Pressure stability with CPAP devices: A bench evaluation

Mask interfaces for home non-invasive ventilation in infants and children

The selection of the mask interface for non-invasive ventilation (NIV) is recognized to be an essential part for therapy success. While nasal masks are the first recommended option in children and adults, there are indications for other mask types such as intolerance or complications from nasal masks. Evidence comparing performance, adherence and complication risk among mask interfaces in pediatrics is, however, scarce and information is often extrapolated from adult studies. Given this gap in knowledge and the lack of guidelines on NIV initiation in children, mask selection often relies on the clinicians' knowledge and expertise. Careful mask selection, a well-fitting headgear and time investment for mask desensitization are some important recommendations for adequate mask adaptation in children. Frequent mask-related complications include nasal symptoms, unintentional leak, mask displacement, skin injury, and midface hypoplasia. Close monitoring and a pro-active approach may help to minimize complications and promote the optimal use of home NIV.

Control system design for a Continuous Positive Airway Pressure ventilator

Continuous Positive Airway Pressure (CPAP) ventilation remains a mainstay treatment for obstructive sleep apnea syndrome (OSAS). Good pressure stability and pressure reduction during exhalation are of major importance to ensure clinical efficacy and comfort of CPAP therapy. In this study an experimental CPAP ventilator was constructed using an application-specific CPAP blower/motor assembly and a microprocessor. To minimize pressure variations caused by spontaneous breathing as well as the uncomfortable feeling of exhaling against positive pressure, we developed a composite control approach including the feed forward compensator and feedback proportional-integral-derivative (PID) compensator to regulate the pressure delivered to OSAS patients. The Ziegler and Nichols method was used to tune PID controller parameters. And then we used a gas flow analyzer (VT PLUS HF) to test pressure curves, flow curves and pressure-volume loops for the proposed CPAP ventilator. The results showed that it met technical criteria for sleep apnea breathing therapy equipment. Finally, the study made a quantitative comparison of pressure stability between the experimental CPAP ventilator and commercially available CPAP devices.

Effect of tubing condensate on non-invasive positive pressure ventilators tested under simulated clinical conditions

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(2)O 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(2)O/L, inspiratory pressure fell by 2-15 cm H(2)O 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.