Expiratory Activity Recorded During Exercise from Human M. Biceps Brachii Reinnervated by Internal Intercostal Nerves

Abstract

In 1972, Clark and von Euler¹ proposed the inspiratory off-switch theory to explain the relationship between inspiratory activity and duration. It was proposed that the inspiratory activity is terminated, and inspiratory duration (T_I) is determined when the tidal inspiratory activity reaches a certain off-switch level. One major difference between the study of inspiratory and expiratory activities is that the volume curve does not give as much information on expiratory activity as it does on inspiratory activity. Thus, direct measurements from the expiratory neuromuscular units are necessary to study the relationship between expiratory activity and duration. This is possible in brachial plexus injury (root avulsion type) patients who have undergone the intercostal transfer operation.² From the studies of the expiratory activity in both humans and lab animals, an “expiratory off-switch mechanism” has been proposed. This mechanism is considered to be an independent system from the inspiratory off-switch system.^2,3,4 Another substage within the second stage of expiration (E2 stage)⁵ has been defined from the onset of the tidal expiratory activity to the suppression of the expiratory activity by the off-switch mechanism. Masato Sibuya would like to dedicate this paper to his grandmother, Raku Sibuya, who passed away during the time of the Oxford Meeting. This was designated the stage of active expiration (Ea stage).²