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(Chest. 2000;118:1441-1449.)
© 2000 American College of Chest Physicians

Nasal Continuous Positive Airway Pressure Devices Do Not Maintain the Set Pressure Dynamically When Tested Under Simulated Clinical Conditions*

Jeffery P. Bacon, MD; Robert J. Farney, MD, FCCP; Robert L. Jensen, PhD; James M. Walker, PhD and Tom V. Cloward, MD, FCCP

* From the Department of Medicine (Dr. Bacon), University of Utah Medical Center; Intermountain Sleep Disorders Center (Drs. Farney, Walker, and Cloward), LDS Hospital; and the Pulmonary Division (Dr. Jensen), Department of Medicine, LDS Hospital, Salt Lake City, UT.

Correspondence to: Robert J. Farney MD, FCCP, Intermountain Sleep Disorders Center, LDS Hospital, 325 8th Ave, Salt Lake City, UT 84143; e-mail: rjfmd{at}msn.com


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Study objectives: Nasal continuous positive airway pressure (CPAP) is standard therapy for obstructive sleep apnea syndrome. The effective nasal mask pressure may be adversely affected by factors that increase system resistance (eg, long tubing and/or water condensation) and by dynamic variables (breathing frequency [f] and tidal volume [VT]). The present study was conducted in order to assess the performance of CPAP machines throughout a range of simulated clinical conditions.

Design: Four currently used CPAP machines were tested at settings of 5, 10, 15, and 20 cm H2O using a pulmonary waveform generator to produce VTs of 0.4, 0.8, and 1.2 L at frequencies of 10, 20, and 30 breaths/min. Machines were tested under five conditions: 6-foot and 12-foot tubing, with and without an in-line humidifier, and 12-foot tubing with humidifier and water condensation.

Measurements: Maximum and minimum mask pressure measurements were obtained during five respiratory cycles for each dynamic variable under each of the five conditions and CPAP settings (180 experiments on each of four CPAP models).

Results: Using typical clinical parameters (VT, 0.4 L and 0.8 L; f, 10 breaths/min and 20 breaths/min; and CPAP, 5 to 15 cm H2O), mask pressure consistently varied above and below the set point when additional tubing and/or a humidifier were added to the system (0.7 to 2.9 cm H2O below and 0.5 to 1.0 cm H2O above the set pressure). Water condensation caused large pressure deviations (inspiratory pressure ranged from 3.5 to 5.6 cm H2O below set pressure, and expiratory pressure ranged from 0.7 to 3.5 cm H2O above set pressure).

Conclusions: Therapy and compliance could be adversely affected because some CPAP machines in current use do not maintain constant continuous mask pressure when tested using simulated conditions, especially when water condenses in the tubing.

Key Words: compliance • humidifier • nasal continuous positive airway pressure • obstructive sleep apnea


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Obstructive sleep apnea (OSA) is common and affects 1 to 2% of women and 4 to 6% of men in the general adult population from 30 to 70 years old.1 2 3 Nasal continuous positive airway pressure (CPAP) is currently the standard therapy for OSA because it prevents upper airway collapsibility and closure by creating a "pneumatic stent." However, this therapy is effective only if it is able to reduce end-expiratory upper airway closure and exceed the minimum intraluminal pressure necessary to maintain airway patency.4 Because the optimal level of CPAP varies from patient to patient, polysomnography is indicated to determine the correct therapeutic setting for each individual.5 6 The precise prescription of CPAP is important because subtherapeutic pressures will not reverse sleep fragmentation or prevent hypoxemia. However, pressures that are higher than necessary are poorly tolerated, can cause excessive air leaking, and can disrupt sleep. Obviously, either condition will adversely affect long-term treatment outcome.

We became interested in assessing the response of CPAP machines to various clinical conditions because of reports by some of our patients that their CPAP machines seemed to be less forceful after a humidifier was used. Our patients also find that the gurgling of water in the tubing and excessive moisture condensing in the mask are annoying. Previous studies of pressure stability have tested the performance of some CPAP devices under steady flow conditions using variable resistance valves and vacuum motors to simulate constant inspiration.7 Demirozu and coworkers7 demonstrated that CPAP mask pressure fell when inspiratory flow increased from 20 to 60 L/min. With set pressures of 5, 10, and 15 cm H2O, the mask pressure decreased in all nine machines by as much as 5 cm H2O, and the pressure drop varied between machines. However, the operation of nasal CPAP devices and the maintenance of adequate pharyngeal pressure may be affected by the dynamic events of breathing and the static variables introduced by additional components within the circuit.

