24 or whether a
continuous work period is used with a method of increasing the work level by a constant increment at stated time intervals.
it is constancy of energy requirement in well standardized tasks that makes the measurement of blood pressure and pulse rate at the end of the performance of a
fixed standardized task a practical matter. 2. THE MAXIMAL OXYGEN IrA. The maximal oxygen intake (Max V02) can be
determined in several ways. In healthy, well motivated males, Dill30 and Robinson’ have found that it is satisfactory simply to
ask the subject to run on the motor-driven treadmill at a rate which will exhaust him in 5 minutes or less. Astrand26 has felt that
an objective measure of whether or not the subject has pushed himself to the point
where a large oxygen debt has been ac-cumulated is important and this author has used a post exercise concentration of lac-tate in the blood of 100 mgm per 100 ml. of blood as the criterion for this. Taylor, Buskirk, and Henschel have used the dem-onstration of an oxygen intake plateau with
increasing increments of work as an index of the attainment of Max VO2.
The method employed by these investi-gators is illustrated in Figures 4 and 5. The basic procedure is a 3 minute run at 7 miles per hour. The oxygen consumption is measured during the time period shown
in Figure 4. Figure 5 illustrates what hap-pens when this procedure is begun at zero
grade and repeated at grades that are 2.5 per cent higher with rest intervals which
ACCELERATION OF OXYGEN INTAKE
I”
a
*
a
0
a.
ROUTINE
SAMPLE
OF EXPIRED
AIR
DATA OF OINSDA I3I
4
TIME OF RUN IM MINUTES AT 7 MILES PER HOUR
MAXIMAL 02 INTAKE AND HEART RATE IN DIFFERENT TYPES OF WORK. THE SAME INDIVIDUALS TOOK
PART IN ALL THE TESTS. (MODIFIED FROM ASTRAND AND SALTIND)
0.0 25 5.0 75 10.0 125 0.0 2.5 5.0 73 10.0
0.0 23 5.0 75 10.0 123 0.0 25 5.0 73 10.0
TREADMILL GRADE IN PER CENT
FIG. 5. Oxygen intakes of 4 individuals running at 7 miles an hour on the indicated grade. Note the plateau when the Max VO, is reached. (Reproduced by permission from Taylor, Buskirk and Henchel.’)
to Taylor, Buskirk and
Fic. 4. The oxygen intake plotted against time of running at 7 miles an hour on a grade calculated to elicit a Max V02. The time of obtaining a sample of expired air which is used for the measurement
of Max VO, is illustrated by the dotted lines (modi-from Robinson, S.”).
reached beyond which further increases in work load fail to increase the oxygen
in-take. It is clear that at this point the cardiac output must be close to maximal and the
A-VO2 difference must also be very close to the maximum attainable under condi-tions of physical activity. Mitchell, et al.32
have provided data on cardiac output and
A-VO2 differences under these specific con-ditions. At Max VO2 the cardiac output was
23.4 ± 5.5 1/m with A-VO, difference 14.3 ± 2, 5 ml of 02 per 100 ml of blood.
It is important to recognize the
conch-tions established by this procedure. Objec-tive evidence is provided that the subject has the motivation to push himself to attain
Max VO2. The rate of energy expenditure far exceeds the oxygen supplied the
mus-cles. Since the oxygen debt is large at this rate of work it is immaterial whether the individual has great skill in running on the
treadmill or whether he is inept. The me-chanical efficiency of work is unlikely to
affect the value of Max VO2.
There has been some question whether the Max VO2 was specific for each type of exercise or whether it was a relatively
con-stant value which would be reached if enough muscles were employed in the task to require a maximal effort of the cardio-vascular pulmonary system. Astrand and
Saltin34 have recently provided data on this point. The results are summarized in Table
IV.
