Methodological Issues Related To Blood Flow Measurements In Obese Subjects

Abstract

A high body mass index is being implicated in a variety of health problems such as heart disease, hypertension, diabetes, cancer and pulmonary disease. Understanding vascular hemodynamics in obese subjects is an important measurement in elucidating the untoward effects that obesity has on human health. Two major methods of measuring forearm blood flow (FBF) in humans are venous occlusion plethysmography (VOP) and Doppler ultrasound. PURPOSE: To examine if blood flow responses measured by Doppler ultrasound and VOP would elicit similar results in obese subjects. Due to the large amount of subcutaneous fat associated with obesity we hypothesized that VOP would not accurately measure forearm blood flow as compared to Doppler ultrasound in response to physical stressors. METHODS: FBF was measured in normal (n=12; BMI=23±1) and obese (n=7; BMI=40±2) subjects with VOP and Doppler ultrasound. FBF was measured at rest and during four interventions using both techniques. The interventions were reactive hyperemia (RH), mental stress, isometric handgrip, and cold pressor test. RESULTS: In the normal subjects, no differences in blood flow measurements were observed using either technique during the four interventions. However, differences between Doppler ultrasound and VOP in the obese subjects were observed during RH and mental stress. During RH changes in FBF (Δ790 ± 217% vs. Δ430±133%) and forearm vascular conductance (FVC) (Δ802±221% vs. Δ444±128%) was significantly greater using Doppler ultrasound than VOP (P<0.03). Using VOP mental stress elicited increases in FBF (Δ54±13%) and FVC (Δ35±11%) whereas using Doppler ultrasound mental stress elicited no significant changes in FBF (Δ-2±9%) or FVC (Δ-7±11%). However, VOP and Doppler ultrasound elicited comparable decreases in FBF and FVC during isometric handgrip and cold pressor test. CONCLUSION: Differences in FBF measurements occurred in obese subjects comparing VOP versus Doppler ultrasound. These observed differences manifested themselves during maneuvers that elicit forearm vasodilation. Therefore these findings indicate that interpretation of blood flow data from obese subjects must be carefully evaluated across studies in which different methods of measuring FBF have been utilized. Support: GCRC Student Research Award.