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Oscillometry Versus Spirometry – Initial Insights
Binu Krishnan*, Nevin Jacob Kannukettiyil and Amrutha Gopal
Department of Pulmonary and Sleep medicine, PRS Hospital, India
Received Date: 17/04/2025; Published Date: 26/05/2025
*Corresponding author: Binu Krishnan, MD, FCCP, FAPSR,Senior Consultant Pulmonologist, Department of Pulmonary and Sleep medicine, PRS Hospital, Kerala, India
ORCID id: 0000-0002-3493-0279
Abstract
Oscillometry has emerged as a pivotal tool in pulmonary function testing, demonstrating significant utility in both clinical and research settings. Numerous studies have highlighted its effectiveness, particularly in asthma, concerning the assessment of bronchodilator response and therapeutic efficacy of various drugs. Additionally, oscillometry has been recognized for its sensitivity in evaluating disease control across a range of respiratory conditions. Its applications extend beyond asthma to include Chronic Obstructive Pulmonary Disease (COPD), interstitial lung diseases, functional impairment due to occupational exposures, central airway obstructions, cystic fibrosis, and the monitoring of lung mechanics during mechanical ventilation and sleep. Moreover, it plays a role in lung transplant assessment and the evaluation of neuromuscular diseases and graft function. Conversely, spirometry remains essential for diagnosing airway obstruction and monitoring chronic respiratory diseases, as highlighted in national and international guidelines. Given that a significant number of respiratory conditions are diagnosed and managed by general practitioners, spirometry is commonly incorporated into primary healthcare practices. This review aims to evaluate the comparative utility of oscillometry versus spirometry in the assessment and management of respiratory diseases.
Keywords: Spirometry; Oscillometry; Asthma; COPD
Introduction
Spirometry is widely recognized as the gold standard for assessing airway reversibility in clinical practice. However, its effectiveness is often limited by the need for patient cooperation and the requirement for forceful respiratory maneuvers. These limitations are particularly evident in young children, the elderly, individuals with neuromuscular disorders, post-cardiothoracic surgery patients, and those with cognitive impairments.
In recent years, Impulse Oscillometry (IOS) has emerged as a promising alternative for pulmonary function assessment due to its ability to measure respiratory mechanics during tidal breathing, thereby eliminating the need for forced respiratory efforts [1]. By assessing respiratory impedance across multiple frequencies, IOS provides a detailed evaluation of airway function and is particularly useful in populations where traditional spirometry may be challenging.
Recent studies suggest that IOS may offer greater sensitivity than spirometry in detecting airway obstruction in conditions such as asthma and Chronic Obstructive Pulmonary Disease (COPD). Its ability to detect small airway dysfunction makes it a valuable complementary tool in pulmonary diagnostics. Additionally, IOS has demonstrated high measurement repeatability, with variability primarily reflecting the degree of airway obstruction.
The stability of IOS parameters over time further underscores its potential utility in clinical assessments, particularly in asthma management. Research indicates that IOS and the forced oscillation technique exhibit long-term repeatability across diverse populations, including healthy individuals and those with respiratory diseases. However, variability in IOS parameters may differ across disease states, necessitating further investigation into long-term trends. [2].
A comprehensive understanding of these variations in clinically stable patients during routine outpatient evaluations is essential for identifying meaningful changes over time, ultimately enhancing disease monitoring and management.
Historical Context
Impulse Oscillometry (IOS) is a refinement of the Forced Oscillation Technique (FOT), originally introduced by DuBois et al. in 1956 to assess respiratory functions. In 1975, Michaelson et al. enhanced this method by developing a computer-driven loudspeaker system that applied bursts of square wave oscillatory pressures at multiple frequencies, analyzing the pressure-flow relationship using spectral analysis. This advancement led to the development of IOS, which provides a detailed understanding of airway resistance and reactance across discrete frequencies, offering insights beyond traditional spirometry [3].
Principle
The IOS system comprises several key components:
Loudspeaker: Generates pressure oscillations transmitted into the respiratory system via an adapter connected to a mouthpiece or face mask.
Pneumotachograph: Measures airflow and is typically attached to the mouthpiece or face mask.
Pressure and Flow Sensors: Collect data on pressure changes and airflow patterns within the airways.
Bias Flow Mechanism: Eliminates dead space to ensure accurate measurements [4].
During the assessment, the loudspeaker introduces pressure waves of varying frequencies (commonly between 5 and 35 Hz) into the respiratory system during tidal breathing. These oscillatory pressure waves cause subtle changes in airway pressure and airflow. Lower frequencies (e.g., 5 Hz) penetrate deeper into the peripheral airways, while higher frequencies (e.g., 20 Hz) primarily assess the central airways [3,4].
