The purpose of this work was to study the factors determining aortic input impedance in hypertensive patients. Aortic input impedance (simultaneous measurements of aortic pressure and blood flow), mean (Wm) and pulsatile (Wp) powers and the Wp/Wm ratio were compared in normal subjects (n = 13) and hypertensive patients (n = 12) under basal conditions and during blood pressure manipulation--angiotensin infusion in five normal patients and nitroprusside infusion in six hypertensive patients. Pulse wave velocity (Möens-Korteweg equation; simultaneous measurement of aortic pressure and radius) was determined under basal conditions in normal subjects and in 11 hypertensive patients. The results show that: 1) the changes in impedance curves in hypertensive patients are related to increased peripheral resistance, pulse wave velocity, wave reflection and aortic radius; 2) in most hypertensive patients impedance curves are normalised when blood pressure is reduced, whereas the Wp/Wm ratio remains higher. This latter result demonstrates that pulsatile energy losses are greater in hypertensive patients and suggests either that the aortic wall remains stiffer, despite the reduction in aortic pressure, or that the flow wave becomes more pulsatile since impedance curves of hypertensive patients seen after lowering blood pressure are similar to those of normal subjects.
In 30 patients, simultaneous measurements of ascending aortic pressure and diameter were performed, allowing one to evaluate: (1) the influence of age, the aortic diastolic pressure, and the radius on the aortic elasticity; (2) the correlations between characteristics impedance of the aorta (Zo), systemic arterial resistance, age and diastolic aortic pressure; and (3) the importance of Zo when comparing two indices of left ventricle performance; one during isovolumic phase ([dP/dt]/Pt)max and the other during the outflow phase (maximum acceleration of aortic blood flow).
This study was aimed at the evaluation of aortic impedance in patients with congestive heart failure. Aortic impedance (simultaneous measurements of aortic pressure and blood flow), mean (Wm) and pulsatile (Wp) powers were compared in 11 normal subjects and in 12 patients with heart failure. Pulse wave velocity (C: modified Moëns-Korteweg equation, simultaneous measurements of aortic pressure and radius) was determined under control conditions in all normal subjects and in 7 patients with heart failure. Impedance curves in patients with heart failure were characterized by increased values of the impedance modulus at 0 Hz (peripheral resistance) and at low frequencies. The characteristic impedance, C, and phase were not different from normal subjects. In six patients with heart failure, impedance curves were studied during nitroprusside infusion. During the infusion of the vasodilator, the impedance modulus at 0 Hz and at low frequencies decreased. The characteristic impedance was unchanged. The zero intercept of the phase was shifted towards lower frequencies. These results show that the changes in impedance curves in patients with heart failure are due to greater peripheral resistance and wave reflection. During nitroprusside infusion the stroke volume increased and the aortic blood flow became more pulsatile (greater values of low frequency components). This modification accounts for the increased values of Wm and Wp, and is related to decreased peripheral resistance and wave reflection.
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