The difference between (1) cycling, cy-cling with arms and legs,(2)
cycling and running, (3) cycling and skiing are all 5% or less. On the other hand, cycling in asupine position, swimming and operating the ergometer with arms alone all produced markedly lower Max V02. Maximal pulse rates for the several types of work were in general similar. The range of the mean of 6
TABLE IV
Type of Activity
N Mean
liters/mm
Pulse ratsa at maximal
work
Cycingr 5 4.47 190.6
Cycling with
arms and legs 5 4.48 189.6
Running 5 4.69 189.4
Running* 5 4.54
-Skiing 5 4.48 193.6
Cycling supine 5 3.85 181.4
Cycling 3 4.66 190
Cranking 3 3.27 177
* Procedure according
FIG. 6. The rate of increase in 0 intake at different rates of work on a bicycle ergometer. The rate of work in kilogram meters is given above the arrow which indicates the point at which the subject stopped from exhaustion. (Reproduced
by permission from Astrand and Saltin’.)
subjects was 10 beats/mm. These same authors studied the effect of time and rate of work. The subject worked at a rate which was calculated to produce an oxygen
consumption of 55% of maximal. At a spe-cific time a new rate of work started (as marked in the graph) and continued until
the subject was exhausted. The data pre-sented in Figure 6 are representative of the information obtained on one female and four male subjects. The heavier the rate of work, the faster the oxygen intake increases.
Figure 4 illustrates the point that several rates of work can be chosen. Max V02 can be attained with rates of work that result in exhaustion in as litfie as one and one half minutes or as much as 8 minutes.
The data of Astrand and Saltin make it clear that the Max V02 can be compared with precision from one laboratory to
an-other and that a wide variety of work tasks, rates of work and times of work are avail-able to the investigator. Furthermore,
in-vestigators working in different laboratories
obtain results in the test-retest situation which have a standard deviation of the
same order of magnitude. Astrand and Saltin normalized the data by obtaining the difference between the highest value for
any one person and the mean in per cent and then calculating the standard
devia-tion. This resulted in standard deviation of 3.1% in the study of Astrand and Saltin,34
3.0% in that of Mitchell, et al.32 and 2.8%
in that of Taylor,
et
al.Both Astrand26 and Taylor, et al.3 have
found that there are some subjects which do not actually demonstrate a clear cut plateau although all subjects show falling
off from the rate of increase of 02 consump-tion with a standard increase in the work load. Wyndham, Ct al. used 4 Bantus and
studied this problem exhaustively. These authors came to the conclusion that the Max V02 is approached asymptotically and
that criteria such as those used by Taylor, et al. can in some cases lead to an under-estimation of Max V02. The mathematical formulation necessary to determine an
asymptote requires careful determination of the point at which the straight line rela-tionship between oxygen consumption and work load no longer holds. This means as
many as 20 to 25 determinations of oxygen consumption and work load for each in-dividual. The work of Wyndham, et al. is
712 STANDARDIZATION OF TESTS
the problem of testing a large number of individuals by actual measurement.
Balke’s9 procedure for measurement of
work capacity can be used as a device for estimating the Max VO2. This consists of asking a man to walk on a motor driven treadmill at 3.5 mph and increasing the grade 1% every minute. If the investigator
wished to examine the work capacity, the subject walks until the pulse rate has
reached 180 beats/mm. But if the investi-gator wishes to obtain the Max V02 and
thus obtain a measure of maximal cardiac capacity (always assuming normal lung
function) the subject walks until he is ex-hausted. Elsewhere in this symposium, Dill
and his colleagues have shown that the values of oxygen intake at exhaustion ob-tained under the conditions employed by
Balke are in good agreement with other methods.
The continuously increasing work load procedure used by Balke has one charac-teristic which is quite different from that of the intermittent work procedures used by Taylor, et al. Wyndham, Ct al. and
Astrand.”26 By using intermittent work loads a plateau of oxygen intake can be established in 60 to 70 per cent of the sub-jects. On the other hand, the plateau phe-nomenon does not appear when several work loads are combined in a single
con-tinuous task. In the procedure used by Balke the subject works for from 15 to 30
minutes before the pulse rate end point of 180 beats per minute is reached. The reason for this difference is not entirely clear but it seems likely that the large internal heat load generated by subjects taking part in the continuous work step up procedure is related to the observed difference.
