Oscillometry, also called the forced oscillation technique, works by superimposing small, multi-frequency pressure oscillations on a person’s ordinary tidal breathing. Unlike spirometry, which demands forceful, coordinated blows, oscillometry is effort-independent and requires only passive cooperation, making it attractive for children, elderly patients, and people who cannot perform forced maneuvers. The technique reports two fundamental quantities: respiratory resistance, which reflects how hard it is for air to move through the airways, and respiratory reactance, which captures the elastic and inertive properties of the lungs and chest wall. Both are derived from respiratory system impedance, measured across a spectrum of frequencies from 5 to 37 hertz in modern devices.

The Toronto team compared the Tremoflo C-100, made by Thorasys Medical Systems in Canada, with the Resmon Pro, made by Restech srl in Italy. Their cohort of 76 participants included 49 patients with chronic lung disease and 27 healthy volunteers. Among the patients were 37 double-lung transplant recipients, 10 people with interstitial lung disease, one with chronic obstructive pulmonary disease, and one with lymphangioleiomyomatosis. Standard pulmonary function tests classified the group into 36 people with normal lung function, 26 with restriction, 8 with obstruction, and 5 with mixed patterns. Participants completed paired oscillometry with both devices in alternating order, each calibrated daily and performed according to European Respiratory Society technical standards.

The results were unambiguous. For all five primary oscillometry parameters, resistance at 5 hertz (R5), the resistance difference between 5 and 19 hertz (R5-19), reactance at 5 hertz (X5), resonant frequency (Fres), and the area of reactance (AX), the differences between devices reached statistical significance at p at or below 0.001. The Resmon Pro consistently reported lower R5, R5-19, Fres, and AX, and a less negative X5 than the Tremoflo C-100. In practical terms, the Resmon Pro painted a rosier picture of airway mechanics than the Tremoflo did for the same pair of lungs on the same day.

Statistical agreement analysis told a similar story. Intraclass correlation coefficients ranged from 0.59 to 0.85, and Spearman correlations were strong, between 0.779 and 0.920, meaning the devices rank-ordered patients similarly. But correlation is not agreement. Bland-Altman analysis, which plots the difference between paired measurements against their average, revealed systematic bias with wide limits of agreement for every parameter. The bias for AX, a reactance-derived index that integrates the frequency-dependent behavior of reactance, was minus 4.10 centimeters of water per liter, with limits of agreement stretching from minus 14.99 to plus 6.80. For Fres, the limits spanned from minus 6.46 to plus 4.75 hertz. Cohen’s d effect sizes were large for R5, R5-19, X5, and AX, confirming that the differences were not merely statistically detectable but substantively meaningful.

One of the study’s most clinically important findings concerned where the disagreement mattered most. When the researchers applied per-patient Oostveen reference limits, they found that agreement between devices was excellent, 91 to 100 percent within the Bland-Altman limits, when measurements fell within the normal reference range. But when measurements fell outside that range, agreement dropped to 81 to 92 percent. In other words, the systematic bias does little harm when a patient’s lungs are clearly normal, but becomes clinically consequential precisely when the lungs are abnormal, which is when monitoring decisions are being made.

The researchers also tested whether the inter-device differences translated into different patient classifications. They applied two schemes: a two-step decision tree the team had previously developed and validated in over 1,800 patients, and recently published Delphi consensus thresholds for asthma and COPD. Neither device showed clearly superior agreement with the pulmonary-function-test-derived gold standard, with kappa values of roughly 0.30 for the decision tree and only 0.09 to 0.12 for the Delphi thresholds. More concerning, individual participants could be classified differently depending on which device was used, meaning the same patient might be labeled normal by one machine and abnormal by the other.

Why do two devices measuring the same physical quantity disagree so much? The authors point to several technical factors. Hardware differences in oscillation waveform and amplitude can influence the measured signal. The two devices also handle mouthpiece dead space differently and use different calibration procedures: the Tremoflo completes an 8-second calibration against a 15-centimeter-water-second-per-liter reference load, while the Resmon Pro performs an 86-second calibration against a manufacturer-supplied load with distinct resistance and reactance characteristics. Signal processing differs too. The Tremoflo records for 20 seconds with 9 frequencies, while the Resmon Pro records for 60 seconds with 10 frequencies. The longer Resmon recording may improve low-frequency reactance estimation but increases susceptibility to drift and within-test changes in lung mechanics. Tidal volume was also higher during Tremoflo testing in this study.

