Intrathoracic pressure changes and cardiovascular effects induced by nCPAP and nBiPAP in sleep apnoea patients

The effect of nasal continuous positive airway pressure (nCPAP) and nasal bi-level positive airway pressure (nBiPAP) on intrathoracic pressure and haemodynamics during wakefulness was studied in a group of nine patients with severe sleep apnoea. No patient took cardiovascular medication. Patients were studied with a Swan Ganz catheter, an arterial line and an oesophageal balloon. nCPAP and nBiPAP were applied in the following pressure sequence: 5, 10 and 15 cm H2O of CPAP and 10/5 and 15/10 cm H2O of nBiPAP. Measurements were made at the end of a 5-min period at each pressure level. Intrathoracic pressure was noted to increase to a level of approximately 50% of the pressure delivered at the mask. At a CPAP of 10 cm H2O and above, as well as at BiPAP of 10/5 or higher, there was a decrease in cardiac output (CO) and cardiac index (CI). CI fell below the normal value in two of the patients. Transmural pulmonary artery pressure (PPAtm) decreased at a CPAP of 15 cm H2O and at both BiPAP levels. Transmural right atrial pressure (PRAtm) decreased at both BiPAP levels. There were no differences in CO, CI, PPAtm and PRAtm between nCPAP and nBiPAP at equal inspiratory pressures. SaO2 increased during BiPAP 15/10 cm H2O, whereas heart rate and arterial blood pressure did not change significantly. The data presented here are consistent with the literature on positive end-expiratory pressure (PEEP) applied via intratracheal tube and are likely to be due to a reduced venous return. It is concluded that nasally applied positive pressure may have acute negative effects on cardiac function in patients with sleep apnoea.