Introduction The human temperature control within the thermoneutral zone (TNZ) depends on the regulation of skin blood flow to hands and feet (acral skin) [1]. The acral skin blood flow is regulated by absolute level and fluctuations in arterio‐venous anastomoses’ vasculature resistance. We hypothesized that a change in ambient temperature would not affect the hemodynamic responses within the TNZ in healthy humans. Methods Twenty‐four young healthy human subjects were exposed to three ambient temperatures (20°C, 26°C and 32°C) while supine and lightly dressed in a climate chamber. Each temperature plateau lasted for 40 minutes. The protocol either started at 20°C or 32°C, with a subsequent increase or decrease in temperature, respectively, and the order was randomized. Beat‐by‐beat blood flux from both index fingers and the left forearm were recorded simultaneously by laser Doppler flowmetry (DRT4, Moor Instruments, Devon, UK), together with heart rate (HR, from ECG). Non‐invasive finger arterial blood pressure (Finometer, Finapres Medical System, Netherlands; calibrated at each temperature plateau) was recorded continuously from the right middle finger, providing mean arterial pressure (MAP) and estimated beat‐to‐beat cardiac stroke volume (SV). The medians and their corresponding 95% confidence intervals were calculated by Hodges‐Lehmann’s estimates. Wilcoxon signed rank sum test for paired samples tested differences between states. Preliminary results Increasing ambient temperature from 20°C to 32°C caused a five‐fold increase in left fingertip flux (p<0.003) while left forearm flux doubled (p<0.008). The fluctuations in the bilateral fingertip flux were maximum correlated at 26°C (>0.82) and significantly higher than the correlation at 32°C (0.73, p<0.01 as compared to 26°C). The hemodynamic variables changed significantly within the TNZ. MAP decreased from 74 (70,77) mmHg at 20°C to 64 (60,68) mmHg at 32°C (p<0.0001). SV decreased from 102 (93, 113) ml at 20°C to 97 (86, 106) ml at 32°C (p<0.0004). HR increased minimally from 20°C (56 bpm (52, 59) to 32°C (58 bpm (56, 61) (p=0.01). Conclusions The marked changes in acral skin blood flow within TNZ affected the central hemodynamic variables, with the vasodilation reflected in MAP decrease coinciding with an increase in ambient temperature. HR and SV showed minimal changes within TNZ. Support or Funding Information The Research Council of Norway (grant no: 230354) Responses in acral and non-acral skin vasomotion and temperature during lowering of ambient temperatureMElstadLVanggaardAHLossiusLWalløeTK.BergersenJ Therm Biol.4516874

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