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Breathing easier: rigidity, stability critical for respiratory device component.

When DHD Healthcare was designing its acapella choice vibratory Positive Expiratory Pressure (PEP) system for patients suffering respiratory difficulties, it was faced with various material challenges. PEP systems direct pulsated air to lungs break up fluid build-up. Under a physician's guidance, DHD's system further allows the patient to adjust the pulsation frequency, for optimum effect. In addition, the system can be disassembled easily for regular cleaning via steam autoclaving, boiling or machine washing (as in a dishwasher).

For the device's internal rocker arm component, material rigidity and dimensional stability were critical requirements. The rocker arm is the key internal component that positions a pulse-generating magnet. The position of the magnet controls the frequency and ensures that therapy is dispensed precisely as directed. Any excessive creep or elongation could interfere with accurate operation.

To meet these criteria, an RTP 100 series glass-reinforced polypropylene compound was selected. It has a flexural modulus of 800,000 psi and a heat deflection temperature of 295[degrees]F at 264 psi, which proved capable of maintaining dimensions through repeated autoclaving. In addition, the FDA compliant ingredients used in the compound satisfied bio-compatibility requirements.

The outer shell required a material capable of withstanding repeated autoclaving under pressures of 30 psi and temperatures of 270[degrees]F. An unfilled polycarbonate was chosen initially, but testing indicated that it lacked sufficient heat resistance. Polysulfone (PSU) was recommended as an alternative for its heat resistance, dimensional stability and relative ease of processing.

The shell material also required a precise FDA-compliant color, both for model identification and to correspond with existing corporate color schemes. While PSU can present challenges in coloring, was able to match the specific aqua shade that fit between pre-existing blue and green models. According to Ken Pelerossi, DHD's engineering manager, "It was critical to us, and to patients, so that there are no mistakes in identifying oar various models. And, [RTP] nailed it!"

Circle 170--RTP Corp., or connect directly at

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Title Annotation:Application Ideas
Date:Sep 1, 2004
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