Takeo Ozaki

Tissue oxygenation monitor using NIR spatially resolved spectroscopy

A new clinical tissue oxygenation monitor, the NIRO-300, has been developed. In addition to monitoring changes in hemoglobin concentration and redox state of cytochrome oxidase, the instrument can measure a Tissue Oxygenation Index (TOI), which is the ratio of oxygenated to total tissue hemoglobin, by utilizing NIR spatially resolved spectroscopy (SRS). In SRS, the slope of light attenuation versus distance is measured at a distant point from the light input, from which the TOI is calculated using photon diffusion theory. Four laser diodes are used as the light source and Class 1 laser light (IEC 825) is irradiated onto the skin. A high gain and low noise amplifier is used in the detector, which enables a large emitter-detector separations of around 5cm. To evaluate the TOI measured by the NIRO-300, it was compared to the data from a blood gas analyzer (S02 value) in measurements made on phantoms containing intralipid and blood. We also made simultaneous measurements by the NIRO-300 and an NIRS machine based on time resolved spectroscopy (TRS) on human arms. In the both measurements, TOI showed an excellent correlation with the data from blood gas analyzer and the TRS machine, which suggests the efficacy of the TOI data also in clinical use.

Human Visual Cortical Function during Photic Stimulation Monitoring by Means of near-Infrared Spectroscopy

Near-infrared spectroscopy (NIRS) was used to monitor human visual cortical function during and after photic stimulation (PS) in five adult volunteers. Cerebral blood volume (CBV) increased on the occipital surface during PS, but NIRS parameters did not change on the frontal surface. The increase in CBV was caused by a rapid increase in oxyhemoglobin with but a small increase in deoxyhemoglobin, suggesting cerebral vascular dilatation with decreased oxygen consumption. After PS stopped, CBV promptly decreased and then slightly increased again. Cytochrome aa3 did not show any change during and after PS. These phenomena reappeared following repeated PS in all five subjects. These results may represent the first step in the development of NIRS imaging.

Monitoring of the intracranial hemodynamics and oxygenation during and after hyperventilation in newborn rabbits with near-infrared spectroscopy

ABSTRACT: Oxyhemoglobin, deoxyhemoglobin, total hemoglobin, and oxidized cytochrome aa3 were monitored, blood pressure and heart rate were continuously recorded, and cerebral hemodynamic changes were analyzed during and after hyperventilation (arterial CO2 tension < 2.67 kPa) and/or hyperoxemia (100% O2 inhalation) in 11− to 12-d-old rabbits. Oxyhemoglobin, deoxyhemoglobin, total hemoglobin, and oxidized cytochrome aa3 were monitored by means of near-infrared spectroscopy. Near-infrared spectroscopy ideally demonstrated decreases in Oxyhemoglobin and total hemoglobin and an increase in deoxyhemoglobin during hyperventilation and a return to the previous values after hyperventilation. Cytochrome aa3 decreased during hyperventilation. On hyperventilation with 100% O2 inhalation, however, cytochrome aa3 was not reduced, although the changes in Oxyhemoglobin and total hemoglobin were more significant. This reduction of cerebral oxygenation during hyperventilation without the administration of oxygen may induce hypoxic-ischemic brain damage. Noninvasive monitoring of cerebral oxygenation and hemodynamics, for which near-infrared spectroscopy is useful, is a requisite for the prevention of brain injury caused by severe hypocarbia in hyperventilation therapy.

A Clinical Tissue Oximeter Using NIR Time-Resolved Spectroscopy.

The tNIRS-1, a new clinical tissue oximeter using NIR time-resolved spectroscopy (TRS), has been developed. The tNIRS-1 measures oxygenated, deoxygenated and total hemoglobin and oxygen saturation in living tissues. Two-channel TRS measurements are obtained using pulsed laser diodes (LD) at three wavelengths, multi-pixel photon counters (MPPC) for light detection, and time-to-digital converters (TDC) for time-of-flight photon measurements. Incorporating advanced semiconductor devices helped to make the design of this small-size, low-cost and low-power TRS instrument possible. In order to evaluate the correctness and reproducibility of measurement data obtained with the tNIRS-1, a study using blood phantoms and healthy volunteers was conducted to compare data obtained from a conventional SRS device and data from an earlier TRS system designed for research purposes. The results of the study confirmed the correctness and reproducibility of measurement data obtained with the tNIRS-1. Clinical evaluations conducted in several hospitals demonstrated a high level of usability in clinical situations and confirmed the efficacy of measurement data obtained with the tNIRS-1.

Responses of Cerebral Blood Volume and Oxygenation to Carotid Ligation and Hypoxia in Young Rabbits: Near-Infrared Spectroscopy Study

After ligation of the bilateral common carotid arteries with exposure to hypoxia in young rabbits, cerebral blood oxyhemoglobin, deoxyhemoglobin, and total hemoglobin were measured by near-infrared spectroscopy. Ligation of common carotid arteries decreased oxyhemoglobin, increased deoxyhemoglobin, and slightly decreased total hemoglobin. Exposure to hypoxia with bilateral carotid ligation more remarkably decreased oxyhemoglobin and increased deoxyhemoglobin than that without carotid ligation. However, the total cerebral blood volume did not change very much. This marked reduction in the cerebral oxygenation may cause brain damage and may be an important monitoring marker for the prevention of hypoxic-ischemic encephalopathy. (J Child Neurol 1993;8:237-241).

The effect of acetazolamide and carbon dioxide on cerebral hemodynamic changes on near-infrared spectroscopy in young rabbits

The changes of cerebral blood oxyhemoglobin (HbO2), deoxyhemoglobin (HbR), and total hemoglobin (tHb) induced by acetazolamide and CO2 loading on near-infrared spectroscopy (NIRS) were recorded. In anesthetized 2-week-old rabbits, acetazolamide (10 mg/kg i.v.) increased HbO2 and tHb, concomitant with an increase in tissue PCO2, and decreased HbR only at 5 and 10 min. CO2 loading significantly increased HbR and decreased HbO2, and after the termination of CO2 loading, tHb and HbO2 significantly increased and HbR decreased to nearly the baseline value. Thus, NIRS demonstrated cerebral hemodynamic responses as a function of vasomotor reactivity to acetazolamide as well as CO2 loading.