Capnometers are large bedside machines used in hospitals to measure the amount of CO2 in a patient’s exhaled air via a face mask or sensor embedded in life support equipment. They perform an important medical function—assessing the health of a patient’s lungs—but conventional capnometers are bulky and designed for use by trained medical personnel. Product design and development consultancy Wideblue (Glasgow) was tasked by client Cambridge Respiratory Innovations Ltd. (CRiL; Cambridge, UK) to miniaturize the device and simplify its operation, such that it could be used effectively by patients at home. The resulting N-Tidal device is designed to be used as a personal respiratory monitor in the home as well as by general practitioners and respiratory specialists.
The technology behind the medical device encompasses an infrared light-emitting diode tuned to the peak CO2 absorption wavelength and patented infrared optics that measure CO2 levels as the patient breathes through the N-Tidal. Miniaturization allowed the sensor to be located directly in front of the mouth, achieving high resolution of the CO2 concentration in each individual breath profile, said Wideblue.
|The patient breathes normally into the mouthpiece and, within seconds, the device indicates the healthiness of his
or her lungs.
The patient simply breathes in and out through the breath tube in a normal, relaxed manner. Within seconds, a traffic light system (red, amber, green) on the device will tell the user the health status of his or her lungs and will, if necessary, indicate whether follow up by a medical professional is required. Electronics within the device capture the data from the sensor, analyze the breath record and wirelessly transmit the data to a secure server. The breath tube with integrated infrared window is replaceable, allowing the device to be used by multiple patients while preventing cross-contamination. The tube presented Wideblue with several plastic design challenges, which it shared with PlasticsToday.
“The breath tube assembly had a number of design constraints and requirements,” explained Wideblue Mechanical Engineer Callum Stewart. “It needed to be sealed so that no breath from one patient could be inhaled by another patient. It needed to be solid so that electronics connections could reliably be made to the breath tube. And it needed to be relatively soft so that a patient could put the mouthpiece in the mouth,” said Stewart. A medical-grade ABS was selected for the body to hold the electronics and infrared components, and a compliant medical-grade polypropylene was chosen for the mouthpiece. “The two materials provided a good seal, a solid fit and are comfortable to use,” said Stewart.
A further challenge was to design a breath path through the device with sufficient clearance to insert the breath tube but with enough alignment accuracy to carry out a precision infrared measurement. “We designed a robust infrared optical platform suitable for injection molding,” Wideblue Mechanical Engineer Colin Phimister, who worked on this aspect of the design, explained to PlasticsToday. “The material needed to accept specialist infrared optical coatings but also be stiff enough to avoid warping in normal handheld use. We selected a glass-filled polycarbonate material. Optical coatings have good adhesion and durability on polycarbonate,” said Phimister, “but the material was not sufficiently stiff without the addition of the glass filling.”
Lenexa, KS–based Pivot International, which acquired Wideblue in April 2018, molded, assembled and tested the device. Pivot was “able to manufacture the injection mold tooling, mold the parts to the required tolerances and finally assemble the plastic parts, infrared optical parts and electronics, and program the electronics and test the assemblies,” said Managing Director Russell Overend. “This made it easy for us to make the transition from design and development into production.”
Wideblue is calling the N-Tidal a breakthrough medical device—the world’s first personal capnometer. While there are other respiratory devices on the market, such as peak flow meters and spirometers, they typically require the “patient to blow hard through a tube,” said Overend, and they lack an intuitive interface—the N-Tidal device has a simple, two-button “power” and “go” operation. And it’s no exaggeration to say that it can save lives.
“The device is to be used by patients with respiratory-related diseases such as asthma, COPD and CHF. Early clinical results show that the data from the device can be used to predict attacks or exacerbations in advance by measuring changes in CO2 profiles. Doctors can then decide if a change in medication is required to prevent an attack,” said Overend.
The device is currently undergoing clinical/user trials and has already produced superb clinical results, according to Overend. Subject to successful completion of these trials and regulatory approvals, the device is expected to go into commercial production in 2020.