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New Dietary Advice, A New Government Program, A New Drug -- and a Truly Novel New BP Measurement Device: Nonintrusive Monitoring of Blood Pressure on a Toilet Seat


Nonintrusive Monitoring of Blood Pressure on a Toilet Seat

Toilet design has become increasingly sophisticated, particularly in countries in Asia, where recent research has focused on ways that the toilet can be used to monitor health, including taking measurements of weight, body fat, pulse, and blood pressure. Toilets with blood pressure-measuring capability have mostly been designed with cuffs attached to the tank or within reach of the seat, although sightings of "smart" toilets with electronic sensors and the ability to transmit test results wirelessly back to the physician's office have been reported.

Now Korean researchers at Seoul National University have developed a method for measuring blood pressure using a specially designed apparatus that is set up underneath the toilet seat. Jung Soo Kim, MS, and colleagues describe their device in the February issue of Physiological Measurement, published by the Institute of Physics (UK).[26] The apparatus is particularly useful for long-term blood pressure monitoring because it is nonintrusive, it is convenient for everyday usage, and it can be used in a home environment.

Blood pressure measurements with this seat are based on the relationship between pulse arrival time (PAT) and blood pressure. PAT has been shown to be most closely related to SBP, although the relationship varies greatly from patient to patient. This problem can be overcome if PAT is estimated for each individual patient, the researchers believe. PAT is calculated from a photoplethysmogram (PPG) and an ECG measured nonintrusively from a femoral artery via a toilet seat apparatus. ECGs are measured through contact between 3 copper-coated electrodes placed on the toilet seat and the subject's thigh skin. PPGs are measured with a reflective-type PPG sensor set up beneath the seat. With readings from these devices, PAT is calculated as the time delay between the ECG R peak and the maximum first derivative point of the PPG signal.

When nonintrusively measured PATs were compared with PATs measured by the standard method under various conditions in 3 healthy male subjects, the results showed a good correlation. An equation was used to estimate blood pressure from the measured PAT during a training period for each subject. Estimated blood pressures were compared with measured blood pressures in a series of blood pressure-varying experiments. For each subject, the estimated blood pressure was similar to the measured blood pressure within a tolerable error range. The same method was used in one subject who took part in the experiments for 15 days. In this subject, calculated SBP correlated well with measured SBP, demonstrating the value of this method for long-term blood pressure monitoring, the investigators believe.

Although the toilet seat blood pressure-monitoring apparatus was only validated in 3 subjects, the researchers believe that their study has shown that this apparatus can be reliably used daily, with patient-specific calibration. They acknowledge that it needs to be tested in a larger number of subjects.