The dynamic performance of CPAP devices has not been tested using a system that precisely controls tidal volume (VT) and breathing frequency (f) in conditions that might exist in a domiciliary setting. Therefore, we tested four new model CPAP devices using a computerized breathing simulator. We measured mask pressure at four CPAP settings with various VTs and fs. In order to simulate various possible clinical situations, data were obtained (1) with different lengths of tubing between the device and the mask, (2) with and without a humidifier added to the circuit, and (3) with and without a small amount of water instilled into the tubing.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Testing was performed in the Pulmonary Laboratory at LDS Hospital in Salt Lake City, UT. The average ambient barometric pressure at the altitude of 1,400 m is 647 mm Hg, average temperature was 22°C, and average relative humidity was 37%.

A schematic of the experimental design is shown in Figure 1 . A pulmonary waveform generator (PWG) was used to simulate tidal breathing of a patient (PWG System S/N 714; MH Custom Design & Manufacturing; Midvale, UT). The PWG is precise and reproducible and has been used extensively in testing and validating pulmonary function measuring equipment.8 For each experiment, the PWG delivered five complete respiratory cycles using a sinusoidal respiratory waveform because this pattern resembles normal, tidal breathing during the dominant sleep state (nonrapid eye movement). Rapid eye movement sleep is characterized by a highly erratic breathing pattern9 and could not be simulated with current technology. Various minute ventilation rates were obtained by programming the PWG for different VTs and fs.



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  		Figure 1. Schematic of CPAP testing configuration. VT and f are controlled by the stepper motor and PWG. Six-foot or 12-foot lengths of tubing were connected to a CPAP unit with and without a humidifier. Condensation was simulated by adding 10 mL water into a dependent loop of tubing (12-foot length only). Pressure was measured at the mask and device outlet.

 
Pressure was measured at the mask and at the device outlet with a short piece of noncompliant tubing connected to a differential pressure transducer (Validyne MP 45, ± 50 cm H2O; Validyne Engineering; Northridge, CA) independent of the pressure transducer within the PWG and each CPAP device. The signals from the transducer were processed through a demodulator (Validyne CD 12; Validyne Engineering) and then sampled by a computer at 50 Hz.

Four currently used nasal CPAP models were tested: Horizon (Devilbiss; Sunrise Medical; Somerset, PA), Aria (Respironics; Murrysville, PA), Tranquility Quest Plus (Healthdyne; Marietta, GA), and Sullivan V Elite (ResMed; Sydney, Australia). These machines were selected because they were produced by the major manufactures of CPAP equipment and were the four most commonly used in our area at the time. Each regulates a blower motor by means of a pressure transducer within the machine, but we were not provided proprietary information regarding the specific mechanical design and software algorithms used for feedback control. A number was arbitrarily assigned to each machine so as not to disclose the model in presentation of the results. A new standard model mask (Sullivan, small adult) was connected to the tubing using a cylindrical adapter and then sealed with tape to an incompressible section of tubing to represent the patient-device interface that was then connected to the PWG (the expiration valve on the mask was functional). A cold pass-over humidifier (Respironics Oasis; Respironics) and 6-foot or 12-foot lengths of standard tubing were used in the various testing conditions. Experiments were not duplicated with the heated humidifier (model HC100; Fischer-Paykel; Auckland, New Zealand) because the component resistance (provided by the manufacturer) is similar and the additional measurements would have doubled the number of experimental setups to 360 per tested device.

Before each experiment was performed, the pressure transducer was calibrated with a standard water manometer (Dwyer; Michigan City, IN). Each calibration was then verified by measuring two intermediate pressures with the pressure measurement system. To validate the reproducibility of measurements, the testing apparatus was dismantled and reassembled several times, after which several experiments were repeated. We verified that all four devices delivered the particular set pressure at the device outlet within 0.1 to 0.2 cm H2O of each other.

