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

Central neurogenic hyperventilation (CNH), for which there is no effective therapy, can eventually result in respiratory fatigue and death. This report describes a patient with CNH due to a brainstem anaplastic astrocytoma who also exhibited disturbances of sleep and ocular motor function. The CNH responded clinically to morphine sulfate and methadone. Analysis of ventilatory response to CO2 before and after morphine demonstrated a depression of ventilatory response (49 to 53% of baseline) and occlusion pressure response (35 to 50% of baseline) to CO2, with a requirement for high doses of naloxone (10 mg IV) to reverse the effect. Polysomnography revealed sustained hyperventilation, elevated O2 saturation, and low end-tidal CO2 throughout all stages of non-rapid eye movement (NREM) sleep, and absence of rapid eye movement (REM) sleep. Ocular motor evaluation disclosed absence of horizontal and reflexive saccades with compensatory head thrusts. Correlation of the clinical and physiologic data with the MRI abnormalities suggested that the lesion responsible for CNH in this patient might reside in the medial tegmental parapontine reticular formation. Since recurrent episodes of hyperventilation responded in a sustained fashion to IV and oral opiates, this treatment may warrant consideration in other patients with CNH.
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PMID:Central neurogenic hyperventilation: pharmacologic intervention with morphine sulfate and correlative analysis of respiratory, sleep, and ocular motor dysfunction. 223 27

The effect of acute hypercapnia on skeletal muscle contractility and relaxation rate was investigated. The contractile force of fresh and fatigued quadriceps femoris (QF) and adductor pollicis (AP) was studied in normal humans by use of electrical stimulation. Maximum relaxation rate from stimulated contractions was measured for both muscles. Acute hypercapnia led to a rapid substantial reduction of contraction force. The respiratory acidosis after 9% CO2 was breathed for 20 min [mean venous blood pH 7.26 and end-tidal PCO2 (PETCO2) 65.1 Torr] reduced 20- and 100-Hz stimulated contractions of QF to 72.8 +/- 4.4 and 80.0 +/- 5.1% of control values, respectively. After 8 and 9% CO2 were breathed for 12 min, AP forces at 20- and 50-Hz stimulation were also reduced. Twitch tension of AP was reduced by a mean of 25.5% when subjects breathed 9% CO2 for 12 min [mean arterialized venous blood pH (pHav) 7.25 and PETCO2 66 Torr]. Over the range of 5% (pHav 7.38 and PETCO2 47 Torr) to 9% CO2, there was a linear relationship between twitch tension loss and pHav, arterialized venous blood PCO2, and PETCO2. Acute respiratory acidosis (mean PETCO2 61 Torr) increased the severity of low-frequency fatigue after intermittent voluntary contractions of AP. At 20 min of recovery, twitch tension was 63.2 +/- 13.4 and 46.8 +/- 16.4% of control value after exercise breathing air and 8% CO2, respectively. Acute hypercapnia (mean PETCO2 65.1 and 60.5 Torr) did not alter the maximum relaxation rate from tetanic contractions of fresh QF and from twitch tensions of AP.
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PMID:Effect of acute hypercapnia on limb muscle contractility in humans. 226 73

Factors contributing to maximal incremental and short-term exercise capacity were measured before and after 12 wk of high-intensity endurance training in 12 old (60-70 yr) and 10 young (20-30 yr) sedentary healthy males. Peak O2 uptake in incremental cycle ergometer exercise increased from 1.60 +/- 0.073 to 2.21 +/- 0.073 (SE) l/min (38% increase) in the old subjects and from 2.54 +/- 0.141 to 3.26 +/- 0.181 l/min (29%) in the young subjects. Peak cardiac output, estimated by extrapolation from a series of submaximal measurements by the CO2 rebreathing method, increased by 30% (from 12.7 to 16.5 l/min) in the old subjects, associated with a 6% increase (from 126 to 135 ml/l) in arteriovenous O2 difference; in the young subjects there were equal 14% increases in both variables (18.0 to 20.5 l/min and 140 to 159 ml/l, respectively). Submaximal mean arterial pressure and cardiac output were lower posttraining in the old subjects; total vascular conductance and cardiac stroke volume increased. Although peak power at the start of a short-term maximal isokinetic test did not change, total work accomplished in 30 s at a pedaling frequency of 110 revolutions/min increased in both groups, from 11.2 to 12.6 kJ and from 15.7 to 16.9 kJ in the old and young, respectively; fatigue during the 30-s test was less, and postexercise plasma lactate concentrations were lower. In older subjects, increases in aerobic power after high-intensity endurance training are at least as large as in younger subjects and are associated with increases in vascular conductance, maximal cardiac output, and stroke volume.
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PMID:High-intensity endurance training in 20- to 30- and 60- to 70-yr-old healthy men. 227 73

