Abstract
BackgroundInspiratory activity is a prerequisite for successful application of patient triggered ventilation such as proportional assist ventilation (PAV). It has recently been reported that surfactant instillation increases the activity of slowly adapting pulmonary stretch receptors (PSRs) followed by a shorter inspiratory time (Sindelar et al, J Appl Physiol, 2005 [Epub ahead of print]). Changes in lung mechanics, as observed in preterm infants with respiratory distress syndrome and after surfactant treatment, might therefore influence the inspiratory activity when applying PAV early after surfactant treatment.ObjectiveTo investigate the regulation of breathing and ventilatory response in surfactant-depleted young cats during PAV and during continuous positive airway pressure (CPAP) early after surfactant instillation in relation to phrenic nerve activity (PNA) and the activity of PSRs.MethodsSeven anesthetized, endotracheally intubated young cats were exposed to periods of CPAP and PAV with the same end-expiratory pressure (0.2–0.5 kPa) before and after lung lavage and after surfactant instillation. PAV was set to compensate for 75% of the lung elastic recoil.ResultsTidal volume and respiratory rate were higher with lower PaCO2 and higher PaO2 during PAV than during CPAP both before and after surfactant instillation (p < 0.05; both conditions). As an indicator of breathing effort, esophageal deflection pressure and PNA were lower during PAV than during CPAP in both conditions (p < 0.02). Peak PSR activity was higher and occurred earlier during PAV than during CPAP (p < 0.01), and correlated linearly with PNA duration in all conditions studied (p < 0.001). The inspiratory time decreased as tidal volume increased when CPAP was changed to PAV, with the highest correlation observed after surfactant instillation (r = -0.769). No apneic periods could be observed.ConclusionPSR activity and the control of breathing are maintained during PAV in surfactant-depleted cats early after surfactant instillation, with a higher ventilatory response and a lower breathing effort than during CPAP.
Highlights
Inspiratory activity is a prerequisite for successful application of patient triggered ventilation such as proportional assist ventilation (PAV)
Tidal volume and respiratory rate were higher with lower PaCO2 and higher PaO2 during PAV than during continuous positive airway pressure (CPAP) both before and after surfactant instillation (p < 0.05; both conditions)
As an indicator of breathing effort, esophageal deflection pressure and phrenic nerve activity (PNA) were lower during PAV than during CPAP in both conditions (p < 0.02)
Summary
Inspiratory activity is a prerequisite for successful application of patient triggered ventilation such as proportional assist ventilation (PAV). Proportional assist ventilation (PAV) is a new mode of assisted ventilation wherein the applied airway pressure is servo-controlled continuously throughout spontaneous inspiration, changing in proportion to the patient's breathing effort and allowing the patient to control the extent and timing of lung inflation [1,2,3]. In comparison with spontaneous breathing on continuous positive airway pressure (CPAP), PAV has been reported to increase the tidal volume and decrease arterial PaCO2 in cats with severe respiratory failure [6]. In a clinical study of low birth weight infants with mild respiratory distress syndrome (RDS), at a postnatal age of >24 hours, PAV maintained gas exchange with lower transpulmonary pressures compared with assist control ventilation and intermittent mandatory ventilation [7]
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