DIFFERENCES
OF
SOMATIC
AND
RESPIRATORY
RESPONSE
TO
HYPOXIA
IN NEWLY
BORN
AND
OLDER
INFANTS
By Franklin C. Behrle, M.D., and Ned W. SmulI, M.D.
Department of Pediatrics, Univerrity of Kansas School of Medicine
(Submitted February 1, accepted April 12, 1957.)
Supported in part by a grant from The National Association for the Aid of Crippled Children.
ADDRESS: (F.C.B.) Kansas City 12, Kansas.
601
P
REVIOUS STUDIES from this 2have indicated that infants under 24
hours of age breathing mixtures containing
10% or 12% oxygen developed respiratory
depression manifested by decreases in
mi-nute and tidal volumes. Older infants, like
adults, responded with increases in minute
volume, although their responses were less
sustained than those of adults. These
find-ings suggested that the peripheral
chemo-receptors were deficient in the immediate
neonatal period. Other differences in
be-havior were also apparent throughout these
studies. In the younger babies the sleeping
state usually persisted throughout the
en-tire period of exposure to low
concentra-tions of oxygen. These infants remained
relatively hypotonic and rarely struggled
despite the fact that their respiratory
ac-tivity was diminished; nor did they show
any other overt signs of discomfort or
dis-tress. On the other hand, the older infants
usually wakened, cried and struggled
vigor-ously after comparatively brief exposures to
the same low concentrations of oxygen.
The present study was undertaken in an
effort to measure the somatic responses of
infants of different age groups to moderate
hypoxia and to correlate these
measure-ments with respiratory activity.
METHODS
AND MATERIALS
A device was constructed to record body
movement (Fig. 1). It consisted of a bassinet
suspended by a spiral spring at one end and
pivoted at the other. A suspending spring was
selected which responded to all movements
of groups of skeletal muscles but not to fine or
brief twitches of an isolated muscle or to the
small movements caused by heart beats and
respirations. Movements of the bassinet were
transmitted to an ink-writing pen by a simple
string and pulley system. Two pneumograph
tubes were placed over the bower chest and
abdomen respectively, and connected to an
ink-writing tambour to record respiratory rate
and amplitude. Body movements and
respira-tions were recorded simultaneously on a
kvmo-graph. Mixtures containing 10% and 12%
OXy-gen were administered through a small
plexi-glass hood placed over the infant’s head and
upper chest. The hood was especially
Con-structed with a series of baffles to obviate the
stimulating effects of air flow on exposed
por-tions of the face and body. The hood allowed some exchange with surrounding air to
pre-vent a build-up of concentration of carbon
dioxide within. Previous experience with this
method had shown that the concentration of
carbon dioxide did not rise above 0.3%. Tile
concentration of oxygen within the hood was
measured at intervals of 1 minute with a Mini
oxygen analyzer. In all instances
concentra-tions of oxygen fell below 14% by the end of the third minute of the period of exposure. De-terminations of the oxygen saturation of the
blood were made at intervals of 1 minute with a
Waters ear oximeter, utilizing an infant
ear-piece. The right ear of the infant was used in
each case. The accuracy of this instrument was checked by frequent comparisons with
gaso-metric determinations on blood obtained
simul-taneously from the femorab artery of infants and children with congenital cardiac lesions.
Agree-ment between the two techniques was within 3%
in the ranges of oxygen saturation encountered
in this study.
Two groups of infants were studied. One
group consisted of infants under 24 hours of age, and the other of infants 16 to 82 days of
age. All of the younger group were healthy full-term infants whose mothers had received little
or no anesthesia during delivery. Many of
the older infants weighed less than 2500 gm at
the time of study; all were considered to be in
excellent health. All infants were asleep and
be-irn
-:J
_%
Ik.1
I
t
-; f3
-
..-c. 1. Apparatus used in the studies.
(mm)
1 2 3
Control Period Breathing 10% or 12% Oxygen
4 5
(mm)
1 2 3 4 5
602
fore tests were begun. The test situation
con-sisted of three consecutive periods of 5 mm-utes each, the infant first breathing room air,
then 10% or 12% oxygen, followed by a return
to breathing room air again. Each minute of
the test period was divided into intervals of 3
seconds each, and the total somatic activity for
a given minute was scored as the number of
3-second intervals in which movement, regardless
of magnitude, was present. Thus, if the infant
was without movement for a full minute the
scoring for that minute was 0. A score of 20 indicated activity in each 3-second interval of
that minute.
