Accelerated respiratory response to moderate exercise in late pregnancy

We studied the rates of change of expired ventilation (VE, BTPS), O2 consumption (VO2, STPD) and CO2 production (VCO2, STPD) at the start and stop of 6 min of 50-W bicycle exercise, comparing 20 healthy young women at 38 weeks of pregnancy (G) and 3 months postpartum (NG). VO2, VCO2 and VE were significantly greater at rest for G than for NG. The absolute increases of VO2 and VCO2 from steady-state rest (SSR) to steady-state exercise (SSE) were the same for G and NG. The absolute increase of VE from SSR to SSE was significantly greater for G than NG. VCO2 and VE increased more rapidly in G than NG, but only during the first 90 sec of exercise. Recovery rates after exercise were equal for G and NG. We believe that lower extremity muscles of G contract on more distended veins at the onset of exercise, forcing increased volumes of venous blood through the lungs, increasing VO2 and VCO2. VE follows VCO2 closely.