Changes in ventilatory muscle function with negative pressure ventilation in patients with severe COPD

Patients with severe COPD may be in a state of ventilatory muscle (VM) fatigue. In these patients, rapid and shallow breathing has been hypothesized to be a compensatory mechanism that prevents more severe fatigue from taking place. To test these hypotheses, we studied the effects of VM resting in a group of patients with severe COPD. Eleven clinically stable patients with COPD and chronic hypercapnia were studied. Six of them (group A) had a seven-day period of negative pressure-assisted ventilation (NPV), and five (group B) with similar functional characteristics served as a control group. Compared with a normal age-matched control group, both A and B groups exhibited significantly lower tidal volume (VT), inspiratory time (TI), total time of the respiratory cycle (Ttot) and Ti/Ttot ratio, decrease in muscle strength, and greater electromyographic activity of diaphragm (EMGd) and parasternal muscles, but similar ventilation and VT/TI. After the study period, group A exhibited significant increase in VT, Ti, and TI/Ttot (p less than 0.05), and decrease in PaCO2 (p less than 0.05), EMGd, and EMGint (p less than 0.05 for both), and a slight but significant increase in maximal inspiratory pressure (MIP) (p less than 0.05). These data suggest that NPV rests VM, increases their strength, and reduces hypercapnia in patients with severe COPD.     

Respiratory muscle fatigue limiting physical exercise?

Inspiratory muscle fatigue has been documented during loaded breathing or acute respiratory failure, but its role in exercise limitation is still undetermined. Electromyographic (EMG) signs of diaphragmatic fatigue develop in normal subjects hyperventilating above 70% of maximal voluntary ventilation (MVV), a ventilatory level commonly attained at peak exercise. EMG signs of diaphragmatic fatigue also occur during high power cycling exercise in normal subjects and chronic obstructive pulmonary disease (COPD) patients. However, a loss of respiratory muscle strength has rarely been documented following strenuous physical exercise with techniques independent of the subjects' collaboration. Prior inspiratory muscle fatigue decreases exercise tolerance in normal subjects but its effect is largely unknown in COPD patients. Respiratory muscle rest by negative pressure ventilation was reported to improve exercise tolerance in COPD, but this beneficial effect was not confirmed by controlled studies. The effect of inspiratory muscle training on exercise tolerance is still undefined by existing data, in part because of differences in methods and selection criteria between studies. Although respiratory muscle fatigue may occur during exercise, it is not clearly established whether interventions directed at respiratory muscles may improve exercise tolerance in COPD.     

慢性阻塞性肺疾病呼吸训练新方法的临床应用研究

目的 观察针对COPD呼气流速受限的呼吸训练新方法的有效性,期望为COPD患者呼吸训练提供新的更为有效的方法.方法 选取2015年1月至2015年12月我院就诊的40例重度与极重度COPD稳定期患者作为研究对象,随机分成A组和B组,各20例,B组给予基础性药物治疗,A组在B组的基础上给予呼吸训练新方法,比较2组治疗前后的6分钟步行距离(6MWD)、功能性呼吸困难评分(MRC)、最大呼气压力(MEP)、最大吸气压力(MIP)及肺通气功能,同步由患者完成圣乔治呼吸问卷(SGRQ)评分.结果 A组治疗后的MRC、SGRQ评分显著低于治疗前,6MWD、MEP、MIP及深吸气量(IC)显著高于治疗前,差异有统计学意义(P＜0.01),肺功能其他指标包括FEV1、FVC、FEV1/FVC、MVV较训练前无显著性变化(P值均＞0.05).B组6MWD、MRC、SGRQ评分、MEP、MIP及肺通气功能各项指标较8周前无显著变化(P＞0.05).结论 针对COPD呼气流速受限的呼吸训练能明显改善重度至极重度COPD患者的呼吸困难,提高日常生活活动能力和生存质量,增加运动耐力和呼吸肌功能,是一种简单易行的适合于重度至极重度COPD患者的呼吸训练锻炼方法.     

Control of breathing in patients with myasthenia gravis.

