Pulmonary Pathology: Spirometry and Interpretation

Pulmonary Pathology: Calibration and Quality Control, Spirometry Interpretation, and Factors Affecting Spirometry

Pulmonary pathology encompasses a wide range of respiratory disorders, from chronic obstructive pulmonary disease (COPD) to asthma, and accurate diagnosis and management of these conditions rely on the use of spirometry, a simple and non-invasive lung function test. Spirometry is used to assess the patient's airflow patterns and lung volumes, providing valuable information about the patient's respiratory health. This article focuses on key aspects of pulmonary pathology, including calibration and quality control, spirometry interpretation, and factors affecting spirometry.

Calibration and Quality Control

Calibration is a crucial step in ensuring the accuracy of spirometry results. The 2005 American Thoracic Society/European Respiratory Society (ATS/ERS) spirometry guidelines recommend that spirometers should be calibrated daily and whenever a flow sensor is changed. Calibration ensures that the spirometer is functioning correctly and providing reliable results. Failure to calibrate the spirometer can lead to inaccurate results, reducing the clinical utility of the test.

The quality of spirometry is affected by various factors, and poorly trained or incompetent testing personnel are a significant cause of low-quality tests. To improve test quality, personnel must be adequately trained, including classroom education and extensive practice[6, 12, 13]. Regular performance monitoring and feedback is essential, with the goal of achieving a high percentage of tests that meet ATS/ERS acceptability and repeatability standards. Technologists should be trained in calibration, recognition of unacceptable maneuvers, and other related aspects of spirometry performance.

Spirometry Interpretation

The interpretation of spirometry results involves two tasks: classifying the derived values with respect to a reference population and assessing the reliability of the test. Spirometry data must be compared with data collected from biologic peers who are non-smokers with healthy lung size and function. The test results can be divided into two large classes: normal and impaired, with impaired results further classified into obstructive, spirometric restriction, and mixed patterns. These patterns help in determining the severity of airflow limitation and guiding the clinician's decision-making process.

Factors Affecting Spirometry

Several factors can affect spirometry results, including the patient's age, sex, height, race, and lung growth. Accurate age is crucial, as lung growth is complete by early adulthood and later declines with senescent changes. Sex is another important determinant of pulmonary function, with males typically having larger lungs than females of the same age, height, and race. Height is also used to estimate expected spirometry values, as it serves as an estimate of chest size.

Normal Spirometry

Normal spirometry results are characterized by an FVC% ≥ 80% of the predicted value, an FEV1% ≥ 80% of the predicted value, and an FEV1/FVC ratio ≥0.7 in absolute value. These values provide a baseline for assessing lung function and can detect abnormalities when they occur.

Control of Breathing

Control of breathing is essential for accurate spirometry results. Technicians should instruct patients to breathe out as quickly as possible, achieving maximum airflow, and to avoid premature maneuvers. Patient cooperation and clear instructions from the technician can significantly improve the quality of spirometry data.

Mechanics of Breathing

Understanding the mechanics of breathing is crucial for interpreting spirometry results. Spirometry measures the volume and flow of air in and out of the lungs, providing insights into the patient's respiratory health. The test results can help identify obstructive, restrictive, or mixed patterns of lung dysfunction, guiding appropriate diagnostic and therapeutic interventions.

In conclusion, pulmonary pathology encompasses various aspects of respiratory health, and spirometry plays a vital role in its assessment. Ensuring the accuracy of test results through calibration and quality control, interpreting results appropriately, and considering factors affecting spirometry are all essential components of effective diagnosis and management of respiratory disorders.