So firstly, we can look at a waveform demonstrating a high peak pressure. Remembering that important fact, let’s look at a couple of examples that we might encounter. So, remember, peak pressure (circled) is a reflection of the airways, and plateau pressure is a reflection of lung compliance. You can see on the flow line the period between (5) and (6) where there is no flow as the breath-hold takes place. The pressure will reach a peak (4), and then as the breath-hold comes in there will be an equilibrium pressure (5), (remember the balloon analogy here: it takes high pressure to inflate the balloon, but once inflated, a lot less effort to keep it inflated) until the release of the pressure as exhalation takes place (6). Let us then say that we inflate the lungs but then hold them at inflation for a period of time. When we release the breath, the pressure will go down, and the flow will move in the opposite direction as the air moves out (2). If we ventilate the lung then the airway pressure will go up and the flow will increase (1). So, let’s work through this diagram to help our understanding of the difference, and how it can help us interpret the information. So, it follows that if there is a problem with compliance, the plateau pressure will rise. This pressure is determined by lung compliance. Plateau pressure applies when there is no airflow in the circuit.
So, it follows that if there is a problem with the airways the peak pressure will rise. What determines the peak pressure is the airway resistance in the lungs.
Peak pressure applies when there is airflow in the circuit, i.e., during inspiration. Differentiating Peak Inspiratory Pressure from Plateau Inspiratory Pressure Peak Pressure
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