OXYGEN CONSUMPTION
AT REST AND DURING EXERCISE IN PREGNANCY’
M. L. PERNOLL, JAMES METCALFE, THOMAS L. SCHLENKER, WELCH AND JEAN A. MAT~UMUTO
J. EUGENE
Abstract.
The oxygen consumption (Y,,) of 12 normal women was measured at monthly intervals during pregnancy and 2, 6 and 12 weeks and 6 months postpartum. At each study session, measurements were made sitting at rest. during standard steady-state exercise on a bicycle ergometer. and for 10 minutes of recovery, A significant increase jn exercise f;oz was observed in late pregnancy when compared to paired postpartum values. The oxygen debt incurred by standard exercise was also greater in late pregnancy than C-f4 weeks postpartum.
Exercise Oxygen consumption
Oxygen debt Pregnancy
In this discussion we will dehne “elliciency” as the cost. measured by the rate of oxygen consumption (idol) in the steady state, of performing a standard intensity of exercise. By this definition, the effect of pregnancy on the efficiency of performing muscular work is unclear. It is generally accepted that weight-bearing exercise requires more oxygen consumption during pregnancy, but more work is performed in carrying the extra weight of pregnancy, Data regarding the oxygen cost of nonweight-bearing exercise are convicting and subject to a variety of interpretations. This report de& with serial studies of oxygen consumption at rest, during bicycle exercise and during recovery from exercise in normal women throughout pregnancy and postpartum. Materials and methods Twelve pregnant subjects were selected on the basis of the absence of obesity and disease of the heart, lungs, and blood detectable by routine screening procedures. They ranged in age from 25 to 34 years and averaged 60.6 kg in weight, with a range from 53.2 to 69.5 kg near the onset of pregnancy. All were considered to be Accepted
,fnr p~bli~~tjor~
21 August
1975.
’ This research was supported in part by U.S. Public Heafrh Service Grant No. HIM8025 from the National Insitutes of Health and the Oregon Heart Association. 285
286
et al.
M. L. PERNOLL
SAMPLE
COLLECTION
AT EACH
,;. .,.
..:.
‘.
”
..:
; ,. :” i’..
‘:. ‘.‘.
:
:
2
4
‘6’
I
I 8
.,
.,.
::
j;, : t
.:
.Collection’ (3 min) ‘:
I I
.-.
..
.,. -:: .:: .:..::.i,
y
:’ :‘:
‘.’
Collection
/
13min)
.:
:.‘;:.., .‘.
,‘:,
;
,“.
.:‘,
:
i.?‘.; ,,
.I.’ ..
.‘.‘.,. ...b ‘,
..:.
,‘..f .. ..
.:,
:,;...
.:
,.
‘.
:::..:
.; : :
SESSION
Recovery
Exercise
Resting
0
STUDY
.,) _,.
‘..
.,: .::
:’ ,,,
..,,,.”
., ;., ,,,,
,;; .::.I ’
‘. ,.
,.:
.’ :
:,
.:i:_.;,‘.’
:
..’
:
.::.
Collection, (IO
,’
.,
,, -:..:.:,, ,. .::.:‘.i., ;
. . .; :
min)
: I:
;
‘.:...
..
:. ‘_ ::, :.;_...;..? .;::.‘Y::..;
‘~‘.$j
,,. ,..,:: :‘:.,y’., ::,,:: .. ,. ..:...:, ..,, .; ‘1.,-.:.:.~.:~.::.:.:.~r .::., ...., .,: :. :: ‘1 .,:.: “’ ‘.:.., .L:. . .::.: .....:,y.:.: .:‘;:.:;,...... ::,.: _.: :. :: .; :.,‘-‘: .:. .;_: ,. ..‘;,,, ,,,, :._ : ‘. ‘.:y.,‘::;;.: >:.. / .:,. ..::::::.::.:y j ..:.., :. ,,:.;...< ,.,:: ::,:j ,..’;.i:.!, . .,.,_.,::yi.::‘: ;,;..:::.:+): ,. :. .. ..I ‘, ” .‘::. ..:,2,.,’ ‘. ..,. :.:, ;.,,: :.,.>,. ..,.,..., ;; 12. 14 16 I8 2d’ 22 IO
Minutes
Fig. 1. The times of sample areas indicate
collections
the times of sampling.
