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

Diaphragm pacing, which entails electrical stimulation to the phrenic nerve, is an effective means of managing patients with ventilatory insufficiency and intact lowermotor-neurone innervation of the diaphragm. The pacing apparatus is used to pace the right and left hemidiaphragms alternately to avoid fatigue, which may damage the muscle irreversibly. Among the important benefits of pacing in quadriplegics with paralysis or respiratory muscles are the social and psychological advantages of not being dependent on a mechanical ventilator.
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PMID:Diaphragm pacing in ventilatory failure. 679 43

We studied the power spectrum of the diaphragm electromyogram (EMG) at frequencies between 31 and 246 Hz in four young normal subjects and five patients with chronic obstructive lung disease (COPD). Diaphragm EMGs were analyzed during spontaneous breathing and maximum inspiratory efforts to determine the effect of signal-to-noise ratio on the power spectrum and if treadmill exercise to dyspnea was associated with diaphragm fatigue. We found that the centroid frequencies of the power spectra (fc) were strongly correlated (r = 0.93) with ratios of power at high frequencies to power at low frequencies (H/L) for all subjects. Of the two indices, H/L had the largest standard deviation expressed as a percentage of the mean. The mean values of both of these decreased significantly after exercise, fc from 100.2 to 97.3 and H/L from 1.07 to 0.97. Signal-to-noise ratios were higher in maximal inspiratory efforts and after exercise in normal subjects and higher in COPD patients. The signal-to-noise ratio was correlated negatively with fc and H/L, indicating that these indices of the shape of the power spectrum are influenced by signal strength and noise levels as well as muscle function. We conclude that the fc and H/L index similar qualities of the power spectrum, that they are partially determined by the signal-to-noise ratio, and that, in some cases, exercise to dyspnea is associated with apparently mild diaphragm fatigue.
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PMID:Power spectral analysis of the diaphragm electromyogram. 687 80

Diaphragm strips from young rats (45--60 g) about 0.3 mm thick were fatigued by tetanic stimulation at a train repetition rate of 2 HZ for 3 min. The isometric tension developed was measured during fatigue and recovery in solutions containing 25, 10, or 2 mM bicarbonate at both 37 and 30 degrees C. Tension fell during fatigue to between 20 and 30% of the initial value and this was not significantly influenced by external bicarbonate concentration or temperature over the range considered. Recovery of tension was complete and rapid (t1/2 < 1 min) in 25 mM bicarbonate at both temperatures. In 10 and 2 mM bicarbonate recovery was slowed (t1/2 3.5 and 7 min, respectively, at 30 degrees C, 1.6 and 4.5 min at 37 degrees C) and incomplete (85 and 72% at 30 degrees C, 82 and 61% at 37 degrees C). Muscle creatine phosphate fell during fatigue but was completely restored within 4 min at 30 degrees C in either 2 or 25 mM HCO3. Lactate increased less in muscles fatigued in 2 mM HCO3 and fell at a slower rate during recovery. The results seem to exclude intracellular creatine phosphate concentration as a major determinant in recovery. The evidence suggests that external bicarbonate can affect the recovery of tension following fatigue by altering intracellular acid-base balance.
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PMID:The effect of bicarbonate concentration on fatigue and recovery in isolated rat diaphragm muscle. 742 82

Diaphragm fatigue occurs during heavy exercise. Acidosis leads to skeletal muscle fatigue, yet the diaphragm is not a net producer of either lactic acid or hydrogen ions. We tested the hypothesis that hydrogen ion and lactic acid concentrations similar to those seen in arterial blood at maximal exercise decrease contractility of the in vitro isolated rat diaphragm. Diaphragm strips were exposed to a control solution for 15 min and then to one of the following treatment solutions: control (C, pH = 7.4) or 10 mM lactic acid buffered to pH 7.4 (L74), pH 7.2 (L72), pH 7.1 (L71), or pH 6.8 (L68). After 15 min, the force-frequency relationship of the strip was measured. The strips were then stressed with 75 contractions at 25 Hz (250-ms train duration) at the rate of one per second and the force-frequency curve was measured after 15 min of recovery. The L74, L72, and L71 strips responded similarly to the C strips at all times and frequencies. Decrements in force associated with acidosis were only seen in L68. Within L68, we found decreases in force at stimulation frequencies < 100 Hz. These data suggest that physiologic levels of exogenous hydrogen ions are not a primary cause of in vitro diaphragm fatigue.
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PMID:Lactic acidosis and diaphragmatic function in vitro. 758 9

