REFLEX CONTROL OF AUTONOMIC FUNCTION INDUCED BY POSTURE CHANGE DURINGTHE MENSTRUAL-CYCLE

This study was designed to determine whether autonomic regulation indu ced by posture changes varies during the menstrual cycle. Heart rate v ariability (HRV) was analyzed in women with normal menstrual cycles (n = 10, age range 20-37 years) during 3 min periods of controlled frequ ency breathing (15 breaths/min) in supine followed by sitting position s. In a supine or sitting position, high frequency (HF) components of HRV, which reflects only parasympathetic activity, were significantly high in the follicular phase compared with those in the menstrual phas e, suggesting that parasympathetic nerve activity increases in this ph ase. Following the change of position to sitting from supine, the HF c omponent decreased significantly in the menstrual, ovulatory and lutea l phases, but not the follicular or premenstrual phase. After changing the position to sitting, the low to high frequency component ratio, w hich reflects the balance of autonomic nerve activities, was increased significantly in the menstrual, luteal and premenstrual phases, indic ating that sympathetic nerve activities in these phases became predomi nant by the sitting position. These results suggest that parasympathet ic nerve activity is predominant in the follicular phase, resulting in an impairment of baroreflex caused by posture changes. Moreover, baro reflex control of the sympathetic component, not the parasympathetic c omponent, increases in the premenstrual phase, while the reflex respon se of the sympathetic component is less in the ovulatory phase compare d with the menstrual or luteal phase. We concluded that baroreflex reg ulation of autonomic functions induced by changing positions is modifi ed during the menstrual cycle. A difference of a balance of ovarian ho rmones may be responsible for these changes of autonomic functions dur ing the menstrual cycle. (C) 1997 Elsevier Science B.V.