The pressure and flow sensors detect the resulting signals, which are separated from the patient’s normal breathing pattern using signal filtering mechanisms [5]. By analyzing the ratio of pressure to flow for each frequency, IOS calculates respiratory impedance (Z), encompassing:
Resistance ®: Reflects the resistive forces within the airways
Reactance (X): Represents the elastic and inertial properties of the lung and thoracic cage
This detailed frequency analysis provides valuable insights into respiratory mechanics, aiding in the diagnosis and monitoring of various respiratory conditions across diverse patient populations [4,5].
Advantages of Oscillometry Compared to Spirometry
Non-Invasive and Effortless Testing
Oscillometry is a non-invasive lung function test that requires minimal patient effort, unlike spirometry, which relies on forceful breathing maneuvers. Because oscillometry measures lung function during normal breathing, it is particularly suitable for children, elderly individuals, and patients with severe respiratory conditions. This reduces patient discomfort and eliminates challenges associated with effort-dependent tests.
Research by Liu et al (2017) emphasized the value of Impulse Oscillometry (IOS) in geriatric COPD patients, highlighting its ability to detect small airway dysfunction with greater sensitivity than spirometry. The study concluded that IOS serves as an effective and patient-friendly tool for diagnosing and monitoring COPD in elderly individuals[1].
Similarly, Desiraju and Agrawal (2016) explored IOS as an advanced lung function assessment tool, stressing its minimal effort requirements, making it particularly advantageous for pediatric, geriatric, and physically compromised populations [3].
Comprehensive Lung Function Assessment
Oscillometry provides a more detailed analysis of lung function by measuring airway resistance, reactance, and compliance. Unlike spirometry, which primarily assesses large airway function, oscillometry offers insights into both proximal and distal airways, making it more effective in detecting Small Airway Dysfunction (SAD). This allows for early recognition of subtle changes in respiratory health that may otherwise go undetected.
Li et al. (2021) demonstrated that IOS detected a higher prevalence of SAD compared to spirometry, identifying abnormalities even in symptomatic individuals with normal spirometry results [6].
Porojan-Suppini et al. (2020) reviewed IOS’s applications in various respiratory conditions, including asthma, COPD, interstitial lung diseases, and small airway diseases. They emphasized its usefulness in assessing lung function impairments caused by occupational hazards and smoking while also detecting central airway obstructions [4].
Early Detection of Airway Abnormalities
One of the key benefits of oscillometry is its ability to detect small airway changes before they become clinically apparent. This early identification is crucial for managing conditions such as asthma and Chronic Obstructive Pulmonary Disease (COPD), as timely intervention can help prevent exacerbations and slow disease progression. By identifying functional impairments before significant symptoms appear, oscillometry supports a more proactive approach to treatment.
Xu et al. (2022) found that IOS resistance parameters exhibited higher repeatability over time than spirometry, making it a more reliable tool for tracking airway function [2].
Eddy et al. (2019) demonstrated that IOS parameters significantly correlated with MRI ventilation defect percent (VDP) and other pulmonary abnormalities, supporting its role in detecting early airway dysfunction [7].
Effective for Serial Monitoring
Oscillometry enables continuous tracking of lung function over time, allowing clinicians to assess disease progression and evaluate treatment effectiveness. Because the test can be easily repeated without patient fatigue, it is well-suited for long-term monitoring. Real-time data obtained through oscillometry helps healthcare providers make informed adjustments to treatment plans based on individual patient responses, improving overall disease management.
Saadeh et al. (2015) found that IOS was more sensitive than spirometry in assessing bronchodilator response in COPD patients, making it a valuable tool for monitoring treatment efficacy [5].
Su et al. (2018) conducted ROC analysis to differentiate never-smokers from COPD patients, further demonstrating IOS’s utility in detecting small airway disorders (SADs) with high sensitivity and specificity [8].
Versatility Across Patient Populations
Due to its minimal reliance on patient effort, oscillometry is highly adaptable for various patient groups, including pediatric, geriatric, and severely ill individuals. This makes it particularly valuable in cases where spirometry may be difficult or unreliable. Its ease of use and suitability for a wide range of respiratory conditions contribute to better patient outcomes
Sarkar et al. (2023) emphasized that oscillometry’s non-invasive nature and ability to assess lung function during quiet breathing make it an ideal tool for pediatric and severe respiratory patients.
Limitations and Challenges in Oscillometry
Complex Interpretation of Results
Oscillometry generates detailed impedance data that requires specialized knowledge for accurate interpretation. Unlike spirometry, which provides easily recognizable parameters like FEV₁ and FVC, oscillometry data—such as resistance and reactance (X)—demands additional training for healthcare providers. The need for expertise in data analysis may slow its widespread adoption.
Sarkar et al. (2023) reviewed the challenges of oscillometry and noted that its complex interpretation remains a barrier to routine clinical use. Their study highlighted the need for further education and training among healthcare providers to ensure accurate analysis and clinical application [9].
Lack of Standardized Protocols and Reference Values
A significant challenge in oscillometry is the lack of universal testing protocols and reference values. Differences in methodologies across laboratories or equipment manufacturers can lead to inconsistencies in results. While efforts are being made to establish standardized guidelines, variations in testing procedures continue to pose challenges in ensuring uniformity.
