Extra‐segmental reflexes derived from intercostal afferents: phrenic and laryngeal responses

Abstract

SUMMARY1. Phrenic and recurrent laryngeal efferent responses were evoked by brief tetani or single shocks to the cut external intercostal nerves of anaesthetized cats. The reflexes derived from middle thoracic segments (T5 and 6) were compared with those emanating from caudal thoracic segments (T9 and 10).2. During inspiration, middle intercostal nerve stimulation transiently inhibited the spontaneous discharge in both efferent neurograms, whereas stimulation of caudal intercostal nerves facilitated phrenic discharge and usually inhibited recurrent laryngeal activity.3. During expiration, stimulation at either thoracic level enhanced recurrent laryngeal discharge while provoking little or no phrenic response.4. Superficial lesions of the lateral cervical cord, ipsilateral to the stimulus sites, above or below the phrenic outflow, eliminated all reflex responses except the phrenic response to caudal thoracic stimuli. Similarly, in the spinal animal, middle intercostal afferents could not be shown to decrease phrenic excitability. Caudal intercostal afferents cause phrenic excitation by a spinal reflex.5. Group

Effect of chest wall vibration on the canine diaphragm during breathing

“…The mechanism of this beneficial effect is uncertain, but high-frequency vibration is known to be a potent stimulus of spindle primary endings in limb muscles [5,6]. In addition, in agreement with earlier animal experiments by REMMERS [7,8], HOMMA et al [9] have reported a decrease in diaphragmatic and parasternal intercostal inspiratory electromyographic (EMG) activity during vibration of the lower intercostal spaces in normal subjects. To the extent that medullary inspiratory neurone activity appears to be one of the determinants of dyspnoea [10][11][12], the suggestion has therefore been made that the beneficial effect of ribcage vibration might be, in part, related to a reduction in central respiratory drive induced by increased afferent inputs from intercostal muscles [1,3,4].…”

“…In additional experiments, REMMERS [8] and DECIMA et al [21] have reported a similar inhibition of the diaphragm during electrical stimulation of group I and II afferent fibres in external intercostal nerves. Since this inhibitory response was also observed during high-frequency mechanical vibration of the ribs and was accentuated by the administration of succinylcholine, it was attributed to the stimulation of intercostal muscle spindles [7].…”

“…Furthermore, BOLSER et al [22], in agreement with the current findings, have found in decerebrate, unanaesthetized cats, that low-amplitude (v100 mm) vibration of external and internal intercostal muscles, leading to exclusive stimulation of muscle spindles, has no effect on phrenic or medullary inspiratory activity. Inhibitory responses were observed only when the amplitude of vibration was increased above 700 mm and produced concomitant stimulation of large numbers of intercostal tendon organs, thus indicating that the reflex inhibition of the diaphragm described by REMMERS [7,8] was due to tendon organ afferents, rather than muscle spindle afferents.…”

Spinal inhibition of phrenic motoneurones by stimulation of afferents from peripheral muscles.

“…Such a conclusion does not rule out the possibility, however, that there is a direct spinal reflex component of the respiratory response to stimulation of leg muscle afferents. There are precedents for this hypothesis in that stimulation of receptors in the intercostal muscles or their afferents do have a spinally mediated facilitatory effect on phrenic motoneurones in spinal cats (Downman, 1955;Decima, von Euler & Thoden, 1969;Remmers, 1973), although in animals with intact ponto-medullary control centers the net effect is inhibitory.…”

Effect of lateral cervical cord lesions on the respiratory rhythm of anaesthetized, decerebrate cats after vagotomy

“…These cord lesions eliminated the inhibition of diaphragmatic discharge caused by chest compression. Previous work (Remmers, 1973) indicates that this change can be attributed to loss of reflex inhibition of inspiratory activity by intercostal afferents, probably as a result of interruption of tracts ascending in the lateral columns.3. Decerebrate cats with bilateral cervical cord lesions displayed abnormal respiratory patterns, ranging from apnoea to apneusis.…”