RESUMO
PURPOSE: This study examines the effect of static and dynamic leg exercises on heart rate variability (HRV) and blood pressure variability (BPV) in humans. METHODS: 10 healthy male subjects were studied at rest, during static exercise performed at 30% of maximal voluntary contraction (SX30), and during dynamic cycling exercises done at 30% of VO2max (DX30) and at 60% of VO2max (DX60). Respiration, heart rate, and blood pressure signals were digitized to analyze temporal and spectral parameters involving short and overall indexes (SD, deltaRANGE, RMSSD, Total power), power of the low (LF), middle (MF), and high (HF) frequency components, and the baroreceptor sensitivity by the alphaMF index. RESULTS: During SX30, indexes of HRV as SD, deltaRANGE, Total power, and MF in absolute units increased in relation with rest values and were significantly higher (P < 0.001) than during DX30 and DX60; HF during SX30, in normalized and absolute units, was not different of the rest condition but was higher (P < 0.001) than HF during DX30 and DX60. Parameters of BPV as SD and deltaRANGE increased (P < 0.001) during both type of exercises, and significant (P < 0.01) increments were observed on MF during SX30 and DX30; systolic HF was attenuated during DX30 (P < 0.05), whereas diastolic HF was augmented during DX60 (P < 0.001). Compared with rest condition, the alphaMF index decreased (P < 0.01) only during dynamic exercises. CONCLUSION: Because HRV and BPV response is different when induced by static or dynamic exercise, differences in the autonomic activity can be advised. Instead of the vagal withdrawal and sympathetic augmentation observed during dynamic exercise, the increase in the overall HRV and the MF component during static exercise suggest an increased activity of both autonomic branches.
Assuntos
Pressão Sanguínea/fisiologia , Exercício Físico , Frequência Cardíaca/fisiologia , Adulto , Eletrocardiografia , Teste de Esforço , Humanos , Perna (Membro) , Masculino , Pressorreceptores/fisiologia , RespiraçãoRESUMO
The behavior of temporal and spectral parameters of the heart rate variability was determined during 5 different maneuvers in order to characterize the level of sympathetic-vagal activity. The discriminating capacity of two spectral parameter estimation schemes were compared, and the respiratory influence was evaluated. One hundred and ten records of instantaneous heart rate and respiratory amplitude were analyzed, both in temporal and spectral perspectives. The records were obtained from 22 healthy subjects, under a five-stage protocol: supine, controlled breathing, standing, exercise, and recovery. A discriminating and characteristic behavior was found among the maneuvers, specifically for the dispersion parameters, low and intermediate partial components. The two integration-normalization procedures used in the estimation of the spectral components showed similarities, producing a functional interpretation independent of the selected procedure. The division of the low frequency component in two separate bands, allowed an improved discriminating capacity. The respiration had an important influence in the controlled breathing maneuver while being lower in the rest of the stages. In conclusion, the maneuvers determined a typical behavior of the dispersion and spectral parameters (low and intermediate partial components) of the heart rate variability, showing adequate distinctive levels in the sympathetic-vagal activity for each maneuver.
Assuntos
Exercício Físico/fisiologia , Frequência Cardíaca/fisiologia , Postura/fisiologia , Respiração , Adulto , Algoritmos , Feminino , Humanos , Masculino , Valores de ReferênciaRESUMO
OBJECTIVE: To assess the reliability of 29 prediction models for vital capacity when these are applied as reference for young females, natives and residents in Mexico City (altitude = 2,240 m). DESIGN: Transversal, prospective and comparative study. SETTING: Metropolitan Autonomous University, Mexico. SUBJECTS: Sixty females clinically healthy, 17 to 29 years old, non-smokers. PROCEDURE: Vital capacity was predicted from 29 models and measured with a bell spirometer (Collins 9 L) according to the American Thoracic Society guidelines. Statistical comparison was done between measured and predicted values by linear regression, analysis of variance and analysis of residuals. RESULTS: Mean of measured vital capacity was 3,625 mL while mean values of predicted vital capacities varied from 2,644 mL to 3,962 mL. Actual and reference values showed a small but significative correlation (r = 0.40 to 0.49). By Dunnett's test, means from six of the 29 models showed non-significant differences (p > 0.05) with the mean of the measured vital capacity; however, all 29 models presented significative bias in the regression line between actual values and the residuals of predicted values (correlation coefficient, slope and intercept statistically different from zero, p < 0.05). CONCLUSION: Due to the large bias found, models tested in the present study have limitations to predict accurate reference values for young mexican females.
Assuntos
Modelos Teóricos , Capacidade Vital , Adolescente , Adulto , Altitude , Antropometria , Viés , Estudos de Avaliação como Assunto , Feminino , Humanos , México , Estudos Prospectivos , Valores de Referência , Reprodutibilidade dos Testes , Fumar , EspirometriaRESUMO
The reliability of 33 prediction models for vital capacity was assessed in university students living in Mexico City (altitude = 2,240 m). Forced vital capacity (FVC) was predicted and measured in 83 healthy male students, 18 to 30 years old and non-smokers. Spirometric tests were performed with a 9 liter bell spirometer, according to ATS guidelines. Mean measured FVC was 5,094 +/- 555 mL (BTPS) while mean predicted FVC by the models ranged from 3,700 mL to 5,350 mL (BTPS) with a small but significative correlation between actual and reference values (r = 0.398 to 0.474, p < 0.05). The residual standard deviation showed values from 503 to 577 mL which were similar to those seen in the original population. Although 11 of the 33 models were able to predict mean observed FVC by Dunnett's test (p < 0.05), all of them showed significant bias on the regression between measured values and residuals of predicted values, i.e. intercepts (2,435 to 4,127 mL), slopes (-0.61 to -0.87) and correlations (-0.59 to -0.95) were statistically different from zero (p < 0.01). Our data remark the need to obtain appropriate reference FVC values in young Mexican males due to the questionable predictability of the models tested.
