More accurate systolic blood pressure measurement is required for improved hypertension management: a perspective

Abstract

The commonly used techniques for systolic blood pressure (SBP) and diastolic blood pressure (DBP) measurement are the auscultatory Korotkoff-based sphygmomanometry and oscillometry. The former technique is relatively accurate but is limited to a physician's office because its automatic variant is subject to noise artifacts. Consequently, the Korotkoff-based measurement overestimates the blood pressure in some patients due to white coat effect, and because it is a single measurement, it cannot properly represent the variable blood pressure. Automatic oscillometry can be used at home by the patient and is preferred even in clinics. However, the technique's accuracy is low and errors of 10-15 mmHg are common. Recently, we have developed an automatic technique for SBP measurement, based on an arm pressure cuff and a finger photoplethysmographic probe. The technique was found to be significantly more accurate than oscillometry, and comparable to the Korotkoff-based technique, the reference-standard for non-invasive blood pressure measurements. The measurement of SBP is a mainstay for the diagnosis and follow-up of hypertension, which is a major risk factor for several adverse events, mainly cardiovascular. Lowering blood pressure evidently reduces the risk, but excessive lowering can result in hypotension and consequently hypoperfusion to vital organs, since blood pressure is the driving force for blood flow. Erroneous measurement by 10 mmHg can lead to a similar unintended reduction of SBP and may adversely affect patients treated to an SBP of 120-130 mmHg. In particular, in elderly patients, unintended excessive reduction of blood pressure due to inaccurate SBP measurement can result in cerebral hypoperfusion and consequent cognitive decline. By using a more accurate technique for automatic SBP measurement (such as the photoplethysmographic-based technique), the optimal blood pressure target can be achieved with lower risk for hypotension and its adverse events.

Keywords: cognitive impairment; hypotension; oscillometry; photoplethysmography.

Figure 1

The PPG-based SBP measurement apparatus includes a pressure cuff wrapped around the arm and two photoplethysmographic probes on the fingers of the two hands. Abbreviations: PPG, photoplethysmography; SBP, systolic blood pressure.

Figure 2

(A) The PPG probe. Light is transmitted from the light-source (LED) through the fingertip to the photodetector (PD). (B) Some pulses of the original PPG signal: the changes in transmitted light intensity as a function of time, due to cardiac activity. Maximal transmitted light intensity occurs at end diastole, when the tissue blood volume is at a minimum. V_p is the voltage pulses measured by the photodetector PD.

Figure 3

The PPG pulses (V_P) in the two hands of one of the subjects during cuff deflation for cuff pressures P_C in the neighborhood of the SBP value. The lower PPG curve is in the hand distal to the cuff and the upper one in the cuff-free hand. The vertical dotted lines indicate the start time of the systolic decrease in the cuff-free hand PPG pulses. The star indicates the time of the first detection of the Korotkoff sounds and the arrow indicates the start of the corresponding PPG pulse. In this examination, the first Korotkoff sounds were heard at nearly the same heart beat at which the first PPG pulse was detected. From Nitzan M, Adar Y, Hoffman E, et al. Comparison of systolic blood pressure values obtained by photoplethysmography and by Korotkoff sounds. Sensors (Basel). 2013;13(11):14797–14812. Abbreviation: PPG, photoplethysmography; SBP, systolic blood pressure.