Positive end expiratory pressure and expiratory flow limitation: a model study.
Patients suffering from chronic obstructive pulmonary diseases, frequently exhibit expiratory airflow limitation. We propose a mathematical model describing the mechanical behavior of the ventilated respiratory system. This model has to simulate applied positive end-expiratory pressure (PEEP) effects during expiration, a process used by clinicians to improve airflow. The proposed model consists of a nonlinear two-compartment system. One of the compartments represents the collapsible airways and mimics its dynamic compression, the other represents the lung and chest wall compartment. For all clinical conditions tested (n=16), the mathematical model simulates the removal of expiratory airflow limitation at PEEP lower than 70-80% of intrinsic end-expiratory pressure (PEEPi), i.e. the end-expiratory alveolar pressure (PAet) without PEEP. It also shows the presence of an optimal PEEP. The optimal PEEP contributes to decrease PAet from 7.4+/-0.9 (SD) to 5.4+/-0.9 hPa (p < 0.0001; mild flow limitation) and from 11.8+/-1.1 to 7.8+/-0.7 hPa (p < 0.0001; severe flow limitation). Resistance of the collapsible compartment is decreased from 53+/-7 to 8.2+/-5.9 hPa.L(-1).s (p < 0.0001; mild flow limitation) and from 80+/-11 to 6.9+/-5.4 hPa.L(-1).s (p < 0.0001; severe flow limitation). This simplistic mathematical model gives a plausible explanation of the expiratory airflow limitation removal with PEEP and a rationale to the practice of PEEP application to airflow limited patients.
Khirani
S
S
Laboratoire Techniques en Imagerie Modélisation et Cognition (Institut IMAG), Faculté de Médecine, La Tronche, France.
Biot
L
L
Eberhard
A
A
Baconnier
P
P
D000403:Airway Resistance / Q000502:physiology*; D005540:Forced Expiratory Flow Rates / Q000502:physiology; D006801:Humans; D008962:Models, Theoretical; D017711:Nonlinear Dynamics; D011175:Positive-Pressure Respiration / Q000706:statistics & numerical data*; D011650:Pulmonary Alveoli / Q000503:physiopathology; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*