7.3: measuring gas exchange

What is a spirometer?

A device used to measure lung volumes and airflow during breathing.

What are examples of devices that can be used to measure lung volume during breathing?

A peak flow meter, a vitalographs and a spirometer

What is carbon dioxide that’s exhaled absorbed by in a spirometer?

Soda lime

What happens as a person breathes into a spirometer?

Air is inhaled and exhaled through the device, causing changes in volume that are recorded as a graph (spirometer trace) which can be viewed on a computer

Why does the air in a spirometer gradually decrease?

The person uses oxygen for respiration, and the carbon dioxide produced is absorbed (e.g. by soda lime), so the total gas volume decreases.

Example of spirometer trace

What is the vital capacity?

The volume of air that can be breathed in when the strongest possible exhalation is followed by the deepest possible intake of breath

What is the tidal volume?

The volume of air that moves into and out of the lungs with each resting breath

what’s the tidal volume for most adults?

500cm3

What is the inspiratory reserve volume?

The extra amount of air you can force out of your lungs over and above the normal tidal volume of air you can breathe out

What is the expiratory reserve volume?

The extra amount of air you can force out of your lungs over and above the normal total volume of air you can breathe out

What is the residual volume?

The volume of air that is left in your lungs when you have exhaled as hard as possible which cannot be directly measured

What is the total lung capacity?

The sum of the vital capacity and the residual volume

What is breathing rate?

Breathing rate is the number of breaths taken per minute

What is ventilation rate?

Ventilation rate is the total number of air inhaled in one minute

how to calculate ventilation rate?

Tidal volume x breathing rate