Comparison of Systolic Blood Pressure Values Obtained by Photoplethysmography and by Korotkoff Sounds

Korotkoff-sounds based auscultatory sphygmomanometry is considered the gold-standard of non-invasive blood pressure measurement for the systolic and diastolic blood pressure. The systolic blood pressure (SBP) can also be measured by using a pressure cuff and a photoplethysmographic (PPG) probe on a finger. In our study, we examined the accuracy of the PPG technique by comparing it to the auscultatory technique. SBP was measured by the Korotkoff sounds in two ways: by making use of an electronic recording of the sounds using a microphone (Kmic) and by having a trained observer use a stethoscope (Kobs). The PPG and the auscultatory techniques were compared by examining adult males aged 20–73 years. The average difference between the PPG-based SBP measurement and the Kmic SBP measurements was -0.1±1.84 mmHg and between the Kobs SBP and the Kmic SBP was -1.96±1.7. We also examined the correlation of the PPG signal and the Kmic signal and found that the mean correlation between the pulses amplitude in the first 20 pulses was 0.824±0.096. A high correlation is also obtained when an auscultatory gap occurs: When there is an ausculatory gap, the pulses in the PPG and in the electronic recording both simultaneously show several pulses, then no pulses, and then pulses return in both.