1. Limb Specific Differences in Vasomotion Response to Varying Rates of Local Heating.
Andrew T. Del Pozzi1 James T Miller2, and Gary J Hodges3
1The Integrative Exercise Physiology Laboratory, Ball State University, Muncie, IN 47306
2Human Performance Laboratory, The University of Alabama, Tuscaloosa, AL, 35487
3Environmental Ergonomics Laboratory, Brock University, ON L2S 3A1
Program # 729.7
ABSTRACT
METHODS
RESULTS
Table 1. Subject Characteristics N = 7 Male and 7 Female
Figure 1. Representative tracing of laser-Doppler flux in mV from a single study participant. Four skin sites, two on the forearm (solid) and two on the leg (open). Local skin temperature was maintained at 33 °C for 10 min during basal measures. Two rates of heating were used, slow (0.1 °C · 10 s-1; circles) and fast (0.5 °C · 10 s-1; triangles). Skin temperatures at forearm and leg sites were increased from 33 °C to 42 °C. Sections A through E indicate 5 min periods of data analysis. A = Baseline. B = First five minutes of heat response for fast protocol. C = First five minutes of heat response for slow heating protocol. D = final 5 min of local skin heating for fast heated skin sites. E = final 5 min of local skin heating for slow heated skin sites. ↑indicates time period of increasing local skin temperature.
We examined skin blood flow (SkBF) and vasomotion in the forearm and leg using laser-Doppler fluxmetry (LDF) and spectral analysis to investigate endothelial, sympathetic, and myogenic activity in response to slow (0.1 °C · 10 s-1) and fast (0.5 °C · 10 s-1) local heating. At 33 °C (thermonuetral) endothelial activity was higher in the legs than the forearms (P ≤ 0.02). Fast-heating increased SkBF more than slow heating (P = forearm; P = leg). At onset of 42 °C, endothelial (P = forearm; P = 0.48 leg) activity increased in both regions during the fast-heating protocol. Following prolonged heating (42 °C) endothelial activity was higher in both the forearm (P = 0.002) and leg (P < 0.001) following fast-heating. These results confirm regional differences in the response to local heating and suggest that the greater increase in SkBF in response to fast local heating is initially due to increased endothelial and sympathetic activity. Furthermore, with sustained local skin heating, greater vasodilatation was observed with fast heating compared to slow heating. These data indicate that this difference is due to greater endothelial activity following fast heating compared to slow heating, suggesting that the rate of skin heating may alter the mechanisms contributing to cutaneous vasodilatation.
Male
Female P
Combined
Stature (cm)
178 ± 4
165 ± 3.0
0.027
171 ± 5
Mass (kg)
82.2 ± 1.5
58.2 ± 3.9
<0.001
68 ± 6
Age (yr)
28 ± 1
25 ± 2
0.061
27 ± 2
SBP (mm Hg)
100 ± 3
99 ± 2
0.433
DBP (mm Hg)
53 ± 2
0.421
53 ± 3
MAP (mm Hg)
68 ± 2
67 ± 2
0.413
68 ± 3
All experimental protocols were conformed to the guidelines set forth by the Declaration of Helsinki and approved by the Institutional Review Board at The University of Alabama. All participants were healthy free of any known disease and not taking any medication other than oral contraceptives. Data collection occurred during the low hormone phase of the birth control regime (Charkoudian, 2001; Charkoudian and Johnson, 2000; Del Pozzi et al., 2013; Del Pozzi and Hodges, 2015a; Hodges and Del Pozzi, 2014; Stephens et al., 2002).
The current study required each participant to report two times to the laboratory, once for each heating rate. All protocols were performed in the same manner in a temperature controlled room ranging from 20 to 22°C, beginning at 07:00. Local skin temperature was monitored and adjusted using an integrated monitor (SH02, Moor, Devon, UK). Red blood cell flux was measured via laser-Doppler fluxmetry (LDF) (MoorVMS-LDF2). LDF probes (VP12) were placed within a small aperture on the local skin heaters.
Following instrumentation the participant then rested quietly in a dimly lit room for 15 min while the LDF measurements stabilized. Baseline measurements were then recorded. Tloc was increased to 42 °C using one of two heating protocols: the slow protocol (0.1 °C · 10 s-1, 15 min in duration) or the fast protocol (0.5 °C · 10 s-1, 3 min in duration). Tloc was held at 42 °C for 35 min at which point stable plateaus were confirmed, representing a physiological maximum (Taylor et al., 1984). Figure 1 details representative data and protocol outline.
