[Respiratory Muscle Training: State of the Art]. / Atemmuskeltraining: State-of-the-Art.

Specific respiratory muscle training (IMT) improves the function of the inspiratory muscles. According to literature and clinical experience, there are 3 established methods: 1.) resistive load 2.) threshold load and 3.) normocapnic hyperpnea. Each training method and the associated devices have specific characteristics. Setting up an IMT should start with specific diagnostics of respiratory muscle function and be followed by detailed individual introduction to training. The aim of this review is to take a closer look at the different training methods for the most relevant indications and to discuss these results in the context of current literature. The group of neuromuscular diseases includes muscular dystrophy, spinal muscular atrophy, amyotrophic lateral sclerosis, paralysis of the phrenic nerve, and injuries to the spinal cord. Furthermore, interstitial lung diseases, sarcoidosis, left ventricular heart failure, pulmonary arterial hypertension (PAH), kyphoscoliosis and obesity are also discussed in this context. COPD, asthma, cystic fibrosis (CF) and non-CF-bronchiectasis are among the group of obstructive lung diseases. Last but not least, we summarize current knowledge on weaning from respirator in the context of physical activity.

Idiopathic diaphragmatic paralysis--satisfactory improvement of inspiratory muscle function by inspiratory muscle training.

Daily inspiratory muscle strength and endurance training (IMT) was performed in a 44-year-old patient with idiopathic bilateral diaphragmatic paralysis (BDP) in addition to nocturnal non-invasive ventilation (NIV). After 4 months of training inspiratory muscle function improved satisfactorily whereas phrenic nerve latency remained pathological. Due to the improvement of inspiratory muscle capacity nocturnal NIV could be stopped without inducing nocturnal respiratory insufficiency.

No effect of naloxone on ventilatory response to progressive hypercapnia in IDDM patients.

The ventilatory response to hyperoxic progressive hypercapnia was examined by comparing 3 test groups: 7 diabetic patients with AN, 8 diabetic patients without AN, and 8 normal control subjects. In each group, a significant linear correlation was found between PaCO2 and VE. The slopes of the regression curves relating PaCO2 to VE were significantly steeper in the healthy control subjects and diabetic patients without AN than in those with AN (P < 0.01). We conclude that the ventilatory response to progressive hypercapnia is reduced in diabetic patients with AN. By analyzing the power spectrum and the amplitude behavior of the diaphragmatic EMG (calculated from the fc and RMS, respectively), we could exclude a disturbance of neural descending pathways and respiratory muscle dysfunction as possible causal mechanisms for the impaired ventilatory response to increasing CO2. By using lung function analysis, causal factors such as alterations in respiratory system mechanics also could be excluded. As diabetes is known to affect the endogenous opioid system, which, in turn, affects the ventilatory response to CO2, naloxone, as a specific opioid antagonist, was administered in all 3 test groups. Naloxone produced a significant increase of ventilatory response to hypercapnia in the healthy control subjects (P < 0.01), but produced no effect in either of the diabetic groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Acceptance of CPAP therapy for sleep apnea.

Although NCPAP is the most efficient nonsurgical treatment for patients with OSA, many patients do not accept sleeping with a nose mask. To determine the factors influencing acceptance, treatment with NCPAP was offered to 95 patients with an AHI greater than 15. After the first night on NCPAP, 47 of 65 patients decided to have NCPAP as a home therapy. Excessive daytime sleepiness was more frequently reported by acceptors than refusers. The frequency of complaints about psychomental symptoms such as poor mental performance and bad memory, was not different between the two groups. There was a close correlation between the rate of acceptance and the AHI as well as the number of positive answers to questions about symptoms of daytime sleepiness in a questionnaire, which correlated with the number and length of apneas. Acceptance of NCPAP was found to be dependent on the subjective feeling of impairment by hypersomnolence due to OSA.

Breathing during sleep in patients treated for obstructive sleep apnea. Nasal CPAP for only part of the night.

