Effects of human pregnancy on cardiac autonomic function above and below the ventilatory threshold

This study examined the effects of human pregnancy on heart rate variabilit y (HRV), spontaneous baroreflex (SBR) sensitivity, and plasma catecholamine s at rest and during exercise. Subjects were 14 healthy, physically active pregnant women (PG; mean gestational age = 33.9 +/- 1.0 wk). Results were c ompared with an age-matched nonpregnant central group (NPG; n. = 14) with s imilar characteristics. The electrocardiographic R-wave-R-wave interval and systolic blood pressure (via finger plethysmograph) were measured on a bea t-to-beat basis at rest and during upright cycling at 60 and 110% of the ve ntilatory threshold (T-vent). Parasympathetic nervous system (PNS) modulati on (as reflected by HRV high-frequency/total power and SBR slope) was signi ficantly reduced at rest in the PG vs. the NPG. During exercise, PNS modula tion decreased significantly in both groups, but the magnitude of PNS withd rawal from rest to 110% T-vent was smaller in the PG vs. NPG. Sympathetic n ervous system (SNS) modulation (reflected by the low-frequency power-to-hig h-frequency power ratio) increased above resting values at 60 and 110% T-ve nt in the NPG. SNS modulation at 110% T-vent was significantly lower in the PCT compared with the NPG. Plasma norepinephrine and epinephrine levels we re also lower at 110% T-vent in the PG. It was concluded that healthy pregn ant women exhibit lower PNS modulation at rest and blunted SNS modulation d uring exercise above T-vent in late gestation.