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StO2 Proof of Concept

Noninvasive Method for Measuring Local Hemoglobin Oxygen Saturation in Tissue Using Wide Gap Second Derivative Near-Infrared Spectroscopy
Myers DE , Anderson LD , Seifert RP , Ortner JP , Cooper CE , Beilman, GJ , Mowlem JD
Journal of Biomedical Optics 10(3), 034017 (May/June 2005)

Near infrared spectroscopy (NIRS) uses specific, calibrated wavelengths of near infrared light to noninvasively illuminate the tissue below the skin. Previous NIRS technologies relied on diffusion theory resulting in measurement errors from approximations inherent in applying diffusion theory equations to heterogeneous tissue. Using diffusion theory equations requires in vivo derived calibration sets; however, there are no known calibration sets for actual tissue oxygen saturation or total hemoglobin.

Myers et al proposed an alternate approach to NIRS tissue chromophores quantification with the application of derivative spectroscopy to multi-wavelength data. Unlike previous second derivative methods, which focused primarily on measuring deoxyhemoglobin concentration, HTI’s technology relies on a wide gap 40 nm wavelength interval to calculate the second derivative attenuation. The wide gap contains spectral regions that are sensitive to both oxyhemoglobin, deoxyhemoglobin concentration, and allows quantification of hemoglobin oxygen saturation with four wavelengths of 680, 720, 760, and 800 nm, significantly improving sensitivity to oxyhemoglobin absorption. The combination of wide gap and second derivative approaches results in a technology that eliminates the issue of light scattering in heterogeneous tissue.

InSpectra™ Tissue Spectrometer StO2 Accuracy Compared to CO-Oximeter SO2
Gallea B, Norsted S. (HTI Internal Study, 2000)

Using an in vitro blood loop, the InSpectra™ System provides measurements of hemoglobin oxygen saturation that are equivalent over a range of saturations to measurements taken with an IL482 CO-Oximeter.

Correlation of StO2 to CO-Oximeter SO2 in Isolated Porcine Hearts With Inhibited Oxygen Consumption
Myers D (HTI Internal Study, 1997)

In isolated, blood-perfused porcine hearts, measurements of hemoglobin oxygen saturation using Hutchinson Technology's InSpectra™ System correlate to the mean of arterial and venous hemoglobin saturation values measured with a CO-Oximeter.

Comparative Hemoglobin Oxygen Saturation Values Measured by Hutchinson Technology (HTI) NIR Tissue Spectrometer and IL 482 CO-Oximeter in Forearm Muscle
(HTI Internal Study 1996)

Using the human forearm, there is no statistical difference at baseline, light exercise, rigorous exercise, and return to baseline between StO2 measured with Hutchinson Technology's InSpectra™ System in skeletal muscle and peripheral SvO2 measured with a CO-Oximeter. Statistical difference is demonstrated in isometric exercise and ischemia.

Validation of Near-Infrared Spectroscopy in Humans
Mancini DM, Bolinger L, Li H, Kendrick K, Chance B, Wilson JR.
J Appl Physiol. 1994;77:2740-2747

In four different tests, NIR measures of oxy- and deoxyhemoglobin: 1) are affected by ischemia-inducing forearm exercise and minimally affected by skin blood flow; 2) correlate to venous O2 saturation measured with a deep-seated venous catheter in resting and exercising skeletal muscle; 3) correspond to known changes in skeletal muscle perfusion, and 4) are not significantly impacted by myoglobin.

StO2 Changes During Acute Cuff Ischemia in Healthy Volunteers
Anderson L, Norsted S. (HTI Internal Study, 2001)

Induced ischemia via arterial occlusion in healthy volunteers demonstrates that the InSpectra™ System can directly detect tissue hypoxia when placed on the thenar eminence, dorsal compartment of the forearm, and tibialis anterior muscle.

The InSpectra™ StO2 Tissue Oxygenation Monitor provides a direct, absolute measurement of hemoglobin oxygen saturation in tissue (StO2), providing trauma teams the ability to measure tissue oxygenation and monitor it during resuscitation. It is the only tissue oxygenation monitor designed for trauma environments. The InSpectra StO2 Tissue Oxygenation Monitor uses near infrared light to illuminate tissue, and then analyzes the returned light to produce a quantitative measurement of oxygen saturation in the tissue's microcirculation.

The StO2 Trauma Study researched the role that tissue oxygen saturation monitoring could play in hemorrhagic shock and resuscitation. Study results demonstrate that StO2 measurements less than 75% may indicate serious hypoperfusion in trauma patients and that StO2 functions as well as base deficit in indicating hypoperfusion in trauma patients.