Control of breathing has seldom been investigated in patients with myasthenia gravis (MG). We evaluated lung volumes and respiratory muscle strength by measuring maximal inspiratory (MIP) and expiratory (MEP) pressures in 12 patients with moderate generalized (IIb) MG before and after an orally administered therapeutic dose (120 mg) of Mestinon, and in 11 age- and sex-matched normal subjects. Breathing pattern, mouth occlusion pressure (P0.1), and surface electromyographic activity of the diaphragm (EMGd) and intercostal (EMGint) muscles were evaluated during both room-air breathing and hypercapnic rebreathing. Before Mestinon, patients exhibited a slight decrease in VC, and normal TLC and FEV1/VC ratio. Compared with the normal control group, patients also exhibited respiratory muscle weakness (marked decrease in MIP and MEP; p less than 0.001 for both), and more rapid and shallower breathing (RSB): lower tidal volume (VT), inspiratory time (TI), expiratory time (TE), and greater respiratory frequency (f); mean inspiratory flow (VT/TI) and P0.1 were slightly supernormal, whereas both EMGd and EMGint were significantly higher in patients. During hypercapnic rebreathing, ventilation (VE) (p less than 0.001), VT (p less than 0.001), VT/TI, (p less than 0.003), P0.1 (p less than 0.003), and EMGd (p less than 0.001) response slopes to increasing PCO2 were found to be lower, whereas EMGint response slope was normal. At 60 mm Hg of PCO2 in the two groups the difference in terms of breathing pattern, P0.1, and EMGd were similar to that observed during room-air breathing. After Mestinon, VC (p less than 0.005), MIP (p less than 0.02), and MEP (p less than 0.01) significantly increased, whereas spontaneous breathing remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)     

Breathing pattern during and after maximal exercise in patients with chronic obstructive lung disease, interstitial lung disease, and cardiac disease, and in normal subjects

Inspiratory muscle fatigue and pulmonary edema are both known to cause rapid shallow breathing. It has been suggested that exercise tolerance in patients with pulmonary disease and cardiac disease may be limited by the development of inspiratory muscle fatigue and pulmonary edema, respectively, at maximal exercise. If these hypotheses are correct, breathing pattern during recovery from maximal exercise in these patients should be rapid and shallow compared with that during exercise. This study was performed to test these hypotheses. Seven patients with chronic obstructive pulmonary disease (COPD), 8 patients with interstitial lung disease (ILD), 7 patients with cardiac disease (CD) (mitral valve disease or left ventricular dysfunction) and 8 normal (NR) subjects each performed maximal incremental exercise on a cycle ergometer. Exercise breathing pattern was compared with that during recovery by calculating the mean difference in tidal volume (at the same levels of minute ventilation) between exercise and recovery for each subject. Recovery breathing pattern was similar to that during exercise for the COPD, ILD, and NR subjects. In contrast, breathing pattern during recovery was rapid and shallow compared with that during exercise for the CD patients; recovery tidal volume was less than that during exercise for the same level of minute ventilation. The fact that rapid shallow breathing does not develop during recovery from maximal exercise in patients with COPD or ILD suggests that inspiratory muscle fatigue does not limit their exercise tolerance. The relative rapid shallow breathing during recovery from maximal exercise in patients with CD is probably due to the development of pulmonary edema at maximal exercise, but further studies are needed to confirm this.(ABSTRACT TRUNCATED AT 250 WORDS)     

Domiciliary nocturnal nasal intermittent positive pressure ventilation in COPD: mechanisms underlying changes in arterial blood gas tensions.

The improvement in arterial blood gas tensions following assisted ventilation in chronic obstructive pulmonary disease (COPD) has usually been attributed to the relief of incipient or established respiratory muscle fatigue. The contribution of changes in the load placed upon and the drive to the respiratory muscle pump have not been evaluated. We have investigated the contribution of changes in respiratory muscle strength, the ventilatory response to CO2 and ventilatory function to changes in arterial blood gas tensions in eight patients with severe COPD completing six months domiciliary nasal intermittent positive pressure ventilation. Six patients showed a reduction and two an increase in arterial carbon dioxide tension (PaCO2), median (range) for eight patients, -0.9 kPa (-1.5 to +0.4) (p less than 0.05) and seven showed an improvement in arterial oxygen tension (PaO2), +0.7 kPa (-0.4 to +1.7) (p less than 0.05) during daytime spontaneous breathing. The reduction in PaCO2 was not related to increased inspiratory muscle strength but was correlated with a decrease in gas trapping (Spearman rank correlation coefficient (r(S)) 0.85, p less than 0.05) and in the residual volume (r(s) 0.78, p less than 0.05), suggesting reduced small airway obstruction and, therefore, a reduction in load. The change in PaCO2 also correlated with the increase in ventilation at an end-tidal CO2 of 8 kPa during rebreathing (r(s) -0.76, p less than 0.05) suggesting improved chemosensitivity to CO2. Our data do not support the hypothesis that improvements were due to the relief of muscle fatigue. We suggest that the contribution of changes in load and central drive warrant further investigation.     

