Advanced Volume-Compensation Method for Indirect Finger Arterial Pressure Determination: Comparison with Brachial Sphygmomanometry

Objective: The so-called volume-compensation method (VCM) allows noninvasive instantaneous arterial blood pressure (BP) measurement in human fingers. The VCM is mostly carried out with photoplethysmography (PPG) to detect arterial volume pulsations. However, measurement errors may occur due to movement of the PPG sensors relative to skin and underlying vasculature. We report here the effectiveness of a new technique, 'advanced VCM' (AVCM), developed by us to resolve this significant problem. Methods: The AVCM described uses a control system with procedures for adjusting system parameters derived from the pulsatile PPG signal and the finger cuff pressure. In open loop pre-operation, mean BP is estimated from a finger using the volume-oscillometric method. The control system reference is then adjusted to yield approximately equal values in mean BP and this gives optimum performance for instantaneous BP measurement. Systolic and diastolic BP values (SBP, DBP) from the instantaneous BP by the VCM and the AVCM were compared with the conventional brachial SBP/DBP measured simultaneously during 5-min baseline. SBP/DBP from the AVCM were also compared with brachial SBP/DBP during 36-min bicycle ergometer exercise. Results: Measurement errors that occurred when the BP measurement was run using the previous VCM essentially disappeared in the AVCM. Bland-Altman analysis revealed negligible fixed and proportional bias between finger SBP/DBP and brachial SBP/DBP. Conclusion: These findings suggest that the AVCM could be an effective technique to resolve the problem of measurement errors occurring with standard VCM. Significance: The newly proposed AVCM is potentially useful for all research and clinical situations where noninvasive continuous BP measurement is needed.