INTERACTION OF CARDIOVASCULAR REFLEXES IN EXERCISE

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During exercise in the heat the human cutaneous circulation participates in both temperature and blood pressure regulation, with the level of skin blood flow (SKBF) determined by the competing influences of active vasodilation (AVD) and vasoconstriction. We propose to examine the role of cardiopulmonary (CP) and arterial baroreceptors in the reflex control of forearm blood flow (and thus SKBF) during exercise by emphasizing in our studies how these reflexes interact with each other and with thermoregulatory reflexes. We will examine the stimulus-response characteristics of each baroreflex by selectively manipulating either carotid sinus transmural or central venous pressure. The linear relationship between forearm vascular resistance (FVR) and CVP determined during low levels of LBNP (0 to -20 mm Hg) will be used to define the sensitivity f the CP baroreflex. Arterial baroreflex sensitivity will be defined as the change in vascular resistance (total or forearm) per unit change in carotid sinus transmural pressure. We will monitor the following afferent inputs into the regulatory centers during selective and combined baroreceptor stimulation: arterial blood pressure (non-invasive, Dinamap), central venous pressure (19 gauge CVP line), and body temperature (core and skin). We will also monitor the following efferent responses as outputs from the regulatory centers: cardiac output (impedance cardiography or CO2 rebreathing), heart rate, and forearm blood flow (FBF). SKBF will be estimated from FBF measurements (venous occlusion plethysmography). We will examine the possibility that AVD may be modulated by baroreflex activity. Assuming, as others, that AVD activity is closely linked to sudomoter activity, modulation of AVD during baroreceptor unloading should be indicated by an altered control of local sweating (dew-point hygrometry).