(D-143) Laser Doppler Flowmetry for Cuffless, Continuous Pulse Wave Velocity Vascular Monitoring During Post-Exercise Hypotension

Introduction:: Arterial stiffness is a crucial risk factor for cardiovascular disease that is typically assessed by measuring the time delay of a pulse wave's propagation along an arterial segment, known as pulse wave velocity (PWV).[1] The standard method for measuring PWV using pressure cuffs and tonometers has limitations, including discomfort, alteration of arterial sites, and expensive equipment.[2] Laser Doppler flowmetry (LDF) is a cuff-less alternative that uses light to measure pulsatile blood flow in the microvasculature. This study aims to validate LDF as an alternative to measure PWV and its response to post-exercise hypotension (PEH). We hypothesize that LDF will not differ significantly from tonometry, and we expect to observe a decrease in peripheral PWV following exercise due to vasodilation and little change in central PWV due to unchanging vessel compliance.


Materials and Methods:: 33 participants (19-22 years-old) were recruited with IRB approval. Data was collected using a BIOPAC MP36 and Student BIOPAC as a customized DAQ system, and a Periflux PF 3 (Perimed, Sweden). Signals were analyzed using in-house software (MATLAB 2023). Several site specific PWV velocities reflecting the vessel stiffness and tone of the proximal vascular bed were calculated. (Fig.1) Baseline PWV were measured while participants were in a seated position for at least 5 minutes. Isometric grip exercise was performed to assess maximum grip strength and participants were then asked to maintain 40% of their maximum force for 2 minutes while central, global, and peripheral PWV were continuously measured. Post-exercise PWV were obtained immediately after the exercise challenge for 1.5 minutes by measuring at least 10 heart cycles during the final rest time.


Results, Conclusions, and Discussions:: LDF PWV_cf and gold-standard tonometry PWV_cf showed a mean bias of -0.14 and 95% confidence intervals of [-0.27, -0.01] using Bland-Altman analysis (rho = 0.74). (Fig.1) In response to exercise, there was a significant decrease in peripheral PWV_fa, PWV_ft, and global LDF PWV_ct, although no significant changes were detected for central tonometry PWV_cf or global tonometry PWV_ca. (Fig.1) The study validated the LDF method as a reliable alternative to tonometry for measuring arterial stiffness and demonstrated its ability to detect changes in peripheral PWV after an exercise challenge. The results suggest that peripheral PWV is influenced by arterial tone and decreases due to the hypotensive post-exercise response. Conversely, more compliant central arteries exhibit little exercise-related effect, and global tonometry is more influenced by physiological noise.

The findings have implications for future research in cuffless, continuous vascular tone and blood pressure monitoring. Although no correlation in the exercise response was observed between the peripheral PWV measurements, it is possible that PWV_ft is more influenced by resistance vessels and less susceptible to physiological noise than PWV_fa.



Acknowledgements (Optional): :

References (Optional): : [1] S. Laurent et al., “Aortic stiffness is an independent predictor of all-cause and cardiovascular mortality in hypertensive patients,” Hypertension, vol. 37, no. 5, pp. 1236–1241, 2001, doi: 10.1161/01.HYP.37.5.1236/FORMAT/EPUB.

[2] M. F. O’Rourke, “Carotid Artery Tonometry: Pros and Cons,” Am J Hypertens, vol. 29, no. 3, pp. 296–298, Mar. 2016, doi: 10.1093/AJH/HPV194.