Somatic Activity
RESULTS
Twenty-eight tests were run on 17
full-term infants under 24 hours of age and
TABLE I
COMPARISON OF SOMATIC AcrIvITY IN THE VERY OUNG AN!) OLDER INFANTS DURING THE CONTROL PEIu0D AND THE PERIOD OF HYPOXIA
(Results represent the number of 3-second periods of activity for each minute of the test period)
Infants, Age: 24 hours
Mean 1.3 .9 .8 .8 1.2 1.6 1.1 .8 1.5 1.6
S.D. ±1.0 ±1.5 ±1.1 ±1.0 ±1.4 ±1.6 ±1.3 ±1.5 ±1.8 ±.4
Infants, Age: 16-8 days
Mean .7 1.0 1.6 1.3 .6 .7 1.6 6.6 9.4 10.5
Control
PeriothRoom
Air
, Infants 16-82 Days Old
.. Infants under 24 Hours C
lO-I2%
02/
I I I
-..
1 2 3 4 5 I 2 3 4 5
Minutes
I I I I L
603
FIG. 2. Comparison of somatic activity.
weighing between 2,535 and 3,960 gm.
Twenty-one tests were performed on 14
in-fants ranging in age from 16 to 82 days
and weighing from 1,940 to 3,920 gm. The
mean results and standard deviations are
incorporated in Table I. A graphic
corn-parison of the results from both groups of
infants for each minute of the control and
exposure periods is shown in Figure 2. The
older infants did not differ from the
younger in the level of their physical
ac-tivity during the control period. However,
the level of somatic activity increased
sharply and progressively in most of the
older infants beginning with the third
mm-ute of hypoxia. Vigorous crying invariably
accompanied the struggling, which was so
forceful that several infants managed to
wriggle free of the hood. Absence of
strug-gbing with hypoxia was observed in some of
the older infants. This appeared to be
di-rectly rebated to the ability of these infants
to maintain oxygen saturations of the blood
above 90% for longer than 5 minutes. This
was accomplished by increased respiratory
activity as discussed below.
In the younger group the mean value for
somatic activity during the period of
hy-poxia did not differ significantly from that
10
C> 9
0+.
(no 7
0 5
0U)
2
3.0
Ew 2
z
0during the control period, which
repre-sented a state of quiet sleep. Absence of
struggling was demonstrated not only in
different infants of the younger group but
also in repeated tests on the same infant.
The placidity of these infants was
remark-able inasmuch as the arterial oxygen
satura-tions showed a sharp decline by the fourth
minute of hypoxia (Table III).
The differences between the mean values
for somatic activity of the two groups for
minutes 3, 4 and 5 of the period of hypoxia
are such that the possibilities are less than
1 in 500 that this is a chance finding.
Rate and Amplitude
The mean respiratory rates for both
groups during the control and hypoxic
pe-nods are presented in Table II. Figure 3
represents a graphic portrayal of these
re-suits. The younger infants demonstrated
appreciable decreases in respiratory rate as
hypoxia progressed, amounting to
approxi-mately a 20% change by the fourth and fifth
minutes. However, the rates of the older
in-fants remained fairly constant. This latter
response is similar to that obtained in
adults. Measurements of the amplitude of
Control Period (mm)
1 2 3 4 5
Breathing 10% or 12% Oxygen
(mm)
3 4
51 49 47 49 59 48
±18 ±17 ±15 ±18 ±17 ±15
SI).
46
+14
Room
Air
0-
02
a.
0
0
0
a.
0,
50#{149}
40-
30-
20-
10-N
. -.
Infants
16-82
Days
Old
.-.-..
Infants
under
24
Hours
Old
I I I I I I
I
2
3
4
5
Minutes
I
2
3
4
5
604 PEDIATRICS OCTOBER 1957
FIG. 3. Comparison of respiratory rates.
TABLE II
COMPARISON OF RESPIRATORY RATE IN THE VERY \OUNG AND OLDER INFANTS I)UHINO
THE CONTROL PERIOD AND THE PERIOD OF hYPOXIA
Infants, Age : 24 hours
Mean
5.1).
