Pulmonary function in Duchenne muscular dystrophy related to stage of disease

Pulmonary function and sleep disordered breathing in patients with traumatic tetraplegia: a longitudinal study

The purpose of this study was to determine longitudinal changes in nocturnal blood gas tensions in individuals with stable traumatic tetraplegia. Ten individuals initially evaluated at least 6 months postinjury were reevaluated 5 years later. When initially evaluated, all the patients had normal daytime blood gases. Six (60%), however, had nocturnal oxyhemoglobin desaturations (dSATs) below 90%, 3 (30%) had mean nocturnal oxyhemoglobin saturation (SAT) below 90% for 10% or more of at least 1 hour, and 4 had maximum end-tidal carbon dioxide tensions (EtCO2) greater than 45mmHg. At 5-year follow-up evaluation, then a mean of 11.6 +/- 5.7 years postinjury, the vital capacities (VCs) of these individuals had improved significantly by a mean of 1242 +/- 545mL without treatment, and daytime blood gases were still normal for 9 out of 10 patients. Five of the individuals (50%), however, had an increased number of transient nocturnal dSATs and 8 of 9 (88%) re-studied by capnography were hypercapnic. We conclude that nocturnal dSAT and hypercapnia appear to be common in tetraplegia and may increase as the patient ages, despite significant increases in VC. Oximetry and capnography are useful in diagnosing nocturnal dSAT and in monitoring treatment.

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.

Long-term nasal intermittent positive pressure ventilation in advanced Duchenne's muscular dystrophy

The aim of our study was to evaluate the long-term effect of nasal ventilation in patients with advanced Duchenne's muscular dystrophy (DMD). To this end, we compared the clinical and pulmonary function course of five subjects affected with chronic ventilatory failure due to DMD and treated with nasal intermittent positive pressure ventilation (NIPPV) with that of an unventilated comparison group; the latter consisted of another five patients with DMD, with a similar degree of clinical and respiratory functional impairment, who refused long-term mechanical ventilation. The duration of the follow-up was 24 months. At the conclusion of the trial, all patients treated with NIPPV were still alive; in contrast, four of five patients who underwent simple conservative treatment had already died (mean survival, 9.7 +/- 5.8 months). After 6 months of follow-up, mean loss of FVC and maximal voluntary ventilation was considerably higher in nonventilated subjects (respectively: -0.23 L vs +0.03 L and -5 L/min vs -1.5 L/min). These are the first comparative results confirming that long-term NIPPV helps to stabilize pulmonary function and to prolong the expectancy of life of patients with DMD.

Lung and respiratory muscle function in limb girdle muscular dystrophy

BACKGROUND

Pulmonary involvement is frequently observed in patients with limb girdle muscular dystrophy and occurs early in the disease. The aim of this study was to establish the prevalence of pulmonary dysfunction; the type of dysfunction; and any correlation between patient age, disease duration, or limb weakness and lung or respiratory muscle dysfunction.

METHODS

Twenty patients with strictly delineated limb girdle muscular dystrophy and 20 healthy controls were evaluated. Full inspiration chest radiographs were obtained. Standard lung and respiratory muscle function tests were performed and the data were statistically analysed.

RESULTS

The mean age of the patients was 40.6 years, the mean disease duration was 18.9 years, and the mean average muscle score (a numerical expression of limb weakness) was 5.73 out of 10. Chest radiography showed unilateral paresis of the diaphragm in three patients. Increased residual volumes, with either increased or decreased total lung capacity, correlated inversely with disease duration. Respiratory muscle weakness was common but mild. Expiratory muscle function was more impaired than inspiratory muscle function and correlated positively with expiratory reserve volume.

CONCLUSIONS

Respiratory muscle strength is commonly impaired in limb girdle muscle dystrophy. A dissociation of the limb and mild respiratory muscle involvement is observed; wheelchair restriction does not predict worsening of pulmonary function, and patient age, disease duration, or degree of limb weakness do not predict pulmonary morbidity. The diaphragm is not disproportionately affected by the dystrophic process compared with limb muscles.

Inappropriate weaning and late onset ventilatory failure of individuals with traumatic spinal cord injury

Eight traumatic spinal cord injured (SCI) individuals are described. Four tetraplegic patients who were weaned from initial ventilator use despite severe restrictive pulmonary syndromes experienced multiple pulmonary complications, episodes of acute respiratory failure, and 3 of the 4 required long term ventilatory support within 2 years of initial weaning. Three other SCI individuals developed chronic late-onset ventilatory failure 17, 25, and 29 years postinjury. One other tetraplegic patient was mechanically ventilated for 8.2 years post-injury despite complete recovery of autonomous ventilatory function years earlier. Of the 6 patients requiring long term ventilatory support, 4 were managed by noninvasive techniques of intermittent positive pressure ventilation (IPPV), one by negative pressure body ventilators, and one by tracheostomy IPPV. At least one and possibly as many as 5 patients were spared bronchoscopy and/or pulmonary complications by using mechanical insufflation-exsufflation (MI-E). We conclude that patients who are weaned despite having significant restrictive pulmonary syndromes are at risk for ventilatory decompensation weeks to decades after weaning. Ongoing clinical assessment, evaluation of respiratory muscle function and, at times, nocturnal blood gas analyses are warranted in the follow up of traumatic SCI individuals.

