The Use Of Personalized Pressures For Strain Gauge Estimated Blood Flow

Strain gauge plethysmography is a non-invasive method for estimating limb blood flow (BF). Typically, a cuff is inflated to 50 mmHg, blocking venous return. The limb circumference increases proportionally to the rate of BF. Since the applied pressure is made without considering individual differences (e.g. arterial pressure), it is possible that BF measurements could vary depending on the pressure applied to block venous return. Purpose: (1) To compare strain gauge estimated BF with different relative pressures. (2) To investigate the agreement between strain gauge estimated BF with absolute and relative applied pressures. Methods: Forty participants completed Experiment one (EX1). Following five minutes of rest, arterial occlusion pressure (AOP) was measured at the wrist. After an additional five minutes forearm BF was estimated by strain gauge plethysmography using 15, 30, 45, 60, and 75 percent of AOP. The order of the pressures either ascended from 15% to 75% or descended from 75% to 15%. Fifty participants completed Experiment two (EX2). EX2 followed the same procedures as EX1 however, forearm BF was estimated by using an absolute pressure of 50 mmHg and a relative pressure of 45% AOP. A Bayesian repeated measures ANOVA was performed in EX1. A Bland-Altman was used to investigate agreement in EX2. Data are presented as mean (SD). Results: EX1: The average AOP was 119 (9) mmHg. There were differences in estimated BF among the five pressures applied to block venous return (BF10 = 1.358*1020). Post hoc tests reveal that BF was different between each relative pressure except between 45% and 60% (BF10 = 1.685) and between 60% and 70% (BF10 = 1.436). The estimated BF was 1.73 (0.78), 2.64 (0.94), 2.92 (1.03), 3.23 (1.32), and 3.62 (1.50) for 15, 30, 45, 60, and 75% AOP respectively. EX2: The average AOP was 118 (9) mmHg. The mean difference in estimated BF between 50 mmHg pressure (2.99 ml/min) and 45% AOP (3.09 ml/min) was -0.101 (95% confidence interval: -0.224, 0.022) ml/min. The 95% limits of agreement were -0.950 to 0.748 ml/min. Conclusions: BF increased with higher applied pressures, suggesting that strain gauge plethysmography is more reflective of blood pooling, at higher pressures, rather than blood flow. Nonetheless, there is good agreement between absolute (50 mmHg) and relative (45% AOP) pressure estimated BF. Supported by: T32HL105324