Effect of digoxin on respiratory muscle performance in patients with COPD.

The effect of 2 weeks oral digoxin administration on respiratory muscle performance (RMP) in 14 patients with chronic obstructive lung disease (COPD) was investigated in a randomized double-blind placebo-controlled cross-over study. All patients were ambulatory with severe air flow obstruction. FEV1/FVC was 0.44 +/- (SD) 0.11, FEV1 was 0.88 +/- (SD) 0.35 liter/s RMP was assessed by measuring maximal inspiratory pressure (PImax), maximal expiratory pressure (PEmax), and maximal voluntary ventilation. Although these parameters were significantly reduced in the COPD patients, 2 weeks of digoxin administration (with serum levels in the therapeutic range) did not alter any parameter of RMP or spirometry. We conclude that digoxin has no effect on RMP or spirometry in ambulatory patients with severe COPD.     

Inspiratory muscle training in patients with COPD: effect on dyspnea, exercise performance, and quality of life

OBJECTIVE: The aim of the study was to assess the effect of target-flow inspiratory muscle training (IMT) on respiratory muscle function, exercise performance, dyspnea, and health-related quality of life (HRQL) in patients with COPD. PATIENTS AND METHODS: Twenty patients with severe COPD were randomly assigned to a training group (group T) or to a control group (group C) following a double-blind procedure. Patients in group T (n = 10) trained with 60 to 70% maximal sustained inspiratory pressure (SIPmax) as a training load, and those in group C (n = 10) received no training. Group T trained at home for 30 min daily, 6 days a week for 6 months. MEASUREMENTS: The measurements performed included spirometry, SIPmax, inspiratory muscle strength, and exercise capacity, which included maximal oxygen uptake (VO(2)), and minute ventilation (VE). Exercise performance was evaluated by the distance walked in the shuttle walking test (SWT). Changes in dyspnea and HRQL also were measured. RESULTS: Results showed significant increases in SIPmax, maximal inspiratory pressure, and SWT only in group T (p < 0.003, p < 0.003, and p < 0.001, respectively), with significant differences after 6 months between the two groups (p < 0.003, p < 0.003, and p < 0.05, respectively). The levels of VO(2) and VE did not change in either group. The values for transitional dyspnea index and HRQL improved in group T at 6 months in comparison with group C (p < 0.003 and p < 0.003, respectively). CONCLUSIONS: We conclude that targeted IMT relieves dyspnea, increases the capacity to walk, and improves HRQL in COPD patients.     

慢性阻塞性肺疾病患者运动耐力下降的生理学研究

目的研究平板踏车联合无创正压通气（NIPPV）运动锻炼对COPD患者呼吸生理学的影响,探讨与运动耐力改善相关的生理学机制,期望为COPD患者呼吸康复提供新的更为有效的方法。方法按2011年修订版GOLD标准选择稳定期重度至极重度COPD患者为研究对象,分为3组：即平板踏车联合NIPPV运动锻炼组（A组）、平板踏车运动锻炼组（B组）、既无NIPPV又无平板踏车运动锻炼组（C组）,每组观测20例。在运动锻炼前后分别测定6MWD、MRC评分、MEP、MIP及肺通气功能。结果经平板踏车联合NIPPV运动锻炼后COPD患者6MWD、MEP、MIP明显增加（P〈0．01）,MRC评分明显降低（P〈0．01）,肺功能FEV1％pred、FEV1／FVC、MVV、PEF等指标稍有改善,但锻炼前后差异无统计学意义（P〉0．05）;而MVV则有明显改善（P〈0．01）,差异具有统计学意义。结论重度至极重度稳定期COPD患者在平板踏车上进行面罩NIPPV运动锻炼有助于改善其运动耐力和吸气肌力,缓解呼吸困难,是一种较好的适合于重度至极重度稳定期cOPD患者的呼吸康复锻炼方法。     

