Quantitative relation between increased intrapericardial pressure and Doppler flow velocities during experimental cardiac tamponade

To establish whether a quantitative relation exists between pericardial pressure and respiratory variation in intracardiac blood flow velocities, a spontaneously breathing closed chest canine model of pericardial tamponade was created. In seven dogs, pericardial pressure was sequentially increased in stages, from a mean of −4 ± 1 to 10 ± 2 mm Hg while aortic and pulmonary Doppler flow velocities, pleural pressure changes (respiratory effort), blood pressure and cardiac output were measured.The variation in the Doppler-detected peak transaortic velocity (AV) during inspiration (IV) increased linearly from −5 ± 3% at baseline (pericardial pressure −4 mm Hg) to −32 ± 9% at a pericardial pressure of 10 mm Hg [IVAV = −2 (pericardial pressure) − 13.1; r = 0.78, p < 10-6]. The inspiratory variation in the peak transpulmonary velocity increased from 13 ± 3% at baseline to 71 ± 19% at a pericardial pressure of 10 mm Hg. The inspiratory variation in the pulmonary Doppler peak velocity (IVpy) was dependent on both pericardial pressure and degree of respiratory effort [IVPV = 3.8 (pericardial pressure) + 2.6 (respiratory effort) + 10.9; r = 0.88, p < 10−8].Thus, quantitative relations exist between increases in intra-pericardial pressure and increases in inspiratory variation of peak aortic and pulmonary flow velocities. Additionally, pulmonary artery flow velocity is influenced more than aortic velocity by intrathoracic pressure