Designing and Constructing an Optical System to measure Continuous and Cuffless Blood Pressure Using Two Pulse Signals

Blood pressure (BP) is one of the important vital signs that need to be monitored for personal healthcare. Arterial blood pressure is estimated from pulse transit time (PTT). This study uses two pulse sensors to get PTT. The aim of this study was to construct an optical system and to monitor blood pressure continuously and without cuff in people with different ages. To measure blood pressure changes, two infrared optical transmitters were used at the distances of 5 mm to the receivers. Output of the optical receivers was inserted in analog circuits. PTT was defined as the time between the two peaks of pulse signals by the software. Signals were measured continuously through a serial network communication. An external personal computer monitored measured waveforms in real time. BP was related to PTT and the relationship coefficients were calculated at different physical activities. After determining the linear correlation coefficients for each individual, blood pressure was measured by the cuff and the PTT method and the results were compared. PTT computed between the two peaks of wave pulses was strongly correlated with systolic blood pressure (R=0.88±0.034) and the diastolic blood pressure (R=0.82±0.058). Systolic blood pressure (SBP) was measured more accurately than the diastolic blood pressure (DBP). The results of SBP showed that the maximum difference and the error percentages between the cuff method and the present method were 7.98±2.88 and 6.33±2.51%, respectively. Moreover, the maximum difference and the percentage errors between the cuff method and the present method of DBP were 10.13±3.82 and 10.97±3.89%, respectively. Monitoring blood pressure with the designed system can be recommended as a useful method to indicate cardiovascular diseases and used for personal healthcare purposes.