RESUMEN
Most launch vehicles and satellites in the US inventory rely upon the use of hypergolic rocket propellants, many of which are toxic to humans. These fuels and oxidizers, such as hydrazine and nitrogen tetroxide have threshold limit values as low as 0.01 PPM. It is essential to provide space workers handling these agents whole body protection as they are universally hazardous not only to the respiratory system, but the skin as well. This paper describes a new method for powering a whole body protective garment to assure the safety of ground servicing crews. A new technology has been developed through the small business innovative research program at the Kennedy Space Center. Currently, liquid air is used in the environmental control unit (ECU) that powers the propellant handlers suit (PHE). However, liquid air exhibits problems with attitude dependence, oxygen enrichment, and difficulty with reliable quantity measurement. The new technology employs the storage of the supply air as a supercritical gas. This method of air storage overcomes all of three problems above while maintaining high density storage at relatively low vessel pressures (<7000 kPa or approximately 1000 psi). A one hour prototype ECU was developed and tested to prove the feasibility of this concept. This was upgraded by the design of a larger supercritical dewar capable of holding 7 Kg of air, a supply which provides a 2 hour duration to the PHE. A third version is being developed to test the feasibility of replacing existing air cooling methodology with a liquid cooled garment for relief of heat stress in this warm Florida environment. Testing of the first one hour prototype yielded data comparable to the liquid air powered predecessor, but enjoyed advantages of attitude independence and oxygen level stability. Thermal data revealed heat stress relief at least as good as liquid air supplied units. The application of supercritical air technology to this whole body protective ensemble marked an advancement in the state-of-the-art in personal protective equipment. Not only was long duration environmental control provided, but it was done without a high pressure vessel. The unit met human performance needs for attitude independence, oxygen stability and relief of heat stress. This supercritical air (and oxygen) technology is suggested for microgravity applications in life support such as the Extravehicular Mobility Unit.
Asunto(s)
Aire Acondicionado/métodos , Sustancias Peligrosas , Sistemas de Manutención de la Vida/instrumentación , Ropa de Protección , Nave Espacial/instrumentación , Adulto , Medicina Aeroespacial , Temperatura Corporal , Diseño de Equipo , Ergonomía , Tolerancia al Ejercicio , Trastornos de Estrés por Calor , Humanos , Hidrazinas , Masculino , Persona de Mediana Edad , Óxidos de Nitrógeno , Exposición ProfesionalRESUMEN
We tested the hypothesis that one bout of maximal exercise performed at the conclusion of prolonged simulated microgravity would improve blood pressure stability during an orthostatic challenge. Heart rate (HR), mean arterial blood pressure (MAP), norepinephrine (NE), epinephrine (E), arginine vasopressin (AVP), plasma renin activity (PRA), atrial natriuretic peptide (ANP), cardiac output (Q), forearm vascular resistance (FVR), and changes in leg volume were measured during lower body negative pressure (LBNP) to presyncope in seven subjects immediately prior to reambulation from 16 days of 6 degrees head-down tilt (HDT) under two experimental conditions: 1) after maximal supine cycle ergometry performed 24 h before returning to the upright posture (exercise) and 2) without exercise (control). After HDT, the reduction of LBNP tolerance time from pre-HDT levels was greater (P = 0.041) in the control condition (-2.0 +/- 0.2 min) compared with the exercise condition (-0.4 +/- 0.2 min). At presyncope after HDT, FVR and NE were higher (P < 0.05) after exercise compared with control, whereas MAP, HR, E, AVP, PRA, ANP, and leg volume were similar in both conditions. Plasma volume (PV) and carotid-cardiac baroreflex sensitivity were reduced after control HDT, but were restored by the exercise treatment. Maintenance of orthostatic tolerance by application of acute intense exercise after 16 days of simulated microgravity was associated with greater circulating levels of NE, vasoconstriction, Q, baroreflex sensitivity, and PV.
