Pulmonary Function Testing
Pulmonary function testing is used to detect the presence of obstructive or restrictive pulmonary disease. A pneumotachometer (flowmeter) attached to a mask fitted around the nose is used to measure flow during normal breathing at rest. Esophageal pressure and airflow at the nose are used to calculate the change in pleural pressure, pulmonary resistance, and lung compliance.
Forced Air Expiration
Forced expiration is used as part of advanced pulmonary function testing. The horse is sedated and fitted with an esophageal balloon and a nasotracheal tube inserted into the proximal third of the trachea. The horse’s lungs are manually inflated to capacity, and then the lungs are exposed to a vacuum reservoir to induce a forced expiration.From this, data is collected by a computer and forced vital capacity of the lungs, forced expiratory volume, and forced expiratory flow can be calculated and a flow-volume curve is made.
The esophageal balloon is used to measure pleural pressure using a pressure transducer outside the body. The esophageal balloon consists of a small tube with a thin walled balloon at the end. It is placed in the lower third of the esophagus (mid-thoracic level) since changes in esophageal pressure at this location mimic changes in pleural pressure.