THE RELATIONSHIP OF BODY DIMENSIONS
TO THE MAXIMAL OXYGEN INTAKE. It has
been recognized for many years that the
Max V02 is a function of body size. Many
investigators have systematically related the observed values of Max V02 to body
weight.2’4’11 It is possible to estimate the fat free body weight from density measure-ments of man35 and since excess body fat
does not take part in the metabolism during exercise it is useful to eliminate this from the reference weight. Buskirk and Taylor36
have shown that the correlation coefficient between Max V02 and body weight was
0.65 while that between Max V02 and fat free body weight was 0.85. It was shown
that a more precise differentiation between athletes and sedentary college students could be made if standards were set up in terms of fat free body weight of normal sedentary young men than if the total body weight were employed as a reference value.
Blood volume can also be used as a ref-erence value.36 Sj#{246}strand37 emphasized the use of total circulating hemoglobin. It has been pointed out that there is a high
cor-relation between blood volume or total cir-culating hemoglobin and body weight.lGls
It seems reasonable to suggest that in the absence of anemia which can markedly re-duce the Max VO2 the determining factors are the dimensions of the heart, blood ves-sels and working muscle mass. If one wishes to make very precise distinction between
men whose body fat varies a great deal, under-water weighing with the calculation of fat free body weight will be an ad-vantage. Otherwise the total body weight is more than adequate as a reference point which one might use to set up standards
for judging individuals.
PHYSIOLOGICAL CoNDrnoNs AND TEST
STANDARDIZATION. It was pointed out earlier
that submaximal work pulse rates can be markedly affected by (a) temperature; (b)
meals; (c) previous activity and the time of
day, and (d) emotion. The Max V02 ap-pears to be relatively free of influence by these factors. Williams, et al.17 have made determinations of the Max VO2 at 97#{176}F wet bulb. The subjects (3 Bantus) were
carefully acclimatized to high temperatures before being studied. These authors found
Max V02 between 62#{176}Fand 78#{176}F,while the decrease at 110#{176}Fwas of the order of
magnitude of 6%. Taylor, Buskirk and Henschel studied the effects of a meal of 750 calories and found no change in Max
v02. It is generally agreed that a warm up walk requiring an oxygen intake of 40 or
50 per cent of Max VO2 will increase the Max V02 by 5% and that such a waem up
is an integral part of the testing procedure. There is little or no information on the
ef-fects of emotion on the Max V02. If the use of catheters for the determination of car-diac output by the dye dilution method can
be regarded as a stress or emotion produc-ing factor or both, it is of interest to note that catheterizing the superior vena cava through the brachial vein and the aortic arch through the brachial artery resulted
in a decrease of 3% before training and 7% after training in the Max V02.
It is clear that the Max VO2 is
consider-ably more stable than the submaximal work pulse rates. It follows from the observations given above that the investigator who chooses to use the Max VO2 does not have
to practice as rigid standardization of con-ditions as the investigator who elects to work with pulse rate oriented testing
proce-dures.
EFFECT OF PHYSIOLOGICAL SmEss. Since
the pediatric cardiologist has a real interest in studying the effectiveness of surgical re-pair of congenital heart lesions and the valvular damage produced by rheumatic fever, the effects of stress associated with
surgery and the malnutrition occasionally seen with disease states is of some direct interest. The effects of bed rest,
dehydra-tion, weight loss through loss of calories or by loss of protein and the development of
anemia are states in which information is available and that might be considered in this connection. Three weeks of bed rest with no weight loss produces a 17% decline
in the Max V02.3’ Experimental malaria40
resulted in a decline of 19% in liters per
minute. A loss of 10% in weight on a 1000
calorie diet resulted in a 10% loss in liters per minute and no change in cc per kg of
body weight.” A 24% loss of weight pro-duced a 43% decline in absolute quantity and a 26% loss in terms of cc per kg of body weight.42 Dehydration without salt loss was
studied in six men eating 1000 calories per day in a moderate environment. The sub-jects were restricted to a water intake of 900 cc for a period of 5 days. Weight loss
was 8.5% about one-half of which was due
to dehydration resulting from an accum-ulated negative water balance of 5 liters,43
Max V02 in these men in the dehydrated
state showed no change in the absolute values and a corresponding increase in
cc/kg. The nitrogen lost in the latter ex-periment was 138 grams. Since surgery and other stress are associated with a nitrogen loss which is independent of caloric bal-ance, it was relevant when it was
dis-covered that dehydration produced by withholding water from men working in a moderate temperature (78#{176}F) resulted in
marked nitrogen loss.