Asunto(s)
Gravitación , Resistencia Física , Esfuerzo Físico , Postura , Adulto , Barorreflejo/fisiología , Volumen Sanguíneo , Inclinación de Cabeza , Hemodinámica , Hormonas/sangre , Humanos , Presión Negativa de la Región Corporal Inferior , MasculinoRESUMEN
INTRODUCTION: The purpose of this study was to determine the effectiveness of a USAF anti-gravity suit (G-suit) on the stability of a patient with chronic orthostatic hypotension. METHODS: A 37-yr-old female with a history of insulin-dependent diabetes mellitus (IDDM) and symptomatic orthostasis was evaluated and the results were compared with those of non-diabetic controls, matched for age, height, and weight. Cardiac vagal tone was assessed by determination of standard deviation of 100 R-R intervals (R-R SD). We assessed the carotid-cardiac baroreflex response by plotting R-R intervals (ms) at each of eight neck pressure steps with their respective carotid distending pressures (mm Hg). Heart rate and blood pressure were recorded in response to the Valsalva maneuver (VM) performed at an expiratory pressure of 30 mmHg to assess integrated baroreflex responses. Blood pressures and heart rate were measured during three 5-min stand tests to assess orthostatic responses: a) without G-suit; b) with noninflated G-suit; and c) with inflated G-suit (50 mm Hg). RESULTS: The IDDM patient had minimal baseline cardiac vagal tone (R-R SD = 8.5 ms) compared with the average response of a control group of 24 subjects with orthostatic stability (R-R SD = 67.2 +/- 7.1 ms). Carotid-cardiac baroreflex response was virtually non-existent in the IDDM patient (Gain = 0.06 ms.mm Hg-1) compared to the control subjects (4.4 +/- 0.8 ms.mm Hg-1). VM responses corroborated the lack of cardiac baroreflex response in the IDDM patient, while blood pressure changes during the VM were similar to those of the controls. Upon standing, the IDDM patient demonstrated severe orthostatic hypotension (90 mm Hg SBP) and tachycardia without the G-suit. The G-suit, with and without pressure, reduced hypotension and tachycardia during standing. CONCLUSION: These results demonstrate successful application of Air Force technology as a useful alternative to pharmacologic intervention in the treatment of a patient with autonomic dysfunction leading to supine hypertension and orthostatic hypotension.
Asunto(s)
Medicina Aeroespacial , Angiopatías Diabéticas/terapia , Trajes Gravitatorios , Hipotensión Ortostática/terapia , Adulto , Arginina Vasopresina/sangre , Factor Natriurético Atrial/sangre , Barorreflejo/fisiología , Femenino , Transferencias de Fluidos Corporales/fisiología , Frecuencia Cardíaca , Humanos , Norepinefrina/sangre , Volumen Plasmático , Renina/sangre , Maniobra de Valsalva/fisiología , Sistema Vasomotor/fisiologíaRESUMEN
Seven healthy men performed maximal exercise 24 h before the end of 16 days exposure to 6 degrees head-down tilt (HDT) to test the hypothesis that such an exercise technique could restore plasma volume (PV) at the end of a simulated space mission. Exercise consisted of supine cycling with graded work rates increasing by 16 W/min to volitional fatigue and required an average of 16 min. The experimental protocol was a standard cross-over design in which the order of treatment (exercise or control) was counterbalanced across all seven subjects. PV, fluid intake (ad libitum), urine output, renal function, and hormones associated with fluid homeostasis were measured before HDT, 24 h before the end of HDT just prior to exercise, and at the end of HDT 24 h after exercise. HDT reduced PV by 16% in both control and exercise conditions. Maximal exercise completely restored plasma volume within 24 h to 3.9 +/- 3.2% of pre-HDT levels despite continued HDT. Compared with control, exercise induced a 660-ml larger positive fluid balance because of greater fluid intake and reduced urine volume during the 24 h after exercise. These results suggest that one bout of maximal leg exercise before return from 16 days of spaceflight may be completely effective in stimulating thirst and restoring plasma volume to preflight levels.
