-
[show abstract]
[hide abstract]
ABSTRACT: The pulmonary circulation is a high flow and low pressure circuit, with an average resistance of 1 mmHg.min.L(-1) in young adults, increasing to 2.5 mmHg.min.L(-1) over 4-6 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 20-25 mmHg threshold associated with interstitial lung edema and altered ventilation/perfusion relationships. Pulmonary artery pressures of 40-50 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.
Comprehensive Physiology. 01/2012; 2(1):711-741.
-
[show abstract]
[hide abstract]
ABSTRACT: Exercise stress tests have been used for the diagnosis of pulmonary hypertension, but with variable protocols and uncertain limits of normal. The pulmonary haemodynamic response to progressively increased workload and recovery was investigated by Doppler echocardiography in 25 healthy volunteers aged 19-62 yrs (mean 36 yrs). Mean pulmonary artery pressure ((Ppa)) was estimated from the maximum velocity of tricuspid regurgitation. Cardiac output (Q) was calculated from the aortic velocity-time integral. Slopes and extrapolated pressure intercepts of (Ppa)-Q plots were calculated after using the adjustment of Poon for individual variability. A pulmonary vascular distensibility alpha was calculated from each (Ppa)-Q plot to estimate compliance. (Ppa) increased from 14+/-3 mmHg to 30+/-7 mmHg, and decreased to 19+/-4 mmHg after 5 min recovery. The slope of (Ppa)-Q was 1.37+/-0.65 mmHg x min(-1) x L(-1) with an extrapolated pressure intercept of 8.2+/-3.6 mmHg and an alpha of 0.017+/-0.018 mmHg(-1). These results agree with those of previous invasive studies. Multipoint (pa)-Q plots were well described by a linear approximation, from which resistance can be calulated. We conclude that exercise echocardiography of the pulmonary circulation is feasible and provides realistic resistance and compliance estimations. Measurements during recovery are unreliable because of rapid return to baseline.
European Respiratory Journal 11/2009; 35(6):1273-8. · 5.89 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Pulmonary hypertension (PH) is initially a disease of the small, peripheral resistance arteries. Changes in these vessels are best assessed by measurement of pulmonary artery pressure at several levels of flow to generate multi-point pressure-flow curves. This approach is superior to the traditional single-point measurement of pulmonary vascular resistance (PVR) because it allows a flow-independent definition of the resistive properties of that portion of the pulmonary vascular bed and also provides information on its distensibility. In animal models, multi-point pressure-flow curves can be obtained using an isolated, ventilated, perfused lung system. Clinically, cardiopulmonary exercise testing (CPET) with non-invasive echocardiography is feasible and provides realistic values of the resistance and peripheral compliance. Together, these values can be used to better understand and screen for PH and exercise-induced PH.
Engineering in Medicine and Biology Society, 2009. EMBC 2009. Annual International Conference of the IEEE; 10/2009
