EFFECTS OF CHRONICALLY ELEVATED PULMONARY ARTERIAL-PRESSURE AND FLOW ON RIGHT-VENTRICULAR AFTERLOAD

The effects of pulsatile hemodynamics on right ventricle-pulmonary cir culation interactions were studied in control lambs and in two lamb mo dels of altered pulmonary hemodynamics induced at infancy: elevated pu lmonary arterial pressure (PAP) was created by the infusion of monocro taline pyrrole (MCTP), and elevated pulmonary arterial blood flow was obtained by the creation of an arteriovenous fistula (Shunt). High-fid elity PAP, midvessel Doppler blood velocity (PAV), and cardiac output (CO) were measured in open-chest, anesthetized lambs. PAV waveforms we re normalized to match the measured CO. Measured pressure and flow sig nals were separated in the time domain into forward and backward compo nents. Pulmonary input impedance and indexes quantifying the timing of the reflected wave pulse (beginning of reflected pulse, duration of r eflected pulse in systole; and duration of reflected wave in diastole) were calculated for each group. Results indicate that in control anim als the reflected wave returned late in systole and extended through m uch of diastole, thereby increasing diastolic pressure like a counterp ulsation balloon. No significant differences in the timing indexes wer e found between Shunt and control animals. In the MCTP group, the refl ected wave returned significantly earlier than normal with the peak re flected pulse occurring before valve closure. The resulting augmentati on of systolic pressure and, therefore, large pulse pressure is consis tent with pressure waveforms observed in clinical pulmonary hypertensi on. We conclude that early wave reflection exerts a detrimental effect in pulmonary hypertension by unfavorably loading the still-ejecting r ight ventricle.