Prof. Avraham Mayevsky

The functioning brain in vivo; the effects of various pathological conditions on the metabolic, ionic, and electrical activities of the brain.

Effects of Hypoxia, Ischemia and Spreading Depression of the Functioning Brain In vivo. In order to evaluate the functional state of the brain in vivo, a multi-parametric monitoring approach (MPA) was developed. The metabolic activity is monitored by a Laser Doppler flowmeter and a fiber optic surface fluorometer. The ionic homeostasis is determined by monitoring the extracellular levels of K⁺ and H⁺. The electrical activities monitored are the DC steady potential (using Ag/AgCl electrodes) and electroenceph-alography. The animal is exposed to various pathological situations such as hypoxia, ischemia of the carotid arteries or ischemia of the middle cerebral artery (a well-known model for stroke) for different durations, and the various responses are recorded in real-time mode.

In Vivo Monitoring of Brain Functions under Hyperbaric Oxygenation (Oxygen Toxicity Processes). We developed an in-vivo approach for monitoring brain functions under hyperbaric oxygenation in unanaesthetized animals. Using the MPA, the researchers hope to describe the cascade of events that occur during the development of O₂ toxicity. This information will be significant for the better utilization of O₂ treatment in patients, as well as in the development of new drugs to be used as protective agents against O₂ toxicity.

Body vitality evaluation of critical pathological conditions using real-time multiorgan monitoring. In many pathophysiological events, body metabolic state is deteriorated leading to redistribution of blood towards the vital organs (brain, heart) at the expense of less-vital organs (i.e., GI tract and skin). Under these conditions, oxygen supply to vital organs is preserved, while energy failure will occur in less-vital organs. Thus, the ability to detect early less-vital organ dysfunction before damage to vital organs has developed, is strongly desired. We have developed a multiparametric multisite monitoring device that enables simultaneous monitoring of a vital organ (the brain)and a less vital organ (small intestine or skin). This monitoring system is applied in various pathophysiological conditions such as hypoxia, hypercapnia, sepsis, hemorrhagic shock, and in various developmental stages of the newborn rat.

CBF autoregulation and mitochondrial function evaluation: Several vasoactive factors are involved in CBF regulation under normal or pathophsiological conditions. Nitric oxide (NO) is a major agent in the cerebral autoregulatory mechanism, as well as the tissue levels of oxygen, CO₂ and pH. The involvement of NO will be tested using L-NAME (nitric oxide synthase inhibitor), or nitrite (exogenous NO). Tissue level of O₂ and CO₂ will be changed by inhalation of different gas mixtures for various durations.