Changes in blood gases, ions, lactate, pH, hemoglobin, blood temperature, total body metabolism, and muscle metabolites were measured before and during exercise (except muscle), at fatigue, and during recovery in normal and acetazolamide-treated horses to test the hypothesis that an acetazolamide-induced acidosis would compromise the metabolism of the horse exercising at maximal O2 uptake. Acetazolamide-treated horses had a 13-mmol/l base deficit at rest, higher arterial Po2 at rest and during exercise, higher arterial and mixed venous Pco2 during exercise, and a 48-s reduction in run time. Arterial pH was lower during exercise but not in recovery after acetazolamide. Blood temperature responses were unaffected by acetazolamide administration. O2 uptake was similar during exercise and recovery after acetazolamide treatment, whereas CO2 production was lower during exercise. Muscle [glycogen] and pH were lower at rest, whereas heart rate, muscle pH and [lactate], and plasma [lactate] and [K+] were lower and plasma [Cl-] higher following exercise after acetazolamide treatment. These data demonstrate that acetazolamide treatment aggravates the CO2 retention and acidosis occurring in the horse during heavy exercise. This could negatively affect muscle metabolism and exercise capacity.
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PMID:Effects of acetazolamide on metabolic and respiratory responses to exercise at maximal O2 uptake. 231 72

Whilst the sequelae of extensive tuberculous infections generally manifest as an overall respiratory failure, characterised by a rise in the alveolar arterial gradient for oxygen and often CO2 retention, we report some observations on six patients with significant pleural and parenchymal tuberculosis; these patients presented with a restrictive syndrome associated with an apparently isolated alveolar hypoventilation. In four of these patients an effort test showed that there was adequate adaptation to alveolar ventilation on effort. In one patient measurement of PO.1 in a resting state and then during the course of a test of CO2 responsiveness revealed an absence of any response to CO2. On the basis of these results, we propose that in certain subjects suffering from significant sequelae of tuberculous disease the major functional abnormalities can be expressed as alveolar hypoventilation. This latter is not necessarily followed by a mechanical overload leading to an eventual fatigue of respiratory muscles but rather to a disorder of the regulation of ventilation. The basic mechanism of such an anomaly remains undetermined.
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PMID:[Isolated alveolar hypoventilation as a tubercular sequellae]. 232 Jul 85

1. Changes in force and stiffness were recorded simultaneously during 1 s isometric (fixed ends) tetani of single fibres isolated from the anterior tibialis muscle of Rana temporaria (temperature 1-3 degrees C; sarcomere length, 2.10 micron). Stiffness was measured as the change in force that occurred in response to a 4 kHz sinusoidal length oscillation of the fibre. Some experiments were performed in which stiffness was determined from a fast (0.2 ms) length step that was applied to a 'tendon-free' segment of the muscle fibre during the tetanus plateau. 2. A moderate degree of fatigue was produced by decreasing the time between tetani from 300 s (control) to 15 s. By this treatment the maximum tetanic force (Ftet) was reversibly reduced to 70-75% of the control value. Maximum tetanic stiffness (Stet) was related to Ftet according to the following regression (both variables expressed as percentage of their control values): Stet = 0.369 Ftet + 62.91 (correlation coefficient, 0.95; P less than 0.001). A 25% decrease in isometric force during fatigue was thus associated with merely 9% reduction of fibre stiffness. 3. Whereas the rate of rise of force during tetanus was markedly reduced by fatiguing stimulation, the rate of rise of stiffness was only slightly affected. 4. Intracellular acidification (produced by raised extracellular CO2 concentration) largely reproduced the contractile changes observed during fatigue. However, for a given decrease in tetanic force there was a smaller reduction in fibre stiffness during acidosis than during fatigue. 5. Caffeine (0.5 mM) added to the fibre after development of fatigue and intracellular acidosis greatly potentiated the isometric twitch but did not affect maximum tetanic force. This finding provides evidence that the contractile system was fully activated during the tetanus plateau both in the fatigued state and during acidosis. 6. The results suggest that the decrease in contractile strength after frequent tetanization (intervals between tetani, 15 s) is attributable to altered kinetics of cross-bridge function leading to reduced number of active cross-bridges and, most significantly, to reduced force output of the individual bridge. The possible role of increased intracellular H+ concentration in the development of muscle fatigue is discussed.
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PMID:Changes in force and stiffness induced by fatigue and intracellular acidification in frog muscle fibres. 239 50

Theophylline improves diaphragmatic contractility of the respiratory muscles both in isolated muscle preparations, as well as in animals and normal human beings. Furthermore, theophylline restores diaphragmatic fatigue and prevents fatigue of the diaphragm when given prophylactically. Finally, it was recently shown that theophylline improves diaphragmatic function in COPD patients, all of whom were CO2 retainers (PaCO2 53 +/- 3 mm Hg) and hypoxemic (PaO2 57 +/- 8 mm Hg). Patients improved transdiaphragmatic pressure and were less susceptible to fatigue. Presently the mechanisms of action of theophylline regarding its effects on diaphragmatic function are not fully elucidated. Experimental evidence, however, suggests that theophylline may have an effect on transmembrane calcium movements by blocking adenosine receptors.
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PMID:Effect of theophylline on respiratory muscle function. 241 Feb 4