Long-term follow-up of patients with Duchenne muscular dystrophy receiving ventilatory support

We, retrospectively, examined the clinical course, decline in pulmonary function, and requirements for ventilatory assistance in 54 patients with Duchenne-type muscular dystrophy (DMD) who were followed in the muscle disease ward of the National Hospital in Kagoshima, Japan, over the past 20 years. The percentage of the predicted vital capacity (%VC) declined in relation to age and stage of disease. Most patients required assisted ventilation when the %VC fell below 10%. Twenty patients were treated with a negative pressure chest respirator. Six of these died at the mean age of 23.2 years after being on the respirator for a mean period of 18 months. Fourteen patients are surviving at a mean age of 23.5 years after being on the respirator for a mean period of 39 months.

Sleep-disordered breathing in patients with Duchenne muscular dystrophy using negative pressure ventilators

We studied the occurrence of nocturnal disordered breathing events and O2 desaturations in 12 patients with late-stage Duchenne muscular dystrophy (DMD) using negative pressure ventilators. We also assessed the effects of O2 supplementation and nasal continuous positive airway pressure (CPAP) on disordered breathing events in selected patients and examined sleep quality in a small subgroup. Average age was 23 + 2 years and FVC was 293 + 33 ml. Eleven of the 12 patients had more than five disordered breathing events per hour during nocturnal monitoring, and the lowest O2 saturation was < 85 percent in nine patients. Nasal O2 (2 L/min) during negative pressure ventilation in four patients did not alter the frequency of disordered breathing events, prolonged the mean and maximum durations of events, and failed to eliminate severe O2 desaturations in two patients. Nasal CPAP was used in two patients during negative pressure ventilation and completely eliminated disordered breathing events in both. Overnight polysomnography during negative pressure ventilation in three patients demonstrated frequent awakenings that fell in frequency following elective tracheostomy in two patients and use of nasal CPAP in one. We conclude that negative pressure ventilation in patients with late-stage DMD is associated with frequent disordered breathing events and severe O2 desaturations in many patients. Concomitant use of O2 supplementation may prolong the events, but a switch to positive pressure ventilation or addition of nasal CPAP is effective therapy.

Spinal fusion in Duchenne muscular dystrophy

Sixty-eight patients from a clinical population of 183 patients with Duchenne muscular dystrophy underwent posterior spinal fusion with instrumentation for progressive spinal deformity. Pulmonary complications were the most common postoperative problem, occurring in 17 per cent of the patients. A 35 per cent normal forced vital capacity was a reliable indicator of pulmonary complication risk. The patients with surgically stabilized spines were more comfortable in the later years of life and easier to care for, but deteriorating pulmonary function was not affected by the spinal fusion. The average age at death for the 29 boys who underwent spinal fusion was 18.3 years, which was similar to that of the 58 boys with scoliosis. Factors that improved the patients' quality of life included segmental instrumentation, fusion from T2 to the pelvis, correcting or balancing scoliosis, creating normal sagittal plane alignment and correcting pelvic obliquity.

Height measurement of patients with neuromuscular disease and contractures

Patients with neuromuscular diseases frequently have joint contractures, which preclude standard measurements of standing height. Standing height, arm-span, forearm and ulnar-segment measurements were taken of 116 normal children without contractures. Measurement of the forearm segment had the highest correlation with standing height, but it requires a special ruler. Arm-span measurement had good correlation with standing height, although this cannot be used if elbow or shoulder contractures are present; in such patients ulnar segment measurement can be used, but it has the lowest correlation with standing height.

