Exploring the Relationship between Blood Flux Signals and HRV following Different Thermal Stimulations using Complexity Analysis

Abstract

To investigate the relationship between local blood flux and heart rate variability following different thermal stimulations, healthy subjects were recruited and subject to different thermal stimulations on the right forearm. Multiscale entropy and multiscale fuzzy entropy were used to measure the complexity of the local blood flux, and the approximate entropy was calculated to evaluate the HRV complexity. The results indicated that thermal stimulation significantly increased local blood flux and that different temperature stimulations resulted in different complexities in local blood flux. A 42 °C or 44 °C thermal stimulation, other than stimulations below 42 °C, resulted in a moderate correlation between local blood flux and heart rate variability complexity. The results provide a new perspective in terms of complexity to explore the relationship between skin blood flux signals and cardiac function.

Figure 1

Experimental design and case subject raw data for blood perfusion flux. (a) Experimental design. (b) Thermal stimulation point (red) and control point (blue) location on the right forearm. The thermal stimulation point is on the anterior aspect of the forearm, between the tendons of the palmaris longus and the flexor carpi radials, 5 B-cun proximal to the palmar wrist crease. The control point is 7 B-cun proximal to the palmar wrist creas. (c) Temperature of the stimulation point (left) and the blood perfusion signal at both the stimulation and control points (right).

Figure 2

Blood perfusion flux signals at both the stimulation and control points. (a) 38 °C thermal stimulation. (b) 40 °C thermal stimulation. (c) 42 °C thermal stimulation. (d) 44 °C thermal stimulation. **P < 0.01, paired-t test (n = 30).

Figure 3

Complexity of the blood perfusion flux signals. (a) MSE result of different scales at the stimulation point. (b) MSE result of different scales at the control point. (c) Complexity area index of different conditions and different points. The complexity area index was obtained as the area under the multiscale entropy curve of Fig. 3a,b. (d) MFE result of different scales at the stimulation point. (e) MFE result of different scales at the control point. (f) The complexity area index of different conditions and different points. The complexity area index was obtained as the area under the multi-scale entropy curve of Fig. 3d,e. *P < 0.05; **P < 0.01, paired-t test (n = 30). MSE, multi-scale entropy. MFE, multiscale fuzzy entropy. BL, baseline condition without stimulation. Data are presented as the mean ± SE.

Figure 4

Contrast in MSE between baseline and other thermal stimulation conditions. (a) Stimulation point with 38 °C stimulation. (b) Control point with 38 °C stimulation. (c) Stimulation point with 40 °C stimulation. (d) Control point with 40 °C stimulation. (e) Stimulation point with 42 °C stimulation. (f) Control point with 42 °C stimulation. (g) Stimulation point with 44 °C stimulation. (h) Control point with 44 °C stimulation. Paired-t test (n = 30). Data are presented as the mean ± SE.

Figure 5

Contrast in MFE between baseline and other thermal stimulation conditions. (a) Stimulation point with 38 °C stimulation. (b) Control point with 38 °C stimulation. (c) Stimulation point with 40 °C stimulation. (d) Control point with 40 °C stimulation. (e) Stimulation point with 42 °C stimulation. (f) Control point with 42 °C stimulation. (g) Stimulation point with 44 °C stimulation. (h) Control point with 44 °C stimulation. Paired-t test (n = 30). Data are presented as the mean ± SE.

Figure 6

Relationship of the complexity between blood perfusion flux and heart rate variability. (a) MSE result at baseline condition. (b) MFE result at baseline condition. (c) MSE result at 38 °C thermal stimulation. (d) MFE result at 38 °C thermal stimulation. (e) MSE result at 40 °C thermal stimulation. (f) MFE result at 40 °C thermal stimulation. (g) MSE result at 42 °C thermal stimulation. (h) MFE result at 42 °C thermal stimulation. (i) MSE result at 44 °C thermal stimulation. (j) MFE result at 44 °C thermal stimulation. SCC, Spearman’s correlation coefficient.