IlifIllitS, Age: 16-82 (lays
Mean Is! 49 51 50
±10 ±9 ±8 ±9
tile pneurnograph gave a rougil estimation
of the changes wilicil took place in tidal
volume. Comparison of the average height
of the excursions during the control period
witil that of tile average for minutes 3, 4
and 5 of the hypoxic period showed a 20%
decrease for tile younger infants and a 25%
increase for the older group. These findings
are collsistent with the more accurate
meas-urements obtained in previous 2
Oximeter Studies
Table III shows the results of continuous
oximetry througblout the control, hypoxic,
and recovery periods on 10 infants in the
c60
_*4 4() 40
±l2 ±15 ±15
50 53 49 47 50 5!
±7 ±7 ±6 ±7 ±10 ±9
younger and 8 infants in the older group.
The relationship of saturation and changes
in the state of physical activity are
graph-icalby represented in Figure 4. The decline
in oxygen saturation of the bbood in the
very young babies was much more rapid
and pronounced than in the older group.
Although all of the younger infants
main-tained saturations above 91% during the
control period, all but one had fallen below
85% by tile fifth minute of hypoxia. Return
to control period values in this group
oc-curred by the end of the third minute of
the recovery period.
de-(o.,e Weigh! (gm) Ha Ca Ir McK Mi Ba Coo Fe Th Lo 3800 7I0 335 3000 3803 3885 3875 3100 305 98O (he) 6 6 9 F! 15 18
97 97 97 97 97 99 99 99 99 99
98 98 98 98 98
99 99 99 99 99
100 100 100 100 100
101 101 101 101 101
91 91 91 91 91
100 100 100 100 100
99 99 99 99 99
98 98 98 98 98
78
93 87 85 83 83 80
97 94 9! 91 89 86 8&
96 93 89 87 55 8! 80
97 95 90 86 8
96 90 8 78 76
98 97 87 8! 75 69
SO 78 68 65
99 97 93 83 76
95 9! 87 83 SO 70
95 90 84 80 76 74
87 90 95 97 97
91 96 100 100 100
9! 100 100 100 100
96 98 99 99 99 9 99 97 99 100
80 87 101 101 101
75 85 9! 94 93
91 97 101 10! lOt
85 99 99 99 99 87 89 97 99
Mean 98 98 95 98 98 95 91 86 8! 80 77 8! 78 88 1)1 99 99 99
B. Infants 16-8! days of age
(days)
Ha 3!30 16
Ro 3070 18
Ri 390 18
Mo !460 38
Pi !31O 45
Jo !380 64
Ne 3550 70
Sini !!O0 8!
95 95 95 95 95
99 99 99 99 99
99 99 99 99 99
98 98 98 98 98
98 98 98 98 98
97 97 97 97 97
98 98 98 98 98
97 97 97 97 97
93 91 87 8! 80
97 93 88 83 85
97 93 89 86 85
98 97 93 95 95 94 94 94
97 95 95 93 9! 90 90 90
93 91 90 90 90 89 89
98 96 94 9 9! 90 89
96 95 93 9! 91 91 89 88
93 97 97 97 97
90 97 99 99 99
9! 95 99 99 99
97 97 98 98 98
97 98 98 98 98
95 97 97 97 97
94 97 97 97 97
94 96 96 97 97
Mean 97 97 97 97 97 96 94 91 89 H) 91 90 91 94 97 98 98 98
TABLE III
DIFFERENCES IN OXYGEN SATURATION (%) OF BLOOD FOLLOWING EXPOSURE TO HYPOXIA
A. Infants less than 4 hours of a
Co Age
nirol Period (mis)
10% or 1% 0.rygen (miii)
iiec orery Period (miii)
1 2 .? 4 I 2 . 4 3 6 7 8 1 1’ .? 4 .5
grees of resistance to a fall in oxygen
satura-lion which appeared to be directly related
to age. Generally speaking, the older the
infant, regardless of body weight, the
longer he was able to compensate for the
decrease in environmental tension of oxygen
by increasing respiratory activity. It was
also evident (Fig. 4) that the older infants
began struggling and crying after only
slight lowering of the oxygen saturation of
the blood. In all instances struggling and
crying were apparent by the time the
satu-ration had fallen to 89%. The return of the
oxygen saturation of the blood to normal
values during the recovery period in this
group was more rapid than in the younger
infants but somewhat slower than that
re-ported in the adult.3
DISCUSSION
The sharp onset of the struggling and
crying at about the third minute of hypoxia,
which most of the older infants in this
study exhibited, resembled a reflex action.
