The variation in transit time between an ultrasonic transmitter and receiver can be a measure of molecular weight of gases inside a specific volume. This method is used for carbon dioxide measurement for demand-controlled ventilation. The measurement principle is cheaper than those that are based on spectra photometry or the absorption of infrared light. Ultrasonic devices do not require as large air volume sample as these other methods.
The topic of this study was if this measurement principle could be useful for breath monitoring, preferably on patients in postoperative clinics. This was first verified by a provocation study on healthy test subjects. This study was made with a simple prototype and was performed by personal on the postoperative clinic at the central hospital in VÃ¤sterÃ¥s. The result was that the method works acceptable, but needs to be refined.
To improve the method, the sensor has been further developed. The receiver has been replaced by a reflector and instead of measuring the transit time, the transmitters electrical impedance is measured. This has made the sensor even cheaper and simpler to use. A parallel project is working on miniatyrisation of the sensor.
A literature study has been made to verify which parameters that are important to monitor for postoperative patients, which methods makes this most reliable, and how to adapt to the clinical situation. The literature study emphasize that detection of carbon dioxide in expiratory air is the most reliable method to verify respiratory rate, apnoea. Measuring of carbon dioxide in expiratory air is also the best way for monitoring that the bloodgases are in acceptable levels. The literature study also gives an idea about how to collect the expiratory air. The best suggestion so far is a divided canula giving oxygen in one of the nostrils and measure carbon dioxide in the other one. This solution is limited caused to the facts that air from the mouth cannot be measured and that the position of the canula can disturb the patient or worse affect the breath.
[Show all publications]
Influence from breathing pattern on alcohol and tracer gas expirograms-Implications for alcolock use
(Oct 2010) Annika Kaisdotter Andersson (Jonsson), Bertil Hök, Mikael Ekström, Göran Hedenstierna Forensic Science International
Temperature independence of an electro acoustic capnograph
(Jun 2005) Mia Folke, Bertil Hök IFMBE, NBC05 UMEÅ 13th Nordic-Baltic Conference on Biomedical Engineering & Medical Physics
Measurements of Respiratory Carbon Dioxide
(Jun 2005) Mia Folke
Modelling of an electroacoustic gas sensor
(May 2005) Fredrik Granstedt
, Mia Folke, Mikael Ekström, Bertil Hök, Ylva Bäcklund Sensors and Actuators B
End tidal carbon dioxide measurement using an electro acoustic sensor
(Sep 2004) Mia Folke, Bertil Hök, Mikael Ekström, Ylva Bäcklund Proceedings of the 26th Annual International Conference of the IEEE EMBS
Critical review of non-invasive respiratory monitoring in medical care
(Jul 2003) Mia Folke, Lars Cernerud
, Mikael Ekström, Bertil Hök Medical and Biological Engineering and Computing