Diaphragm shortening and EMG activity during Continuous Positive Airway Pressure

<bold>Background:</bold> Continuous positive airway pressure (CPAP) is widely used in sleep disordered breathing. But, physiologic impact on respiratory parameters, diaphragm function and pre-inspiratory resting length (i.e. FRC) is not known. As the predominant muscle of respiration, diaphragm function during CPAP warrants investigation. <bold>Methods:</bold> Data from N=10 canines, from a database completed in 2009, previously implanted with sonomicrometers and EMG electrodes into costal diaphragm, was analyzed breath by breath. Breathing pattern, and muscle length, shortening and EMG activity per breath, of costal diaphragm were measured, with incremental CPAP levels: 0/0, 4/4, 8/8, and 12/12 cmH2O. <bold>Results:</bold> Minute ventilation decreased with increasing CPAP, brought about by reduction in respiratory rate (P<0.01) without change in tidal volume and mean inspiratory flow. Costal diaphragm resting length decreased significantly with increasing CPAP (LBL; P<0.05), accompanied by reduction in both shortening and EMG activity of costal diaphragm (SHORT, EMGDIFF; P<0.01) <bold>Conclusion:</bold> Positive airway pressure causes significant decrease in diaphragm resting length coupled with reduction in diaphragm shortening and EMG activation respiratory drive. Thus, despite a mechanically disadvantaged diaphragm from CPAP induced lung hyperinflation, paradoxical reduction in EMG/ respiratory drive was noted. <fig><object-id>erj;64/suppl_68/PA4473/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig>