Effects of long-lasting stimulation of extensor muscle nerves on pulmonary ventilation in cats

Increments in pulmonary ventilation were shown to occur in anaesthetized cats during long-lasting stimulation of a peripherally cut extensor muscle nerve at maximal intensity for group I afferent fibers. However, these increments tended to gradually adapt to a lower value when stimuli were delivered at high frequency and constant rate whereas a tendency to potentiation, up to a steady state, occurred when stimulation was intermittent. End-tidal PCO2 initially decreased with a tendency to adaptation in the case of continuous stimulation, and decreased progressively in the case of intermittent stimulation. It is concluded that the nervous mechanisms producing hyperpnoea exhibit fatigue during their constant excitation while their effects sum up during intermittent stimulation.