SLEEP BREATHING PHYSIOLOGY AND DISORDERS • LETTER TO THE EDITORS Unexpected pressure swings in a positive airway pressure device: an unknown cause for bad CPAP tolerance? Charlotte Mauclet 1 & Giuseppe Liistro 1 & Daniel Rodenstein 1 & Myriam Dury 1 & Valérie-Anne Chantrain 1 & Gimbada Benny Mwenge 1 Received: 18 June 2019 /Revised: 22 August 2019 /Accepted: 7 September 2019 # Springer Nature Switzerland AG 2019 To the Editors, Efficient continuous positive airway pressure (CPAP) treat- ment requires the pressure to be as constant as possible during the respiratory cycle [1]. Significant differences in pressure stability of devices have been described previously [2]. These reported pressure changes occur during inspiration, causing a drop in the CPAP pressure [2, 3]. Technical im- provements have since been implemented to compensate for these pressure decreases and other manipulations have been incorporated with the intent of improving therapy tolerance and compliance, such as an expiratory pressure relief (EPR) or a slow increase in the applied pressure at start of the night (Ramp). As a consequence, new CPAP devices are no longer set at a fixed pressure, but oscillate around a targeted pressure. The oscillation depends on the device and is determined by algorithms implemented by the designer. There is no evidence that these algorithmic improvements have any effect on treat- ment acceptance or compliance [4]. We were recently confronted with an unexpected form of pressure variations in a CPAP device. A 55-year-old woman consulted at our Sleep Clinic for insomnia and fatigue. Her medical history included obesity, type 2 diabetes mellitus, arterial hypertension, treated hypothyroidism, depression, and a rhinoseptoplasty. Polysomnography revealed that the patient had an apnea-hypopnea index (AHI) of 28 events per hour of sleep and L that the pressure of the CPAP device, measured with the pressure transducer of the polysomno- graphic recorder, was not stable. The pressure rose 1 cm H 2 O at each inhalation and returned to base level at time of expiration. Surprisingly, the pressure reached values as high as 19 cm H 2 O and the high pressures persisted during most of the night. This was accompanied by oxygen desaturations. The reading of the CPAP memory card reported a significant air leak (60 L/min) and a residual AHI of 4 events/h, concordant with the AHI calculated on the PSG (4 events/h), but pressure increases were not reported. We hypothesized that the big pressure fluctuations imposed by the device explained the intolerance expressed by our patient. We therefore tried a new adjustment period to another brand of CPAP device with the same pressure setting of 8 cm H 2 O and the same oro-nasal mask. The patient’ s tolerance was better and similar pressure fluctuations were no longer observed (Fig. 1). We have noticed similar unexpected CPAP pressure swings in other patients using the first described brand of CPAP with a nasal mask, although not resulting in intolerance. For exam- ple, a 60-year-old patient with severe OSAS (AHI 32 events/ h) was offered CPAP with a nasal mask, set at a pressure of 9 cm H 2 O. We observed that the pressure of the machine measured with the pressure transducer of the polysomno- graphic recorder was not stable. During the PSG, the pressure varied from 9 to 12 cm H 2 O. However, the patient did not report discomfort and treatment was proven effective with disappearance of the respiratory events. A third patient (AHI 32 events/h) with a nasal mask also experienced pressure fluc- tuations from 11 to 17 cm H 2 O, without causing intolerance. Differing from our first patient, we observed that the pressure increases rapidly and spontaneously decreased towards the set pressure. We contacted the manufacturer about these fluctua- tions, but they could not give an explanation or details about the embedded algorithm, which was private proprietary infor- mation for commercial reasons. The manufacturer offered to perform a bench test, which will take place in a near future. We thus report an unexpected behavior of a particular brand of CPAP device, whose applied pressures greatly di- verge from the set pressure. This device behavior is not de- scribed in the device’ s technical manual. Pressure deviations ranged as high as 11 cm H 2 O above the set pressure on a fixed * Gimbada Benny Mwenge gimbada.mwenge@uclouvain.be 1 Pneumology Department and Center for Sleep Medicine, Cliniques Universitaires Saint-Luc, Université Catholique de Louvain, Av Hippocrate 10, 1200 Brussels, Belgium Sleep and Breathing https://doi.org/10.1007/s11325-019-01938-9