Alteration in breathing of the awake rat after laryngeal and diaphragmatic muscle paralysis

The respiratory rate (f), tidal volume ( Vt) and ventilation (V̇) were measured in 3 groups of rats: 10 rats before and after cutting both recurrent laryngeal nerves (RLNX), 10 rats before and after bilateral phrenicotomy (PNX) and 5 sham transected (SHAMX) rats. All rats were exposed to air and gas mixtures, deficient in O 2 and/or enriched with CO 2. The barometric method was used to measure ventilatory parameters. The sham operation did not affect breathing pattern or ventilation. In RLNX rats, breathing the various gas mixtures exhibited no changes in V̇ because f uniformly increased as Vt declined. Therefore, loss of the neural control of the respiratory function of the larynx in awake rats exposed to selected gas mixtures has no untoward effects on alveolar ventilation. Changes in ventilation of PNX ratsm compared with SHAMX rats, depends on the gas composition breathed. With increasing severity of hypoxia and/or hypercapnia, PNX rats show a marked reduction in alveolar ventilation over that the SHAMX rats. Thus, when the diaphragm is no longer able to participate in ventilatory responses, gas exchange is likely to become deficient.