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

We investigated whether fatigue of the expiratory muscle may account for a change in the respiratory effort sensation in normal subjects. We also examined the effects of inspiratory muscle training (IMT) and a beta 2-agonist, fenoterol, on respiratory effort sensation during loaded breathing. Experiment 1: Expiratory threshold loading was performed until exhaustion or 30 min, to induce expiratory muscle fatigue. The respiratory effort sensation was scored using a modified Borg scale. The maximum static expiratory pressure during loading (PEmaxload) decreased with time, and the Borg score rose with time. The relationship between the sensory score and PEmaxload was virtually linear. Experiment 2: Twice daily, IMT was performed using a pressure threshold device for 15 min in each session. The inspiratory threshold was set to 30% of each subject's maximum inspiratory pressure (Plmax) and IMT was continued for 4 weeks. Respiratory sensation (Borg score) was evaluated during a progressive exercise test. IMT increased inspiratory muscle pressure by 30%. However, there was no change in Borg score during the exercise test. Experiment 3: Fenoterol (5 mg) was given 2 hours before the inspiratory threshold loading, and then threshold loaded breathing was continued until exhaustion or 60 min. Endurance time increased by 50% in fenoterol group compared to placebo group. The increase in Borg score with time was less in fenoterol group than in placebo group. The decrease in respiratory muscle strength after loading was comparable in both groups. We conclude that the increased respiratory effort sensation during expiratory threshold loading is closely related to expiratory muscle fatigue as indicated by the decrease in expiratory muscle force.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Relationship of respiratory muscle fatigue and respiratory effort sensation: mechanisms and treatment]. 140 66

We have studied the effects and mechanism of fenoterol (a beta 2-agonist) on contractility of the fatigued canine diaphragm. Transdiaphragmatic pressure (Pdi) was measured by a pair of balloons, and diaphragmatic contractility was assessed from changes in tetanic contraction, produced by supramaximal electrical stimulation of the phrenic nerves. Diaphragmatic fatigue was developed by applying an inspiratory resistive load to a spontaneously breathing dog for approximately 30 min. Fenoterol improved the Pdi of the fatigued canine diaphragm at all stimulation frequencies, and the increases in Pdi at low frequencies were greater. The potentiation of Pdi by fenoterol occurred in a dose-dependent manner with doses of 2.5 to 10 micrograms/kg and was equal to that of aminophylline. Dibutyryl cyclic AMP did not have significant effect on the Pdi at all stimulation frequencies. The augmentation of Pdi in the fatigued diaphragm by fenoterol was abolished by administration of a calcium antagonist, verapamil, and fenoterol did not change the diaphragmatic contractility in nonfatigued dogs. We thus have concluded that fenoterol improves contractility in the fatigued canine diaphragm and the effect might be brought about by an increased influx of calcium to the muscle cell.
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PMID:Effects and mechanism of fenoterol on fatigued canine diaphragm. 284 26

We studied the effects of a single dose of fenoterol on the relationship between inspiratory effort sensation (IES) and inspiratory muscle fatigue induced by inspiratory threshold loading in healthy subjects. The magnitude of the threshold was 60% of maximal static inspiratory mouth pressure (PI,mmax) at functional residual capacity, and the duty cycle was 0.5. Subjects continued the threshold loaded breathing until the target mouth pressure could no longer be maintained (endurance time). The intensity of the IES was scored with a modified Borg scale. Either fenoterol (5 mg) or a placebo was given orally 2 h before loading in a randomized double-blind crossover protocol. The endurance time with fenoterol (34.4 +/- 8.6 min) was longer than that with the placebo (22.2 +/- 7.1 min; P < 0.05). The ratio of high- to low-frequency power of the diaphragmatic electromyogram (EMGdi) decreased during loading; the decrease was less with fenoterol (P < 0.05). The EMGdi also decreased with loading; the decrease was greater on fenoterol treatment (P < 0.01). The PI,mmax and maximal transdiaphragmatic pressure (Pdi) were similarly decreased after loading on either treatment. The intensity of the IES rose with time during loading in both groups but was lower with fenoterol than with the placebo (P < 0.05). The ratio of Pdi to integrated activity of the EMGdi increased with fenoterol (P < 0.05). Fenoterol treatment increased both superimposed Pdi twitch and Pdi twitch of relaxed diaphragm and decreased the value of (1-superimposed Pdi twitch/Pdi twitch of relaxed diaphragm). Thus we conclude that in normal subjects fenoterol reduces diaphragmatic fatigue and decreases the motor command to the diaphragm, resulting in a decrease in IES during inspiratory threshold loading and a prolongation of endurance.
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PMID:Effects of fenoterol on inspiratory effort sensation and fatigue during inspiratory threshold loading. 896 29