Li et al. (2021) investigated the variability in oscillometry measurements and emphasized the need for standardized protocols to improve result consistency across different clinical settings. The study underscored how differences in reference values could impact the identification of small airway dysfunction [6].
Cost and Equipment Availability
High-quality oscillometry devices can be expensive, limiting access in resource-constrained healthcare settings. The cost of purchasing and maintaining the equipment, combined with a limited number of available devices, can restrict its use in certain regions or medical facilities.
Saadeh et al. (2015) examined the economic constraints associated with oscillometry and found that high equipment costs significantly hinder its widespread implementation. Their findings suggest that more affordable devices and increased funding could help improve accessibility [5].
Limited Normative Data
Compared to spirometry, oscillometry has less established normative data, particularly for certain age groups and populations. This makes it challenging to determine normal versus abnormal values in some cases. More research and extensive data collection are needed to refine reference standards for different demographics.
Su et al. (2018) highlighted the limitations in existing normative data and suggested that larger-scale studies are required to establish more precise reference values for different populations, particularly in individuals with early-stage small airway disease [8].
Influence of Patient Factors
While oscillometry requires less effort than spirometry, results can still be affected by patient cooperation, attention, and breathing patterns. Ensuring proper training and instruction for patients is essential to obtaining reliable and reproducible measurements.
Xu et al. (2022) analyzed the long-term variability of oscillometry results in stable COPD and asthma patients, demonstrating that patient cooperation and breathing patterns significantly impact test reliability. Their study reinforced the importance of proper patient instruction to minimize variability in measurements [2].
Potential Pitfalls in Interpretation
Calibration and Equipment Maintenance
To ensure accurate results, oscillometry equipment must be properly calibrated. Clinicians should follow manufacturer recommendations for calibration procedures and conduct routine maintenance checks to verify the device’s accuracy. Poor calibration can compromise the reliability of test results, potentially leading to misinterpretation of lung function abnormalities (Su et al., 2018) [8]. Research has shown that well-maintained and calibrated oscillometry devices improve the precision of detecting small airway dysfunction, particularly in patients with chronic respiratory conditions (Li et al., 2021) [6].
Variability in Measurements
Oscillometry results can fluctuate due to factors such as patient breathing patterns, cooperation, and even the time of day the test is performed. To improve accuracy, multiple measurements may be necessary to establish a consistent lung function profile
Xu et al. (2022) examined the long-term variability of impulse oscillometry in COPD and asthma patients, concluding that while IOS offers valuable insights, multiple measurements may be necessary to establish a consistent lung function profile. This highlights the importance of repeatability in clinical assessments [2].
Additionally, Sarkar et al. (2023) emphasized that standardizing test conditions and patient preparation can help mitigate measurement variability [9].
Clinical Correlation Required
Although oscillometry provides valuable physiological data, it should be interpreted in conjunction with a patient’s clinical history and symptoms. Research by Saadeh et al. (2015) demonstrated that while IOS has advantages over spirometry in detecting airway obstruction, it should not be used as a standalone diagnostic tool [5]. Instead, abnormal IOS findings should prompt further evaluation using complementary tests such as spirometry or imaging (Eddy et al., 2019) [7]. Clinicians should be cautious about over-relying on IOS without considering a comprehensive clinical context.
Need for Education and Training
Both healthcare providers and patients may require education on oscillometry’s role in respiratory care. Clinicians should receive training on interpreting oscillometry data, while patients should be informed about how the test contributes to their diagnosis and management plan.
Desiraju and Agrawal (2016) highlighted the importance of training clinicians to properly interpret oscillometry data, ensuring its appropriate use in diagnosis and disease management [3].
Additionally, van de Hei et al. (2020) found that the quality of respiratory function testing in primary care settings is often inconsistent, emphasizing the need for standardized training programs. Educating patients about the purpose and significance of oscillometry testing can also improve cooperation and test accuracy [10].
Conclusion
Comparative research consistently demonstrates the superior sensitivity of Impulse Oscillometry (IOS) over traditional spirometry (e.g., FEV1) in the early detection of COPD symptoms and airway abnormalities. IOS reliably identifies chronic bronchitis and emphysema by detecting increases in pulmonary resistance and decreases in pulmonary reactance, even in patients with normal spirometry results.
IOS offers a distinct advantage in monitoring airway dynamics, including bronchomotor tone in COPD patients, and captures daily variations in respiratory function even when spirometry results remain unchanged. Additionally, it proves invaluable in assessing asymptomatic individuals with subtle airway dysfunction enabling early intervention.
Long-term studies further validate IOS’s reliability in monitoring COPD progression under bronchodilator therapy. The technique’s ability to detect small airway disease, coupled with its non-invasive nature and minimal patient effort requirements, positions it as a critical tool in respiratory diagnostics and disease management.
Conflict of Interest: None
Grant Information: The author(s) received no specific funding for this work.
Acknowledgement: None
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