CPAP increased respiratory effort compared to both NIV and breathing at atmospheric pressure, but ventilator system resistance appeared to be a more relevant determinant of respiratory effort at higher minute ventilation induced by exercise.
Key Findings
Results
During rest, esophageal tidal swing (respiratory effort) was highest when CPAP was applied compared to atmospheric pressure and NIV conditions.
Study involved 38 healthy volunteers measured under 4 airway pressure conditions: atmospheric pressure (A), ventilator without applied pressures (V), CPAP of 5 cmH2O, and NIV with PEEP of 5 cmH2O plus inspiratory support of 5 cmH2O
Esophageal tidal swings were used as the measure of respiratory effort
The investigator reading esophageal pressures was blinded to condition, and the sequence of airway conditions was randomized
At rest, CPAP generated higher respiratory effort than both atmospheric breathing and NIV
Results
During light and strenuous exercise, both breathing on the ventilator without applied pressures (V) and CPAP increased respiratory effort compared to atmospheric pressure and NIV.
This pattern emerged at both light and strenuous exercise levels
The increase in respiratory effort under V and CPAP conditions during exercise suggests an increase in ventilator system resistance at higher minute ventilation
NIV (PEEP 5 cmH2O + ΔPinsp 5 cmH2O) reduced respiratory effort relative to CPAP and unassisted ventilator breathing during exercise
Three exercise levels were tested: rest, light exercise, and strenuous exercise
Results
Ventilator system resistance appeared to be a more relevant determinant of respiratory effort than CPAP pressure at higher minute ventilation induced by exercise.
At higher minute ventilation (exercise conditions), the resistance of the ventilator circuit became the dominant factor increasing respiratory effort
Both the ventilator-without-pressure (V) and CPAP conditions showed similarly elevated effort during exercise, suggesting the shared ventilator circuit resistance was driving the increase rather than CPAP pressure alone
NIV with inspiratory support overcame the ventilator system resistance, resulting in lower respiratory effort during exercise compared to CPAP
Results
NIV with inspiratory support pressure reduced respiratory effort compared to CPAP across all exercise levels.
NIV was delivered with PEEP of 5 cmH2O and inspiratory support (ΔPinsp) of 5 cmH2O
During rest, NIV resulted in lower esophageal tidal swings than CPAP
During both light and strenuous exercise, NIV continued to show lower respiratory effort than CPAP
The addition of inspiratory support pressure to PEEP appeared to compensate for ventilator circuit resistance at higher minute ventilation
Conclusions
The study was a physiological study conducted in healthy volunteers, with findings intended to prompt further investigation in patients with acute respiratory failure.
38 individuals were included in the final analysis
Participants were healthy volunteers, not patients with respiratory failure
The authors note that acute respiratory failure is often associated with high minute ventilation, making ventilator system resistance potentially clinically relevant
Authors called for further studies to examine the potential clinical implications of these findings in patient populations
What This Means
This research suggests that the type of breathing support provided by a ventilator machine matters not just because of the pressures it applies, but also because of the physical resistance of the ventilator circuit itself. In a study of 38 healthy volunteers, researchers measured how hard people had to work to breathe under four conditions: normal room air, connected to a ventilator with no pressure applied, CPAP (continuous positive airway pressure at 5 cmH2O), and non-invasive ventilation (NIV, which adds extra pressure to help with each breath). At rest, CPAP actually made breathing harder than normal air or NIV. During exercise—when people were breathing faster and deeper—both CPAP and simply being connected to the ventilator circuit with no pressure increased breathing effort compared to normal air or NIV, suggesting the machine's tubing and valves create resistance that the lungs must work against.
The finding that NIV reduced respiratory effort compared to CPAP, especially during exercise, is notable because the inspiratory support component of NIV appears to help overcome the resistance of the ventilator system itself. This means that for patients who are breathing rapidly due to illness, simply applying CPAP may not fully account for the added work imposed by the ventilator equipment.
This research suggests that ventilator circuit resistance could be a clinically important but underappreciated factor when choosing respiratory support strategies for patients with acute breathing problems, who typically breathe at high rates. The authors caution that these findings come from healthy volunteers and that further studies in actual patients with respiratory failure are needed before drawing clinical conclusions.
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Lindner S, Doerflinger L, Drotleff L, Link B, Neetz B, Michels-Zetsche J, et al.. (2026). Impact of CPAP and ventilator system resistance on respiratory effort in healthy volunteers.. BMC pulmonary medicine. https://doi.org/10.1186/s12890-026-04649-6