The data collected consisted of maximum and minimum pressure across five breath cycles. The pressure range was calculated as the difference between maximum and minimum pressure. Measurements were obtained at the device outlet and at the mask during the experimental conditions, which are shown in Table 1 . Each CPAP device was tested at four pressure levels that could be used in clinical practice (5, 10, 15, and 20 cm H2O). Either 6-foot or 12-foot lengths of standard tubing were attached to the machines with and without the humidifier in circuit. In order to simulate excessive water accumulation within the tubing (12-foot length only), 10 mL of water was injected into the tubing, which was just enough to create a slight gurgling sound during inspiration.


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  		Table 1. Testing Configurations

 
Experiments were performed at each CPAP pressure under dynamic airflow conditions using the PWG with three different programmed VTs (0.4, 0.8, and 1.2 L) and three different fs (10, 20, and 30 breaths/min). Each CPAP device being tested was allowed to "equilibrate" with no flow for approximately 30 s before running the experiments and before any measurements were made. In order to quantify the pressure drop produced by adding various components to the CPAP circuit, limited measurements were obtained at the mask and at the device outlet with steady flow from the CPAP devices without the PWG operating (10 cm H2O setting only).


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Steady Flow Conditions
All four devices performed equivalently under steady flow conditions (ie, without simulated respiration). There was no significant pressure drop due to increasing resistance with any system configuration during steady flow. The mean pressure decrease from the device to the mask was 0.36 cm H2O.

Dynamic Flow Conditions
Pressure measured at the mask was found to vary substantially in parallel with the respiratory cycle, with minimal phase delay and with very little difference between machines. For example, in the poor performance condition (ie, VT, 0.8 L; CPAP, 15 cm H2; f, 20 breaths/min and water in the tubing), minimum and maximum mask pressures obtained with the four CPAP units were 8.8 to 16.5, 8.4 to 15.8, 10.3 to 16.3, and 10.0 to 16.0 cm H2O, respectively. The mean minimum and maximum pressures are shown in Table 2 . In order to simplify the extensive data, only the mean results for the four devices using VTs of 0.4 L and 0.8 L, CPAPs of 5, 10, and 15 cm H2O, and fs of 10 breaths/min and 20 breaths/min are shown. The degree of variability was predominantly related to system resistance and minute ventilation or inspiratory flow rate. Increased resistance in the CPAP circuit in the form of extra tubing, a humidifier, and especially excessive water in the tubing, progressively and consistently added to the inability of the CPAP devices to maintain the set pressure; hence, more variability in mask pressure was observed. While there was an increase in pressure above the set pressure at near end-exhalation in each respiratory cycle, most of the difference in pressure between the CPAP device and the mask was measured as a drop in pressure below the CPAP set pressure during inspiration and the initial part of exhalation.


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  		Table 2. Mask Pressures*

 
Depending on the test condition, mean pressure variation ranged from 1.2 to 18.1 cm H2O. When VT was 0.4 to 0.8 L and f was 10 to 20 breaths/min, and the addition of either a humidifier, an extra length of tubing, or both, the mean mask pressure range was 2 to 4 cm H2O. When water was added to the tubing to reproduce water condensation in dependent loops, a condition that is often recognized clinically when gurgling sounds are heard, the mean pressure range at the mask increased to approximately 4 to 8 cm H2O. The most extreme variations of mask pressure occurred in the presence of very high ventilatory demand (VT of 1.2 L and/or f of 30 breaths/min), with an in-line humidifier, 12 feet of tubing, and water condensation. Under these conditions, the mean pressure range was 15 to 18 cm H2O, and some of these experiments actually resulted in subatmospheric pressure at the mask.

The results of a representative experiment using typical clinical parameters are shown in Figure 2 . Mask and device pressures were obtained from device number 2 using 6-foot lengths of tubing and in-line humidifier. The CPAP device was set at 10 cm H2O, and the PWG was programmed to deliver VT of 0.4 L with f of 10 breaths/min. Very slight variation of pressure was recorded at the device outlet. The mask pressure varied from 9.3 cm H2O during inspiration to 10.1 cm H2O during expiration. Figure 2 shows the dramatic pressure variation that occurred with an additional 6 feet of tubing and water condensation (5.8 cm H2O during inspiration to 10.8 cm H2O during expiration). The rapid fluctuations of pressure observed at the device outlet and at the mask are due to the succession effects of water in the tubing (gurgling) with corresponding rapid changes in airway resistance.



