CLINICAL INVESTIGATION Ventricular/vascular interaction in patients with mild systemic hypertension and normal peripheral resistance

Total left ventricular external power and aortic input impedance spectra were calculated from recordings of pulsatile pressure and flow in the ascending aorta of 22 human subjects undergoing cardiac catheterization. Eleven subjects had increased aortic pressure (systolic 153 + 3.8[SEM] mm Hg, p < .001; diastolic 91 + 2.4 mm Hg, p < .03; mean 118 ± 2.4 mm Hg, p < .001) and constituted the group with mild hypertension (average age 50 ± 1.9 years). The other 11 (age-matched) subjects had normal arterial pressures and constituted the control group. Cardiac output in the hypertensive group was abnormally high (6.9 ± 0.3 liters/min, p < .04) compared with that in control subjects (6.1 + 0.2 liters/min), so that peripheral resistance was similar. Characteristic aortic impedance (index of aortic elastance) was increased in the hypertensive group (142 + 19 vs 72 ± 4.5 dyne-sec-cm-5, p < .002), as was the fluctuation of impedance moduli and phase. These elevated pulsatile components of arterial load were associated with a significant (p < .002) increase in pulsatile left ventricular external power (89%), and the increased cardiac output was associated with a significant (p < .001) increase in steady flow power (31%). The ratio of pulsatile to total power was also increased (38%) in the hypertensive group (p < .001). Increased characteristic aortic impedance in the hypertensive group suggests that the human aorta is stiffer, and fluctuations in the impedance spectra suggest increased or less dispersed wave reflections. These alterations in the systemic arterial tree suggest that factors other than blood pressure and peripheral resistance impose an additional, functionally important hydraulic load on the left ventricle of subjects with mild or borderline hypertension. Circulation 74, No. 3, 455-462, 1986. THE TOTAL external hydraulic power developed by the left ventricle to propel blood through the systemic circulation can be determined from analysis of pulsatile pressure and flow recordings at the entrance to the system.",2 Hydraulic power determined in this manner depends not only on the ability of the left ventricle to do external work but also on the properties of the arterial tree into which blood is ejected. The aortic input impedance spectrum can be used as an expression of these properties.3 For example, the stiffer the aorta, the larger the impedance moduli',6 and the greater the amount of power required to produce a given blood flow.",6 External ventricular power can be From the Division of Cardiovascular Medicine, College of Medicine, University of Florida, and Veterans Administration Medical Center, Gainesville, FL, and the Department of Medicine, St. Vincent's Hospital, Sydney, Australia. Supported in part by grant HL-17717-02 from the NIH and by the Veterans Administration Central Office. Address for correspondence: Wilmer W. Nichols, Ph.D., Department of Medicine, Box J-277, College of Medicine, University of Flonrda, Gainesville, FL 32610. Received Feb. 18, 1986; revision accepted May 1, 1986. separated into two componentsone associated with mean blood flow (steady power) and the other with vascular pulsations (pulsatile power)., 2, 6 Experimentally produced hypertension, arteriosclerosis, and aortic coarctation6' cause higher impedance values over the frequency band that contains most of the energy of the flow wave delivered from the ventricle. Under these conditions more energy is lost in vascular pulsations. Porje8 has measured pulsatile and steady components of external left ventricular power in humans and has shown increases in pulsatile as well as steady components when blood pressure was elevated with norepinephrine. In patients with aortic coarctation, he found the ratio of pulsatile to total external power increased from between 10% and 17% to between 24% and 37%. Milnor et al.9 measured pulsatile and steady components of right ventricular power in patients with pulmonary hypertension and found both to be increased compared with control values. The purpose of this investigation was to study pulsatile pressure-flow relationships and vascular impedVol. 74, No. 3, September 1986 455 by gest on A ril 3, 2017 http://ciajournals.org/ D ow nladed from