Local heating induces an increase in the pulse wave velocity in peripheral vessels

Figures

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  Fig. 1. Layout of the multimodal measurement system providing synchronous recording of an electrocardiogram (ECG) and images of forearm. Area under study is illuminated by green light-emitting diodes (LEDs). The local temperature is monitored by a temperature sensor (TS). Image frames are digitalized in a laptop, while ECG data and sync pulses from the camera are digitalized in the ECG module to provide system’s synchronization. A timeline of the experimental recording is shown in the lower part of the figure.

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  Fig. 2. An example of processing the average pixel value in a small ROI for one cardiac cycle. (A) The red curve shows the dynamics of the average pixel value estimated from a series of raw images. The magenta curve shows the mean pixel intensity dynamics after digital stabilization. The blue curve shows the signal after stabilization and high-frequency filtering. The dashed green line indicates the linear trend of the pixel value during the cardiac cycle. (B) The resulting waveform \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$PP{G_{norm}}$$\end{document} is shown by the blue line after inverting, detrending and normalizing the filtered signal. In both panels, the black line shows the ECG signal, which defines the position in time of the cardiac cycle.

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  Fig. 3. Raw images of the area under study and spatial distributions of the amplitude of the pulsatile component (APC) of the photoplethysmographic waveform and the pulse arrival time (PAT) in this area, obtained under initial conditions (upper row: A, B, C) and after skin heating to 41 °C (lower row: D, E, F). Grayscale images of the forearm area with the heater (black frame) illuminated by green light are shown on panels A and D. The APC and the PAT maps were assessed for the same cardiac cycle during baseline (panels B and C, respectively) and during another cycle after heating (panels E and F, respectively). All mappings are displayed in pseudo colors with respective color scales on the right.

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  Fig. 4. Spatial and temporal characteristics of pulse waves. (A) An example of the spatial distribution of the amplitude of the pulsatile component (APC) of the photoplethysmographic waveform measured before heating at 2.5 min for one cardiac cycle. (B) APC distribution measured at the 9th minute (four minutes after turning on the heater). Red and blue circles in panels A and B indicate selected ROIs. (C) Photoplethysmographic (PPG) waveform averaged within the ROI selected in the area of skin contact with the heater (red line) and outside the heater (blue line) assessed during seven seconds in the baseline before the heating. (D) PPG waveform in the same ROIs but assessed 3.9 min after the heater was switched on. (E) Enlarged PPG waveforms with notations of the pulse arrival time (PAT) assessed in the ROIs inside and outside the heater for one cardiac cycle at the 9th minute. The black curves in panels C, D, and E show the synchronously recorded electrocardiogram (ECG).

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  Fig. 5. Typical examples of the response of blood flow parameters to local heating of the forearm. Vertical red dotted lines in each panel indicate when the heater was turned on. Blue lines show changes in the amplitude of the pulsatile component (APC), while green lines refer to changes in the pulse arrival time (PAT). Changes in skin temperature in the area of contact with the heater are shown by black curves on all panels.

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  Fig. 6. Box-whisker diagrams of the amplitude of pulsatile component (APC) of the photoplethysmographic waveforms and pulse arrival time (PAT) in the sample under study. (A) APC before and after heating. (B) Gain in APC due to heating. (C) PAT before and after heating. (D) Difference in PAT (ΔPAT) caused by heating. (E) The relative decrease in the slowly varying component (DC) of the photoplethysmographic waveform assessed after heating compared to the baseline.

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  Fig. 7. Diagram of microcirculatory nodes and variations of their components under the influence of local heating. The microcirculation node consists of a feeding arteriole, an arteriovenous anastomosis (AVA), capillaries, and a venule.