Arterial blood pressure and carotid baroreflex function during arm and combined arm and leg exercise in humans

During arm cranking (A) blood pressure is higher than during combined arm and leg exercise (A + L), while the carotid baroreflex (CBR) is suggested to reset to control a higher blood pressure in direct relation to work intensity and the engaged muscle mass.

This study evaluated the function of the CBR by using neck pressure and neck suction during upright A, L and A + L in 12 subjects and, in order to evaluate a potential influence of the central blood volume on the CBR, also during supine A in five subjects. Exercise intensities for A and L were planned to elicit a heart rate response of c. 100 and 120 beats min(-1), respectively, in the upright position and both workloads were maintained during A + L and supine A.

The CBR operating point, corresponding to the pre-stimulus blood pressure, was 88 +/- 6 mmHg (mean +/- SE) at rest. During upright A, L and A + L and supine A it increased to 109 +/- 9, 95 +/- 7, 103 +/- 7 and 104 +/- 4 mmHg, respectively, and it was thus higher during upright A than during A + L and supine A (P < 0.05). In addition, the CBR threshold and saturation pressures, corresponding to the minimum and maximum carotid sinus pressure, respectively, were higher during upright A than during supine A, A + L, L and at rest (P < 0.05) with no significant change in the maximal reflex gain.

These findings demonstrate that during combined arm and leg and exercise in the upright position the CBR resets to a lower blood pressure than during arm cranking likely because the central blood volume is enhanced by the muscle pump of the legs.