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BACKGROUND: In the intensive care unit we have observed that patients have different adherence to 2 commonly used positive-expiratory-pressure (PEP) therapy devices: the PEP bottle and the PEP mask. The reason for this difference is not clear. METHODS: In a randomized prospective study, we made continuous recordings of airway pressure and airflow, with 20 healthy volunteers, with the PEP bottle and the PEP mask. The measurement sequence consisted of 3 sessions of 10 breaths with the PEP bottle and the PEP mask, in a randomized crossover design. A rest period of 15 min separated the PEP bottle and PEP mask measurements. RESULTS: With the PEP bottle the expiratory phase began with a zero-flow period of 0.39 s, during which airway pressure rose 11.9 cm H2O. With the PEP bottle the mean expiratory pressure was 11.7 cm H2O, and end-expiratory pressure was 9.5 cm H2O. With the PEP mask the initial expiratory zero-flow period was almost nonexistent (0.04 s) and without any change in airway pressure. With the PEP mask the shape of the expiratory pressure curve was different; mean expiratory pressure was 8.6 cm H2O, and end-expiratory pressure was zero. With the PEP bottle the inspiration also began with a zero-flow period of 0.43 s, during which airway pressure decreased 9.6 cm H2O from the end-expiratory airway pressure. With the PEP mask the initial inspiratory zero-flow period was only 0.01 s and there was no concomitant change in airway pressure. CONCLUSIONS: The PEP bottle and the PEP mask showed major differences in the relationship between airflow and airway pressure. These findings might explain the observed differences in patient adherence to these therapies.

BACKGROUND: The Boussignac CPAP has been found to effectively treat acute pulmonary oedema. However, data on airway pressure in association with the Boussignac CPAP are sparse. We therefore designed this study to evaluate the stability of the Boussignac CPAP in terms of maintaining adequate inspiratory and expiratory pressure levels. We also wanted to evaluate the perceived exertion when breathing with the Boussignac CPAP.

METHODS: Continuous recordings of airway pressure and airflow were made in 18 healthy volunteers during breathing with the Boussignac CPAP at 5, 7.5 and 10 cm H₂O for three sessions of 10 minutes at each CPAP level. Participants were blinded for the sequential order of the investigated CPAP levels. They terminated each session, at the respective CPAP level, by taking 10 forced breaths.

RESULTS: During 10 minutes normal breathing periods, when participants breathed at 20 % of their VC with a peak expiratory airflow of 14 % of FEV₁, the maximal pressure difference was 4.0 cm H₂O between inspiration and expiration at CPAP 10 cm H₂O. Changes in airway pressure were never large enough to reduce airway pressure below zero. When taking forced breaths, expiratory volume was 38-42 % of VC and peak expiratory airflow was 49-56 % of FEV ₁. As airflow increased, both the drop in inspiratory airway pressure and the increase in expiratory airway pressure were enhanced.

CONCLUSIONS: Pressure changes during breathing with CPAP are considered to be associated with increased work of breathing. The pneumatic performance of the Boussignac CPAP is adequate during normal breathing with low airflow. However, during forced breathing resulting in increased airflow, the Boussignac CPAP is unable to maintain stable airway pressure levels, possibly resulting in increased work of breathing and respiratory fatigue. Thus, the Boussignac CPAP system might be less suitable for patients breathing at a higher frequency.

Introduction: Positive expiratory pressure (PEP) and continuous positive airway pressure (CPAP) are used to enhance breathing parameters such as functional residual capacity (FRC) in patients. Studies comparing effects of PEP and CPAP on FRC are sparse. One reason for this may be that sophisticated equipment, not suitable in the clinical setting, is required. Total lung capacity consists of inspiratory capacity (IC) and FRC and a change in IC should therefore result in a corresponding change in FRC. We aimed to investigate if PEP and CPAP induced changes in IC could be used as an indirect measure of changes in FRC and also to evaluate immediate effects of PEP and CPAP devices, with different kinds of resistors, on IC. 

Methods: 20 healthy volunteers breathed with two PEP devices, a PEP-mask (flow resistor) and a PEP-bottle (threshold resistor) and two CPAP devices, a flow resistor device and a threshold resistor device, in a randomized order. The measurement sequence consisted of 30 breaths with an IC measurement performed before and immediately after the 30^th breath, while the participants were still connected to the respective breathing device. Perceived exertion of the respective 30 breaths was measured with Borg CR10 scale.

Results: Three of the four breathing devices, the PEP-mask and the two CPAP devices, significantly decreased IC (p < 0.001). Median perceived exertion was quite low for all four breathing devices but the difference in perceived exertion within the different breathing devices was large.

Conclusion: When measured in direct continuation of PEP and CPAP breathing, changes in IC could be used as an indirect measure of changes in FRC. All investigated breathing devices except the PEP-bottle decreased IC, i.e. increased FRC.

INTRODUCTION: Continuous positive airway pressure (CPAP) is used in air ambulances to treat patients with impaired oxygenation. Differences in mechanical principles between CPAP devices may affect their performance at different ambient air pressures as will occur in an air ambulance during flight. METHODS: Two different CPAP systems, a threshold resistor device and a flow resistor device, at settings 5 and 10 cm H₂O were examined. Static pressure, static airflow and pressure during simulated breathing were measured at ground level and at three different altitudes (2400 m (8 kft), 3000 m (10 kft) and 10700 m (35 kft)). RESULTS: When altitude increased, the performance of the two CPAP systems differed during both static and simulated breathing pressure measurements. With the threshold resistor CPAP, measured pressure levels were close to the preset CPAP level. Static pressure decreased 0.71 ± 0.35 cm H₂O, at CPAP 10 cm H₂O, comparing ground level and 35 kft. With the flow resistor CPAP, as the altitude increased CPAP produced pressure levels increased. At 35 kft, the increase was 5.13 ± 0.33 cm H₂O at CPAP 10 cm H₂O. DISCUSSION: The velocity of airflow through the flow resistor CPAP device is strongly influenced by reduced ambient air pressure leading to a higher delivered CPAP effect than the preset CPAP level. Threshold resistor CPAP devices seem to have robust performance regardless of altitude. Thus, the threshold resistor CPAP device is probably more appropriate for CPAP treatment in an air ambulance cabin, where ambient pressure will vary during patient transport.