Respiratory muscle weakness and fatigue

Respiratory muscle weakness can result from a variety of neuromuscular disorders, and it is now possible to identify different patterns of weakness and quantify the extent of this weakness using reliable, sensitive tests of respiratory muscle strength. However the quantification of respiratory muscle 'fatigue' has proved more difficult, and it is now recognized that there is unlikely to be one single index of fatigue, rather a whole sequence of changes that occur in response to loading. It is likely that in practice, a close interplay between respiratory pump capacity, demands on the pump and more especially, adaptive changes in respiratory drive, protect the respiratory muscles from overt peripheral contractile failure, and that the fall in tension following prolonged muscular activity involves many different closely inter-related processes. Investigation of these processes is likely to be more rewarding than attempts to develop a single 'test of fatigue', and may lead to an improved understanding of the role of respiratory muscle dysfunction in ventilatory failure.     

In vivo quantification of muscle contractility in humans: healthy subjects and patients with myotonic muscular dystrophy.

The purpose of this study was to use direct in vivo contractility measurements to assess muscle function in patients with myotonic muscular dystrophy (MMD). The tetanic and twitch responses and several time parameters of muscle contraction were obtained from nine MMD subjects and nine able-bodied, age-matched controls. After a routine nerve conduction study, in vivo contractility measurements were obtained by stimulating the ulnar nerve at the wrist and recording the isometric flexor function of the intrinsic muscles at the metacarpophalangeal joint of the index finger. A series of single stimuli, paired stimuli, and fused tetanic stimulations were generated during a 20-minute experimental protocol. A stable tetanus was produced at 50Hz for 1.2 seconds. M-wave and contractile data were recorded at 1,000Hz by digitization of the analog signal and storage by the microcomputer. The MMD patients were weaker than controls (p less than .05), as shown by the 39% reduction in tetanic tension and 57% reduction in twitch tension. The MMD patients also had a significant impairment in relaxing their muscles as shown by the 1,100% increase in half-relaxation time after contraction, even though there was no evidence of repetitive firing after cessation of stimulus. These data show that MMD patients exhibit failure of sarcolemmal activation, altered excitation-contraction coupling mechanisms, and failure of the contractile machinery. The myotonia is due in part, to some defect in the contractile machinery; it is not solely due to failure of sarcolemmal activation.     

Relationship between weakness and phase angle in advanced cancer patients with fatigue

Objective

This study aims to determine the relationship between weakness and bioimpedance analysis (BIA)-derived phase angle in a population of untreated cancer patients with fatigue.

Methods

We prospectively evaluated 41 treatment-naive cancer patients of several origins that presented with performance status 1–2, weight loss >5 % in the last 6 months, and Fatigue Numeral Scale score >4. Weakness was considered a physical component of the multidimensional fatigue syndrome and was evaluated through several parameters utilizing hand grip strength technique by dinamometry. The same assessment was also performed on a healthy control population (n?=?20). BIA-derived phase angle was also determined by BIA.

Results

Compared to healthy controls, cancer patients exhibited significant differences in all the parameters: median fatigue was 6 (range 5–9), evaluated maximal strength mean was 27?±?10.71 vs. 42?±?10.74 kg (p?<?0.0001 for patients vs. control, respectively), and muscle strength difference (max–min muscle strength) was also statistically different (p?<?0.0001). We also determined parameter associations within the patient population. We found statistical significant correlations between median phase angle score and endurance muscle with percentage of weight loss (r?=?0.43, p?=?0.03) for head and neck cancer patients, and in non-small cell lung cancer patients, grip work correlated significantly with normal or decreased phase angle (r?=?0.85), p?=?0.006 (Spearman Rank Correlation).

Conclusions

Weakness could be correlated with normal or decreased phase angle in a population with ambulatory advanced cancer with fatigue naive of treatment. We also found a significant relationship between median phase angle score and endurance muscle with percentage of weight loss in the subpopulation of patients with head and neck carcinoma.     

