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 breathing pattern in patients with chronic obstructive pulmonary disease (COPD) and dynamic hyperinflation (DH) during controlled mechanical ventilation.

DESIGN: Prospective, controlled, randomized, non-blinded study.

SETTING: Respiratory intensive care unit of a university hospital.

PATIENTS: Nine patients with acute respiratory failure and DH due to acute exacerbations of COPD.

INTERVENTIONS: Keeping tidal volume and total breath duration (TTOT) constant, patients were ventilated at six different values of expiratory time (TE). TE changes were randomly induced by alterations of constant inspiratory flow (VI) and/or end-inspiratory pause (EIP). Patients were studied at three levels of VI(0.93 +/- 0.08, 0.72 +/- 0.06 and 0.55 +/- 0.04 l/s, mean +/- SE), with and without EIP (10% of TTOT).

MEASUREMENTS AND RESULTS: Lung volumes, airflows, airways pressures, oxygenation indices and dead space were measured. Alveolar pressure and airway resistance (Rmin), as well as the additional resistance (delta R) due to viscoelastic pressure dissipation and time-constant inequalities, were estimated by rapid airway occlusion during inflation. In seven out of nine patients, right-heart catheterization was performed and hemodynamic parameters were obtained at each value of TE. A significant decrease of intrinsic positive end-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 airway pressure, Rmin, stroke volume index and mixed venous PO2 (PvO2) were observed when VI increased. At each VI, the addition of EIP significantly decreased iso-volume expiratory flows and PvO2 and increased Vtrap and mPaw.

CONCLUSIONS: We conclude that in mechanically ventilated patients with COPD, the pattern of lung inflation and TE alteration have a significant impact on respiratory system mechanics, gas exchange and hemodynamics. Addition of EIP in patients with COPD may be detrimental.