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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
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PMID:Respiratory muscle blood flow. 329 24

This article discusses the role of respiratory muscle rest therapy in hypercapnic ventilatory failure and/or inspiratory muscle fatigue associated with primary lung disease, diseases of the chest wall, and neuromuscular diseases. Some animal data on the role of ventilatory muscle rest therapy in states characterized by a low cardiac output and arterial hypotension are also reviewed. Additionally, a method for quantitating the degree of respiratory muscle rest elicited by negative pressure ventilation devices is presented.
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PMID:Respiratory muscle rest therapy. 329 29

The respiratory muscles constitute a pump as vital to life as the heart. In patients with severe lung disease, the work of breathing is increased greatly, whereas the capacity of the respiratory muscles to generate tension and ventilation is impaired. In these circumstances, respiratory muscle fatigue may occur. When the cardiac pump fails, it often is possible to improve its performance by drug therapy with inotropic agents. In recent years, attention has been focused on the possibility of enhancing respiratory muscle function with drugs. The agents most studied have been the methylxanthines, theophylline and aminophylline. In vitro studies have demonstrated an inotropic effect of theophyllines on all skeletal muscles tested, including the diaphragm. The effect of theophyllines on skeletal muscle is dose related and animal studies show that any effect in humans, where dosage is limited by toxicity, is likely to be small. Early studies in humans showed a substantial positive inotropic effect on the diaphragm, but subsequently, a large number of studies have yielded mixed results. Up to the present time, most studies have failed to demonstrate a positive action of theophyllines. Although is it possible that these drugs may have a very small beneficial effect on contractility, not easily detected by the methods of some investigators, such as small effect of potentially toxic drugs is likely to be of limited clinical value.
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PMID:Aminophylline and the respiratory muscles: an alternative view. 329 31

Malnutrition may be an important complicating factor in acute and chronic lung disease. Animal studies have demonstrated significant atrophy of diaphragm muscle fibers following prolonged undernutrition resulting in a marked reduction in diaphragm muscle strength as well as alteration in other contractile and fatigue properties of the muscle. In severe chronic obstructive pulmonary disease (COPD), malnutrition is common and may, in conjunction with the influences of hyperinflation on diaphragm performance, predispose to respiratory muscle fatigue and failure. The course of progressive weight loss in patients with COPD is not known but may, in part, be related to a "hypermetabolic" state arising from an increased oxygen consumption of the respiratory muscles secondary to enhanced resistive loads and impaired mechanical efficiency of the respiratory muscles. Reports of the impact of nutritional repletion on respiratory muscle performance in critically ill patients, as well as in patients with COPD, are preliminary. Further studies are necessary to establish whether such measures impact meaningfully on both the morbidity and mortality of these patients.
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PMID:Nutrition and the respiratory muscles. 329 32

Although the respiratory system is not fully developed at birth, the human newborn infant has flexible strategies to sustain breathing and defend blood gas homeostasis in both health and disease conditions. Initially the thresholds for chemoreceptor response to PO2 and PCO2 closely mimic those of the fetus, but the threshold resets to sustain ventilation adequate for blood gas homeostasis appropriate to the extrauterine milieu. The muscles of respiration have been "trained" in utero and effectively assume the function of the respiratory pump, despite their marginal reserve against fatigue. The pliable chest wall is functionally stabilized by the tonic activity of the intercostal muscles, thereby allowing effective ventilation. Finally, expiration is prolonged by the postinspiratory activity of the diaphragm and laryngeal braking as a means of maintaining an elevated lung volume and augmenting FRC. The ventilatory response of the newborn to respiratory disease is limited. The magnitude of the VE response is smaller than that of the adult, and is characterized by an increase in the respiratory rate and a limited increase in the VT. The poor effort reserve of the muscles, especially the diaphragm, predisposes the newborn to muscle fatigue and ventilatory failure. To avoid fatigue, recruitment of accessory muscles occurs, along with laryngeal braking of expiration, thereby decreasing the work of the diaphragm, recruiting new alveoli by an auto-PEEP effect, increasing the FRC volume, and improving gas exchange by an increase in the pulmonary surface area. These mechanisms help to avoid muscle exhaustion and facilitate adequate gas exchange in the presence of lung disease. We do not know precisely the postconceptual age at which the newborn is sufficiently developed to adopt these various defensive strategies of breathing, but the presence of tachypnea and grunting in 28-week-old premature infants suggests that long before term the human infant is capable of remarkable variation in the defense of breathing.
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PMID:Pulmonary and chest wall mechanics in the control of respiration in the newborn. 331 39

