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

We have previously demonstrated that diaphragmatic muscle fatigue can be diagnosed in infants from spectral frequency analysis of the surface diaphragmatic electromyogram. This requires a digital computer, but the analysis takes several days. Spectral frequency changes, however, can be accurately reflected by band pass filtering and expressing the ratio of high-frequency power to low-frequency power. A fall in this ratio of greater than 20% indicates muscle fatigue. Using a simple analog device to obtain this ratio permits the results to be immediately available; we have used this method to study weaning from mechanical ventilators in ten infants. With a successful weaning step there is no significant change in the ratio, whereas an unsuccessful weaning step invariably leads to a decrease in the ratio of greater than 20%, which precedes CO2 retention and clinical deterioration. These data indicate that diaphragmatic muscle fatigue plays an important role in the infant's response to lung disease. Monitoring of the high/low frequency ratio may be helpful in weaning infants from assisted ventilation.
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PMID:The consequences of diaphragmatic muscle fatigue in the newborn infant. 38 13

To evaluate the frequency of the causes of exercise limitation in patients with chronic pulmonary disease and to assess the relationship between the resting pulmonary functional parameters and the degree of exercise dyspnea, we reviewed the data from 88 consecutive stable patients with chronic lung disease (62 COPD, 16 interstitial lung disease [ILD]). In each patient, the intensity of dyspnea was measured by a Borg scale (BS) during an incremental symptom-limited exercise test. COPD patients stopped exercise due to fatigue (46%), dyspnea (36%), cardiac limitation (12%), and peripheral circulatory limitation (6%). ILD patients stopped exercise due to dyspnea (62%), fatigue (25%), and cardiac limitation (12%). In all patients, dyspnea severity increased linearly with exercise intensity as measured as VO2, VE, and VE/MVV. The severity of dyspnea expressed as the slope of the relationship between BS and VE/MVV (DBS/D[VE/MVV]) showed in COPD a significant inverse correlation with VC, FEV1, MIP, and a positive correlation with PaCO2 and VE/MVV at rest. In ILD, DBS/D(VE/MVV) showed a significant inverse correlation with VC, FEV1, TLC, and PaO2 and a positive correlation with VE/MVV at rest. The predicting power of all equations was very low.
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PMID:Dyspnea on exercise. Pathophysiologic mechanisms. 157 44

We have examined the role of the Chronic Respiratory Questionnaire in practice. The questionnaire covers aspects of disability in patients with chronic lung disease in terms of dyspnoea, fatigue, emotional function and mastery. It therefore provides a measure of physical disability and quality of life in patients with lung disease. The questionnaire was validated in older patients with chronic obstructive lung disease and is particularly responsive to changes within an individual. Its major disadvantages include the lack of sensitivity in patients with minor symptoms or possibly those in a younger age group and that it is also not possible to make comparisons between populations with the CRQ. It is, however, particularly good at demonstrating changes in disability in older patients with chronic airways disease.
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PMID:Experience of using the CRQ (Chronic Respiratory Questionnaire). 175 17

The traditional role of theophylline as a bronchodilator has been expanded by recent findings that suggest this drug has more than smooth muscle relaxant properties. Several investigators indicate that theophylline has an inotropic effect on respiratory muscle, causing enhanced muscular contraction and prevention of muscle fatigue. In animal studies, the drug enhanced respiratory muscle contraction by 15-20%, with levels in the upper end of the therapeutic range (15-20 mg/L). Results of studies in healthy volunteers and patients with lung disease, however, are conflicting. Five clinical trials demonstrated increased diaphragmatic contractility, whereas seven trials showed no effect, with five referring to the diaphragm and the remaining two to the sternomastoid muscle. Disparity in outcomes may be attributed to differences in patient populations, study designs, and techniques used to determine diaphragmatic contractility. Few long-term trials exist that document significant clinical benefit. Theophylline may prove to be of value in selected populations, such as adults with hypercapnic obstructive lung disease.
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PMID:The effect of theophylline on respiratory muscle contractility and fatigue. 220 60

Pulmonary hypertension occurs frequently in patients with chronic lung disease and contributes to morbidity and mortality. The most common symptoms are dyspnea, fatigue, chest pain, and syncope; sudden death can occur. Signs of pulmonary hypertension include prominent a-waves in the jugular venous pulse, a prominent P2 and murmur of tricuspid regurgitation. Introduced in 1964, cardiac catheterization is still required for the clinical assessment. Many patients reveal a vasoconstrictive component in their lung vessels that is potentially reversible therapeutically. Accurate noninvasive diagnostic methods and an understanding of the mechanisms causing pulmonary hypertension are necessary, as is appropriate therapy based upon the results.
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PMID:[Pulmonary hypertension. Clinical picture and therapy]. 266 41

In recent years quality of life instruments have been featured as primary outcomes in many randomized trials. One of the challenges facing the investigator using such measures is determining the significance of any differences observed, and communicating that significance to clinicians who will be applying the trial results. We have developed an approach to elucidating the significance of changes in score in quality of life instruments by comparing them to global ratings of change. Using this approach we have established a plausible range within which the minimal clinically important difference (MCID) falls. In three studies in which instruments measuring dyspnea, fatigue, and emotional function in patients with chronic heart and lung disease were applied the MCID was represented by mean change in score of approximately 0.5 per item, when responses were presented on a seven point Likert scale. Furthermore, we have established ranges for changes in questionnaire scores that correspond to moderate and large changes in the domains of interest. This information will be useful in interpreting questionnaire scores, both in individuals and in groups of patients participating in controlled trials, and in the planning of new trials.
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PMID:Measurement of health status. Ascertaining the minimal clinically important difference. 2716 75

