P870

        Physiol Res 1992;41(5):375-80

        Hypoventilation after acute phrenicotomy of the urethane anaesthetized

        rats.

        Nacházel J, Paleček F.

        Institute of Pathological Physiology, Second Medical Faculty, Charles

        University, Prague.

        The aim of this study was to explore the mechanism resulting in

        hypoventilation in rats with denervated diaphragm. Bilateral cervical

        phrenicotomy (PX) was performed in 15 male rats anaesthetized with

        urethane (1.3 g/kg i.p.); other 8 rats were sham operated (SX).

        Ventilation, PaCO2 and the integrated EMG of the external intercostal

        muscles (iEMG) were measured before and after the surgery, at regular

        intervals, up to 4 hours postoperatively. During the 4 hours after PX

        there was a progressive decrease in minute ventilation and an increase

        in PaCO2 compared with the control values and with that in the SX rats.

        The increase in PaCO2 was accompanied by an increase in the peak

        amplitude of the iEMG to 155  18% of control values after PX and to

        228  33% 4 hours later. Despite the augmented EMG activity tidal

        volume gradually decreased. The iEMG of the intercostal muscles,

        however, did not reach a maximum because the shortlasting stimulation of

        breathing by acute hypercapnia and hypoxia as the result of added dead

        space (0.5 ml) increased the iEMG still further. These results indicate

        that both the central and peripheral mechanisms contribute to

        hypoventilation in anaesthetized rats with denervated diaphragm.