Comparison of two devices using near-infrared spectroscopy for the measurement of tissue oxygenation during a vascular occlusion test in healthy volunteers (INVOS^® vs. InSpectra™)

The aim of this study was to compare tissue oxygen saturation as measured by INVOS^® and InSpectra™ during a vascular occlusion test (VOT) in the same subject. Twenty healthy adults were investigated. The INVOS^® and InSpectra™ probes were placed randomly on the right and left thenar eminence in the same participant and monitoring of tissue oxygen saturation (SrO₂ from INVOS^® and StO₂ from InSpectra™) were begun. Pneumatic cuffs placed around each upper arm were inflated simultaneously to 30 mmHg above the initial systolic blood pressure and maintained until the tissue oxygen saturation had decreased to 40 % or below. The cuff pressure was then released rapidly. The time to achieve initial stability, the baseline value, the time from the baseline value to 40 %, the rate of deoxygenation, the rate of reoxygenation, and the hyperemic area under the curve were calculated from SrO₂ and StO₂. The baseline value by INVOS^® was lower than that by InSpectra™ (75.6 ± 8.2 vs. 81.8 ± 3.4 %, p < 0.01). The time to reach stable baseline value was significantly longer for SrO₂ than for StO₂ (249 ± 86 and 54 ± 40 s respectively; p < 0.01). SrO₂ declined to 40 % more rapidly than did the StO₂ (147 ± 38 vs. 199 ± 41 s, p < 0.01). The deoxygenation and reoxygenation rates were higher (p < 0.01) and the reactive hyperemic area was more extensive for INVOS^® than for InSpectra™ (p = 0.015). In conclusion, the VOT on the thenar muscle using INVOS^® was as clinically applicable as InSpectra™, but baseline values and dynamic changes of INVOS^® differed from those of InSpectra™.