RESUMO
PURPOSE: Exercise interventions have been shown to increase motor capacities in adolescents with cerebral palsy; however, how they affect habitual physical activity (HPA) and sedentary behavior is unclear. The main objective was to correlate changes in HPA with changes in mobility capacity following exercise interventions. METHODS: A total of 54 participants (aged 12-20 y) with bilateral spastic cerebral palsy at Gross Motor Function Classification System (GMFCS) levels II and III received 4 months of group progressive resistance training or treadmill training. Mobility measurements and HPA (averaged over 96 h) were made before and after interventions. RESULTS: Averaged baseline mobility and HPA measures and improvements in each after both interventions were positively correlated in all participants. Percentage of sedentary/awake time decreased 2%, with significant increases in HPA measures of step count (16%), walk time (14%), and upright time (9%). Mobility measures and HPA changes were quite similar between Gross Motor Function Classification System levels, but improvement in HPA after group progressive resistance training was greater than after treadmill training (12% vs 4%) and correlated with mobility improvement. CONCLUSIONS: Mobility capacity improved after these interventions and was clearly associated with improved HPA. The group progressive resistance training intervention seems preferable to improve HPA, perhaps related to greater social interaction and motivation provided by group training.
Assuntos
Comportamento do Adolescente/psicologia , Paralisia Cerebral/reabilitação , Terapia por Exercício/psicologia , Exercício Físico/psicologia , Comportamento Sedentário , Acelerometria , Adolescente , Comportamento do Adolescente/fisiologia , Paralisia Cerebral/fisiopatologia , Paralisia Cerebral/psicologia , Criança , Exercício Físico/fisiologia , Terapia por Exercício/métodos , Feminino , Humanos , Masculino , Resultado do Tratamento , Adulto JovemRESUMO
BACKGROUND: We hypothesized the existence of different hormonal response patterns to repeated lower body negative pressure (LBNP) and head-up tilt (HUT) in healthy males. We compared hormonal, cardiovascular and plasma volume changes from rest to stress within- and between-LBNP and HUT applications. Hormones investigated included adrenocorticotropic hormone (ACTH), aldosterone, plasma renin activity (PRA), atrial natriuretic peptide (ANP) and arginine vasopressin (AVP). MATERIALS AND METHODS: Three sequential 30-min bouts of LBNP at -55mmHg (n=14) or 70° HUT (n=9) were preceded by 30-min supine rest, and a 60-min supine rest followed the 3rd stimulus. RESULTS: Plasma renin activity increases above baseline, in relation to aldosterone, were larger with LBNP than with HUT. The 3rd HUT application resulted in a greater increase in aldosterone compared to LBNP. Mean arterial blood pressure was elevated significantly during 1st and 3rd HUT application. ACTH responses were highly correlated with those of aldosterone in both LBNP and HUT (r(2) =0·96). AVP responses, in contrast to ANP, to the three consecutive stress situations were not significantly different, both with LBNP and HUT. CONCLUSIONS: We speculate that the observed differences in blood pressure and hormonal responses to LBNP and HUT are caused by divergent effects of blood pooling in the splanchnic region, despite similar reductions in splanchnic perfusion. Apparently with repeated central hypovolaemia, especially by the 3rd application of stress, plasma aldosterone levels rise (along with ACTH), conceivably increasing its volume-guarding effect.
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Hormônio Adrenocorticotrópico/sangue , Pressão Sanguínea/fisiologia , Pressão Negativa da Região Corporal Inferior , Postura , Adulto , Aldosterona/sangue , Arginina Vasopressina/sangue , Fator Natriurético Atrial/sangue , Circulação Cerebrovascular/fisiologia , Decúbito Inclinado com Rebaixamento da Cabeça , Hemodinâmica/fisiologia , Humanos , Masculino , Radioimunoensaio , Renina/sangue , Teste da Mesa Inclinada/métodos , Adulto JovemRESUMO
Hypovolemic and orthostatic challenge can be simulated in humans by the application of lower body negative pressure (LBNP), because this perturbation leads to peripheral blood pooling and, consequently, central hypovolemia. The classic paper by Foux and colleagues clearly shows the effects of orthostasis simulated by LBNP on fluid shifts and homeostatic mechanisms. The carefully carried out experiments reported in this paper show the interplay between different physiological control systems to ensure blood pressure regulation, failure of which could lead to critical decreases in cerebral blood flow and syncope. Here, a teaching seminar for graduate students is described that is designed in the context of this paper and aimed at allowing students to learn how Foux and colleagues have advanced this field by addressing important aspects of blood regulation. This seminar is also designed to put their research into perspective by including important components of LBNP testing and protocols developed in subsequent research in the field. Learning about comprehensive protocols and carefully controlled studies can reduce confounding variables and allow for an optimal analysis and elucidation of the physiological responses that are being investigated. Finally, in collaboration with researchers in mathematical modeling, in the future, we will incorporate the concepts of applicable mathematical models into our curriculum.
