RESUMEN
In order to develop effective countermeasures to maintain the health and well-being of crew members during prolonged spaceflight, such as a mission to Mars, an integrated physiologic view is necessary. Future spacecraft to deep space will be constrained by limited volume, food, water, shelter and other resources. Thus, it's important to understand the highest risks and to direct research into these areas. This review paper examines important risks during a 2-3 year mission to Mars with a view to provide devices and methods to integrate across many physiologic systems in an attempt to reproduce activities of daily living on Earth. Because effective hardware for artificial gravity by centrifugation may be decades away, we propose use of lower body negative pressure (LBNP) as means to simulate multiple beneficial effects of gravitational stress including blood and fluid shifts towards the feet and mechanical loading of the body. LBNP-devices are reconfigurable as wearable suits to reduce mass or combined with exercise devices to increase efficacy of exercise in weightlessness.
Para desarrollar contramedidas efectivas para mantener la salud y el bienestar de los miembros de la tripulación durante un vuelo espacial prolongado, como una misión a Marte, es necesaria una visión fisiológica integrada. Las naves espaciales futuras al espacio profundo estarán limitadas por un volumen limitado, alimentos, agua, refugio y otros recursos. Por lo tanto, es importante comprender los riesgos más altos y dirigir la investigación en estas áreas. Este documento de revisión examina riesgos importantes durante una misión de 2-3 años a Marte con el fin de proporcionar dispositivos y métodos para integrarse en muchos sistemas fisiológicos en un intento de reproducir las actividades de la vida diaria en la Tierra. Debido a que el hardware efectivo para la gravedad artificial por centrifugación puede estar a décadas de distancia, proponemos el uso de la presión negativa de la parte inferior del cuerpo (LBNP) como un medio para simular múltiples efectos beneficiosos del estrés gravitacional, incluidos los cambios de sangre y fluidos hacia los pies y la carga mecánica del cuerpo. Los dispositivos LBNP son reconfigurables como trajes portátiles para reducir la masa o combinados con dispositivos de ejercicio para aumentar la eficacia del ejercicio en la ingravidez.
RESUMEN
Objective To observe pre-syncopal limited tolerance and cardiovascular responses to head-up tilt combined with lower body negative pressure (HUT/LBNP) following exposure to head-down tilt (HDT, -1 Gz). Method Exposures to HUT/LBNP (-60 mmHg) in control session (without preceding 30 s -1 Gz treatment) and in simulated push-pull effect (PPE) session (with preceding 30 s -1 Gz treatment) were performed in 8 healthy adults. The changes of hemodynamic parameters were monitored by electrical impedance instrument during the experiments. Result The mean endurance time in presyncopal symptom limited HUT/LBNP in control session and in simulated PPE session were 8.4±2.1 min and 4.5±2.4 min, respectively, the two means were significantly different (P< 0.01). In simulated PPE session, as compared with baseline, heart rate (HR) during HDT was significantly lowered (P<0.01), while stroke volume (SV) and cardiac output (CO) were increased significantly (P<0.01). During HUT/LBNP, the increased percentage (relative to baseline) of HR in PPE session was lower than these in control session (P<0.05); the decreased percentages of SV and CO during HUT/LBNP in PPE session were both higher than those in control session (P<0.05). During HUT/LBNP, arterial pulse pressure (PP) of control session was significantly decreased than the value of baseline value (P<0.05); Total peripheral resistance (TPR) of PPE session was significantly increased than baseline value (P<0.05). Conclusion Tolerance time before the appearance of presyncopal symptoms during HUT/LBNP decreases and cardiovascular responses to HUT/LBNP are impaired, preceding exposure to HDT.
RESUMEN
The purpose of this study was to investigate the effects of contraction force and the pooled blood volume in the calf on the pumping action of calf muscle contraction. Calf blood volume was controlled by lower body negative pressure (LBNP) and isometric contraction of calf extensor muscle was performed using a handmade dynamometer in recumbent position. The relative volume changes (ΔV/V%) of calf were determined using rubber straingage, when isometric contractions (5, 10, 20, 40 and 60 kg) of the calf muscle were repeated under LBNP of 0, -20, -40, and -60 mmHg.<BR>During resting condition, Δ V/V was increased by 1.04% under -20 mmHg LBNP, 1.88% under -40 mmHg, and 2.54% under -60 mmHg. These increases of ΔV/V were due to the increased blood pooling in the calf. It was shown that the increased blood volume was almost expelled by several bouts of muscle contractions of proper force. The optimum force of contractions for expelling pooled blood was 20 kg under -20mmHg LBNP, and 40 kg under -40 and -60 mmHg LBNP. And it was apparent that the effectiveness of muscle pump was accumulated with repeating contractions, arriving to a plateau after several bouts.<BR>It was shown that the effect of muscle pump in the given contraction force was more effective under the condition with more amount of blood contained in the calf, but the muscle pumping action by light contraction forces couldn't overcome the effect of severe LBNP.
