Isobaric Compliance: Pressure-Independent Effects on the Arterial Wall Structure

pp 455-460

Abstract

Background

Increased arterial diameter and decreased arterial compliance are frequently found in arterial hypertension. They may be the consequence of both high blood pressure and changes related to the structure of the arterial wall.

Objective

To evaluate the changes in the arterial wall structure in hypertensives by means of the compliance calculation, independently of the blood pressure levels (isobaric compliance).

Material and methods

Thirty-two normotensive subjects (NT, mean age 51 ± 14 years) and 61 patients with mild to moderate essential hypertension (HT, mean age 54±10 years) were studied. Mean blood pressure (MBP: Dinamap, Critikon), mean brachial arterial diameter (Dm: Hewlett Packard Sonos 1500) and pulse wave velocity (PWV: Tonometry, Millar) were recorded in the whole population. The effective compliance (Ceff) was calculated with a formula de-rived from the Branwell and Hill equation. Then, employing a mathematical logarithmic model, we calculated the diameter-pressure curves and from them, the compliance-pressure curves. Finally, the results obtained from both groups were compared in isobaric conditions. The isobaric compliance (Ciso) value (at 110 mm Hg) was calculated as theMBP value obtained from all the patients studied.

Results

Mean blood pressure (NT: 86 ±11; HT: 114 ±12 mmHg; p< 0.0001) and Dm (NT:0.34 ± 0.05;HT: 0.40±0.07 cm; p < 0.0001) were significantly higher in HT. Conversely, the Ceff (NT: 3.38 ± 1.42; HT: 2.11 ± 0.56101cm/mm Hg; p < 0.05) and the Ciso (NT:2.64 ±1.09; HT: 2.20 ± 0.66 10-4cm/mm Hg; p < 0.05) were significantly lower in HT than in NT in a 38% and 13%, respectively.

Conclusion

The reduction in arterial compliance observed in HT seems not to be fully explained by the mechanical effect of stretching, since 13% of the whole changes observed were due to structural changes in the arterial wall (Ciso).