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.

Method for assessment of vascular reactivity in bone: in vitro studies on resistance arteries isolated from porcine cancellous bone.

Knowledge about vascular regulation in bone is central to the understanding of both normal and pathological bone physiology. This article describes a new method for direct assessment of the reactivity of bone blood vessels. Resistance arteries (diameter approximately 250 microns) were isolated from epiphyseal cancellous bone (porcine femoral condyle). Arterial segments (2 mm long) were mounted as ring preparations on a myograph, and isometric force development was measured continuously. Fifty-nine vessels from 31 pigs were investigated. The active force development was maximal at 0.9 x L100 in nine of 12 investigated arteries (L100 corresponds to the circumference the vessel would have if relaxed and exposed to a luminal pressure of 100 mm Hg [13.3 kPa]). In all subsequent experiments, the vessels were stretched to 0.9 x L100. Noradrenaline (2 x 10(-8) to 10(-5) M) induced a concentration-dependent vasoconstriction; mean maximal tension development was 3.69 N/m. This force development would enable the arteries to contract against a pressure of more than 22 kPa (165 mm Hg), indicating preserved function of the media smooth muscle. Response to acetylcholine (10(-7) to 10(-5) M) was observed in only two of 12 arteries. Bradykinin (10(-11) to 10(-6) M) induced a concentration-dependent and reproducible relaxation in all vessels; the relaxation was endothelium-dependent, since no effect of bradykinin was detected after mechanical removal of the endothelium. Sodium nitroprusside (10(-4) M) induced a reproducible and endothelium-independent vasorelaxation. The results demonstrate preserved function of both smooth muscle and endothelium in this preparation. The model allows pharmacological investigations of bone arteries under well defined conditions and enables studies on focal bone lesions and human bone tissue.