THE COMPLIANCE OF THE PORCINE PULMONARY-ARTERY DEPENDS ON PRESSURE AND HEART-RATE

1. The influence of mean pulmonary arterial pressure (mean P-pa) on dy namic (C-d) and pseudostatic compliance (C-ps) of the pulmonary artery was studied at a constant and a changing heart rate. C-d is the chang e in cross-sectional area (CSA) relative to the change in P-pa through out a heart cycle. C-ps is the change in mean CSA relative to the chan ge in mean P-pa. If C-d is known, pulmonary blood flow can be computed from the P-pa using a windkessel model. We investigated whether C-ps can be interchanged with C-d. 2. In nine anaesthetized pigs, we determ ined the mean CSA and C-d of the pulmonary artery at various P-pa leve ls, ranging from approximately 30 to 10 mmHg, established by bleeding. Two series of measurements were carried out, one series at a spontane ously changing heart rate (n = 9) and one series at a constant heart r ate (n = 6). To determine CSA a conductance method was used. 3. C-ps d epended on pressure. The mean CSA versus mean P-pa curves were sigmoid and steepest in the series with the increasing heart rate (establishe d by bleeding). The CSA versus P-pa loop during a heart cycle, giving C-d, was approximately linear and almost closed. The C-d versus mean P -pa relationship was bell shaped. Its width was smaller if the heart r ate increased during the series of measurements. The pressure, where C -d was maximum, was higher at higher heart rates. Furthermore, the max imum C-d was not affected by the heart rate. 4. Because the pulmonary artery constricts with increasing heart rate, C-ps will be overestimat ed during procedures where heart rate increases. C-d should be determi ned on a beat-to-beat basis to calculate flow because it changes with mean pulmonary arterial pressure and heart rate.