RESUMEN
The purpose of this study was to investigate the effects of contraction force and the pooled blood volume in the calf on the pumping action of calf muscle contraction. Calf blood volume was controlled by lower body negative pressure (LBNP) and isometric contraction of calf extensor muscle was performed using a handmade dynamometer in recumbent position. The relative volume changes (ΔV/V%) of calf were determined using rubber straingage, when isometric contractions (5, 10, 20, 40 and 60 kg) of the calf muscle were repeated under LBNP of 0, -20, -40, and -60 mmHg.<BR>During resting condition, Δ V/V was increased by 1.04% under -20 mmHg LBNP, 1.88% under -40 mmHg, and 2.54% under -60 mmHg. These increases of ΔV/V were due to the increased blood pooling in the calf. It was shown that the increased blood volume was almost expelled by several bouts of muscle contractions of proper force. The optimum force of contractions for expelling pooled blood was 20 kg under -20mmHg LBNP, and 40 kg under -40 and -60 mmHg LBNP. And it was apparent that the effectiveness of muscle pump was accumulated with repeating contractions, arriving to a plateau after several bouts.<BR>It was shown that the effect of muscle pump in the given contraction force was more effective under the condition with more amount of blood contained in the calf, but the muscle pumping action by light contraction forces couldn't overcome the effect of severe LBNP.
RESUMEN
In order to evaluate the effect of muscle pump on blood circulation at the start and end of exercise, cardiac responses to pedaling exercise at 75 watt in the supine position were investigated under lower body negative pressure (LBNP) of -60mmHg. Six healthy male college students volunteered for subjects. Cardiac output (Q), stroke volume (SV), thoracic impedance (ZO) and heart rate (HR) were determined by using ensemble-averaged impedance cardiogram and ECG.<BR>The results obtained were as follows.<BR>1) By the initiation of exercise under LBNP, SV and Q promptly and more markedly increased and ZO decreased than the control experiment which were done under normal pressure. These changes were suggested to be caused by mobilization of previously pooled blood in the legs by muscle pump. Effects of muscle pump arrived to a plateau within about 30 sec after the start of exercise. And these effects were immediately disappeard by the cessation of exercise.<BR>2) By the release of LBNP during resting condition, the same changes were observed in SV, Q and ZO as in the start of exercise under LBNP. However HR decreased in the case while it increased in the case of exercise in LBNP. This difference in HR might be the result of the chronotropic effects by the exercise.<BR>3) In the very early phase of exercise in the control exercise, SV decreased and ZO increased. These changes were probably caused by superiority of chronotropic action by the exercise to increase in venous return in this position.<BR>These results led us to a conclusion that the effect of muscle pump appeares immediately by the start of the exercise and it arrives at plateau within about 30 sec. This effect is immediately disappeared by the cessation of exercise.
RESUMEN
The purpose of this investigation is to evaluate the effects of muscle pump by pedaling exercise on blood circulation and define its properties. Lower body pressurization device equipped with bicycle ergometer was used to provide negative pressure on the lower body of subjects in recumbent position. Seven healthy male collage students volunteered for subjects.<BR>Whole experiment for each subjects was divided into control stage (0 mmHg), -20, -40, and -60 mmHg LBNP (lower body negative pressure) stage. Preceeded by resting period, 25, 75, and 125 W exercise in experiment 1, 50 and 100 W exercise in experiment 2 were loaded using bicycle ergometer with revolution of 60 rpm during each stage. Following parameters were determined: HR, SV, Q, and blood pressure.<BR>The results obtained were as follows;<BR>(1) In resting condition, LBNP caused significant decrease in SV and Q in spite of marked compensatory increase in HR.<BR>(2) These effects of LBNP were cancelled in -20 mmHg or mostly cancelled in -40 and -60 mmHg by pedaling exercise of 50 W or more.<BR>(3) Effect of muscle pump by pedaling exercise is apparent in light exercise such as 25 or 50 W arriving to a plateau with more intensive load.<BR>(4) Muscle pump action by the same exercise condition is more effective under more severe LBNP.<BR>(5) Light exercise in LBNP caused decrease in HR, probably because of pressure reflex initiated by restoration of blood pressure.<BR>These results leed us to a conclusion that light pedaling exercise produces a powerful pumping action nearly enough to compensate the circulatory disturbance by strong LBNP.
RESUMEN
The purpose of this study is to evaluate the effects of muscle pump of pedaling exercise on blood circulation. Lower body pressurization device was used to provide negative pressure and positive pressure on the lower body of subjects in recumbent position. This device is also equipped with bicycle ergometer in it. Five healthy male college students volunteered for subjects.<BR>Whole experiment for each subject was divided into pre-control stage (0 mmHg), LBPP (lower body positive pressure) stage (+40mmHg), LBNP (lower body negative pressure) stage (-40 mmHg) and post-control stage (0 mrHg) . 50 (watt) exercise and 100 (watt) exercise preceded by resting period were loaded during each stage and following parameters were determined: ECG, phonocardiogram, carotic pulse wave, VO<SUB>2</SUB>, cardiac output, and blood pressure. Pre-ejection period index (PEPi), Left ventricular ejection time index (LVETi), PEP/LVET and stroke volume (SV) were calculated from the recorded data.<BR>Results suggested following conclusions:<BR>1) In rest condition, LBNP caused marked increase in HR, PEPi, and PEP/LVET and remarkable decrease in Q, SV, and LVETi. These findings indicate that LBNP affects venous return and exaggerates venous pooling in lower body.<BR>2) It was shown that muscle pump of pedaling exercise counteracts the effects of LBNP and the findings mentioned above were largely abolished by pedaling exercise of 100 (watt) .<BR>3) LBPP caused no apparent change in the studied parameters except blood pressure. Blood pressure increased by LBPP probably because of rising in total peripheral resistance.