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  		Figure 2. Pressure measured at the mask and at the CPAP machine (device number 2). Initial data shown on the left side were obtained with standard 6-foot tubing and humidifier in the circuit (only two of five breaths are shown for simplicity). Using the same machine and PWG settings, data shown on the right side were obtained with an additional 6-foot tube and 10 mL of water in the tubing. Rapid marked oscillations of the mask pressure are due to gurgling of water in the tubing. f = f; VT = VT

 
The magnitude of the pressure difference at the mask was proportional to the peak inspiratory flow rate and was not an independent function of either VT or f. The inspiratory flow rate of the PWG increases with increased minute ventilation and is unrelated to the specific f or VT. At the minimum minute ventilation of 4 L/min (VT of 0.4 L and f of 10 breaths/min), the peak inspiratory flow rate measured 0.24 L/s, compared to 1.90 L/s at the maximum minute ventilation of 36 L/min (VT of 1.2 L and f of 30 breaths/min). As an example, the range of mask pressure data from device number 4, which was set to deliver a pressure of 10 cm H2O with a 6-foot tube and in-line humidifier, is presented in Figure 3 . The range of pressure was 2.3 cm H2O at a peak flow rate of 0.64 L/s, compared to 5.0 cm H2O at a peak flow rate of 1.28 L/s, regardless of the specific VT and f.



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  		Figure 3. Range of pressure measured at both the mask and CPAP machine outlet (device number 4), obtained with various VTs, f settings (FREQ), and corresponding peak inspiratory flow rates. The CPAP machine set pressure was 10 cm H2O. Inspiratory flow rate increases with either increasing VT or f. The variation of mask pressure is consistently and positively correlated with inspiratory flow rate. bpm = breaths/min; see Table 2 for abbreviation.

 
The degree of variation from the set pressure was not a function of the specific CPAP level. Figure 4 shows the mean minimum and maximum mask pressures present when the PWG was programmed for a VT of 0.8 L and fs ranging from 10 to 30 breaths/min under each condition. For each level of CPAP tested, deviation from the set pressure measured at the mask was similar, but the difference from set pressure progressively increased with higher peak inspiratory flow rates and with additional system components. Because the absolute pressure differences were similar, there was a greater impact on the effective mask pressure at lower CPAP settings.



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  		Figure 4. Mean minimum pressures (inspiration) and mean maximum pressures (expiration) are graphed as the differences below the machine set pressure and above the set pressure, respectively, for CPAP levels of 5, 10, and 15 cm H2O with a VT of 0.8 L. Data are shown for all five tubing and humidifier conditions described in Table 1 and fs of 10 to 30 breaths/min. The absolute differences increase with adding system components and increasing breathing or inspiratory flow rates but are similar for each level of CPAP. Hum = humidified.

 

   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
The major conclusion from this study is that some currently used CPAP machines do not maintain a constant continuous set mask pressure when tested using simulated ordinary clinical conditions. Differences among the four machines used in this study were not clinically important with either steady-state or dynamic tests; with all devices, the main deviation from the set pressure was a decrease during early inspiration. Various alterations of the apparatus and especially the accumulation of water condensation consistently produced large rapid fluctuations in mask pressure, which would easily be annoying as well as subtherapeutic. When used in actual clinical practice, the lower-than-prescribed mask pressure could be further compounded by factors that result in greater flow-resistive pressure drop between the mask and the pharynx, such as increased nasal congestion and obstruction. Although less striking, higher-than-prescribed pressures during expiration were measured that could lead to discomfort and intolerance of therapy.

The primary determinants of pressure variability were system resistance and breathing patterns associated with high inspiratory flow rates. The results of this study show that the full magnitude of all these effects becomes evident only during dynamic testing conditions. The absolute machine pressure setting was less important (Fig 4) . Testing of CPAP machines using constant flow is not adequate to detect the operational performance of these devices that might occur in clinical usage. During steady-state flow, there was a small consistent drop in pressure (generally < 1 cm H2O) measured at the mask, as system resistance was increased by adding longer tubing, humidifier, and water in the tubing to the breathing circuit. Testing with constant suction to simulate inspiration reveals the limitations of CPAP better,7 but testing with a PWG is more meaningful because this technique can simulate a realistic clinical comparison.