Asunto(s)
Inclinación de Cabeza , Esfuerzo Físico , Volumen Plasmático , Adulto , Peso Corporal , Diuresis , Ingestión de Líquidos , Electrólitos/sangre , Hematócrito , Hormonas/sangre , Humanos , Riñón/fisiología , Masculino , Factores de TiempoRESUMEN
The purpose of this study was to quantify the gas exchange between plants growing in a Closed Environmental Life Support System (CELSS) and the metabolism of human subjects undergoing various levels of physical exercise, and subsequently determine the buffer characteristics in relation to the carbon exchange established for plants in this closed loop life support system. Two men (ages 42 and 45 yr) exercised on a cycle ergometer at three different work intensities, each on a separate day. The CELSS, a 113 m3 chamber, was sized to meet the needs of one human. The plants, consisting of 20 m2 of potato, provided oxygen to the human during an artificially lighted photosynthesis phase and the human provided CO2 to the plants. The average rates of exchange for the subjects were 0.88, 1.69, and 2.47 liters O2/min and 0.77, 1.47, and 2.21 liters CO2/min at approximately 25%, 50%, and 75% of their maximal aerobic capacity, respectively. The photosynthetic rate for the CELSS was 0.95 liters/min. A balance between human CO2 production and plant utilization was noted at approximately the 50% VO2max level. The oxygen balance and changes were not within detectable limits of the CELSS instrumentation for the durations of these exercise exposures. If a CELSS environment is the methodology selected for long term spaceflight, it will be important to select plants that efficiently grow at the available light and nutrient levels while balancing the needs for the human crew at their levels of physical activity.
Asunto(s)
Dióxido de Carbono/metabolismo , Sistemas Ecológicos Cerrados , Metabolismo Energético , Ejercicio Físico/fisiología , Sistemas de Manutención de la Vida , Solanum tuberosum/metabolismo , Adulto , Medicina Aeroespacial , Temperatura Corporal , Respiración de la Célula , Frecuencia Cardíaca , Humanos , Masculino , Persona de Mediana Edad , Consumo de Oxígeno , Fotosíntesis/fisiología , Temperatura CutáneaRESUMEN
We tested the hypothesis that one bout of maximal exercise performed 24 h before reambulation from 16 days of 6 degrees head-down tilt (HDT) could increase integrated baroreflex sensitivity. Isolated carotid-cardiac and integrated baroreflex function was assessed in seven subjects before and after two periods of HDT separated by 11 mo. On the last day of one HDT period, subjects performed a single bout of maximal cycle ergometry (exercise). Subjects did not exercise after the other HDT period (control). Carotid-cardiac baroreflex sensitivity was evaluated using a neck collar device. Integrated baroreflex function was assessed by recording heart rate (HR) and blood pressure (MAP) during a 15-s Valsalva maneuver (VM) at a controlled expiratory pressure of 30 mmHg. The ratio of change in HR to change in MAP (delta HR/ delta MAP) during phases II and IV of the VM was used as an index of cardiac baroreflex sensitivity. Baroreflex-mediated vasoconstriction was assessed by measuring the late phase II rise in MAP. Following HDT, carotid-cardiac baroreflex sensitivity was reduced (2.8 to 2.0 ms/mmHg; P = 0.05) as was delta HR/ delta MAP during phase II (-1.5 to -0.8 beats/mmHg; P = 0.002). After exercise, isolated carotid baroreflex activity and phase II delta HR/ delta MAP returned to pre-HDT levels but remained attenuated in the control condition. Phase IV delta HR/ delta MAP was not altered by HDT or exercise. The late phase II increase of MAP was 71% greater after exercise compared with control (7 vs. 2 mmHg; P = 0.041).(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Barorreflejo/fisiología , Inclinación de Cabeza , Resistencia Física , Esfuerzo Físico , Adulto , Presión Sanguínea , Arterias Carótidas/fisiología , Corazón/fisiología , Frecuencia Cardíaca , Humanos , Presión Negativa de la Región Corporal Inferior , Masculino , Persona de Mediana Edad , Factores de Tiempo , Maniobra de ValsalvaRESUMEN
The stimulus-response characteristics of cardiopulmonary baroreflex control of forearm vascular resistance (FVR) were studied in 11 healthy men before and after 7 days of 6 degrees head-down bedrest to test the hypothesis that microgravity alters this reflex response. We assessed the relationship between stimulus [changes in central venous pressure (delta CVP)] and reflex response (delta FVR) during unloading of cardiopulmonary baroreceptors with lower body negative pressure (LBNP; 0 to -20 mmHg). delta CVP during bedrest and LBNP was estimated from peripheral vein pressures in the dependent right arm. Compared with prebedrest baseline, plasma volume and estimated CVP were decreased by 13 and 33%, respectively, at 7 days of bedrest. Progressive reflex forearm vasoconstriction occurred in response to graded reductions in estimated CVP during LBNP, and delta FVR per unit delta CVP was doubled after bedrest. The increase in sensitivity of the cardiopulmonary baroreflex control of FVR was related to reduced circulating blood volume, suggesting that enhanced peripheral vasoconstriction in individuals adapted to microgravity can be attributed, in part, to hypovolemia. In addition, microgravity appears to alter the stimulus for cardiopulmonary baroreceptors to a lower operational range of CVP, suggesting the possibility of chronic resetting.
