Functional classification of afferent phrenic nerve fibres and diaphragmatic receptors in cats.

Abstract

1. Single afferent fibres with receptive fields in the diaphragm (272 units) dissected from the right phrenic nerve were classified according to the following properties: reaction to contraction of the diaphragm, resting activity, conduction velocity, location and properties of receptive fields, and reaction to injection of bradykinin and lactic acid into the internal thoracic artery. Nine additional fibres dissected from the phrenic nerve had receptive fields outside the diaphragm. The experiments were performed on chloralose-anaesthetized cats. 2. Ninety-six fibres (36%) had high resting activity when unloaded by contraction of the diaphragm, had low-threshold receptive fields in the muscle and were mostly group II and III fibres. They probably innervated muscle spindles. 3. Eighty-eight fibres (32%) were vigorously activated by contraction of the diaphragm. They had low-threshold receptive fields located in the musculotendinous border and central tendon. Their conduction velocity was in the range for group II and III fibres. We infer that they may innervate tendon organs. 4. Eighty-eight fibres (32%) were slightly affected or not affected by diaphragmatic contraction. They had low- and high-threshold receptive fields located mostly in the muscular part of the diaphragm, and negligible resting activity. Most of them were group III and IV afferent fibres and were activated when bradykinin and lactic acid were applied to their receptive fields. Possibly these low- and high-threshold receptors innervated diaphragmatic ergo- and nociceptors, respectively. 5. Sensory outflow from the diaphragm was found to be somatotopically organized, so that fibres with receptive fields in the sternocostal portion were predominantly located in the upper phrenic nerve root, and those with lumbar receptive fields were in the lower root. 6. It is concluded that the phrenic nerve contains fibres from several distinct classes of sensory receptors: muscle spindles, tendon organs, ergoceptors and nociceptors. The sensory diaphragmatic outflow to the spinal cord is somatotopically organized.

Role of airway receptors in the reflex responses of human inspiratory muscles to airway occlusion.

“…However, their stimulus was larger and not necessarily comparable to that used here. The possibility of a contribution from vagally mediated reflexes to the responses to brief occlusion cannot be eliminated given the conduction velocity of the relevant vagal afferent fibres (Paintal, 1973 Kukula & Szulczyk, 1995). When tendon organ afferents in intercostal muscles are stimulated electrically or mechanically, inspiratory muscle activity is inhibited in part via the medullary inspiratory neurones (Shannon, 1986;Shannon, Bolser & Lindsay, 1988).…”

Effect of dorsal neck muscle fatigue on cervicocephalic kinaesthetic sensibility

“…This may be attributable to ionic or metabolic changes in free nerve endings, such as elevated interstitial potassium concentration, or reduced oxygen input attributable to reduced blood flow [5,34,35]. The errors were seen only in the sagittal plane, probably because of the anatomical orientation of the dorsal neck muscles.…”

Referred shoulder pain (C4 dermatome) can adversely impact diaphragm pacing with intramuscular electrodes

“…Our observations are compatible with this mechanism. Phrenic nerve afferents comprise diaphragmatic C-fibres [11]. These small unmyelinated fibres have a high excitation threshold; they are not likely to be depolarised by the low-intensity currents used for intrathoracic phrenic stimulation (maximum 2.2 mA in table 1) that are permitted by the close electrode-nerve proximity.…”