POTASSIUM-40: SERIAL DETERMINATIONS IN INFANTS

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POTASSIUM-40:

SERIAL

DETERMINATIONS

IN INFANTS

Marion Maresh, M.D., and David S. Groome, B.S.

From Child Research Council, Department of Pediatrics, University of Colorado School of Medicine and Colorado State Department of Public Health, Denver

(Received January 12; revision accepted for publication April 15, 1966.)

This study supported in part by Grant HD 00675, National Institutes of Health, U. S. Public Health

Service, Bethesda, Maryland.

ADDRESS: (MM.) University of Colorado Medical Center, 4200 East Ninth Avenue, Denver,

Cob-rado 80220.

PEDIATRICS, Vol. .38, No. 4, Part I, October 1966

642

O

lYE interest in the changes in body

composition of the newborn infant

as he grows through his first postnatal year

has been accelerated in recent years as we

look to the total body counter for further

evidence1 of the variability in the relative

amounts of adipose and nonadipose tissue

in tile body. Anderson and Langham2 in

Los Alamos and Forbes and Hursh4 in

Rochester, New York, have shown that K4#{176}

measurements can be used in the

deter-minations of total potassium in children of

school age and adults of all ages. There

have been few K’#{176}counts on infants,

al-though some infants were included in the

Los Alamos data.

In 1961 the Colorado State Department

of Public Health installed a total body

counter. Learning of our interest in body

potassium studies in 1963, they offered us

the use of tile facility for a pilot infant

study. After 6 months of experimenting

with position of detector and child and

means of monitoring the sleeping infant,

most of the difficulties had been

satisfacto-nily met.

The counting shield is a 2.4 X 2.4 X 2.4

m (8 x 8 X8 ft) room with 12.7 cm (5 in.)

steel walls lined with 3 mm (3 in.) lead.

The child is quiescent in a prone position

on a tight canvas frame supported from

the walls of the room. A 10.2 X 22.9 cm

(4 X 9 in.) NaI (Ti) detector utilizing four

photomultiplier tribes is located under the

canvas with the position dependent upon

the height and weight of the child, varying

from contact with the canvas to 7.5 cm

(3 in.) from the infant. The edge of the

detector is located at the shoulder. Signals

from the detector are resolved and stored!

by a 512 channel analyzer. Monitoring of

the infant is by closed circuit television and

intercom. Standard procedure is to examine

the quiescent infant for four 10-minute

in-tenvals followed by a 40-minute

back-ground measurement.

Calibration for potassium was by means

of repeated measurements of six cloth

phantoms, sized from anthropometnic data

at successive ages during infancy and

child-hood. These phantoms were filled with

brown rice, similar in density and

potas-sium content to fat-free tissue. Calibration

errors due only to counting amounted to

less than 5% (2 standard deviations). Figure

1 is a spectrum reproduction showing the

detector data obtained during an infant

cx-amination.

The data for this report are 109 total

potassium determinations from K4#{176}

mea-surements on 13 second-generation subjects

in tile Child Research Council study series.

Nine consecutively born subjects, six boys

and three girls, were started at 1 month of

age, and six of them had had monthly

cx-aminations for at least a year for this study.

Four older subjects, between 9 months and

2 years of age, were examined at 3-month

intervals as were all the younger infants

after 1 year of age.

For the 83 determinations made during

the first year of life, there is little difference

between median and mean values at each

month of age. Mean values increased from

6.68 gm potassium at 1 month in an

essen-tially linear pattern to 15.11 gm at 12

months with a range of variation between 3

(2)

to .

NET - #{149}.

0.I

... .. #{149}#{149}.,#{149}:#{149}#{149}#{149}

ARTICLES 643

correlation between potassium and age was

0.90. The ranges in weigilt and iengtil

in-creased from about 1.5 kg and 6.5 cm at 1

month of age to 3 kg and 9 cm toward the

end of the year. The coefficient of

correla-tion for the 83 potassium determinations and

body length was 0.94. Sample data for four

babies are shown in Table I. Potassium

de-terminations are given as calculated along

with the two standard deviation counting

errors for each examination.

