[Correlation between empirical and statistical indices of cardiovascular deconditioning in response to orthostatic...

Data of heart rate and blood pressure from 26 astronauts during orthostatic testing before and after space flight and 15 healthy men during orthostatic testing before and after 10-days head-down tilt (HDT) were used to correlate two integral indices of cardiovascular deconditioning. The first, very simple index, was used earlier by Bungo M. W. et al. in order to ascertain the efficiency of peroral body dehydratation as a measure to prevent orthostatic intolerance in astronauts after space flight. This index sums up HR and BP variations from one orthosatic probe to another. The choice of the another index was based on our investigation of HDT effects on the healthy human cardiovascular system. This index was determined as a difference between linear discriminant function values separating distinctly groups of men with normal and lowered orthostatic tolerance. Analysis of regression showed a high correlation between these indices: 0.71 for the group of astronauts and 0.88 for the group of healthy men. The linear regression equations allowed calculate value of one index from value of the other with an admissible standard error.