In all likelihood it represents a protective
mechanism which works toward extricating
the infant from the hypoxic environment
while sounding the alarm for help. It is
like-ly that this particular reaction to hypoxia
is limited to the early portion of life. Jonxis3
is of the opinion that hypoxia causes a
de-gree of restlessness in infants which is not
manifested by adults. Review of the
litera-ture has failed to uncover mention of
strug-gling as a feature of the behavior of adults
exposed to concentrations of oxygen similar
to those employed in this study. Indeed,
Van Liere4 along with Ironside and
Batche-br5 have stated that with acute hypoxia
un-consciousness develops so insidiously and
painlessly in adults that not only are they
unaware of any danger but they may find
the early effects not at all unpleasant.
Although the factors governing this
reac-tion in the infant are not clear, a definite
association between struggling and the
abil-ity to hyperventilate with hypoxia was
1
2
345
1
234
5678
12345
Room
Air
l0#{176}6
#{176}2
Room
Air
MINUTES
FIG. 4. Differences in oxygen saturation of blood.
young infants who failed to hyperventilate,
but was present in the older group in which
hyperpnea was the characteristic response.
Moreover, struggling invariably appeared
when the oxygen saturation of blood was
about 90%, which suggests that a specific
re-lationship between somatic response and
oxygen tension of the blood may exist.
Clinically it has been long recognized
that infants have a remarkable capacity to
struggle whenever normal body activity is
restricted. To our knowledge this is the first
time that this phenomenon has been
objec-tively documented in relation to a
dimin-ished supply of oxygen. This finding gives
considerable support to the empirical
con-cept that suffocation does not occur in
healthy infants except under extraordinary
circumstances.
Absence of hyperventilation and
strug-gling displayed by very young infants
seem-ingly renders them vulnerable to hypoxic
insult at a particularly crucial period in life.
However, it is well known that the newborn
enjoys a tolerance to hypoxia not possessed
by the adult. The findings of this and
pre-vious studies from this clinic in no way
con-tradict the latter fact, but indicate that
re-sistance of the newborn to hypoxia is
de-pendent upon factors other than reflex
res-piratory stimulation from the peripheral
mdi-cates that a partially anaerobic metabolism
may be of cardinal importance in that
re-spect.
The failure of hypoxia to produce
res-piratory and somatic stimulation in these
very young infants may well reflect a
linger-ing of fetal behavior on their part. Barcroft#{176}
observed that the fetal lamb and goat exist
largely in a quiescent and apneic state
dur-ing the latter days of gestation (the stage of
“inhibition”) at a time when the oxygen
saturation of umbilical vein blood is
ap-proximately 50%. Hypotonia is likewise
characteristic of the human fetus, and
al-though comparable measurements of
oxy-gen saturation in the infant at various stages
of gestation are lacking, saturations similar
to those noted by Barcroft have been
ob-tamed in the blood from the umbilical veins
of infants immediately prior to and at the
time of birth.712 Since in no instance in the
present study was there a fall in oxygen
saturation below 65%, the absence of
res-piratory and somatic stimulation observed
among the younger infants may mean that
the degree of hypoxia imposed upon them
was no greater than that to which they had
successfully adapted in utero and therefore
constituted no serious threat to their
borneo-stasis. What effect severer degrees of
hy-poxia might have cannot be stated, but it is
quite clear that the very young infant is not
stimulated by the same degree of hypoxia
as is the older infant.
The differences in the rate and extent of
decrease in oxygen saturation of the blood
bebveen the two groups of infants merits
comment. While the more rapid and
pro-nounced declines in the younger infants
were felt by us to be explained adequately
by the decreases in ventilation which were
observed, the work of several
investiga-tors35 indicates that in very young infants
hypoxia can produce a reversal of blood
flow through the ductus arteriosus and
fora-men ovale in the fetal direction. Although
the placing of the oximeter earpiece on the
right ear of infants in the present study
eliminated the ductus as a factor
contribut-ing to the decrease in oxygen saturation,
the possibility of a right to left shunt
occur-ring through the foramen ovale cannot be
excluded.
