Arterial compliance is part of the load faced by the heart. Decreased compliance increases this load. We have studied the cardiovascular consequences of decreased systemic compliance in six closed chest anaesthetised dogs where ascending aortic flow transducers and left ventricular crystals had previously been implanted. A stiff tube was put into the abdominal aorta from the left flank and moved to the ascending aorta. Inflation of a cuff on the proximal end of the tube forced the heart to eject into a non-compliant outflow conduit. The distal end of the tube was connected to the distal aorta and, via a pump, to a carotid artery where mean pressure was kept above 80 mmHg. We measured systemic pressures (catheter-tip manometer), cardiac output (electromagnetic flowmeter) and either left ventricular end-diastolic pressure (fluid filled catheter, Statham P23Db) or left ventricular diameter (ultrasound transit time method). From these variables we calculated systemic compliance and input impedance. A 35% decrease in compliance caused a 12% increase in systolic, and a 12% decrease in diastolic pressure while mean pressure and cardiac output did not change significantly. With a decrease in compliance of 63% systolic pressure increased by 18%, while diastolic pressure decreased by 24%. Mean pressure did not change significantly but cardiac output fell by 21%. In both groups of altered compliance peripheral resistance rose slightly but this was not significant. Decreased compliance mainly caused changes in the low frequency range of the input impedance: moduli increased and phase angles became more negative.(ABSTRACT TRUNCATED AT 250 WORDS)
Randall et al. (Wed,) studied this question.