1. Single muscle fibres were dissected from Xenopus lumbrical muscles and microinjected with the photoprotein aequorin in order to measure the myoplasmic free calcium concentration ([Ca2+]i). Fatigue was produced by repeated intermittent tetanic stimulation continued until tension had declined to approximately 50% of the initial level. Fibres were then allowed to recover by giving tetani at less frequent intervals. Aequorin light (a measure of [Ca2+]i) and tension were measured during fatiguing stimulation and recovery. 2. During fatiguing stimulation, tetanic tension declined steadily, but peak aequorin light first increased before declining substantially. The largest light signal was about 155% of initial control while at the end of fatiguing stimulation the tetanic light fell to about 14% of control. 3. Fibres showed a characteristic slowing of relaxation in the fatigued state. This was associated with a slowing of the rate of decline of the aequorin light signal. 4. Intracellular acidosis produced by equilibrating the Ringer solution with either 5 or 15% CO2 caused an increase in the light signal associated with a tetanus. Carbon dioxide also caused a reduction of tension and a slowing of relaxation. 5. In vivo pCa-tension curves were constructed by exposing the fibres to a series of K+ concentrations which produced contractures of different sizes. Light and tension were measured during periods when both were relatively stable and the light signal was subsequently converted to pCa. 6. Exposure of fibres to 5 or 15% CO2 caused the pCa-tension curve to be shifted to the right of the control curve. This indicates a reduced Ca2+ sensitivity of the contractile proteins, which is in agreement with results from skinned fibre studies. 7. The pCa-tension points obtained from tetani during the early part of fatiguing stimulation also deviated to the right of the control pCa-tension curve, suggesting a reduced Ca2+ sensitivity of the contractile proteins. At the end of fatiguing stimulation, however, pCa-tension points did not differ greatly from the control pCa-tension curve, suggesting that Ca2+ sensitivity was approximately normal. Thus the reduced [Ca2+]i during tetani at the end of fatiguing stimulation (when tension was reduced to approximately 50%) could explain all of the reduction in tension. 8. After fatiguing stimulation, tension and light recovered monotonically in some fibres; however, in the majority of fibres, tension and light showed a secondary decline followed by a slower recovery (post-contractile depression). 9. During post-contractile depression, caffeine contractures or tetani in the presence of caffeine gave increased aequorin light signals and the tension developed was close to that produced in an unfatigued tetanus.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Intracellular calcium and tension during fatigue in isolated single muscle fibres from Xenopus laevis. 251 88

1. Longitudinal movements of marked segments of single fibres from the anterior tibialis muscle were recorded during tetanus and relaxation under isometric (fixed-end) conditions. 2. During relaxation, shortening and lengthening of different segments occurred simultaneously, starting at about the same time as the end of the linear fall of force (shoulder on the force record). 3. Variations in intracellular pH, measured with pH-sensitive microelectrodes, along the length of fibres were not statistically significant, and are unlikely to be responsible for the non-uniform behaviour of different segments. 4. As expected from earlier studies, both fatigue (produced by increasing tetanus duration or decreasing the time between tetani) and intracellular acidification (produced by raised extracellular CO2), reduced the tetanus force and prolonged the linear phase of force decline in relaxation. Each treatment delayed the start and markedly reduced the amount of segment movement in relaxation. 5. Fatigue and intracellular acidification have a smaller effect on force during stretching than on force produced under isometric conditions. This may contribute to making the segments behave in a more uniform way during relaxation under these conditions. 6. Changes in the Ca2+ uptake mechanisms are also discussed as possible causes for the changes in segment behaviour in relaxation.
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PMID:Effects of fatigue and reduced intracellular pH on segment dynamics in 'isometric' relaxation of frog muscle fibres. 260 Aug 46

Chest negative pressure ventilation (CNPV) and intermittent positive pressure ventilation (IPPV) through a nose mask were used for ventilatory support of 4 patients with chronic respiratory failure due to old tuberculosis (2 patients), chronic pulmonary emphysema, and kyphoscoliosis (VC, 0.91 +/- 0.16 L; %VC 31.2 +/- 3.2; FEV1.0, 0.62 +/- 0.19 L). These ventilatory supports were used for relief of chronic arterial CO2 retention, weaning from the mechanical ventilation, therapy for the acute exacerbation on the chronic respiratory failure, and the relief of the respiratory muscle fatigue. After CNPV and IPPV through a nose mask, PaCO2 showed a significant fall from 75.7 +/- 14.8 Torr to 60.2 +/- 12.3 Torr (p less than 0.01). All patients showed improvement of clinical symptoms. Two patients have continued CNPV at home on a regular basis. We conclude that CNPV and IPPV through a nose mask significantly improve hypoventilation and quality of life in some patients with chronic respiratory failure.
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PMID:[Noninvasive ventilatory support on chronic respiratory failure with hypoventilation]. 262 Jan 35


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