Physiological responses of astronaut candidates to simulated +Gx orbital emergency re-entry.

INTRODUCTION: We investigated astronaut candidates' physiological and pathological responses to +Gx exposure during simulated emergency return from a running orbit to advance astronaut +Gx tolerance training and medical support in manned spaceflight. METHODS: There were 13 male astronaut candidates who were exposed to a simulated high +Gx acceleration profile in a spacecraft during an emergency return lasting for 230 s. The peak value was 8.5 G. Subjective feelings and symptoms, cardiovascular and respiratory responses, and changes in urine component before, during, and after +Gx exposure were investigated. RESULTS: Under high +Gx exposure, 15.4% of subjects exhibited arrhythmia. Heart rate (HR) increased significantly and four different types of HR response curves were distinguished. The ratio of QT to RR interval on the electrocardiograms was significantly increased. Arterial oxygen saturation (SaO2) declined with increasing G value and then returned gradually. SaO2 reached a minimum (87.7%) at 3 G during the decline phase of the +Gx curve. Respiratory rate increased significantly with increasing G value, while the amplitude and area of the respiratory waves were significantly reduced. The overshoot appeared immediately after +Gx exposure. A few subjects suffered from slight injuries, including positive urine protein (1/13), positive urinary occult blood (1/13), and a large area of petechiae on the back (1/13). CONCLUSIONS: Astronaut candidates have relatively good tolerance to the +Gx profile during a simulation of spacecraft emergent ballistic re-entry. However, a few subjects exhibited adverse physiological responses and slight reversible pathological injuries.

[Repeated body position change training can improve human head-down tilt tolerance].

AIM: To verify the hypothesis that repeated body position change training can improve human head-down tilt (HDT) tolerance. METHODS: Six young healthy subjects were trained with repeated position change for 9 times and 11 days according to protocol of alternative head-down and head-up tilts, each time of training lasted for about 35 min. Their HDT tolerance (- 30 degrees/30 min) were determined before and after training. RESULTS: (1) Compared with the data before training, subjects' symptom scores during HDT test after training decreased significantly (6.00 +/- 3.79 vs 1.00 +/- 0.63, P < 0.05), magnitude of the decreased heart rate increased significantly (-0.6 +/- 2.5 vs -4.4 +/- 3.6, P < 0.01). (2) Before training, blood flow volume of internal jugular vein (IJV) during HDT decreased significantly and that of internal carotid artery (ICA) increased significantly at the beginning period of HDT compared with pre-HDT (P < 0.01), while blood flow volume of the common carotid artery (CCA) presented increasing trend. After training, there was no significant difference in blood flow volume of IJV between during HDT and pre-HDT, that of ICA and CCA presented decreasing trend in the final period of HDT compared with Pre-HDT. CONCLUSION: Repeated body position change training can improve human head-down tilt tolerance. And its main causation is that headward shift of blood volume is restrained to some extend during HDT after training.

[A study on training method for increasing adaptability to blood redistribution in human].

OBJECTIVE: To verify validity of the increase in adaptability of blood redistribution in human body with repeated body position change training and to find preferable training method for increasing astronaut's adaptability of blood redistribution. METHOD: Twelve subjects were randomly divided into group A and B. Six subjects in each group were trained with mode A and B repeated position change (9 times in 11 d) respectively. Their head-down tilt (HDT -30 degrees/30 min) tolerance and orthostatic tolerance were determined before and after training to verify training effects. RESULT: 1) Two kinds of repeated body position change training modes increased all subjects' HDT tolerance. Compared with pre-training, during HDT test subjects' symptom scores in group B were significantly lower than those in group A (P<0.05) and after training decreasing magnitude of heart rate in group B increased significantly (P<0.01). Then mode B to be preferable training method in increasing HDT tolerance was suggested. 2) Two kinds of training modes improved all subjects' orthostatic tolerance. Compared with pre-training, during orthostatic tolerance test increasing magnitude of mean arterial blood pressure in group B increased significantly (P<0.05) and a trend of increasing magnitude of heart rate in group B was appeared smaller than in group A (P<0.10). Mode B to be preferable training method in increasing orthostatic tolerance was suggested too. CONCLUSION: Repeated body position change training could increase adaptability to blood redistribution in human body. Mode B was preferable training method and would be hopeful to be used in astronaut training.

