Reactive Hyperemia Between Young Adults With and Without Obesity: The Influence of Forearm Lean Tissue Mass

Introduction: After a period of ischemia, there is a reflexive increase in blood flow (i.e., reactive hyperemia; RH), so oxygen reperfusion can occur. RH is an index of microvascular function that is prognostic for cardiovascular mortality. Previous work found that RH is inversely associated with body mass index (BMI) and other cardiovascular disease risk factors. Additionally, past findings demonstrate that the amount of lean tissue mass in the occluded limb partially explains the difference in the post-occlusion RH response. When comparing age and sex groups, more lean mass in the occluded limb is associated with higher RH. However, this has not been explored in young adults with obesity and without other overt diseases. Purpose: The purpose of this investigation was to compare RH among young adults with and without obesity who do not have other overt diseases and determine whether ischemic lean tissue mass influences RH. We hypothesized that adults with obesity would have lower RH, and ischemic lean tissue mass would influence RH. Methods: We assessed brachial artery RH among adults with and without obesity who did not have other overt diseases. To elicit RH, we placed an occlusion cuff on the participant’s right arm distal to the antecubital fossa (~3 cm) and inflated it to 250 mmHg for five minutes. We quantified RH as peak blood flow, peak blood flow velocity, and the 10s and 30s velocity time integral (10s- or 30s-VTI) during the three-minute post-occlusion recovery. We measured RH via Doppler ultrasound and automated arterial edge and velocity envelope tracking software (n = 16). In a subset, we measured forearm lean tissue mass via dual-energy X-ray absorptiometry (n = 12). We adjusted RH outcomes to forearm lean tissue mass (e.g., 10s-VTI/forearm lean tissue mass). We present normal data as Mean ± SD and non-normal data as Median [IQR]. We compared groups via independent samples t-test and quantified differences with Cohen’s d. α ≤ 0.05. Results: Adults with obesity (W; n=9, 2 Female:7 Male; Age: 25 ± 3 years; BMI: 34.8 ± 3.0 kg/m 2 ) had a higher BMI ( P < 0.001, d = 4.42) than adults without obesity (WO; n=7, 2 Female:5 Male; Age: 21 [3] yrs, BMI: 23.2 ± 2.0 kg/m 2 ). Peak blood flow (W: 542 ± 176 vs. WO: 433 ± 95 mL/min, P = 0.16, d = 0.74), peak systolic blood flow velocity (W: 136 ± 21 vs. WO: 117 ± 15 cm/s; P = 0.07, d = 1.00), and forearm lean tissue mass (W: 1306 ± 334 vs. WO: 991 ± 353 g, P = 0.147, d = 0.92) were not different between groups but effect sizes were moderate-to-large. Adults with obesity had higher 10s-VTI (W: 898 ± 150 vs. WO: 722 ± 101 cm, P = 0.02, d = 1.35) and 30s-VTI (W: 2883 ± 428 vs. WO: 2445 ± 369 cm, P = 0.05, d = 1.08). When accounting for forearm lean tissue mass, peak systolic blood flow (W: 0.44 ± 0.08 vs. WO: 0.47 ± 0.09, P = 0.62, d = 0.30), peak systolic blood flow velocity (W: 0.11 ± 0.03 vs. WO: 0.13 ± 0.06 cm/s/g, P = 0.39, d = 0.53), 10s VTI (W: 2.96 ± 0.64 vs. WO: 2.83 ± 0.77 cm/g, P = 0.76, d = 0.19), and 30s VTI (W: 9.66 ± 1.79 vs. WO: 9.95 ± 1.69 cm/g, P = 0.78, d = 0.17) were not different between groups. Conclusion: Young adults with obesity had higher 10s and 30s velocity-time integral (area under the velocity curve) compared to adults without obesity. However, this difference was not maintained when VTIs were adjusted for forearm lean tissue mass. These preliminary data support previous findings that lean tissue mass is an important consideration for interpreting RH results when comparing groups. Florida State University Graduate School Legacy Fellowship (CD), National Institutes of Health K01HL160772 (JCW), and American Heart Association 23CDA1037938 (JCW). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.