A 33-year-old man suffered chronic ventilatory insufficiency with tetraplegia after an operation for atlantoaxial dislocation. He was alert and his tetraplegia gradually improved. However, continuous mechanical ventilation was necessary for him. Thirteen months after the operation, a diaphragm pacer (Avery Laboratory Inc.) was implanted on the right phrenic nerve in the cervical region. Nineteen days after the implantation of the right side pacer, a left side diaphragm pacer was also implanted. Diaphragm pacing was started two weeks after the second implantation. The pacing period was gradually prolonged and continuous pacing for 9 hours by the right side pacer and three hours by the left side pacer was able to be obtained. One year after implantation, twelve continuous hours of diaphragm pacing became possible. During diaphragm pacing, blood gas analysis was satisfactory and the patient could move sitting on a wheel chair, watch television and write letters using a word processor. We were unable to achieve total ventilatory support for him using these diaphragm pacers. We thought that the main cause of our partial failure originated from the procedure used in implanting the electrode onto the phrenic nerve. Left side pacing needs higher amplitude than that used on the right side to obtain sufficient tidal volume. The patient refused our continuing the left side pacing because of pain around the anterior chest and shoulder. Another problem to be watched is diaphragm fatigue. However, diaphragm pacing has been continued for six years and it has been useful in improving his quality of life.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Ventilatory insufficiency due to upper cervical injury treated by diaphragm pacing: a case report]. 773 75

The purpose of the present study was to evaluate the effects of chronic mass loading produced by obesity on the structural and functional characteristics of the diaphragm in lean and obese Zucker rats. The trapezius muscle served as an internal control. The studies were carried out on 17 lean (303 +/- 24 g) and 16 obese (698 +/- 79 g) Zucker rats. We observed that the diaphragms from obese animals were restructured such that the overall contribution of type I and IIa fibers was significantly increased. As a consequence of this remodeling, overall diaphragm thickness was selectively greater in obese animals. In small isolated diaphragm bundles studied in vitro, we also detected a reduction in specific force in obese animals that was not detected in the trapezius muscle. In vitro fatigue resistance, assessed by repeated stimulation, was similar in muscles of lean and obese animals. Diaphragm fiber oxidative capacity (succinate dehydrogenase activity) was also comparable in lean and obese animals. We conclude that in obesity the diaphragm undergoes modest remodeling that may be beneficial in enhancing force generation.
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PMID:Histochemical and mechanical properties of diaphragm muscle in morbidly obese Zucker rats. 786 42

Recent reports suggested that exercise intolerance associated with congestive heart failure (CHF) may be due to changes in peripheral limb muscle function. Our purpose was to determine whether CHF also elicits alterations in diaphragmatic function. CHF was induced in dogs by rapid ventricular pacing for a period of 4-6 wk. After signs of CHF developed, dogs were anesthetized and an acute study was performed to assess diaphragm function. Diaphragm strips were dissected in situ in the left costal diaphragm, the phrenic artery supplying these strips was cannulated, and strips were perfused with arterial blood at arteriovenous pressure gradient of 90 mmHg. Diaphragm strength and fatiguability were then determined, and phrenic flow response to transient arterial occlusion was assessed. A group of nonpaced normal dogs was similarly studied and served as controls. We found that CHF dogs had a significant reduction in diaphragm strength. For example, tetanic force in response to 100 Hz of stimulation was 25.5 +/- 1.0 N/cm2 in control dogs but only 19.6 +/- 1.9 kg/cm2 in CHF dogs (P < 0.02). In addition, CHF dogs had increased diaphragm fatiguability. Diaphragm force fell to 27 +/- 3% of its baseline value during a 30-min fatigue trial in CHF dogs but only to 44 +/- 4% in control dogs (P < 0.01). CHF dogs also had a altered phrenic arterial hyperemic response to arterial occlusion and a reduction in phrenic arterial blood flow achieved during the fatigue trial. We conclude that development of CHF is associated with significant alterations in diaphragmatic function, causing a marked increase in fatiguability.
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PMID:Alterations in diaphragm strength and fatiguability in congestive heart failure. 792 4