Pulmonary function in individuals with a history of poliomyelitis

We examined the relationship between the lung function of 74 individuals with a history of poliomyelitis and reports of shortness of breath during activities of daily living, and the presence of post-polio sequelae risk factors. First, we studied the spirometry of 60 individuals (group 1) and second, we studied the relationship between the spirometry of an additional 14 individuals (group 2) and their respiratory muscle strength (Pimax and Pemax). In both groups, we examined the relationship between factors associated with post-polio sequelae including ventilation at polio-onset, having contracted polio after the age of 10, and having had polio for over 35 years; and lung function. In group 1, the FEV1 and FVC were lower for individuals with shortness of breath than individuals without (p less than 0.01). With respect to risk factors, FEV1 and FVC were lower in individuals who were ventilated at polio-onset, in individuals who contracted polio over 10 years of age, and in individuals who had had polio for less, rather than more than 35 years (p less than 0.05). The results for group 2 were comparable to group 1. In addition, the observed Pimax and Pemax were significantly lower than predicted values (p less than 0.05). Although FEV1 and FVC were positively correlated with both Pimax and Pemax (p less than 0.05), Pemax was disproportionately impaired compared to Pimax (40 +/- 12.1 and 82 +/- 38.8 percent predicted respectively). We conclude that individuals with a history of poliomyelitis can have compromised lung function irrespective of shortness of breath, that risk factors such as ventilation at polio-onset and polio-onset after 10 years of age can help predict those at risk of respiratory compromise, and that the measurement of respiratory muscle strength and of Pemax in particular, can augment the assessment of lung function of these individuals. Such assessment may avert respiratory complications in the post poliomyelitis population including those secondary to health care interventions.

Respiratory muscle strength and control of ventilation in patients with neuromuscular disease

To assess the relationship between respiratory mechanics and muscle strength and control of ventilation in patients with neuromuscular disease (NMD), we compared PImax and PEmax at RV, FRC and TLC, total respiratory elastance (Ers) with VT, TI, TT, VE, VT/TI, TI/TT, P.01, and P.01/(VT/TI) effective impedance in 21 patients with NMD and 21 healthy control (C) subjects, in seated position breathing room air. Ers in NMD patients was 79 percent higher than in the C subjects. While TI, TT, and VT in NMD were approximately half the corresponding C values, P.01 was 66 percent greater than in the C subjects (both p less than 0.001). NMD PImax and PEmax ranged from 37 to 52 percent of corresponding C values, respectively. Despite significant respiratory muscle weakness, only 7 of 16 patients demonstrated a PaCo2 greater than 45 mm Hg. Ventilatory output in NMD was modulated by respiratory mechanics as indicated by the increased P.01. In spite of muscle weakness, central drive in patients with NMD is not decreased, and in fact, is often increased. VE is not an accurate measure of central drive because of abnormal intrinsic respiratory mechanics and the effects of conscious responses or reflexes.

Airway pressures during crying: an index of respiratory muscle strength in infants with neuromuscular disease

The purpose of this study was to assess the strength of the respiratory muscles in 12 infants with neuromuscular disease (age range: 0.17-2.08 years) by measuring the maximal inspiratory and expiratory airway pressures (Pimax and PEmax) during crying efforts. Infants were divided into two groups according to their respiratory history. Group A included six infants in stable condition without clinical evidence of respiratory abnormalities, and Group B included six infants with severe generalized muscle weakness and previous respiratory failure. The infants in Group B had been weaned from mechanical ventilation 6 to 14 days before being studied. For infants of Group A, Pimax and PEmax values were 77 +/- 28 cmH2O and 62 +/- 18 cmH2O, respectively; for infants of Group B, they were 38 +/- 8 cmH2O and 34 +/- 8 cmH2O, respectively. A positive correlation was found between PEmax and body mass percentile. No infant had hypercapnia at the time of the study, and Pao2 values in infants of Group B were significantly lower than those of Group A. These results suggest that measurements of airway pressures during crying may provide an index of respiratory muscle strength in infants with generalized muscle weakness.

Peripheral mechanisms of fatigue in muscles of normal and dystrophic mice

We evaluated the contribution of different processes to fatigue of normal and dystrophic mouse muscles using an in vitro electromyography chamber. Fatigue was induced by repetitive nerve stimulation at 30 Hz for 0.5 s, every 2.5 s until tension decreased by about 50%. We monitored the compound nerve action potential (AP), compound muscle AP, and isometric tension responses to nerve stimulation, and compound muscle AP and tension responses to direct muscle stimulation. In normal mice, about 50% reduction in nerve-evoked tension occurred by 2.4 min in extensor digitorum longus (EDL), 4.8 min in diaphragm, and 9 min in soleus. Analysis of the responses revealed that the fatigue was caused by failure of more than one process in all muscles, and failure of nerve conduction did not contribute to fatigue in any muscle. Failure of neuromuscular transmission, muscle membrane excitation, and excitation-contraction (E-C) coupling and contractility accounted for 55, 45, and 0%, respectively, of the fatigue in EDL, for 21, 74, and 5% of the fatigue in diaphragm, and for 2, 54, and 44% of the fatigue in soleus. In dystrophic mice, while about 50% reduction in nerve-evoked tension occurred by 8.1 min in EDL and 5.6 min in diaphragm, only 29% reduction in tension occurred by 80 min in soleus. Failure of neuromuscular transmission, muscle membrane excitation, E-C coupling and contractility accounted for 22, 63 and 15% of the fatigue in EDL, for 21, 79, and 0% of the fatigue in diaphragm, and for 15, 59, and 26% of the fatigue in soleus. The proportion of slow-twitch oxidative fibers was more than normal in dystrophic EDL, but the same as normal in dystrophic diaphragm and soleus. The slower onset of fatigue was attributable to lesser failure of neuromuscular transmission in dystrophic EDL, and to lesser failure of E-C coupling and contractility in dystrophic soleus.