Asunto(s)
Barorreflejo/fisiología , Gravitación , Corazón/fisiología , Pulmón/fisiología , Resistencia Vascular/fisiología , Adulto , Reposo en Cama , Presión Sanguínea , Femenino , Antebrazo/irrigación sanguínea , Hemodinámica , Humanos , Presión Negativa de la Región Corporal Inferior , Masculino , Persona de Mediana Edad , Postura , Factores de TiempoRESUMEN
Reflex peripheral vasoconstriction induced by activation of cardiopulmonary baroreceptors in response to reduced central venous pressure (CVP) is a basic mechanism for elevating systemic vascular resistance and defending arterial blood pressure during orthostatically-induced reductions in cardiac filling and output. The sensitivity of the cardiopulmonary baroreflex response [defined as the slope of the relationship between changes in forearm vascular resistance (FVR) and CVP] and the resultant vasoconstriction are closely and inversely associated with the amount of circulating blood volume. Thus, a high-gain FVR response will be elicited by a hypovolemic state. Exposure to microgravity during spaceflight results in reduced plasma volume. It is therefore reasonable to expect that the FVR response to cardiopulmonary baroreceptor unloading would be accentuated following adaptation to microgravity. Such data could provide better insight about the physiological mechanisms underlying alterations in blood pressure control following spaceflight. We therefore exposed eleven men to 6 degrees head-down bedrest for 7 days and measured specific hemodynamic responses to low levels of the lower body negative pressure to determine if there are alterations in cardiopulmonary baroreceptor stimulus-FVR reflex response relationship during prolonged exposure to an analog of microgravity.
Asunto(s)
Barorreflejo/fisiología , Reposo en Cama , Antebrazo/irrigación sanguínea , Inclinación de Cabeza , Resistencia Vascular/fisiología , Simulación de Ingravidez/métodos , Adulto , Presión Sanguínea/fisiología , Presión Venosa Central/fisiología , Hemodinámica/fisiología , Humanos , Presión Negativa de la Región Corporal Inferior , Masculino , Persona de Mediana Edad , Presorreceptores/fisiología , Vasoconstricción/fisiologíaRESUMEN
We tested the hypothesis that a bout of graded exercise designed to elicit maximal effort would increase the sensitivity of autonomically mediated baroreflexes and enhance blood pressure (BP) stability in subjects prone to postural hypotension. Therefore, we measured heart rate (HR), BP, forearm vascular resistance (FVR), and vasoactive hormone responses before and during 15 min of 70 degrees head-up tilt (HUT) in 10 paraplegic subjects (21-65 yr) on two occasions: 1) 24 h after maximal arm-crank exercise (postexercise) and 2) without exercise (control). During HUT, HR increased 30 beats/min in both postexercise and control, but the reduction in systolic BP (SBP) during control (-12.0 +/- 4.6 mmHg) was larger (P = 0.017) than that during HUT after exercise (-0.3 +/- 4.3 mmHg). The postexercise increase in FVR from supine to HUT of 17.0 +/- 2.4 to 24.8 +/- 3.2 peripheral resistance units (PRU) was greater (P = 0.042) than the increase observed during control (18.3 +/- 3.7 to 19.5 +/- 3.1 PRU). The gain of the carotid-cardiac baroreflex was also increased (P = 0.049) after exercise. Responses in norepinephrine, vasopressin, and plasma renin-angiotensin induced by HUT were similar for control and postexercise, and there was no difference in either leg compliance or plasma volume between the two conditions. Additionally, HR and SBP responses to phases II and IV of the Valsalva maneuver, indexes of integrated baroreflex sensitivity, were increased (P < 0.05) after maximal exercise compared with control. Thus acute intense exercise eliminated orthostatic hypotension in paraplegics, was associated with increased FVR and baroreflex sensitivity, and was independent of blood volume changes.
