MINIMUM TIME TO ALTERED NEUROLOGICAL FUNCTION: THE VERTICAL ASYMPTOTE OF THE +CZ-TIME TOLERANCE CURVE

INTRODUCTION: Conservative estimates suggest that 21 million animal and 141,000 human loss of consciousness (LOC) episodes occur daily. Understanding the complex signs and symptoms associated with LOC is therefore an essential aspect of understanding life in our environment. Consciousness is an integrated organismal process requiring an adequate supply of energy (oxygen) to cephalic neurological substrates. These substrates tolerate energy reductions for only a minimal amount of time. A complex of time dependent signs and symptoms results in organisms when normal oxygen supply is compromised. Alterations that compromise adequate oxygen supply through ischemia and hypoxia include exposure to altitude, acceleration, choking, hanging, asphyxiation, exsanguination, cardiac rate and rhythm disturbances, and vascular compromise. METHODS: Minimum time to neurological compromise and LOC resulting from these various alterations was established from a meta-analysis of studies associated with LOC. The time course of the symptom complex (LOC syndrome) was also analyzed for each type of alteration. The minimum time to acceleration (+Gz) induced loss of consciousness (G-LOC) was determined from the horizontal asymptote of the C-time tolerance curve resulting from the analysis of over 800 C-LOC episodes in healthy USAF and USN personnel. RESULTS: Plotting +Cz-onset rate (y) versus time (x) gives the equation y= 15.603x(-0.0607) describing a hyperbolic curve with the limiting value of time being 6.1s. This limiting value of the vertical asymptote was then compared to the minimum time to produce LOC by other alterations. Comparison of the minimum time to induce G-LOC and other time-dependent neurological symptoms provide data that allow determination of differences and similarities in the mechanisms of energy compromise of the different alterations that produce LOC. DISCUSSION: LOC is an important and widespread aspect of the human and animal life experience as well as necessary survival, economic, clinical, social, and scientific topics for investigation. These data provide key parameters that may be input to computational physiological modeling to improve our understanding of these alterations.