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Variation in plethysmographically measured limb blood flow using two study designs.

Ingestion of food is known to influence peripheral blood flow. In clinical drug trials it is important to obtain values which do not fluctuate because of exogenous factors. In the study reported here, the variability of limb blood flow was assessed using two study designs: after a light standard breakfast with nothing more to eat (Day A); and after an overnight fast followed by a heavy non-standardized lunch (Day B). Calf and forearm blood flow (BF), venous capacity (VC) and maximal venous outflow (MVO) were measured by means of strain-gauge venous occlusion plethysmography in 10 young healthy subjects six times during a period of 8 h. The most stable values were recorded from the calf on Day A, when no statistically significant variation occurred in any of the parameters. Mean values for calf BF ranged from 3.9 to 4.3 ml min-1 100 ml-1 (SEM 0.3-0.4) at the different time points on Day A. The corresponding values for VC were 3.4-3.7 ml 100 ml-1 (SEM 0.2-0.3) and for MVO were 100-112 ml min-1 100 ml-1 (SEM 7-10). Within-subject coefficients of variation were 13-16%. After lunch on Day B, both calf and forearm BF increased significantly, by 40-60%, as compared with prelunch values, and remained at about this level throughout the rest of the day. The corresponding postlunch increase in VC was 25-40%, and that in MVO was 20-25%. A study design in which the subjects ate a light, standard breakfast before the start of measurements and fasted thereafter gave fairly stable plethysmographic results.