Restrictive lung disease patients exhibit a wide range of breathing and oxygenation abnormalities during sleep. The combination of degree of restriction, whether it is intrapulmonary or extrapulmonary, and confounding factors, such as obesity, age, and sex, will ultimately determine the degree of disturbed nocturnal physiology. The sleep literature is still sparse in most restrictive diseases. For patients with interstitial lung disease, the role of nocturnal oxygen in chronic established fibrosis, and also in acute alveolitis (e.g., farmer's lung, bird fancier's lung, etc.), has not been addressed. As fibrotic lung disease progresses, the degree of nocturnal desaturation and breathing dysrhythmias will progress. Changes in sleep architecture are likely related to the progression of the disease, but this is not known with certainty. Long-term evaluation of sleep and breathing in interstitial lung disease will give further insight into whether or not sleep changes are primary or secondary events. For kyphoscoliosis patients, again, we need more information on sleep as the thoracic deformity changes. In addition, the use of drugs (acetazolomide, medroxyprogesterone, and almitrine) and/or nasal CPAP to treat nocturnal desaturation needs to be assessed in a controlled fashion. In neuromuscular disease, the dynamics of gas exchange and sleep structure need to be defined in a larger group of patients. Factors such as degree of muscle weakness, degree of underlying lung diseases, and medications must be taken into consideration. Nocturnal hypoxemia may cause muscle weakness and fatigue, which in time, could cause more nocturnal hypoventilation and further hypoxemia. Supplemental nocturnal oxygen should be evaluated in this population.
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PMID:Sleep in restrictive lung disease. 331 24

Chest wall distortion is common in infants and is especially visible in preterm infants. It has been suggested that this distortion increases the volume displacement of the diaphragm during inspiration, which may be associated with muscular fatigue and apnea. We studied 10 preterm infants who had no evidence of lung disease, investigating the effect of chest wall distortion on the volume displacement and work of the diaphragm. The volume changes of the respiratory system were partitioned using an inductance plethysmograph. The minute volume displacement and the work of the diaphragm were calculated using the partitioned abdominal volume change and the gastric and esophageal pressures. The paradoxical movement of the chest wall lasted an average of 36% of inspiration. The minute volume displacement of the diaphragm ranged from 72 to 176% of the minute pulmonary ventilation, and diaphragmatic work ranged from 94 to 793% of that performed on the lungs. The amount of chest wall distortion, as reflected by the duration of the paradoxical chest wall movement, the minute volume excursion, or work of the diaphragm, was not related to the mechanical properties of the lungs. This estimated work load may represent a significant expenditure of calories in these infants and may contribute to the development of diaphragmatic fatigue, apnea, and a prolonged need for mechanical ventilation.
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PMID:Distortion of chest wall and work of diaphragm in preterm infants. 355 76

Eight patients with sarcoidosis seen at the Royal Children's Hospital, Melbourne, during the past 10 years were reviewed. Five of the eight patients came from non-metropolitan areas. The major presenting symptoms were cough, fatigue and weight loss; peripheral lymphadenopathy and hepatomegaly were common. None of the patients had eye or central nervous system involvement. Seven patients had bilateral hilar adenopathy on chest radiograph and six had parenchymal lung changes. Angiotensin converting enzyme was measured in six patients and was elevated in all, while hypercalcaemia was present in three patients. Five patients had a tissue biopsy showing the characteristic non-caseating granulomas. Corticosteroid therapy was used for four patients and was given for hypercalcaemia in three patients and for severe restrictive lung disease in one patient.
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PMID:Sarcoidosis in children. 356 75

Present methods of assessing the work of breathing in human infants do not account for the added load when intercostal muscle activity is lost and rib cage distortion occurs. We have developed a technique for assessing diaphragmatic work in this circumstance utilizing measurements of transdiaphragmatic pressure and abdominal volume displacement. Eleven preterm infants without evidence of lung disease were studied. During periods of minimal rib cage distortion, inspiratory diaphragmatic work averaged 5.9 g X cm X ml-1, increasing to an average of 12.4 g X cm X ml-1 with periods of paradoxical rib cage motion (P less than 0.01). Inspiratory work was strongly correlated with the electrical activity of the diaphragm as measured from its moving time average (P less than 0.05). Assuming a mechanical efficiency of 4% in these infants, the caloric cost of diaphragmatic work may reach 10% of their basal metabolic rate in periods with rib cage distortion. When lung disease is superimposed, the increased metabolic demands of the diaphragm may predispose preterm infants to fatigue and may contribute to a failure to grow.
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PMID:Diaphragmatic work of breathing in premature human infants. 359 17

Many controlled trials rely on subjective measures of symptoms or quality of life as primary outcomes. The relative merits of different response options for these measures is an important, but largely unexplored, issue. Therefore, we compared the responsiveness of seven-point Likert vs visual analogue scales (VAS) in a questionnaire measuring quality of life in chronic lung disease. The VAS and seven-point scale versions of the questionnaire were administered to 28 patients before and after completing an inpatient respiratory rehabilitation program of known benefit. For all four dimensions of the questionnaire (dyspnea, fatigue, emotional function, and mastery) the VAS showed a larger improvement than the seven-point scale when both were standardized on a scale of 0-10. However, in each case the variability of the improvement was greater using the VAS. The difference in improvement between the two scales was not statistically significant. We conclude that the two methods of presenting response options show comparable responsiveness. The ease of administration and interpretation of the seven-point scale recommend its use in clinical trials.
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PMID:A comparison of Likert and visual analogue scales for measuring change in function. 368 Apr 71


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