Study: NCT05923840

Intervention type: DIAGNOSTIC_TEST
Group type: ACTIVE_COMPARATOR
Intervention: Chemoreflex Testing
Description: The carotid body chemoreflex can be tested by holding carbon dioxide (CO2) constant (isocapnic) and applying hypoxia and hyperoxia. Measurements are then made of expiratory minute volume and of sympathetic activity. The central chemoreflex measures isocapnic and hypercapnic responses in the presence of hyperoxia to suppress the carotid body chemoreflex.

Intervention type: DIAGNOSTIC_TEST
Group type: ACTIVE_COMPARATOR
Intervention: Chemoreflex Testing
Description: The carotid body chemoreflex can be tested by holding carbon dioxide (CO2) constant (isocapnic) and applying hypoxia and hyperoxia. Measurements are then made of expiratory minute volume and of sympathetic activity. The central chemoreflex measures isocapnic and hypercapnic responses in the presence of hyperoxia to suppress the carotid body chemoreflex.

Intervention type: DIAGNOSTIC_TEST
Group type: ACTIVE_COMPARATOR
Intervention: Chemoreflex Testing
Description: The carotid body chemoreflex can be tested by holding carbon dioxide (CO2) constant (isocapnic) and applying hypoxia and hyperoxia. Measurements are then made of expiratory minute volume and of sympathetic activity. The central chemoreflex measures isocapnic and hypercapnic responses in the presence of hyperoxia to suppress the carotid body chemoreflex.

Intervention type: DIAGNOSTIC_TEST
Group type: ACTIVE_COMPARATOR
Intervention: Baroreflex testing
Description: Baroreceptors are measured by the change of heart rate (HR) and sympathetic activity with changing blood pressure using the modified Oxford technique. Blood pressure is lowered an amount by a bolus of sodium nitroprusside and then raised by a bolus of phenylephrine. When standing baroreflexes are activated and the investigators will measure chemoreflex activity upright to see how baroreflex effects the chemoreflexes. Similarly chemoreflexes affect the baroreflexes best observed when the patients are supine.

Intervention type: DIAGNOSTIC_TEST
Group type: ACTIVE_COMPARATOR
Intervention: Baroreflex testing
Description: Baroreceptors are measured by the change of heart rate (HR) and sympathetic activity with changing blood pressure using the modified Oxford technique. Blood pressure is lowered an amount by a bolus of sodium nitroprusside and then raised by a bolus of phenylephrine. When standing baroreflexes are activated and the investigators will measure chemoreflex activity upright to see how baroreflex effects the chemoreflexes. Similarly chemoreflexes affect the baroreflexes best observed when the patients are supine.

Intervention type: DIAGNOSTIC_TEST
Group type: ACTIVE_COMPARATOR
Intervention: Baroreflex testing
Description: Baroreceptors are measured by the change of heart rate (HR) and sympathetic activity with changing blood pressure using the modified Oxford technique. Blood pressure is lowered an amount by a bolus of sodium nitroprusside and then raised by a bolus of phenylephrine. When standing baroreflexes are activated and the investigators will measure chemoreflex activity upright to see how baroreflex effects the chemoreflexes. Similarly chemoreflexes affect the baroreflexes best observed when the patients are supine.

Intervention type: DIAGNOSTIC_TEST
Group type: ACTIVE_COMPARATOR
Intervention: Orthostatic stress testing
Description: Orthostatic Stress tests are administered in two forms: a standing test to evoke the initial orthostatic hypotensive response that sensitizes and triggers the carotid body chemoreflex by intermittent stagnant ischemia. And the 70 degree upright tilt test that best identifies causal changes in regional blood volumes and flows and in respiratory patterns of hyperpneic hypocapnia.

Intervention type: DIAGNOSTIC_TEST
Group type: ACTIVE_COMPARATOR
Intervention: Orthostatic stress testing
Description: Orthostatic Stress tests are administered in two forms: a standing test to evoke the initial orthostatic hypotensive response that sensitizes and triggers the carotid body chemoreflex by intermittent stagnant ischemia. And the 70 degree upright tilt test that best identifies causal changes in regional blood volumes and flows and in respiratory patterns of hyperpneic hypocapnia.

Intervention type: DIAGNOSTIC_TEST
Group type: ACTIVE_COMPARATOR
Intervention: Orthostatic stress testing
Description: Orthostatic Stress tests are administered in two forms: a standing test to evoke the initial orthostatic hypotensive response that sensitizes and triggers the carotid body chemoreflex by intermittent stagnant ischemia. And the 70 degree upright tilt test that best identifies causal changes in regional blood volumes and flows and in respiratory patterns of hyperpneic hypocapnia.