Thixotropy conditioning of inspiratory muscles at lower lung volumes decreases functional residual capacity (FRC) of following breath cycles with increases in inspiratory capacity. It remains uncertain whether this conditioning would improve exercise tolerance in chronic obstructive pulmonary disease (COPD). Sixteen male stable COPD patients with mild to severe airway obstruction participated. Before the study, all patients completed the 6-min walk test at least twice. The 6-min walk distance (6MWD) was measured after single inspiratory muscle training (IMT) maneuver or without intervention (control) in a randomized cross-over fashion. The 6MWD was also measured after thixotropy conditioning of inspiratory muscles at the maximal expiratory position or without intervention (control). There were no significant differences in the 6MWD after the IMT maneuver (493.2+/-83.7m, P>0.05) versus without intervention (495.7+/-85.9m). The 6MWD after thixotropy conditioning (526.2+/-96.3m, P=0.030) was significantly higher than the 6MWD without intervention (504.3+/-94.1m). The 95% confidence interval of the difference was from 2.6 to 41.2m. Percentage predicted FRC correlated positively with differences in the 6MWD between control and after the thixotropy conditioning maneuver (r=0.78, P=0.007), whereas percentage predicted forced expiratory volume in 1s or the BODE index did not correlate with differences in the 6MWD (P>0.05). Thixotropy conditioning increases self-paced walking distance in patients with COPD. Patients with higher resting FRC benefited more from the conditioning with greater walking distance.
PMID: 18396028 DOI: 10.1016/j.rmed.2008.02.007

We examined the effect of a 6-wk period of ventilatory muscle endurance training on the maximal sustained ventilatory capacity (MSVC) and on exercise tolerance in 10 patients with chronic obstructive pulmonary disease (COPD). No significant changes occurred in lung volumes or spirometric indices. After training, the MSVC increased from 32 +/- 11 to 42 +/- 13 l/min (P less than 0.001) and the MSVC/FEV1 ratio from 40.2 +/- 8.8 to 47.8 +/- 8.0 (P less than 0.001). Oxygen consumption during the MSVC increased from 460 +/- 94 to 647 +/- 107 ml/min (P less than 0.001), and MSVC heart rate increased from 99 +/- 15 to 114 +/- 15 (P less than 0.001). The post MSVC blood lactate increased from 1.55 +/- 1.29 to 2.85 +/- 1.05 mM/l (P less than 0.001). Maximal exercise ventilation measured by an incremental ergometer test increased from 32 +/- 8 to 36 +/- 11.5 l/min for leg exercise and from 30.4 +/- 8.4 to 33.7 +/- 8.9 l/min (P less than 0.01) for arm exercise. Endurance time at a constant submaximal load increased from 6.98 +/- 4.30 to 10.76 +/- 6.00/min (P less than 0.01) for leg exercise and from 5.76 +/- 3.53 to 10.47 +/- 6.57/min (P less than 0.01) for arm exercise. The maximal distance covered in a 12-min walk increased from 1,058 +/- 161 to 1,188 +/- 201 m (P less than 0.01). We concluded that ventilatory muscle training in patients with COPD improved the ventilatory muscle performance, as indicated by the increased MSVC, oxygen consumption during the MSVC, and the maximal exercise ventilation. There was a substantial increase in submaximal exercise endurance for both arm and leg work.
PMID: 7362134 DOI: 10.1164/arrd.1980.121.2.273

To overcome the problem of altered breathing strategy during resistive ventilatory muscle training (VMT), we used a single-orifice inspiratory resistance together with a target feedback device (TFD) in patients with chronic obstructive pulmonary disease (COPD). In a preliminary study (study A), we showed that the resistance plus TFD was effective in controlling breathing strategy. We subsequently used the resistor plus TFD in a 5-wk study (study B) of VMT in 17 COPD patients who were randomized into high-intensity (HI) and low-intensity (LI) training groups. Compared with the LI group, the HI group showed significant increases in static maximal inspiratory pressure (21.3 vs. 5.0 cmH2O), maximal sustained ventilatory capacity (MSVC, 3.2 vs -0.1 l/min, sustained maximal mouth pressure (12.1 vs. 0.6 cmH2O), mean mouth pressure (6.9 vs. 3.9 cmH2O), peak inspiratory flow rate (12.3 vs. 4.0 l/min), and maximal sustained work rate (12.2 vs. 4.2 cmH2O.l-1.min-1). We conclude that targeted VMT with control of breathing strategy improves both ventilatory muscle strength and endurance.
PMID: 3215873 DOI: 10.1152/jappl.1988.65.6.2726