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Modelos Biológicos , Capacidade Vital , Adolescente , Adulto , Fatores Etários , Altitude , Antropometria , Viés , Humanos , Masculino , México , Valores de Referência , EspirometriaRESUMO
Body density by hydrostatic method and anthropometric variables were measured in 29 young males, natives of Mexico City, in order to test the validity of nine currently used equations for predicting body composition. Tested equations were those reported for body density by Sloan, Wilmore, Jackson and Pollock, Durnin and Womersley, Lohman, and Pollock et al.; for lean body weight by Wilmore, and Hume-Rathbun; and for fat percentage by Yuhasz. Mean values for body density, fat percentage and lean body weight obtained by hydrostatic weighing were 1.0560 +/- 0.0149 kg/l, 18.9 +/- 6.7%, and 52.6 +/- 5.3 kg, respectively, while the means for predicted body density using the six regression equations varied from 1.0538 to 1.0654 kg/l, with a range of correlation from 0.846 to 0.900, and total errors from 0.0077 to 0.0124 kg/l. Mean lean body weight predicted by Wilmore was 55.7 +/- 5.9 kg, with an R of 0.902 and a total error of 4.0 kg, while values given in the same order by Hume-Rathbun were 52.8 +/- 4.8 kg, R of 0.892 and total error of 2.3 kg. Mean fat percentage predicted by Yuhasz was 17.8 +/- 5.6%, R of 0.869 and total error of 3.5%. Although by analysis of variance there were no significant differences among the means of the models, statistical analysis of individual differences between predicted and measured values were significant in six of them.(ABSTRACT TRUNCATED AT 250 WORDS)
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Antropometria/métodos , Composição Corporal , Densitometria , Tecido Adiposo/anatomia & histologia , Adolescente , Adulto , Peso Corporal , Humanos , Imersão , Medidas de Volume Pulmonar , Masculino , Matemática , Pletismografia , Valor Preditivo dos Testes , Análise de Regressão , Dobras CutâneasRESUMO
In order to compare 1) predicted values of aerobic capacity (VO2Max) and, 2) direct VO2Max reported in the literature for sedentary subjects, direct VO2Max was measured in 27 sedentary males (18-25 years old), residents at 2240 meters (588.5 +/- 1.0 mmHg). To get direct VO2Max, ventilation and expired gases were measured while the subjects performed maximal exercise on a motor treadmill. Predicted VO2Max was estimated from the Astrand and Ryhming nomogram by measuring submaximal heart rate (HR) during a step test protocol. The mean results from the maximal protocol were: HR 194.9 +/- 5.4 beats/min, direct VO2Max 3.15 +/- 0.46 L/min and 47.67 +/- 5.07 ml/min/Kg, absolute and relative to body weight, respectively. From the submaximal protocol, mean HR was 171 +/- 8.3 beats/min and predicted VO2Max 2.50 +/- 0.39 L/min. In spite of a good correlation (r = 0.79) between predicted and direct VO2Max, the predicted values underestimated 20.3 +/- 7.2% direct measurements. Our data point out that 1) indirect measuring of aerobic capacity from the Astrand and Ryhming nomogram is discouraged in sedentary subjects living at moderate altitudes and, 2) in contrast to other author's suggestions, aerobic capacity is not diminished by chronic exposure to moderate hypoxia.
Assuntos
Altitude , Exercício Físico , Consumo de Oxigênio , Adolescente , Adulto , Teste de Esforço , Frequência Cardíaca , Humanos , MasculinoRESUMO
An exercise program based on growing intensity loads (50 watts) was applied to 21 healthy, middle-aged subjects, who were divided into two groups: the physically actives and the sedentaries, according to their physical activity habits. During exercise, which was made on a treadmill, the following variables were measured: oxygen intake (VO2), cardiac frequency (FC), left ventricule ejection time (TEVI), maximal value of the first derivative of ear ensitogram (VMPDDO) and indirect arterial pressure. The active group reached higher values of power and VO2 (absolute and by pulse) and lower values of FC at under maximal works; these data therefore show their best cardiopulmonary capacity. The TEVI in the active group was higher at 150 watts because of the lower FC presented by its assigned subjects. For a maximal exercise condition, both groups had similar ejection times, but the reduction rate of actives' TEVI decreased, which in turn indicates the handling of higher stroke volumes. The VMPDDO relation with the successive increments of work loads was non linear. This index had higher values in the active group, for an exercise strength over 100 watts; this fact allowed the statistical differentiation of both groups. Accordingly, the VMPDDO did indicate the higher left ventricular function of the active subjects during exercise; this findings supports the notion which establishes that resistance training enhances myocardial contraction. In the recovery stage, the sedentaries' VMPDDO increases in a significant way, due to a possible mechanism as to hold stroke volume. In conclusion, the active subjects heart is a more efficient pump than the sedentaries', because of its capacity to handle under maximal exercise higher stroke volumes in the same ejection time, and thus in a higher ejection rate, with equal cardiac frequencies arterial pressures and myocardial oxygen intake.