The opinion that newborn infants, and
particularly premature infants, are not
lack-ing in peripheral chemoreceptor function
has stemmed chiefly from the conclusions of
Cross and Opp#{233}.1#{176}However, an analysis of
their work reveals that infants from 1 to 45
days of age were used and only the mean
values of the results were reported. It is
highly probable that their results were
greatly influenced by the responses of the
older infants in the group, for in previous
reports from this evidence
sug-gesting the presence of chemoreceptor
func-tion was obtained in infants beyond 16 days
of age. Furthermore, Cross and Malcolm’7
recorded action potentials from the sinus
nerve while subjecting a variety of animals
to hypoxia. Positive evidence of
chemo-receptor activity was obtained in each of
three animals beyond 14 days of age, but
in six animals ranging in age from 8 days
prior to term to 3 days post partum, the
re-suits were negative or doubtful in five. In
view of our findings it would appear that
modification of their conclusions is in order.
It is our contention based on previous
studies that tile onset of chernoreceptor
function is a gradual rather than abrupt
process in the period from birth to several
weeks of age. The physiologic mechanisms
underlying this gradual change are obscure
at the moment, and are the subject of
cur-rent investigation by us. Meanwhile, in
view of the conflicting opinions on the
sub-ject, it would seem wise to reserve
judg-ment concerning the status of the
periph-erab chemoreceptors in the immediate
neo-natal period pending the results of further
study.
SUMMARY
The somatic and respiratory responses to
hypoxia of two groups of infants were
studied. Infants 16 to 82 days of age
mani-fested both increased somatic and
respira-tory activity, whereas infants under 24
demon-strated respiratory depression. The
re-sponses in the younger group of infants
oc-curred despite a pronounced decline in
oxygen saturation of the blood.
The findings suggested the presence of
a somatic reflex in tile older infants which,
like tile peripheral chemoreceptors, is
stirn-ulated by a fall in arterial oxygen tension.
Neither this reflex nor evidence of
chemo-reflex function were observed in the very
young infants, suggesting a lingering of
fetal behavior.
REFERENCES
1. Miller, H. C., and Behrle, F. C. : The
effects of hypoxia 011 respiration of new-born infants. PEDIATRICS, 14:93, 1954.
2. Miller, H. C., and Smull, N. W. : Further
studies on the effects of hypoxia on the
respiration of newborn infants. PEDI-ATRICS, 16:93, 1955.
3. Jonxis,
J.
H. P.: Some results of the regis-tration of the oxygen saturation of young infants’ skin blood which has been ar-terialized by means of histamine, in Anoxia of the Newborn Infant, edited byDelafresnaye,
J.
F., and Opp#{233},T. E.Springfield, Thomas, 1953, p. 127.
4. Van Liere, E.
J.
: Anoxia, Its Effect on theBody. Chicago, Univ. Chicago Press,
1942, p. 15.
5. Ironside, R. N., and Batchelor, I. R. C.: Aviation Neuropsychiatry. Edinburgh, Livingstone, 1945, pp. 2-3.
6. Wilson,
J.
L., Reardon, H. S., andMurayama, M. : Anaerobic metabolism in the newborn infant. PEDIATRICS, 1:
581, 1948.
7. Bareroft,
J.
: Researches on Pre-natal Life. Springfield, Thomas, 1948, p. 263. 8. Eastman, N.J.
: Foetal blood studies. I.The oxygen relationships of umbilical
cord blood at birth. Bull. Johns Hopkins Hosp., 47:221, 1930.
9. Walker,
J.
: Foetal anoxia.J.
Obst. &Cvnaec. Brit. Emp., 61:162, 1954.
10. Smith, C. A., and Kaplan, E. : Adjustment of blood oxygen levels in neonatal life. Am.
J.
Dis. Child., 64:843, 1942.1 1. Watts,
J.,
Henderson, H., Kaump, D. H.,and Davis, R. M. : Oxygen studies of
the arterial blood in newborn infants.
Am.
J.
Obst. & Gynec., 61:1025, 1951.12. Pennoyer, M. M., et al.: The relationship
of paranatal experience to oxygen
satu-ration in newborn infants.
J.
Pediat., 49:685, 1956.
13. Eldridge, F. L., and Hultgren, H. N.: Physiologic closure of the ductus
arteriosus in the newborn infant.
J.
Clin.Invest., 34:987, 1955.
14. Rowe, R. D., and James, L. S. : The pattern of response of pulmonary and
systemic arterial pressures in newborn
and older infants to short periods of hypoxia (abstract). Am.
J.
Dis. Child.,93:12, 1957.
15. Lind,
J.
