Forearm plethysmography in the assessment of vascular tone and resistance vasculature design: new methodological insights.

AIM

High peripheral resistance and structural alteration in resistance arteries are central phenomena in essential hypertension and have been widely examined by forearm venous occlusion plethysmography; at rest for studying vascular tone, and during reactive hyperaemia for studying vascular structure. This work concerns the influence of venous pressure on hyperaemic vascular resistance (Rmin), the reproducibility of hyperaemic and resting vascular resistances (Rrest) and the relation between forearm and total peripheral vascular resistance (TPR).

METHODS

In four healthy subjects, intravenous and intra-arterial blood pressures were measured simultaneously with plethysmographic recordings of hyperaemic and resting forearm blood flows. Reproducibility was examined in 15 young and 14 middle-aged healthy subjects and in 21 untreated hypertensive patients.

RESULTS

Rmin remained low in the first recorded cardiac cycle, but rose in the second, even though corrected for the venous pressure rise, suggesting vascular tone recovery along with venous congestion. Between-day reproducibility of Rmin was high in middle-aged normotensive (8.7%) and hypertensive subjects (10.6%), but Rmin fell significantly between successive days in the young subjects. Rrest correlated with TPR, but required up to 40 min to reach steady state and showed high day-to-day variation in young (21.8%) and hypertensive subjects (16.2%).

CONCLUSIONS

During hyperaemia, vascular resistance should be measured in the first cardiac cycle following venous occlusion to minimize influences of venous pressure rise and possible tone recovery. Rrest seems to reflect TPR. About 20 subjects may be needed to detect 15% changes between days in Rrest, fewer when concerning Rmin and TPR.