Estimating respiration rate from heart rate using a smartphone camera

Current physiological sensing (measuring heart rate (HR), breathing rate (BR) and heart rate variability (HRV)) is commonly done using worn sensors such as chest straps, electrodes or finger clips. However, these sensors are uncomfortable (e.g. finger clip sensors cannot be used while walking and can also restrict activities such as grasping) and introduce additional costs to the users. In addition, users tend to be very concerned with the way sensors affects their appearance or habits; thus, the use of external sensors poses additional usability concerns.

Several recent studies have demonstrated that it is feasible to measure heart rate using a built-in cellphone camera without any additional hardware. By placing a finger over the cellphone’s camera lens with its flash turned on, the average intensity of the image captures fluctuations in blood flow with each heartbeat.

There are some mobile applications in the market that measures heart rate and respiration rate. Among them, we use as examples: cardio buddy, What’s my heart rate, Vital Signs Camera. These applications use the front camera to measure the micro color changes of the face produced by every heartbeat to estimate HR and analyze the motion of the chest to compute respiration rate. These applications require certain amount of light to work properly, under poor lighting conditions they do not work effectively. In order to deal with the issue of variation in ambient lighting, applications such What’s my heart rate, or cardio buddy use as an option the back camera to measure the heart rate using the fingertip over the cellphone’s camera and the flash turned on. However, these apps do not measure respiration rate. BR measurement is important because it could help subjects to achieve a calm state and to detect and prevent abnormal respiratory rates that may lead to cardiac arrest, stroke and chronic obstructive pulmonary diseases.

This research proposes a simple approach to measure heart and respiration rate even under poor lighting conditions. The purpose of our study is to establish the feasibility of extracting respiration rate derived from the heart rate (HR) using the index finger over a cellphone camera. The study will be based on the principle of respiratory sinus arrhythmia (RSA), which refers to the periodic fluctuations in heart rate that are linked to breathing. This research will follow the following procedure for heart rate measurement and from which the respiration measurements will be extracted. Specifically, once the data is collected, peak detection will be performed in order to detect heartbeats. Respectively, respiration rate will be computed by tracing the height of the heart beat peaks.