Microvascular Circulation And Pulse Arrival Time Variability: Implications For Non-invasive Blood Pressure Devices

Although pulse arrival time (PAT) has been widely used in non-invasive blood pressure devices using near-infrared spectroscopy (NIRS), its inconsistent accuracy should be improved. The inconsistent accuracy may be caused by several sources of variance contributing to PAT. Of note, microvascular circulation significantly contributes to the NIRS derived PAT, and changes in the microvasculature environment may cause variability in PAT that leads to inaccurate blood pressure predictions. PURPOSE: Therefore, the purpose of this study was to examine the contribution of microvasculature to PAT variability. Our hypothesis was that microvascular activity substantially contributes to variance in PAT. METHODS: NIRS from the forearm and electrocardiogram (ECG) were collected from 15 subjects (18-25 yrs) for 30-min. PAT time series were generated by calculating the differences in time between ECG R-waves and successive NIRS pulse waves. Heart rate variability (HRV) tachograms represented autonomic nervous system activity, which was used as a standard comparison. NIRS time series represented changes in microvascular activity. Wavelet scalograms were produced for PAT, HRV, NIRS, and brown noise between the frequencies of 0.01-0.4 Hz. Wavelet coherence was then used to determine locations in time and frequency where HRV, NIRS, and brown noise explained PAT spectral power. PAT spectral power explained by HRV, NIRS, and brown noise were summed, respectively, and divided by the total PAT spectral power. The percentages of PAT power explained by HRV, NIRS, and brown noise were compared with a one-way analysis of variance and Tukey’s test was used for post hoc analysis. RESULTS: NIRS explained 21.3 ± 5.9%, HRV explained 38.4 ± 19.3%, and brown noise explained 8.4 ± 0.8% of PAT spectral power. NIRS explained more PAT spectral power than brown noise (Δ13.0 ± 5.9%, p = 0.01), but less PAT spectral power than HRV (Δ-17.0 ± 20.2%, p < 0.01). CONCLUSION: Based on our current findings, although the contribution of the autonomic nervous system was more dominant, the microvasculature also significantly contributed to variance in PAT. Therefore, to improve the accuracy of non-invasive blood pressure devices that utilize PAT, variance in PAT contributed by the microvasculature should be attenuated or eliminated. This research was supported by the National Institutes of Health (R01HD106911) and the Great Plains IdeA-CTR (U54 GM115458).