Inspiratory Capacity Calculator

How does the inspiratory capacity calculator work?

This health tool computes the inspiratory capacity in litres based on the inspiratory reserve volume and on tidal volume. IC is one of the lung capacities inferred from lung volumes after lung function tests.

■ Inspiratory reserve volume – represents the maximal volume possible to be forcefully inhaled after a normal tidal inspiration. It is approximately 3 litres.

■ Tidal volume – represents the normal volume of air moved during normal inspiration and expiration and is of approximately 0.5 litres per breath at a respiratory rate of 12 to 20 breaths per minute. It is often measured in mL, meaning 500 mL and plays an essential role in the management of mechanical ventilation.

The formula used in the inspiratory capacity calculator is:

Inspiratory capacity = Inspiratory reserve volume + Tidal volume

In short: IC = IRV + TV

Spirometry normal values for inspiratory capacity are on average 3.5 L for males and 2.4 L for females.

When measuring lung capacity, IC offers information on the total amount of air which can be inhaled, during the normal and forced inspiration. This is useful when diagnosing both obstructive and restrictive lung disease.

Obstructive respiratory disease, such as COPD leads to a reduction in both the inspiratory and total lung capacity.

When added the expiratory reserve volume, IC contributes to the determination of the vital capacity.

Example calculation

Let’s take the following lung volumes:

■ Inspiratory reserve volume (IRV) = 3.1 L;

■ Tidal volume (TV) = 0.4 L.

Inspiratory capacity (IC) = IRV + TV = 3.5 L

References

1) Zaman M, Mahmood S, Altayeh A. (2010) Low inspiratory capacity to total lung capacity ratio is a risk factor for chronic obstructive pulmonary disease exacerbation. Am J Med Sci; 339(5):411-4.

2) Ricard JD. (2003) Are we really reducing tidal volume--and should we? Am J Respir Crit Care Med; 167(10):1297-8.

3) Lisboa C, Leiva A, Pinochet R, Repetto P, Borzone G, Díaz O. (2007) Reference values for inspiratory capacity in healthy nonsmokers over age 50 years. Arch Bronconeumol; 43(9):485-9.