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Auckland, New Zealand

Hart D.E.,Middlemore Hospital | Forman M.,Fisher and Paykel Healthcare | Veale A.G.,Middlemore Hospital
Sleep and Breathing | Year: 2011

Rationale: Water condensate in the humidifier tubing can affect bi-level ventilation by narrowing tube diameter and increasing airflow resistance. We investigated room temperature and tubing type as ways to reduce condensate and its effect on bi-level triggering and pressure delivery. In this bench study, the aim was to test the hypothesis that a relationship exists between room temperature and tubing condensate. Methods: Using a patient simulator, a Res-med bi-level device was set to 18/8 cm H 2O and run for 6 h at room temperatures of 16°C, 18°C and 20°C. The built-in humidifier was set to a low, medium or high setting while using unheated or insulated tubing or replaced with a humidifier using heated tubing. Humidifier output, condensate, mask pressure and triggering delay of the bi-level were measured at 1 and 6 h using an infrared hygrometer, metric weights, Honeywell pressure transducer and TSI pneumotach. Results: When humidity output exceeded 17.5 mg H 2O/L, inspiratory pressure fell by 2-15 cm H 2O and triggering was delayed by 0.2-0.9 s. Heating the tubing avoided any such ventilatory effect whereas warmer room temperatures or insulating the tubing were of marginal benefit. Conclusions: Users of bi-level ventilators need to be aware of this problem and its solution. Bi-level humidifier tubing may need to be heated to ensure correct humidification, pressure delivery and triggering. © 2010 Springer-Verlag. Source

Moller W.,Comprehensive Pneumology Center | Moller W.,Helmholtz Center for Environmental Research | Celik G.,Comprehensive Pneumology Center | Celik G.,Helmholtz Center for Environmental Research | And 9 more authors.
Journal of Applied Physiology | Year: 2015

Recent studies showed that nasal high flow (NHF) with or without supplemental oxygen can assist ventilation of patients with chronic respiratory and sleep disorders. The hypothesis of this study was to test whether NHF can clear dead space in two different models of the upper nasal airways. The first was a simple tube model consisting of a nozzle to simulate the nasal valve area, connected to a cylindrical tube to simulate the nasal cavity. The second was a more complex anatomically representative upper airway model, constructed from segmented CT-scan images of a healthy volunteer. After filling the models with tracer gases, NHF was delivered at rates of 15, 30, and 45 l/min. The tracer gas clearance was determined using dynamic infrared CO2 spectroscopy and 81mKr-gas radioactive gamma camera imaging. There was a similar tracer-gas clearance characteristic in the tube model and the upper airway model: clearance half-times were below 1.0 s and decreased with increasing NHF rates. For both models, the anterior compartments demonstrated faster clearance levels (half-times < 0.5 s) and the posterior sections showed slower clearance (half-times < 1.0 s). Both imaging methods showed similar flow-dependent tracer-gas clearance in the models. For the anatomically based model, there was complete tracer-gas removal from the nasal cavities within 1.0 s. The level of clearance in the nasal cavities increased by 1.8 ml/s for every 1.0 l/min increase in the rate of NHF. The study has demonstrated the fast-occurring clearance of nasal cavities by NHF therapy, which is capable of reducing of dead space rebreathing. Copyright © 2015 the American Physiological Society. Source

Mundel T.,Massey University | Feng S.,Fisher and Paykel Healthcare | Tatkov S.,Fisher and Paykel Healthcare | Schneider H.,Johns Hopkins University
Journal of Applied Physiology | Year: 2013

Nasal high flow (NHF) has been shown to increase expiratory pressure and reduce respiratory rate but the mechanisms involved remain unclear. Ten healthy participants [age, 22 ± 2 yr; body mass index (BMI), 24 ± 2 kg/m2] were recruited to determine ventilatory responses to NHF of air at 37°C and fully saturated with water. We conducted a randomized, controlled, cross-over study consisting of four separate ∼60-min visits, each 1 wk apart, to determine the effect of NHF on ventilation during wakefulness (NHF at 0, 15, 30, and 45 liters/min) and sleep (NHF at 0, 15, and 30 liters/min). In addition, a nasal cavity model was used to compare pressure/air-flow relationships of NHF and continuous positive airway pressure (CPAP) throughout simulated breathing. During wakefulness, NHF led to an increase in tidal volume from 0.7 ± 0.1 liter to 0.8 ± 0.2, 1.0 ± 0.2, and 1.3 ± 0.2 liters, and a reduction in respiratory rate (fR) from 16 ± 2 to 13 ± 3, 10 ± 3, and 8 ± 3 breaths/min (baseline to 15, 30, and 45 liters/min NHF, respectively; P < 0.01). In contrast, during sleep, NHF led to a ∼20% fall in minute ventilation due to a decrease in tidal volume and no change in fR. In the nasal cavity model, NHF increased expiratory but decreased inspiratory resistance depending on both the cannula size and the expiratory flow rate. The mechanisms of action for NHF differ from those of CPAP and are sleep/wake-state dependent. NHF may be utilized to increase tidal breathing during wakefulness and to relieve respiratory loads during sleep. Copyright © 2013 the American Physiological Society. Source

White D.E.,Auckland University of Technology | Al-Jumaily A.M.,Auckland University of Technology | Bartley J.,University of Auckland | Somervell A.,Fisher and Paykel Healthcare
Current Respiratory Medicine Reviews | Year: 2011

It has been reported that continuous positive airway pressure therapy introduces negative nasal side-effects including sneezing, itching, nasal dryness, nasal congestion and/or a runny nose. As these symptoms are suggestive of nasal dysfunction, heated humidification is often used to fully saturate and heat the inhaled air to core body temperature. It is expected that this relieves the nasal mucosa from having to supply, or recover, heat and moisture from inspired and expired air. This review summarizes the current in vitro and in vivo knowledge relevant to nasal air-conditioning, and identifies further investigations necessary to improve our understanding the changes that occur during nasal continuous positive airway pressure therapy. Investigations into nasal airway fluid transportation, airflow regulation and heat and fluid supply may lead to a therapy temperature/pressure/humidification algorithm that optimizes these parameters for a prescribed therapy pressure. Optimization could lead to a reduction in titration pressure and improved treatment compliance. © 2011 Bentham Science Publishers Ltd. Source

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