慢性阻塞性肺疾病撤机困难呼吸力学特征10例分析

目的为提高慢性阻塞性肺疾病(COPD)患者撤机成功率提供生理学依据。方法检测2006年1月至2009年12月广州医学院第一附属医院收治的10例撤机困难COPD患者的呼吸力学指标,观察患者自主呼吸(SB)及机械通气时的呼吸力学指标变化。结果 SB时的呼吸频率(RR)、潮气量(VT)和分钟通气量(Ve)分别为(27.94±8.23)次/min、(0.266±0.107)L和(6.843±1.333)L/min,机械通气时的RR降低,而VT和Ve时升高(均P<0.05)。SB和机械通气时的动态内源性呼吸末正压分别为(0.82±0.19)kPa和(0.41±1.12)kPa,SB时明显增高(P<0.01),吸气中期气道阻力(RL)(2.43±0.94)kPa/(L.S)。SB时的P0.1为(0.61±0.16)kPa。SB时的最大跨膈压、最大食管负压和最大吸气口腔压分别为(5.08±0.93)kPa、(-5.00±0.95)kPa和(-3.78±0.86)kPa。SB时跨膈压(Pdi)和吸气压力时间乘积(PTPins)分别为(0.82±0.20)kPa和(48.93±11.94)kPa.s;机械通气时较SB显著降低,分别为(0.67±0.17)kPa和(30.33±11.72)kPa.s(P均<0.05)。结论撤机困难COPD患者存在显著的呼吸力学异常,SB时呼吸浅快,动态内源性呼吸末正压、RL与呼吸中枢驱动等均增高,吸气肌肉无力;应用PSV(1.57 kPa)联合PEEP(48%动态内源性呼吸末正压)可降低约50%的动态内源性呼吸末正压、17.8%的Pdi和38%的PTPins。     

Importance of noninvasively measured respiratory muscle overload among the causes of hospital readmission of COPD patients

AIM: To evaluate the influence of respiratory muscle overload and right cardiac overload among the possible risk factors of hospital readmission in a 1-year follow-up of a cohort of patients with moderate-to-severe COPD. METHODS: A total of 112 COPD patients who were admitted consecutively to the hospital for acute exacerbation. At hospital discharge, we evaluated the conventional clinical and functional determinations in addition to the pressure-time index (PTI), which is obtained using the equation PTI = (Pawo/Pimax) x (Ti/Ttot) x 100, where Pawo represents the mean airway pressure measured at the mouth during spontaneous breathing, Pimax is the maximal inspiratory pressure, Ti is the inspiratory time, and Ttot is the total breathing cycle time. A cardiac echo-Doppler examination was carried out when patients were in stable condition and presented clinical signs of right cardiac overload prior to inclusion in the study. RESULTS: Multivariate analysis showed that the use of long-term oxygen therapy (LTOT) and high PTI (> 0.25) were independently related to the risk of hospital readmission. Patients receiving LTOT had higher Paco(2) (p < 0.05), FEV(1) percent predicted (p < 0.05), FVC percent predicted (p < 0.05), and Pao(2) (p < 0.05), and had higher Paco(2) (p < 0.05). An elevated systolic pulmonary arterial pressure (> 40 mm Hg) was also independently related, but only 28 patients had echo-Doppler data that could be used. CONCLUSIONS: At hospital discharge, noninvasively measured respiratory muscle overload as well as the use of LTOT were associated with an increased risk of hospital readmission for exacerbation in patients with moderate-to-severe COPD.     