Decline in respiratory function and experience with long-term assisted ventilation in advanced Duchenne's muscular dystrophy

We present 17 patients with advanced DMD who required long-term assisted ventilation. Eleven patients used part-time assisted ventilation. Five of the patients received BV and/or M-IPPV or N-IPPV between two and nine years before requiring full-time T-IPPV, while six others initially used part-time T-IPPV. One patient used all three modes before requiring full-time T-IPPV. Mean (+/- SD) FVC and rebreathe PCO2 at the outset of assisted ventilation were 0.62 +/- 0.20 L and 47.4 +/- 7.5 mm Hg, respectively. Clinical features were divided between symptoms suggesting respiratory muscle fatigue and sleep-related disordered breathing. We found that, while useful in early respiratory insufficiency, BV is associated with recurrent aspiration. In our experience, N-IPPV offers the safest and most convenient form of noninvasive ventilation. When the VC has decreased to about 300 ml, most patients will require full-time ventilation; T-IPPV is advised to provide airway access to suction secretions.

Respiratory function in handicapped children

The aim of this study was to evaluate respiratory function of severely handicapped children. Tidal volumes and respiratory rates were determined in a total of 130 children with different clinical motor abilities. Tidal volume of non-sitters (n = 39) was significantly lower than ambulators (n = 49) or sitters (n = 42) (p less than 0.01). There was no difference in respiratory rate among the three groups. Among 45 children whose vital capacity could be determined, the tidal volumes showed a significant correlation with vital capacity (r = 0.56, p less than 0.001). Among four children whose tidal volume was less than 200 ml and respiratory rate was more than 30 cpm, blood gas analysis revealed hypoxia in three of them. The tidal volumes, therefore, would be a useful guide to estimate respiratory functions. It was concluded that the respiratory function in a non-sitter with reduced tidal volume is impaired, and that preventive measures must be taken against respiratory infection.

Long-term follow-up of nocturnal ventilatory assistance in patients with respiratory failure due to Duchenne-type muscular dystrophy

We followed eight patients with Duchenne-type muscular dystrophy for an average of 39 months after initiation of noninvasive intermittent ventilatory assistance using body ventilators. After one to three months of nocturnal use averaging 8 h, mean daytime PaCO2 fell from 63 +/- 2 to 45 +/- 3 mm Hg. At late follow-up, PaCO2 remained stable at 47 +/- 4 mm Hg, but vital capacity fell 33 percent compared with the initial value and the average duration of ventilator use had increased to 18 +/- 2 h daily. Three patients died and five survived; two continued using negative pressure ventilators and three had tracheostomies placed for administration of positive pressure ventilation. We conclude that noninvasive intermittent ventilatory assistance effectively reverses hypoventilation and symptoms in patients with late-stage Duchenne muscular dystrophy, but pulmonary function continues to deteriorate necessitating longer periods of ventilation, and often tracheostomy, within a few years.

Diaphragmatic weakness and paralysis

Diaphragmatic weakness implies a decrease in the strength of the diaphragm. Diaphragmatic paralysis is an extreme form of diaphragmatic weakness. Diaphragmatic paralysis is an uncommon clinical problem while diaphragmatic weakness, although uncommon, is probably frequently unrecognized because appropriate tests to detect its presence are not performed. Weakness of the diaphragm can result from abnormalities at any site along its neuromuscular axis, although it most frequently arises from diseases in the phrenic nerves or from myopathies affecting the diaphragm itself. Presence of diaphragmatic weakness may be suspected from the complaint of dyspnea (particularly on exertion) or orthopnea; the presence of rapid, shallow breathing or, more importantly, paradoxical inward motion of the abdomen during inspiration on physical examination; a restrictive pattern on lung function testing; an elevated hemidiaphragm on chest radiograph; paradoxical upward movement of 1 hemidiaphragm during fluoroscopic imaging; or reductions in maximal static inspiratory pressure. The diagnosis of diaphragmatic weakness is confirmed, however, by a reduction in maximal static transdiaphragmatic pressure (Pdimax). The diagnosis of diaphragmatic paralysis is confirmed by the absence of a compound diaphragm action potential on phrenic nerve stimulation. There are many causes of diaphragmatic weakness and paralysis. In this review we outline an approach we have found useful in attempting to determine a specific cause. Most frequently the cause is either a phrenic neuropathy or diaphragmatic myopathy. Often the neuropathy or myopathy affects other nerves or muscles that can be more easily investigated to determine the specific pathologic basis, and, by association, it is presumed that the diaphragmatic weakness or paralysis is secondary to the same disease process.

