Body Position Affects Capillary Blood Flow Regulation Measured with Wearable Blood Flow Sensors

Abstract

In this study we demonstrate what kind of relative alterations can be expected in average perfusion and blood flow oscillations during postural changes being measured in the skin of limbs and on the brow of the forehead by wearable laser Doppler flowmetry (LDF) sensors. The aims of the study were to evaluate the dynamics of cutaneous blood perfusion and the regulatory mechanisms of blood microcirculation in the areas of interest, and evaluate the possible significance of those effects for the diagnostics based on blood perfusion monitoring. The study involved 10 conditionally healthy volunteers (44 ± 12 years). Wearable laser Doppler flowmetry monitors were fixed at six points on the body: two devices were fixed on the forehead, on the brow; two were on the distal thirds of the right and left forearms; and two were on the distal thirds of the right and left lower legs. The protocol was used to record three body positions on the tilt table for orthostatic test for each volunteer in the following sequence: (a) supine body position; (b) upright body position (+75°); (c) tilted with the feet elevated above the head and the inclination of body axis of 15° (-15°, Trendelenburg position). Skin blood perfusion was recorded for 10 min in each body position, followed by the amplitude-frequency analysis of the registered signals using wavelet decomposition. The measurements were supplemented with the blood pressure and heart rate for every body position analysed. The results identified a statistically significant transformation in microcirculation parameters of the average level of skin blood perfusion and oscillations of amplitudes of neurogenic, myogenic and cardiac sensors caused by the postural changes. In paper, we present the analysis of microcirculation in the skin of the forehead, which for the first time was carried out in various positions of the body. The area is supplied by the internal carotid artery system and can be of particular interest for evaluation of the sufficiency of blood supply for the brain.

Keywords: blood perfusion; blood perfusion in forehead; blood perfusion in shins; blood perfusion in wrists; blood perfusion oscillations; body position; laser Doppler flowmetry; ortostatic test; postural changes; vasomotions; wearable blood flow sensors.

Figure 1

Representative trace of laser Doppler flowmetry (LDF) recordings by the employed measuring system (a), the wavelet analysis of the LDF signal with the highlighted frequency ranges for E—endothelial (e, 0.095–0.021 Hz), N—neurogenic (n, 0.021–0.052 Hz), M—myogenic (m, 0.052–0.145 Hz), R—respiratory (r, 0.145–0.6 Hz) and C—cardiac (c, 0.6–2 Hz) regions of blood flow modulation (b).

Figure 2

The measurements have been conducted and compared for three distinct body positions on a tilt table: (A) supine; (B) upright; (C) tilted with the feet elevated above the head and an inclination of body axis of 15° (Trendelenburg position).

Figure 3

Analysis of average blood perfusion parameters on the wrists for three tested body positions: supine, upright and tilted (Trendelenburg position): (a) average blood perfusion; (b) cardiac oscillations; (c) respiratory oscillations; (d) endotelial oscillations; (e) neurogenic oscillations; (f) myogenic oscillations (* the significance of a difference between values was confirmed with p < 0.05 using the the Mann–Whitney test).

Figure 4

Analysed blood perfusion parameters measured on the shins for three body positions: supine, upright and tilted (Trendelenburg position): (a) average blood perfusion; (b) cardiac oscillations; (c) respiratory oscillations; (d) endotelial oscillations; (e) neurogenic oscillations; (f) miogenic oscillations (* the significance of a difference between values was confirmed with p < 0.05 using the Mann–Whitney test).

Figure 5

Analysis of blood perfusion parameters in the skin of the brow of the forehead for three tested body positions: supine, upright and tilted (Trendelenburg position): (a) average blood perfusion; (b) cardiac oscillations; (c) respiratory oscillations; (d) endotelial oscillations; (e) neurogenic oscillations; (f) miogenic oscillations (* the significance of a difference between values was confirmed with p < 0.05 using the Mann–Whitney test).

Figure 6

Analysis of parameters of blood pressure and hear rate measured in the tested body positions: supine, upright and tilted (Trendelenburg position): (a) systolic blood pressure; (b) diastolic blood pressure; (c) heart rate (* the significance of a difference between the values was confirmed with p < 0.05 using the Mann–Whitney test).