To determine whether long-term NCPAP therapy influences severity of sleep disordered breathing during the second part of a night when NCPAP is applied for only the first four hours of sleep, we studied 21 patients with OSA receiving NCPAP therapy for 253 +/- 41.6 days. Results from polysomnography for the period after withdrawal from NCPAP (night B) were compared to the corresponding period of sleep prior to initiation of NCPAP therapy (night A). There was no significant change in RDI from night A (53.9 +/- 8.6) to night B (28.7 +/- 3.3), but maximal apnea length diminished from 55 +/- 2.9 s to 40 +/- 2.9 s (p less than 0.05). Whereas daytime Po2 and the amplitude of desaturations during sleep remained equal, overall oxygenation during sleep improved slightly (mean SaO2 night A = 90.6 +/- 0.9 percent; night B = 92.8 +/- 0.5 percent; p less than 0.05). Differences between nights A and B were more prominent the more severe sleep apnea had been prior to treatment and could not be explained by weight loss. There was strong correlation between improvements in oxygenation measurements and the daily time of NCPAP use. In conclusion, we found a subgroup of OSA patients receiving long-term NCPAP therapy with less disturbed ventilation during sleep following use of NCPAP for only the first part of the night, but in the majority of patients, sleep disordered breathing off NCPAP remained unchanged.

Neural drive to the diaphragm after lung volume reduction surgery.

STUDY OBJECTIVES: The aim of this study was to investigate prospectively the changes in neural drive to the diaphragm in the first year after lung volume reduction surgery (LVRS) in patients with COPD. PATIENTS AND METHODS: In 14 patients with severe emphysema (mean +/- SD; age, 53.7 +/- 8.3 years; FEV(1), 0.64 +/- 0. 18 L; residual volume [RV], 5.33 +/- 1.25 L; PaO(2), 62.3 +/- 9.0 mm Hg; PaCO(2), 39.0 +/- 6.0 mm Hg), we assessed lung function, arterial blood gases, maximal exercise capacity (Wmax), and oxygen uptake (f1.gif" BORDER="0">O(2)max); intrinsic positive end-expiratory pressure (PEEPi); diaphragmatic strength (transdiaphragmatic pressure, Pdisniff) and endurance capacity (tlim); central diaphragmatic drive assessed by root mean square analysis of the esophageal electromyogram (rmsdia); and isotime dyspnea during loaded breathing tests (BS). RESULTS: Despite a significant increase (expressed as a percentage of baseline) in FEV(1) (40.6%) and a decrease in RV (30.0%) and PEEPi (75.7%) 1 month after LVRS, the improvements in Wmax (31.2%) and f1.gif" BORDER="0">O(2)max (13.7%); Pdisniff (25.4%) and tlim (64.9%); rmsdia (34.6%); and BS (21.7%) did not reach statistical significance (p < 0.05) until 6 months after LVRS. Arterial blood gases did not change significantly. Significant correlations were found between decrease in rmsdia and changes in PEEPi (r = 0.69), Wmax (r = -0.56), Pdisniff (r = -0.65), tlim (r = -0.59), and BS (r = 0.71) 6 months after LVRS. CONCLUSIONS: Our results show that LVRS is able to increase the efficacy of the respiratory pump and by this way reduce ventilatory drive and respiratory effort sensation.

2 Years' experience with inspiratory muscle training in patients with neuromuscular disorders.

PURPOSE: The aim of our study was to assess the long-term effects of specific inspiratory muscle training (IMT) in patients with neuromuscular disorders (NMDs) who have various degrees of respiratory impairment. PATIENTS AND METHODS: Twenty-seven patients with NMDs (Duchenne's muscular dystrophy, 18 patients; spinal muscular atrophy, 9 patients) underwent 24 months of IMT. Patients were divided into three groups according to their vital capacity (VC) values. VC was measured as the parameter for the respiratory system involvement of the disease. Maximal inspiratory pressure (PImax) was assessed as the parameter for respiratory muscle strength, and the results of the 12-s maximum voluntary ventilation test (12sMVV) were assessed as the parameter for respiratory muscle endurance. Pulmonary and inspiratory muscle function parameters were assessed 6 months before training, at the beginning of training, and then every 3 months. RESULTS: The PImax values improved in group A (VC, 27 to 50% predicted) from 51.45 to 87.00 cm H(2)O, in group B (VC, 51 to 70% predicted) from 59.38 to 94.4 cm H(2)O, and in group C (VC, 71 to 96% predicted) from 71.25 to 99.00 cm H(2)O. The 12sMVV values improved in group A from 52.69 to 69.50 L/min, in group B from 53.18 to 62.40 L/min, and in group C from 59.48 to 70.5 L/min. For all three groups, there was a significant improvement of PImax (p < 0.007) and 12sMVV (p < 0.015) until the 10th month when a plateau phase was reached with no decline in the following month until the end of training. CONCLUSION: With IMT, respiratory muscle function can be improved in the long term of up to 2 years.

