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

The intracellular pH of frog sartorius muscles exposed to an extracellular pH 8.0 (25 mM HCO3-, 1% CO2) was 6.9-7.1. Following a fatiguing stimulation period (one tetanic contraction per second for 3 min), the intracellular pH was 6.5-6.7. When similar experiments were repeated with frog sartorius muscles exposed to pH 6.4 (2mM HCO3-, 1% CO2), the intracellular pH was 6.8-6.9 at rest and 6.3-6.4 following fatigue. So, in both experiments the intracellular pH decreased by 0.4-0.5 pH unit during fatigue. When the CO2 concentration of the bathing solution was increased from 1 to 30%, the intracellular pH of resting muscles decreased from 7.0 to 6.2-6.3. Although the effect of CO2 on the intracellular pH was greater than the fatigue effect, the decrease in tetanic force with CO2 was less than 40%, while during fatigue the tetanic force decreased by at least 70%. Therefore in frog sartorius muscle the decrease in tetanic force during fatigue exceeds the decrease that is expected from just a change in intracellular pH.
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PMID:Is the change in intracellular pH during fatigue large enough to be the main cause of fatigue? 309 36

In experiments on 10 adult anaesthetized cats (pentobarbital 30 mg.kg-1 i.p.) the effect of stimultaneous hypoxia and hypercapnia was studied on the defence respiratory reflexes of the airways. Expiratory reflex and cough were elicited by mechanical stimulation of the airways mucosa, and the obtained values were evaluated on basis of the intrapleural pressure. Inhalation of the hypoxic-hypercapnic gas mixture (11% + 7% CO2 in N2) for 15 minutes led to a significant decrease of respiratory frequency, tidal volume and PaCO2, while pHa and PaCO2 also decreased significantly together with the intensity of the expiratory reflex and that of cough. Recent studies, showed that in the course of the effect of hypoxia (11% O2) and of hypercapnia (5% CO2), cough intensity decreased, but the change was not significant. The decrease of the intensity of respiratory defence reflexes under hypoxic-hypercapnic conditions might have been due to the changes of centrally controlling structures, or to the effector part of the reflex arc, resulting from fatigue of the respiratory muscles. The possible effect of anaesthesia exerting a significant influence on the intensity and character of airways defence reflexes could not be excluded.
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PMID:Effect of hypoxia and hypercapina on the airways defence reflexes. 312

Continuous monitoring of important respiratory indices has the potential for predicting catastrophes and providing an opportunity for the timely institution of lifesaving measures. Arterial oxygenation can be monitored noninvasively using oximetry or transcutaneous oxygen electrodes, while mixed venous oxygenation can be recorded continuously with modified pulmonary artery catheters. A satisfactory method of monitoring carbon dioxide tension does not exist. Measurements of respiratory drive can be obtained at the bedside, but their clinical usefulness remains unknown. Assessment of respiratory muscle strength is helpful in determining the need for mechanical ventilation, but a practical method of diagnosing respiratory muscle fatigue remains elusive. Measurement of thoracic compliance and detailed examination of the breathing pattern, i.e., tidal volume, respiratory frequency, and the pattern of rib cage-abdominal motion, are helpful in assessing abnormal pulmonary mechanics. The detailed information provided by respiratory monitoring can complement but not replace careful bedside examination.
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PMID:Respiratory monitoring in the intensive care unit. 314 22

Inspired by Traditional Chinese Medicine and Qigong, we designed a new anti-G maneuver, the Q-G Maneuver, which has proved promising. This maneuver consists of volition mobilization, stepwise tensing of leg and abdominal muscles, and maintenance of a shallow thoracic respiration throughout. It was tested on 24 pilots on the ground and 3 pilots on a centrifuge. All pilots were monitored with heart level blood pressure, oximetry, ear lobe pulse, CO2 concentration in exhaled gas, EEG and ECG; in centrifuge runs, peripheral vision was also monitored. Blood pressure was maintained at 180-240 mm Hg for more than 30 s without fatigue. On the centrifuge, the pilots tolerated a G load 2.25-3.0 G higher than without the maneuver, without any visual disturbance. Oximetry readings were 96-97%, and there was no evidence of hyperventilation. The ear lobe pulse was even enhanced during G load with the maneuver. Follow-up visits to 18 out of 24 pilots with 455 inflight applications of the maneuver showed that the maneuver is feasible and can be used effectively during high-G load.
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PMID:A preliminary report on a new anti-G maneuver. 319 Jun 25

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

Recent investigations have shown that theophylline improves diaphragmatic contractility of the respiratory muscles in isolated muscle preparations in animals and in normal human subjects. It has also been demonstrated that theophylline can reverse diaphragmatic fatigue and prevent fatigue of the diaphragm when given prophylactically. These effects have also been demonstrated in patients with severe chronic obstructive pulmonary disease, all of whom retained CO2 (PaCO2 53 +/- 3 mm Hg) and had hypoxia (PaO2 57 +/- 8 mm Hg). Theophylline, which increases respiratory muscle strength and delays the onset of diaphragmatic fatigue therefore could be a very useful agent in the treatment of patients with chronic airway obstruction.
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PMID:Effect of theophylline on diaphragmatic muscle function. 329 24

