Build a clear concept of ventilation based on the requirement is the first step to
begin with. One of the main requirements is the wave form for analyzing patient’s
health. All the waveform that we obtain through the ventilator used to monitor patient
health is obtained through the interaction of four parameters pressure, flow, volume
and time. We need to plot the pressure, volume and flow with time in the x axis will
obtain us pressure time scalar, volume time scalar and flow time scalar respectively.
Flow time scalar will be having both positive and negative deflection along the time
axis where as other two has only positive deflection.
Respiratory cycle consists of inspiratory part and expiratory part. There are three
different phase variables, like trigger, limit and cycle. Ventilation starts with a trigger
which can be patient controlled or ventilator controlled. When it is ventilator
controlled it is time trigger. When the trigger is patient controlled then its either flow
trigger or pressure trigger depending on what ventilator senses. Limit can be of flow
limit in case of volume control and pressure limit in case of pressure control. Cycle
means the change of ventilation from inspiration to expiration. Cycling can be of
volume in volume control, time in pressure control mode, flow cycled in pressure
support ventilation.
There are various modes in our ventilator ,one of the most commonly used mode in
conventional ventilators is volume control mode and its time triggered in most of the 

time as the patient is deeply sedated , flow limited that is flow is in square wave

pattern and volume cycled, that is flow terminate when set amount of volume is