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Volume Sanguíneo , Tontura/fisiopatologia , Educação de Pós-Graduação/métodos , Hipovolemia/fisiopatologia , Publicações Periódicas como Assunto , Fisiologia/educação , Ensino/métodos , Equilíbrio Hidroeletrolítico , Pesquisa Biomédica/métodos , Pressão Sanguínea , Circulação Cerebrovascular , Currículo , Tontura/etiologia , Homeostase , Humanos , Hipovolemia/etiologia , Aprendizagem , Pressão Negativa da Região Corporal Inferior , Fatores de TempoRESUMO
In 1959, Brigadier General Donald Flickinger and Dr. W. Randolph Lovelace II suggested that it would be more practical from an engineering standpoint to send women rather than men into space due to their lower body weights and oxygen requirements. When the Air Force decided not to pursue this project, Dr. Lovelace assumed leadership of the Woman in Space Program and began medical and physiological testing of a series of accomplished women aviators at the Lovelace Medical Clinic in Albuquerque, NM, in 1960. The tests that these women underwent were identical to those used to test the original Mercury astronauts, with the addition of gynecological examinations. Thirteen of the nineteen women tested passed these strenuous physiological exams (for comparison, 18 of 32 men tested passed); a subset of these pilots was further tested on a series of psychological exams that were similar to or, in some instances, more demanding than those given to male Mercury candidates. Despite these promising results, further testing was halted, and the Woman in Space Program was disbanded in 1962. Although the Woman in Space Program received a great deal of publicity at the time, the story of these women was somewhat lost until they were reunited at the 1999 launch of the shuttle Columbia, commanded by Colonel Eileen Collins.
Assuntos
Fisiologia/história , Voo Espacial/história , Feminino , Órgãos Governamentais , História do Século XX , HumanosRESUMO
PURPOSE: To determine the smallest significant change in mechanical efficiency (MEnet) measured by a stair-climbing test. METHODS: Duplicate stair-climbing tests (T1 and T2), with more than a 30-minute rest between, were performed by 51 children with diplegic cerebral palsy (CP) at levels II and III of Gross Motor Function Classification System (GMFCS) and 9 children with typical development, aged 5.5 to 13.0 years. RESULTS: The T2 versus T1 slope values of MEnet for CP and typical development did not significantly differ from 1.00. MEnet was significantly higher for GMFCS level II (7.0%) than level III (1.2%). The mean percentage of difference was 7.8% (T2 > T1) for the children with CP, with a 95% confidence interval of -39% to +54%. The 95% confidence interval for MEnet scores computed from the standard error of the mean (SEM) of the percentage of differences was 4.0 to 4.5 for CP. CONCLUSIONS: An increase of >13.4% in MEnet score (eg, mean increase from 4.0% to 4.5%) can indicate improved motor status resulting from interventions.
