Case study on analysis of vocal frequency to estimate blood pressure

Preventive healthcare is a precaution for a premorbid state. Because of its demonstrable mortality rate, hypertension is a disease that should be prevented before it becomes severe. To decrease the mortality rate for hypertension, it is desirable for people to measure their own blood pressure (BP) on a routine basis. At present, many ambulatory BP gauges are available. However, people are unlikely to carry around a gauge to measure their BP — even those with a high risk of illness. Such methods are ineffective for preventive healthcare. Therefore, it would be preferable to measure factors related easily to BP without a dedicated gauge. In this research, a BP estimation method is proposed using voice spectrum analysis. If BP estimations from the voice spectrum are accurate, we can possibly measure BP using the voice recorder of a smartphone. To evaluate the feasibility of BP estimation, measurement experiments were conducted with two subjects. In the experiments, 60 sets of BP and voice data were measured from each subject, and the correlation coefficients were examined. Results showed that both diastolic and systolic BPs were not uncorrelated with the spectral component of the voice (> |0.6|) at specific frequency bands. To estimate the BP value from voice data, a relationship between BP and voice spectrum was modeled. In the proposed model, BP can be expressed as the polynomial function in terms of the voice spectrum. As a result, correlation coefficients between measured and estimated BPs were approximately 0.9, and average BP estimation errors were small to a certain extent.