Inspiratory force reserve of the respiratory muscles in children with chronic obstructive pulmonary disease

The purpose of this study was to evaluate inspiratory muscle force reserve in children with chronic obstructive pulmonary disease (COPD). In 15 hyperinflated (FRC/TLC, 65 +/- 0.7%) children, maximal mouth inspiratory static pressure (PImax) at FRC, mouth occlusion pressure (P0.1), tidal volume (VT), inspiratory time (TI), and total duration of the respiratory cycle (Ttot) were all measured. It was found that PImax at FRC was reduced compared with predicted values. However, after lung volume correction, PImax was in the normal range, and P0.1 was higher, TI was shorter, and Ti/Ttot was lower than predicted. The estimated mean inspiratory pressure for breathing at rest (PI) was significantly higher than predicted and was related to total pulmonary resistance (r = 0.74, p less than 0.001). The fraction of PImax developed by the respiratory muscles for breathing at rest (PI/PImax) significantly increased. The higher the PI/PImax ratio, the more the TI/Ttot ratio decreased (r = -0.64, p = 0.01). At rest, our subjects had to develop a mean inspiratory power (W) of as much as 48% (range, 30 to 76%) of the critical W above which fatigue occurs. Thus, even minimal increases in breathing load might expose children with COPD to respiratory muscle fatigue and to respiratory failure.     

The pattern of respiratory muscle recruitment during pursed-lip breathing.

Data from the present study indicate a change in the pattern of chest wall muscle recruitment and improved ventilation with pursed-lip breathing (PLB) in COPD. Pursed lip breathing led to increased rib cage and accessory muscle recruitment during inspiration and expiration, increased abdominal muscle recruitment during expiration, decreased duty cycle of the inspiratory muscles and respiratory rate, and improved SaO2. In addition, PLB resulted in no change in pressure across the diaphragm and a less fatiguing breathing pattern of the diaphragm. Changes in chest wall muscle recruitment and respiratory temporal parameters concomitant with the increased SaO2 indicate a mechanism of improving ventilation with PLB while protecting the diaphragm from fatigue in COPD. Alterations in the pattern of respiratory muscle recruitment with PLB may be associated also with the amelioration of dyspnea. Further investigation is necessary to explore the relationship between the pattern of respiratory muscle recruitment during PLB and dyspnea.     

Respiratory and limb muscle function in lung allograft recipients.

Lung transplantation recipients have reduced exercise capacity despite normal resting pulmonary and hemodynamic function. The limiting factor may be contractile dysfunction of skeletal muscle. To test this postulate, we measured limb and respiratory muscle function in nine clinically stable lung allograft recipients (six men and three women, aged 30 to 65 yr, at 5 to 102 mo after transplantation) with reduced exercise capacity. Respiratory muscle strength was tested by measuring maximal inspiratory and expiratory pressure (MIP and MEP, respectively). Ankle dorsiflexor muscle strength was measured during maximal voluntary contraction (MVC). In a subset of six recipients, we also measured contractile properties and fatigue characteristics of the tibialis anterior muscle, using electrical stimulation of the motor point. Data were compared with values from age- and sex-matched control subjects. MIP values of transplant recipients did not differ from control values; however, MEP was blunted by 30% relative to control (p < 0.05), and MVC was decreased by 39% (p < 0.05). The force-frequency relationships and fatigue characteristics of the tibialis anterior were not different between the patient and control groups. We conclude that stable lung allograft recipients experience expiratory and lower limb weakness that may contribute to exercise intolerance.     

Maximal inspiratory and expiratory pressure measurement in tracheotomised patients.

The present study compared four different sites and conditions for the measurement of maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) in 38 spontaneous breathing tracheotomised patients. Of the patients, 28 had chronic obstructive pulmonary disease (COPD). The four different conditions were: 1) through a cuff inflated cannula (condition A); 2) through the mouth with a deflated cannula (condition B); 3) through the mouth with a phonetic uncuffed cannula (condition C); and 4) through the mouth after stoma closure (condition D). Five trials in each condition were performed using a standardised method. The measurement of both MIP and MEP differed significantly depending on the condition of measurement. MIP taken in condition A was significantly higher when compared with conditions B, C and D. MEP in condition A was significantly higher when compared with condition B and D. In condition A the highest frequency of the best measurement of MIP and MEP was observed at the fourth and fifth effort, respectively. The same results were obtained after the selection of only COPD patients. In conclusion, respiratory muscle assessment differs significantly depending on measurement condition. Measurement through inflated cannula tracheotomy yields higher values of both maximal inspiratory and maximal expiratory pressure.     

