Assessment of the viscosity of the pulmonary artery wall.

Large artery wall viscosity reduces the efficiency of heart/vessel coupling. The aim of the present study was to assess pulmonary artery wall viscosity through comparison of the static (Dst) and dynamic distensibility (Ddyn) of the vessel wall. Right pulmonary artery pressure and diameter was measured in 13 patients and eight healthy volunteers. Ddyn was calculated as the relative change in end-diastolic diameter induced by the pressure pulse, and Dst as the relative change in mean diameter induced by the change in mean pressure during steady-state exercise. Dst did not differ significantly from Ddyn (mean+/-SD 22.8+/-19.2 versus 21.0+/-18.3 10(-3) mmHg(-1)), as tested by paired t-test and analysis of covariance, with age as covariant. End-diastolic diameter increased, whereas Dst and Ddyn decreased as a function of age (r=-0.69 and -0.67, respectively; p<0.01 for both). Ddyn did not change from rest to exercise in spite of a 23+/-16-beats-min(-1) increase in cardiac frequency. Pulmonary artery wall viscosity was negligible and no increase in wall viscosity occurred during cardioacceleration.