The circulatory response to lifting and carrying and its modification by beta-adrenoceptor blockade

Abstract

The circulatory effects of lifting and holding weighted suitcases of 5, 10 and 15 kg, and carrying the same suitcases at two different walking speeds were evaluated in 6 normal subjects before and after beta-adrenoceptor blockade with 160 mg oxprenolol. Lifting and holding induced significant weight-induced increments in systolic and diastolic blood pressure which were not attenuated by beta-blockade. There was a significant increase in heart rate only on lifting the 15 kg weight which was attenuated by oxprenolol. Dynamic exercise (walking) with the same weighted suitcases resulted in rate and speed related increase in systolic pressure and heart rate, the magnitude of which was greater than that of lifting alone. The isometric pressor response was attenuated when walking and carrying at 2 mph, but completely abolished by the metabolic and heat induced vasodilatation when walking at 4 mph. Following beta-blockade both the absolute blood pressure and the systolic pressor and heart rate responses to combined lifting and carrying were attenuated. The diastolic pressor response induced by lifting, which was offset in the control period by the vasodilation induced by dynamic exercise was progressively attenuated proportionate to the load carried following beta-blockade; presumably this reflected systemic vasoconstriction to maintain mean perfusion pressure in the presence of central beta-blockade. These observations suggest that the isometric component which predominates at slow walking speeds when carrying weights between 5 and 15 kg is completely suppressed by the vasodilatation at fast walking speeds. Beta-blockade, while reducing heart rate and systolic pressor response to the same stimuli, leads to an augmented systemic vascular resistance which is particularly evident at high metabolic workloads.