Assuntos
Paralisia Cerebral/reabilitação , Movimento , Caminhada , Adolescente , Criança , Pré-Escolar , Intervalos de Confiança , Avaliação da Deficiência , Metabolismo Energético , Teste de Esforço , Feminino , Humanos , Masculino , Destreza Motora , Movimento/fisiologia , Estudos Prospectivos , Análise de Regressão , Estatística como Assunto , Resultado do Tratamento , Caminhada/fisiologiaRESUMO
Measuring mechanical efficiency (ME) is potentially useful to assess motor performance in individuals with physical disabilities. The purpose of this study was to determine the accuracy of predicting ME from heart rate (HR) during a self-paced stair-climbing test in children with a range of motor abilities. The participants were 12 normally developed children (ND) and 24 with cerebral palsy (CP), ranging in age from 5 to 15 years (mean: 8 years). Five were at level II, 11 at level III and 8 at level IV according to the gross motor function classification system. ME was calculated as the ratio of external work to O(2) uptake (VO(2) ml/min) measured or predicted from HR. The absolute values of VO(2) and HR during stair-climbing were not significantly correlated. However, the correlation between values above resting (dVO(2) and dHR) was significant (r=0.61). Furthermore, when including body weight as a second variable the prediction of dVO(2) was significantly improved (r=0.85). This resulted in a high correlation (r=0.96) between measured and predicted net ME (ME(net)). Predicted ME(net) for 25 stair-climbing tests repeated after an average of 6 months resulted in an r-value of 0.92 with predicted ME(net) of the first test. This study demonstrates that ME(net) during stair-climbing can be predicted in children with a broad range of motor abilities from dHR and may be a simple tool to help define developmental stages or evaluating intervention efficacy.
Assuntos
Paralisia Cerebral/fisiopatologia , Frequência Cardíaca/fisiologia , Locomoção/fisiologia , Adolescente , Fenômenos Biomecânicos , Peso Corporal , Criança , Metabolismo Energético , Feminino , Humanos , Masculino , Consumo de Oxigênio/fisiologia , Valor Preditivo dos Testes , Análise de RegressãoRESUMO
Hypoxemia is usually associated with acute mountain sickness (AMS), but most studies have varied in time and magnitude of altitude exposure, exercise, diet, environmental conditions, and severity of pulmonary edema. We wished to determine whether hypoxemia occurred early in subjects who developed subsequent AMS while resting at a simulated altitude of 426 mmHg (approximately 16,000 ft or 4880 m). Exposures of 51 men and women were carried out for 8 to 12 h. AMS was determined by Lake Louise (LL) and AMS-C scores near the end of exposure, with spirometry and gas exchange measured the day before (C) and after 1 (A1), 6 (A6), and last (A12) h at simulated altitude and arterial blood at C, A1, and A12. Responses of 16 subjects having the lowest AMS scores (nonAMS: mean LL=1.0, range=0-2.5) were compared with the 16 having the highest scores (+AMS: mean LL=7.4, range=5-11). Total and alveolar ventilation responses to altitude were not different between groups. +AMS had significantly lower PaO2 (4.6 mmHg) and SaO2 (4.8%) at A1 and 3.3 mmHg and 3.1% at A12. Spirometry changes were similar at A1, but at A6 and A12 reduced vital capacity (VC) and increased breathing frequency suggested interstitial pulmonary edema in +AMS. The early hypoxemia in +AMS appears to be the result of diffusion impairment or venous admixture, perhaps due to a unique autonomic response affecting pulmonary perfusion. Early hypoxemia may be useful to predict AMS susceptibility.
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Doença da Altitude/complicações , Hipóxia/complicações , Troca Gasosa Pulmonar/fisiologia , Ventilação Pulmonar/fisiologia , Doença Aguda , Adulto , Suscetibilidade a Doenças , Exposição Ambiental , Feminino , Humanos , Masculino , Valor Preditivo dos Testes , Estudos Prospectivos , Testes de Função Respiratória , Fatores de TempoRESUMO
INTRODUCTION: Lower body negative pressure (LBNP) has been used for decades to simulate orthostatic stress and the effects of blood loss in humans. Since the definitive review of LBNP in 1974, new applications have been developed and research has revealed conflicting cardiovascular and neurohormonal responses during and after LBNP. METHODS: A search of the literature was conducted for 1964-2007 using the Web of Science and the search terms "cardiovascular system," "orthostasis," "spaceflight," and "methodologies" to identify publications in English that describe human studies where LBNP was used to simulate orthostasis. Publications cited in the earlier review were excluded, leaving a total of 215 articles for consideration. RESULTS: We divided the reported protocols into eight categories based on the pressure, pattern, and duration of the stimulus: 1) mild, constant, short; 2) mild, constant, long; 3) mild, ramp, short; 4) mild, ramp, long; 5) moderate-to-strong, constant, short; 6) moderate, constant, long; 7) moderate-to-strong, ramp, short; and 8) strong, ramp, long. The review showed that these protocols stimulate different reflexes and can be used to produce particular responses. DISCUSSION: Based on the review, we developed guidelines for using LBNP in a predictable and reproducible manner. Variables that must be controlled include subject characteristics, procedures, and environmental conditions as well as specifications for the LBNP chamber and seal positioning. An understanding of the many technical details of such experiments and the nature of elicited cardiovascular and neurohormonal responses is required to design optimal protocols to address specific research questions.
