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document
Effects of fenoterol on inspiratory effort sensation and fatigue during inspiratory threshold loading . 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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Intervention_Pharmacological
fenoterol
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Intervention_Pharmacological
fenoterol
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Intervention_Pharmacological
fenoterol
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Intervention_Pharmacological
placebo
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Intervention_Pharmacological
fenoterol
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Intervention_Pharmacological
fenoterol
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Outcome_Physical
endurance time
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Outcome_Physical
ratio of high- to low-frequency power of the diaphragmatic electromyogram ( EMGdi )
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Outcome_Physical
EMGdi
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Outcome_Physical
PI , mmax and maximal transdiaphragmatic pressure ( Pdi )
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Outcome_Physical
intensity of the IES rose with time
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Outcome_Physical
ratio of Pdi
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Outcome_Physical
superimposed Pdi twitch and Pdi twitch of relaxed diaphragm
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Outcome_Physical
value of ( 1-superimposed Pdi twitch/Pdi twitch of relaxed diaphragm ) .
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Participant_Condition
healthy subjects .