无创正压通气抑制慢性阻塞性肺疾病急性加重期患者吸气肌肉活动的机制

目的探讨无创正压通气（NIPPV）抑制慢性阻塞性肺疾病（COPD）急性发作期患者吸气肌肉活动的机制。方法12例COPD急性加重期患者接受感觉最舒适通气压力水平时的NIPPV,观察患者吸气肌肉用力和呼吸方式的变化。结果与自主呼吸（SB）相比,NIPPV时的潮气量（VT）显著增高（从408ml升到462ml,P〈0.05）;接受NIPPV后VT的增高很迅速,第一呼吸周期时即明显增高。SB时的跨膜压（Pdi）为14.04cmH2O,而NIPPV时为10.98cmH2O,比SB时约减少22%（P〈0.05）。NIPPV时Pdi的下降从第一个呼吸周期即开始,然后进一步迅速下降,治疗至第5个呼吸周期时与SB时相比开始有显著差异（P〈0.05）。SB时的呼吸肌做功（Wp）分别为0.47J/breath和0.95J/L;而NIPPV时分别为0.34J/breath和0.69J/L,比SB时分别减少28%和27%（P〈0.05）。NIPPV时Wp的下降也是从第一个呼吸周期即开始,然后进一步迅速下降,治疗至第5个呼吸周期时与SB时相比开始有显著差异（P〈0.05）。结论本实验证实了NIPPV治疗COPD急性加重期患者时吸气肌肉活动的非化学性抑制作用的存在;这种非化学性抑制作用的产生与NIPPV治疗的开始基本同步,能有效改善患者的呼吸肌肉疲劳。     

The effect of hyperinflation on respiratory muscles and breathing pattern in COPD

Lung hyperinflation is a consequence of airway obstruction, increased airway resistance and compliance in patients with chronic obstructive pulmonary disease (COPD) which may result in respiratory muscle fatigue and deterioration of gas transfer. The aim of this study was to investigate the influence of hyperinflation on respiratory muscles, gas transfer and breathing pattern and compare the differences between mild and severe COPD. Twenty-eight COPD patients with radiological and tomographic evidence of emphysema were included in the study and they were divided into two groups according to the severity of COPD. Group I= FEV(1) < or = 49% (n= 16). Group II= FEV(1) > or = 50% (n= 12). Airflow rates were decreased and airway resistance was increased significantly in Group I. Maximal inspiratory pressure (MIP) was significantly reduced in Group I. FRC, RV and RV/TLC ratio were increased above 120% in both groups with more significant increase in Group I. Group I showed moderate hypoxemia (PaO(2) = 54.02 mmHg) with hypercapnia (PaCO(2)= 46.65 mmHg) whereas Group II patients were mildly hypoxemic (PaO(2)= 63.78 mmHg) with normocapnia. Parameters of breathing pattern were similar in both groups. Diaphragm height index (DHI) didn't showed significant difference between groups. But there were significant correlations between DHI and RV, FRC. MIP showed significant positive correlation with airflow rates and DLCO, negative correlation with lung volumes, positive correlation with PaO(2) and negative correlation with PaCO(2). FRC also negatively correlated with Ti and Ti/Ttot. In conclusion, hyperinflation present even in the mild forms of COPD causes inspiratory muscle weakness which in return results in impairment in gas transfer.     

Effects of 8-week, interval-based inspiratory muscle training and breathing retraining in patients with generalized myasthenia gravis

STUDY OBJECTIVE: To assess the effect of interval-based inspiratory muscle training (IMT) combined with breathing retraining (BR) in patients with generalized myasthenia gravis (MG) in a partial home program. DESIGN: A randomized controlled trial with blinding of outcome assessment. SETTING: A secondary-care respiratory clinic. PATIENTS: Twenty-seven patients with generalized MG were randomized to a control group or a training group. INTERVENTIONS: The training group underwent interval-based IMT associated with BR (diaphragmatic breathing [DB] and pursed-lips breathing [PLB]) three times a week for 8 weeks. The sessions included 10 min each of DB, interval-based IMT, and PLB. Interval-based IMT consisted of training series interspersed with recovery time. The threshold load was increased from 20 to 60% of maximal inspiratory pressure (P(Imax)) over the 8 weeks. MEASUREMENTS AND RESULTS: Lung function, respiratory pattern, respiratory muscle strength, respiratory endurance, and thoracic mobility were measured before and after the 8 weeks. The training group improved significantly compared to control group in P(Imax) (p = 0.001), maximal expiratory pressure (P(Emax)) [p = 0.01], respiratory rate (RR)/tidal volume (V(T)) ratio (p = 0.05), and upper chest wall expansion (p = 0.02) and reduction (p = 0.04). Significant differences were seen in the training group compared to baseline P(Imax) (p = 0.001), P(Emax) (p = 0.01), maximal voluntary ventilation (p = 0.02), RR/V(T) ratio (p = 0.003), Vt (p = 0.02), RR (p = 0.01), total time of RR (p = 0.01), and upper chest wall expansion (p = 0.005) and reduction (p = 0.005). No significant improvement was seen in lower chest wall or lung function. CONCLUSIONS: The partial home program of interval-based IMT associated with BR is feasible and effective in patients with generalized MG. Improvements in respiratory muscle strength, chest wall mobility, respiratory pattern, and respiratory endurance were observed.     

