Clinical science
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The objective of the present study was to evaluate the influence of posture on the responses of blood pressure (BP) and heart rate (HR) to the Valsalva manoeuvre (VM). Neurohumoral activation, as well as changes in intravascular and intracardiac volumes and pressures, are well known effects of orthostatic stress. These changes are likely to have significant effects on cardiovascular reflexes, such as the response to the VM. ⋯ We conclude that posture has a significant influence on BP responses to the VM, probably resulting from changes in the intrathoracic blood volume. Standing results in a lower rate of 'flat-top' responses, but also seems to reduce the specificity of this test. Sympathetic activation in the upright position seems to blunt baroreflexes, leading to similar HR responses in spite of larger changes in BP.