Inspiratory muscle training in patients with Duchenne muscular dystrophy.

PURPOSE: The aim of this study was to assess the usefulness of a specific inspiratory muscle training in Duchenne muscular dystrophy (DMD). PATIENTS AND METHODS: Fifteen patients with DMD started 6 months of training the inspiratory muscles and 15 patients served as a control group. Pulmonary and inspiratory muscle function parameters were assessed 3 months before and at the beginning of training, in the first and third month of training, at the end, and 6 months after its cessation. Maximal sniff assessed esophageal and transdiaphragmatic pressure values served as indices for global inspiratory muscle strength and diaphragmatic strength, respectively. Inspiratory muscle endurance was assessed by the length of time a certain inspiratory task could be maintained. RESULTS: In 10 of the 15 patients, respiratory muscle function parameters improved significantly after 1 month of training. Further improvements were to be seen after 3 and after 6 months. Even 6 months after the end of training, those effects remained to a large extent. In the other five patients, there was no such improvement after 1 month of training, which was therefore discontinued. All these five patients had vital capacity values of less than 25 percent predicted and/or PaCO2 values of more than 45 mm Hg. The 15 control patients had no significant change in their respiratory muscle function parameters. CONCLUSION: We conclude that a specific inspiratory muscle training is useful in the early stage of DMD.

Defective endogenous opioid response to exercise in type I diabetic patients.

Plasma beta-endorphin (beta-E) concentration was determined before, during, and after a standardized incremental exercise test to maximal capacity in eight type I diabetic patients and eight normal control subjects. Diabetic patients were studied under normoglycemic and hyperglycemic conditions in a single-blind random fashion to differentiate between the effects of acute hyperglycemia and of diabetes per se on the beta-E response to exercise. The perceived magnitude of leg effort elicited by exercise was evaluated using a category scale. Whereas plasma beta-E concentrations increased in control subjects with increasing workload, causing significantly higher beta-E levels at the end of exercise than at the beginning (P < .001), no such increase could be observed in the diabetic patients under normoglycemic and hyperglycemic conditions. In addition, baseline plasma beta-E concentrations were significantly lower in normoglycemic (P < .01) and hyperglycemic (P < .001) diabetic patients than in control subjects. Even during the recovery period, patients' beta-E levels remained significantly lower than those of control subjects. At submaximal levels of power output, the perceived intensity of leg effort was significantly higher in normoglycemic and hyperglycemic diabetic patients than in control subjects. We conclude that in type I diabetic patients, the ability of the endogenous opioid system to respond to exercise-induced stress is impaired under hyperglycemic and even under normoglycemic conditions. Considering the effect of endogenous opioids on stress tolerance, such changes may compromise exercise performance in diabetic patients.

Functional improvement after volume reduction: sternotomy versus videoendoscopic approach.

BACKGROUND: Volume reduction has been proved to increase ventilatory mechanics in diffuse, nonbullous lung emphysema. However, the best approach is still controversial. METHODS: We retrospectively compared the perioperative data of and functional results in 15 patients having sternotomy (group I) with those of 15 patients having a videoendoscopic approach (group II). RESULTS: The 30-day mortality was 2 patients in group I and 1 patient in group II. Mean duration of chest tube drainage was 8.7 +/- 1.8 days and 8.0 +/- 1.9 days and mean hospital stay, 12.3 +/- 1.9 and 12.5 +/- 2.1 days in groups I and II, respectively. Work of breathing decreased from 1.89 +/- 0.33 J/L and 1.76 +/- 0.22 J/L preoperatively to 0.75 +/- 0.06 J/L and 0.8 +/- 0.06 J/L (p < 0.01 and p < 0.05, respectively) after 3 months; and intrinsic positive end-expiratory pressure decreased from 7.15 +/- 1.31 cm H2O and 6.24 +/- 1.33 cm H2O to preoperatively 0.79 +/- 0.46 cm H2O and 1.13 +/- 0.44 cm H2O (p < 0.005 and p < 0.01, respectively) after 3 months in groups I and II, respectively. Forced expiratory volume in 1 second increased from preoperative values of 21.6% +/- 2.9% and 25.3% +/- 2.4% of predicted to 34.5% +/- 5.0% and 40.9% +/- 7.5% of predicted after 3 months (p < 0.05 in both groups) in groups I and II, respectively. CONCLUSIONS: Both surgical approaches resulted in similar substantial improvement in lung function and physical fitness. The incidence of air leakage, the duration of chest tube drainage, and the hospital stay were the same for both procedures.

