Why Traditional Ambulatory Blood Pressure Monitoring Outshines Photoplethysmography (PPG): Evidence of Superior Accuracy and Clinical Reliability.

Traditional ambulatory blood pressure monitoring (ABPM), which uses cuff-based devices to take intermittent readings over 24 hours or more, is widely regarded as the noninvasive gold standard for diagnosing blood pressure (BP) dysregulation and assessing hypertension, as it captures variations throughout daily activities and sleep. (1)

In contrast, photoplethysmography (PPG)-based methods, often employed in wearable devices for cuffless BP estimation, face several limitations that demonstrate ABPM’s superiority in accuracy, reliability, and clinical validation

Supporting Evidence from Scientific Literature and Comparative Analysis

Established Predictive Value for Clinical Outcomes: ABPM has been shown through multiple studies to be superior to clinic-based or home BP measurements in predicting cardiovascular events, mortality, and hypertension-mediated organ damage, as it better accounts for phenomena like white coat hypertension, masked hypertension, and nocturnal dipping. (2) PPG-based cuffless monitoring, while promising for continuous data, lacks large-scale clinical trials establishing similar predictive reliability, limiting its use as a standard of care. (3)
Higher Accuracy and Validation Standards: ABPM provides more accurate BP readings compared to PPG, which often fails to meet international validation criteria such as the Association for the Advancement of Medical Instrumentation (AAMI) standards or achieves only low grades (e.g., B or D) on the British Hypertension Society (BHS) protocol for systolic and diastolic BP estimation. (4) PPG signals contain BP-related information but are insufficient for precise predictions, underperforming when compared to normalized invasive arterial BP signals, which serve as a benchmark for direct measurement. (5)
Susceptibility to Artifacts and Noise: PPG is highly prone to motion artifacts from arm or finger movements, ambient light, low perfusion, or exercise, which can render signals unusable and lead to inaccurate BP estimates, requiring patient immobility for reliable readings. (6) ABPM, being cuff-based and designed for ambulatory use, is less affected by such interferences and provides consistent data during normal activities without these constraints.
Need for Frequent Calibration: Unlike ABPM, which operates independently once applied, PPG-based devices require regular calibration with a cuff-based standard to maintain accuracy, as their performance degrades over time due to physiological changes; this dependency undermines the “cuffless” advantage and introduces potential errors. (7)
Impact of Individual Variations and Long-Term Limitations: PPG accuracy is compromised by interindividual differences in arterial stiffness, skin tone, age, and other factors, making it less reliable across diverse populations. (7)
Challenges in Signal Processing and Interpretation: PPG signals are sensitive to filtering, with performance dropping under certain frequency ranges, and deep learning models for PPG BP estimation often involve high computational demands and lack interpretability, complicating real-time use. (8) ABPM data, by contrast, is more straightforward to interpret without these processing hurdles.

Overall, while PPG offers convenience and potential for unobtrusive monitoring, current evidence highlights ABPM’s superiority in clinical accuracy, robustness, and outcome prediction, with cuffless PPG methods requiring further development and validation to bridge these gaps.

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