The results of the latter experiment are
of interest then, not only because of the re-sistance to dehydration but also because of
the nitrogen loss produced by stress. It has been demonstrated that well
de-veloped anemia (6-9 grams of hemoglobin per 100 ml of blood) is accompanied by a marked reduction of the Max V0244; mean
of 9 men was found to be 27.9 cc/kg of body weight. However, there appears to be
a fairly wide range of hemoglobin values that do not effect the level of the Max V02.
Rowell and Taylor5 (unpublished work) studied the effects of bleeding on hemoglo-bin concentration Max VO2. The
experi-ments resulted in a decrease in mean hemo-globin values from 15.7 to 13.5 grams per
100 ml of blood eight days after bleeding. The mean decrement in Max VO2 from con-trol to eight days post bleeding was 4%.
Under circumstances in which the sub-ject can exercise by walking every day and one or two times a week run to exhaustion,
the effects of 3 weeks of rest in bed are lost in less than a month; the effects of malaria, in 4 to 6 weeks; the effects of a 24% loss of
TABLE V
MAXIMAL OXYGEN INTAKES IN SELEC-rED GROUPS OF MALE SUBJECTS-AGES 18 TO SO
Subjects N
Max. JO2 cc/kg.
body weight
Mean S.D.
Lash 1 81
Varsity Trackf 5 65.8 ±3.4
College Athletest 15 52.8 ±5.5
Soldiers 13 52.9 ±3.8
College Studentst 39 44.6 ± 5.5
* Reference No. 2.
t Reference No. 36.
Reference No. 41.
These recovery times must be taken with a note of caution. With the exception of
bed rest, and malaria, the subjects main-tamed a moderate level of activity through-out the experimental and recovery periods. It should be noted that the addition of malaria to bed rest doubled the recovery
time although the absolute loss of Max VO2 was not markedly increased.
THE RANGE OF NORMAL VALUES AND
EFFECTS OF PRIOR EXERCISE. Table Number
V gives the range of normal values as
gen-erally encountered in healthy young men. The range of normal values is quite large
from approximately 30 to 81 cc/kg. per minute. It is of considerable interest to examine this range against the changes which can be introduced by such factors as training, high temperature, dehydration,
age, loss of weight and loss of nitrogen. There have been 3 attempts to evaluate the effects of a conditioning program.46’47’48 The results are presented in Table VI. In groups of college males normal values are
approximately 50 cc per kg. of body weight. The increases which resulted from these were 9,47 8.248 and 1.846 cc/kg. or at the most one-fifth of normal range (see Table 5). The effects of conditioning are not large and it
is clear that short term conditioning (3 to 9 months) will not create a cardiovascular capacity necessary for championship track performance. Robinson has reported that
Lash (see Table V) has a son who does not engage in sports but at the age of 15 had
Max VO2 of 4 liters/min.9 This leads to
the suggestion that the genetic determi-nants are more important than the
environ-mental factors.
Along this same line deconditiomng
pro-duces declines of the Max V02 which are of the same order of magnitude that are
achieved by conditioning of sedentary young men. It has been mentioned above that bed rest for 3 weeks results in a 17% decline of Max V02,3#{176}and an attack of ma-laria produces a slightly larger decrease
(19%) but this again is of the same order of magnitude and is enhanced by the
develop-ment of anemia.4#{176}
THE CARDIAC OUTPUT. The cardiac output during exercise was first effectively studied by Bock and his colleagues.#{176} The work has been reviewed by Bock and Dill in their revision of Bainbridges’ monograph on the ‘Physiology of Exercise.” The general picture of an increasing cardiac output and
A-VO2 difference with an increasing in-tensity of exercise has stood the test of time. The question of the relative role of
the increase in pulse rate versus the in-crease in stroke volume has been under question in recent years but it would ap-pear that the posture in which the testing values were taken is critical to the question
of whether the stroke volume plays an im-portant role in the adaptation to work in
TABLE VI
THE EFFECTS OF SYSTEMATIC CONDITIONING PROGRAMS ON THE MAXIMAL 02 IN RELATIVELY SEDENTARY
COLLEGE STUDENTS. VALUES ARE IN ML. OF 02 PER KILOGRAM OF BODY WEIGHT.
