The core of the debate lies in a trade-off that every intensivist performs at the bedside, often several times a day. When lung-protective limits cap the tidal volume, the ventilator must increase the respiratory rate to sustain adequate minute ventilation, the total volume of air moved in and out of the lungs each minute. Minute ventilation is simply the product of tidal volume and respiratory rate, so mathematically the two settings can be traded against one another while the total remains constant. In theory, halving the tidal volume and doubling the rate should deliver the same gas exchange. In practice, the lungs and the body do not obey such neat arithmetic, and the consequences of shifting the balance in one direction or the other have remained surprisingly difficult to pin down.

The reason the trade-off is not neutral lies in the architecture of the respiratory system. Not all inhaled air reaches the alveoli, the tiny sacs where oxygen and carbon dioxide are actually exchanged. A substantial fraction of each breath fills the conducting airways, the trachea, bronchi and bronchioles, where no gas exchange takes place. This volume is known as anatomical dead space. When tidal volume is reduced, each breath carries a proportionally larger burden of dead space gas, air that is inhaled and exhaled without ever contributing to gas exchange. To compensate, the respiratory rate must rise even further than simple minute ventilation calculations would suggest, because the effective, alveolar ventilation falls faster than the total ventilation. Higher rates, in turn, shorten the time available for exhalation, raising the risk of air trapping and the build-up of intrinsic positive end-expiratory pressure, a phenomenon that can quietly strain the lungs and the right side of the heart.

Jung and her colleagues frame this problem through the lens of ventilatory efficiency, a concept that captures how much of the work of breathing actually translates into useful gas exchange. Ventilatory efficiency is commonly assessed by relating ventilation to carbon dioxide elimination, and it deteriorates when dead space fraction rises or when the matching between ventilation and perfusion within the lung worsens. The Hannover group contends that when clinicians and researchers trade tidal volume against respiratory rate, they typically track pressures, volumes and driving pressure, but rarely ask whether the resulting pattern of breathing is actually efficient. Two ventilator configurations that look equivalent on a monitor, delivering identical minute ventilation and similar airway pressures, can differ substantially in how much carbon dioxide they clear per liter of air moved, and that difference carries metabolic and mechanical consequences for the patient.

The correspondence appears alongside and responds to a study by Grieco and colleagues, also published in Intensive Care Medicine, which examined how respiratory mechanics modify the impact of ventilator settings on clinical outcomes in patients with acute brain injury. That work adds an important dimension to the debate, because patients with injured brains are exquisitely sensitive to changes in carbon dioxide levels, intrathoracic pressure and the hemodynamic effects of ventilation. In this population, the choice between a low tidal volume with a high rate and a slightly larger tidal volume with a lower rate is not merely a question of lung protection. It can influence cerebral blood flow, intracranial pressure and brain tissue oxygenation, making the trade-off a matter of neurological as well as pulmonary consequence.

To probe the physiological side of the question directly, the Hannover authors point to their own prospective physiological pilot study, published in Annals of Intensive Care, in which they systematically increased respiratory rate during low tidal volume ventilation and measured what happened to ventilatory efficiency and to the mechanical costs of breathing. The study, led by Jung with colleagues including Markou and Storch, was designed to isolate the effect of rate under controlled conditions, allowing the researchers to observe how the efficiency of carbon dioxide elimination and the energetic burden on the respiratory system changed as breaths became faster and smaller. Although pilot studies of this kind involve limited numbers of patients and are intended to generate hypotheses rather than definitive answers, they provide the kind of granular physiological data that large outcome trials often cannot capture.

The significance of this line of research extends beyond the physiology laboratory. Mechanical ventilation is one of the most common interventions in critical care, and the energy cost of breathing, whether performed by the patient’s own muscles or by a machine, is a real metabolic burden for patients whose reserves are already depleted. Inefficient ventilation means that the body, or the ventilator, must move more air to achieve the same gas exchange, and every liter of air moved imposes stress on the lung tissue, on the airways and on the circulation. If a high rate strategy systematically degrades ventilatory efficiency, then the apparent safety of very low tidal volumes may come with a hidden price that current protective ventilation protocols do not account for. Conversely, if efficiency is preserved across a wide range of rate settings, clinicians would gain welcome flexibility in tailoring ventilation to individual patients.

The Hannover authors also emphasize that respiratory mechanics, the elastic and resistive properties of the individual patient’s respiratory system, modify how these trade-offs play out. A stiff, poorly compliant lung in acute respiratory distress syndrome behaves very differently from a more compliant one, and the same ventilator settings can impose very different stresses depending on the underlying disease, the body size and the geometry of the airways. This is precisely the message reinforced by the Grieco study in brain-injured patients, where the impact of ventilator settings on outcomes depended on respiratory mechanics. The implication is uncomfortable but important: there may be no universal answer to the question of how to distribute ventilation between volume and rate, and the optimal balance may need to be determined for each patient rather than dictated by a single protocol.