Breathing patterns and HbSaO2 changes during nocturnal sleep in patients with Duchenne muscular dystrophy

A night-time polygraphic sleep recording with continuous HbSaO2 monitoring was performed in 11 chair-bound Duchenne muscular dystrophy patients with severe restrictive lung disease but with blood gas values within normal limits when awake. No abnormalities of sleep pattern were detected. Nocturnal sleep did not have significant adverse effects on respiration. However, in 6 patients, infrequent central apnoeas or hypopnoeas occurred which were associated with falls in HbSaO2 greater than those that have been reported to be in normal subjects. The magnitude of HbSaO2 falls appeared to be significantly correlated with functional residual capacity values. Overall, the findings revealed a relatively preserved, although unstable, blood O2 balance during nocturnal NREM and REM sleep in patients with Duchenne muscular dystrophy, even in an advanced stage of their illness.

Training inspiratory resistance in Duchenne dystrophy using adapted computer games

Computer games were modified to encourage respiratory effort by two groups of patients with Duchenne muscular dystrophy. One group trained during the first six months of the study, the other during the second six months. Inspiratory effort was increased by their having to breathe through a mask to both start and continue the games. Pulmonary function tests were done at the beginning of the trial and six, 12 and 18 months later, when forced vital capacity, respiratory muscle endurance and strength were measured. Although there were some individual improvements, over-all the results were not statistically significant.

Hypercapnia in relation to pulmonary function in Duchenne muscular dystrophy

Arterialized blood gases were analyzed in 143 patients with Duchenne muscular dystrophy (DMD) to assess the relationship between forced vital capacity (FVC) and hypercapnia. The majority of patients studied had PaCO2 values in the low or normal range. Only six older patients had hypercapnia (PaCO2 greater than or equal to 45 mm Hg), and all these patients had FVC values less than or equal to 40% predicted. We conclude that hypercapnic respiratory failure occurs as a late preterminal event in DMD.

Cough capacity in patients with muscular dystrophy

Cough capacity was evaluated in 22 patients with muscular dystrophy (MD) using subjective cough assessment, cough flow-volume curves, maximum expiratory pressures (MEP), forced vital capacity (FVC), and peak expiratory flow rates (PEFR). In ten of the 22 patients transients of peak flow were generated during cough flow-volume maneuvers, indicating dynamic compression of the airways, which is considered important in the physiology of an efficient cough. Patients who could not generate peak flow transients had significantly reduced PEFR, FVC, and MEP values. Measurement of MEP was the most sensitive predictor of flow transient production during coughing; all of the patients who exhibited transients had MEP values of above 60 cmH2O, whereas the highest value of MEP recorded in patients without transients was 45 cmH2O. Three of the 12 patients who were unable to generate flow transients were considered to have an adequate cough by subjective assessment. We concluded that the measurement of MEP is extremely useful for assessment of cough strength in patients with MD.

Ventilator use in progressive neuromuscular disease: impact on patients and their families

The question of extending the lives of patients with progressive neuromuscular disease by means of ventilator support is controversial. It has been documented that ventilators can prolong the lives of patients with Duchenne muscular dystrophy by between two and 25 years, but few studies have assessed the effects of their use on individual or family functioning, or the quality of survival. A sample of patients with progressive disease and families living in the community was surveyed to assess these effects. Most of the sample were satisfied with their decision to extend life with the ventilator, but they found the experience significantly stressful in the home. Both patients and families believed their health-care team could have met their needs more comprehensively. Recommendations are made for health-care professionals working with patients with late-stage neuromuscular disease who need to use ventilators.

