PHYSICAL CONDITIONING ATTENUATES RESPIRATORY RESPONSES TO STEADY-STATE EXERCISE IN LATE-GESTATION

Purpose: To study the ventilatory effects of closely monitored cycle e rgometer conditioning (HR target, 145-150 beats.min(-1); 25 min/sessio n; three sessions per week) during the second and third pregnancy trim esters (TMs) in healthy human pregnancy. Methods: Subjects were 27 pre viously sedentary pregnant women (exercised group, EG). A sedentary co ntrol group (CG, N = 20) was also studied. Subjects were tested at res t and during upright cycle ergometry at three steady-state power outpu ts (similar to 20, 45, and 65 W) at the start of the second TM (ENTRY) , al the end of the second and third TMs (post-training), and 3 months postpartum (PP, nonpregnant control). Results: Significant reductions in exercise HR were observed in the EG at each exercise level, confir ming achievement of an aerobic conditioning effect. In both groups the ventilatory equivalent for oxygen ((V)over dot(E)/(V)over dot O-2) wa s significantly higher at all work rates during pregnancy compared wit h that during PP. This effect was caused by significantly higher exerc ise tidal volumes (V-T) at each work rate in both groups during pregna ncy versus PP. Respiratory sensitivity as reflected by the ventilatory equivalent for carbon dioxide ((V)over dot (E)/(V)over dot CO2) and c alculated arterial carbon dioxide tension (PaCO2) was significantly in creased at all three work rates in late gestation versus PP and increa sed slightly with advancing gestational age in both groups. The main e ffects of physical conditioning were attenuation of increases in (V)ov er dot(E)/(V)over dot O-2 observed at all exercise levels between the end of TM2 and TM3 and reductions in respiratory perception of effort (RPEr) between ENTRY and the end of TM3. Attenuation of increases in ( V)over dot(E)/(V)over dot O-2, during TM3 in the EG was attributed to the combined effects of enhanced fat versus carbohydrate utilization ( resulting in reduced CO2 output and drive to ventilate) and attenuatio n of pregnancy-induced increases in dead space ventilation in late ges tation. Conclusion: The study results support the hypothesis that phys ical conditioning reduces both ventilatory demand and respiratory perc eption of effort in late gestation.