CAROTID-ARTERY DISTENSIBILITY AND DISTENDING PRESSURE IN HYPERTENSIVE HUMANS

Whether the decrease in large-artery distensibility observed in hypertensive patients is due primarily to an increase in distending pressure or to hypertension-induced changes in structural properties has been much debated. We determined noninvasively the diameter-pressure curve of the common carotid artery over the systolic-diastolic range by continuously recording both the pulsatile changes in internal diameter (high-resolution echo-tracking system) and, simultaneously on the contralateral artery, the pressure waveform (high-fidelity applanation tonometry). We then derived the distensibility/pressure curve and compared arterial distensibility in 14 normotensive subjects and 15 age- and sex-matched hypertensive subjects at their respective mean arterial pressures (MAP) and at a common distending pressure: 100 mm Hg. Distensibility decreased as blood pressure increased, and distensibility at MAP was significantly lower in hypertensive than in normotensive subjects (7.8+/-0.7 versus 11.7+/-1.7 kPa(-1).10(-3), mean+/-SEM; P<.05). In hypertensive subjects, the distensibility-pressure curve was shifted toward higher levels of blood pressure, and a large part of the curve overlapped that of normotensive subjects. No significant downward shift of the distensibility-pressure curve was observed in hypertensive subjects, and distensibility at 100 mm Hg was not significantly different from that of normotensive subjects (10.0+/-1.0 versus 9.0+/-1.1 kPa(-1).10(-3)). Distensibility at 100 mm Hg decreased with aging (P<.05) and was not reduced in hypertensive subjects compared with normotensive subjects after adjustment for age. These results suggest that the decrease in common carotid artery distensibility in hypertensive subjects is due primarily to the increased distending blood pressure and that age-independent structural modifications of the arterial wall play only a minor role.