This patient is passive and ventilated in pressure-control mode. Why is the flow curve shaped this way?
Answer: This shape indicates a severe flow limitation in a COPD patient. A flow limitation usually occurs during expiration and is represented by bicompartmental expiration. The initial spike of expiratory flow corresponds with a dynamic compression of gas in the central airways. Thereafter, the flow decreases rapidly because it is limited at the choke point. In the case of severe bronchospasm, the inspiratory flow may display the same shape with an initial fast compartment followed by a slow compartment due to the flow limitation at the choke point.
- Lourens MS, van den Berg B, Verbraak AF, Hoogsteden HC, Bogaard JM (2001) Effect of series of resistance levels on flow limitation in mechanically ventilated COPD patients. Respir Physiol 127:39–52
- Valta P, Corbeil C, Lavoie A, Campodonico R, Koulouris NG, Chasse´M, Braidy J, Milic-Emili J. Detection of expiratory flow limitation during mechanical ventilation. Am J Respir Crit Care Med 1994;150:1311–1317.
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