A device and method in accordance with the invention for determining the
oxygen partial pressure (PO.sub.2) of a tissue by irradiating the tissue
with optical radiation such that the light is emitted from the tissue, and
by collecting the reflected or transmitted light from the tissue to form
an optical spectrum. A spectral processor determines the PO.sub.2 level in
tissue by processing this spectrum with a previously-constructed spectral
calibration model. The tissue may, for example, be disposed underneath a
covering tissue, such as skin, of a patient, and the tissue illuminated
and light collected through the skin. Alternatively, direct tissue
illumination and collection may be effected with a hand-held or endoscopic
probe. A preferred system also determines pH from the same spectrum, and
the processor may determine critical conditions and issue warnings based
on parameter values.