Asunto(s)
Sistema Nervioso Autónomo/fisiopatología , Hipotensión Ortostática/fisiopatología , Esfuerzo Físico , Adulto , Anciano , Brazo/fisiopatología , Barorreflejo/fisiología , Presión Sanguínea , Frecuencia Cardíaca , Humanos , Persona de Mediana Edad , Paraplejía/fisiopatología , Factores de TiempoRESUMEN
To test the hypothesis that an acute bout of maximal exercise can ameliorate orthostatic hypotension consequent to prolonged wheelchair confinement, we evaluated heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressure responses during 15 minutes of 70 degrees head-up tilt (HUT) in 10 paraplegic subjects 24 hours after arm crank exercise designed to elicit maximal effort, and during a control (no exercise) conditions. Additionally, the carotid baroreceptor stimulus-cardiac response relationship was determined by measurement of R-R interval during external application of graded pressures to the carotid sinuses. One week separated the treatment conditions. The maximum slope of the carotid-cardiac baroreflex response was increased (p = 0.049) by exercise (6.2 +/- 1.7 msec/mmHg) compared to control (3.3 +/- 0.6). During control HUT, HR increased from 61 +/- 1 to 90 +/- 7 bpm (p = 0.001) while SBP decreased from 118 +/- 5 to 106 +/- 9 mmHg (p = 0.025). During HUT 24 hours after exercise, HR increased from 60 +/- 2 to 90 +/- 4 bpm (p = 0.001), but the reduction in SBP was essentially eliminated (116 +/- 5 to 113 +/- 5 mmHg). The reduction in SBP during control HUT (-12.0 +/- 4.6 mmHg) was four-fold larger (p = 0.017) than during HUT following exercise (-3.1 +/- 3.9 mmHg). DBP during HUT was not altered in either condition. A single bout of intense, dynamic arm crank exercise eliminated orthostatic hypotension in paraplegics. Equal HR response with smaller reduction in SBP during HUT after exercise was consistent with a measured increased sensitivity of the carotid-cardiac baroreflex.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Arterias Carótidas/fisiopatología , Ejercicio Físico/fisiología , Corazón/fisiopatología , Hipotensión Ortostática/fisiopatología , Paraplejía/fisiopatología , Presorreceptores/fisiología , Reflejo/fisiología , Adulto , Presión Sanguínea/fisiología , Ergometría , Frecuencia Cardíaca/fisiología , Humanos , Hipotensión Ortostática/terapia , PosturaRESUMEN
We measured carotid baroreceptor-cardiac reflex responses in six healthy men, 24 h before and 24 h after a bout of leg exercise during 6 degrees head-down bed rest to determine if depressed vagal baroreflex function associated with exposure to microgravity environments could be reversed by a single exposure to acute intense exercise. Baroreflex responses were measured before bed rest and on day 7 of bed rest. An exercise bout consisting of dynamic and isometric actions of the quadriceps at graded speeds and resistances was performed on day 8 of bed rest and measurements of baroreflex response were repeated 24 h later. Vagally-mediated cardiac responses were provoked with ramped neck pressure-suction sequences comprising pressure elevations to +40 mm Hg, followed by serial, R-wave triggered 15 mm Hg reductions, to -65 mm Hg. Baroreceptor stimulus-cardiac response relationships were derived by plotting each R-R interval as a function of systolic pressure less the neck chamber pressure applied during the interval. Compared with pre-bed rest baseline measurements, 7 d of bed rest decreased the gain (maximum slope) of the baroreflex stimulus-response relationship by 16.8 +/- 3.4% (p < 0.05). On day 9 of bed rest, 24 h after exercise, the maximum slope of the baroreflex stimulus-response relationship was increased (p < 0.05) by 10.7 +/- 3.7% above pre-bed rest levels and 34.3 +/- 7.9% above bed rest day 7. Our data verify that vagally-mediated baroreflex function is depressed by exposure to simulated microgravity and demonstrate that this effect can be acutely reversed by exposure to a single bout of intense exercise.
