Effects of withdrawal and reinfusion of blood on limb circulation at rest and during contralateral isometric handgrip

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Abstract
An isometric handgrip induces a rapid decrease in vascular resistance in the resting contralateral forearm presumably mainly mediated by β-adrenergic effects. This response was used to elucidate if a moderate blood loss provokes an altered peripheral vascular reactivity. Thus, heart rate, arterial pressures and forearm and calf blood flow were studied in eight healthy males at rest, and during contralateral isometric handgrip (CIH) before and after withdrawal of about 16% of the blood volume and again after reinfusion. Resting values of cardiac output, right atrial and pulmonary arterial pressures were also measured. Blood withdrawal reduced stroke volume and cardiac output by one fifth and slightly decreased arterial pressure compared to control state, thus total systemic resistance was increased. Mean forearm and calf blood flows were not significantly changed although forearm vascular resistance increased moderately. The response to CIH of heart rate and arterial mean pressure was similar in the normovolaemic and hypovolaemic states. In normovolaemia the effect of CIH on forearm resistance was an initial reduction which is in accordance with previous findings. After blood withdrawal the fractional reduction in forearm vascular resistance was less than in the control state. Thus the circulatory response to CIH was changed in hypovolaemia but it cannot be assessed whether the altered vascular reaction to CIH should be attributed to a less marked β-adrenergic activity or to a more marked sympathetic vasoconstrictor drive counteracting the β-adrenergic effects.