The relationship of pulmonary vascular resistance and compliance to pulmonary artery wedge pressure during submaximal exercise in healthy older adults.

Abstract

A consistent inverse hyperbolic relationship has been observed between pulmonary vascular resistance and compliance, although changes in pulmonary artery wedge pressure (PAWP) may modify this relationship. This relationship predicts that pulmonary artery systolic, diastolic and mean pressure maintain a consistent relationship relative to the PAWP. We show that, in healthy exercising human adults, both pulmonary vascular resistance and compliance decrease in relation to exercise-associated increases in PAWP. Pulmonary artery systolic, diastolic and mean pressures maintain a consistent relationship with one another, increasing linearly with increasing PAWP. Increases in PAWP in the setting of exercise are directly related to a decrease in pulmonary vascular compliance, despite small decreases in pulmonary vascular resistance, thereby increasing the pulsatile afterload to the right ventricle. The resistive and pulsatile components of right ventricular afterload (pulmonary vascular resistance, Rp; compliance, Cp) are related by an inverse hyperbolic function, expressed as their product known as RpCp-time. The RpCp-time exhibits a narrow range, although it may be altered by the pulmonary artery wedge pressure (PAWP). Identifying the determinants of RpCp-time should improve our understanding of the physiological behaviour of pulmonary arterial systolic (PASP), diastolic (PADP) and mean (mPAP) pressures in response to perturbations. We examined the effect of exercise in 28 healthy non-athletic adults (55±6years) who underwent right heart catheterization to assess haemodynamics and calculate Rp and Cp. Measurements were made at rest and during two consecutive 8-10min stages of cycle ergometry, at targeted heart-rates of 100beatsmin(-1) (Light) and 120beatsmin(-1) (Moderate). Cardiac output increased progressively during exercise. PASP, PADP, mPAP and PAWP increased for Light exercise, without any further rise for Moderate exercise. RpCp-time decreased for Light exercise (0.39±0.08 to 0.25±0.08, P<0.001) without any further change for Moderate exercise, and the decrease in RpCp-time was related to changes in PAWP (r(2) =0.26, P<0.001). Changes in PASP (r(2) =0.43, P<0.001), PADP (r(2) =0.47, P<0.001) and mPAP (r(2) =0.50, P<0.001) were linearly correlated with changes in PAWP, although they were not significantly related to changes in cardiac output. In healthy adults, exercise is associated with decreases in Cp and a resultant decline in RpCp-time, indicating increased pulsatile right ventricular afterload. Changes in RpCp-time, PASP, PADP and mPAP were systematically related to increases in PAWP.