the bicycle ergometer
but disconnected
at each study After the resting
session are graphically sample collection.
from the mouthpiece
of short duration
and is noted
for reasons
by the asterisk
demonstrated.
the subject of comfort.
remained
The darker seated on
This interval
was
(*).
healthy and physically tit. Each subject was studied at monthly intervals during pregnancy and again at 2, 6 and 12 weeks and 6 months postpartum. All studies were performed in the morning with outpatient subjects after a breakfast of only orange juice and dry toast. On the first visit, the procedures were carefully explained to each subject, a complete history and physical examintion was performed, and a practice session with the equipment was conducted. At each subsequent study session the subject was weighed, her blood pressure was determined, her temperature was obtained and an obstetrical or gynecological examination was performed. During this study, the subject was seated on a Godart bicycle ergometer and a nose clip completely occluded the nares. A mouthpiece designed to prevent the undirected escape of air was attached to a respiratory valve which, in turn. was connected by a short tubing through a three-way valve to a series of rubber (neoprene) collecting bags. Three collections of expired air were made during each study (fig. 1). The first was collected for the last three minutes of six minutes at rest before exercise began. The second collection was made during the last three minutes of a six-minute exercise period. The third sample was collected throughout the first ten minutes of recovery following the exercise. Exercise was conducted at a load of 50 watts and at pedaling rates between 40 and 50 r.p.m. According to the manufacturer’s specifications this imposes a fixed work load of 306 kpm/min. Each collection of expired air (resting, exercise and recovery) was analyzed for oxygen partial pressure by a Beckman (Pauling principle) oxygen analyzer and the concentration of oxygen in expired air (FEDS) was calculated from this and the atmospheric pressure. The analyzer was calibrated with test gases alternately with each sample. Expired CO, concentration (FE,,,) was measured using a Beckman infrared photometer; results of CO, analyses are reported separately (Pernoll et al., 1975). The volume of each collection was
OXYGEN ~NSUM~ION
AT REST AND DURING EXERCISE IN PREGNANCY
287
measured in a Tissot spirometer and corrected to standard conditions. All measurements were completed within 30 minutes of air collection. Measured volumes of expired gas were corrected for sampling losses, converted to body temperature and ambient pressure (BTPS), and expressed per minute of collection (QE). Oxygen consumption was calculated: (see Dejours, 1966b) voz
=
h(F]~o,- FIo&zoz -Fd 1 - FIN,
Since room air was inspired in all our studies, this equation simpli~es to: V = &(0.21-0.21 FE,,,-FE,,) 02 0.79 i’oZ was converted to STPD conditions (0 “C, 760 mm Hg, dry). The oxygen debt was calculated by subtracting the 7;‘02at rest from the Vo, during recovery and multiplying by ten for the ten-minute recovery collection. Unpublished data from this laboratory have shown that pregnant subjects repay the oxygen debt accrued by exercise of this intensity and duration within ten minutes of completing exercise. Several subjects required hospitalization in the final weeks of pregnancy; therefore, data for 35-38 weeks were obtained on only ten patients and for 3942 weeks on only eight patients. Consequently, statistical comparison of those data with postpartum values by paired t-test is handicapped by the smaller number of patients, and group data are used for statistical comparison of some of the results. In all cases, evaluation of probability was made against 2-tailed tables. Percentage changes were calculated in relation to the values at 12-14 weeks postpartum, because no significant changes were observed between those values and the sixmonth postpartum values. The data are presented in table 1 and figs. 224. Results GENERAL
The patients had an average weight decline of 12.3 kg following delivery (from 74.1 to 61.8 kg), a 20% difference from the last pregnancy value (obtained at 39-42 weeks) when compared to 12-14 weeks postpartum. Six of the twelve were lactating during all of the postpartum evaluations and were not taking oral contraceptives or menstruating. There were no estrogens, progestins or androgens administered to prevent lactation. Three of the 12 subjects started combination oral contraception at four weeks postpartum after the first evaluation was performed (type and dosage varied). RESTING OXYGEN CONSUMPTION
Figure 2 represents the data on qo, at rest and with exercise. There is a progressive increase in resting if,, as pregnancy advances. This increase is significant by paired f-test throughout pregnancy compared to the value 12-14 weeks postpartum (table
288
M. L. PERNOLL et Ul.
I), Resting idol is increased by 3391 at 39-42 weeks of pregnancy 12-14 weeks postpartum.
