DIFFERENTIAL EFFECT OF VENTROLATERAL MEDULLARY COOLING ON RESPIRATORYMUSCLES OF GOATS

The objective was to determine whether there is an inhomogeneous respo nse of respiratory muscles during cooling-induced ventrolateral medull ary (VLM) neuronal dysfunction in anesthetized and awake goats. Thermo des for cooling were chronically implanted on all or portions of rostr al, intermediate, and caudal areas of the VLM of 16 adult goats. Elect romyograms (EMGs) were obtained from chronically implanted wires in th e diaphragm (di), transversus abdominis (TA), and triangularis sterni (TS) muscles. During some periods of cooling in 9 of 16 anesthetized a irway-intubated goats, complete cessation of EMG(di) coincided with a reduced yet sustained inspiratory flow. In six awake tracheotomized go ats, VLM cooling decreased (P < 0.05) EMG(di) duration and minute acti vity more than inspiratory duration and minute ventilation. Cooling th us decreased activation of the diaphragm more than activation of other respiratory muscles. On the other hand, during VLM cooling in 3 of 10 airway-intact awake goats, cessation of inspiratory flow coincided wi th sustained EMG(di), suggesting that cooling decreased stimulation of the upper airway muscles more than stimulation of the diaphragm. Fina lly, VLM cooling in a majority of goats decreased EMG(TA) and EMG(TS) more than EMG(di). We conclude that VLM neuronal dysfunction has a dif ferential effect on respiratory muscles of adult anesthetized and awak e goats.