К ВОПРОСУ ОБ ОЦЕНКЕ ОРТОСТАТИЧЕСКОЙ УСТОЙЧИВОСТИ ОРГАНИЗМА ЧЕЛОВЕКА

Abstract

Ratio of blood pressure (BP) and heart rate (HR) has been used as a quantitative indicator of the human orthostatic tolerance. The indicator was conventionally designated as an efficiency coefficient (EC) of the mechanisms involved in systemic BP control during the passive orthostatic test (POT). The coefficient is measured in conventional units and calculated by formula EC (conv.unit) = BP (mm Hg) / HR (beats/min). Informativity of this indicator was verified by means of a retrospective analysis of 118 POTs performed by 30 essentially healthy male subjects (aged 19 to 40 yrs) before and after bed rest of varying duration. Prior to POT, EC in supine position made up 1.88 ± 0.04 conv. units. The EC decrease to 1.3 – 0.95 conv. units during POT evidenced clearly the extent of changes in the cardiovascular functioning and POT endurance. After bed rest, all subjects demonstrated an increased cardiovascular strain and reduced POT endurance; however, EC values were reliably higher for the subjects who had shown a higher POT endurance before bed rest. Based on analysis of individual reactions, the EC reduction to 1 conv.unit corresponded to the first pre-collapse signs and called for immediate POT termination. These results of the investigation make us believe that EC is an informative objective criterion for orthostatic tolerance evaluation that can be proposed for aerospace medicine applications.