Asunto(s)
Reposo en Cama/efectos adversos , Presión Sanguínea/fisiología , Seno Carotídeo/fisiología , Ejercicio Físico/fisiología , Presorreceptores/fisiología , Adulto , Medicina Aeroespacial , Humanos , Masculino , Nervio Vago/fisiologíaRESUMEN
Biomedical engineering is an evolving science that seeks to insert technically oriented and trained personnel to assist medical professionals in solving technological problems in the pursuit of innovations in the delivery of health care. Consequently, engineering solutions are brought to bear on problems that previously were outside the training of physicians and beyond the understanding or appreciation of the conventionally educated electrical or mechanical engineers. This physician/scientist/engineer team has a capability to extend medicine and research far beyond the capability of a single entity operating alone. How biomedical engineering has added a new dimension to medical science at the Kennedy Space Center is described.
Asunto(s)
Ingeniería Biomédica , Vuelo Espacial , Adaptación Fisiológica , Fenómenos Fisiológicos Cardiovasculares , Servicios Médicos de Urgencia , Humanos , Informática Médica , Ciencia del Laboratorio Clínico , Monitoreo Fisiológico , Músculos/fisiología , Equipos de Seguridad , InvestigaciónRESUMEN
Published information on the reproducibility of human baroreflex responses in the absence of interventions is limited. Therefore, we analyzed retrospectively vagally mediated carotid baroreceptor-cardiac reflex responses of 34 healthy young adult volunteers whom we studied twice, 7-10 days apart (all 34 subjects) or 10 wk apart (8 subjects). We delivered a sequence of neck pressure changes during held expiration: A computer-driven bellows initially raised pressure to approximately 40 mmHg for five heart beats, and then reduced pressure in a stepwise series of R-wave-triggered 15-mmHg decrements to about -65 mmHg. R-R interval changes were plotted as functions of the carotid distending (systolic less neck) pressure occurring within each interval. Each experimental session yielded one stimulus-response relation, which comprised the average of seven separate trials. Six measures were derived from these relations: minimum, maximum, and range of R-R intervals; maximum slope; and operational point [(R-R interval shortening/R-R interval range) x 100%]. Linear regression correlation coefficients for measurements made on two occasions were all highly significant (range: 0.64-0.99). Our results indicate that human vagally mediated carotid baroreceptor-cardiac reflex responses, studied serially under exacting experimental conditions, are highly reproducible.
Asunto(s)
Arterias Carótidas/fisiología , Corazón/fisiología , Presorreceptores/fisiología , Reflejo/fisiología , Nervio Vago/fisiología , Adulto , Femenino , Humanos , Masculino , Persona de Mediana Edad , Reproducibilidad de los Resultados , Estudios RetrospectivosRESUMEN
Eight subjects were studied in the supine position at rest, during normal dynamic leg exercise (control exercise) and with blood-flow restriction in the working legs (flow-restricted exercise). Graded muscle blood-flow restriction was accomplished by applying a supra-atmospheric pressure of 50 mmHg to the working legs. During incremental-load exercise, flow restriction reduced exercise performance and peak heart rate by 36% and 13%, respectively. The function of the cardiac branch of the carotid baroreflex was studied over its full operational range, at rest and during constant-load control and flow-restricted exercise, by measuring R-R intervals during application of pulse-synchronous graded pressures (40 to -65 mmHg) in a neck-chamber device. Heart rate and arterial pressure were higher during flow-restricted than control exercise, indicating that the flow restriction activated the muscle chemoreflex. Raising the carotid transmural pressure (systolic arterial pressure minus neck-chamber pressure) was accompanied by increasing R-R intervals in all conditions. The set point (point of baseline carotid transmural pressure and R-R interval) coincided with the midportion of the pressure-response curve at rest and with the threshold point of the curve during exercise. The maximal rate of change in relative R-R intervals and the corresponding carotid transmural pressure range were higher during control exercise than at rest and highest during flow-restricted exercise, indicating that exercise and especially flow-restricted exercise increased carotid baroflex sensitivity, and shifted the carotid baroreflex optimal buffering range to higher pressures. The results suggest that the carotid baroflex attenuates exercise heart rate increases mediated by the muscle chemoreflex and/or by central command.
