3.2 ORIGINS OF THE BACKWARD TRAVELING WAVE IN THE ARTERIAL TREE

Abstract

Backward traveling waves, an important determinant of central haemodynamics, are usually regarded as being due to reflections from discontinuities in the arterial tree. However, consideration of a single tube model of the arterial with a single site of reflection shows that a backward pressure wave may be generated by elastic recoil of large arteries, in which case the magnitude of the backward wave is proportional to that of the forward wave. A 55-segment 1-D model of the arterial which allows reflection as a continuum along the arterial tree and, for a given prescribed aortic flow, generates physiological aortic pulse waveforms was used to examine the relation of the backward to forward pressure waves in 4107 “virtual subjects” with arterial parameters spanning the physiological range. Backward pressure wave was closely correlated with the forward wave (R = 0.931, P < 0.001). Clinical data was obtained by carotid tonometry and aortic Doppler sonography during modulation of cardiovascular function in healthy volunteers (n = 13, age 46.5 ± 10.1 years with inotropic, vasopressor and vasodilator drugs (dobutamine, norepinephrine phentolamine and nitroglycerin). The magnitude of backward pressure was highly correlated with forward pressure over a range 5–15 mmHg (R = 0.824, P < 0.001) with a constant ratio of backward to forward wave magnitude except during treatment with nitroglycerin, a vasodilator known to be highly selective for large muscular arteries. These numerical and experimental data suggest that backward pressure waves can be generated by elastic recoil of large arteries independent of pressure wave reflection and this effect dominates in human physiology.