used to estimate the lung parameters from the pressure waveform: the value of the

pressure at the plateau indicates the pressure needed to inflate the lungs and hence their

compliance C; the amount of drop in pressure before the plateau indicates the pressure

due to flow resistance of the patient and the endotracheal tube, and can be used to

estimate the lungs' resistance R [16]. Such breaths are called "mandatory" because the

patient does not initiate them: the ventilator is set to administer a minimum number of

breath cycles per minute, and they are used at the pressure pattern we saw to provide the

physician with more information, even though ventilator measurement and calculations

are made mostly outside the patient's body, so it is difficult to obtain accurate estimates.

Also, this data set has been chosen for a particular feature: the plateau in pressure is

perfectly readable, which means that the patient is not fighting the ventilator. All patients

indeed do not react the same way under artificial respiration, and the data is not always so

close to the theoretic waveforms.

 The second and third breaths reflect a different pattern: they exhibit a slight

negative deflection immediately before the rise in pressure. This deflection indicates that

the patient is trying to inhale, and triggers a breath, which is why they are called

"spontaneous" breaths. They do not actually represent a breath that the patient takes on

its own, just a breath that was spontaneously triggered by the patient. Lastly, for both

kind of breath, the exhalation phase is performed by the patient since it is passive leveling

of the lung pressure to the outside pressure, and depends only on the resistance of the

airway and the compliance of the lung [17].

 Knowing just how many spontaneous and mandatory breaths the patient takes per

minute is important information for a physician, but ventilators usually do not record how