Maternal Heart Rate and Stroke Volume in the Pygmy Goat: Effects of Exercise and Cardiac Autonomic Blockade

Abstract

SUMMARYTo determine the normal maternal heart rate and stroke volume response to exercise and the role of the autonomic nervous system in this response, pregnant and non-pregnant pygmy goats were studied at rest, during and following treadmill exercise, and after autonomic blockade. Resting heart rates, stroke volumes and cardiac outputs were 10%, 60%, and 76% higher in pregnant compared to non-pregnant animals (P < 0 05, 0 001, and 0 001 respectively). During exercise, heart rate and stroke volume rose in both pregnant and non-pregnant animals by similar amounts. Immediately post-exercise, stroke volume in pregnant animals dropped precipitously below resting levels by 15% (P < 0005) but cardiac output was preserved by heart rate. This fall in stroke volume was not seen in control animals. Autonomic blockade lowered resting and exercise heart rates in both groups without changing stroke volume. The elevations in heart rate and stroke volume in pregnancy are not primarily mediated via the autonomic nervous system. Although the maternal cardiac output response to exercise appears normal, the post-exercise fall in stroke volume, presumed secondary to a reduction in preload, could potentially be harmful to both mother and fetus.

The effects of aerobic exercise on the pregnant woman, fetus, and pregnancy outcome A review

“…Additionally, stroke volume in pregnant women fell to control values within 3 minutes of recovery whereas it remained above control values at 5 minutes after exercise in postpartum subjects. This fall in stroke volume immediately after exercise also has been observed in pregnant goats, but not in nonpregnant goats 7 . The authors hypothesized that decreased stroke volume after exercise was due to a reduction in preload resulting from decreased venous return in pregnant subjects.…”

“…Cardiac output is a function of stroke volume and heart rate, and is increased by 30 to 50% during pregnancy 21 . Several investigators have reported that cardiac output increases further during exercise in pregnant animals 5,7 and humans, 13,15,19 and these values are higher throughout gestation than those of nonpregnant controls 19,22 . In contrast, other investigators have reported similar cardiac outputs in pre‐ and post‐partum subjects after short‐term cycle exercise 14,15 .…”

“…Maternal heart rate is increased during exercise in animals 4–7 and humans 8–19 . Depending on the study, the amount of increase is either slightly higher 4,9,13,14 or not significantly different from nonpregnant, exercising controls 5,7,10,15,19 . Resting heart rate is elevated in both trained and untrained women during pregnancy 14,15,20,21 …”

“…Studies of stroke volume during maternal exercise have yielded conflicting results. Several investigators have reported that stroke volume increases in response to exercise in pregnant goats 5,7 and women 13,15,19 . Stroke volume has been reported to be higher in pregnant than in nonpregnant women both during exercise and at rest 13 .…”

Telemetric registration of heart rate and blood pressure in the same unrestrained goats during pregnancy, lactation and the non‐pregnant, non‐lactating period

“…Similar results have been reported earlier in goats ( Hoversland et al . 1974 , Hosenpud et al . 1986 , Olsson et al .…”