RESUMEN
The focus was placed on the physiological mechanisms of correction of the blood redistribution during the head-down tilt (HDT) with a discrete or complex use of the methods of negative pressure respiration (NPR) and lower body negative pressure (LBNP). It was evidenced that rise in the intracranial hydrostatic pressure in HDT (-6 degrees) can be compensated by NPR within a range of -10 to -15 cm of water column causing decrease in the intrasternal pressure from -5.04 to -7.74 cm w.c. Bioimpedance and ultrasonic investigations led to the conclusion that the decreased transpulmonary pressure is responsible for blood outflow from the intracranial venous system till the level adequate to the horizontal position of the body. The results were verified in experiments with unconscious cats: pressure in the exterior jugular vein and v. cava superior during HDT (-30 degrees) with NRP at -5 cm w.c. decreased by 3.2. and 4.3. w.c., respectively. Experiments with human subjects also demonstrated that the complex use of NPR and LBNP produces an additive hemodynamic effect and can be considered a new method for correcting the adverse consequences of redistribution of the local blood volumes toward the head end.
Asunto(s)
Volumen Sanguíneo/fisiología , Frecuencia Cardíaca/fisiología , Hipocinesia/sangre , Respiración , Adulto , Hemodinámica/fisiología , Humanos , MasculinoRESUMEN
Orthostatic tolerance (OT) and physical performance were tested against the ground simulation of several spaceflight factors. Before and after prolonged isolation and confinement three human subjects were tested by tilting, LBNP, and graded incremental aerobic exercise in the sitting position. Results suggested good OT in all the subjects. However, the pattern of orthostatic reaction was modified depending on the initial functional state of each subject. This was especially distinct in subjects 002 and 003 whose OT was slightly reduced by the experimental conditions. Orthostatic reactions in subject 004 showed greater stability in the baseline data collection period and was not much affected by isolation and confinement. HR variations at rest carried an individual character. On the whole, HR tended downward, particularly in 002. Indices of AP and, to a higher degree, its systolic constituent wandered outside the region of baseline values and even the norm limits in 002 and 004. Maximum variations were documented at the end of the second (003 and 004) and the third (002) months in experiment. ECG parameters in all the operators displayed different patterns of the norm. Diffusive repolarization, especially in the left chest leads, was noted to decline in the experiment. Tolerance of LBNP was qualified as good. Meanwhile, subject 003 developed symptoms of strained functioning of compensatory/adaptive mechanisms responsible for the OT maintenance. Repeated testing by LBNP was found to raise HR. Hence, prolonged simulation of space flight causes some reduction of orthostatic and LBNP tolerance, and degradation of physical performance.
Asunto(s)
Hipotensión Ortostática/diagnóstico , Vuelo Espacial , Evaluación de Capacidad de Trabajo , Adulto , Humanos , Masculino , Factores de TiempoRESUMEN
With the use of dispersion analysis the variation of indices of central and peripheral hemodynamics in healthy volunteers stayed from 1 to 7 days under conditions of "dry" immersion (DI) was studied. Nine persons were investigated at rest, 5 individuals during orthostatic tests before and after dry immersion sessions. The central hemodynamic indices were calculated, the arterial pressure (AD) was measured by Korotkoff's method, indices of rheoencephalographic and rheoplethysmographic indices of lower leg were found. The significant differences of mean values of measured parameters before and after DI at rest were not revealed. Two-factor dispersion analysis of the orthostatic test data revealed the high levels of significance of influencing immersion and personality factors as well as their interaction on the variation of most indices. For excluding an individual uniformity there has been done an analysis of dynamics of indices according to their relative values which allowed one to isolate qualitative peculiarities of changes and distinctions between persons with different orthostatic tolerance even before orthostatic testing.