The close relationship between

chemical-ly determined potassium values by direct

analysis and lean body mass has been

shown for tile fetal and neonatal period by

Widdowson and Dickerson,5 for the infant

and neonatal period in infants of diabetic

and non-diabetic mothers by Fee and

Weil,6 and for the adult by Forbes and

7 These data are evidence that there

is a cilange in the potassium pen unit of

lean body mass between the circumnatal

and adult periods. From Forbes’ data,4 this

change has already occurred by the age of 7

years, but we have no information about

\vilen this transition occurs or if it occurs

rapidly or gradually after birth. Without

attempting to calculate lean body mass for

our subjects from the K4#{176}data, we have

graphed potassium levels from K4#{176}

mea-surements for our subjects and tile chemical

determinations of potassium in the

litena-tune for subjects weighing more than 100

gm against the total weight of each subject

in Figure 2. It can be seen that data from

K4#{176}measurements in the first year of life

are essentially linear and that tile

coefficient of correlation of 0.94 produces a

straight line that has its x:y intercept near

zero. The chemically determined potassium

levels for the Widdowson and Dickerson

subjects and the infants of diabetic mothers

(1DM) and non-diabetic mothers (INDM)

in the Fee and \Veil data are in close

prox-imity to the calculated straight line, except

for the one subject whose mother was

grossly potassium-deficient according to

Fee.6 The values from the K4#{176}data for the

subjects who were more than 1 year of age

are obviously at higher levels and, although

few in number, may be reflecting tile

tran-sition toward the higher K/kg levels found

by both Forbes’ and Anderson2 in children

of school age.

Anderson and Langham2 presented their

K4#{176}data in childhood as a straight line, with

I00OC w z z i_I > rj cC 0. z cC Li 0.

. 0.2 04 a. o.e

ENERGY -MEV

0 L2 .4 .6

Fcc.. 1. Gamiria detection spectrum of an infant. Net data shows Cs#{176}7(0.66

ME\’) and K” (1.46 MEV). Energy range used for potassium determinations

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TABLE I

SAMI’LE l)AT.& F)1I Focu I5ABIF>

.1ye height H’eig/il K±2o

(,,,o) ((.1,1) (kg) (gin)

Age

(,io)

height U’eight K±2o

(c,,i) (Ig) (gut)

(‘a.se O6 (Girl) (‘ate 709 (Boy)

1 . liisitisfactory (Iat.a

‘2 tinsatisfactory data

3 I .57.6 5.14 6.9±0.7

4 38.6 3.95 8.8±0.7

5 61 .9 6.59 9.1±0.8

6 63.? (;.76 9.1±0.9

7 63.8 . 7.08 10.6±1.

8 65. 7.31 12.0±1.’2

9 67.1 7.44 H.9±1.’.?

10 (;(Ls 7.80 13.1±.0

II 67 .8 7.6() I 1 .0±I.0

l’2 (t).’ 7.59 11.2±1.

1 .5.5.5 4.7 9.1±0.8

.j9.9 595 9.0±0.8

3 61 .0 (;.55

,

9.8±1.1

4 6.5.i2 7.50 10.0±0.9

.5 67.5 7.96 10.0±1.1

6 69.0 8.4’2 10.2±1.1

7 69.3 8.7 l0.±1.1

8 71.3 8.88 H.9±1.4

9 73. 9.35 14.5±1.

10 75.0 9.98 . 14.8±1.7 1 1 Appointnient cancelled H 78.1 10.34 16.1±1.

(‘axe 707 (Boy) (‘aze 71() (Boy)

I 5.5 4.31 (1.0±0.8 36.4 5.19 7.9±0.7

3 58.4 5.85 8.5±0.8

4 . ti2.0 6.46 9.2±0.9

5 64. 7.30 11.6±0.8

6 (15.5 7.66 11.1±1.

7 68.0 8.00 12.0±1 .‘

S 70.1 8.15 U.4±1.2

9 70.1 8.54 11.9±1.1

10 71.3 9.06 13.t)±1.2

ii 73.3 9.’21 14.5±1.4

H 74.6 9.64 14.9±1.4

1 3 4 5 6 7 8 9 10 11 H

56.6 4.64 8.5±0.8

57.9 5.57 9.±0.9

61.4 6.54 10.6±1.1

63.6 7.48 10.0±1.3

67.2 7tH 11.6±1.7

(;8.l 8.68 13.0±1.3

70.() 9.’.6 14.0±1.6

71.8 9.71 13.4±1.4

7’L9 10.16 13.2±1.6

73.3 10.() 14.9±1.4

Appointnient cancelled

74.8 10.69 15.5±1.5

110 SCX dlifferellce, increasing from about

1.64 gIi K/kg body weight at birth to about

2.17 lT) K/kg weight at age 8 on 9 years.

