Muscle oxygen monitoring accuracy

BSXinsight SmO2 is calibrated for absolute measurements within a range from 0% to 100%, where 0% indicates that all hemoglobin in the tissue volume directly below the sensor have completely given out their oxygen and, thus, consist of deoxyhemoglobin, while 100% indicates that all hemoglobin in the tissue directly below the sensor are oxygenated (oxyhemoglobin).

The Figure below shows SmO2 values monitored in the forearm during a long ­term arterial occlusion. During long occlusion living tissue continues to consume oxygen to sustain its metabolic processes, up to the point when all oxygen has been consumed. Once the occlusion is terminated oxygenated blood rushes to re­oxygenate the arm, leading to high oxygenation values. In the experiment below we see a minimum SmO2 value of 2.8% and a maximum (after occlusion) value of 83.6%, demonstrating the BSXinsight’s ability to monitor the full ­range of oxygenation values in tissue.

Comparing those values to an expected baseline of 80.6% (using arterial and venous values available in the literature ­ for example, from Medbo1 or Bloos2), and an absolute minimum oxygenation level of 0%, we see that the range of 2.8% to 83.6% is very close to the expected range, with a maximum deviation of 2.8% and 3% at the lowest and highest values, respectively.

References
1. J. Medbo, “Examination of blood haemoglobin concentration measured using the OSM2,” in The Scandinavian Journal of Clinical & Laboratory Investigation, v.6, pp. 92­101 (2009)
2. F. Bloos and K. Reinhart, “Venous oximetry,” in Intensive Care Med., v. 31, pp. 911–913 (2005)

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If you prefer it as a basic, common-term explanation: The BSXinsight Gen2 has gone through extensive testing, where blood flow was cut off, with a tourniquet, to measure max and min values reported by the BSXinsight Gen2.

The testing was performed the same as in the clinical lab tests, and the results were as expected. The graph above represents the consistent results found, where the range was 2.8% to 83.6%.

This IS repeatable, but we don’t recommend trying it, especially on the leg, given the required force to stop flow in the arteries. We’re very confident your BSinsight Gen2 devices will show this range with a 10 minute, properly used tourniquet that cuts off blood flow. However, you risk tissue damage and blood clots doing this, so, again, we DON’T recommend you doing it.

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