Flow-volume loop changes reflecting respiratory muscle weakness in chronic neuromuscular disorders

In order to identify the changes in pulmonary function and in the flow-volume loop due to respiratory muscle weakness, two groups of 10 nonsmokers with stable, chronic neuromuscular disease but without respiratory symptoms were studied: one without (Group 1) and one with (Group 2) respiratory muscle weakness as assessed by measurement of maximal static inspiratory and expiratory pressures. In Group 1, pulmonary function was normal except for increased ratio of one-second forced expiratory volume to forced vital capacity and forced expiratory flow at 25 to 75 percent forced vital capacity, which may reflect increased elastic lung recoil. Group 2 had mild volume restriction, appropriate for the degree of respiratory muscle weakness, and reduced inspiratory and expiratory flow rates. Pulmonary function was significantly more disturbed in Group 2 than in Group 1, and correlated well with maximal static inspiratory and expiratory pressures. Analysis of the flow-volume loop configuration revealed that four parameters describing effort-dependent portions were significantly related to maximal static inspiratory pressure and maximal static expiratory pressure. These parameters were peak expiratory flow, the slope of the ascending limb of the maximal expiratory curve, a drop of forced expiratory flow near residual volume, and forced inspiratory flow at 50 percent of vital capacity. A flow-volume loop score obtained from these four parameters was significantly higher in Group 2 than in Group 1 (2.8 +/- 1.03 versus 1.1 +/- 1.37; p less than 0.01). A flow-volume loop score of 2 or more had 80 percent specificity and 90 percent sensitivity in predicting respiratory muscle weakness in these patients with chronic neuromuscular disease. These data suggest that sensitive assessment of the flow-volume loop configuration as part of routine pulmonary function testing may help to suspect and identify respiratory muscle weakness.

Determinants of respiratory muscle weakness in stable chronic neuromuscular disorders

In neuromuscular disease, the precise relationship between general and respiratory muscle weakness is at present unclear. That relationship and the influence on respiratory muscle strength of such factors as type and duration of neuromuscular disease, distribution of general muscle weakness, and nutritional status were studied in 30 patients with stable chronic neuromuscular disease not presenting with respiratory symptoms. The degree of general muscle weakness was assessed by clinical examination of the strength of 17 muscle groups, yielding a general muscle strength index. The degree of respiratory muscle weakness was assessed by measuring maximal static inspiratory and expiratory mouth pressures. Maximal inspiratory (mean +/- SD: 68 +/- 28 percent predicted) and expiratory (66 +/- 29 percent predicted) mouth pressures were frequently reduced, but did not correlate with general muscle strength. The ability to estimate the degree of respiratory muscle weakness improved to some extent when the type of neuromuscular disease and the distribution of general muscle weakness were taken into account: thus, maximal expiratory mouth pressure was significantly lower (p less than 0.05) in myopathy than in polyneuropathy, and in proximal than in distal muscle weakness. Duration of neuromuscular disease and nutritional status did not influence respiratory muscle strength. It is concluded that in stable chronic neuromuscular disease, respiratory muscle involvement depends on a complexity of factors, in particular the type of neuromuscular disease and the distribution, rather than the degree, of general muscle weakness. In the individual patient, however, only direct measurement of maximal inspiratory and expiratory mouth pressures allows accurate assessment of respiratory muscle strength. These tests ought to complement neurologic examination.

Clinical applications of body ventilators

Interest has been increasing in providing ventilatory support in the home for patients with chronic respiratory failure, mainly with the use of positive pressure ventilation via a chronic tracheostomy. However, body ventilators that assist ventilation by applying intermittent negative or positive pressure to the thorax, abdomen, or airway without requiring an artificial airway, can offer distinct advantages for selected patients over systems requiring a permanent airway. These ventilators include the iron lung, portable lung (Portalung), pneumowrap, chest cuirass, pneumobelt, rocking bed, and positive pressure provided via a face or nose mask. They have successfully stabilized or reversed chronic hypercarbia when used intermittently in patients with slowly progressive chronic respiratory failure due to certain neuromuscular diseases and kyphoscoliosis. How they achieve this stabilization has not been clarified, but reversal of chronic respiratory muscle fatigue following periodic rest probably contributes. These ventilators are generally less effective than positive pressure ventilation through a tracheostomy and should be reserved for patients with relatively stable chronic respiratory failure and intact upper airways. However, they have the advantages of simpler operation and less expense, and they allow maintenance of a normal airway.

Anesthesia for pediatric neurological and neuromuscular diseases

Children with neurological and neuromuscular diseases often present anesthetic problems in the perioperative period. The anesthetic technique can play a significant role in altering the state of the brain during neurosurgical procedures through effects on the cerebral circulation and metabolism. Pre-existing neuromuscular disease may also have specific anesthetic implications such as cardiorespiratory involvement (eg, myotonia dystrophica), the potential for drug interactions (eg, myasthenia gravis) or abnormal responses to commonly used drugs (eg, malignant hyperthermia). In this review, the perioperative anesthetic considerations in a number of common neurological and neuromuscular conditions in the pediatric patient are discussed.

Respiratory muscle training in Duchenne muscular dystrophy

Eighteen boys with Duchenne muscular dystrophy were entered into trials to assess the effects of specific ventilatory strength and endurance training programmes. The findings showed an improvement in ventilatory muscle endurance but not in strength as a result of specific respiratory muscle training. The clinical significance of these findings is uncertain, however, and needs further evaluation.

