High versus low training frequency in cardiac rehabilitation using a systems model of training.

No study has reported the long term effects of cardiac rehabilitation, concerning the duration of beneficial effects of training program. The present study analyzed the influence of training session frequency on long-term beneficial effects in patients with coronary artery disease (CAD) undergoing phase 2 cardiac rehabilitation. Four patients with CAD completed 20 training sessions. Two patients were assigned to low training frequency (LTF) and two to high training frequency (HTF): three and five sessions per week(-1), respectively. The method was based on the systems model of training and required training quantification and the assessment of real exercise tolerance. Convolution of training quantity with real exercise tolerance provided the model exercise tolerance for every patient. The model parameters, the magnitude factor (k), and the time constant of decay (tau), were fitted from real and model exercise tolerances by the least squares method. LTF and HTF resulted in similar increases in exercise tolerance (12-14%). A model with one-component (fitness) allowed fitting exercise tolerance in all patients with r (2) = 0.77, 0.79, 0.84, and 0.91, respectively (p < 0.05). The addition of a second component did not improve the fit in any patient (p > 0.05). The k value was about twice as high with LTF (0.13 and 0.16 AU) than with HTF (0.05 AU for the two patients), whereas the tau value was about twice as low with LTF (37 and 41 days) than with HTF (72 and 89 days). The long term beneficial effects estimated by 4tau, were twice as long with HTF (288 and 356 days) than with LTF (148 and 164 days). We concluded that exercise tolerance was similarly increased with HTF and LTF but HTF training induced beneficial effects which were sustained twice as long.

Gender influence on the oxygen consumption of the respiratory muscles in young and older healthy individuals.

To understand the influence of gender on oxygen consumption of respiratory muscles (VO(2)resp), 32 healthy subjects participated in the study (16 males, 16 females). They were divided into four groups: young males, young females, older males and older females. We used a closed circuit device which allowed a continuous increase in external dead space at a constant rate of 300 ml per 90 s and was equipped with a 9-L Gould spirometer filled with 100 % O(2). As log VO(2)tot (total body O(2) consumption) was linearly related to VE, we calculated the slope value (log VO(2)tot/VE) and the Y-intercept (VE = 0) of the semilog regression, representing the increase of VO(2)resp and log VO(2)met (metabolic O(2) consumption). The main results showed that the mean of the individual slope Delta(logVO(2)tot/VE) was steeper in the females than in the males in young and also in older subjects. In addition, VO(2)met in young and older females was lower compared with that in age-matched males. Therefore, we conclude that the oxygen cost of breathing was higher in females versus males subjects.

A standardized method for the evaluation of respiratory muscle endurance in patients with Duchenne muscular dystrophy.

The aim of the study was to develop a standardized method using controlled breathing to quantify respiratory muscle endurance in children with Duchenne muscular dystrophy (DMD) and to test its reproducibility. In 10 DMD patients, all between 10 and 14 years (mean age, 11.5 +/- 1.5 years), except for two patients of 20 and 22 years, and 10 healthy children (mean age, 12 +/- 1 years), we measured the maximal time (Tlim) that a threshold load fixed at 35% of the individual maximal inspiratory pressure (Pimax) could be tolerated. We asked the children to maintain their rest breathing pattern until exhaustion using visual feedback and an auditory signal. The mean Tlim in the DMD children was 4.45 +/- 1.45 min and values were reproducible. All healthy children were able to obtain Tlim values greater than 30 min. The respiratory muscles of DMD children are more susceptible to fatigue than those of healthy subjects. This method should be satisfactory for estimating the effect of treatment and for the specific training of respiratory muscles in DMD patients without significant learning disability.

Reliability of a new device to assess the oxygen consumption of human respiratory muscles.

PURPOSE: This study tests the reliability of a new device for assessing the oxygen consumption of the respiratory muscles (VO2 resp.). METHODS: Fourteen healthy male volunteers participated in the study. The device consists of an expandable external ventilatory dead space created with pieces of plastic tubing and a spirometer filled with 100% oxygen. It also incorporates a carbon dioxide absorber. Total VO2 (VO2 tot.) was recorded from the spirometric closed circuit and ventilation (V(E)), from the spirometer tracing. For each subject the test procedure was carried out in duplicate (T1 and T2) after an overnight fast. The dead space was increased at a constant rate of 260 mL every 90 s, and VO2 tot. and V(E) increased progressively. Because log VO2 tot. was linearly related to V(E), we calculated the slope value (log VO2-V(E)) and the Y-intercept (VE = 0) of the semilog regression representing, respectively, VO2 resp. and metabolic VO2 (VO2 met.). RESULTS: When compared with values in the literature, these values did not differ from those recorded in subjects of a similar age group. The VO2 resp. and VO2 met. calculated in T1 and T2 were not different (VO2 resp. = 0.0066 +/- 0.0005 for T1 vs 0.0067 +/- 0.0005 log mL x min(-1)/L x min(-1) for T2 and VO2 met. = 269.3 +/- 28.6 for T1 vs 281.9 +/- 24.1 mL x min(-1) for T2). The coefficients of variation were: 25% at T1 and 23% at T2 for VO2 resp. and 34% at T1 and 29% at T2 for VO2 met. Moreover, significant correlations (r = 0.96, P < 0.001 for VO2 resp., r = 0.95, P < 0.001 for VO2 met.), high coefficients of determination (r2 = 0.92 for VO2 resp., r2 = 0.90 for VO2 met.) and negligible SEE (0.0005 for VO2 resp., 0.2 mL x min(-1) for VO2 met.) were found between the two tests. When we plotted the mean values of VO2 resp. and VO2 met. measured at T1 and T2 against their respective differences, more than 95% of the slight differences ranged between the limits defined by mean value +/- 2 SD, reflecting the small discrepancy between duplicate measurements. CONCLUSION: The results confirm that the test performed with this device is useful and reliable for assessing the VO2 resp. in healthy subjects.