The results of testing during dynamic conditions with simulated breathing showed that mask pressures varied substantially with increased system resistance or increased ventilatory demand. Alterations of the apparatus that result in an increased system resistance between the machine and nasal mask may or may not be intentional (eg, insertion of extra components such as longer tubing vs condensation of water). The pressure control feedback systems employed in the machines tested appear to become less reliable when additional load is presented, especially when high inspiratory flow rates are required. In addition, a stable mask pressure is virtually impossible to maintain when water condenses in dependent loops of tubing because of the extremely rapid changes in system resistance coincident with water bubbling or gurgling. Our analysis is that the frequency responses of the control feedback systems in the CPAP machines tested are limited by electromechanical inertia of the blower system. This effect was most obvious with inspiration, but increased mask pressure with expiration also indicates the delayed response of the CPAP machines to adjust when system pressure increases. Evidently, the blower systems can reduce flow more quickly to compensate for increased pressures than they can augment flow to compensate for decreased pressures.

We appreciate that some of the experiments in this study were obtained with ventilatory settings that may not be considered relevant or physiologic (eg, VT of 1.2 L, f of 30 breaths/min, or maximum minute ventilation of 36 L/min). Average minute ventilation in humans during wakefulness measures 6 to 8 L/min and decreases slightly during sleep due to an increased VT and small decrease in respiratory rate.10 However, we intentionally used a broad spectrum of settings in order to maximally "stress" the CPAP devices and to define the limitations of the four machines tested across the entire range of clinical conditions. Moreover, we also found substantial variability in mask pressure using CPAP settings and ventilatory parameters that are common and typical in clinical practice (Table 2) . For example, using 6 feet of tubing, VT of 0.8 L, f of 10 breaths/min, and set pressure of 10 cm H2O, the mean minimum and maximum mask pressures measured 9.2 cm H2O and 10.6 cm H2O, respectively. With the addition of more tubing and a humidifier, the minimum pressure decreased to 8.5 cm H2O, but when water condensation was present, the minimum pressure decreased to 5.5 cm H2O (mean range, 5.2 cm H2O).

We also acknowledge that the PWG is not strictly physiologic and will maintain a sinusoidal breathing pattern despite variations of system resistance. An artificial respiratory system was used in this study in order to control for variables such as VT and f; however, it would be important to verify our results in patients with OSA. When humans and other animals are presented with external mechanical loads, the inspiratory flow rate and f decrease.11 The ventilatory responses to mechanical loading in humans during sleep may be less than in other animals, but modifications of the breathing patterns are consistently present. Therefore, the effect of increased system resistance observed in this study may or may not apply to humans whose respiratory pattern is in part dictated by mechanical loading. Accordingly, reduced ventilatory demand that occurs with an inspiratory load may not generate sufficiently negative pressures to strain the CPAP system. Submaximal ventilatory response in some patients with compromised respiratory effort may allow a less rigorous CPAP system to be clinically effective, even though the response of these machines appears to be inadequate in laboratory testing conditions.

The clinical significance of these findings in the general population of patients being treated with CPAP is uncertain. In view of the widely acknowledged effectiveness, perhaps the maintenance of a precise CPAP level is not as critically important as believed. However, adherence to CPAP therapy for OSA continues to be a significant problem, given the potential health benefits from therapy.12 13 14 Patient-perceived benefit from nasal CPAP therapy is the most important factor leading to patient satisfaction. Patients who are most likely to perceive a benefit are those who initiated their own referral15 and have severe OSA with symptoms of excessive daytime sleepiness, fatigue, and disrupted or restless sleep before being placed on therapy.12 14 16 17 Compliance can be increased with intensive initial training18 and participation in support groups.15 19 Long-term compliance can be determined by the average nightly use of CPAP within the first 3 months, which indicates that the patient’s first experience with this therapy is critically important.

