Assessment of forearm vasodilator responses to acetylcholine and albuterol by strain gauge plethysmography: reproducibility and influence of strain gauge placement

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Abstract
Aims To determine the within-subject reproducibility of the forearm blood flow response to acetylcholine and the β2-adrenoceptor agonist albuterol as measured by strain gauge plethysmography. To examine the influence of strain gauge placement on these responses. Methods Vasodilator response to brachial artery infusion of drugs was assessed by strain gauge plethysmography in six healthy men on each of three occasions separated by 1 week. Strain gauges were placed on both arms at the point of maximum diameter. On the infused arm two further gauges were positioned approximately 4 cm proximal and distal to the middle gauge. Results Within-subject coefficients of variation (WCV) of absolute blood flow responses for each dose of acetylcholine (7.5, 15, 30 µg min−1) ranged from 24% to 27%, as compared with WCV values of 41% to 62% for the percentage changes in blood flow ratio (infused : noninfused arm). For albuterol (0.3, 1, 3 µg min−1) the corresponding WCV values were 16% to 19% and 30% to 55% for absolute blood flow and percentage change in blood flow ratio, respectively. WCV for the area under dose-response curve (AUC) for absolute blood flow was 18% and 13% for acetylcholine and albuterol, respectively. Vasodilator responses were similar whether recorded proximal to or at the point of maximal forearm circumference. Distal strain gauge misplacement underestimated responses and the difference was greater for acetylcholine than for albuterol. Conclusions In healthy men, the WCV for responses expressed as absolute blood flow, to acetylcholine and albuterol ranges from 16% to 27%.