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.     

Inspiratory muscle weakness and dyspnea in chronic heart failure.

Dyspnea is a common, disabling symptom in chronic heart failure, yet the underlying mechanisms remain unknown. The respiratory muscle pump is composed of skeletal muscles whose strength directly influences the pump's performance. Respiratory muscle weakness is important in the dyspnea experienced by some patients with pulmonary disease; however, the role of the respiratory muscle pump in the dyspnea of chronic heart failure has not previously been examined. To assess respiratory muscle strength and its relation to dyspnea during daily activity, we measured maximum inspiratory and expiratory mouth pressures as indices of respiratory muscle strength and the baseline dyspnea index in nine stable, chronic cardiac pump failure patients who had no evidence of primary lung disease, and in nine age- and sex-matched healthy control subjects. The chronic heart failure patients, when compared with their matched control subjects, had reduced inspiratory and expiratory muscle strength, and both inspiratory and expiratory muscle strength were significantly correlated with dyspnea during daily activity (r2 = 0.80, p = 0.001 and r2 = 0.45, p = 0.05, respectively). Inspiratory muscle strength accounted for all of the variance in dyspnea that was correlated with respiratory muscle strength when the relative contributions of inspiratory and expiratory muscle strength were examined. There was no correlation between lung volumes or spirometry and dyspnea in the heart failure patients. These findings indicate that patients with stable chronic heart failure have inspiratory and expiratory muscle weakness and further suggest that the respiratory muscle pump significantly contributes to the dyspnea during the activities of daily living.     

A case of nemaline myopathy with associated dilated cardiomyopathy and respiratory failure

Nemaline myopathy is a representative form of congenital myopathy, and is characterized by nemaline bodies in muscle fibers. Here we report a 47-year-old man with congenital nemaline myopathy complicated with dilated cardiomyopathy-related heart failure, and restrictive respiratory failure. The complication of dilated cardiomyopathy in nemaline myopathy has rarely been reported. In this case, nemaline bodies were detected in the cardiac muscle fibers, demonstrating the presence of underlying disease-related myocardial degeneration. The patient responded to the combination of conventional therapy for heart failure including β-blocker and noninvasive continuous positive-pressure ventilation for respiratory failure. His general condition has been stable during a 10-month follow up period.     

A case of polymyositis complicated with myasthenic crisis

We report a 62-year-old woman who suffered from polymyositis (PM) complicated with myasthenic crisis. Electromyography and muscle biopsy indicated a diagnosis of PM; however, respiratory failure due to respiratory muscle weakness was seen in spite of a normal serum creatine kinase (CK) level. The positive anti-acetylcholine receptor antibody led us to the diagnosis of myasthenic crisis. PM with respiratory muscle weakness is rare. We suggest that the possibility of other neurological disorder complications should be considered when PM patients have respiratory muscle weakness out of proportion to the serum CK level.     

Clinical study on respiratory muscle training for chronic respiratory failure]

The purpose of respiratory muscle training for patients with chronic respiratory failure is to improve exercise performance during daily life. Firstly, to confirm the clinical effect on respiratory muscle training, the abdominal pad method for inspiratory muscle training and abdominal pad method with expiratory resistor for both inspiratory and expiratory muscle training were simultaneously performed. Both methods were clinically useful to increase respiratory muscle power and to subjectively decrease dyspnea. Ventilatory pattern analyzed by the Konno-Mead (K-M) diagram during exercise also showed their effectiveness. Secondly, the influence of hypoxemia and hypophosphatemia, which are important factors producing respiratory muscle fatigue, was investigated in a patient with respiratory failure. (1) O2 inhalation in patients receiving home oxygen therapy was effective in terms of the endurance time and ventilatory pattern analyzed by the K-M diagram during exercise. (2) A case of hypercapnea due to hypoventilation caused by respiratory muscle fatigue developed reduced PaCO2 following correction of serum phosphate level, suggesting that hypophosphatemia is an important clinical factor producing respiratory muscle fatigue.     

