EFFECTS OF BREATHING PATTERNS ON MECHANICALLY VENTILATED PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY-DISEASE AND DYNAMIC HYPERINFLATION

Objective. To examine the circulatory and respiratory effects of breat hing pattern in patients with chronic obstructive pulmonary disease (C OPD) and dynamic hyperinflation (DH) during controlled mechanical vent ilation. Design: Prospective, controlled, randomized, non-blinded stud y. Setting: Respiratory intensive care unit of a university hospital. Patients: Nine patients with acute respiratory failure and DH due to a cute exacerbations of COPD. Interventions: Keeping tidal volume and to tal breath duration (T-TOT) constant, patients were ventilated at six different values of expiratory time (T-E). T-E changes were randomly i nduced by alterations of constant inspiratory flow (V-I) and,or end-in spiratory pause (EIP). Patients were studied at three levels of V-I(0. 93 +/- 0.08, 0.72 +/- 0.06 and 0.55 +/- 0.04 1/s, mean +/- SE), with a nd without EIP (10% of T-TOT). Measurements and results: Lung volumes, airflows, airways pressures: oxygenation indices and dead space were measured. Alveolar pressure and airway resistance (Rmin), as well as t he additional resistance (delta R) due to viscoelastic pressure dissip ation and time-constant inequalities, were estimated by rapid airway o cclusion during inflation. In seven out of nine patients, right-heart catheterization was performed and hemodynamic parameters were obtained at each value of T-E. A significant decrease of intrinsic positive en d-expiratory pressure (PEEPi), end-inspiratory static and mean (mPaw) airway pressures, end-expiratory lung; volume above passive FRC (Vtrap ), delta R and venous admixture and a significant increase of peak air way pressure, Rmin, stroke volume index and mixed venous PO2 (PvO(2)) were observed when V-I increased. At each V-I, the addition of EIP sig nificantly decreased iso-volume expiratory flows and PvO(2) and increa sed Vtrap and mPaW. Conclusions. We conclude that in mechanically vent ilated patients with COPD, the pattern of lung inflation and T-E alter ation have a significant impact on respiratory system mechanics, gas e xchange and hemodynamics. Addition of EIP in patients with COPD may be detrimental.