Pattern of lung emptying and expiratory resistance in mechanically ventilated patients with chronic obstructive pulmonary disease.
OBJECTIVE
To study the pattern of lung emptying and expiratory resistance in mechanically ventilated patients with chronic obstructive pulmonary disease (COPD).


METHODS
A prospective physiological study.


METHODS
A 12-bed Intensive Care Unit.


METHODS
Ten patients with acute exacerbation of COPD.


METHODS
At three levels of positive end-expiratory pressure (PEEP, 0, 5 and 10 cm H(2)O) tracheal (Ptr) and airway pressures, flow (V') and volume (V) were continuously recorded during volume control ventilation and airway occlusions at different time of expiration.


RESULTS
V-V' curves during passive expiration were obtained, expired volume was divided into five equal volume slices and the time constant (tau) and dynamic deflation compliance (Crs(dyn)) of each slice was calculated by regression analysis of V-V' and post-occlusion V-Ptr relationships, respectively. In each volume slice the existence or not of flow limitation was examined by comparing V-V' curves with and without decreasing Ptr. For a given slice total expiratory resistance was calculated as tau/Crs(dyn), whereas expiratory resistance (Rrs) and time constant (tau(rs)) of the respiratory system were subsequently estimated taken into consideration the presence of flow limitation. At zero PEEP, tau(rs) increased significantly toward the end of expiration due to an increase in Rrs. PEEP significantly decreased Rrs at the end of expiration and resulted in a faster and relatively constant rate of lung emptying.


CONCLUSIONS
Patients with COPD exhibit a decrease in the rate of lung emptying toward the end of expiration due to an increase in Rrs. PEEP decreases Rrs, resulting in a faster and uniform rate of lung emptying.
Kondili
Eumorfia
E
Department of Intensive Care Medicine, University Hospital of Heraklion, University of Crete, 711 10 Heraklion, Crete, Greece.
Alexopoulou
Christina
C
Prinianakis
George
G
Xirouchaki
Nectaria
N
Georgopoulos
Dimitris
D
D000368:Aged; D000403:Airway Resistance / Q000502:physiology*; D005260:Female; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D011175:Positive-Pressure Respiration / Q000379:methods; D011446:Prospective Studies; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology* / Q000628:therapy*; D012121:Respiration, Artificial / Q000379:methods*; D012128:Respiratory Distress Syndrome / Q000503:physiopathology / Q000628:therapy; D013997:Time Factors