Nasal proportional assist ventilation unloads the inspiratory muscles of stable patients with hypercapnia due to COPD

This study was undertaken to assess the physiological effects of proportion al assist ventilation (PAV), administered noninvasively through a nose mask , on ventilatory pattern, arterial blood gases, lung mechanics, and inspira tory muscle effort in stable, hypercapnic patients with chronic obstructive pulmonary disease. In 15 patients, PAV was set by adjusting volume assist (VA) and now assist (FA) according to the "run-away" technique and the patient's comfort respec tively. The level of support was fixed at 80% of the total possible assista nce and averaged 13.9+/-4.1 cmH(2)O . L-1 and 4.1+/-1.3 cmH(2)O . L-1.s for VA and FA, respectively. Continuous positive airway pressure (CPAP) was es tablished at 2 cmH(2)O and then increased to 5 cmH(2)O. Physiological measu rements were made during spontaneous breathing (SB), after more than 40 min of PAV, and 20 min after the rise in CPAP. On average, PAV improved ventilation (10.3+/-2.1 to 12.5+/-2.0 L.m(-1)), ti dal volume (0.60+/-0.11 to 0.76+/-0.24 L), arterial oxygen tension and arte rial carbon dioxide pressure (from 6.7+/-0.7 to 7.1+/-0.9 and from 7.6+/-1. 0 to 7.2+/-1.2 kPa, respectively). During SE, pulmonary resistance and dyna mic lung elastance averaged 15.0+/-7.6 cmH(2)O . L-1. s and 15.8+/-8.0 cmH( 2)O . L-1, respectively. Assuming a normal chest wall elastance (5 cmH(2)O . L-1), VA and FA relieved respectively similar to 70% of the elastic and 3 0% of the resistive burden, with PAV set,vith the procedure of this study. The overall magnitude of the patients' inspiratory effort, measured by mean s of the oesophageal and diaphragmatic pressure time product in 10 patients was significantly reduced by PAV, on average, 328+/-122 to 226+/-118 (-31% ) and 361+/-119 to 254+/-126 (-30%) cmH(2)O . min(-1), respectively. In 10 patients the electrical activity of the diaphragm (Edi) was also reduced by PAV to similar to 70%, an average, of the SE activity. The rise of CPAP 2- 5 cmH(2)O did not cause any further significant change in the physiological variables. In all instances there was a good patient-ventilator interactio n, the ventilatory breath never entering into the patient's neural expirato ry time. These data show that nasal proportional assist ventilation can provide phys iological benefits to the stable hypercapnic chronic obstructive pulmonary disease patients. In fact, proportional assist ventilation, which was well tolerated by all patients, unloaded the inspiratory muscles and improved ar terial blood gases. Further studies can clarify whether these beneficial ph ysiological effects of nasal proportional assist ventilation can bear profi table consequences in the overall clinical management of chronic obstructiv e pulmonary disease patients with chronic carbon dioxide retention.