Myotonic dystrophy: quantification of muscle weakness and myotonia and the effect of amitriptyline and exercise

The purpose of this study was to quantify the degree of muscle weakness and myotonia in 12 patients with myotonic dystrophy (MD), and to quantitatively determine the effects of a four- to six-month therapeutic trial of amitriptyline. Patients had exercised with weights for one or more years. Some had shown initial improvement in muscle strength, but had reached a plateau; others had not improved when the study began. Muscle weakness was quantified by comparing the five-second maximum voluntary contraction (MVC) in newtons (N) per kg (body weight) of 12 patients and 20 healthy subjects. Knee extensor, elbow flexor, and first dorsal interosseous (FDI) muscles were compared. Myotonia was quantified by measuring relaxation times (RTs) at the end of the five-second MVC produced by FDI, as the time taken for the MVC to decrease by 50% and 75% (referred to as 1/2 and 3/4RT). The results were as follows: (1) the mean muscle strength of each of the three muscles of the patients was significantly (p less than .001) reduced compared with healthy subjects; and (2) 1/2 and 3/4RT means of the patients (vs healthy subjects) were significantly prolonged (p less than .01). Eight of the patients participated in a therapeutic trial of amitriptyline. Therapeutic effects were quantified by measuring muscle strength, 1/2 and 3/4RT, and percent change in evoked muscle action potential (MAP) from the FDI muscle after a ten-second MVC, to determine change in excitability. Mean muscle strength of FDI improved from .27 to .33N/kg, (p less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Evoked muscle action potentials in patients with muscular dystrophy

Electromyographic study of evoked muscle action potentials was made in a group of 31 patients with muscular dystrophy. Potentials, recorded with bipolar needle electrodes, were evoked by supramaximal stimuli applied to the motor nerve. The potentials recorded in 21 (67.7%) patients appeared markedly polyphasic, with a considerable degree of temporal dispersion. In general, the average number of phases was 20.9 +/- 9.08; the average duration attained 29.1 +/- 10.57 msec. The latency for the first component of the potentials and the motor conduction velocity along the main trunks were normal. The polyphasic potentials of dystrophic patients were similar to the MAP evoked in neuropathic patients. It is concluded that the long-lasting polyphasic potentials of dystrophic patients may represent the involvement of the thin peripheral branches of motor nerves in the pathologic process.     

Respiratory muscle weakness and respiratory muscle training in severely disabled multiple sclerosis patients

OBJECTIVE: To evaluate the contribution of respiratory muscle weakness (part 1) and respiratory muscle training (part 2) to pulmonary function, cough efficacy, and functional status in patients with advanced multiple sclerosis (MS). DESIGN: Survey (part 1) and randomized controlled trial (part 2). SETTING: Rehabilitation center for MS. PATIENTS: Twenty-eight bedridden or wheelchair-bound MS patients (part 1); 18 patients were randomly assigned to a training group (n = 9) or a control group (n = 9) (part 2). INTERVENTION: The training group (part 2) performed three series of 15 contractions against an expiratory resistance (60% maximum expiratory pressure [PEmax]) two times a day, whereas the control group performed breathing exercises to enhance maximal inspirations. MAIN OUTCOME MEASURES: Forced vital capacity (FVC), inspiratory, and expiratory muscle strength (PImax and PEmax), neck flexion force (NFF), cough efficacy by means of the Pulmonary Index (PI), and functional status by means of the Extended Disability Status Scale (EDSS). RESULTS: Part 1 revealed a significantly reduced FVC (43% +/- 26% predicted), PEmax (18% +/- 8% predicted), and PImax (27% +/- 11% predicted), whereas NFF was only mildly reduced (93% +/- 26% predicted). The PI (median score, 10) and EDSS (median score, 8.5) were severely reduced. PEmax was significantly correlated to FVC, EDSS, and PI (r = .77, -.79, and -.47, respectively). In stepwise multiple regression analysis. PEmax was the only factor contributing to the explained variance in FVC (R2 = .60), whereas body weight (R2 = .41) was the only factor for the PI. In part 2, changes in PImax and PEmax tended to be higher in the training group (p = .06 and p = .07, respectively). The PI was significantly improved after 3 months of training compared with the control group (p < .05). After 6 months, the PI remained significantly better in the training group. CONCLUSIONS: Expiratory muscle strength was significantly reduced and related to FVC, cough efficacy, and functional status. Expiratory muscle training tended to enhance inspiratory and expiratory muscle strength. In addition, subjectively and objectively rated cough efficacy improved significantly and lasted for 3 months after training cessation.     