Figure 2. Baseline Vasomotion data presented as a percentage of total power. A) Vasomotion in the endothelial range. B) Vasomotion in the sympathetic range. C) Vasomotion in the myogenic range. P values indicated above brackets of comparison.
INTRODUCTION
Figure 4. Vasomotion data for the final five minutes of local skin heating presented as a percentage of total power. A) Vasomotion in the endothelial range. B) Vasomotion in the sympathetic range. C) Vasomotion in the myogenic range. P values indicated above brackets of comparison
The rhythmic contractions of the vascular smooth muscle leading to oscillations in blood flow are termed vasomotion and occur in all vascular beds (Funk et al., 1983).
These contractions result in variations in the cutaneous blood flow which are under the influence of local factors and autonomic innervations (Bernardi et al., 1997; Hodges and Del Pozzi, 2014; Rossi et al., 2006; Rossi et al., 2008).
A non-invasive method to assess the control systems of the cutaneous circulation can be achieved via the examination of the spectral components entrenched within the oscillatory vasomotion of the vascular beds (Rossi et al., 2008).
Numerous frequencies are observed within vasomotion signals. Ranging from 1 Hz to 0.01 Hz (Rossi et al., 2006; Rossi et al., 2008; Stefanovska et al., 1999). The frequency spectrum can be divided into ranges, enabling the filtering of signals. For this study those would be (endothelial), (sympathetic), and (myogenic) Hz (Soderstrom et al., 2003; Urbancic-Rovan et al., 2004).
We hypothesized that rate of heating would affect both the forearm and the leg equally, with higher initial and sustained vasodilator responses achieved in response to faster local heating. We hypothesized that the greater initial vasodilator responses to fast heating compared to slow heating would be due to increased endothelial and sympathetic activity, while the greater sustained vasodilation would be due to elevated endothelial activity .
Figure 3. Vasomotion data following the first five minutes of local skin heating presented as a percentage of total power. A) Vasomotion in the endothelial range. B) Vasomotion in the sympathetic range. C) Vasomotion in the myogenic range. P values indicated above brackets of comparison.
STATISTICAL ANALYSIS
CONCLUSION
We have observed regional differences in the cutaneous vasodilatory response to differing rates of local skin heating. As per our previous examinations of the cutaneous vasculature of the forearm and leg (Del Pozzi et al., 2013; Del Pozzi and Hodges, 2015a; Del Pozzi and Hodges, 2015b; Hodges and Del Pozzi, 2014), in response to prolonged local heating at a rapid rate skin blood flow was higher in the forearms compared to the legs, consistent with the higher cutaneous and sympathetic activity observed in the forearm over the leg. However, endothelial activity was higher in the leg compared to the forearm for both rates of heating. Furthermore, these results are similar to those that have studied the effect of rate on thermal hyperemia (Hodges et al., 2009) with faster rates of heating eliciting greater skin blood flow responses, we furthered these observations by demonstrating that this rate difference early in the heating process is due to endothelial and sympathetic activity in both the forearm and leg, and with prolonged skin heating is due to increased endothelial activity.
Statistical analysis was completed using SAS v9.13 (SAS institute Inc., Cary, NC, USA). Stable 5 min periods of LDF data were used for both the baseline, the first 5 min of local skin heating, and the final 5 min (plateau phase)(Fig. 1).These data were both used for LDF analysis and for analyzing the spectra of the LDF signal. LDF data were normally distributed while skin vasomotion data were not normally distributed. Therefore, the Wilcoxon signed-rank test was performed for the vasomotion analysis between skin sites. The power spectral density of the LDF signal oscillations was determined using a fast Fourier transformation algorithm in combination with a Parazen function windowing technique (Rossi et al., 2013; Rossi et al., 2014). These data are presented as medians and range and are normalized to total power. The frequency spectrum was separated into five frequency intervals of differing window length: corresponding to the endothelial, sympathetic, myogenic, respiratory, and cardiac activity (fig. 2-4) (Kvernmo et al., 1999; Rossi et al., 2006; Rossi et al., 2008; Urbancic-Rovan et al., 2004).
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