Breath-holding subjects often exhibit involuntary contractions of respiratory muscles which are much stronger and faster than the efforts they would make during unrestricted breathing at the same level of CO2 and O2. To gain a better understanding of the genesis of these contractions, we compared them with the respiratory response to external elastic loading. Normal men rebreathed a mixture of 8% CO2 in oxygen against no load, elastic loads of 25 and 75 cm H2O/L, and held their breath, equivalent to an elastic load of 226 cm H2O/L. At iso-CO2, increasing loads led to progressively smaller tidal volumes, inspiratory flow rates and ventilation. However, respiratory muscles were progressively activated by the loads, as indicated by increasing occlusion pressure, so that inspiratory flow rate and ventilation were defended much better than could be expected if no neural compensation occurred. The pattern of respiratory muscle activity in breath-holding was qualitatively similar to that in elastic loading, and seemed quantitatively to be an extreme form of reaction to a large load. The reduction in inspiratory time and therefore of peak inspiratory pressure and ratio of inspiratory to total time with very large loads could be viewed as an adaptive response to limit respiratory muscle fatigue.
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PMID:Similarities between behavior of respiratory muscles in breath-holding and in elastic loading. 337 9

Gluconeogenesis and alanine metabolism of normal and cirrhotic rats were studied in view of partial hepatectomy. Liver cirrhosis was made by repeated injection of thioacetamide in rat. Partial hepatectomy was performed by modified method of Higgins-Anderson. Liver glycogen and fructose-2, 6-bisphosphate were decreased after hepatectomy and recovered within 7 days in normal groups, while those of cirrhotic group reduced even in preoperative state were further decreased and hardly recovered after hepatectomy. Gluconeogenesis of perfused liver in cirrhosis was increased from both lactate and alanine preoperatively, but gluconeogenesis from alanine was not increased in both hepatectomized rats. ATP and energy charge were decreased after hepatectomy and recovered within two weeks. These level were lower in cirrhotic group, and decreased further and hardly recovered after hepatectomy. Alanine utilization to CO2 in vivo was not impaired in cirrhotic group either preoperatively or postoperatively. ATP and energy charge were increased by alanine injection in hepatectomized rats of both normal and cirrhotic group. In conclusion, glucose-insulin therapy of sufficient amounts is important to improve decreased glycolysis and abnormal gluconeogenesis on both post-hepatectomy period of normal and pre and post-hepatectomy period of cirrhosis. Also alanine is effective for stimulating decreased energy production.
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PMID:[Changes of gluconeogenesis and alanine metabolism following partial hepatectomy in normal and cirrhotic rats]. 339 28

Fatigue is a frequent complaint from patients suffering from the hyperventilation syndrome. Fatigue was quantified in terms of the endurance time that a certain force can be generated in a sustained handgrip contraction, and in terms of the time course of changes in certain parameters of the EMG-power spectrum of the contracting muscles. This was done in a group of 25 normal subjects and a group of 30 patients suffering from the hyperventilation syndrome. No difference in endurance times was found. The EMG-fatiguability in the hyperventilation group developed even slower than in the normal group. In three normals the fatigue parameters were also measured in three conditions of normo-, hypo-, and hyper-capnia. No intraindividual correlations were found between fatigue parameters and CO2-levels. Neither were such correlations found between individuals in the hyperventilation group and the normal group. It is concluded that the subjective feelings of fatigue in the hyperventilation patients cannot be corroborated by the objective measurements used in this study. Thus their fatigue is not of a peripheral type. The levels of CO2 do not have an effect on objectively measured fatigue parameters. The hypothesis that lactate accumulation in contracting muscles mediates EMG-fatiguability, cannot explain the present results, and therefore is not supported by results from this study.
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PMID:Hyperventilation syndrome and muscle fatigue. 340 98

Methylxanthines and particularly caffeine are known to increase skeletal muscle contractility. Recently, it has been shown that theophylline improves diaphragmatic contractility of the respiratory muscles both in isolated muscle preparations and in animals and normal human beings. Furthermore, it has been demonstrated that theophylline reverses diaphragmatic fatigue and prevents fatigue of the diaphragm when it is given prophylactically. Finally, recent evidence indicates that theophylline improves diaphragmatic function in patients with chronic obstructive pulmonary disease, all of whom retained CO2 (PaCO2 43 +/- 3 mm Hg) and had hypoxia (PaO2 57 +/- 8 mm Hg). Patients both improved transdiaphragmatic pressure and were less susceptible to fatigue. These data strongly suggest that theophylline, which increases respiratory muscle strength and delays the onset of diaphragmatic fatigue, could be a very useful agent in the treatment of patients with chronic airway obstruction.
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PMID:Effect of theophylline on diaphragmatic and other skeletal muscle function. 353 59


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