This invention proposes the ear as a location to measure vital signs such as heart rate, blood pressure, cardiac output, and blood oxygenation.
Vital signs such as heart rate, blood pressure, cardiac output, and blood oxygenation are necessary in determining the overall health of a patient. Continuous monitoring of these vital signs can help identify a patient's risk for stroke, heart attack, heart failure, arterial aneurysm, and renal failure. Currently, heart monitoring is usually done by Holter monitors which continuously measure the electrocardiogram (ECG) from the chest. Although wearable for short term, these monitors use adhesives and wet electrodes that can cause skin irritation, making them impractical for long term wear. Automatic blood pressure monitors do exist for home use, but they use a cuff, which temporarily cuts off blood flow to the arm, thus making this method unsuitable for continuous blood pressure monitoring. A method that is correlated to cardiac output is ballistocardiography (BCG), which is a measure of the body's reaction force to the blood expelled by the heart. However, most BCG measurement systems involve a chair or a bed which do not allow for continuous and wearable monitoring. To measure blood oxygenation, photoplethysmography (PPG) is typically obtained through an optical transmission measurement at the finger or the ear lobe. Both locations are non-rigid and yield significant motion artifacts. Reflectance PPG has been shown to be feasible on the forehead due to its reflective bony structure. Unfortunately, the forehead is an impractical location for a long term wearable device due to low patient acceptance.
To gain patient acceptance, the vital signs monitors must be wearable and unobtrusive. To address the issues with the current technologies and their respective attachment sites, the inventors propose the site behind the ear as a location for vital signs monitoring. This location is ideal for both physiological and mechanical reasons. Physiologically, the reflectance PPG signal behind the ear shows similar signal quality when compared to a traditional finger transmission PPG measurements. PPG enables the measurement of blood oxygenation and heart rate. BCG can be obtained behind the ear using differential capacitive electrodes constructed using fabric. The BCG signal is able to provide continuous heart rate and respiratory rate, and correlates to cardiac output and blood pressure. Mechanically, the ear remains in the same orientation relative to the heart when upright, thus simplifying pulse transit time calculations. Furthermore, the ear provides a discreet and a natural anchoring point that reduces device visibility and the need for adhesives.
- Superior location for continuous and wearable vital signs monitoring
- Provides a location for device attachment without the use of adhesives