Morphologic grading of the emphysematous lung and its relation to improvement after lung volume reduction surgery.

BACKGROUND: The morphologic criteria for lung volume reduction surgery, such as severity and heterogeneity of disease, differ widely between patients, and this makes any comparison of functional results between centers difficult. Here we present a morphologic scoring system and describe its possible relation to functional results after lung volume reduction operations. METHODS: Between September 1994 and December 1996, 47 consecutive patients underwent bilateral lung volume reduction operations. The morphology of emphysema was quantified with standard chest roentgenograms and computed tomographic imaging, which were used to define the following four variables: degree of hyperinflation (grade 0 to 4), degree of impairment in diaphragmatic mechanics, degree of heterogeneity (grade 0 to 4), and severity of parenchymal destruction (range, 0 to 48). RESULTS: All four variables showed good reproducibility. Degree of heterogeneity had a significant influence on functional improvement in terms of forced expiratory volume in 1 second (p = 0.0413, r2 = 0.11). Severity of parenchymal destruction was significantly associated with 30-day mortality: patients who died after operation (n = 4) had a severity of parenchymal destruction of 28.4 +/- 2.1 compared with 21.3 +/- 1.0 for those who survived (n = 43) (p = 0.003). CONCLUSIONS: This morphologic scoring system is easy to use, is reproducible, and allows quantification of the morphology of emphysema, thereby allowing definition of different patient subgroups. Such an exact morphologic quantification may help in the comparison of functional results between centers. Furthermore, the risk factors for certain morphologic subgroups, such as patients with a homogeneous distribution pattern, may be clarified in the future.

Inspiratory muscle performance relative to the ventilatory threshold in healthy subjects.

Inspiratory muscle performance, ventilation, and gas exchange were studied during exercise in healthy subjects to look for typical changes of pattern of contraction at the ventilatory threshold (VT). The steepening of the slope of carbon dioxide output (VCO2) vs oxygen uptake (VO2) at the VT was accompanied by a nonlinear increase of the mean rate of esophageal pressure development (Pes/TI) vs the esophageal pressure time index (PTIes) reflecting both the relative force (Pbreath/Pesmax) and duration (TI/TTOT) required for inspiration. The esophageal pressure time integral within one breath (Pbreath.dTI) was one of the best single predictors of the ventilatory equivalent for oxygen (VE/VO2) at the VT. Moreover, we presented inspiratory muscle load indices as a mirror image of breathing pattern, with the obvious advantage that the ventilation component can be compared with better established methods of presenting ventilatory output. Inspiratory muscle performance during exercise should link the increased metabolic rate to ventilatory output. We conclude that 1) there exists an inspiratory muscle threshold that is well correlated to commonly used gas exchange thresholds, and 2) the efficiency of ventilation and gas exchange during exercise could be linked to pressure and timing of inspiratory muscle contraction.

Is long-term functional outcome after lung volume reduction surgery predictable?

