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Updated: Jul 19, 2025
Pulse Wave Velocity Testing in the Baltimore Longitudinal Study of Aging
Published on: February 7, 2014
Filtering-induced changes of pulse transmit time across different ages: a neglected concern in
Shangdi Liao1, Haipeng Liu2, Wan-Hua Lin3
1Department of Electronic and Electrical Engineering, Southern University of Science and Technology, Shenzhen, China.
Insights
Filtering photoplethysmography (PPG) signals significantly alters pulse transit time (PTT) measurements, with effects varying by age and PPG feature definition. These findings are crucial for accurate wearable blood pressure monitoring.
Area of Science:
- Biomedical Engineering
- Physiological Measurement
- Wearable Technology
Background:
- Pulse transit time (PTT) is vital for cuffless blood pressure monitoring using photoplethysmography (PPG).
- Signal filtering in wearable PPG sensors can introduce inaccuracies in PTT estimation.
- Limited research exists on how filtering affects PTT across different age groups.
Purpose of the Study:
- To quantitatively assess the impact of age and PTT definition on filtering-induced PTT changes.
- To investigate the influence of infinite impulse response (IIR) filtering on PTT measurements.
- To provide insights for improving PPG-based cuffless blood pressure accuracy.
Main Methods:
- Recruited 100 healthy subjects across five age groups (20-60+ years).
- Recorded simultaneous electrocardiogram (ECG) and PPG signals.
- Calculated PTT using eight definitions based on PPG waveform features and compared filtered vs. unfiltered signals, analyzing age-group differences via ANOVA.
Main Results:
- Filtering significantly altered PTT, influenced by both age and the specific PTT definition (p < 0.001).
- Aging showed a consistent trend in filtering-induced PTT changes across all definitions.
- PTT defined by the PPG maximum peak exhibited minimal filtering changes (16.16 ms, 5.65%), while the maximum first derivative showed the strongest age correlation (R-squared: 0.47).
Conclusions:
- Age and PTT definition critically impact filtering-induced PTT changes.
- These factors must be considered for enhancing the accuracy of wearable PPG-based blood pressure devices.
- Further research is needed to optimize filtering and PTT definitions for diverse populations.
Abstract:
Background: Pulse transit time (PTT) is a key parameter in cuffless blood pressure measurement based on photoplethysmography (PPG) signals. In wearable PPG sensors, raw PPG signals are filtered, which can change the timing of PPG waveform feature points, leading to inaccurate PTT estimation. There is a lack of comprehensive investigation of filtering-induced PTT changes in subjects with different ages. Objective: This study aimed to quantitatively investigate the effects of aging and PTT definition on the infinite impulse response (IIR) filtering-induced PTT changes. Methods: One hundred healthy subjects in five different ranges of age (i.e., 20-29, 30-39, 40-49, 50-59, and over 60 years old, 20 subjects in each) were recruited. Electrocardiogram (ECG) and PPG signals were recorded simultaneously for 120 s. PTT was calculated from the R wave of ECG and PPG waveform features. Eight PTT definitions were developed from different PPG waveform feature points. The raw PPG signals were preprocessed then further low-pass filtered. The difference between PTTs derived from preprocessed and filtered PPG signals, and the relative difference, were calculated and compared among five age groups and eight PTT definitions using the analysis of variance (ANOVA) or Scheirer-Ray-Hare test with post hoc analysis. Linear regression analysis was used to investigate the relationship between age and filtering-induced PTT changes. Results: Filtering-induced PTT difference and the relative difference were significantly influenced by age and PTT definition (p < 0.001 for both). Aging effect on filtering-induced PTT changes was consecutive with a monotonous trend under all PTT definitions. The age groups with maximum and minimum filtering-induced PTT changes depended on the definition. In all subjects, the PTT defined by maximum peak of PPG had the minimum filtering-induced PTT changes (mean: 16.16 ms and 5.65% for PTT difference and relative difference). The changes of PTT defined by maximum first PPG derivative had the strongest linear relationship with age (R-squared: 0.47 and 0.46 for PTT difference relative difference). Conclusion: The filtering-induced PTT changes are significantly influenced by age and PTT definition. These factors deserve further consideration to improve the accuracy of PPG-based cuffless blood pressure measurement using wearable sensors.
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