Forearm plethysmography in the assessment of vascular tone and resistance vasculature design: new methodological insights O. N. Mathiassen, 1 N. H. Buus, 1,2 H. W. Olsen, 3 M. L. Larsen, 4 M. J. Mulvany 1 and K. L. Christensen 1,4 1 Department of Pharmacology, University of Aarhus, Aarhus C, Denmark 2 Department of Nephrology C, Aarhus University Hospital, Aarhus C, Denmark 3 Department of Intensive Care, Aarhus University Hospital, Aarhus C, Denmark 4 Department of Medicine and Cardiology A, Aarhus University Hospital, Aarhus C, Denmark Received 11 November 2005, revision requested 16 February 2006, revision received 30 March 2006, accepted 25 June 2006 Correspondence: Ole. N. Mathiassen, Department of Pharmacology, University of Aarhus, University Park 240, 8000 Aarhus C, Denmark. E-mail: onm@farm.au.dk Abstract 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 hyperae- mic vascular resistance (R min ), the reproducibility of hyperaemic and resting vascular resistances (R rest ) and the relation between forearm and total per- ipheral 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 exam- ined in 15 young and 14 middle-aged healthy subjects and in 21 untreated hypertensive patients. Results: R min remained low in the first recorded cardiac cycle, but rose in the second, even though corrected for the venous pressure rise, suggesting vas- cular tone recovery along with venous congestion. Between-day reproduci- bility of R min was high in middle-aged normotensive (8.7%) and hypertensive subjects (10.6%), but R min fell significantly between successive days in the young subjects. R rest 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. R rest seems to reflect TPR. About 20 subjects may be needed to detect 15% changes between days in R rest , fewer when concerning R min and TPR. Keywords forearm blood flow, intra-arterial pressure, minimum vascular resistance, reproducibility, resting vascular resistance, venous occlusion plethysmography, venous pressure. Acta Physiol 2006, 188, 91–101 Ó 2006 Scandinavian Physiological Society, doi: 10.1111/j.1748-1716.2006.01611.x 91