The transformation of pressure wave traveling along the aorta was studied in 37 patients. The pressure waves were recorded by the catheter with a micromanometer inserted percutaneously from the femoral artery up to the aortic root at intervals of 10 cm. The amplitude ratio of the pressure wave at the bifurcation of the common iliac arteries to the pressure wave at the aortic root was 1.31 ± 0.03 and decreased with age. The upstroke of the pressure wave became steeper along the aorta, particularly at the abdominal aorta. Fourier analysis of the pressure wave showed that for harmonics 1, 2, 3, 4, 5, and 6, the moduli increased with distance along the aorta and that for harmonics 5, and 6, there was the inflextion point at the distance of 20 cm from the aortic root. In the old patients ( n=7, 65.9± 1.4 years ), the moduli for each harmonic less increased than that in the young patients ( n=8, age 33.3 ± 0.6 years ) and the inflextion points were prominent in the young patients. The regional wave velocity in the descending thoracic aorta was smaller than that in the ascending aorta.
These observations give us the following suggestions : 1) in the young patients, there is one predominant reflection site in the peripheral arterial system, 2) the degree of elastic non-linearity of the vessel walls is larger at the abdominal aorta, 3) the elasticity in the ascending aorta is smaller than that in the descending thoracic aorta.

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Changes in the shape of pressure wave traveling along the aorta are caused variously by reflection from the periphery, attenuation, and the elastic non-linearity of the vessel walls. The effect of nitroglycerin (NTG) on the waveform along the aorta was studied in 23 patients (16 males, 7 females, mean age 53 years) following a dose of 3μg/kg/min NTG given intravenously. NTG infusion reduced the late systolic peak in the pressure waves and increased the similarity of the contour between the proximal and distal pressure waves. The ratio of the distal to the proximal pulse amplitude was reduced. The steepening of ascending limb of the pressure wave along the aorta was also reduced. The compliance of the artery increased. Following NTG infusion, the vascular impedance moduli of the upper thoracic aorta decreased for harmonics 1, and 2, and increased for harmonic 6. The velocity of the pulse wave along the aorta did not change significantly. These observations give us the following suggestions : 1) the reflection from the periphery, 2) the non-linearity of the vessel walls were decreased by NTG infusion.

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