Question

Mokun and Miguel made a bet about who could decrease their alveolar Pco2 the most by changing their breathing pattern. They used a spirometer to make sure they started with the same tidal volume and frequency. Mokun doubled her tidal volume and decreased her respiratory rate by one-half. Miguel decreased his tidal volume by one-half and doubled his respiratory rate. Assume that their total lung capacity and dead space were the same. Who probably won? How did you know?

Answer 1

Minute ventilation is the volume of air entering the respiratory tract per minute.

Minute ventialtion = Tidal volume* Respiratory rate

Alveolar ventilation is the volume of air entering the lungs per minute.

Alveolar ventilation = (Tidal volume-Dead space volume) * Respiratory rate

So if alveolar ventilation will be more ; then more CO2 will be expelled from the lungs and pCO2 will be lower.

Let their initial tidal volumes be x ; respiratory rate be y and dead space volume be z.

New alveolar ventilation for Mokun = (2x-z) * y/2=xy-(zy/2)

New alveolar ventilation for Miguel = (x/2 -z) *2y = xy-2zy

Since zy/2 will be smaller than 2zy ; new alveolar ventilation for Mokun will be more .

So Mokun will be the winner.