Indiana* Massachusettst Minnesot44
N 6 14 7
Before 52.0 49.5 48.5
After 61.0 51.5 57.1
9.0 2.0 8.2
% 17.3 4.0 16.9
* Ref. no. 46. t Ref. no. 47.
Fic. 7. The cardiac outputs of 2 Bantu subjects determined in cool conditions and in hot humid con-ditions after acclimatization plotted against the 02 consumption. Multiple determinations made it
pos-sible to establish the 78% confidence limits. (Reproduced by permission from Williams, et al.”) 715
the lighter levels of activity. In exercise in the supine position, the stroke volume
changes very little in the transition from rest to work. On the other hand, the stroke volume at standing rest is low and in the
transition to exercise the stroke volume re-turns to the general level of the stroke
vol-ume in supine position.5’ Cardiac output
studies0 on the well known marathon runner De Mar demonstrated that the well conditioned athlete worked at any specific
energy level with a high stroke volume and a low pulse rate when compared to the un-trained individuals in the study. The cardiac output (1/mm/sq m surface
area) in a fixed task situation was larger in the marathon runner than in the non-athlete. The original studies were done with the CO2 method of Bock, et
Dex-ter, et al.52 re-examined the situation in the
lower levels of work with a catheter in the
pulmonary artery in order to obtain direct Fick cardiac outputs. Good agreement was
found with the study by Bock, et on sedentary subjects. De Mar’s cardiac output in terms of the cardiac index was
substan-tially larger than the sedentary subjects’. Since Bock’s subjects were studied in the upright position and Dexter’s were studied
supine, the agreement between the 2 meth-ods is not as good as it appears since
Reeves54 has shown that the cardiac output
in the supine position is roughly 10% larger than in the upright position. This fact does not obscure the larger cardiac output dur-ing work in De Mar. Furthermore, it is
equally clear that the cardiac index in sedentary individuals up to an oxygen
con-sumption of 800 cc per minute shows very small inter-individual variability.
The majority of the cardiac output stud-ies have been carried out on individuals whose performance capacities differed very widely. Asmussen and Nielsen55 have
re-viewed the cardiac output measurements
made up to 1958. The data have been plotted against 02 consumption and one is struck by the fact that the variability of the cardiac output is small as compared to either the stroke volume or the pulse rate. It is also clear that measurements made on
the same individual in different physiologi-cal states during work might yield some very interesting data.
The study of Williams, et al.17 is a case
in point. These authors studied the cardiac outputs of 2 Bantu mine laborers in great
em-4 $ SO Si
Fic. 8. The excess lactate calculated according to
Huckabee in 3 Bantu subjects who were tested in cool and hot humid conditions after acclimatiza-tion. Multiple determinations made it possible to
calcualte the confidence limits. (Reproduced by permission from Williams, et a!.”)
ployed and at each work load 5 repetitive determinations were carried out in each of the two environmental temperatures. This experimental design allowed the estimate of
a standard error of the cardiac output of the man over the whole range of work load.
The results in the cool and hot environment
are plotted together for the 2 subjects in
Figure 7. In spite of the fact that in both subjects the hot humid conditions produced a displacement to the left in the pulse-rate! work-rate curve (the data for subject 2 is illustrated in Fig. 2 above), the cardiac
output in the hot humid conditions did not differ from that in the cool environment.
This must mean, then, that the circulation
blood per unit time which was going pri-manly to the muscles in the cool condition
was divided between skin and muscles in
the hot humid conditions. The resulting effects of increase in the size of the
vas-cular bed were reflected in an increased pulse rate until the subject began to ap-proach conditions which elicited a Max
vO2.