Reversible respiratory muscle weakness in hyperthyroidism

Breathlessness is a common complaint in patients with hyperthyroidism, and respiratory failure requiring artificial ventilation, although rare, can occur. While a proximal myopathy is frequently recognized, diaphragm muscle function has not hitherto been studied in detail in thyrotoxicosis. The strength of the quadriceps femoris and respiratory muscles was therefore assessed in seven consecutive thyrotoxic patients, on presentation and during medical treatment, when euthyroid. Prior to therapy, reduced quadriceps muscle strength, vital capacity, and global expiratory and inspiratory muscle strength were found. Diaphragmatic weakness was present in one of four patients studied by measuring transdiaphragmatic pressures during maximal sniffs and during bilateral phrenic nerve stimulation at 1 Hz (twitch). After treatment, significant improvement occurred in quadriceps muscle strength, vital capacity, and global respiratory muscle strength. Sniff and twitch transdiaphragmatic pressures also increased significantly. These results indicate that respiratory muscle weakness occurs in hyperthyroidism and that such weakness is reversible with medical treatment. It is important to realize that respiratory muscles may be directly affected when assessing thyrotoxic patients with breathlessness, as severe involvement of the respiratory muscles may cause respiratory failure.     

Use of volume-targeted non-invasive bilevel positive airway pressure ventilation in a patient with amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease in which most patients die of respiratory failure. Although volume-targeted non-invasive bilevel positive airway pressure (BPAP) ventilation has been studied in patients with chronic respiratory failure of various etiologies, its use in ALS has not been reported. We present the case of a 66-year-old woman with ALS and respiratory failure treated with volume-targeted BPAP ventilation for 15 weeks. Weekly data downloads showed that disease progression was associated with increased respiratory muscle weakness, decreased spontaneous breathing, and increased use of non-invasive positive pressure ventilation, whereas tidal volume and minute ventilation remained relatively constant.     

无创正压通气治疗慢性阻塞性肺疾病急性呼吸衰竭

无创正压通气已经广泛用于慢性阻塞性肺疾病急性加重期的治疗,主要适应证包括呼吸增快、动脉氧分压下降、二氧化碳分压升高和呼吸性酸中毒,颜面部畸形、严重意识障碍、呼吸心跳停止以及血流动力学不稳定是其主要禁忌证。无创正压通气能够减轻呼吸肌负荷、减轻呼吸肌疲劳,具有降低患者病死率和气管插管率的作用。无创正压通气治疗时给予足够的压力支持和治疗时间是取得治疗效果的重要保证。     

Respiratory muscle blood flow

Respiratory muscle fatigue appears to be the cause of hypercapnic respiratory failure in many patients with lung disease. Recent studies have suggested that the rate of development of respiratory muscle fatigue largely depends on the balance between the level of respiratory muscle blood flow and the metabolic demands of these muscles. Physiological factors that alter muscle blood flow (for example, cardiogenic or septic shock, alterations in muscle length) or respiratory muscle metabolic demands (for example, increases in the work of breathing) may influence this balance, affecting the rate of development of respiratory muscle fatigue in these patients. Therapeutic measures that augment respiratory muscle blood flow (restoration of normal arterial pressure in patients in shock) or reduce the work of breathing (for example, mechanical ventilation) may prevent or reverse respiratory muscle fatigue.     

Noninvasive measurement of respiratory muscle performance after exhaustive endurance exercise.

The use of noninvasive techniques to measure respiratory muscle performance after different types of endurance exercise has not been entirely successful, as the results have not consistently indicated diminished performance for similar types of exercise. The aim of the present study was 1) to compare different, noninvasive methods to assess respiratory muscle performance before and after an exhaustive cycling endurance test (which has previously been shown to induce diaphragmatic fatigue) and 2) to determine which of the tests best reflect published results of measurements of diaphragmatic fatigue. Twelve healthy subjects participated in the study and performed three different test series in a random order on three different days. These tests were performed before, and 5, 40 and 75 min after an exhausting task (a cycling endurance run at 85% of maximal oxygen uptake (V'O2,max)). The tests of the three test series were 1) breathing against a constant inspiratory resistance to task failure, 2) determination of 12-min sustained ventilatory capacity, and 3) spirometric and maximal inspiratory and expiratory mouth pressure measurements. The only measurement that was affected by exhaustive cycling was the time to task failure breathing against inspiratory resistance. It was significantly reduced from (mean+/-sD) 364+/-88 s before exercise to 219+/-122 s at 5 min after cessation of exercise. It is concluded that the constant-load resistive breathing test to task failure is the only noninvasive respiratory muscle performance test evaluated in this study which shows a decrease in respiratory muscle performance after exhaustive endurance exercise.     

