AORTIC ELASTICITY Regional wave travel and reflections along the human aorta : a study with six simultaneous micromanometric pressures
چکیده
The human aorta and its terminal branches were investigated in normal subjects during elective cardiac catheterization to evaluate regional wave travel and arterial wave reflections. A specially designed catheter with six micromanometers equally spaced at 10 cm intervals was positioned with the tip sensor in the distal external iliac artery and the proximal sensor in the aortic arch. Simultaneous pressures were obtained and analyzed for foot-to-foot wave velocity, and Fourier analysis was used to derive apparent phase velocity. These quantities were assessed during control (n = 9), during Valsalva (n = 8) and Muller (n = 4) maneuvers, and during femoral artery occlusion by bilateral manual compression (n = 8). During control, regional cross-sectional areas, determined from aortography, and regional foot-to-foot pulse wave velocities were used to calculate the local reflection coefficient in the proximal descending aorta (F = 0.05), at the junction of the renal arteries (F = 0.43), and at the terminal aortic bifurcation (F = 0.13). To test the hypothesis that significant reflections originate in the aorta, at the level of the renal arteries, aortograms were used to design a latex tube model with geometric properties similar to the descending aorta. Velocities and reflection characteristics in the model and in vivo were compared. Inspection of thoracic aortic pressures under control conditions revealed a reflected wave originating from the region of the aorta at the level of the renal arterial branches while abdominal pressures exhibited reflection from a site peripheral to the terminal aortic bifurcation. In the low frequency range, apparent phase velocity was found to be higher proximal to the renal arteries as compared with at the distal sites. In addition, the minimum value occurred at a higher frequency in the lower thoracic aorta than at more distal sites. The effects of reflection on apparent wave velocity in the tube model were consistent with data obtained in vivo. The Valsalva maneuver diminished the reflection from the aortic region of the renal arteries, thus allowing the distal reflected wave to become more evident on the thoracic pressure waveforms. Bilateral femoral artery occlusion usually enhanced the distal reflection and the Muller maneuver usually resulted in small increases in reflections. In conclusion, the geometric and elastic nonuniformity of the aorta results in two major sites of arterial wave reflection that influence the aortic pressure waveforms in man. The first major reflection site is located at the aortic level of the renal arterial branches and the second reflection site is located distal to the terminal aortic bifurcation. Circulation 72, No. 6, 1257-1269, 1985. ALTERATIONS in the contour of the pressure wave along the aorta have been noted since the turn of the century,'-' but the mechanisms responsible for these changes have not been fully explained.4 There have been few detailed investigations of the transmission From the Cardiology Service, Department of Medicine, Brooke Army Medical Center, Fort Sam Houston, TX, and Laboratory for Physiology, Free University, Amsterdam. Address for correspondence: Ricky D. Latham, MAJ, MC, Cardiology Service, Department of Medicine, Brooke Army Medical Center, Fort Sam Houston, TX 78234. Received Dec. 27, 1984; revision accepted Sept. 19, 1985. The opinions or assertions contained herein are the private views of the authors and are not to be construed as reflecting the views of the Department of the Army or the Department of Defense. Vol. 72, No. 6, December 1985 characteristics of pressure along the human aorta.2' 3 Studies by Luchsinger et al.2 and O'Rourke3 described and analyzed pressure waveforms in the human aorta, but pressures were not obtained simultaneously and a fluid-filled manometer system was used. Most of the previous laboratory investigations on this subject have been in animal preparations'0'5; however, it has been shown that the proximal aortic pulse contour in man differs from that of most laboratory animals,1 9 16 making it difficult to extrapolate all results in animals to man. Furthermore, quantitative assessment of changes in the arterial pressure waveform in man has been attempted in few laboratories because of the complex1257 by gest on N ovem er 3, 2017 http://ciajournals.org/ D ow nladed from