Respiratory

Respiratory Airflow and Volume

In this laboratory, you will be introduced to spirometry as a technique for recording respiratory variables and you will analyze a recording to derive respiratory parameters. You will examine lung volumes and capacities, as well as the basic tests of pulmonary function and simulate an airway restriction.

Written by staff of ADInstruments.

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Background

Gas exchange between air and blood occurs in the alveolar air sacs. The efficiency of gas exchange is dependent on ventilation; cyclical breathing movements alternately inflate and deflate the alveolar air sacs (see Figure 1). Inspiration provides the alveoli with some fresh atmospheric air and expiration removes some of the stale air, which has reduced oxygen and increased carbon dioxide concentrations.

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Figure 1. A schematic diagram of the human respiratory system.

Spirometry is becoming more and more important, as respiratory diseases are increasing world wide. Spirometry is the method of choice for a fast and reliable screening of patients suspected of having Chronic Obstructive Pulmonary Disease (COPD). COPD is the 12th leading cause of death worldwide and the 5th leading cause in Western countries. Studies suggest COPD could climb to be the 3rd leading killer by 2020. Most COPD cases are completely avoidable; 85-90% of cases are caused by tobacco smoking.

Many important aspects of lung function can be determined by measuring airflow and the corresponding changes in lung volume. In the past, this was commonly done by breathing into a bell spirometer, in which the level of a floating bell tank gave a measure of changes in lung volume. Flow, F, was then calculated from the slope (rate of change) of the volume, V:

[pic] Equation 1

More conveniently, airflow can be measured directly with a pneumotachometer (from Greek roots meaning “breath speed measuring device”). The PowerLab pneumotachometer arrangement is...