EFFECT OF CONTINUOUS POSITIVE AIRWAY PRESSURE ON RESPIRATORY MECHANICS AND PATTERN OF BREATHING IN INDUCED ASTHMA

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Abstract
Effects of continuous positive airway pressure (CPAP) were studied in 8 asthmatic [human] subjects in whom bronchospasm was induced by aerosolized histamine. The CPAP (12.0 .+-. 0.9 cm H2O) increased functional residual capacity by only 0.27 .+-. 0.12 l, raised the minimal pleural pressure (Ppl) during inspiration from -32.2 .+-. 2.6 to -22.8 .+-. 2.3 cm H2O (P < 0.01) and decreased the swings in transdiaphragmatic pressure (Pdi) from 35.1 .+-. 2.4 to 29.6 .+-. 3.7 cm H2O (P < 0.05). Although ventilation (.ovrhdot.VE) increased, the inspiratory work per liter of .ovrhdot.VE fell significantly. The pressure-time product for the inspiratory muscles (.intg.Ppl.dt) measured over 60 s fell from 830 .+-. 111 to 573 .+-. 41 cm H2O.cntdot.s (P < 0.05); that for the diaphragm (.intg.Pdi.dt) fell from 690 .+-. 91 to 497 .+-. 74 cm H2O.cntdot.s (P < 0.05). In induced asthma, CPAP reduces the load on the inspiratory muscles, improving their efficiency and decreasing the energy cost of their action. The role of CPAP in the treatment of respiratory failure caused by severe bronchial asthma should be investigated.