Childhood muscular dystrophy: an African review

This is a review of muscular dystrophies seen in African children, with special reference to severe autosomal recessive forms of the disease seen in North African communities with high rates of consanguinity.

Pulmonary function and ventilatory response to chemical stimuli in familial myopathy

We studied the pulmonary function and ventilatory response to carbon dioxide and hypoxia in three sisters aged 16, 13, and 10 years who presented with droopy eyelids, external ophthalmoplegia, hearing loss, speech difficulty, and truncal muscular weakness. Pulmonary function test results showed decreased maximum static pressure, reduced vital capacity and total lung capacity, normal functional residual capacity, elevated residual volume, and reduced dynamic pulmonary volumes. The degree of functional abnormality paralleled the severity of clinical manifestations. The characteristic picture of pulmonary functional abnormality was distinct from either restrictive disorders of pulmonary origin or obstructive pulmonary diseases. The ventilatory response to hypoxia was markedly diminished and hypercapnic response was moderately diminished in all three patients.

The effects of inspiratory resistive training on respiratory muscle function in patients with muscular dystrophy

The effects of inspiratory resistive training on respiratory muscle function was evaluated in 11 patients with Duchenne, limb-girdle, and facio-scapulo-humeral (FSH) type muscular dystrophy. Muscle training consisted of breathing against an inspiratory resistance for two 15-minute sessions each day while at home. Following 6 weeks of training, there were significant increases in the maximum resistance that could be tolerated for at least 5 minutes (P < 0.01) and also in the maximum duration that ventilations equal to 30%, 50%, 70%, and 90% of the maximum voluntary ventilation could be sustained (P < 0.05). In six patients who trained for an additional 6-week period, respiratory muscle endurance increased even further. The degree of improvement in respiratory muscle endurance was positively correlated with baseline vital capacity (r = 0.84, P < 0.05) and maximal inspiratory pressure (r = 0.76, P < 0.05). Spirometry, functional residual capacity, and maximal inspiratory and expiratory pressures were not affected by training. We conclude that inspiratory resistive training improves respiratory muscle endurance in muscular dystrophy patients. Improvement in respiratory muscle function may serve to delay the onset of respiratory complications in patients with muscular dystrophy.

Lipidosis of pulmonary macrophages in the dystrophic hamster

Lavaged pulmonary macrophages of Bio 14.6 myopathic hamsters were compared with those from Bio F1B controls. Enlarged foamy macrophages were prevalent in the dystrophic strain. Lipidosis within this cell population was confirmed by morphologic and chemical analyses. The percentage of lipid-positive cells obtained from Bio 14.6 hamsters was three times greater than from control animals, but the total number of macrophages recovered from the lungs of dystrophic animals was approximately one-third lower compared to controls. Nearly two-thirds of the lipid-positive cells from the dystrophic strain were moderately to excessively engorged, whereas a similar percentage of the positive cells from control animals contained only sparse lipid inclusions. Qualitative ultrastructural differences were not observed between strains, but engorged macrophages of the dystrophic strain typically showed a predominance of lipid droplets with grey homogeneous material, crowded cytoplasmic organelles, and fewer primary lysosomes. Lipid analyses showed an 85% increase of total cellular lipids, a 486% increase of cholesteryl esters in neutral lipids, and increased 18:1 fatty acids in total lipids and the cholesteryl esters in cells from the Bio 14.6 strain. The etiology of the lipid excess has not been determined, but elevated chylomicrons and reduced alpha-lipoprotein values were observed in the serum of the dystrophic strain.

Predicted normal values for maximal respiratory pressures in caucasian adults and children

Maximal respiratory pressures at the mouth (PEmax and PImax) have been measured in 370 normal caucasian children and adults. Age, height, and weight were recorded for all subjects and incorporated in a stepwise multiple regression analysis to determine prediction equations for the maximal respiratory pressures in the children and adults for both sexes. In men PImax and PEmax were significantly correlated only with age (p less than 0.001 and less than 0.035 respectively), whereas in women they were correlated with height (p less than 0.035 and less than 0.03). In both boys and girls PImax was related to weight (p less than 0.0001 and less than 0.01 respectively) and PEmax to age (p less than 0.001 for both). The values for PImax and PEmax in adults were lower than in previously reported series, but in children the values obtained were similar to those reported for several smaller series.