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Medicina Aeroespacial , Pressão Negativa da Região Corporal Inferior , Adaptação Fisiológica , Tontura/fisiopatologia , Hemodinâmica , Humanos , Hipotensão Ortostática/fisiopatologia , Pele/fisiopatologia , Voo Espacial , Circulação Esplâncnica/fisiologiaRESUMO
Ventilation (V (A)) to perfusion (Q ) heterogeneity (V (A)/Q ) analyses by a two-compartment lung model (2C), utilizing routine gas exchange measurements and a computer solution to account for O(2) and CO(2) measurements, were compared with multiple inert gas elimination technique (MIGET) analyses and a multi-compartment (MC) model. The 2C and MC estimates of V (A)/Q mismatch were obtained in 10 healthy subjects, 43 patients having chronic obstructive pulmonary disease (COPD) and in 14 dog experiments where hemodynamics and acid-base status were manipulated with gas mixtures, fluid loading and tilt-table stressors. MIGET comparisons with 2C were made on 6 patients and 32 measurements in healthy subjects before and after exercise at normoxia and altitude hypoxia. Statistically significant correlations for logarithmic standard deviations of V (A)/Q distributions (SD(V (A)/Q )) were obtained for all 2C comparisons, with similar values between 2C and both other methods in the 1.1-1.5 range, compatible with mild to moderate COPD. 2C tended to overestimate MC and MIGET values at low and underestimate them at high SD(V (A)/Q ) values. SD(V (A)/Q ) weighted by Q agreed better with MC and MIGET estimates in the normal range, whereas SD(V (A)/Q ) weighted by V (A) was closer to MC at higher values because the V (A)-weighted SD(V (A)/Q ) is related to blood-to-gas PCO(2) differences that are elevated in disease, thereby allowing better discrimination. The 2C model accurately described functional V (A)/Q characteristics in 26 normal and bronchoconstricted dogs during non-steady state rebreathing and could be used to quantify the effect of reduced O(2) diffusing capacity in diseased lungs. These comparisons indicate that 2C adequately describes V (A)/Q mismatch and can be useful in clinical or experimental situations where other techniques are not feasible.
Assuntos
Pulmão/fisiologia , Modelos Biológicos , Respiração , Relação Ventilação-Perfusão/fisiologia , Adulto , Animais , Cães , Humanos , Doença Pulmonar Obstrutiva Crônica/fisiopatologia , Troca Gasosa Pulmonar/fisiologia , Reprodutibilidade dos TestesRESUMO
Reduced blood flow to the gut may contribute to weight loss and gastrointestinal symptoms of acute mountain sickness (AMS) at altitude. A study in humans tested the hypothesis that acute hypobaric hypoxia (ALT) would attenuate the normal postprandial hyperemia in the superior mesenteric artery (SM). Blood pressure, cardiac output (CO), and (SM) were measured with previously validated noninvasive Doppler ultrasonic flowmetry in 9 (3 women) healthy young adults (mean age: 23; range: 18-33 yr) residing at 1700 m. Baseline measurements were made after 2 h at ALT in a chamber at 430 mmHg (asymptotically equal to 4800 m = 15,750 ft) after 10-12-h fasting, and the next day the control (CON) measurements were made at 615 mmHg (1850 m). Postprandial measurements were made 45 to 60 min after ingesting a 1000-cal liquid meal under both conditions. At ALT, 5 of the 9 subjects had AMS by the Lake Louise score criteria of headache > or =1 and total score > or =3. ALT significantly reduced fasting, baseline SM relative to CON by 15%, and increased CO by 16%. The postprandial CO increase was not different between ALT and CON, but (SM) increased 115% at CON, but only 75% at ALT, the attenuation being significant (p < 0.006). Neither the diminution of fasting (SM) at ALT nor the attenuation of the postprandial increase in (SM) correlated significantly with AMS symptom scores. These results suggest that baseline and postprandial gut blood flow are altered during acute altitude exposure because of increased intestinal sympathetic tone, inferred from increased local resistance, and may be related to reduced energy intake if sustained during prolonged exposure.