Asunto(s)
Arterias Carótidas/fisiología , Ejercicio Físico/fisiología , Presorreceptores/fisiología , Adulto , Velocidad del Flujo Sanguíneo , Humanos , Isquemia/fisiopatología , Pierna/irrigación sanguínea , Masculino , Reflejo/fisiologíaRESUMEN
The stimulus-response characteristics of cardiopulmonary baroreflex control of forearm vascular resistance (FVR units in mm Hg.min.100 ml.ml-1) were studied in 14 volunteers before and after 10 wk of endurance training. We assessed the relationship between reflex stimulus (changes in central venous pressure, CVP) and response (FVR) during unloading of cardiopulmonary baroreceptors with lower body negative pressure (LBNP, 0 to -20 mm Hg). Changes in CVP during LBNP were estimated from pressure changes in a large peripheral vein in the dependent arm of the subject in the right lateral decubitus position. Maximal oxygen uptake (VO2max) and total blood volume increased with endurance training from 37.8 +/- 1.4 ml.min-1.kg-1 and 63.6 +/- 2.1 ml.kg-1 to 45.3 +/- 1.4 ml.min-1.kg-1 and 69.3 +/- 2.8 ml.kg-1, respectively (P less than 0.05). Reflex forearm vasoconstriction occurred in response to a reduction in estimated CVP, and the absolute change in FVR per unit of CVP was reduced from -5.96 +/- 0.79 to -4.06 +/- 0.52 units.mm Hg-1 (P less than 0.05) following exercise training but was unchanged from -6.10 to 0.57 to -6.22 +/- 0.94 units.mm Hg-1 for the time control group (N = 7). Resting values for FVR were similar before and after exercise training; however, resting estimated CVP was elevated from 9.5 +/- 0.5 mm Hg before training to 11.3 +/- 0.6 mm Hg after training.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Antebrazo/irrigación sanguínea , Corazón/fisiología , Pulmón/fisiología , Educación y Entrenamiento Físico , Aptitud Física/fisiología , Presorreceptores/fisiología , Reflejo/fisiología , Resistencia Vascular/fisiología , Adulto , Volumen Sanguíneo , Presión Venosa Central , Antebrazo/fisiología , Hemodinámica , Humanos , Masculino , Consumo de Oxígeno/fisiologíaRESUMEN
We evaluated performance of a modified Combat Task Test (CTT) and of standard fitness tests in 20 male subjects to assess the prediction of occupational performance standards for Kennedy Space Center fire fighters. The CTT consisted of stairclimbing, a chopping simulation, and a victim rescue simulation. Average CTT performance time was 3.61 +/- 0.25 min (SEM) and all CTT tasks required 93% to 97% maximal heart rate. By using scores from the standard fitness tests, a multiple linear regression model was fitted to each parameter: the stairclimb (r2 = .905, P less than .05), the chopping performance time (r2 = .582, P less than .05), the victim rescue time (r2 = .218, P = not significant), and the total performance time (r2 = .769, P less than .05). Treadmill time was the predominant variable, being the major predictor in two of four models. These results indicated that standardized fitness tests can predict performance on some CTT tasks and that test predictors were amenable to exercise training.
