Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, C43
Influence of ovarian cycle on muscle metaboreflex control of spontaneous cardiac baroreflex sensitivity in young women.
D. Hartwich1, W. E. Dear1, L. A. Kirtley1, S. M. Taylor1, J. L. Waterfall1, J. P. Fisher1
1. School of Sport & Exercise Sciences, University of Birmingham, Birmingham, United Kingdom.
The partial restriction of blood flow to the dynamically exercising skeletal muscles decreases spontaneous cardiac baroreflex sensitivity (cBRS) in dogs. The augmented activation of metabolically-sensitive skeletal muscle afferents (i.e. muscle metaboreflex) might explain this apparent reduction in cBRS, however whether this occurs in humans remains unclear. Accumulating evidence suggests that ovarian hormones may modulate resting baroreflex sensitivity and the muscle metaboreflex mediated cardiovascular responses to exercise. However, it is presently unknown whether ovarian cycle influences muscle metaboreflex control of spontaneous cBRS. To examine this, 11 healthy women not taking oral contraceptives (age 20±1 years, weight 61±3 kg, height 164±2 cm) were studied during two phases of their ovarian cycle: the early follicular phase (days 1-5) and the late follicular phase (days 10-15; identified using an ovulation kit). Steady-state leg cycling exercise was performed at low (90 bpm; 19±3 Watts) and moderate (120 bpm; 70±5 Watts) intensities, under free-flow conditions and with muscle metaboreflex activation induced by bilateral thigh cuff inflation (100 mmHg). Heart rate (HR; ECG) and beat-to-beat blood pressure (BP, Portapress) were continuously monitored. Spontaneous cBRS was estimated using the sequence technique. Statistical analyses were performed using two-way repeated-measures ANOVA with Bonferoni post hoc tests. Leg cycling under free-flow conditions induced an intensity dependent increase in HR (P<0.05), while BP remained unchanged from rest. Muscle metaboreflex activation markedly increased HR and BP at low (+12±2 bpm and +14±2 mmHg) and moderate (+19±2 bpm and +19±2 mmHg) exercise workloads (P<0.05). Leg cycling under free-flow conditions tended to evoke an intensity dependent reduction in cBRS (21±5, 7±1 and 1±0.1 ms/mmHg at rest, low and moderate workloads, respectively). Muscle metaboreflex activation reduced cBRS during low intensity exercise (-2.0±0.5 ms/mmHg, P<0.05), but not during moderate intensity exercise (-0.1±0.1 ms/mmHg, P>0.05). The HR, BP and cBRS responses to leg cycling exercise under free-low conditions, or with muscle metaboreflex activation, were no different during early and late follicular phases. Our data suggest that partial restriction of blood flow to the dynamically exercising skeletal muscles (i.e. muscle metaboreflex activation) decreases spontaneous cBRS during low intensity exercise in young women. However, muscle metaboreflex control of spontaneous cBRS is similar during the early and late follicular phases of the ovarian cycle.
Where applicable, experiments conform with Society ethical requirements