Isometric strength measurement for muscle weakness in cancer patients

Our aim was to determine several indexes of reproducibility for strength measurements with a hand-held pull-gauge dynamometer (MFB50K) in cancer patients. Two independent testers performed repeated measurements of maximal isometric elbow and knee strength. The measurements were gathered in a convenience sample of 40 patients (27 men, age 20-72 years) with various types and stages of cancer. These patients were recruited from the medical oncology clinic of a university hospital. The Pearson product moment correlation coefficient, the intraclass correlation coefficient (ICC), the standard error of measurement (SEM) and its associated 95% confidence interval, the smallest detectable difference (SDD) and the limits of agreement were determined as outcome measures for reproducibility. The results for the Pearson product moment correlation and the ICC were 0.90 for elbow and 0.96 for knee extension strength. The results in terms of the SDDs were 29.4 newton (N) for elbow and 54.8 N for knee strength. The limits of agreement for elbow strength were -21.7 N and 38.5 N (mean 8.4 N). For knee strength the limits of agreement were -49.8 N and 59.8 N (mean 5 N). The Pearson product moment correlation and the ICC suggested good reproducibility. However, the more informative indices of reproducibility, i.e. the SEM and the SDD, showed relatively large measurement error between the testers. Therefore, the current use of the MFB50K for the measurement of muscle strength is not supported in cancer patients.     

肌力练习对膝关节骨关节炎肌肉软弱的影响

目的 :了解肌力练习对膝关节骨关节炎患者肌肉软弱的影响。方法 :对照比较 2 6个患肢 3— 6周肌力练习前后和 19个患肢被动活动前后的等速运动肌力参数。结果 :两组均表现出不同程度的肌力增加 ,肌力练习组在减轻肌肉软弱上更为成功。结论 :肌力练习可通过募集来减轻骨关节炎患者的肌肉抑制。     

Breathing during sleep in patients with myotonic dystrophy and non-myotonic respiratory muscle weakness.

Sleep apnoea and hypopnoea have been reported in myotonic dystrophy, but it is unclear whether this is simply attributable to the respiratory muscle weakness which is common in this condition. We therefore investigated whether breathing and oxygenation during sleep were more abnormal in patients with myotonic dystrophy than in patients with non-myotonic muscle weakness. Seven subjects were studied in each of three groups: normal controls, myotonic dystrophy and non-myotonic weakness. Patients in the latter group were chosen to represent a similar range of severity of respiratory muscle weakness to those with myotonic dystrophy. Detailed polysomnography was performed; the severity of breathing disorders during sleep was quantified in terms of the frequencies of apnoea and hypopnoea and the degree of arterial desaturation. The myotonic patients showed more frequent apnoea and hypopnoea and more severe desaturation than the other two groups; the results in the non-myotonic patients were generally intermediate. The results suggest that abnormal breathing during sleep is common in myotonic dystrophy and is not due solely to the direct effects of respiratory muscle weakness. Somnolence, which is a well recognized symptom of myotonic dystrophy, was not clearly attributable to the sleep apnoea/hypopnoea syndrome nor to abnormal sleep architecture in the myotonic patients.     

Increased muscle pain sensitivity in patients with tension-type headache

Nociceptive mechanisms in tension-type headache are poorly understood. The aim was to investigate the pain sensitivity of pericranial muscles and a limb muscle in patients with tension-type headache. Experimental muscle pain was induced by standardized infusions of 0.5 ml of 1 M hypertonic saline into two craniofacial muscles (anterior temporalis (TPA) and masseter (MAS)) and a limb muscle (anterior tibial (TA)) in 24 frequent episodic tension-type headache patients (FETTH), 22 chronic tension-type headache patients (CTTH) and 26 age and gender matched healthy subjects. Headache patients were examined twice, both on days with and on days without headache. The pressure pain thresholds (PPTs) were determined before and after infusions. The subjects continuously reported intensity of saline-induced pain on an electronic visual analogue scale (VAS) and the perceived area of pain was drawn on anatomical maps. Headache patients demonstrated significantly lower PPTs, higher saline-evoked VAS pain scores and greater pain areas than healthy subjects at all the tested muscle sites (P<0.05). There was a significant gender difference for the PPTs in all three groups of participants (P<0.05) and for VAS pain scores in the CTTH patients (P<0.05). There was no difference in pain sensitivity between FETTH and CTTH or between patients with or without headache. In conclusion, the present study demonstrates the presence of generalized pain hypersensitivity both in FETTH and CTTH compared to controls which is unrelated to actual headache status and extends to include responses to longer-lasting stimuli which are clinically highly relevant. Gender differences in deep pain sensitivity seem to be a consistent finding both in healthy controls and patients with tension-type headache.