Cardiac output and total vascular conductance responses to simulated carotid hypertension in young women: exercise and ovarian hormones

Abstract

Previously we reported that compared to men, young women during the early follicular (EF) phase of the menstrual cycle exhibited an enhanced carotid baroreflex (CBR) control of blood pressure (BP) to hypertensive stimuli at rest due to a predominant contribution of cardiac output (CO). Whether such changes are altered during exercise or by fluctuations in endogenous ovarian hormone concentrations is unknown. Thus, 5s pulses of neck suction (NS; −80Torr) were applied at rest and during steady‐state cycling at 50% heart rate (HR) reserve to activate carotid baroreceptors in 10 young women at 3 different menstrual cycle phases (EF, late follicular (LF), and mid luteal (ML)). Beat‐to‐beat HR and BP were measured. Stroke volume was estimated with Modelflow, and CO and total vascular conductance (TVC; CO/meanBP) were calculated. At rest, the change in CO was the major contributor in mediating BP changes to NS during all menstrual cycle phases (CO vs. TVC; 99±15% vs. −3±16%, EF; 105±22% vs. −10±25%, LF; 108±19% vs. −14±22%, ML; P>0.05). This effect was lost during exercise in which a greater contribution of TVC was observed (CO vs. TVC; 14±34% vs. 83±131%, EF; 16±10% vs. 84±9%, LF; 34±14% vs. 66±13%, ML; P>0.05). Our findings suggest that in contrast to rest, exercising women exhibit a greater involvement of TVC in the CBR control of BP to hypertension; an effect that is independent of menstrual cycle phase.Supported by R01HL093167