Assuntos
Doença da Altitude/fisiopatologia , Ingestão de Energia , Artéria Mesentérica Superior/fisiopatologia , Período Pós-Prandial , Circulação Esplâncnica , Adulto , Ingestão de Alimentos , Jejum , Feminino , Humanos , New Mexico , Fluxo Sanguíneo RegionalRESUMO
To examine the effect ("cross-tolerance") of heat acclimation (HA) on exercise performance upon exposure to acute hypobaric hypoxia (4350 m). Eight male cyclists residing at 1600 m performed tests of maximal aerobic capacity (VO2max) at 1600 m and 4350 m, a 16 km time-trial at 4350 m, and a heat tolerance test at 1600 m before and after 10 d HA at 40°C, 20% RH. Resting blood samples were obtained pre-and post- HA to estimate changes in plasma volume (ΔPV). Successful HA was indicated by significantly lower exercise heart rate and rectal temperature on day 10 vs. day 1 of HA and during the heat tolerance tests. Heat acclimation caused a 1.9% ΔPV, however VO2max was not significantly different at 1600 m or 4350 m. Time-trial cycling performance improved 28 sec after HA (p = 0.07), suggesting a possible benefit for exercise performance at acute altitude and that cross-tolerance between these variables may exist in humans. These findings do not clearly support the use of HA to improve exercise capacity and performance upon acute hypobaric hypoxia, however they do indicate that HA is not detrimental to either exercise capacity or performance.
RESUMO
Field studies of acute mountain sickness (AMS) usually include variations in exercise, diet, and environmental conditions over days and development of clinically apparent edemas. The purpose of this study was to clarify fluid status in persons developing AMS vs. those remaining without symptoms during simulated altitude with controlled fluid intake, diet, temperature, and without exercise. Ninety-nine exposures of 51 men and women to reduced barometric pressure (426 mmHg = 16,000 ft. = 4,880 m) were carried out for 8-12 h. AMS was evaluated by Lake Louise (LL) and AMS-C scores near the end of exposure. Serial measurements included fluid balance, electrolyte excretions, and plasma concentrations, regulating hormones, and free water clearance. Comparison between 16 subjects with the lowest AMS scores near the end of exposure ("non-AMS": mean LL = 1.0, range = 0-2.5) and 16 others with the highest AMS scores ("AMS": mean LL = 7.4, range = 5-11) demonstrated significant fluid retention in AMS beginning within the first 3 h, resulting from reduced urine flow. Plasma Na+ decreased significantly after 6 h, indicating dilution throughout the total body water. Excretion of Na+ and K+ trended downward with time in both groups, being lower in AMS after 6 h, and the urine Na+-to-K+ ratio was significantly higher for AMS after 6 h. Renal compensation for respiratory alkalosis, plasma renin activity, aldosterone, and atrial natriuretic peptide were not different between groups, with the latter tending to rise and aldosterone falling with time of exposure. Antidiuretic hormone fell in non-AMS and rose in AMS within 90 min of exposure and continued to rise in AMS, closely associated with severity of symptoms and fluid retention.
