Near-infrared optical responses in feline brain and skeletal muscle tissues during respiratory acid-base imbalance

Abstract

The effects of hyper- and hypocapnia on oxidative metabolism were evaluated by near-infrared (NIR) multiwavelength spectroscopy in intact brain and skeletal muscle tissues of the anesthetized cat. A 3-wavelength NIR algorithm was used to monitor cytochrome a,a 3 oxidation state, regional blood volume, and tissue oxyhemoglobin and O 2 stores simultaneously in brain and muscle in ventilated animals. Incremental hypercapnia was produced in 10 cats by raising arterial pCO 2 from 27.0 ± 1.3to95.1 ± 1.9mmHg with inspired CO 2. Hypercapnia produced progressive increases in cerebral HbO 2, blood volume, and cytochrome a,a 3 oxidation state ( P < 0.01). In contrast, CO 2 simultaneously decreased all 3 NIR parameters in intact hindlimb muscles ( P < 0.01). Blood volume changes during hypercapnia correlated with changes in blood flow measured qualitatively by intravascular injections of indocyanine green dye. Hypocapnia produced by hyperventilation in 8 cats lowered p aCO 2 from 28.5 ± 0.5to13.5 ± 0.5mmHg. Hypocapnia decreased cerebral HbO 2, blood volume, and cytochrome a,a 3 redox level ( P < 0.05), but NIR changes were not seen in skeletal muscle. These experiments demonstrate preferential distribution of oxygen to brain during hypercapnia and the ability of NIR spectroscopy to assess regional oxygenation in multiple tissues non-invasively.