Pattern of lung emptying and expiratory resistance in mechanically ventilated patients with chronic obstructive pulmonary disease
To study the pattern of lung emptying and expiratory resistance in mechanically ventilated patients with chronic obstructive pulmonary disease (COPD).
A prospective physiological study.
A 12-bed Intensive Care Unit.
Ten patients with acute exacerbation of COPD.
At three levels of positive end-expiratory pressure (PEEP, 0, 5 and 10 cmH2O) 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.
Measurements and results
V-V’ curves during passive expiration were obtained, expired volume was divided into five equal volume slices and the time constant (τ) and dynamic deflation compliance (Crsdyn) 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 τ/Crsdyn, whereas expiratory resistance (Rrs) and time constant (τrs) of the respiratory system were subsequently estimated taken into consideration the presence of flow limitation. At zero PEEP, τrs 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.
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.
KeywordsResistance Flow limitation Compliance Time constant
- 3.Ranieri VM, Giuliani R, Cinnella G, Pesce C, Brienza N, Ippolito EL, Pomo V, Fiore T, Gottfried SB, Brienza A (1993) Physiologic effects of positive end-expiratory pressure in patients with chronic obstructive pulmonary disease during acute ventilatory failure and controlled mechanical ventilation. Am Rev Respir Dis 147:5–13PubMedGoogle Scholar
- 6.Georgopoulos D, Brochard L (1988) Ventilatory Strategies in acute exacerbations of COPD. Eur Respir Monogr 8:12–44Google Scholar
- 12.Siafakas NM, Vermeire P, Pride NB, Paoletti P, Gibson J, Howard P, Yernault JC, Decramer M, Higenbottam T, Postma DS, et al (1995) Optimal assessment and management of chronic obstructive pulmonary disease (COPD). The European Respiratory Society Task Force. Eur Respir J 8:1398–1420PubMedGoogle Scholar
- 14.Bates JH, Baconnier P, Milic-Emili J (1988) A theoretical analysis of interrupter technique for measuring respiratory mechanics. J Appl Physiol 64:2204–2214Google Scholar
- 18.Koutsoukou A, Armaganidis A, Stavrakaki-Kallergi C, Vassilakopoulos T, Lymberis A, Roussos C, Milic-Emili J (2000) Expiratory flow limitation and intrinsic positive end-expiratory pressure at zero positive end-expiratory pressure in patients with adult respiratory distress syndrome. Am J Respir Crit Care Med 161:1590–1596PubMedGoogle Scholar
- 19.Valta P, Corbeil C, Lavoie A, Campodonico R, Koulouris N, Chasse M, Braidy J, Milic-Emili J (1994) Detection of expiratory flow limitation during mechanical ventilation. Am J Respir Crit Care Med 150:1311–1317Google Scholar