Application of multivariate statistical analysis to estimate +Gz tolerance based on the changes of hemodynamic...

The application of lower body negative pressure (LBNP) is very useful method for simulation of +Gz stress and for evaluation of orthostatic reaction. The different physiological changes that occur during LBNP test and +Gz acceleration test are similar. Lategola and Trent found that supine LBNP exposure at the level of -50 mmHg may be equivalent to +2Gz in producing the changes of heart rate (HR). Polese and coworkers compared hemodynamic changes occurring during upright and supine LBNP at the levels to -70 mmHg with identical measurements made during accelerations to +2Gz, +3Gz, and +4Gz in the same subjects. They noted for example that HR changes during upright LBNP exceeded HR supine levels. Peak values of HR during +3Gz and +4Gz significantly exceeded HR levels during both kinds of LBNP, but HR values at +2Gz were equivalent to those at -40 mmHg of upright and -70 mmHg of supine LBNP. So, the present study was undertaken to evaluate adaptating responses to LBNP stimulus at the level of -60 mmHg, regulatory mechanisms of the circulatory system (central and peripheral) and to look for the possibility of +Gz tolerance prediction based on the changes of some hemodynamic parameters during LBNP.