Pressure in the lungs and air flow

[albertyh]

I've been really confused about inflation of the lungs and airflow.

Given a lung compliance of 0.25 L/mmHg, this means that 2 mmHg is required to inflate the lungs by 500mL. Does this mean that the pressure difference between intrapleural space and the alveoli must be 2 mmHg more than what it was in order to expand the lung?

My lecture notes then say that this does not allow for the pressure required to generate air flow to the lungs. Given a resistance of the airway of 2mmHg/L/second and a flow rate of 0.5L/second, then 1 mmHg pressure difference is required to generate air flow. Where is this pressure difference coming from?

We were also told that the total pressure difference between intrapleural space and the mouth is ∆ p = ∆ V / compliance + Resistance x Vol flow rate. So this means that 3 mmHg in total between intrapleural space and alveoli is required to inflate the lungs and generate air flow?

Any help with this would be great.

 

[Aaron Barnard]

Yes, that is correct. The pressure difference between the intrapleural space and the alveoli must be 2 mmHg more than what it was in order to expand the lung by 500 mL (given a lung compliance of 0.25 L/mmHg). In addition, the pressure difference between the intrapleural space and the mouth must be at least 1 mmHg greater than the intrapleural pressure in order to generate air flow (given a resistance of the airway of 2 mmHg/L/second and a flow rate of 0.5 L/second). Therefore, the total pressure difference between the intrapleural space and the mouth must be 3 mmHg in order to inflate the lungs and generate air flow.