Presumably they did not separate the infant

data into smaller age units. When our data

are 1)resented in this form (Fig. 3), the data

are certainly non-linear in the first year of

life. The decrease in median and mean

val-ues tilrOugh 5 months of age is followed by

higher median and mean values after 5

months of age. There is no contradiction of

the linear relationship between weight and

total potassium (Fig. 2) in the values

graphed in Figure 3. The differences in

weight at each age and the curvilinear

rela-tionship between weight and age in the first

year of life are not involved in Figure 2. In

Figure 3, the potassium concentration pen

kg of hod’ weight are graphed against

in-creasing age and the non-linearity of the

values is evident. If potassium

concentra-tion were increasing at tile same rate as

weight, there should be no change in these

levels with increasing age. But if fat is

being added faster than lean, actively

me-tabolizing cellular tissue, then the observed

decrease in K/kg weight could be expected.

From tissue widths measured on

roent-genograms,1 fat widths in both boys

and girls increase rapidly in the first 6

months of life. Then in most babies, fat

widths, and presumably fat mass, begin to

decrease in relative amounts. The data in

Figure 3 appear to agree with this

obsenva-tion.

These preliminary data have been

pre-sented in an attempt to describe

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ARTICLES 645

K

4;,

2’3 TOTALPOTASSIUM . . ,

24

22

20

00/56789T1 3i4i1

WEIGHT

-

ccs.

FIG. 2. Potassium values determined from in vivo K’#{176}measurements and

po-tassium values reported in the literature from chemical determinations are

graphed against body weight. The calculated straight line was established from

the K4#{176}data in the first year of life.

K

GM POTASSIUM PER KG. BODY WEIGHT

x

* x

I

J

* -.AN

I. #{149} MEDIAN

Lc; 789101112 I 82124273033363942

AGE - MONTHS

FIG. 3. Changes in potassium concentration (gm K/kg body weight) as a function of

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of the baby as he grows through the first

year of life. Granting the statistical errors in

calculation of K4#{176}in this age period, we

feel the results merit further consideration

for this method of investigating body

corn-position. With nutritional histories and

tis-sue measurements from noentgenognams of

the extremities available to us on all these

subjects, we hope to be able to understand

what “weight” is for the healthy infant.

REFERENCES

1. Maresh, M. M. : Changes in tissue widths

dur-ing growth. Amer. J. Dis. Child., 111:142,

1966.

2. Anderson, E. C., and Langham, W. H. :

Aver-age potassium concentration of the human

body as a function of age. Science, 130:713,

1959.

3. Forbes, C. B., Gallup, J., and Hursh, J. B.:

Estimation of total body fat from

potassium-40 content. Science, 133: 101, 1961.

4. Forbes, C. B., and Flursh, J. B.: Age and sex trends in lean body mass calculated from K4#{176}

measurements. Ann. N.Y. Acad. Sci., 110:255,

1963.

5. Widdowson, E. M., and Dickerson,

J.

W. T.:

Chemical composition of the body. In Comar,

C. L., and Bronner, F., ed. : Mineral

Metab-olism, Vol. II, Part A. New York: Academic

Press, p. 1, 1964.

6. Fee, B. A., and Weil, W. B., Jr. : Body corn-position of infants of diabetic mothers by

direct analysis. Ann. N. Y. Acad. Sci.,

110:869 1963.

7. Forbes, C. B., and Lewis, A. M.: Total sodium,

potassium and chloride in adult man. J.

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1966;38;642

Pediatrics

Marion Maresh and David S. Groome

POTASSIUM-40: SERIAL DETERMINATIONS IN INFANTS

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1966;38;642

Pediatrics

Marion Maresh and David S. Groome

POTASSIUM-40: SERIAL DETERMINATIONS IN INFANTS

http://pediatrics.aappublications.org/content/38/4/642

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