Respiratory insufficiency in a severe autosomal recessive form of muscular dystrophy

In a large Sudanese kindred of 176 individuals, 15 children developed a brief respiratory illness in the course of a severe autosomal recessive muscular dystrophy (MD) and eight of them died. The type of MD in this kindred delineates a newly recognized entity which has been described from Sudan, Tunisia, Libya and Qatar . To assess the role of pulmonary insufficiency in the fatal outcome of this disease, pulmonary function was studied in six of the survivors. Values of lung volume were grossly abnormal and revealed a restrictive pattern. The degree of lung volume restriction varied from 50 to 76% of predicted total lung capacity (TLC) and 31-55% of predicted forced vital capacity (FVC). The high FEV1/FVC ratio (80-100%) in all patients excluded airway obstruction and the elevated ratio of residual volume (RV) to TLC (51-68%) reflected loss of inspiratory capacity. FVC showed no correlation with the degree of muscular disability and did not seem to be affected by the mild scoliosis seen in five children. These results are discussed in view of similar studies in a variety of neuromuscular disorders.

Clinical investigation in Duchenne dystrophy: 2. Determination of the "power" of therapeutic trials based on the natural history

A prospective study of 114 patients with DMD provided data for "power" calculations for future therapeutic trials. There was a decline in strength of 0.4 units per year (on a 0-10 scale). Contractures of the iliotibial bands, hip flexors, and heel cords developed before 6 years. Contractures of other joints accompanied the increased use of wheelchairs. All children walked until 8 years with functional "improvement" between 3-6 years. Children of the same age varied widely in their strength, degree of contracture, and functional abilities. Fifteen percent of the patients appear to have a milder variety of the disease and are termed "outliers." To test a drug which might slow the disease to 25% of its original rate of progression, two groups (placebo and treatment) of 40 patients each would have to be followed for one year.

Respiratory function in the muscular dystrophies

The purpose of this investigation was to compare the respiratory function of patients with different clinical types of muscular dystrophy (MD). A total of 190 patients representing facioscapulohumeral MD (n = 20), limb-girdle MD (n = 50), Becker MD (n = 20), Duchenne MD (n = 90), and the "intermediate" type of MD (n = 10) were studied using simple spirometric respiratory function tests. The respiratory modifications observed in the 3 adult forms indicate that pulmonary function was almost normal. Respiratory function in Duchenne muscular dystrophy (DMD) was always characterized by a restrictive syndrome which severely impaired pulmonary function. The vital capacity (VC) underwent ascending, plateau, and descending phases during the course of the disease. The VC at the plateau stage may be used as an estimate of life span. The most interesting finding was the high degree of variability in the restrictive syndrome associated with DMD. In the DMD group 30% presented a severe restrictive respiratory syndrome associated with a life span of less than 20 years (Type 1), 40% had a serious restrictive syndrome and variable mortality (Type 2), and the remaining 30% had a moderate restrictive respiratory syndrome (Type 3).

Analysis of lung volume restriction in patients with respiratory muscle weakness

We investigated pulmonary mechanics in 25 patients, 9 to 55 years of age, with a variety of generalised neuromuscular diseases and variable degrees of respiratory muscle weakness. The average degree of inspiratory muscle force was 39.2% (range 8-83%) of predicted. The lung volume restriction far exceeded that expected for the degree of muscle weakness: the observed decrement in respiratory muscle force should, theoretically, decrease vital capacity to 78% of its control value, while the mean VC in our patients was only 50% of predicted. Analysis of lung pressure-volume curves indicated that the two principal causes of the disproportionate loss of lung volume were a reduction in lung distensibility probably caused by widespread microatelectasis, and a decrease in the outward pull of the chest wall. Because it reflects both direct (loss of distending pressure) and secondary (alterations in the elastic properties of the lungs and chest wall) effects of respiratory muscle weakness on lung function, we conclude that, in these patients, the vital capacity remains the most useful measurement to follow evolution of the disease process or response to treatment.

Rehabilitation in muscular dystrophy

This paper reviews the types of muscular dystrophy and then their management, considering the Duchenne form in some detail and then the special problems encountered with other types.

The management of muscular dystrophy: a clinical review

The optimal management of muscular dystrophy is multidisciplinary and aggressive in nature. Serial assessment aids in determining the functional stage of the disease and in indicating specific therapies. Physical therapy can augment strength through exercise and relieve contracture through passive stretching. Occupational therapy is employed to help the patient manage his activities of daily living within the restrictions imposed on him by his disease. Progressive disability can be delayed through a variety of physiatric and orthopedic techniques, including surgical release of lower-extremity contracture, repair of foot and ankle deformity, and correction of scoliosis. Appropriate orthoses are available, as are a variety of special devices to facilitate ongoing care for postambulatory patients. Physicians treating the muscular dystrophies should be aware of the complications of these diseases, particularly cardiomyopathy, pulmonary failure, and psychological and social problems.

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.