OBJECTIVE: The aim of this retrospective study was to analyze which preoperative parameters might predict a persistent improvement in forced expiratory volume in 1 s (FeV1) 1 year after surgery. METHODS: Seventy consecutive lung volume reduction surgery (LVRS) patients (age, 56.5+/-1.2 years) with a follow-up period of at least 1 year were analyzed (from September 1994 to September 1997). The patients were described by lung function tests, blood gas analysis, ventilatory mechanics (intrinsic positive endexpiratory pressure (PEEP)) and morphometric data (degree of heterogeneity, DHG; degree of hyperinflation, DHI; severity of parenchymal destruction, SPD) preoperatively. Based on the postoperative course of FeV1 (percentual increase compared with preoperative values, % increase), patients were divided into four groups: group A, (n=21) no improvement (FeV1/=20% increase, which declined to preoperative values after 1 year; group C, (n=18) FeV1, 20-40% increase, sustaining at 1 year; group D, (n=21) FeV1>/=40% increase, sustaining at 1 year. The statistics comprised of analysis of variance (ANOVA) and chi-square testing, with values presented as means+/-SEM. RESULTS: No differences were found for lung function parameters (FeV1: 27.7+/-2.7, 26.0+/-2.5, 23. 9+/-2.2 and 23.9+/-1.9% predicted, in groups A, B, C and D, respectively). Arterial blood gas levels preoperatively revealed significant differences between the groups; the arterial pO(2) was 66.2+/-1.2 mmHg in groups A+B compared with 61.8+/-1.5 mmHg in groups C+D (P=0.030). The arterial pCO(2) was 39.2+/-1.1 mmHg in groups A+B compared with 43.3+/-1.5 mmHg in groups C+D (P=0.038). The morphometric data had a strong trend towards higher heterogeneity in groups C and D. Marked DHI was found in 59 and 81% of patients in groups A+B versus C+D, respectively (P=0.121). Marked DHG was present in 22 and 54% of patients in groups A+B versus C+D, respectively (P=0.010). CONCLUSION: Preoperative arterial pO(2) and pCO(2), and the DHG are predictors for long-term benefit after LVRS with regard to the FeV1, 1 year postoperatively.

Functional improvements in ventilatory mechanics after lung volume reduction surgery for homogeneous emphysema.

OBJECTIVE: Between September 1994 and August 1996 Lung Volume Reduction Surgery (LVRS) was performed through median sternotomy, videoendoscopically or by thoracotomy in 54 consecutive patients (age 34-69 years, mean 48 years). METHODS: The areas with the most destroyed lung parenchyma were resected by means of linear stapling devices. A total of 5 patients died postoperatively due to aspiration pneumonia, multiorgan failure and acute hepatic failure respectively. A marked functional improvement and increase in quality of life was observed in the remaining patients. RESULTS: Residual volume decreased from 317.0 +/- 12.4% of predicted (%p) preoperatively to 226.2 +/- 8.8%p within the first month (P = 0.0001). FeV1 significantly increased from 23.7 +/- 1.3%p preoperatively to 36.3 +/- 4.1%p during the first 6 months postoperatively (P = 0.0016). Radiological signs of hyperinflation and distention of the thorax preoperatively improved to a more dome shaped diaphragm and narrowed intercostal spaces. These morphologic changes resulted in better ventilatory muscle function. The intrinsic PEEP significantly decreased from 5.92 +/- 0.64 cm H2O preoperatively to 1.70 +/- 0.25 cm H2O postoperatively (P = 0.0001). The work of breathing decreased from 1.58 +/- 0.09 J/l preoperatively to 0.99 +/- 0.07 J/l postoperatively (P = 0.0001). CONCLUSIONS: In conclusion, LVRS is an excellent therapeutic option for patients with homogeneous emphysema with additional signs of severe hyperinflation.

Chronic hypercapnia should not exclude patients from lung volume reduction surgery.

OBJECTIVE: Chronic hypercapnia is still considered to increase the risk for perioperative mortality and therefore to be a contraindication for lung volume reduction surgery (LVRS). The aim of this study was to analyse the influences of hypercapnia upon postoperative outcome. METHODS: The functional improvement (preop vs. 3 months postop) and clinical outcome was studied in 22 patients with chronic hypercapnia (preoperative arterial pCO2 > or = 45 mmHg) who underwent LVRS between 9/94 and 2/97 and were compared to all other patients (n = 58) without hypercapnia. Data are expressed as the mean +/- SEM. RESULTS: The 30-day mortality was 9.1% (2/22) in patients with chronic hypercapnia (HC) and 5.2% (3/58) in patients with normal arterial pCO2 levels (control) (P = n.s). The stay on the ICU (3.5 +/- 0.8 vs. 2.1 +/- 0.3 days) and duration of chest drainage (7.3 +/- 1.2 vs. 7.2 +/- 0.8 days) was similar between both groups (HC vs. control) (P = n.s). The preoperative lung function (% of predicted) and blood gas (mmHg) parameters were significantly worse in HC patients compared to control patients. In both groups significant functional improvements were observed: FeV1 in the control group increased by 37% within the first 3 months (29.1 +/- 1.7% of predicted vs. 39.9 +/- 3.1% of predicted, P = 0.0198). In the HC group, FeV1 increased by 73% which was even higher than in the controls (19.5 +/- 1.5% of predicted vs. 33.7 +/- 4.7% of predicted, P = 0.0385). All patients of both groups who died perioperatively had a significantly higher severity of parenchymal destruction than those who survived (P = 0.0277 and 0.0380, respectively). CONCLUSIONS: Patients with chronic hypercapnia alone, had no significantly higher mortality and morbidity, and therefore should not be excluded from LVRS. However, the presence of additional risk factors, such as homogeneity of disease, high degree of parenchymal destruction or pulmonary hypertension should be considered as contraindications for the procedure.