In order to investigate the effect of resistive breathing training on ventilatory muscular endurance, we examined the maximal sustained ventilatory capacity in ten patients with chronic obstructive pulmonary disease (COPD) before and after a six-week program of resistive breathing training. In addition, we investigated the effect of altered breathing strategy on resistive breathing performance. The patients performed two 15-minute sessions of resistive breathing daily for six weeks using an inspiratory resistive device (Pflex). Before and after the training, we found no significant change in spirometric data, pulmonary volumes, maximal inspiratory pressure, and maximal expiratory pressure. Of the ten patients, seven failed to show an improvement in their performance of resistive breathing. Furthermore, the maximal sustained ventilatory capacity was unchanged after the resistive breathing training. After the completion of the training program, seven of the patients participated in an additional experiment in which they were instructed to take long slow inspirations while breathing through the resistive device. With this change in breathing pattern, five of the seven were able to improve their performance of resistive breathing. Analysis of the breathing strategy showed that a reduction in the peak mouth pressure, breathing frequency, and external resistive work with a longer inspiratory time was beneficial. We conclude that neither resistive breathing performance nor ventilatory muscular endurance, as measured by sustained hyperpnea, is improved by resistive breathing training performed according to the current instructions with the resistive device, and alterations in breathing strategy have a profound effect on the performance of resistive breathing. The lack of details of breathing strategy in previous studies of resistive breathing makes it difficult to determine if previously demonstrated improvements were due to a real enhancement of ventilatory muscular performance or merely secondary to a different strategy.
PMID: 3769566 DOI: 10.1378/chest.90.5.662

The aim of this study was to evaluate the impact of inspiratory muscle training on lung function and exercise tolerance in patients with chronic obstructive pulmonary disease (COPD). Thirty-five patients with stable COPD were enrolled. We measured lung function variables and peak inspiratory and expiratory pressures (PImax and PEmax). Tests of progressive maximal exercise tolerance and stable submaximal exercise tolerance were administered. Two study groups were formed. Group A patients (n = 20) were enrolled in a respiratory muscle training program lasting four months. Group B (n = 15) was the control group. At the end of the study period the patients underwent testing similar to the first battery of tests. All showed moderate to severe obstruction with no significant differences between groups (FEV1: group A 37.6 +/- 13%, group B 36.6 +/- 12%; FVC: group A 80.4 +/- 15%, group B 80 +/- 12%). Nor were there any significant differences between the two groups in initial results of either maximal respiratory pressures or exercise tolerance. No lung function changes were observed in either group. PImax in group A increased significantly at the end of the study (from 54 +/- 9 to 78 +/- 16 cmH2O; p < 0.001); there were no changes in group B. No changes were seen in VO2max or ventilatory response and/or gasometry during exercise in any of the groups. The trained group, on the other hand, experienced a significant decrease in dyspnea evaluated on the Borg scale exercise in maximal (5.7 +/- 1.1 versus 4.7 +/- 1.2, p < 0.005) and submaximal (5.9 +/- 0.9 versus 4.9 +/- 1.3, p < 0.005) and an increase in time of submaximal exercise tolerance (5.5 +/- 2 versus 7 +/- 3 min, p < 0.05), changes that were not observed in the control group. Based on these results, and although specific training of inspiratory muscles does not appear to improve lung function in patients with COPD, it is accompanied by a decreased sense of dyspnea during exercise and greater tolerance.
PMID: 9557177