Reflectance spectrophotometric measurement of in vivo local oxygen consumption in the cerebral cortex

Evaluation of circulatory compromise in the leg in lumbar spinal canal stenosis

To evaluate whether hemoglobin oxygen saturation and hemoglobin concentration of the leg are useful indicators for circulatory compromise in patients with lumbar spinal canal stenosis, we investigated the changes in the indices during level gait using reflectance spectrophotometry. Thirty-three patients with lumbar spinal stenosis were studied. Preoperatively, the hemoglobin oxygen saturation was greater in the 33 patients than in the control subjects. The indices increased in the control subjects more than those in the patients. Postoperatively, the increases in hemoglobin oxygen saturation were greater in the patients with lumbar spinal canal stenosis than before decompression and the hemoglobin concentration tended to approximate that in the control subjects. The results suggest these indices might be useful for monitoring disease severity in patients with lumber spinal canal stenosis. In addition to stenotic ischemia in the spinal canal, it is thought that the neurogenic intermittent claudication is secondarily caused by circulatory failure in the lower extremities attributable to the autonomic nervous dysfunction.

Deep hypothermic circulatory arrest during cardiac surgery: effects on cerebral blood flow and cerebral oxygenation in children

Deep hypothermic circulatory arrest has become an essential technique to allow repair of complex congenital cardiac lesions in children. The arrested state has concerned the surgeon, cardiologist, and anesthesiologist alike, and yet deep hypothermic circulatory arrest has been highly successful with a low incidence of neurologic sequelae. Studies of cerebral blood flow and cerebral oxygenation demonstrate that the arrest hypothermic brain does not develop the immediate postarrest hyperemia or hyperoxia seen in normothermic ischemic brain models. However, both hypothermic and normothermic ischemic brains exhibit hypoperfusion beyond the immediate recirculation period, likely coupled with a reduced cerebral metabolic rate. That the hypothermic arrested brain likely becomes anoxic and recovery of the anoxic brain depends in large part on recirculatory hemodynamics suggests that the lack of hyperemia and hyperoxia may play more major roles than was previously believed. The mechanism of protection may be related to suppression of oxygen free radicals.

Real-time measurement of microcirculation of skin by reflectance spectrophotometry

A reflectance spectrophotometric measurement was developed to analyze the microcirculation of the skin in real time. The relative absorption (RA) spectra were obtained from skin tissue 10 times per second using a spectro-multi-channel-photodetector system. In this system, white light was projected onto the skin of the back of the anesthetized rat and the spectrum of the reflected light between 450 and 643 nm was analyzed. Two absorption peaks at wavelengths of about 540 and 577 nm were observed, corresponding to the absorption peaks in the oxyhemoglobin (HbO2) spectrum. Either phlebotomy or the i.v. injection of norepinephrine (NE) reduced the RA spectrum. Peaks of the reduction in spectrum [(RA spectrum before the treatment) - (RA spectrum after the treatment)] were observed at about 540 and 577 nm. Injection of NE (0.75-48 ng/100 g B.W., i.v.) reduced the RA value at 577 nm dose-dependently, suggesting a decrease in the skin blood flow due to vasoconstriction. In addition, the content of HbO2 and capillary permeation were measured at the same time after the i.v. injection of Evans blue (EB) dye. As indices of HbO2 content and capillary permeation, RA changes at 540 and 610 nm (the latter is an absorption peak in the EB spectrum) were measured in real time, respectively. Both RA values increased dose-dependently after the intradermal injection of histamine (0.3-100 micrograms/site), suggesting the presence of vasodilation and an increase in permeability. The time at which the RA value for HbO2 reached a maximum was shorter than that for EB. These observations suggest that the method described here can detect changes in the HbO2 content and permeation of skin microcirculation at the same time, and in real time.

Fiber optic reflectance spectrophotometry system for in vivo tissue diagnosis

Fiber optic probes for a small portable reflectance spectrophotometry system for noninvasive clinical diagnosis have been developed. A slender fiber optic probe, 3 m long, 2.4-mm diameter, which goes into the channel of a fiber optic endoscope, has been developed as the standard probe. To expand the availability and capability of this reflectance spectrophotometry system, some variations of the fiber optic probes were developed: contact sensor, pressure sensor, attachments for dental use, and a modified-shape probe head for continuous monitoring. The feasibility of these fiber optic probes was examined experimentally.