compared
to
EXERCISE OXYGEN CONSUMPTION
From the exercise data (fig. 2). it is seen that ii,, during standard steady-state exercise undergoes a nearly progressive increase as pregnancy advances. When the values obtained during pregnancy are compared to the 12-14 week postpartum Delivery 1500 -
A--A Rest A-A Exercise
1400 -
t 1300 -
T
t 1200 1100 2
IO00
? $
900 -
a@
800 750 It 400
200 300 i -rt
,r
1
I
I
I
I
I
19-22 23-26 27-30 31-34 35-38 39-42
-f-J 2-4
6-8
Postpartum
Pregnancy
Q-14
6 MOS.
Weeks Fig. 2. The oxygen consumption at rest and with mild nonweight-bearing steady-state exercise is illustrated during pregnancy and postpartum. The means (triangles) are connected by a line. The smaller circles represent the individual values corrected to STPD. Length of each vertical line represents the range of values.
values by paired r-test, the increase is statistically signj~cant from 27-30 weeks through delivery (table 1). Exercise irot is increased by an average of 150~;at 39-42 weeks of pregnancy when compared to 12-14 weeks postpartum.
OXYGEN
CONSUMPTION
AT REST AND
DIJRING
EXERCISE
IN PREGNANCY
288
290 OXYGEN
M. L. CONSUM~IO~
CHANGE
WITH
PERNOLL
el Uf.
EXERCISE
(A7j02=
EXERCISE
iio,
MINUS
RESTING ire,)
Figure 3 illustrates the data, which show that Airo2 is increased during gestation. The difference in A\jo2 between 12-14 weeks postpartum and 39-42 weeks of pregnancy is S(;/,. There is no statistical significance by paired t-test during pregnancy when compared to the value 12-14 weeks postpartum (see table 1). This statistical result is explained by the small size of the group at 39-42 weeks, as mentioned above. If a nonpaired t-test is performed, comparing all values from 3142 weeks of pregnancy with all postpartum values, P
AT REST AND DURING EXERCISE IN PREGNANCY’
M. L. PERNOLL, JAMES METCALFE, THOMAS L. SCHLENKER, WELCH AND JEAN A. MAT~UMUTO
J. EUGENE
Abstract.
The oxygen consumption (Y,,) of 12 normal women was measured at monthly intervals during pregnancy and 2, 6 and 12 weeks and 6 months postpartum. At each study session, measurements were made sitting at rest. during standard steady-state exercise on a bicycle ergometer. and for 10 minutes of recovery, A significant increase jn exercise f;oz was observed in late pregnancy when compared to paired postpartum values. The oxygen debt incurred by standard exercise was also greater in late pregnancy than C-f4 weeks postpartum.
Exercise Oxygen consumption
Oxygen debt Pregnancy
In this discussion we will dehne “elliciency” as the cost. measured by the rate of oxygen consumption (idol) in the steady state, of performing a standard intensity of exercise. By this definition, the effect of pregnancy on the efficiency of performing muscular work is unclear. It is generally accepted that weight-bearing exercise requires more oxygen consumption during pregnancy, but more work is performed in carrying the extra weight of pregnancy, Data regarding the oxygen cost of nonweight-bearing exercise are convicting and subject to a variety of interpretations. This report de& with serial studies of oxygen consumption at rest, during bicycle exercise and during recovery from exercise in normal women throughout pregnancy and postpartum. Materials and methods Twelve pregnant subjects were selected on the basis of the absence of obesity and disease of the heart, lungs, and blood detectable by routine screening procedures. They ranged in age from 25 to 34 years and averaged 60.6 kg in weight, with a range from 53.2 to 69.5 kg near the onset of pregnancy. All were considered to be Accepted
,fnr p~bli~~tjor~
21 August
1975.
’ This research was supported in part by U.S. Public Heafrh Service Grant No. HIM8025 from the National Insitutes of Health and the Oregon Heart Association. 285
286
et al.
M. L. PERNOLL
SAMPLE
COLLECTION
AT EACH
,;. .,.
..:.
‘.
”
..:
; ,. :” i’..