It follows from this that the oxygenutilization by the muscles would be re-duced if a widening of the A-V02
differ-ence did not make up for the loss of blood flow in the submaximal work range. Evi-dence that the muscles did not receive the
usual amount of oxygen is presented in Figure 8 which presents the excess lactate
in all three subjects plotted against the work rate. Subjects Z and V show an
in-crease in excess lactate levels of submaxi-mal work in the hot humid conditions which failed to elicit evidence of an oxy-gen debt under cool conditions. Of par-ticular interest is the fact that the maximal excess lactate under hot humid conditions
did not differ from that found in the cool environment. This, of course, is consistent
with the finding (referred to above) that the Max V02’s in the two ambient tem-peratures were virtually identical.
These findings led Williams, Ct al.’ to the hypothesis that the cardiac output dur-ing work is controlled by the metabolic rate and not by the size of the vascular bed. This hypothesis finds considerable
support in the results of Wang, Rowell, Blomqvist and Taylor48 who studied the effects of an intensive conditioning pro-gram on the cardiac output during several
levels of work in 6 young sedentary college males. Cardiac outputs were determined by the dye dilution method at 3 submaxi-ma! work levels and also at a work load which had been shown to elicit Max VO2.
SUPPLEMENT
levels the cardiac output was found to be
slightly higher and at one slightly lower after training than before. All difference in cardiac outputs before and after training were less than 5% of the group mean. Pulse rates were markedly reduced by
condi-tioning and stroke volumes were increased with the exception of the values at Max
vO2
where the variability was large enough so that uncertainty existed regarding any generalization. The general picture was the reverse of exposing men to hot humidcon-ditions. It would appear reasonable to assume that the changes in the pulse rate and stroke volume were directly related to more efficient control of peripheral and! or visceral blood flow with an increase in
blood flow through the muscles, a better “venous return” and a larger stroke volume.
The observations of Williams, et al.’7 and Rowell, et al.18 on the effects of
tempera-ture on the Max VO2 demonstrate that when Max VO2 is reached, temperature regulation is subservient to the
require-ments of supplying the muscle with blood. It follows then that marked vasoconstric-tion is present in those vascular beds which are outside of the brain, heart, lungs and muscle. The observations of Taylor, Ct
(see above) on the Max VO2 during de-hydration support this hypothesis. This ap-pears to be the explanation of why the
Max VO2 is less susceptible to other physi-ological and environmental influences which make the interpretation of the sub-maximal pulse rates tests so difficult.
PULMONARY FUNCTION. Riley57 has
pre-sented the background of the generally accepted thesis that in normal man pul-monary function at sea level is adequate to permit almost full saturation of the ar-terial blood during severe exercise. The
primary adaptation which plays a role in this process is an increase in the number of small pulmonary arteries and capillaries which are actively perfused during exer-cise. In addition it is recognized that the
elastic properties of the chest wall and
lungs must be in the “normal” range since there is some evidence that in pathological
conditions which increase the work of breathing at very high ventilation rates, the oxygen cost of breathing may reach
dimensions which limit the further use of
oxygen for muscular There is
general agreement that the diffusion
ca-pacity of the lungs increases with exer-cise.#{176}#{176}R. H. Shepard has carried out cal-culations to show that for any given value
of diffusing capacity the oxygen saturation of the blood is not affected with increasing oxygen consumption until a critical point is reached. Then the arterial saturation drops very rapidly. It seems likely that the
maximum capacity of an average person would be inadequate for the superior ath-lete.
The Max V02 then is closely related to cardiac performance as long as the arterial
blood is adequately saturated. If there is doubt about this matter, direct measure
of arterial saturation during the last few seconds of a Max VO2 work task is in order. Otherwise the determination must
be regarded as a measure of cardio-pul-monary capacity.
DISCUSSION
The preceding supports the concept that
the measurement of the pulse rate response to a fixed submaximal work task or measur-ing the work required to produce a specific work pulse rate is in fact a measure of the
capacity of the individual to carry on aer-obic work under the environmental and physiological conditions at the time of the
test. Thus the work physiologists have
stud-ied the capacity to perform aerobic work in various ambient temperatures by rigidly
controlling time of meals, previous activity, hydration of the subjects, the emotional
setting of the experimental conditions, etc. and varying the ambient temperature. If, in addition, the ambient temperature is controlled, then the procedure becomes an indirect measure of the aerobic capacity of the respiratory cardiovascular systems
subject to a specific pulse rate and if the
subject stops before the end point is reached then the test becomes a measure of the motivation of the individual and his willingness to bear the discomfort of
physi-cal activity. Such a test result may well be related to the capacity of the individual to
perform aerobic work since there are very real psychological limitations to work ca-pacity. But it will not be known whether the limiting factor was psychological or
physi-ological.