Respiratory failure due to altered central drive during inspiratory loading in rabbits

Mechanisms of respiratory muscle dysfunction leading to respiratory failure during incremental inspiratory threshold loading were studied in unbound spontaneously breathing rabbits during light and deeper anesthesia. Low or high frequency contractile fatigue was not found at the point of respiratory failure in any of the animals. On the other hand, alterations in central drive to the diaphragm played a dominant role in the observed respiratory failure. In animals receiving light anesthesia the intensity of central drive increased with loading, but then fell as respiratory failure approached. In all animals the intensity of central drive at peak activation and at the point of respiratory failure was submaximal, in spite of the diaphragm's ability to generate additional forces. In addition, the time tension index of the diaphragm rose in response to increasing loads to a level reported to produce contractile fatigue, at which time the index peaked and then fell in spite of increasing load demands. The fall in the time tension index as respiratory failure approached was due primarily to a fall in inspiratory time and duty cycle. Ultimately, there was an abrupt cessation in central drive resulting in apnea. These findings suggest that alterations in central drive play a major role in respiratory muscle dysfunction and respiratory failure associated with inspiratory loading in unbound spontaneously breathing rabbits.     

Two cases of nemaline myopathy diagnosed after episodes of respiratory failure]

Here we report two cases of congenital myopathy visited our hospital with respiratory failure. Case 1 was a 31-year-old woman, who had muscular weakness from birth but had never been diagnosed. She had an onset of pneumonia followed by severe type 2 respiratory failure. Even after the healing of pneumonia, hypercapnia remained. A diagnosis of nemaline myopathy was made after muscle biopsy. Case 2 is a 62-year-old man, who had slowly progressing respiratory failure accompanied with severe hypercapnea. His respiratory failure was improved by NIPPV. He also under went muscle biopsy and nemaline myopathy was diagnosed. Nemaline myopathy is one of congenital myopathy and is known to be a nonprogressive or slowly progressive disorder. However, some patients are diagnosed appropriately only when adult onset acute respiratory failure occurs.     

双水平无创正压通气治疗煤工尘肺合并呼吸衰竭临床研究

目的观察双水平无创正压通气(BiPAP)对煤工尘肺(CWP)合并呼吸衰竭的治疗作用。方法将56例煤工尘肺合并呼吸衰竭的患者随机分成治疗组(32例)和对照组(24例),比较两组治疗前后血气分析指标及临床症状改善情况。结果治疗组经无创正压通气治疗后临床症状及血气分析指标恢复正常,呼吸频率下降,心率下降,辅助呼吸肌活动明显减轻和消失,与对照组的血气分析指标及临床疗效比较,差异有显著性(P<0.01),结论双水平无创正压通气在煤工尘肺(CWP)合并呼吸衰竭的治疗中依从性强,解除呼吸肌疲劳,纠正呼吸衰竭,疗效肯定。     

Acute hypercapnic respiratory failure due to thyrotoxic periodic paralysis

Acute hypercapnic respiratory failure is a potentially life-threatening complication of profound hypokalemia usually seen in patients with large total-body potassium (K+) deficits. It has rarely been reported in thyrotoxic periodic paralysis (TPP), which is due to intra-cellular shifts of K+. The authors report on a 29-year-old man who presented with sudden onset of muscle paralysis in all extremities and acute progressive respiratory insufficiency requiring artificial respiratory support. He was treated with intravenous KCl. After six hours, muscular strength had returned to normal, with plasma K+ concentration of 3.0 mmol/L. At the eighth hour, rebound hyperkalemia (6.6 mmol/L) developed with high-tented T waves, even after the KCl was discontinued. Ventilatory support was uneventfully weaned at 14 hours. Elevated free thyroxine and undetectable thyroid-stimulating hormone confirmed the diagnosis of TPP. TPP should be kept in mind as a cause of acute respiratory failure in association with acute muscle weakness to avoid delayed diagnosis and improper management.     