‘:. ‘.‘.
:
:
2
4
‘6’
I
I 8
.,
.,.
::
j;, : t
.:
.Collection’ (3 min) ‘:
I I
.-.
..
.,. -:: .:: .:..::.i,
y
:’ :‘:
‘.’
Collection
/
13min)
.:
:.‘;:.., .‘.
,‘:,
;
,“.
.:‘,
:
i.?‘.; ,,
.I.’ ..
.‘.‘.,. ...b ‘,
..:.
,‘..f .. ..
.:,
:,;...
.:
,.
‘.
:::..:
.; : :
SESSION
Recovery
Exercise
Resting
0
STUDY
.,) _,.
‘..
.,: .::
:’ ,,,
..,,,.”
., ;., ,,,,
,;; .::.I ’
‘. ,.
,.:
.’ :
:,
.:i:_.;,‘.’
:
..’
:
.::.
Collection, (IO
,’
.,
,, -:..:.:,, ,. .::.:‘.i., ;
. . .; :
min)
: I:
;
‘.:...
..
:. ‘_ ::, :.;_...;..? .;::.‘Y::..;
‘~‘.$j
,,. ,..,:: :‘:.,y’., ::,,:: .. ,. ..:...:, ..,, .; ‘1.,-.:.:.~.:~.::.:.:.~r .::., ...., .,: :. :: ‘1 .,:.: “’ ‘.:.., .L:. . .::.: .....:,y.:.: .:‘;:.:;,...... ::,.: _.: :. :: .; :.,‘-‘: .:. .;_: ,. ..‘;,,, ,,,, :._ : ‘. ‘.:y.,‘::;;.: >:.. / .:,. ..::::::.::.:y j ..:.., :. ,,:.;...< ,.,:: ::,:j ,..’;.i:.!, . .,.,_.,::yi.::‘: ;,;..:::.:+): ,. :. .. ..I ‘, ” .‘::. ..:,2,.,’ ‘. ..,. :.:, ;.,,: :.,.>,. ..,.,..., ;; 12. 14 16 I8 2d’ 22 IO
Minutes
Fig. 1. The times of sample areas indicate
collections
the times of sampling.
the bicycle ergometer
but disconnected
at each study After the resting
session are graphically sample collection.
from the mouthpiece
of short duration
and is noted
for reasons
by the asterisk
demonstrated.
the subject of comfort.
remained
The darker seated on
This interval
was
(*).
healthy and physically tit. Each subject was studied at monthly intervals during pregnancy and again at 2, 6 and 12 weeks and 6 months postpartum. All studies were performed in the morning with outpatient subjects after a breakfast of only orange juice and dry toast. On the first visit, the procedures were carefully explained to each subject, a complete history and physical examintion was performed, and a practice session with the equipment was conducted. At each subsequent study session the subject was weighed, her blood pressure was determined, her temperature was obtained and an obstetrical or gynecological examination was performed. During this study, the subject was seated on a Godart bicycle ergometer and a nose clip completely occluded the nares. A mouthpiece designed to prevent the undirected escape of air was attached to a respiratory valve which, in turn. was connected by a short tubing through a three-way valve to a series of rubber (neoprene) collecting bags. Three collections of expired air were made during each study (fig. 1). The first was collected for the last three minutes of six minutes at rest before exercise began. The second collection was made during the last three minutes of a six-minute exercise period. The third sample was collected throughout the first ten minutes of recovery following the exercise. Exercise was conducted at a load of 50 watts and at pedaling rates between 40 and 50 r.p.m. According to the manufacturer’s specifications this imposes a fixed work load of 306 kpm/min. Each collection of expired air (resting, exercise and recovery) was analyzed for oxygen partial pressure by a Beckman (Pauling principle) oxygen analyzer and the concentration of oxygen in expired air (FEDS) was calculated from this and the atmospheric pressure. The analyzer was calibrated with test gases alternately with each sample. Expired CO, concentration (FE,,,) was measured using a Beckman infrared photometer; results of CO, analyses are reported separately (Pernoll et al., 1975). The volume of each collection was
OXYGEN ~NSUM~ION
AT REST AND DURING EXERCISE IN PREGNANCY
287
measured in a Tissot spirometer and corrected to standard conditions. All measurements were completed within 30 minutes of air collection. Measured volumes of expired gas were corrected for sampling losses, converted to body temperature and ambient pressure (BTPS), and expressed per minute of collection (QE). Oxygen consumption was calculated: (see Dejours, 1966b) voz
=
h(F]~o,- FIo&zoz -Fd 1 - FIN,
