Intrinsic PEEP has commonly been identified in patients with COPD during acute exacerbations, either during invasive or non-invasive ventilation. This further increases the workload of muscles as their efficiency and mechanical advantage are reduced. The presence of PEEPi also implies dynamic hyperinflation, with consequent worsening of thoracic wall geometry and muscle length-tension relationships. Intrinsic PEEP has therefore been described as an inspiratory threshold load on the inspiratory muscles, increasing work of breathing. 1 In order to initiate inspiratory airflow, the respiratory muscles must generate a negative pressure equal in magnitude to PEEPi. The residual inward elastic recoil creates a positive alveolar pressure at end expiration, known as intrinsic positive end expiratory pressure (intrinsic PEEP or PEEPi). In patients with chronic obstructive pulmonary disease (COPD), because of severe airflow obstruction, the time available for expiration may be insufficient to allow the system to return to Vr. In normal subjects the end expiratory lung volume (EELV) corresponds to the relaxation volume (Vr) or elastic equilibrium volume of the respiratory system. PTPoes, oesophageal pressure time product.PTPdi, diaphragmatic pressure time product.CPAP, continuous positive airway pressure.EELV increased by 1.1 (0.3) l (p<0.01).Ĭonclusion: High levels of CPAP reduce PEEPi and indices of muscle effort in patients with severe stable COPD, but only at the expense of substantial increases in lung volume. PTPoes/min decreased, although this did not reach statistical significance. EMGdi remained stable while EMGic increased significantly. There were no changes in respiratory pattern but V̇ i increased from 9.2 (0.6) l/min to 10.7 (1.1) l/min (p<0.05). In two subjects expiratory muscle activity contributed to PEEPi at higher pressures. In the remaining eight, PEEPi was reduced from a mean (SE) of 2.9 (0.6) cm H 2O to 0.9 (0.1) cm H 2O (p<0.05). Results: Expiratory muscle activity was present at baseline in one subject. Breathing pattern and minute ventilation (V̇ i), dynamic PEEPi, expiratory muscle activity, diaphragmatic (PTPdi/min) and oesophageal (PTPoes/min) pressure-time product per minute, integrated diaphragmatic (EMGdi) and intercostal EMG (EMGic) and end expiratory lung volume (EELV) were measured. Methods: Nine patients were studied at baseline and with CPAP increasing in increments of 1 cm H 2O to a maximum of 10 cm H 2O. This study examined the effect of CPAP on the inspiratory threshold load, muscle effort, and lung volume in this patient group. The role of continuous positive airway pressure (CPAP) in alleviating PEEPi in patients with severe stable chronic obstructive pulmonary disease is uncertain. Background: Intrinsic positive end expiratory pressure (PEEPi) constitutes an inspiratory threshold load on the respiratory muscles, increasing work of breathing.
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