Alterations in forearm position and environmental temperature influences the segmental volume expansion during venous occlusion plethysmography--special attention on hand circulation.

Aim: To find evidence that small changes in the positioning of the strain gauge, the environmental temperature (sympathetic activation) and position of the arm (venous pressure) alters the outcome of the venous occlusion plethysmography (VOP) measurement of forearm blood flow and to investigate if the hand circulation influences the results.

Methods: Forearm blood flow was measured with VOP (n = 6) on three occasions with air temperatures of 13, 20 and 38 degrees C, respectively. At each occasion the arm position was varied; raised by 10 degrees , horizontal or lowered by 15 degrees . Strain gauges were placed on the forearm at the maximal circumference; 5 cm distal; and 5 cm proximal to this site, respectively. The hand circulation was excluded in half of the measurements.

Results: The simple main effect of temperature was highly significant (P<0.001). With excluded hand circulation (but not when included), there was a two factor interaction between arm position - strain gauge position (P<0.05). The highest expansion rate was found in the proximal segment when the arm was elevated, but in the distal segment when the arm was lowered. With hand circulation (but not without) there was a two factor interaction between temperature and strain gauge position (P<0.01). The highest expansion rate was found in the distal segment at normal and high temperatures, but in the proximal segment at low temperature.

Conclusion: The volume expansion rate in a particular segment is dependent not only on arterial inflow. Segmental differences in capacity for venous expansion results in redistribution of blood to and from a segment, thus influencing the results obtained.