Normalization of flow-mediated dilation to shear stress area under the curve eliminates the impact of variable hyperemic stimulus.
BACKGROUND
Normalization of brachial artery flow-mediated dilation (FMD) to individual shear stress area under the curve (peak FMD:SSAUC ratio) has recently been proposed as an approach to control for the large inter-subject variability in reactive hyperemia-induced shear stress; however, the adoption of this approach among researchers has been slow. The present study was designed to further examine the efficacy of FMD normalization to shear stress in reducing measurement variability.


METHODS
Five different magnitudes of reactive hyperemia-induced shear stress were applied to 20 healthy, physically active young adults (25.3 +/- 0. 6 yrs; 10 men, 10 women) by manipulating forearm cuff occlusion duration: 1, 2, 3, 4, and 5 min, in a randomized order. A venous blood draw was performed for determination of baseline whole blood viscosity and hematocrit. The magnitude of occlusion-induced forearm ischemia was quantified by dual-wavelength near-infrared spectrometry (NIRS). Brachial artery diameters and velocities were obtained via high-resolution ultrasound. The SSAUC was individually calculated for the duration of time-to-peak dilation.


RESULTS
One-way repeated measures ANOVA demonstrated distinct magnitudes of occlusion-induced ischemia (volume and peak), hyperemic shear stress, and peak FMD responses (all p < 0.0001) across forearm occlusion durations. Differences in peak FMD were abolished when normalizing FMD to SSAUC (p = 0.785).


CONCLUSIONS
Our data confirm that normalization of FMD to SSAUC eliminates the influences of variable shear stress and solidifies the utility of FMD:SSAUC ratio as an index of endothelial function.
Padilla
Jaume
J
Kinesiology, Indiana University, Bloomington, IN, USA. jpadilla@indiana.edu
Johnson
Blair D
BD
Newcomer
Sean C
SC
Wilhite
Daniel P
DP
Mickleborough
Timothy D
TD
Fly
Alyce D
AD
Mather
Kieren J
KJ
Wallace
Janet P
JP
D000328:Adult; D019540:Area Under Curve; D001783:Blood Flow Velocity; D001809:Blood Viscosity; D001916:Brachial Artery / Q000000981:diagnostic imaging / Q000503:physiopathology*; D005260:Female; D005542:Forearm / Q000098:blood supply*; D006400:Hematocrit; D006801:Humans; D006940:Hyperemia / Q000097:blood / Q000000981:diagnostic imaging / Q000503:physiopathology*; D007511:Ischemia / Q000097:blood / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008297:Male; D012039:Regional Blood Flow; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D014463:Ultrasonography; D014664:Vasodilation; D055815:Young Adult
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