Hemodynamic, hormonal, and renal effects of (pro)renin receptor blockade in experimental heart failure.
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BACKGROUND: The (pro)renin receptor (P)RR is implicated in blood pressure regulation and the pathophysiology of heart failure (HF). The effects of (P)RR blockade in HF have not been previously investigated. METHODS AND RESULTS: Eight sheep received on 2 separate days a vehicle control and incremental intravenous boluses of a (P)RR antagonist, ovine handle region peptide (HRP) (1, 5, and 25 mg at 90-minute intervals), both before (normal) and after induction of HF by rapid left ventricular pacing. In normal sheep, HRP reduced heart rate (P<0.001) and hematocrit (P=0.019) compared with time-matched control data, without significantly affecting any other hemodynamic, hormonal, or renal variables. In sheep with HF, HRP treatment induced progressive falls in mean arterial pressure (P<0.001) in association with decreases in left atrial pressure (P<0.001), peripheral resistance (P=0.014), and hematocrit (P<0.001). Cardiac contractility tended to decline (P=0.096), whereas cardiac output was unaltered. HRP administration produced a dose-dependent decrease in plasma renin activity (P=0.004), with similar trends observed for plasma angiotensin II and aldosterone (P=0.093 and P=0.088, respectively). Circulating natriuretic peptides, endothelin-1, and catecholamine levels were unchanged. HRP also induced a reduction in plasma sodium concentrations relative to control (P=0.024), a natriuresis (P=0.046), and a tendency for creatinine excretion and clearance to improve. CONCLUSIONS: (P)RR antagonism in experimental HF resulted in cardiovascular and renal benefits in association with inhibition of the renin-angiotensin-aldosterone system. These findings suggest that (P)RR contributes to pressure/volume regulation in HF and identifies the receptor as a potential therapeutic target in this disease. (+info)
An angiographic technique for coronary fractional flow reserve measurement: in vivo validation.
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The pulmonary circulation is a high-flow and low-pressure circuit, with an average resistance of 1 mmHg/min/L in young adults, increasing to 2.5 mmHg/min/L over four to six decades of life. Pulmonary vascular mechanics at exercise are best described by distensible models. Exercise does not appear to affect the time constant of the pulmonary circulation or the longitudinal distribution of resistances. Very high flows are associated with high capillary pressures, up to a 20 to 25 mmHg threshold associated with interstitial lung edema and altered ventilation/perfusion relationships. Pulmonary artery pressures of 40 to 50 mmHg, which can be achieved at maximal exercise, may correspond to the extreme of tolerable right ventricular afterload. Distension of capillaries that decrease resistance may be of adaptative value during exercise, but this is limited by hypoxemia from altered diffusion/perfusion relationships. Exercise in hypoxia is associated with higher pulmonary vascular pressures and lower maximal cardiac output, with increased likelihood of right ventricular function limitation and altered gas exchange by interstitial lung edema. Pharmacological interventions aimed at the reduction of pulmonary vascular tone have little effect on pulmonary vascular pressure-flow relationships in normoxia, but may decrease resistance in hypoxia, unloading the right ventricle and thereby improving exercise capacity. Exercise in patients with pulmonary hypertension is associated with sharp increases in pulmonary artery pressure and a right ventricular limitation of aerobic capacity. Exercise stress testing to determine multipoint pulmonary vascular pressures-flow relationships may uncover early stage pulmonary vascular disease. (+info)
Relationship of right- to left-sided ventricular filling pressures in advanced heart failure: insights from the ESCAPE trial.
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