Assuntos
Doença da Altitude/fisiopatologia , Líquidos Corporais , Equilíbrio Hidroeletrolítico , Desequilíbrio Hidroeletrolítico/fisiopatologia , Adaptação Fisiológica , Adulto , Doença da Altitude/complicações , Doença da Altitude/diagnóstico , Feminino , Humanos , Masculino , Índice de Gravidade de Doença , Desequilíbrio Hidroeletrolítico/diagnóstico , Desequilíbrio Hidroeletrolítico/etiologiaRESUMO
To estimate the separate and combined effects of reduced P(B) and O2 levels on body fluid balance and regulating hormones, measurements were made during reduced PB (altitude, ALT; P(B) = 432 mm Hg, F(I(O2)) = 0.207), reduced inspired O2 concentration (normobaric hypoxia, HYX; P(B) = 614 mm Hg, F(I(O2)) = 0.142), and lowered ambient pressure without hypoxia (normoxic hypobaria HYB; P(B) = 434 mm Hg, F(I(O2)) = 0.296). Nine fit and healthy young men were exposed to these conditions for 10 h in a decompression chamber. Lake Louise AMS scores, urine collections, and blood samples were obtained every 3 h, with recovery measurements 2 h after exposure. AMS was significantly greater during ALT than HYX, as previously reported (J. Appl. Physiol. 81:1908-1910. 1996), because the combination of reduced P(B) and P(O2) over the 10 h favored fluid retention by reducing urine volume, while plasma volume (PV) remained higher than during HYX. At ALT the plasma Na+ fell significantly at 6 h, probably from dilution of extracellular fluid, and antidiuretic hormone (ADH) was highest (p = 0.006 versus HYB). The PV, urine flow, free water clearance, and plasma renin activity (PRA) rose significantly during recovery from ALT as AMS symptoms subsided, suggesting increased intravascular fluid and reduced adrenergic tone. During HYB, the plasma aldosterone (ALDO) and K+ levels were significantly elevated, and PRA was highest and ADH lowest, without fluid retention. During HYX, fluid balance was similar to HYB, but PV and ALDO were significantly lower, and ALDO increased significantly in recovery from HYX. The fluid retention at ALT in AMS-susceptible subjects appears related to a synergistic interaction involving reduced P(B) and ADH and ALDO.
Assuntos
Aclimatação , Doença da Altitude/fisiopatologia , Altitude , Equilíbrio Hidroeletrolítico , Desequilíbrio Hidroeletrolítico , Doença Aguda , Adulto , Aldosterona/sangue , Doença da Altitude/sangue , Doença da Altitude/urina , Análise de Variância , Arginina Vasopressina/sangue , Fator Natriurético Atrial/sangue , Líquidos Corporais , Humanos , Masculino , New Mexico , Norepinefrina/sangue , Renina/sangueRESUMO
PURPOSE: Mechanical efficiency can assess motor performance in individuals with physical disabilities. The purpose was to determine the utility of predicting it from heart rate (HR) during a self-paced stair-climbing test in adults with chronic hemiparesis after stroke and to determine the minimal detectable change of net mechanical efficiency (MEnet) measured by this exercise. METHODS: First, 15 subjects with chronic hemiparesis participated in a validation study (A) and then 28 took part in a repeatability study (B). In study A the MEnet was calculated from external work and oxygen uptake above rest (dVO2), as directly measured and as predicted from body weight and increase in heart rate (dHR). In study B, predicted dVO2 was used to obtain MEnet for duplicate stair-climbing tests (T1, T2) with >30 min rest between. RESULTS: Measured MEnet was closely related to predicted MEnet (r = 0.97, p < 0.001). In study B predicted MEnet for T2 and T1 were closely related (r = 0.91, ICC = 0.90). CONCLUSION: With a minimal detectable change of 0.6% (0.053 of average MEnet score of 10.4%), MEnet values from the stair-climbing test seem sufficiently meaningful to estimate ambulatory ability and its changes with interventions or walking aids in adults with hemiparesis. IMPLICATIONS FOR REHABILITATION: Ambulatory ability can be estimated from mechanical efficiency, obtained from a 5-min stair-climbing test utilizing a 4-step stair, to measure external work, and the change in heart rate above rest to estimate the metabolic cost of the task. A change of > 0.6% in mechanical efficiency by this stair-climbing test indicates a significant change in ambulatory ability of persons with hemiparesis.
