Electrical stimulation of arterial and central chemosensory afferents at different times in the respiratory cycle of the cat: I. Ventilatory responses

Ventilatory responses to stimulation of chemoreceptor afferents were studied in the anesthetized, spontaneously breathing cat. Short bursts of electrical stimuli were applied, at various times in the inspiratory or expiratory phase of consecutive breaths, to the carotid sinus (CSN) and aortic nerves (AN) and to the ventral medulla (VM), and effects on tidal volume (V _T), inspiratory, expiratory and cycle durationst _I,t _E,t _tot) and in ventilation (_E) were measured. The responses evoked by stimulating CSN, AN and VM were qualitatively the same, although there were quantitative differences. It was found that effects of stimulation in expiration were restricted to the expiratory phase, and vice versa for inspiration. Stimulation during both inspiration and expiration resulted in increasedV _T, by increasing end-inspiratory or decreasing end-expiratory lung volume, respectively, and also increased ventilation, _E. These effects were most marked in response to stimulation in inspiration. During both phases there was an increasing effect with increasing delay of the stimulus,t _St, from onset of inspiration or expiration, respectively. There was a continuous increase int _I, from below control to above control values, with increasingt _St during inspiration and similarly fort _E during expiration. Hence, the total respiratory cycle duration was shortened when a stimulus was applied early in either phase, and was prolonged, when it was applied late. The results show that stimulation of peripheral and of central chemoafferents exerts qualitatively similar effects on respiration. The central neuronal mechanisms generating both inspiration and expiration show the same changes in reactivity in the respiratory cycle.Supported by the Deutsche Forschungsgemeinschaft, SFB 114 Bionach     

Myelinated nerve fiber supply and muscle spindles in the respiratory muscles of cat: Quantitative study

Summary The present study was undertaken to provide quantitative data on the myelinated fibers of the phrenic and intercostal nerves and the number of spindles in the main respiratory muscles of the cat.The myelinated component of the phrenic and intercostal nerves was studied in the cat. Histograms of sequency distributions as a function of nerve fiber diameter were established for normal nerves. Certain nerves were then examined 35 to 40 days after excision of the dorsal spinal ganglia. The muscle spindles of the corresponding muscles were counted and localized, and, on the basis of several morphological criteria, were classified with those usually described in the interosseous muscles.The study of the nerves, as that of the spindles, demonstrates clear differences of proprioceptive innervation among the respiratory muscles. The lateral part of the diaphragm and the Triangularis sterni have practically no spindles. The external muscles of the first thoracic spaces are very rich in spindles. Respiratory muscles can be ranged in an almost continuous manner between these two extremes.