Arterial Compliance as Load on the Heart

Abstract

Total arterial compliance and peripheral resistance form the main part of the load on the heart. Together with stroke volume and heart rate (or heart period), these are the major determinants of systolic and diastolic pressure in the ascending aorta. A decrease in total arterial compliance will, in the nonregulated cardiovascular system, decrease cardiac output and thus mean pressure while increasing pulse pressure. The result is a large decrease in diastolic pressure and a small increase in systolic pressure. In the intact animal with cardiovascular regulation, a (moderate) decrease in total arterial compliance causes little change in stroke volume, so that mean pressure also remains the same. This results in a decrease in diastolic pressure and an increase in systolic pressure. If total arterial compliance decreases, as in atherosclerosis or aging, peripheral resistance may increase so that both diastolic pressure and systolic pressure increase. However, a change in compliance alone can only result in a decrease of diastolic blood pressure. Several methods are available to derive total arterial compliance from aortic pressure and flow. The pulse pressure method, based on the two-element windkessel model, was shown to be superior to all other methods. This method fits the pulse pressure derived from the two-element windkessel model to the measured pulse pressure. However, waveforms of pressure and flow are not realistic in this model. The methods based on the three-element windkessel all perform poorly in the estimation of total arterial compliance, but the wave shapes produced by this model are very close to the measured wave shapes. Thus, both windkessels have shortcomings and it is concluded that they need to be revised.