Errors in predicting in pregnant women

maximal

oxygen consumption

FREDERIK K. LOTGERING, PIET C. STRUIJK, MARIEKE B. VAN DOORN, AND HENK C. S. WALLENBURG Department of Obstetrics and Gynecology, Erasmus University School of Medicine and Health Sciences, 3000 DR Rotterdam, The Netherlands LOTGERING,FREDERIKK., PIET C. STRUIJK, MARIEKE B. VANDOORN,ANDHENKC.S.WALLENBURG. Errors inpredicting maximal oxygen consumption in pregnant women. J. Appl. Physiol. 72(2): 562~567,1992.-This study was designedto determine the accuracy of estimatedvalues of maximal heart rate (HR,,) and oxygen consumption (vo2) during pregnancy. We measuredHR and maximal vo2 (OO,,,) at rest and during cycle (CE) and treadmill exercise (TE) tests with rapidly increasing exercise intensities during gestation and after delivery. Pregnancy was found to affect the linear relationship of HR and %VO2m8X so that the intercept increaseswith advancing gestation and the slopedecreases.Estimated maximal HR WR,, esJ,220 - age (yr) X beats/min, overestimated measuredfiR,, by 8% (CE) and 5% (TE). For i702 1118x estimatedby Astrand’s nomogram (To2 mae,t ) and by linear extrapolation of submaximalvalues of HR and’ vo2 to HR,, e,t (To2 - estz), individual errors were large (SD 17-28%). Mean 'Ijo, L est overestimatedmeasuredVO, maxby 20% during CE but not dur-’ ing TE (-2%) and elicited the erroneous impression that VO2m8xdecreasesduring CE in pregnancy. Mean VO, maxest2valueswere not significantly different from measuredTO; m8xvalues.This apparent accuracy resulted from two opposingerrors: the I) HRrnax est overestimated HR,, , and 2) above 70%%70, m8x slope of ‘the HR-%To, maxrelationship was significantly reduced. Therefore neither method to estimate i702,, can replace the measurementof vo2 max. maximal exercise; heart

MAXIMAL OXYGEN CONSUMPTION (voZmax) is probably

the best indicator of the capability of an individual to perform endurance exercise. It can be measured reliably in a maximal exercise test, but exercise testing is often limited to submaximal intensities. In pregnant women, the study of exercise responses has been limited largely to submaximal exercise intensities because of fetal health concerns. . Several methods have been developed to estimate vo 2max from measurements made at submaximal exercise intensities, but their accuracy is limited and their validity is questionable (2,3). Resting values of heart rate (l$R) are increased more than oxygen consumption (VO,), whereas maximal values are not influenced markedly by pregnancy (5, 6). This suggests that pregnancy alters the relationship between HR and VO,, most notably at low exercise intensities. Therefore pregnancy may affect the validity of the two most common methods to 562

estimate V02 max: the Astrand nomogram and the technique of linear extrapolation of the HR-VO, line. The present study was designed to assess the accuracy of estimated values of maximal HR (HR,,) and VO, in pregnant and postpartum women. To this purpose, we studied women longitudinally during pregnancy and the postpartum period and measured their HR and VO, at rapidly increasing exercise intensities until maximal aerobic power was reached. METHODS

We studied 33 healthy women at 16,25, and 35 wk of pregnancy and 7 wk after delivery. All women were healthy and had uncomplicated singleton pregnancies. The physical fitness of the subjects who entered the study was variable, ranging between women with a sedentary lifestyle and competitive sportswomen. The study was approved by the Hospital and University Ethics Committee, and all women included in the study gave their informed consent. Details of subjects, study protocol, and data on maximal values of HR, VO,, CO, production, and ventilation have been previously reported (5). In short, a physical and obstetric examination was performed to confirm the health of all individuals participating in the study. After 20 min of rest, the subject was seated on a cycle ergometer and connected to an electrocardiogram monitor, a gas flowmeter, and an oxygen analyzer. After 5 min of rest on the cycle ergometer, during which baseline measurements were taken, the women started to exercise. Three minutes of warming up at 30 W were followed by stepwise increments in exercise intensity of 10 W every 30 s until maximal aerobic power was achieved. This was followed by 5 min of cooling down at 10 W. After 50 min of rest, a treadmill test was performed, preceded by 5 min of standing on the treadmill set at a fixed slope of 12%. Control measurements were taken at this’time. After 3 min of warming up at a speed of 2.0 km/h, the speed was increased by 0.33 km/h every 30 s until maximal aerobic power was achieved. This was followed by 5 min of cooling down at a speed of 1.0 km/h. Maximal aerobic power was defined by subjective maximal effort in the presence of at least two of the following objective criteria: 1) an increase in VO, of

Errors in predicting maximal oxygen consumption in pregnant women.

This study was designed to determine the accuracy of estimated values of maximal heart rate (HRmax) and oxygen consumption (VO2) during pregnancy. We ...
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