Effect of age, cardiovascular disease, and vasomotor changes on transmission of arterial pressure waves through the lower extremities.

Pressure waves were recorded by indwelling needles in the femoral and foot arteries. At the foot the systolic and pulse pressures were greater and the dicrotic wave more prominent. These changes during transmission increased during vasoconstriction and decreased during vasodilatation. The ratio of the distal to femoral pulse pressure (amplification) increasing from 1.13 +/- 0.05 during body heating to 1.47 +/- 0.06 during body cooling (P less than 0.01), and from 1.14 +/- 0.10 during infusion of trimethaphan to 1.42 +/- 0.02 during cooling (P less than 0.05). Amplification was also significantly greater following inhalation of amyl nitrite and during and after Valsalva maneuver. Greater pulse pressure at the foot paralleled greater amplitude of individual harmonics. Phase velocities decreased with increasing frequency and tended to level off at a value similar to the foot-to-foot pulse wave velocity. The findings are consistent with peripheral reflections of the waves which increase during vasoconstriction. In the absence of procedures that elicit vasoconstriction or vasodilatation, amplification averaged 1.35 +/- 0.03 in control subjects less than 35 years of age and 1.24 +/- 0.06 in older subjects (P less than 0.05). Amplification also did not differ significantly between control subjects and patients with hypertension or ischemic heart disease. In the absence of pronounced vasodilatation or encroachment on the lumen by atherosclerotic plaques, systolic and pulse pressures at the foot should be higher than in proximal pulses. These findings provide a firm basis for interpreting measurements of distal systolic pressures by using blood pressure cuffs when examining patients with occlusive arterial disease in the extremities.