EFFECTS OF PULMONARY AND INTERCOSTAL DENERVATION ON THE RESPONSE OF BREATHING FREQUENCY TO VARYING INSPIRATORY FLOW

In mechanically ventilated awake and sleeping humans, it has been show n that increasing inspiratory flow rate ((VI)-I-1) exerted a reflex ex citatory effect on respiratory output. Mechanoreceptors located in int ercostal muscles or within the lung have been suggested as possible pa thways that may mediate the excitatory effect of (VI)-I-1, To test thi s, five patients with bilateral lung transplantation (LTP) and eight q uadriplegics with spinal cord transection at the level of C6-C7 (QP) w ere studied, Patients were connected to a volume cycle ventilator in t he assist volume-control mode and (VI)-I-1 was randomly changed. (VI)- I-1 pattern was square and all breaths were patient-triggered, (VI)-I- 1 values of 30, 60 and 90 L.min(-1) were studied. Each level of (VI)-I -1 was sustained for 15 breaths, Airway pressures, end-tidal partial p ressure of carbon dioxide (P-CO2), airflows and volumes were measured breath by breath. Thirty seven trials in LTP and sixty in QP, where (V I)-I-1 was randomly changed between 30 and 90 L.min(-1), were analysed ,In both groups of patients, minute ventilation increased and total br eath duration decreased significantly as (VI)-I-1 increased. These cha nges were complete in the first breath after (VI)-I-1 transition, with out evidence of adaptation of the response, The magnitude of the respo nse did not differ between the two groups of patients and was comparab le to that observed previously in conscious normal subjects. We conclu de that the excitatory effect of inspiratory how rate on breathing fre quency persists in patients who have pulmonary or intercostal denervat ion, These results do not favour receptors located within the lung (be low the resection lines) or in the intercostal muscles to mediate the response of breathing frequency to how rate.