The most common complaints about CPAP are inconvenience and discomfort with the mask or headgear apparatus, too much pressure, not enough pressure, dry nose or throat, and nasal congestion.20 Some of our patients also complain about the nuisance of maintaining a humidifier, excessive moisture, and cost. In our experience, patient acceptance of CPAP has been enhanced because of improvements in mask comfort and machine-related factors such as noise and size. However, nasal congestion contributing to poor compliance continues to be a significant problem. Patients who have high nasal resistance may mouth breathe on CPAP, which causes a high unidirectional nasal airflow and a large increase in nasal resistance; a vicious cycle can develop that ultimately contributes to ineffective therapy and noncompliance. Heated humidifiers prevent increased nasal resistance, and their use has been recently reported to improve long-term compliance.21 22

The water output of the Fischer-Paykel humidifier (the only commercially available heated humidifier specifically designed for CPAP systems at the time of this study) delivers 32 cm H2O to each liter of gas at 23.3°C, compared to the Respironics Oasis, which provides 10 to 12 cm H2O.23 Obviously, heated in-line humidification is more efficient in terms of water delivery and seems to be more effective, but these devices may also result in greater potential water condensation problems. For example, the gurgling or bubbling sound created when water condenses in the tubing is not uncommon and should be a useful signal of a problem with CPAP delivery. We prefer to use heated humidification whenever possible; however, patients are not generally sophisticated regarding various problems that are routine in the hospital setting when humidifiers are used with respiratory equipment. We emphasize to patients the potential adverse effects of water accumulation in dependent loops that act as water traps and can be easily avoided by proper positioning of the tubing coming from the humidifier into an inverted U configuration.

The obvious problem, as demonstrated in the present study, is that mask pressure may become unreliable or uncomfortable due to rapid pressure changes particularly with water condensation and gurgling, which would also contribute to decreased adherence to CPAP therapy. It is important to understand this possibility when patients present their complaints about their therapy, and to consider the possible difference between the CPAP level determined during attended polysomnography and the pressure provided by the patient’s own system. The home-care companies that supply patients with their equipment may not always provide exactly what is prescribed or may modify the system by adding longer tubing or a humidifier. The data from this study indicate that different tubing lengths, in-line humidifiers, and especially water condensation in the tubing can all substantially affect the transmitted pressure at the mask. Demirozu et al7 have recommended that patients should be prescribed the same CPAP device as they were titrated on in the laboratory to ensure that small differences between devices in their ability to control the pressure at the mask will not be a factor. We found relatively small differences between the devices, but agree that there could be unanticipated differences in the level of pressure determined in the laboratory with one device, compared to the patient’s personal unit.

In summary, dynamic testing of CPAP devices using various combinations of tubing, humidifiers, and water condensation that might occur in ordinary clinical practice showed that these machines do not necessarily maintain constant pressure at the mask. Large variations in mask pressure can occur that can potentially affect the therapeutic outcome and compliance. There are two main factors that will influence the effective mask pressure: system resistance and inspiratory flow rate. Accumulation of water condensing in the tubing is the most important controllable variable that may result in below-therapeutic CPAP levels. It is important for sleep physicians and anyone who is involved in the care of sleep apnea patients to have an in-depth understanding of the operation of these small portable CPAP devices and of their limitations.


   Footnotes
 
Abbreviations: CPAP = continuous positive airway pressure; f = breathing frequency; OSA = obstructive sleep apnea; PWG = pulmonary waveform generator; VT = tidal volume

Financial support was provided by the Deseret Foundation, LDS Hospital, Salt Lake City, UT.

Equipment was provided by the Devilbiss Corporation and Intermountain Home Health Care.