Respiratory muscle fatigue is caused by excessive effort relative to the strength and endurance of the respiratory muscles. It can be manifested by reductions in respiratory drive (central fatigue), by impaired neuromuscular transmission (transmission fatigue), by decreased contractility (contractile fatigue), or by a combination of these factors. Respiratory muscle fatigue probably contributes to the difficulties some patients have with weaning from mechanical ventilation, the symptoms of exercise intolerance and dyspnea in chronic lung disease, and CO2 retention. Therapy depends on a reduction in the required level of respiratory effort and/or an improvement in respiratory muscle strength and endurance.
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PMID:Respiratory muscle fatigue. 283 16

Patients with Parkinson's disease may have more difficulty performing repetitive motor acts than single motor acts because of bradykinesia and skeletal muscle rigidity. We thought that repetitive ventilatory tasks might be similarly limited and that this dysfunction would likely contribute to respiratory muscle fatigue. We studied 9 patients with Parkinson's disease who had no evidence of restrictive or obstructive lung disease and 5 normal age-matched control subjects who performed repetitive, forced inspiratory resistive-loaded tasks. The time a given mean airway opening pressure could be sustained, the incremental oxygen cost of breathing, and the work rate of breathing (W) were measured. Although maximal static inspiratory pressures were comparable in both groups, 8 of the 9 patients could not sustain as high a W in the resistive-loaded tasks as could the normal control subjects (41.0 +/- 23.0 versus 67.7 +/- 29.1 J/min; mean +/- SD, p less than 0.01) and the efficiency of breathing was reduced (2.0 +/- 0.8 versus 3.8 +/- 1.4%; p less than 0.01). These findings are similar to derangements of task performance by peripheral skeletal muscle groups in Parkinson's disease.
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PMID:Respiratory muscle dysfunction in Parkinson's disease. 319 26

Recent evidence suggests that exercise-induced hypoxemia (EIH) may occur in healthy trained endurance athletes. However, at present, no data exist to describe the regularity of EIH in athletes or non-athletes. Therefore, the purpose of the present investigation was to determine the incidence of EIH during exercise in healthy subjects varying in physical fitness. Subjects (N = 68) performed an incremental cycle ergometer test to volitional fatigue with percent arterial oxyhemoglobin saturation (%SaO2) measured min-by-min. For the purpose of data analysis subjects were divided into three groups according to their level of physical training: 1) untrained (N = 16), 2) moderately trained (N = 27), and 3) elite highly trained endurance athletes (N = 25). EIH was defined as a %SaO2 of less than or equal to 91% during exercise. EIH did not occur in any of the untrained subjects or the moderately trained subjects. However, EIH occurred in 52% of the highly trained endurance athletes tested and was highly reproducible (r = 0.95; P less than 0.05). These findings further confirm the existence of EIH in healthy highly trained endurance athletes and suggests a rather high incidence of EIH in this healthy population. Hence, it is important that the clinician or physiologist performing exercise testing in elite endurance athletes recognize that EIH can and does occur in the elite endurance athlete in the absence of lung disease.
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PMID:Incidence of exercise induced hypoxemia in elite endurance athletes at sea level. 322 70

The vast majority of patients who undergo mechanical ventilation are able to discontinue ventilatory assistance within a few days. Typically, patients who require only short-term mechanical ventilation do not have severe underlying lung disease, and the problem for which they require ventilatory support is most commonly rapidly reversible. In these patients on short-term ventilatory support, parameters of spontaneous ventilatory requirements and respiratory muscle strength, including minute ventilation, maximal voluntary ventilation, vital capacity, and maximal inspiratory pressure, are useful in predicting the success of discontinuation of mechanical ventilation. Ventilatory support can generally be discontinued by a variety of techniques in these patients without the need for weaning from the ventilator per se. The smaller group of patients in whom it is not possible to discontinue mechanical ventilation within less than 7 days comprises individuals who frequently have severe acute or chronic lung disease, multisystem extrapulmonary disease, or neuromuscular disease. After a period of prolonged mechanical ventilatory support, these complicated patients require a process of progressive weaning in which they gradually become able to support spontaneous ventilation. Spontaneous ventilatory parameters do not correlate well with weaning ability in patients on long-term ventilatory support. A systematic and comprehensive approach in which attention is focused on optimizing pulmonary and nonpulmonary factors that affect the weaning process provides the best chance for successful withdrawal of ventilatory support after long-term mechanical ventilation. Inadequate ventilatory drive, respiratory muscle weakness and fatigue, increased work of breathing, excessive CO2 production, and cardiac failure are potential mechanisms that may play a role in inhibiting successful weaning. Adverse factors relevant to each of these mechanisms must be addressed and corrected to whatever extent possible. Studies have not demonstrated the superiority of either classic T-piece weaning or IMV weaning methods in difficult-to-wean patients on long-term ventilatory support. Both techniques may be used successfully as long as all patient variables that may adversely affect weaning ability are corrected or optimized and close care and attention to the details of the weaning process itself are provided.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Discontinuation of mechanical ventilation. 328 Feb 25


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