Blood pressure (BP) variability is linked to cardiovascular outcomes. Pulse transit time (PTT), the time taken for the pulse wave to travel between two arterial sites, enables cuffless, continuous BP monitoring. Studies have validated PTT-estimated BP against mercury sphygmomanometry. Beat-to-beat PTT-estimated BP (eBPBTB) might offer a more sensitive assessment of BP variability than methods using intermittent measurements at fixed intervals (eBPINT), particularly in conditions like sleep-disordered breathing (SDB) where acute BP fluctuations occur. This study aimed to compare BP parameters, including variability, from eBPBTB and eBPINT in patients with suspected SDB in a multicenter study. Accurate assessment of BP variability is crucial for managing cardiovascular risk and improving patient outcomes, especially in high-risk populations where BP fluctuations can be significant. Existing methods like ambulatory blood pressure monitoring (ABPM) provide intermittent measurements, potentially missing transient BP changes. The development and validation of continuous, non-invasive BP monitoring techniques, such as those based on PTT, represent a significant advance in cardiovascular research. The potential of PTT-based continuous BP monitoring to capture the dynamic nature of BP changes, particularly the transient peaks associated with SDB, has important clinical implications for diagnosis, risk stratification, and treatment optimization. Understanding the relationship between eBPBTB and eBPINT is vital for determining the clinical utility and optimal implementation strategies for PTT-based BP monitoring.

Several studies have validated PTT-estimated BP against traditional methods like mercury sphygmomanometry, demonstrating its accuracy in assessing average BP values. However, the comparative performance of beat-to-beat versus intermittent PTT-based BP measurements regarding BP variability, especially in dynamic situations such as SDB, has been less explored. Research on BP variability in SDB has shown a correlation between BP fluctuations and desaturation events. While ABPM is commonly used to assess BP variability, its intermittent nature might limit its ability to capture transient BP changes. The potential advantages of continuous BP monitoring using PTT in SDB, given its ability to capture beat-to-beat variations, warrant further investigation. Prior research highlights the association between BP variability and cardiovascular risk. The use of continuous BP monitoring to assess variability may provide a more comprehensive understanding of BP dynamics compared to traditional methods.

This multicenter study enrolled 330 patients with suspected SDB. Nighttime BP was continuously monitored using the SOMNO touch RESP system, which recorded various physiological parameters including nasal airflow, snoring, respiratory effort, ECG, SpO2, PTT, R-R intervals, finger plethysmography, and body position. The 3% oxygen desaturation index (ODI) was calculated using DOMINO Light software. PTT was determined as the time between the R-wave of the ECG and the pulse wave arrival at the finger, with BP calculated using a patented algorithm in the DOMINO Light software. Resting BP was measured before monitoring for calibration. eBPBTB comprised all BP readings estimated by PTT, while eBPINT was defined as the BP every 30 min. Statistical analysis included paired t-tests to compare BP indices between eBPBTB and eBPINT, Bland-Altman analysis to assess agreement, and linear regression to examine associations between BP parameters and ODI tertiles. The study collected demographic data, medical history, and office BP measurements. The Institutional Review Board of Jichi Medical University approved the study with a waiver of informed consent.

Statistically significant differences were observed between eBPBTB and eBPINT for most BP parameters, although the absolute differences were often small. Specifically, average systolic eBPBTB, maximum systolic and diastolic eBPBTB, and standard deviation (SD) and coefficient of variation (CV) of systolic and diastolic eBPBTB were significantly higher than the corresponding eBPINT values. Bland-Altman analysis demonstrated good agreement for average systolic BP, SD of systolic BP, and CV of systolic BP between the two methods. However, significant disagreements were observed for minimum and maximum systolic BP values, particularly in patients with high systolic BP. Stratified analysis based on atrial fibrillation or antihypertensive medication use revealed some differences in the magnitude of disagreement between eBPBTB and eBPINT, but these differences were not consistently significant. Both eBPBTB and eBPINT showed an incremental increase in systolic BP variability with increasing ODI tertiles, but the trend was similar for both methods. These findings suggest that while there is close agreement between eBPBTB and eBPINT on overall BP averages and variability, there may be significant discrepancies in capturing the extreme high and low values that could be clinically significant. Table 2 summarizes the comparison of BP indices between the two methods. Table 3 illustrates the relationship between BP parameters and ODI tertiles for both eBPBTB and eBPINT.

This study demonstrates that while beat-to-beat and intermittent PTT-estimated BP provide comparable estimates of average systolic BP and BP variability, there are significant differences in their ability to capture minimum and maximum BP values. The minimal differences in average systolic BP suggest that intermittent measurements at 30-minute intervals might be sufficient for assessing average BP. However, the disagreement regarding minimum and maximum values highlights the potential limitation of intermittent BP measurement for detecting extreme BP fluctuations, particularly in conditions like SDB where transient, significant BP changes occur. The consistent agreement in BP variability indices between the two methods suggests that intermittent measurement might be adequate to assess overall BP variability, although it might miss important information concerning peak and trough values. The study’s findings support the use of PTT-based methods for assessing BP variability in SDB, and indicate that a balance between the need for continuous monitoring and the practical considerations of intermittent measurements should be considered. Further research is needed to evaluate the clinical implications of these discrepancies for patients with high-risk conditions such as SDB.

This study compared beat-to-beat and intermittent PTT-estimated blood pressure measurements in patients with suspected sleep-disordered breathing. While both methods showed comparable results for average systolic BP and BP variability, significant discrepancies were observed for minimum and maximum values. These findings have implications for clinical practice, highlighting the importance of considering the specific clinical question when selecting a measurement method. Future research could explore the optimal sampling frequency for intermittent PTT-based BP monitoring and investigate the clinical relevance of these discrepancies in larger populations.

The study was conducted in a population with suspected sleep-disordered breathing, which may limit the generalizability of findings to other patient populations. The use of a specific algorithm and device for PTT-based BP measurement may also limit the external validity. Further research in other patient groups, using other PTT-based BP measurement systems, is necessary to validate these findings. Additionally, the study did not compare PTT-based BP measurement to other continuous BP monitoring techniques.