Continuous Cuffless Blood Pressure Estimation Using Pulse Transit Time and Photoplethysmogram Intensity Ratio

Area of Science:

• Biomedical Engineering
• Cardiovascular Physiology
• Signal Processing

Background:

• Cuffless blood pressure (BP) measurement using Pulse Transit Time (PTT) shows promise but suffers from accuracy limitations.
• PTT effectively tracks high-frequency (HF) BP variations but struggles with low-frequency (LF) variations linked to vasomotor tone.
• Existing PTT methods are inadequate for accurate continuous BP monitoring due to poor LF tracking.

Purpose of the Study:

• To develop a novel indicator, Photoplethysmogram Intensity Ratio (PIR), to capture LF BP variations.
• To propose an improved BP estimation algorithm by integrating PTT and PIR.
• To enhance the accuracy of cuffless continuous blood pressure monitoring.

Main Methods:

• Spectral analysis was performed on BP, PTT, PIR, and respiratory signals to understand their frequency-domain relationships.
• A new algorithm was developed combining PTT (for HF) and PIR (for LF) to estimate BP.
• The proposed algorithm was validated against continuous Finapres BP measurements in 27 healthy subjects.

Main Results:

• PTT correlated with BP in the HF range (respiratory frequency), while PIR correlated with BP in the LF range.
• The proposed PTT-PIR algorithm demonstrated high accuracy: Mean ± SD for systolic, diastolic, and mean BP were -0.37 ±5.21, -0.08 ±4.06, and -0.18 ±4.13 mmHg, respectively.
• The new method outperformed two leading PTT algorithms by approximately 2 mmHg in standard deviation and mean absolute difference.

Conclusions:

• The novel PIR indicator effectively captures LF BP variations, complementing PTT's HF tracking.
• The integrated PTT-PIR algorithm significantly improves the accuracy of cuffless continuous BP estimation.
• This approach offers a more reliable solution for cuffless BP monitoring, overcoming previous limitations.