Fast-Fourier transform - transfer function analysis of beat-to-beat finger skin blood flux and arterial blood pressure provides new insights into cold-induced vasodilation

Cold-induced vasodilation (CIVD) is a counterintuitive focal increase in glabrous skin blood flow during cold exposure with unclear local and neural mechanisms. To understand this phenomenon, we tested 12 (8 men, 4 women) healthy subjects’ laser-Doppler flux (LDF) and arterial blood pressure (ABP) on a beat-by-beat basis. The experimental hand was exposed to warm (10 min 35°C water) and then cold (30 min 8°C water) water immersion and contralateral control hand experienced 22-23°C air throughout. Beat-by-beat oscillations in LDF (2 experimental and 1 control finger skin just proximal to the nailbed) and ABP were analyzed via a fast-Fourier transform (FFT) to obtain power spectral density and transfer function analysis (TFA) of LDF to ABP to obtain gain, phase, and coherence between the signals. Frequencies were normalized to total power and binned within very low (nVLF; 0.02-0.07), low (nLF; 0.07-0.20), and high (nHF; 0.20-0.35) Hz ranges. ABP power decreased from warm to cold immersion in the nVLF but no differences were observed in nLF and nHF. LDF power was greater in the control finger than immersed fingers in nVLF and nLF, but not different in nHF. There was an interaction in nLF where cooling decreased power in immersion sites but increased power in the control. There was also an interaction in nHF where cooling increased power in immersion sites but did not change power in the control. Average pooled TFA coherence between LDF and ABP were 0.5±0.2, 0.5±0.1, and 0.4±0.1 for warm and 0.5±0.2, 0.5±0.2, and 0.4±0.1 for cold for VLF, LF, and HF, respectively. TFA gain was lower during cooling for immersion but not control sites in the VLF and LF ranges. In contrast, HF gain was lower in both immersion and control sites. Cooling decreased phase (time-delay) of the LDF to ABP signal in the VLF during cooling immersion sites but these data were somewhat finger dependent. Data from this analysis approach confirms a significant effect of local vasoconstriction within sympathetic vasoconstriction as identified by changes in the VLF and LF, respectively. Comparing CIVD bins (LDF criteria, n=6) to general cutaneous vasoconstriction bins with no CIVD (n=6) yielded increases in nHF (P=0.02) and nLF (P=0.09) and decreases in nVLF (P=0.05) power with CIVD. TFA gain during CIVD did not yield differences across frequency bins compared to cutaneous vasoconstriction alone. Thus, the unique analysis of arterial blood pressure and the FFT-TFA approach appears to be beneficial in providing insights into CIVD events with a local release of vasoconstriction under the tonic sympathetic tone and local vasoconstriction and vasodilation balance. National Institute of Environmental Health Sciences (P30ES026529) awarded through UK Center for Appalachian Research in Environmental Sciences (UK-CARES) This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.