Astrand’ has maintained that the Max VO, is the best measure of the capacity of an individual to perform aerobic work. However, it is clear that a work level which elicits the Max V02 also produces a marked
vasoconstriction in both the skin and (probably) in the visceral vascular beds. This being the case a Max V02 in a hot
humid environment is a very poor indicator of the capacity to perform aerobic work in that particular environment because it fails to take into account the peripheral vaso-dilatation that will exist when the subject performs submaximal work in the hot
en-vironment. By the same token, the Max VO, in a warm environment is still a valid
test of the maximal capacity of the heart and circulation to deliver oxygen to the
muscles when pulmonary function is
ade-quately controlled.
In thinking about the interpretation of
the Max V02 it is important to realize that the A-VO2 difference under the conditions of the procedure used in this laboratory is
very large even in healthy young men. At an oxygen intake of 2.4 liters/mm. a level
of work which must be regarded as
sub-maximal, Reeves, et found an A-VO2 difference by drawing blood from the pul-monary artery of 13-14 cc of 02 per 100 ml of blood. Mitchell, et al.32 measured
the cardiac output by the dye dilution method during the Max VO2 and calculated
the A-VO2 of the mixed venous blood and found an average value of 14.3 cc of 02 intake per 100 ml of blood. In patients with rheumatic heart disease Donald, et
al.61 found a mixed venous A-VO2
differ-ence of 7-15 cc per 10() ml of blood.
How-ever, in his study the patients were only
asked to work hard enough to require 02 intakes of from 500 to 800 cc per minute. On the other hand, Chapman, Ct al.13
stud-ied cases of mitral stenosis who were re-quired to develop a Max V02. Fifteen pa-tients were studied and an oxygen intake
plateau was established with increasing work load. The expected mean preopera-tive Max VO2 in cc per kilogram of body weight was 39.3 while that found was 1.43.
The preoperative A-V02 difference was
17.8 ± 3.4 ml per 100 ml of blood. The point we wish to make here is that in both normals and cardiacs (with unimpaired
pul-monary function) the A-VO2 differences as Max VO2 is approached are of the same
general order of magnitude. The individual with a relatively fixed cardiac output can be expected to develop an oxygen intake of not more than 10 cc per kilogram. If true Max V02’s are achieved in individuals
with normal pulmonary function and with-out anemia, the Max V02 per kilogram of body weight will be roughly proportional to the cardiac output at the level of work
required to elicit the Max V02.
The hypothesis presented by Williams,
et al.17 that the cardiac output during work is determined by the metabolic rate and is independant of blood flow through vas-cular beds other than that of the working muscle leads to an interesting speculation. It may be possible under precisely
stand-ardized conditions of submaximal work to set up standards for cardiac output for a
given work load which would be a useful device for assessing the degree of failure of the cardiac output to respond in a normal manner to a standardized metabolic load.
The variability in the measurement of cardiac output is large enough so that multiple determinations would be neces-sary to detect anything but gross
devia-tions. But it seems likely that if normal reference data were established for several work loads, test conditions could be chosen which would be tailored more closely to
SUPPLEMENT
PART III
Application to Pediatric Heart Disease
There appear to be two types of ques-tions which can be approached by the use of fitness tests in patients with whom the pediatric cardiologist must deal. In
con-sidering these the physician will want to
ask himself whether the procedure will provide information which he cannot
ob-tam in any other way. The questions to be considered are:
1. Will an exercise test assist in making
a decision regarding surgery by determin-ing the degree of disability?
2. Will it be of help in evaluating the results of surgery by determining how
much cardio-pulmonary function has been improved or how close to “normal” has this function been restored?
Before attempting to answer these
ques-tions, it is useful to ask whether such tests should be applied to the individual patient before and after treatment or whether it
would be more informative to study groups of carefully classified patients with the
pur-pose in mind of drawing some general conclusions about specific disease and/or
the indications for and results of surgical therapy.
