Browsing by Author "Tyberg, John Victor"
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Item Open Access Conductance and Capacitance Effects of Acute, Electrical, Carotid Baroreflex Stimulation(2013-04-16) Burgoyne, Steven John Joseph; Tyberg, John VictorBaroreflex activation therapy (BAT) is effective in resistant hypertension; we hypothesized that BAT increases both venous capacitance and arterial conductance. We measured aortic pressure and flow and inferior vena caval flow and used a modified Brooksby-Donald technique to evaluate sub-diaphragmatic blood volume. Data were recorded with BAT, and with sodium nitroprusside (SNP) and Angiotensin II (Ang II) infusions, alone and with BAT. BAT substantially increased venous capacitance and arterial conductance. SNP also increased venous capacitance and arterial conductance. During SNP infusion BAT remained effective, further decreasing blood pressure and increasing capacitance and conductance. Ang II decreased both capacitance and conductance. During Ang II infusion, increased BAT reversed the decrease in venous capacitance while restoring BP completely and conductance to 80% of baseline. BAT decreases blood pressure and increases arterial conductance and venous capacitance, even when combined with powerful vasoactive drugs. These may be important effects in hypertension.Item Open Access Reservoir-Wave Analysis Applied to the Pulmonary Circulation(2012-09-13) Bouwmeester, James Christopher; Tyberg, John VictorThe purpose of applying the reservoir-wave model to the pulmonary circulation is to validate the resulting reservoir and wave parameters against known physiologic responses. The reservoir model represents a modified windkessel and describes the lumped resistance to flow, compliance of vessels and the downstream pressure at which modeled outflow ceases. Applied to arteries and veins in tandem, a complete description of the pulmonary circulation is possible. The reservoir model determines the reservoir pressure, which is subtracted from measured pressure. The difference is called excess pressure and it is used with wave intensity analysis to quantify the effects of incident waves and their reflections. The changes to reservoir function and wave patterns may be helpful in providing extra diagnostic information regarding pulmonary hypertension and providing targets for treatment of this disease. Measurements of pressure and flow were made in the main pulmonary artery and pulmonary vein in 15 anesthetised, open-chest dogs. Six different conditions were created by the addition of blood volume and the application of positive end-expiratory pressure (PEEP). At each condition, hypoxic ventilation was used to create vasoconstriction and then, inhaled nitric oxide was used to create vasodilation. Ventilation changes are the focus of experimentation because hypoxia represents a pulmonary hypertension disease state and nitric oxide represents a common treatment. Both arterial and venous reservoir resistance increased with hypoxia and decreased with nitric oxide but only arterial reservoir resistance was fully reversed with nitric oxide. With excess pressure, arterial wave patterns revealed the presence of a prominent negative reflection occurring from the junction of arteries branching from the left or right pulmonary artery. Venous wave patterns showed that the left atrium and ventricle are responsible for the majority of measured pressure fluctuations but a wave transmitted from the pulmonary arteries is measurable during the filling of the left atrium. Overall, results are in general agreement with hypothesized physiological changes, which serves to validate the application of the reservoir-wave model and allows both the vascular characteristics and wave propagation to be quantified in ways that other models can not.