自発呼吸ネコの横隔神経活動に及ぼす高頻度人工換気法の効果と肺伸展受容器の求心性発射の役割
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概要
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High frequency ventilation(HFV) induces respiratory depression due to vagal afferent inputs. To clarify this inhibitory mechanism, the effects of HFV on efferent phrenic nerve activity and afferent vagal nerve activity from pulmonary stretch receptors were examined in spontaneously breathing cats. The animals were anesthetized with urethane (440mg/kg) and chloralose (35mg/kg). HFV was applied with a piston pump ventilator of a stroke volume of 7 ml. A bias-flow circuit was used and intratracheal pressure at the end of expiration was adjusted to 2.0cm H2O. A C5 branch of the right phrenic nerve was cut for the recording of efferent nerve discharges, which were used as an index for determining inspiratory time(Ti) and expiratory time(Te). Fine strands of ipsilateral cervical vagus were dissected under an operation microscope for recording single unit discharges from the pulmonary stretch receptor. With an application of HFV at 25 Hz, Te increased from 2.47±1.09 sec to 3.53±1.58 sec, while Ti and peak phrenic nerve activity did not change. Bilateral vagotomy abolished these effects. The unit discharges of 21 slowly adapting stretch receptors (SARs) with a high threshold, 4 SARs with a low threshold and 5 rapidly adapting stretch receptors (RARs) were recorded. In most SAR units, at the time of expiration, the average discharge rate increased whereas it did not change at the time of inspiration. At the time of expiration, SAR units discharged synchronously with air pulses of HFV. In 4 SAR units with a high threshold and 1 SAR unit with a low threshold, there were no observable changes in the average discharge rate at the time of expiration. In RAR units, 4 of 5 showed slight increases in the average discharge rate at the time of expiration. These results provide evidence that prolongation of Te during HFV on spontaneous breathing is due to increased afferent discharges of SAR units during HFV.
- 1987-06-01
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