Principles and Test Types

Pulmonary function testing evaluates lung volumes flows and gas exchange and provides objective measures for diagnosis staging and monitoring of respiratory disease. Common tests include spirometry which measures forced expiratory volumes and flows lung volume measurement by plethysmography or gas dilution and diffusion capacity testing which assesses gas transfer across the alveolar capillary membrane. Bronchodilator responsiveness testing and challenge tests assess airway hyperreactivity and exercise testing evaluates functional capacity and exertional desaturation. Proper test selection and interpretation require knowledge of normal predicted values and of factors that influence results such as effort technique and comorbid conditions.

Quality Assurance and Patient Preparation

Accurate pulmonary function testing depends on standardized procedures calibration of equipment and patient cooperation and effort and quality assurance programs include daily calibration checks and periodic proficiency assessments for technicians. Patient preparation includes withholding bronchodilators when indicated avoiding heavy meals and smoking and ensuring that patients understand the maneuvers required for maximal effort. Reproducibility criteria for spirometry require multiple acceptable efforts and technicians coach patients to achieve valid tests while documenting any limitations. Clear reporting of results with interpretation that integrates clinical context supports diagnosis and management decisions.

Interpretation and Clinical Applications

Interpreting pulmonary function tests involves identifying obstructive restrictive and mixed patterns and quantifying severity and reversibility and diffusion impairment and exercise induced desaturation provide additional diagnostic information. Spirometry patterns such as reduced FEV1 to FVC ratio indicate obstruction while reduced total lung capacity suggests restriction and diffusion capacity reductions point to interstitial or vascular pathology. Serial testing monitors disease progression response to therapy and preoperative risk assessment and guides decisions about rehabilitation and oxygen therapy. Collaboration between respiratory therapists pulmonologists and primary clinicians ensures that test results are applied appropriately to patient care.