Cardiovascular autonomic reflexes in mid-pregnancy.

OBJECTIVE

To study the physiological responses to noninvasive cardiovascular autonomic function tests in normal pregnancy.

DESIGN

Cardiovascular autonomic responses in 60 women at 22 to 29 weeks gestation and 62 nonpregnant women were investigated using the Valsalva manoeuvre as well as orthostatic, quiet breathing, deep breathing, and isometric handgrip tests.

RESULTS

Compared with nonpregnant women, those who were pregnant showed significantly lower heart rate variability during normal breathing and a blunted tachycardic reaction to blowing during the Valsalva manoeuvre. The vagally controlled biphasic heart rate response to standing was also attenuated in the pregnant group.

CONCLUSIONS

The cardiovascular responses were blunted in mid-pregnancy indicating a decrease in parasympathetic cardiovascular control.