Since room air was inspired in all our studies, this equation simpli~es to: V = &(0.21-0.21 FE,,,-FE,,) 02 0.79 i’oZ was converted to STPD conditions (0 “C, 760 mm Hg, dry). The oxygen debt was calculated by subtracting the 7;‘02at rest from the Vo, during recovery and multiplying by ten for the ten-minute recovery collection. Unpublished data from this laboratory have shown that pregnant subjects repay the oxygen debt accrued by exercise of this intensity and duration within ten minutes of completing exercise. Several subjects required hospitalization in the final weeks of pregnancy; therefore, data for 35-38 weeks were obtained on only ten patients and for 3942 weeks on only eight patients. Consequently, statistical comparison of those data with postpartum values by paired t-test is handicapped by the smaller number of patients, and group data are used for statistical comparison of some of the results. In all cases, evaluation of probability was made against 2-tailed tables. Percentage changes were calculated in relation to the values at 12-14 weeks postpartum, because no significant changes were observed between those values and the sixmonth postpartum values. The data are presented in table 1 and figs. 224. Results GENERAL
The patients had an average weight decline of 12.3 kg following delivery (from 74.1 to 61.8 kg), a 20% difference from the last pregnancy value (obtained at 39-42 weeks) when compared to 12-14 weeks postpartum. Six of the twelve were lactating during all of the postpartum evaluations and were not taking oral contraceptives or menstruating. There were no estrogens, progestins or androgens administered to prevent lactation. Three of the 12 subjects started combination oral contraception at four weeks postpartum after the first evaluation was performed (type and dosage varied). RESTING OXYGEN CONSUMPTION
Figure 2 represents the data on qo, at rest and with exercise. There is a progressive increase in resting if,, as pregnancy advances. This increase is significant by paired f-test throughout pregnancy compared to the value 12-14 weeks postpartum (table
288
M. L. PERNOLL et Ul.
I), Resting idol is increased by 3391 at 39-42 weeks of pregnancy 12-14 weeks postpartum.
compared
to
EXERCISE OXYGEN CONSUMPTION
From the exercise data (fig. 2). it is seen that ii,, during standard steady-state exercise undergoes a nearly progressive increase as pregnancy advances. When the values obtained during pregnancy are compared to the 12-14 week postpartum Delivery 1500 -
A--A Rest A-A Exercise
1400 -
t 1300 -
T
t 1200 1100 2
IO00
? $
900 -
a@
800 750 It 400
200 300 i -rt
,r
1
I
I
I
I
I
19-22 23-26 27-30 31-34 35-38 39-42
-f-J 2-4
6-8
Postpartum
Pregnancy
Q-14
6 MOS.
Weeks Fig. 2. The oxygen consumption at rest and with mild nonweight-bearing steady-state exercise is illustrated during pregnancy and postpartum. The means (triangles) are connected by a line. The smaller circles represent the individual values corrected to STPD. Length of each vertical line represents the range of values.
values by paired r-test, the increase is statistically signj~cant from 27-30 weeks through delivery (table 1). Exercise irot is increased by an average of 150~;at 39-42 weeks of pregnancy when compared to 12-14 weeks postpartum.
OXYGEN
CONSUMPTION
AT REST AND
DIJRING
EXERCISE
IN PREGNANCY
288
290 OXYGEN
M. L. CONSUM~IO~
CHANGE
WITH
PERNOLL
el Uf.
EXERCISE
(A7j02=
EXERCISE
iio,
MINUS
RESTING ire,)
Figure 3 illustrates the data, which show that Airo2 is increased during gestation. The difference in A\jo2 between 12-14 weeks postpartum and 39-42 weeks of pregnancy is S(;/,. There is no statistical significance by paired t-test during pregnancy when compared to the value 12-14 weeks postpartum (see table 1). This statistical result is explained by the small size of the group at 39-42 weeks, as mentioned above. If a nonpaired t-test is performed, comparing all values from 3142 weeks of pregnancy with all postpartum values, P
