Lung Function Practical - Spirometry
In this virtual simulation, you will be introduced to the technique of spirometry, used for recording respiratory variables. You will analyse recordings to derive respiratory parameters and examine lung volumes and capacities, as well as basic tests of pulmonary function.
Spirometry is a physiological test of lung function. It is a very useful non-invasive test used to detect, quantify and monitor diseases that limit ventilator function. Most large hospitals have a Lung Function Laboratory where these tests are routinely performed on patients by respiratory scientists. The test is relatively easy to perform, although it does require maximal effort and patient cooperation. The need to perform maximal inspiratory and expiratory manoeuvres means that the tests should not be performed in some patients, ie patients who have had recent surgery or have unstable cardiac disease.
A number of lung volumes and capacities can be measured by simple spirometry. In this practical you will measure some of the lung volumes (IRV, ERV, VT) and capacities (IC, VC). By measuring the breathing frequency and multiplying this with the volume of each breath, the tidal volume (VT) we can determine the minute ventilation (MV) of the lungs.
Spirometry can only measure the volumes of the air that can be inhaled and exhaled with time. It cannot measure the total lung capacity (TLC) because at the end of every breath there is still some air remaining within the lungs. At the end of a maximum breath the volume remaining in the lungs is the residual volume (RV). Values for RV can be extrapolated from population data and these values can be used to estimate TLC.
Notice in the figure below, that at the end of a tidal breath the volume of air remaining in the lung is called the functional residual capacity (FRC), and this is just under half that of total lung capacity (TLC).
There is a large capacity of the lung to increase ventilation - theoretically the largest tidal volume is the vital capacity. However, in practice it is not possible to breathe rapidly with such tidal volume for any length of time because we are limited by the strength and endurance of the respiratory muscles. In clinical and sports medicine, it is often important to measure the maximum volume of air that can be exhaled and inhaled (maximum voluntary ventilation) and the corresponding maximum flow rates (maximum inspiratory and expiratory flow rates). Decreases in ventilatory capacity can indicate disease and help quantify its severity (e.g., mild, moderate or severe asthma).