Nucleolar silver staining patterns of lymphocytes in sarcoidosis.

Bronchoalveolar lavage lymphocytes from 15 patients with pulmonary sarcoidosis and 8 healthy controls were investigated for nucleolar silver staining patterns and lymphocyte subpopulations. Patients with sarcoidosis had increased numbers of silver stained dots versus controls (2.20 +/- 0.24 versus 1.78 +/- 0.07; p less than 0.001). The number of silver stained dots showed the strongest positive correlation to helper cells (OKT 4+) (r = 0.781; p less than 0.0001). These results may be interpreted as further evidence of lymphocytic activation, especially of helper cells (OKT 4+) in pulmonary sarcoidosis.

[Leucocytoclastic eosinophilic vasculitis with Löffler syndrome]. / Leukozytoklastische eosinophile Vaskulitis bei eosinophilem Lungeninfiltrat "Löffler"

Histologically, leukocytoclastic vasculitis (LV) presents with neutrophilic granulocytes with leukocytoclasia and erythrocyte extravasation, associated with variable counts of lymphocytes, plasma cells and eosinophilic granulocytes. The association of a LV with eosinophilic granulocytes and eosinophilic pneumonia was first described by Chan et al. in 1982. Our case represents the second report in the literature of this rare disease: a 85 year old patient with LV and numerous eosinophilic granulocytes in association with intermittent blood eosinophilia and Löffler syndrome (eosinophilic pulmonary infiltrates). The recurrent episodes were treated successfully with oral corticosteroids.

Evaluation of inspiratory muscle function in a healthy austrian population--practical aspects.

BACKGROUND: There is no clear evidence whether inspiratory muscle strength (Pi(max)) is closely linked to inspiratory muscle endurance (T(lim)). Moreover, normal values of T(lim), measured by flow-resistive loads, have not been established. OBJECTIVES: We tried to find answers to the following questions: Is it possible to establish normative values of T(lim) when using flow-dependent, resistive loads? Are Pi(max) and Borg scale values predictors of T(lim)? Are anthropometric and spirometric data closely related to T(lim)? Is it really necessary to measure T(lim) in addition to Pi(max) when evaluating inspiratory muscle function? METHODS: Sixty-eight healthy Austrian volunteers between 17 and 75 years of age and with a sedentary lifestyle participated in our study. Pi(max) was defined as the maximal inspiratory mouth pressure, measured with a differential pressure transducer. T(lim) was determined as the time span until exhaustion, while breathing against a resistive loading device. RESULTS: Pi(max) values showed a low intra- and high interindividual variability for both sexes and were significantly age, weight and height dependent. For male subjects, Pi(max) was also significantly related to spirometric parameters. T(lim) values showed a very high interindividual variability, but a low intraindividual variability. Interestingly, no correlation was found between T(lim) and Pi(max), nor lung function parameters and age. CONCLUSIONS: The results indicate that both Pi(max) and T(lim) have to be determined when inspiratory muscle function is measured. Normal values for T(lim), evaluated by flow-resistive loads, cannot be satisfactorily established due to the high interindividual variability.

[Changes in ventilatory mechanics in emphysema]. / Atemmechanische Veränderungen beim Emphysem.

The increased airway resistance and hyperinflation characteristic of chronic obstructive pulmonary disease (COPD) affect respiratory muscle function, particularly that of the diaphragm. The compensatory changes of the breathing pattern due to expiratory flow limitation lead to a further increase of the mechanical load on the ventilatory muscles during forced ventilation. Therapeutic strategies which reduce hyperinflation and the increased airway obstruction, improve the neuromechanical efficiency of the inspiratory muscles.