The study is notable for extending device comparison beyond the healthy volunteers and asthma or COPD populations that dominated earlier work. Prior studies, including work by Dandurand and colleagues using mechanical test loads, Ducharme and colleagues in children, Soares and colleagues with a 3D-printed airway model, and De’s 2026 comparison of the same two devices in 97 symptomatic adults, all found systematic inter-device bias. But the Toronto cohort is the first to directly compare two commercial forced oscillation devices across normal, restrictive, obstructive, and mixed lung function patterns, including patients with interstitial lung disease and stable lung transplant recipients. The restrictive group showed the largest AX discrepancy, with a median Tremoflo value of 13.70 versus 8.23 on the Resmon Pro, a difference the authors note is particularly relevant because reactance abnormalities are the primary oscillometric signature of restrictive disease.

The practical message for clinicians is straightforward: stick with one device when following a patient over time. Changes in oscillometry parameters could otherwise be misattributed to disease progression or treatment response when they actually reflect device-specific differences. The authors also call for standardization of signal generation and processing across manufacturers, which they argue is necessary for cross-device comparability in both clinical practice and multi-center research. Participant feedback added a human dimension: of the 51 people who completed a survey, 61 percent had no preference, but some found the longer Resmon recordings fatiguing, while others preferred the handheld Tremoflo for its easier positioning. As oscillometry moves toward wider clinical adoption, particularly for early detection of lung disease and monitoring of transplant recipients, the Toronto findings make clear that the technology’s promise depends on the field first solving a problem that is less glamorous than the physics itself: getting the machines to speak the same language.

Subject of Research: Agreement between two commercial respiratory oscillometry devices across normal, obstructive, restrictive, and mixed lung function patterns

Article Title: Comparison of two respiratory oscillometers in patients with a broad range of lung function patterns

Article References: Binnie, M., Wu, J. K. Y., & Chow, C.-W. (2026). Comparison of two respiratory oscillometers in patients with a broad range of lung function patterns. Frontiers in Allergy, 7, Article 1896281. https://doi.org/10.3389/falgy.2026.1896281

Image Credits: AI Generated

DOI: 10.3389/falgy.2026.1896281

Keywords: oscillometry, forced oscillation technique, lung function, respiratory resistance, respiratory reactance, Bland-Altman analysis, pulmonary function testing, interstitial lung disease, lung transplant, device standardization, Tremoflo C-100, Resmon Pro

Spirometry, the familiar test in which a patient blows forcefully into a mouthpiece, measures how much air can be exhaled and how quickly. It is cheap, widely available and reproducible, which explains its dominance in both clinics and research studies. Yet it fundamentally measures airflow through large and medium airways. The injury pattern left by extreme preterm birth, often described as chronic lung disease of prematurity or bronchopulmonary dysplasia in its severe forms, is primarily one of disrupted alveolar and vascular development. The distal lung, where gas exchange actually happens, and the pulmonary circulation, which must carry the entire cardiac output through a finely branched vascular tree, are the structures most affected. Spirometry can remain deceptively normal in people whose gas transfer capacity and pulmonary vasculature are substantially impaired.

The evidence for this blind spot is accumulating rapidly. A study by Harris and colleagues, published in Pediatric Research, examined school-aged children born preterm and found that reduced diffusion of carbon monoxide across the lung, a marker of impaired gas exchange surface, was associated with elevated pulmonary artery pressures. This finding is significant because it links two silent abnormalities: a lung that cannot transfer oxygen efficiently and a heart that must pump against higher resistance in the pulmonary circulation. Neither abnormality would necessarily be flagged by a routine spirometry test, and both may progress quietly for decades before producing symptoms.

Longitudinal data reinforce the concern. Research published in the European Respiratory Journal followed individuals born extremely preterm into adulthood and documented persistent deficits in lung diffusion capacity that did not normalize with growth. A systematic review and meta-analysis by Gibbons and colleagues in the European Respiratory Review synthesized findings across lung volumes, gas transfer and oscillometry, a technique that measures airway resistance during quiet tidal breathing rather than forced expiration. Together, these studies sketch a consistent picture: preterm birth leaves a durable imprint on the distal lung and its mechanics that forced expiratory volumes capture only partially, if at all.

The clinical implications extend beyond the lungs. Survivors of extreme preterm birth appear to face elevated long-term risks of pulmonary vascular disease and cardiovascular complications, a concern articulated in a lifespan-oriented framework by Simpson and colleagues in The Lancet Respiratory Medicine. The developing lung and its vasculature are built in tandem during the canalicular and saccular stages of gestation, precisely the window that extreme preterm birth interrupts. When alveolarization is curtailed, the vascular tree that should accompany each new alveolus is curtailed with it. The result is a lung with fewer, larger airspaces and a reduced, remodeled vascular bed, a combination that increases the workload on the right ventricle and may set the stage for pulmonary hypertension and early cardiovascular decline in adult life.

