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Diagnostic Devices
Published in Laurence J. Street, Introduction to Biomedical Engineering Technology, 2016
To look at the respiratory system and how it is monitored, including the parameters used for measurements, inspired and expired CO2 analysis (capnography), inspired and expired oxygen monitoring, and bronchoscopy.
Biosensors and Human Behavior Measurement
Published in Krzysztof Iniewski, Biological and Medical Sensor Technologies, 2017
Signal noise can be an unavoidable result in unobtrusive biosensors and, if not considered appropriately, can plague study results. There are often a variety of sensors that can detect specific biosignals, and a comparison of these sensors proves that there is often a trade-off found between noise and obtrusiveness. One clear example can be seen from the comparison of two different respiration sensors. A capnograph can be used to measure levels of CO2 exhaled from the body. This type of sensor can be very accurate. Not only can the CO2 levels provide a quantitative analysis for respiration but also directly measuring CO2 can provide a clean signal. Noise could only be created through the form of other CO2 sources. This type of noise could come from other nearby people. To account for this, the sensor commonly collects samples directly from the mouth or nose of a subject. In Ref. [6], data are transported to a capnograph by creating a constant airflow in tubes that run from the nostrils to the sensor. This type of accuracy does not come without sacrifice, however. While tubes running form the nostrils might not hinder a wide range of movements, tubes running across your face can be distracting. This method also dictates how the subject must breathe. The constant flow from nostril to sensor in the tubes means that the subject must inhale through the mouth. Additionally, the subject must exhale through the nose for CO2 levels to be detected. This may not require a strenuous effort, but remembering to do so can be distracting to the subject. Another method for measuring respiration involves wrapping a flexible sensor around the subject’s torso, measuring expansion and contraction of the subject’s thoracic and abdominal cavities as a result of respiration. This sensing method is much less obtrusive to the user. The single strap can be embedded into or worn under clothing, making it hardly noticeable to the subject or anyone else. The use of wires, compared to tubes, introduces the possibility of wireless signal transmission. This practically eliminates mobility restrictions larger sensors require. Again, these advantages are not without trade-offs. Any movement experienced by the torso can be picked up as signal noise. This can include bending the torso to reach up, down or side to side, along with talking and laughter. While talking and laughter do have an influence over the rates of inhalation and exhalation, they do not actually alter the rate of respiration. While these “false breaths” are a source of noise not detected by the capnograph, performing a visual or kinematic analysis of the subject’s torso could provide enough information to filter these out. Both sensor types clearly have their own advantages and disadvantages. Sensor effectiveness depends heavily on the activity of the subject during data collection. If the subject is sitting still and focusing on one specific area, the accuracy of the capnograph may be preferred. If the subject is going to be mobile or is required to interact with other individuals, the unobtrusiveness of the flex sensor could be the best choice.
Hearables, in-ear sensing devices for bio-signal acquisition: a narrative review
Published in Expert Review of Medical Devices, 2021
Colver Ken Howe Ne, Jameel Muzaffar, Aakash Amlani, Manohar Bance
RR measurements are typically taken via manual counting in non-emergency settings. This is regarded as the ‘industry standard’ while the gold standard is via capnography. This method involves recording the concentration of carbon dioxide in respiratory gases through attaching a capnograph (carbon dioxide sensor) to a plastic cannula worn over the nose and mouth [34]. Understandably, these measurement techniques are not suitable for ubiquitous monitoring of RR.