Mechanism of CO(2) retention in patients with neuromuscular disease

BACKGROUND: In many studies of patients with muscle weakness, chronic hypercapnia has appeared to be out of proportion to the severity of muscle disease, indicating that factors other than muscle weakness are involved in CO(2) retention. In patients with COPD, the unbalanced inspiratory muscle loading-to-strength ratio is thought to trigger the signal for the integrated response that leads to rapid and shallow breathing and eventually to chronic hypercapnia. This mechanism, although postulated, has not yet been assessed in patients with muscular dystrophy. SUBJECTS: Twenty consecutive patients (mean age, 47.6 years; range, 23 to 67 years) were studied: 11 patients with limb-girdle dystrophy, 3 with Duchenne muscular dystrophy, 1 with Charcot-Marie-Tooth syndrome, 1 with Becker muscular dystrophy, 1 with myotonic dystrophy, 1 with facioscapulohumeral dystrophy, and 2 with amyotrophic lateral sclerosis, without any respiratory complaints. Seventeen normal subjects matched for age and sex were studied as a control group. METHODS: Routine spirometry and arterial blood gases, maximal inspiratory and expiratory muscle pressures (MIP and MEP, respectively), and pleural pressure during maximal sniff test (Pplsn), were measured. Mechanical characteristics of the lung were assessed by evaluating lung resistance (RL) and dynamic elastance (Eldyn). Eldyn was assessed as absolute value and as percent of Pplsn; Eldyn (%Pplsn) indicates the elastic load per unit of inspiratory muscle force. Breathing pattern was assessed in terms of time (inspiratory time [TI]; respiratory frequency [Rf]) and volume (tidal volume [VT]) components of the respiratory cycle. RESULTS: A rapid shallow breathing pattern, as indicated by a greater Rf/VT ratio and a lower TI, was found in study patients compared to control subjects. Eldyn was greater in study patients, while MIP, MEP, and Pplsn were lower. PaCO(2) inversely related to VT, TI, and Pplsn (p = 0.012, p = 0.019, and p = 0.002, respectively), whereas it was directly related to Rf, Rf/VT, Eldyn, and Eldyn (%Pplsn) (p < 0.004 to p < 0.0001). Also Eldyn (%Pplsn) inversely related to TI, and the latter positively related to VT. In other words, increase in Eldyn (%Pplsn) was associated with decrease in TI, and the latter was associated with lower VT and greater PaCO(2). Mechanical and breathing pattern variables were introduced in a stepwise multiple regression that selected Eldyn (%Pplsn) (p < 0.0001; r(2) = 0.62) as a unique independent predictor of PaCO(2). CONCLUSIONS: The present study shows that in patients with neuromuscular disease, elastic load and respiratory muscle weakness are responsible for a rapid and shallow breathing pattern leading to chronic CO(2) retention.     

Tests of respiratory muscle function

Respiratory muscle strength and endurance should be assessed when dyspnea, respiratory failure, or poor performance on routine pulmonary function tests are unexplained. Respiratory muscle strength can be measured non-invasively from maximal mouth pressures, but measurement of transdiaphragmatic pressure refines the assessment. The maximal voluntary ventilation test is the only simple index of ventilatory or respiratory muscle endurance. Other tests for endurance and fatigue are more difficult, but some newer techniques may be applicable to the clinical laboratory. Some patients who exhibit tachypnea, marked use of neck inspiratory muscles, and chest-abdomen asynchrony may be developing respiratory muscle fatigue.