Fitbit is researching how its wearable device can help with tracking a person’s smoking habits and help guide the person to kick the habit.
According to CDC, Cigarette smoking is responsible for more than 480,000 deaths per year in the United States, including more than 41,000 deaths resulting from secondhand smoke exposure.
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Current Challenges with tracking smoking behavior
Individuals and healthcare providers have always been interested in tracking an individual’s smoking behavior while the person is attempting to quit or is trying to reduce smoking.
Self-reporting of smoking behavior may not only be an unreliable metric but is also tedious and cumbersome for the individual.
Attempting to track smoking-specific motions with accelerometers may not pick up anything if the user is wearing the sensor on the hand opposite the hand holding the cigarette.
There isn’t an easy way to track an associated metric that can be useful.
Intake of Carbon Monoxide during smoking and its effect on blood
When Carbon monoxide binds to haemoglobin in the blood, it forms carboxyhaemoglobin (COHb). In non-smokers the concentration of COHb in the blood is usually 1%. In smokers this percentage fluctuates between 3% and 8% and can even reach 15% in chain-smokers. A pack-a-day smoker typically has anywhere between 3% and 6% COHb levels in their blood.
Carboxyhemoglobin is a stable complex of carbon monoxide and hemoglobin that forms in red blood cells upon contact with carbon monoxide such as when carbon monoxide is inhaled. This makes carboxyhemoglobin a good indicator of carbon monoxide inhalation.
Fitbit’s research involves tracking this digital biomarker to estimate the volume and timing related to a person’s smoking.
Fitbit’s non-invasive optical spectroscopy
Fitbit is researching how its wearables can use PPG to help read the COHb levels in a non-invasive manner.
The light source in your Fitbit would emit light at a wavelength spectrum corresponding to a carboxyhemoglobin absorption spectrum and an oxyhemoglobin absorption spectrum.
Biometric circuitry is coupled to the photodetector to in your Fitbit to receive a signal from the photodetector and process the signal to determine the intensity of the wavelengths present in the light received at the photodetector.
Wavelengths for biomarker detection
The intensity of the wavelengths is indicative of a level of carbon monoxide inhalation associated with the subject.
According to the latest Fitbit patent on optical spectroscopy, the light source may include a narrow band light sources that correspond to the carboxyhemoglobin absorption spectrum, approximately 550-580 nm. In some embodiments, the light source may correspond to a portion of the 550-580 nm spectrum rather than the entire range. 
The light source may also include a narrow band light source that corresponds to the oxyhemoglobin absorption spectrum, approximately 530-540 nm.
The narrow band light sources could include lasers, resonant cavity LEDs, or optically filtered conventional LEDs. The light source could also include other visible and/or infrared wavelengths to provide a baseline for tissue optical properties and/or blood concentration. This baseline could be used to improve the carboxyhemoglobin reading.
The ratio between the carboxyhemoglobin signal and the oxyhemoglobin signal may be used to make certain determinations about monoxide inhalation by the user.
Combining the carbon monoxide inhalation data with other Fitbit health data may help in accurately pinpoint the time and duration of when the user was smoking along with any other stress signals in the user.
For example, a tracker device may calculate the user’s stress or relaxation levels based on a combination of HR variability, skin conduction, noise pollution, and/or sleep quality.
The Fitbit patent (patent # 10966643) was published today and originally filed by Fitbit in July, 2019. This also happens to another recent patent that discusses a potential wearable ‘ring’ from Fitbit.
As with any patent, it’s hard to tell if and when viable research becomes a product feature but it definitely shows that we are in the infancy of what optical spectroscopy provides for digital health and our well-being.
