P724

         Physiol Bohemoslov 1990;39(5):435-42

        Breathing of phrenicotomized rats.

        Nacházel J, Paleček F.

        Institute of Pathological Physiology, Faculty of Paediatrics, Charles

        University, Prague.

        Bilateral paralysis of the diaphragm can result in normo or

        hypoventilation, according to the species studied. Our aim was to

        ascertain the results of bilateral phrenicotomy in the rat and, if

        hypoventilation should be present, to try to identify its

        pathophysiology. We used 33 male rats under urethane anaesthesia (1.3

        g/kg i.p.). They were divided into three groups: control animals, rats

        with bilateral phrenicotomy and a group with two doses of pentobarbital

        (25 mg/kg i.p. each) on top of the urethane anaesthesia. We observed

        pronounced hypoventilation both in the rats after phrenicotomy and those

        with pentobarbital. At comparable levels of hypoventilation (PaCO2 =

        5.61  0.28 kPa immediately after phrenicotomy and 5.91  0.25 kPa

        after the first dose of pentobarbital; and 7.21  0.47 kPa 4 hours

        after phrenicotomy and 7.38  0.39 kPa after the second dose of

        pentobarbital) the only difference was a longer relative duration of

        inspiration in phrenicotomized rats; (0.39  0.04 and 0.34  0.04

        after phrenicotomy; 0.32  0.04 and 0.24  0.05 in rats after

        pentobarbital). Immediately after phrenicotomy and 2 and 4 hours later,

        and also after both doses of pentobarbital breathing was stimulated by

        hypoxia and hypercapnia due to the additional external dead space (0.5

        ml) for 5 min. There was no pronounced differences in the ventilatory

        response to the dead space between the two groups; the response changed

        from an isocapnic (in control rats and before phrenicotomy or

        pentobarbital) to an isoventilatory one (four hours after phrenicotomy

        and after the second dose of pentobarbital). The rats after the second

        dose of pentobarbital did not, however, survive the added dead

        space.(ABSTRACT TRUNCATED AT 250 WORDS)