Over the last 26 years diaphragm pacing has been used in over 400 adults and 70 children to support ventilation and oxygenation. Diaphragm pacing can be useful for conditions in which the brain stem respiratory centers provide little or no stimulation to the respiratory muscles, i.e. central hypoventilation syndrome, Arnold-Chiari malformation/brain stem dysfunction, and high quadriplegia. Because the pacing systems are so portable, the greatest advantages accrue to those patients who require ventilatory support both while awake and asleep. Infants and children require tracheostomy to avoid upper airway obstruction and bilateral pacing to meet higher metabolic demands. The stimulus parameters most appropriate for pediatric patients have been characterized as low stimulus frequency, short inspiratory time, and moderate respiratory rate. Use of similar stimulus parameters in an immature animal model has resulted in preservation of diaphragmatic structure and function but transformation of the diaphragm from a mixed muscle to one with a uniform population of type 1, fatigue-resistant fibers (physiologic, histochemical, myosin isoform, and ultrastructural evidence). In 33 pediatric patients, representing 96 patient-years of use, there were 26 failures of the pacing systems requiring removal and/or replacement of the internal components. Mean time to failure was 56 months. Of our 36 patients who had diaphragm pacing systems implanted, 26 are alive and 22 are currently using the pacing systems. wo recent advances may further improve the long-term outcome of patients using diaphragm pacing. Smaller, better encapsulated receivers may improve system longevity and a new stimulus electrode may reduce the risk of diaphragmatic damage.
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PMID:Diaphragm pacing: clinical and experimental results. 803 93

The effects of long-term undernutrition (10 wk) on diaphragm contractility, fatigue, and fiber type proportions were studied in male and female rats. Contractility and fatigue resistance indexes were measured in an in vitro diaphragm costal strip preparation by using direct stimulation at 37 degrees C. Undernutrition allowed for continued growth in males and females but with substantial reductions in weight gain. Relative to control rats of the same sex, final weights were significantly lower in undernourished males (74 +/- 3%) than females (90 +/- 5%), but weight gain was not significantly different between undernourished males (58 +/- 5%) and females (60 +/- 3%). Only in males did undernutrition significantly reduce costal diaphragm weight (to 77 +/- 5% of control). Diaphragm forces, normalized for cross-sectional area, were not significantly different from male or female control values. Fatigue resistance indexes (fatigue/baseline force) were increased at all stimulation frequencies in undernourished males but not in undernourished females. Costal diaphragm atrophy, involving types I and II fibers, occurred in undernourished males but not in undernourished females. In conclusion, despite long-term undernutrition reducing weight gain to similar levels in males and females (relative to control), there was excellent preservation of diaphragm weight, function, and structure in females but, although diaphragm atrophy occurred, there was preserved contractility and increased fatigue resistance in males.
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PMID:Effect of long-term undernutrition on male and female rat diaphragm contractility, fatigue, and fiber types. 804 30

The electromyogram (EMG) power spectrum from spontaneous diaphragm contractions has been used to identify the development of fatigue. However, power spectral analysis of the spontaneous diaphragmatic EMG signal is limited and subject to error. In contrast, power spectral analysis of the compound diaphragm action potential (CDAP) may be superior. The aim of the present study was to determine whether the EMG power spectra of evoked CDAPs correlate with those of spontaneous diaphragm contractions. Four anesthetized mechanically ventilated dogs with spontaneous isometric diaphragm contractions were studied using a mechanically isolated in situ diaphragm preparation. CDAPs were elicited via phrenic nerve stimulation, and intramuscular wire electrodes recorded EMG. Diaphragm temperature was changed from 40 to 30 degrees C to elicit changes in the EMG power spectra. The EMG signal from 10 spontaneous contractions and 10 CDAPs were acquired at 1 degrees C intervals. Fast Fourier transform was applied to both spontaneous and CDAP data yielding the power spectra, which were represented by their center frequencies (fc). The CDAP fc correlated well with the EMG fc obtained from spontaneous contractions (r = 0.99). We conclude that evoked CDAPs may provide an accurate alternative to spontaneous contractions for EMG power spectral analysis of the diaphragm.
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PMID:Comparison of diaphragmatic EMG power spectra: spontaneous contractions vs. evoked compound action potentials. 804 67


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