Inhibition of breathing after surfactant depletion is achieved at a higher arterial PCO2 during ventilation with liquid than with gas

Background: Inhibition of phrenic nerve activity (PNA) can be
achieved when alveolar ventilation is adequate and when stretching
of lung tissue stimulates mechanoreceptors to inhibit inspiratory
activity. During mechanical ventilation under different lung
conditions, inhibition of PNA can provide a physiological setting
at which ventilatory parameters can be compared and related to
arterial blood gases and pH. Objective: To study lung mechanics and
gas exchange at inhibition of PNA during controlled gas ventilation
(GV) and during partial liquid ventilation (PLV) before and after
lung lavage. Methods: Nine anaesthetised, mechanically ventilated
young cats ( age 3.8 +/- 0.5 months, weight 2.3 +/- 0.1 kg) ( mean
+/- SD) were studied with stepwise increases in peak inspiratory
pressure ( PIP) until total inhibition of PNA was attained before
lavage ( with GV) and after lavage ( GV and PLV). Tidal volume
(V-t), PIP, oesophageal pressure and arterial blood gases were
measured at inhibition of PNA. One way repeated measures analysis
of variance and Student Newman Keuls-tests were used for
statistical analysis. Results: During GV, inhibition of PNA
occurred at lower PIP, transpulmonary pressure (Ptp) and Vt before
than after lung lavage. After lavage, inhibition of inspiratory
activity was achieved at the same PIP, Ptp and Vt during GV and
PLV, but occurred at a higher PaCO2 during PLV. After lavage
compliance at inhibition was almost the same during GV and PLV and
resistance was lower during GV than during PLV. Conclusion:
Inhibition of inspiratory activity occurs at a higher PaCO2 during
PLV than during GV in cats with surfactant-depleted lungs. This
could indicate that PLV induces better recruitment of
mechanoreceptors than GV.