Your genetics, gender and height all determine the size of your lungs.
The air in your lungs can be measured with lung volumes and lung capacities. Your lung volume is the amount of air your lungs can inhale and exhale. Your lung capacity is how much you can inhale after exhaling.
The volume in your lungs can be divided into four units:
Tidal volume measures how much air is breathed in and expired when you take a breath. This is normally half a litre.
Expiratory reserve volume
The term ‘expiratory reserve volume’ refers to the extra air that can be exhaled after you have already exhaled. It acts as a reserve for when you need to exhale more than you normally would.
Inspiratory reserve volume
Inspiratory reserve volume is the extra air that can be inhaled after you have already inhaled. It acts as a reserve for when you need to inhale more than you normally would.
Your lungs are never completely empty. Residual volume is the excess air left in your lungs after you have exhaled.
It is impossible to measure the residual volume of your lungs as you can’t empty the lung completely. It can only be calculated.
The capacity of your lungs can also be divided into four units:
When you add expiratory reserve volume, tidal volume and inspiratory reserve volume, you get vital capacity. This measures the maximum amount of air you can breathe in and out during a single respiratory cycle.
When you add tidal volume and inspiratory reserve volume, you get inspiratory capacity. This measures the amount of air you can breathe in after breathing out.
Functional residual capacity
When you add the expiratory reserve volume and the residual volume, you get functional residual capacity. This measures the extra air that you can exhale after exhaling.
Total lung capacity
When you add together all four units of volume, you get your total lung capacity. This speaks for itself. It is the total amount of air that your lungs are able to hold.
Your lung volumes can be measured using the following methods:
During spirometry, forced expiratory volume is measured. Forced expiratory volume measures how much air can be forced out of your lungs over a specific period of time. This period of time is usually a second.
Forced vital capacity is also measured during spirometry. Forced vital capacity measures how much air can be forcibly exhaled.
Body plethysmography measures functional residual capacity using Boyle’s law. During this type of test, you are seated in an airtight box, wherein changes in pressure and volume can be measured.
When you breathe 100% oxygen, all the nitrogen in your lungs is washed out. The nitrogen concentration in your exhaled volume is measured. The difference between the nitrogen volume in the initial exhale and the final exhale is used to measure functional residual capacity.
Your lungs are responsible for your breathing. You can measure the amount of air the can inhale and exhale using volume and capacity. Volume and capacity are measured using spirometry, body plethysmography and nitrogen washout techniques.
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