What would a comprehensive assessment look like in practice? The commentary by Beaven and Finlay points toward a battery of complementary tests, each interrogating a different component of the cardiopulmonary system. Lung clearance index, derived from multiple-breath washout, quantifies ventilation inhomogeneity in the small airways and peripheral lung units, and has proven sensitive to early lung disease in other pediatric populations. Body plethysmography measures total lung volumes, revealing the restricted or hyperinflated patterns that spirometry alone can miss. The single-breath or rebreathing diffusing capacity for carbon monoxide directly probes the gas exchange surface. Oscillometry adds information about peripheral airway resistance without requiring maximal effort, an important advantage in young children who cannot reliably perform forced maneuvers.

Cardiovascular assessment deserves equal billing. Echocardiography can estimate pulmonary artery pressures and right ventricular function, while newer techniques such as cardiac magnetic resonance imaging offer precise quantification of right ventricular mass and ejection fraction. Exercise testing integrates the entire system, revealing whether oxygen delivery keeps pace with metabolic demand, and cardiopulmonary exercise testing can unmask limitations that are invisible at rest. Reduced exercise capacity has been documented in preterm-born cohorts, and the physiological basis, whether ventilatory limitation, gas exchange impairment, vascular limitation or deconditioning, can only be disentangled by measuring multiple variables simultaneously during exertion.

The concept of treatable traits offers a compelling rationale for this expanded toolkit. As Zanetto and colleagues argued recently in the American Journal of Respiratory and Critical Care Medicine, clinicians caring for preterm-born individuals with chronic lung disease of prematurity should identify and target specific, modifiable characteristics across the lifespan rather than relying on a single diagnostic label. A patient with preserved spirometry but reduced diffusion capacity and elevated pulmonary artery pressures needs a very different management plan from one with airflow obstruction and air trapping. Without comprehensive phenotyping, the first patient may be falsely reassured and the second may receive therapies that do not address their dominant abnormality. Treatable traits might include airway reactivity, ventilation inhomogeneity, impaired gas transfer, pulmonary vascular dysfunction, muscle weakness and physical deconditioning, each with its own therapeutic levers.

There are practical hurdles to overcome before comprehensive assessment becomes standard care. Many of the recommended tests require specialized equipment, trained personnel and cooperative patients, which limits their availability in ordinary clinical settings and in the low-resource environments where much of the world’s preterm births occur. Reference ranges for children and young adults born preterm are incomplete for several modalities, complicating interpretation. Radiation exposure argues against routine computed tomography, and the research community continues to seek safe, non-invasive imaging surrogates of alveolar and vascular structure. Standardizing protocols across centers and across the age spectrum, from infancy through adulthood, remains an unfinished project, and longitudinal cohorts that follow preterm-born individuals with repeated multi-modal assessments are still relatively rare.

Nevertheless, the direction of travel is clear. The generation born after the widespread adoption of surfactant therapy and gentle ventilation is now reaching adulthood in large numbers, and their long-term cardiopulmonary trajectory is becoming a matter of public health, not just neonatology. Detecting silent gas exchange impairment and early pulmonary vascular change during the school years, when interventions such as exercise programs, vaccination, smoking prevention and targeted follow-up can still alter the course, is far preferable to discovering these problems when symptomatic disease emerges in mid-life. The commentary by Beaven and Finlay makes the case that spirometry, whatever its virtues, cannot carry this burden alone. A comprehensive cardiopulmonary assessment, combining measures of lung volume, ventilation distribution, gas transfer, airway mechanics, pulmonary hemodynamics and exercise capacity, offers the best chance of understanding, monitoring and ultimately improving the lifelong health of the fastest-growing population of adult survivors of neonatal intensive care.

Subject of Research: Cardiopulmonary assessment of lung and cardiovascular outcomes in survivors of extreme preterm birth

Article Title: Beyond spirometry: towards comprehensive cardiopulmonary assessment after extreme preterm birth

Article References: Beaven, M. L., & Finlay, P. (2026). Beyond spirometry: towards comprehensive cardiopulmonary assessment after extreme preterm birth. Pediatric Research. https://doi.org/10.1038/s41390-026-05399-1

Image Credits: AI Generated

DOI: 10.1038/s41390-026-05399-1

Keywords: extreme preterm birth, bronchopulmonary dysplasia, spirometry, lung diffusion capacity, pulmonary hypertension, chronic lung disease of prematurity, lung clearance index, oscillometry, cardiopulmonary exercise testing, treatable traits, pediatric lung function, right ventricular function