: Disturbances in the postnatalclosures of various blood vessels and
channels and their relationship to as-phyxia neonatorum, in Anoxia of the Newborn Infant, edited by Delafresnaye,
J.
F., and Opp#{233},T. E. Springfield,Thomas, 1953, p. 171.
16. Cross, K. W., and Opp#{233},T. E. : The effect
of inhalation of high and bow
concen-trations of oxygen on the respiration of
the premature infant.
J.
Physiol., 117: 38, 1952.17. Cross, K. W., and Malcolm,
J.
L. : Evidence of carotid body and sinus activity innewborn and fetal animals.
J.
Physiol.,118:1OP, 1952.
SUMMARIO
IN INTERLINGUA
Differentias
in le Responsas
Somatic
e
Respiratori a Hypoxia Inter InfantesNeonate e Infantes de Etates Plus Avantiate
Observationes facite in le curso de previe
studios a iste laboratorio indicava que il existe differentias del activitate somatic e etiam del
activitate respiratori inter infantes neonate e
infantes de etates plus avantiate post br expo-sition a basse concentrationes de oxygeno. Le
presente studio esseva interprendite pro mesurar be responsas somatic de infantes de vane gruppos de etate a moderate grados de hypoxia e pro correlationar le resultante valores
con le activitate respiratori.
Esseva construite un dispositivo consistente
de un cuna suspendite per un resorto que
registrava movimentos corporee in un
kymo-grapho. Le respiration esseva registrate
simul-taneemente per duo tubos pneumographic
montate ab thorace inferior e ab abdomine. Mix-turas de 10 o 12 pro cento de oxygeno esseva
administrate al infante per un parve campana
de plexiglass pbaciate supra su capite. Mesuras
special esseva prendite pro evitar stimulation
per be fluxo de aere e un concentration
ARTICLES
Le concentration de oxygeno intra be campana
esseva analysate per medio de un analvsator
de oxygeno typo Mira a intervalbos de 1
minuta, e le saturation arterial de oxygeno
es-seva determinate simubtaneemente per medio
de un oxythetro auricubar.
Duo gruppos de apparelltemente normal
infantes esseva studiate in stato dormiente. Un
del gruppos consisteva de infantes de minus
que 24 horas de etate, le altere de infantes
de inter 16 e 82 dies de etate. Le schema del
test provideva tres periodos consecutive de
5 minutas cata un, con be infante respirante
aere del ambiente durante le prime periodo,
aere a 10 o 12 pro cento de oxvgeno durante
le secunde, e de novo aere del ambiente
durante le tertie. Le grado del activitate
so-matic durante cata minuta del periodo del
test esseva identificate per be numero de inter-valbos de 3 secundas in que movimento esseva 1resente, sin reguardo al magnitude de ilbo.
Vinti-octo tests esseva effectuate in 17 in-fantes nascite a termino con pesos de inter
2535 e 3960 g. Vinti-un tests esseva effectuate in 14 plus avantiate infantes con pesos de inter
1940 e 3920 g. Le duo gruppos non differeva
significativemente in be grado de activitate du-rante be periodo initial de controlo. Le
juvenis-sime infantes manifestava nulle augmento de
activitate post br exposition a hypoxia, durante
que be majoritate del plus avantiate infantes
reageva per marcate augmentos de activitate,
attingente un vigorose debattimento e critar a
partir del tertie minuta del hypoxia. Augmentos
del amplitude in be excursiones respiratori
occurreva in hypoxia in omne be plus avantiate infantes, durante que reductiones del
ampli-tude e etiam del frequentia respiratori esseva
notate in be plus juvene. Esseva etiam constatate
significative differentias del saturation oxygenic arterial in stato de hypoxia. Le plus avantiate
infantes manteneva plus alte grados de satura-tion durante plus bonge periodos de tempore
q’ be plus juvenes, e critar e debattimento
esseva observate frequentemente in le prime
del duo gruppos quando be saturation oxygenic
habeva descendite al vicinitate de 90 pro
cento.
Le datos indica be presentia de tin reflexo
somatic in plus avantiate infantes que es
actu-ate per un reduction del tension arterial de
oxvgeno e que functiona probabilemente como
un mechanismo protective. Le absentia de
debattimento de protesto in be neonatos reflecte
possibilemente un plus abte grado de toleration de hypoxia. Nove provas indirecte esseva
obte-nite pro corroborar previe constatationes in
supporto del these de un deficiente function
chimoreceptori peripheric durante be prime
