Evaluation of cuff-induced ischemia in the lower extremity by magnetic resonance oximetry.
OBJECTIVE
The aim of this study was to evaluate vascular function in the lower extremities by making direct time-course measurement of oxygen saturation in the femoral/popliteal arteries and veins during cuff-induced reactive hyperemia with magnetic resonance imaging-based oximetry.


BACKGROUND
Magnetic resonance imaging-based oximetry is a new calibration-free technique taking advantage of the paramagnetic nature of blood that depends on the volume fraction of deoxyhemoglobin in red blood cells.


METHODS
We compared post-occlusive blood oxygenation time-course of femoral/popliteal vessels in: 1) young healthy subjects (YH) (n = 10; mean ankle-brachial index [ABI] 1.0 +/- 0.1, mean age 30 +/- 7 years); 2) peripheral arterial disease (PAD) patients (n = 12; mean ABI 0.6 +/- 0.1, mean age 71 +/- 9 years); and 3) age-matched healthy control subjects (AHC) (n = 8; mean ABI 1.1 +/- 0.1, mean age 68 +/- 9 years). Blood oxygenation was quantified at 3.0-T field strength with a field mapping pulse sequence yielding the magnetic susceptibility difference between blood in the vessels and surrounding muscle tissue from which the intravascular blood oxygen saturation is computed as %HbO(2).


RESULTS
Significantly longer washout time (42 +/- 16 s vs. 14 +/- 4 s; p < 0.0001) and lower upslope (0.60 +/- 0.20 %HbO(2)/s vs. 1.32 +/- 0.41 %HbO(2)/s; p = 0.0008) were observed for PAD patients compared with healthy subjects (YH and AHC combined). Furthermore, greater overshoot was observed in YH than in AHC (21 +/- 8 %HbO(2) vs. 10 +/- 5 %HbO(2); p = 0.0116).


CONCLUSIONS
Post-occlusive transient changes in venous blood oxygenation might provide a new measure of vascular competence, which was found to be reduced in subjects with abnormal ABI, manifesting in prolonged recovery during the early phase of hyperemia.
Department of Radiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA.
Michael C
MC
Langham
Thomas F
TF
Floyd
Emile R
ER
Mohler
Jeremy F
JF
Magland
Felix W
FW
Wehrli
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005263:Femoral Artery; D005268:Femoral Vein; D006801:Humans; D007511:Ischemia / Q000503:physiopathology*; D035002:Lower Extremity / Q000098:blood supply*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010092:Oximetry / Q000379:methods*; D011150:Popliteal Artery; D011152:Popliteal Vein