Study data were presented at the American Thoracic Society Annual meeting, San Diego, CA, April 23–28, 1999.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Young, T, Palta, M, Dempsey,, et al (1993) The occurrence of sleep-disordered breathing among middle-aged adults. N Engl J Med 328,1230-1235[Abstract/Free Full Text]
  2. Bearpark, H, Elliott, L, Grunstein, R, et al (1995) Snoring and sleep apnea: a population study in Australian men. Am J Respir Crit Care Med 151,1459-1465[Abstract]
  3. Olson, LG, King, MT, Hensley, JJ, et al (1995) A community study of snoring and sleep-disordered breathing: prevalence. Am J Respir Crit Care Med 152,711-716[Abstract]
  4. Sforza, E, Petiau, C, Weiss, T, et al (1999) Pharyngeal critical pressure in patients with obstructive sleep apnea syndrome: clinical implications. Am J Respir Crit Care Med 159,149-157[Abstract/Free Full Text]
  5. . American Thoracic Society. (1994) Indications and standards for use of nasal continuous positive airway pressure (CPAP) in sleep apnea syndrome. Am J Respir Crit Care Med 150,1738-1745[ISI][Medline]
  6. . American Sleep Disorders Association Standards of Practice Committee. (1997) Practice parameters for the indications for polysomnography and related procedures. Sleep 20,406-422[ISI][Medline]
  7. Demirozu, MC, Chediak, AD, Nay, KN, et al (1991) A comparison of nine nasal continuous positive airway pressure machines in maintaining mask pressure during simulated inspiration. Sleep 14,259-262[Medline]
  8. Nelson, SB, Gardner, RM, Crapo, RO, et al (1990) Performance evaluation of contemporary spirometers. Chest 97,288-297[Abstract/Free Full Text]
  9. Phillipson, EA (1978) Control of breathing during sleep. Am Rev Respir Dis 118,909-939[ISI][Medline]
  10. Sullivan, CE (1980) Breathing in sleep. Orem, J Barnes, CD eds. Physiology in sleep ,213-272 Academic Press New York, NY.
  11. Younes, M (1995) Mechanisms of respiratory load compensation. Dempsey, JA Pack, AI eds. Regulation of breathing ,867-922 Marcel Dekker New York, NY.
  12. Waldhorn, RE, Herrick, TW, Nguyen, MC, et al (1990) Long-term compliance with nasal continuous positive airway pressure therapy of obstructive sleep apnea. Chest 97,33-38[Abstract/Free Full Text]
  13. McArdle, NG, Devereux, H, Heidarnejad, HM, et al (1999) Long-term use of CPAP therapy for sleep apnea/hypopnea syndrome. Am J Respir Crit Care Med 159,1108-1114[Abstract/Free Full Text]
  14. Kribbs, NB, Pack, AI, Kline, LR, et al (1993) Objective measurement of patterns of nasal CPAP use by patients with obstructive sleep apnea. Am J Respir Crit Care Med 147,887-895
  15. Hoy, CJ, Vennelle, M, Kingshott, RN, et al (1999) Can intensive support improve continuous positive airway pressure use in patients with the sleep apnea/hypopnea syndrome? Am J Respir Crit Care Med 159,1096-1100[Abstract/Free Full Text]
  16. Rauscher, H, Popp, W, Wanke, T, et al (1991) Acceptance of CPAP therapy for sleep apnea. Chest 100,1019-1023[Abstract/Free Full Text]
  17. Engleman, HM, Asgari-Jirhandeh, N, McLeod, AL, et al (1996) Self-reported use of CPAP and benefits of CPAP therapy: a patient survey. Chest 109,1470-1476[Abstract/Free Full Text]
  18. Meurice, J, Dore, P, Paquereau, J, et al (1994) Predictive factors of long-term compliance with nasal continuous positive airway pressure treatment in sleep apnea syndrome. Chest 105,429-433[Abstract/Free Full Text]
  19. Likar, LL, Panciera, TM, Erickson, AD, et al (1997) Group education sessions and compliance with nasal CPAP therapy. Chest 111,1273-1277[Abstract/Free Full Text]
  20. Richards, GN, Cistulli, PA, Ungar, RG, et al (1996) Mouth leak with nasal continuous positive airway pressure increases nasal airway resistance. Am J Respir Crit Care Med 154,182-186[Abstract]
  21. Massie, CA, Hart, RW, Peralez, K, et al (1999) Effects of humidification on nasal symptoms and compliance in sleep apnea patients using continuous positive airway pressure (CPAP). Chest 116,403-408[Abstract/Free Full Text]
  22. Kline, LR, Carlson, P (1999) NCPAP acceptance and compliance is altered by humidification [abstract]. Sleep 22(suppl),S230
  23. Airway humidification. Apria’s Health Line 1997; 27:1–4



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