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Continuous and Noninvasive Blood Pressure Estimation by Two-Sensor Measurement of Pulse Transit Time

Continuous and noninvasive monitoring of blood pressure is of vital importance in critical care. Its role in management of patients with or at risk of cardiovascular disease is ever increasing. Pulse-transit-time based approaches for estimation of blood pressure hold potential to provide a convenient solution, however there is a need to improve their accuracy. We employ a novel two-sensor technique using photoplethysmogram and piezo sensors for a more accurate measurement of pulse transit time (PTT). PTT is then mapped to arterial blood pressure via calibration process. We implement two different techniques for the PTT measurement. The first technique uses two pulse sensors, while the second technique makes use of one pulse sensor and one piezo element. Clinical data is collected from 46 subjects in the form of systolic, diastolic and mean blood pressure to provide a reference for the calibration step in two techniques. The results show decrease in error of systolic arterial pressure (SAP) and mean arterial pressure (MAP) for the second technique. The root mean square (RMS) error, measured for the calibration equations, reduced from 7.72 mm Hg to 5.26 mm Hg for SAP and from 7.07 mm Hg to 6.30 mm Hg for MAP. RMS error, measured by leave-one-out method, reduced from 8.45 mm Hg to 5.77 mm Hg for SAP and from 7.67 mm Hg to 6.90 mm Hg for MAP.