What the correspondence ultimately calls for is a change in perspective rather than a change in practice. The authors do not dispute the value of low tidal volume ventilation, which remains one of the most robustly supported interventions in critical care. Instead, they argue that ventilatory efficiency deserves a place at the table when ventilator settings are chosen and when clinical trials are designed. Modern ventilators already measure many of the variables needed to estimate dead space and efficiency at the bedside, and incorporating these measurements into routine monitoring could allow clinicians to see not just how much air they are moving, but how effectively that air is working. As the field moves toward increasingly personalized ventilation strategies, the question posed by Jung, Gillmann and Stueber is likely to shape both research agendas and bedside decision-making in the years ahead.

For now, the message for the intensive care community is one of measured caution and renewed curiosity. The trade between tidal volume and respiratory rate is not a zero-sum game played out on the ventilator display; it is a physiological negotiation with consequences for gas exchange, energy expenditure, hemodynamics and, in vulnerable populations such as patients with brain injury, the injured organ itself. By insisting that ventilatory efficiency be considered in that negotiation, the Hannover group has added a compelling voice to a growing conversation about what protective ventilation truly means. The answer to their title question, on the evidence they marshal, appears to be a qualified yes, and the next generation of studies will need to determine exactly how that consideration should change the numbers entered on the ventilator each morning.

Subject of Research: Ventilatory efficiency in the trade-off between tidal volume and respiratory rate during protective mechanical ventilation

Article Title: Should ventilatory efficiency be considered when trading tidal volume against respiratory rate?

Article References: Jung, C., Gillmann, H.-J., & Stueber, T. (2026). Should ventilatory efficiency be considered when trading tidal volume against respiratory rate?. Intensive Care Medicine. https://doi.org/10.1007/s00134-026-08627-8

Image Credits: AI Generated

DOI: 10.1007/s00134-026-08627-8

Keywords: mechanical ventilation, tidal volume, respiratory rate, ventilatory efficiency, dead space, acute respiratory distress syndrome, intensive care medicine, respiratory mechanics, carbon dioxide elimination, acute brain injury, lung protection, minute ventilation

The research team followed 92 adolescents with obesity, with an average age of 13.1 years and a mean body mass index of 34.31 kilograms per square meter, through a 16-week multidisciplinary weight-loss intervention, or MWLI. Roughly 58 percent of the participants were girls. Before the program began and again after it ended, each teenager underwent a battery of physiological assessments: spirometry to measure resting lung volumes and flows, cardiopulmonary exercise testing to probe breathing during graded exertion, dual X-ray absorptiometry to quantify body composition, and measurements of peak oxygen consumption to gauge cardiorespiratory fitness. This combination allowed the investigators to track changes in the lungs, the muscles, and the fat mass simultaneously, a pairing that has rarely been attempted in this age group.

The spirometry results were unambiguous. After 16 weeks, the adolescents showed significant increases in forced vital capacity, the total amount of air that can be forcefully exhaled after a maximal inhalation, as well as in forced expiratory volume in one second and in mid-expiratory flow between 25 and 75 percent of the vital capacity, a marker of smaller airway function. All three improvements were statistically significant at the p < 0.001 level. In practical terms, the teenagers could move more air, move it faster, and empty their lungs more completely after losing weight, which suggests that the mechanical compression imposed by excess adipose tissue on the chest and diaphragm was at least partially relieved.

The exercise findings were equally revealing, though in a subtler way. During cardiopulmonary exercise tests performed at identical calibrated power outputs before and after the intervention, the adolescents consumed less oxygen and moved less air per minute at the same absolute workloads. Ventilatory efficiency, a measure of how much ventilation is required to eliminate a given amount of carbon dioxide, improved significantly. The authors interpret this as evidence of a lower work of breathing and fewer ventilatory limitations during exercise. In other words, the same physical task demanded less of the respiratory system after weight loss, freeing up breathing reserve that these adolescents could then devote to sustaining activity for longer or at higher intensities.

Alongside these respiratory gains, the expected metabolic shifts materialized. Body mass fell, as did total fat mass, trunk fat mass, and visceral fat mass, the deep abdominal fat deposits that are particularly implicated in metabolic and inflammatory disease. Crucially, lean mass increased in relative terms, and cardiorespiratory fitness, indexed by peak oxygen consumption, rose significantly. The pattern matters because it indicates that the intervention did not merely shrink the teenagers indiscriminately; it shifted their body composition toward a healthier ratio of metabolically active muscle to energy-storing fat, while simultaneously building the capacity of their cardiovascular and respiratory systems to deliver oxygen during effort.