Asunto(s)
Evaluación del Rendimiento de Empleados/métodos , Incendios , Administración de Personal/métodos , Aptitud Física , Adulto , Frecuencia Cardíaca , Humanos , Masculino , Persona de Mediana Edad , Resistencia Física , Análisis de Regresión , Análisis y Desempeño de TareasRESUMEN
We studied vagally mediated carotid baroreceptor-cardiac reflexes in 11 healthy men before, during, and after 30 days of 6 degrees head-down bed rest to test the hypothesis that baroreflex malfunction contributes to orthostatic hypotension in this model of simulated microgravity. Sigmoidal baroreflex response relationships were provoked with ramped neck pressure-suction sequences comprising pressure elevations to 40 mmHg followed by serial R-wave-triggered 15-mmHg reductions to -65 mmHg. Each R-R interval was plotted as a function of systolic pressure minus the neck chamber pressure applied during the interval. Compared with control measurements, base-line R-R intervals and the minimum, maximum, range, and maximum slope of the R-R interval-carotid pressure relationships were reduced (P less than 0.05) from bed rest day 12 through recovery day 5. Baroreflex slopes were reduced more in four subjects who fainted during standing after bed rest than in six subjects who did not faint (-1.8 +/- 0.7 vs. -0.3 +/- 0.3 ms/mmHg, P less than 0.05). There was a significant linear correlation (r = 0.70, P less than 0.05) between changes of baroreflex slopes from before bed rest to bed rest day 25 and changes of systolic blood pressure during standing after bed rest. Although plasma volume declined by approximately 15% (P less than 0.05), there was no significant correlation between reductions of plasma volume and changes of baroreflex responses. There were no significant changes of before and after plasma norepinephrine or epinephrine levels before and after bed rest during supine rest or sitting.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Reposo en Cama/efectos adversos , Hipotensión Ortostática/etiología , Postura , Presorreceptores/fisiopatología , Nervio Vago/fisiopatología , Adulto , Presión Sanguínea , Epinefrina/sangre , Cabeza , Frecuencia Cardíaca , Humanos , Hipotensión Ortostática/fisiopatología , Masculino , Norepinefrina/sangre , Volumen Plasmático , ReflejoRESUMEN
The purpose of these experiments was to test the hypothesis that reduced size of the leg muscle compartment following exposure to long-duration microgravity would be associated with increased leg compliance. Eight men, 31-45 years of age, were measured for vascular compliance of the calf and serial circumferences of the thigh and calf before, during and after 30 d of continuous 6 degrees head-down bedrest. Cross-sectional areas (CSA) of muscle, fat, and bone compartments in the thigh and calf were determined pre- and post-bedrest by computed tomography. Calculated leg volumes decreased (p less than 0.05) in the calf by 9.9% and in the thigh by 4.5% from pre- to post-bedrest. Muscle compartment CSA also decreased (p less than 0.05) in both calf (-4.8%) and thigh (-8.1%); leg compliance (vol%/mm Hg x 100) increased (p less than 0.05) from 3.9 +/- 0.7 to 4.9 +/- 0.5. Calf compliance measured before and after bedrest was inversely related to calf muscle compartment CSA (r = -0.61, p less than 0.05) and the percent decrease in calf muscle compartment CSA from pre- to post-bedrest was inversely correlated with an increase in calf compliance (r = -0.72, p less than 0.05). Increased leg compliance following long-duration spaceflight is associated with reduced size of the leg muscle compartment.
Asunto(s)
Pierna/patología , Ingravidez/efectos adversos , Tejido Adiposo/diagnóstico por imagen , Tejido Adiposo/patología , Adulto , Huesos/diagnóstico por imagen , Huesos/patología , Humanos , Pierna/irrigación sanguínea , Pierna/fisiopatología , Masculino , Persona de Mediana Edad , Músculos/diagnóstico por imagen , Músculos/patología , Músculos/fisiopatología , Flujo Sanguíneo Regional , Vuelo Espacial , Factores de Tiempo , Tomografía Computarizada por Rayos X , Pérdida de PesoRESUMEN
Increased leg venous compliance may contribute to postflight orthostatic intolerance in astronauts. We reported that leg compliance was inversely related to the size of the muscle compartment. The purpose of this study was to test the hypothesis that reduced muscle compartment after long-duration exposure to microgravity would cause increased leg compliance. Eight men, 31-45 yr old, were measured for vascular compliance of the calf and serial circumferences of the calf before and after 30 days of continuous 6 degrees head-down bed rest. Cross-sectional areas (CSA) of muscle, fat, and bone compartments in the calf were determined before and after bed rest by computed tomography. From before to after bed rest, calculated calf volume (cm3) decreased (P less than 0.05) from 1,682 +/- 83 to 1,516 +/- 76. Calf muscle compartment CSA (cm2) also decreased (P less than 0.05) from 74.2 +/- 3.6 to 70.6 +/- 3.4; calf compliance (ml.100 ml-1.mmHg-1.100) increased (P less than 0.05) from 3.9 +/- .7 to 4.9 +/- .5. The percent change in calf compliance after bed rest was significantly correlated with changes in calf muscle compartment CSA (r = 0.72, P less than 0.05). The increased leg compliance observed after exposure to simulated microgravity can be partially explained by reduced muscle compartment. Countermeasures designed to minimize muscle atrophy in the lower extremities may be effective in ameliorating increased venous compliance and orthostatic intolerance after spaceflight.