Maximal dynamic expiratory pressures with fast and slow inspirations

Maximal dynamic expiratory pressures are higher when forced expiration is preceded by a fast inspiration to total lung capacity (TLC) than when preceded by a slow inspiration and a few seconds pause at TLC. We hypothesized that these pressure differences are due to the stretch-shorten cycle (SSC), w...

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Bibliographic Details
Published in:European journal of applied physiology 2003-03, Vol.89 (1), p.74-78
Main Authors: Altarifi, Ashraf, Badr, M Safwan, Tzelepis, George E
Format: Article
Language:English
Subjects:
Adult
Electromyography
Forced Expiratory Volume - physiology
Humans
Inspiratory Capacity - physiology
Muscle Contraction - physiology
Pressure
Respiratory Mechanics - physiology
Respiratory Muscles - physiology
Total Lung Capacity - physiology
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Summary:Maximal dynamic expiratory pressures are higher when forced expiration is preceded by a fast inspiration to total lung capacity (TLC) than when preceded by a slow inspiration and a few seconds pause at TLC. We hypothesized that these pressure differences are due to the stretch-shorten cycle (SSC), which refers to enhancement of muscle force when a concentric muscle contraction is immediately preceded by an eccentric contraction. Seven volunteers [36 (2) years; mean (SEM)] performed maximal forced expirations against minimal resistance with fast (F) or slow (S) maneuvers. F maneuvers consisted of a fast inspiration to TLC followed immediately by a fast expiration, whereas S consisted of a slow inspiration to TLC and a 4- to 5-s pause at TLC prior to forced expiration. We measured esophageal pressure ( P(es)), peak expiratory flow rate (PEFR), and the EMG activity of the transversus abdominis (Tr) by means of intramuscular fine-wire electrodes. The subjects performed several runs of each maneuver in a random order, and runs with the greatest expiratory P(es) were analyzed. In comparison with S, F yielded greater P(es) [182 (15) versus 167 (15) cm H(2)O; P=0.003)] but similar PEFR [9.8 (0.7) versus 9.6 (0.7) l/s, P>0.05] and EMG activity of the Tr during forced expiration [221 (31) versus 208 (34) a.u., P>0.05]. Further analysis revealed significant EMG activity of Tr during end-inspiration (eccentric contraction) with F maneuvers only [73 (22) versus 32 (17) a.u., P
ISSN:1439-6319
1439-6327
DOI:10.1007/s00421-002-0773-3