Assuntos
Teste de Esforço/métodos , Frequência Cardíaca/fisiologia , Consumo de Oxigênio/fisiologia , Paresia/reabilitação , Reabilitação do Acidente Vascular Cerebral , Caminhada/fisiologia , Adulto , Idoso , Peso Corporal , Doença Crônica , Feminino , Humanos , Masculino , Pessoa de Meia-IdadeRESUMO
A few studies have reported increased body temperature (T(o)) associated with acute mountain sickness (AMS), but these usually include exercise, varying environmental conditions over days, and pulmonary edema. We wished to determine whether T(o) would increase with AMS during early exposure to simulated altitude at rest. Ninety-four exposures of 51 men and women to reduced P(B) (423 mmHg = 16,000 ft = 4850 m) were carried out for 8 to 12 h. AMS was evaluated by LL and AMS-C scores near end of exposure, and T(o) was measured by oral digital thermometer before altitude and after 1 (A1), 6 (A6), and last (A12) h at simulated altitude. Other measurements included ventilation, O(2) consumption and autonomic indicators of plasma catecholamines, HR, and HR variability. Average T(o) increased by 0.5 degrees F from A1 to A12 in all subjects (p < 0.001). Comparison between 16 subjects with lowest AMS scores (mean LL = 1.0, range = 0 to 2.5) and 16 other subjects with highest AMS scores (mean LL = 7.4, range = 5 to 11) demonstrated a transient decline in T(o) from A1 to A6 in AMS, in contrast to a rise in non-AMS (p = 0.001). Catecholamines, HR, and HR variability (increased low F/high F ratio) indicated significant elevation of sympathetic activity in AMS, where T(o) fell, but no change in metabolic rate. The apparently greater heat loss during early AMS suggests increased hypoxic vasodilation in spite of enhanced sympathetic drive. Greater hypoxic vasodilation and elevated HR in AMS in the absence of other changes suggest that augmentation of beta-adrenergic tone may be involved in early AMS pathophysiology.
Assuntos
Aclimatação/fisiologia , Doença da Altitude/fisiopatologia , Sistema Nervoso Autônomo/fisiopatologia , Temperatura Corporal/fisiologia , Doença Aguda , Adulto , Altitude , Doença da Altitude/metabolismo , Arginina Vasopressina/metabolismo , Catecolaminas/metabolismo , Feminino , Humanos , Masculino , Consumo de Oxigênio/fisiologia , Descanso/fisiologiaRESUMO
HYPOTHESIS: Measurements of plasma volume (PV) and its changes (delta%PV) by Evans blue (EB) dye are presumed to be valid only in fasting subjects. In addition, delta%PVEB with acute altitude exposure has not been compared with other methods employing the concentration or dilution of naturally occurring blood (hematocrit (Hct), hemoglobin (Hb)) and plasma (density, proteins) components, but should be similar if capillary permeability and the sampled vein/whole body Hct ratio remain unchanged. METHODS: PVEB was determined in six subjects while fasting or eating on different days, with injection and sampling in the same arm, 4-h extrapolation to time zero and correcting readings with the 620-740 A method. For 93 experiments at altitude, delta%PVEB was obtained similarly from a 3-h extrapolation near the end of a 12-h chamber exposure to 426 mm Hg (-4,880 m =16,000 ft) and at the same time on the preceding control day. RESULTS: Mean PVEB with and without eating was not significantly different (SE of absolute difference = +/- 2.8%). The EB decay curves had significantly more scatter with eating than fasting. The fasting vs. non-fasting values for the single 20-min post-injection point also gave a close comparison (r = +0.97). At altitude the loss in PV measured with EB was significantly greater (delta%PVEB = -6.3%) than losses estimated from Hct-Hb (-2.9%), plasma protein (-3.7%), and plasma density (-3.9%). The expected larger PV loss in subjects tolerant to altitude sickness compared with intolerant ones was most clearly shown by delta%PVEB (8.8%). CONCLUSIONS: Obtaining more samples can offset reproducibility lost by eating. The delta%PVEB were largest and nearest to values previously reported at altitude, perhaps because the single baseline and altitude samples utilized by the other methods are more sensitive to subtle, transient fluctuations in body water and vasomotor tone associated with apprehension, vomiting, fluid intake, and regional vasodilation and constriction.
