What parameters does Artificial Lung Ventilation (ALV) device measure? These parameters are:

• volume
• time
• flow
• pressure

Let's start form time. From the position of respiratory mechanics we should measure the time of inhalation and exhalation. Hence we are able to count inspiratory and expiratory volume, multiplying inspiratory and expiratory time on the flow. And what is inspiration? Inspiration = entry of the air into lungs. It lasts until the begining of expiration. Expiration = exit of the air from lungs. Experts divide inspiration into two parts:

Inspiratory time = Inspiratory flow time* + Inspiratory pause**

* - _{As it was mentioned above, inspiratory flow time is a time interval, when air enters the lungs.}

** - _{Inspiratory pause is a time interval, when the inspiration valve is already closed and the expiration valve hasn't opened yet.}

When we speak about spontaneous breathing inspiratory pause is a breathing delay at the height of inspiration. By the way, this is meanly a breathing delay at the height of inspiration that Indian yogis are able to control, as well as numerous specialist in the field of respiratory gymnastics.

Expiration is also divided into two parts:

Expiratory time = Expiratory flow time* + Expiratory pause**

* - _{Expiratory flow time is a time interval, when air exits lungs.}

** - _{Expiratory pause is a time interval, when air doesn't exit lungs anymore, but the inspiration hasn't started yet.}

If the time of expiratory pause is over and inspiration hasn't begun yet, a smart ALV device will consider this situation as apnoe and trigger an alarm in order to rescue the patient.

So, we can present total respiratory cycle time as following:

Total cycle time (Ventilatory period) = Inspiratory time + Expiratory time

or

Total cycle time = Inspiratory flow time + Inspiratory pause + Expiratory flow time + Expiratory pause