Perhaps the most scientifically valuable component of the study lies in its correlation analyses, which connect the dots between these separate domains. Changes in forced vital capacity, forced expiratory volume in one second, and mid-expiratory flow were positively associated with increases in lean mass percentage and in cardiorespiratory fitness, and negatively associated with decreases in total, trunk, and visceral fat mass percentages, with the strongest associations reaching p < 0.001. Meanwhile, reductions in oxygen consumption and minute ventilation at matched exercise intensities tracked the same body-composition and fitness changes. The directionality of these relationships supports a mechanical and physiological model: as fat mass, especially the visceral and trunk depots, recedes, the chest wall unloads, the diaphragm works against less resistance, and the lungs expand more freely, while improved fitness amplifies the efficiency of gas exchange.

Why does this matter beyond the laboratory? Adolescents with obesity have long been documented to suffer reduced exercise tolerance, a problem that feeds a vicious cycle in which breathlessness discourages physical activity, which in turn worsens fitness and perpetuates weight gain. Prior research has linked childhood obesity to lower lung function, airway dysanapsis, heightened asthma risk, and increased cardiovascular mortality in adulthood. By demonstrating that a lifestyle-based intervention, rather than surgery or pharmacotherapy, can meaningfully improve both resting spirometry and exercise ventilatory dynamics, the study provides clinicians with a concrete, non-invasive rationale for treating respiratory health as an explicit target of pediatric weight management, not merely an afterthought.

The study also adds nuance to a technical debate in exercise physiology. Ventilatory efficiency, often expressed through relationships between ventilation and carbon dioxide output, is known to be altered in obesity, and researchers have questioned whether obese individuals represent a distinct ventilatory phenotype during exercise. The Clermont-Ferrand findings suggest that whatever ventilatory inefficiency exists in adolescent obesity is at least partly reversible and is coupled to reversible changes in fat mass and fitness. This positions ventilatory efficiency as a potential monitoring tool: a cheap, non-invasive parameter that clinicians could track during weight-loss programs to verify that respiratory health is actually improving, rather than relying on scale weight alone.

Methodologically, the investigation was rigorous for its field. Spirometry followed international standardization guidelines, the anaerobic threshold and gas-exchange measurements relied on established techniques, and the statistical analysis, led by Bruno Pereira of the hospital’s biostatistics department, applied appropriate tests with effect-size reporting and corrections for multiplicity. The trial was registered in the ClinicalTrials.gov database and conducted in accordance with the Declaration of Helsinki, with written informed consent from the adolescents and their parents. Participants were recruited through pediatric obesity centers in La Bourboule and Romagnat in France, and the multidisciplinary program combined dietary counseling, supervised physical activity, and medical follow-up delivered by pediatricians, pulmonologists, nutrition specialists, and exercise physiologists.

The authors acknowledge the limitations inherent in an intervention study without a control group of adolescents with obesity who did not participate in the program, and the correlations reported here demonstrate association rather than causation. Nevertheless, the convergence of evidence is striking: fat mass fell, lean mass and fitness rose, resting lung volumes expanded, and the metabolic cost of breathing during exercise dropped, all moving together in the directions predicted by respiratory mechanics. For a generation of young people in whom obesity is increasingly common and its cardiovascular consequences increasingly well documented, the message is both mechanistically grounded and hopeful. A 16-week multidisciplinary program did more than slim these adolescents down; it measurably opened up their breathing, and the lungs, it turns out, keep score of everything the body loses and gains.

Subject of Research: Effects of a multidisciplinary weight-loss intervention on resting and exercise respiratory function in adolescents with obesity

Article Title: Impact of a multidisciplinary intervention on resting and exercise respiratory functions in adolescents with obesity

Article References: Fadel, B., Gaucherot, A., Pereira, B., Egron, C., Budjemma, S., Oost, P., Masurier, J., Cardenoux, C., Isacco, L., Boirie, Y., Duclos, M., Thivel, D., & Julian, V. (2026). Impact of a multidisciplinary intervention on resting and exercise respiratory functions in adolescents with obesity. Pediatric Research. https://doi.org/10.1038/s41390-026-05523-1

Image Credits: AI Generated

DOI: 10.1038/s41390-026-05523-1

Keywords: obesity, adolescents, lung function, spirometry, ventilatory efficiency, cardiorespiratory fitness, body composition, weight loss intervention, visceral fat, peak oxygen consumption, pediatric research, exercise testing