It is believed that the study of the oxy-gen intake is a more precise tool to exam-ine patients and that in most situations the
results are more susceptible to physiologi-cal analysis and interpretation. In discuss-ing this matter it is useful to examine the
types of disability found in patients with valvular or congenital heart disease which
can be expected to interfere with the
cardio-pulmonary capacity and therefore with work performance. The classification listed below is based on factors which can be expected to result in loss of cardio-pul-monary capacity in pediatric cardiac pa-tients:
1. Low or fixed cardiac outputs such as
may be found in valvular stenosis, myo-cardiopathy, endocardial fibroelastosis, yen-tricular failure, etc.
2. Increasing pulmonary capillary
pres-sure in the absence of left ventricular
fail-ure as in mitral valve disease (Cor Triatri-atum or left atrial tumors).
3. Increasing systemic arterial desatura-tion from right-to-left shunting as in the tetralogy of Fallot, transposition of the
great vessels, Eisenmenger’s complex,
pul-monary arteriovenous fistula, etc.
4. Substernal discomfort or angina such
as in anomalies of the coronary arteries, aortic stenosis and severe pulmonary hy-pertension.
5. Large left-to-right shunts resulting in excessive pulmonary flow, as in atrial
sep-tal defect.
6. Decreased or relatively fixed
pulmo-nary flow such as in severe pulmonary stenosis with right-to-left shunting at the
atrial level, and the tretralogy of Fallot. It is evident that in situations 2, 5 and 6
pulmonary factors are of great importance even in the absence of intrinsic lung dis-ease, in that pulmonary compliance,
func-tional lung volume, diffusion capacity and perfusion may be affected. Furthermore, in 3 a decreased cardio-pulmonary
per-formance will not necessarily be due to an intrinsically poor performance by the heart
itself, the situation being in fact a “func-tional anemia.” Factors limiting
cardio-pulmonary performance and therefore work performance in pediatric cardiacs differ
from the normal in that some assessment
must be made of the pulmonary function during work. As pointed out above, the measurement of oxygen saturation of the
arterial blood during work is the simplest method of monitoring pulmonary function. Impairment of Max VO2 in the presence of
a normal arterial saturation will be due to
cardiovascular factors.
In category 1 above tests based on pulse rate will provide satisfactory answers par-ticularly when used in groups of patients so
that the occasional patient who has an in-creased pulse rate induced by emotion will not overweight the results. However, the effects of pulmonary disability such as is seen in categories 2, 5 and 6 on a
carefully studied and it would appear diffi-cult to interpret them. Furthermore, failure
of motivation or limitation of work per-formance by symptoms will probably not
be recognized when pulse rate tests are used.
On the other hand, measurement of oxy-gen consumption and pulse rate in a series of carefully graded steps of external work which are properly standardized with re-gard to rate of work in an attempt to esta-blish a Max V02 plateau will provide more precise information. These steps of
in-creased work should be separated by rest periods in order to be sure of
demonstrat-ing a plateau phenomenon. Oxygen intake plateaus have been demonstrated in pa-tients with mitral stenosis.13 congestive
heart failure,12 aortic insufficiencr and a
variety of debilitating conditions.3 There is good reason to believe that 02 intake plateaus demonstrating attainment of Max
VO2 will be found in most of the types of
disabilities listed above but this is some-thing that has to be investigated. This is worth doing since when a Max V02 plateau
has been demonstrated, one has an objec-tive measurement of cardio-pulmonary ca-pacity. Failure to reach a plateau or to show deviation with the expected rate of
02 increase will be strong evidence that work capacity is either limited by
symp-toms or cardiac neurosis.
Cardiovascular surgery in pediatric
cardiology is either palliative or curative. The measurement of Max V02 after re-covery from surgery and comparison of
the results with carefully conceived norms
will allow an estimate of whether the
cardio-pulmonary function has been re-stored to normal. Furthermore, if it has not been restored to the normal range for the individual in question, it will be possible
to decide whether part of the disability
is pulmonary or whether the residual dis-ability lies in the cardiovascular capacity.
The importance of post surgical
observa-tions can be evaluated by careful follow-up studies.
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