Maximal exercise testing in late gestation: Maternal responses

Objective: To study the effects of human pregnancy on metabolic and respira tory responses to maximal cycle ergometer testing and to test the hypothesi s that the respiratory exchange ratio at maximal exercise and peak postexer cise lactate concentration are lower in the pregnant compared with the nonp regnant state and that these effects are associated with lower excess poste xercise oxygen consumption during pregnancy. Methods: The pregnant (n = 14, mean gestational age 34.7 +/- 0.4 weeks) and nonpregnant control group (n = 14) included healthy, physically active wom en. Groups were matched for age, height, parity, prepregnant body mass and body mass index (BMI), and aerobic fitness. Breath-by-breath gas exchange w as measured at rest, during exercise, and 15 minutes after exercise. The mi nimum sample size to detect a statistically significant result for a reason able difference (0.25 L/min) in the ventilatory threshold was calculated to be ten subjects per group; thus, 14 was considered adequate. Results: Maximal oxygen uptake, the ventilatory threshold, the point of res piratory compensation, and calculated work efficiency did not differ signif icantly between groups. However, the respiratory exchange ratio at maximal exercise, peak postexercise lactate, and excess postexercise oxygen consump tion were significantly lower in the pregnant group. Peak lactate was signi ficantly correlated With the respiratory exchange ratio and excess postexer cise oxygen Consumption. Conclusion: The capacity for weight-supported work is preserved in late ges tation, and work efficiency is unchanged. However, carbohydrate utilization might be blunted at high levels of exertion. Blunted respiratory responses were attributed to reduced lactate production and/or dilution of lactate i n an expanded blood volume. (C) 2001 by The American College of Obstetricia ns and Gynecologists.