In the intensive care setting, continuous non-invasive optical functional imaging could be critically important and, with further study, may provide a bedside monitoring tool for prospectively identifying patients at high risk for brain injury.

We present a noninvasive method to measure the venous oxygen saturation (Sv O 2 ) in tissues using near-infrared spectroscopy (NIRS). This method is based on the respiration-induced oscillations of the near-infrared absorption in tissues, and we call it spiroximetry (the prefix spiro means respiration). We have tested this method in three piglets (hind leg) and in eight human subjects (vastus medialis and vastus lateralis muscles). In the piglet study, we compared our NIRS measurements of the Sv O 2 (Sv O 2 -NIRS resp ) with the Sv O 2 of blood samples. Sv O 2 -NIRS resp and Sv O 2 of blood samples agreed well over the whole range of Sv O 2 considered (20-95%). The two measurements showed an average difference of 1.0% and a standard deviation of the difference of 5.8%. In the human study, we found a good agreement between Sv O 2 -NIRS resp and the Sv O 2 values measured with the NIRS venous occlusion method. Finally, in a preliminary test involving muscle exercise, Sv O 2 -NIRS resp showed an expected postexercise decrease from the initial baseline value and a subsequent recovery to baseline. Keywords tissue spectroscopy; frequency-domain; pulse oximetry; hemoglobin saturation THE POSSIBILITY OF USING LIGHT to measure the oxygen saturation of hemoglobin in vivo has been explored since the 1940s (37). The feasibility of optical blood oximetry stems from the oxygenation dependence of the optical spectrum of hemoglobin. This is illustrated in Fig. 1, which shows the absorption spectra of 100 M hemoglobin for oxygen saturation values of 0,20,40, 60, 80, and 100%. The spectra of Fig. 1 were calculated from published values of the molar extinction coefficients of oxyhemoglobin (HbO 2 ) and deoxyhemoglobin (Hb) (43,53).Oxygen saturation of the pulmonary capillary blood in rabbits has been measured by using dynamic invasive techniques (48). Near-infrared light in the wavelength range from 700 to 900 nm results in a sufficient penetration depth for the noninvasive optical monitoring of skeletal muscle, cerebral gray matter, and breast tissue. As a result, near-infrared techniques allow a noninvasive assessment of hemoglobin saturation for a wide range of applications, such as the study of muscle metabolism (7,9,12,29,45), the diagnosis of vascular disorders NIH Public AccessAuthor Manuscript J Appl Physiol (1985). Author manuscript; available in PMC 2013 September 30.Published in final edited form as: J Appl Physiol (1985). 2002 January ; 92(1): 372-384. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript (2,20,32,33,44,49), functional brain imaging (3,10,24,30,35,50), and breast cancer detection (23,28,40,42,46).If near-infrared light is highly sensitive to the oxygen saturation of hemoglobin, then its large penetration depth inside tissues implies that the arterial, venous, and capillary compartments all contribute to the optical signal. The average hemoglobin oxygenation measured with near-infrared spectroscopy (NIRS) (19,34,41 Hb] at the breathing rate are mostly representative of the...

Pulse oximetry (oxygen saturation monitoring) has markedly improved medical care in many fields, including anesthesiology, intensive care, and newborn intensive care. In obstetrics, fetal heart rate monitoring remains the standard for intrapartum assessment of fetal well being. Fetal oxygen saturation monitoring is a new technique currently under development. It is potentially superior to electronic fetal heart rate monitoring (cardiotocography) because it allows direct assessment of both the fetal oxygen status and fetal tissue perfusion. Here we present the analysis for determining the most optimal wavelength selection for pulse oximetry. The wavelengths we chose as the most optimal are the first in the range of 670-720 nm and the second in the range of 825-925 nm. Further, we discuss the possible systematic errors during our measurements and their contribution to the obtained saturation results. We present feasibility studies for fetal pulse oximetry, monitored noninvasively through the maternal abdomen. Our preliminary experiments show that the fetal pulse can be discriminated from the maternal pulse and thus, in principle, the fetal arterial oxygen saturation can be obtained. We present the methodology for obtaining these data, and discuss the dependence of our measurements on the fetal position with respect to the optode assembly.

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