Pulmonary Function Testing (PFT) is a complete evaluation of the respiratory system including patient history, physical examinations, chest x-ray examinations, arterial blood gas analysis, and tests of pulmonary function. The primary purpose of pulmonary function testing is to identify the severity of pulmonary impairment. [1]Pulmonary function testing has diagnostic and therapeutic roles and helps clinicians answer some general questions about patients with lung disease. PFT's are usually performed by a Registered Pulmonary Function Technician, a Certified Pulmonary Function Technician or a Registered Respiratory Therapist.
Spirometry
Spirometry includes the tests of pulmonary mechanics, the measurements of FVC, FEV<sub1, FEF values, forced inspiratory flow rates (FIFs), and the MVV. Measuring pulmonary mechanics is assessing the ability of the lungs to move large volumes of air quickly through the airways to identify airway obstruction.
Complications
Spirometry is a safe procedure however there is cause for concern regarding untoward reactions. The value of the test data should be weighed against potential hazards. Some complications have been reported such as; pneumothorax, increased intracranial pressure, syncope, chest pain, paroxysmal coughing, nosocomial infections, oxygen desaturation, and bronchospasm.
Lung Volumes and Capacities
There are four lung volumes and four lung capacities. A lung capacity consists of two or more lung volumes. The lung volumes are tidal volume (VT), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), and residual volume (RV). The four lung capacities are total lung capacity (TLC), inspiratory capacity (IC), functional residual capacity (FRC) and the vital capacity (VC).
Helium Dilution
The helium dilution technique for measuring lung volumes uses a closed, rebreathing circuit.[2] This technique is based on the assumptions that a known volume and concentration of helium in air begin in the closed spirometer, that the patient has no helium in their lungs, and that an equilibration of helium can occur between the spirometer and the lungs.
Nitrogen Washout
The nitrogen washout technique uses a non-rebreathing open circuit. The technique is based on the assumptions that the nitrogen concentration in the lungs is 78% and in equilibrium with the atmosphere, that the patient inhales 100% oxygen and that the oxygen replaces all of the nitrogen in the lungs.[3]
Plethysmography
The plethysmography technique applies Boyle's law and uses measurements of volume and pressure changes to determine lung volume, assuming temperature is constant.[4]
Significance
Changes in lung volumes and capacities are generally consistent with the pattern of impairment. TLC, FRC and RV increase with obstructive lung diseases and decrease with restrictive impairment.
References
- ^ Pulmonary terms and symbols: a report of the ACCP-ATS Joint Committee on Pulmonary Nomenclature, Chest 67:583, 1975
- ^ Hathirat S, Renzetti AD, Mitchell M: Measurement of the total lung capacity by helium dilution in a constant volume system, Am Rev Respir Dis 102:760, 1970.
- ^ Boren HG, Kory RC, Snyder JC: The veterans Administration-Army cooperative study of pulmonary function, II: the lung volume and its subdivisions in normal men, Am J Med 41:96, 1966.
- ^ Dubois AB, et al: A rapid plethysmographic method for measuring thoracic gas volume: a comparison with a nitrogen washout method for measure FRC in normal patients, J Clin Invest 35:322, 1956.