Reversible respiratory failure due to rhabdomyolysis associated with cytomegalovirus infection

A 58-year-old woman presented with muscle weakness, whole body myalgia, and dyspnea. On admission, neurological examination showed proximal muscle weakness in the extremities. The weakness gradually extended to the bulbar and respiratory muscles, necessitating an artificial ventilator. Serum CK level was markedly increased (33,774 IU/L; normal <150 IU/L) and myoglobinuria was noted in urinalysis. There was no sign of renal failure. Nerve conduction study was normal, but needle EMG showed myopathic changes in the weak muscles. Serological studies for virus titers showed more than a four-fold increase of cytomegalovirus (CMV) antibody titer during the disease course. The IgM anti-GM2 antibody was also elevated in the acute phase and decreased in the recovery phase. The muscle weakness and respiratory failure gradually improved after intravenous methylprednisolone administration, and the serum CK level was normalized in several days. CMV infection was thought to have played a central role in the rhabdomyolysis, leading to critical but reversible respiratory muscle paralysis.     

Acid maltase deficiency in adults presenting as respiratory failure.

During the past nine years 10 patients with the adult form of acid maltase deficiency have been observed at the Mayo Clinic. Three of the adults presented with respiratory failure. In all three the respiratory manifestations dominated the clinical picture and the cause of the respiratory failure (muscle weakness) and the underlying myopathy (glycogen storage disease) were initially unsuspected. Careful evaluation of the respiratory function tests, including the maximal static respiratory pressures, electromyographic examination and histochemical and biochemical studies of muscle biopsy specimens eventually led to the correct diagnosis.     

Nocturnal nasal IPPV stabilizes patients with cystic fibrosis and hypercapnic respiratory failure.

Nocturnal nasal intermittent positive pressure ventilation (nIPPV) has been used successfully in the management of patients with respiratory failure due to chest wall deformity and neuromuscular disease. In order to determine if nIPPV is useful in patients with cystic fibrosis (CF) complicated by respiratory failure, we treated four hypercapnic patients for up to 18 months. All patients had failed to respond to intensive conventional therapy, including nocturnal nasal CPAP in three of the patients. Within a few days of commencing nIPPV, all reported improved length and quality of sleep. There was lessening of the degree of hypercapnia and an increase in respiratory muscle strength. After stabilization in the hospital, all patients were able to be discharged home receiving nocturnal assisted ventilation. The improvements seen in these patients have been maintained for up to 18 months. We believe nIPPV offers an effective therapeutic approach for patients with end-stage CF in hypercapnic respiratory failure and may be particularly advantageous for those awaiting heart-lung transplant.     

Respiratory muscle dysfunction and training in chronic heart failure

A characteristic feature of chronic heart failure (CHF) is reduced exercise tolerance. Several factors contributing to this have been identified, including alterations in central haemodynamics, skeletal muscle oxygen utilisation and respiratory muscle dysfunction. This review focuses on abnormalities identified in respiratory muscle structure and function in CHF and recent evidence for the benefit of selective inspiratory muscle training in CHF. Included in this review are findings from original investigations, with a specific focus on recent published data.     

Diaphragm paralysis causing ventilatory failure in an adult with the rigid spine syndrome

A syndrome consisting of a rigid spine and myopathy predominantly affecting proximal limb muscles has been previously described in children, and as with most neuromuscular disorders, the respiratory muscles appear to be affected only at an advanced stage in the disease. We describe an adult male with this syndrome who presented with ventilatory failure caused by severe respiratory muscle weakness and who demonstrated profound nocturnal arterial oxygen desaturation, particularly during rapid eye movement sleep. Treatment with negative pressure ventilation initially resulted in only modest improvements in symptoms, blood gas tensions, and nocturnal desaturation. The cause of this only partial improvement was upper airway obstruction provoked by the mode of ventilatory support used. After tracheostomy there was a dramatic and sustained improvement in symptoms and blood gas tensions and complete abolition of nocturnal arterial oxygen desaturation. This is the first report of an adult with the rigid spine syndrome presenting with ventilatory failure and cor pulmonale due to severe respiratory muscle weakness.     

Visual Hallucinations in a Patient with Adult Onset Acid Maltase Deficiency Disorder

A 66-year-old male presented with visual hallucinations. He had chronically elevated serum creatine kinase (CK) levels without muscle weakness. His hospital course was complicated by hypercapnic respiratory failure requiring mechanical ventilation. His hallucinations completely subsided on mechanical ventilation. Elevated CK levels prompted a muscle biopsy, which showed myopathy consistent with acid maltase deficiency disorder (AMDD). This is the first reported case of adult onset AMDD presenting with psychiatric symptoms. Our objective in reporting this case is to encourage early recognition of neuromuscular respiratory failure in AMDD and to reinforce that respiratory failure may develop without associated extremity muscle weakness.