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  • Title: A comparison of cross-sectional and longitudinal methods of assessing the influence of pregnancy on cardiac function during exercise.
    Author: Khodiguian N, Jaque-Fortunato SV, Wiswell RA, Artal R.
    Journal: Semin Perinatol; 1996 Aug; 20(4):232-41. PubMed ID: 8888449.
    Abstract:
    To evaluate the influence of pregnancy on resting and exercise cardiac function, we studied 16 nonpregnant and 26 pregnant females in a two-phase study. During phase I, all pregnant subjects (P1) (mean gestational age = 29.5 +/- 7 weeks) were compared with 16 control (C) subjects. In phase II, 8 of the pregnant subjects (P2) (mean gestational age = 32.6 +/- 6 weeks) were evaluated again at 12.5 +/- 7 weeks postpartum (PP). Using Collier's CO2 rebreathing technique, exercise cardiac output (Q) was measured on a cycle ergometer during rest and at three submaximal work levels (25, 50, and 75 W), during the last minute of 5 to 7 minutes of steady-level power output. Metabolic parameters [ventilation (VE), heart rate (HR) and oxygen consumption (VO2)] were measured during the submaximal tests and throughout the progressive increase in work after the last measure of Q, until peak VO2 was achieved. The results from the phase I comparison indicated (as expected) higher resting heart rates [(90.0 +/- 3 P1; 81.8 +/- 3 bpm C), ventilation (9.5 +/- 0.3 P1; 7.5 +/- 0.5 L min-1 C), and resting oxygen consumption (0.263 +/- 0.07 P; 0.221 +/- 0.01 L min-1 C) associated with pregnancy, and these findings were similar when the pregnant subjects were compared with their postpartum values. Analysis of the various indices of cardiac function [Q, stroke volume (SV), and arteriovenous oxygen difference (A-VO2 diff)] resulted in statistically higher resting Q in pregnancy when compared with C and PP conditions. No resting differences were observed for SV or A-VO2 diff in either phase of the study. The results of the submaximal exercise tests indicated no significant differences in HR nor VO2 between P1 and C; however, P2 had significantly higher submaximal heart rates and oxygen consumption when compared with PP. Further, no significant differences were observed between P1 and C for Q, SV or A-VO2 diff, whereas P2 versus PP resulted in significantly lower SV and higher A-VO2 diff in the pregnant subjects. These findings suggest that pregnancy/control versus pregnancy/ postpartum studies yield statistically different results and that an effort needs to made by the research community to develop standardized methodologies to evaluate physiological processes in pregnancy.
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