Assuntos
Altitude , Corantes , Ingestão de Alimentos , Azul Evans , Volume Plasmático , Adulto , Técnica de Diluição de Corante/normas , Feminino , Humanos , MasculinoRESUMO
BACKGROUND: The ventilation ( ) response to inspired CO(2) has been extensively studied, but rarely with concentrations >10%. AIMS: These experiments were performed to determine whether would increase correspondingly to higher concentrations and according to conventional chemoreceptor time delays. MATERIALS AND METHODS: We exposed anesthetized dogs acutely, with and without vagotomy and electrical stimulation of the right vagus, to 20-100% CO(2)-balance O(2) and to 0 and 10% O(2)-balance N(2). RESULTS: The time delays decreased and response magnitude increased with increasing concentrations (p<0.01), but at higher concentrations the time delays were shorter than expected, i.e., 0.5 s to double at 100% CO(2), with the response to 0% O(2) being ~3 s slower. Right vagotomy significantly reduced baseline breathing frequency (fR), increased tidal volume (VT) and increased the time delay by ~3 s. Bilateral vagotomy further reduced baseline fR and , and reduced the response to CO(2) and increased the time delay by ~12 s. Electro-stimulation of the peripheral right vagus while inspiring CO(2) caused a 13 s asystole and further reduced and delayed the response, especially after bilateral vagotomy, shifting the mode from VT to fR. CONCLUSIONS: Results indicate that airway or lung receptors responded to the rapid increase in lung H(+) and that vagal afferents and unimpaired circulation seem necessary for the initial rapid response to high CO(2) concentrations by receptors upstream from the aortic bodies.
RESUMO
This study estimated changes in whole body oxygen stores (O(2)s) and carbon dioxide stores (CO(2)s) during steady state exercise with leg ischemia induced by leg cuff inflation. Six physically fit subjects performed 75 W steady state exercise for 15 min on a cycle ergometer. After 5 min of exercise, cuffs on the upper and lower legs were inflated to 140 mmHg. Cuffs were deflated after 5 min and exercise continued for another 5 min. O(2 )uptake (VO(2)) and CO(2) output (VCO(2)) significantly increased during the first 30 s after inflation, significantly decreased between 60 and 90 s, and then rose linearly until deflation. VO(2) and VCO(2) significantly increased further after cuff deflation, peaking between 30 and 60 s and then returned to near baseline exercise levels. Model-estimated changes in total O(2)s and CO(2)s were compared with time-integrated store changes from VO(2) and VCO(2). During 5 min after cuff deflation, VO(2) and VCO(2) exceeded the model-estimated change in stores by 273 and 697 mL, respectively. These results reflect the O(2) cost repayment of the anaerobic component and lactate buffering to neutralize circulating metabolites caused by the preceding ischemia.
Assuntos
Dióxido de Carbono/metabolismo , Exercício Físico/fisiologia , Isquemia/fisiopatologia , Perna (Membro)/irrigação sanguínea , Perna (Membro)/fisiologia , Consumo de Oxigênio , Adulto , Teste de Esforço , Terapia por Exercício/métodos , Estudos de Viabilidade , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Resistência Física , Treinamento Resistido , Adulto JovemRESUMO
Rebreathing in a closed system can be used to estimate mixed venous PCO2 (PvCO2) and cardiac output, but these estimates are affected by VA/Q heterogeneity. The purpose of this study was to validate a mathematical model of CO2 exchange during CO2 rebreathing in 29 patients with chronic obstructive pulmonary disease (COPD), with baseline arterial PCO2 (PaCO2) ranging from 28 to 60 mmHg. Rebreathing increased end-tidal PCO2 (PETCO2) by 20 mmHg over 2.2 min. This model employed baseline values for inspired (bag) PCO2, estimated PvCO2, distribution of ventilation and blood flow in one high VA/Q and one low VA/Q compartment, the ventilation increase and conservation of mass equations to simulate time courses of PICO2, PETCO2, PvCO2, and PaCO2. Measured PICO2 and PETCO2 during rebreathing differed by an average (SEM) of 1.4 (0.4) mmHg from simulated values. By end of rebreathing, predicted PvCO2 was lower than measured and predicted PaCO2, indicating gas to blood CO2 flux. Estimates of the ventilatory response to CO2, quantified as the slope (S) of the ventilation increase versus PETCO2, were inversely related to gas-to-blood PCO2 disequilibria due to VA/Q heterogeneity and buffer capacity (BC), but not airflow limitation. S may be corrected for these artifacts to restore S as a more valid noninvasive index of central CO2 responsiveness. We conclude that a rebreathing model incorporating baseline VA/Q heterogeneity and BC can simulate gas and blood PCO2 in patients with COPD, where VA/Q variations are large and variable.