[Effects of repeated body position change training for human orthostatic tolerance].

OBJECTIVE: To verify the validity that repeated position change training can increase human orthostatic tolerance and to explore its mechanism. METHOD: Six subjects were trained with repeated position change for 11 d according to a protocol of alternative head-down and head-up tilts, each set of training lasted for about 35 min. Their orthostatic tolerances were determined before and after training. RESULT: Compared with the data before training, subjects' symptom scores during orthostatic tolerance test after training decreased significantly (4.50 +/- 1.05 vs. 2.83 +/- 1.60, P<0.05), magnitude of the increased heart rate increase lowered significantly [(29.3 +/- 4.3) bpm vs. (13.5 +/- 7.5) bpm, P<0.01], magnitude of mean arterial blood pressure augmentation increased significantly [(4.8 +/- 4.4) mmHg vs. (9.0 +/- 3.0) mmHg, P<0.05] and cardiovascular response index decreased significantly (34.42 +/- 5.00 vs. 22.33 +/- 8.27, P<0.01). In brief, the responses to orthostatic stress were improved after training. CONCLUSION: Repeated alternative body position change training can increase human orthostatic tolerance. This kind of training is promising for pilot, especially astronaut training.

[Effects of +Gx stress on contractility of rat diaphragm and its mechanism].

Objective. To observe the effect of sustained +Gx exposure on contractility of rat diaphragm and explore its mechanism. Method. Forty-two male Wistar rats were randomly divided into control group (underwent +1 Gx exposure, n=21) and experiment group (underwent +15 Gx for 3 min, n=21). The tension of rat diaphragm in vivo, contents of nucleoside phosphates and lactic acid in diaphragm and ultrastructure of diaphragm were measured and observed respectively. Result. 1) Compared with pre- +Gx, low-frequency tension of diaphragm of experiment group decreased significantly (P<0.01), whereas high-frequency tension did not significantly decrease after +Gx (P>0.05). As to the control group, however, the tension of diaphragm tested at a wide range of frequencies was almost unchanged (P>0.05). 2) Compared with control group, ATP decreased (P<0.01), while ADP and lactic acid contents in diaphragm increased significantly (P<0.05 and P<0.01) after +Gx in experiment group. In addition, ratios of ADP/AMP and AMP/ATP increased significantly (P<0.01). 3) After +Gx exposure, hypoxic changes in ultrastructure of rat diaphragm occurred in experiment group, but not in control group. Conclusion. Sustained +Gx exposure could cause diaphragm muscle fatigue, which was possibly due to changes in energy metabolism and ultrastructure of rat diaphragm induced by hypoxia under +Gx stress.

[Study on anti +Gx respiratory maneuver and its training method].

Objective. To study the anti +Gx respiratory maneuver and its training method. Method. Seven young male subjects undertook the anti +Gx respiratory maneuver training. Their +Gx tolerances were examined on human centrifuge before and after training. The change of respiratory type, breath rate, electrocardiogram, heart rate, arterial oxygen saturation (SaO2), subjective symptom and vision were real-time monitored during the +Gx tolerance examination. Result. Compared with pre-training, the +Gx tolerance increased after training (P<0.05). Dyspnea and chest pain disappeared or obviously lightened and the magnitude of decrease of SaO2 decreased significantly (P<0.05). Conclusion. The above results suggested that the anti +Gx respiratory maneuver can effectively eliminate or alleviate dyspnea and chest pain induced by +Gx stress and increase human +Gx tolerance.