Relationships between Parameters of the Cardiovascular System, Salivary Lactoferrin Level and Body Temperature during a Short-Term Human Whole-Body Exposure to Cold Air

Abstract

Background: The problem of maintaining body temperature in people working outdoors in the cold air of the Arctic remains relevant. The purpose of this study was to determine the autonomic nervous mechanisms of regulation of heart rate (HR), blood pressure (BP) and local immunity on the example of the dynamics of salivary lactoferrin during a decrease in body temperature in humans (the core and the skin of hands) during and after a short-term, whole-body exposure to cold air. Materials and Methods: A total of 15 healthy Russian male volunteers aged between18 and 20 years, born and living in Arkhangelsk, were examined in the winter. Research stages: the registration of indicators before exposure to the cold air (Stage 1), during the 10-minute exposure to the cold air at-20 °C (Stage 2) and after the 10-minute exposure to the cold air (Stage 3). The registration of indicators in Stages 1 and 3 was carried out indoors at an air temperature of +20 °C. HR (bpm), the heart rate variability (HRV) parameters, systolic and diastolic blood pressure (BPsyst, BPdiast, mm Hg), salivary lactoferrin level (ng/ml) by ELISA and the body temperature in the ear canal (Tear, °C) and on the skin of the dorsum of the right hand (Tskin, °C) were determined at each stage of the study. Results: In Stage 2 with significantly decreased Tear and Tskin, compared to the initial indicators in Stage 1, there was a significant increase in HRV indices reflecting the overall HRV and vagal effects on the heart rhythm. At the same time, HR was significantly decreased, as well as stress index. An increase in the total power (TP) of the HRV spectrum was revealed due to a predominant increase in HF and VLF, and to a lesser degree in LF. Both BPsyst and BPdiast significantly increased. After cooling in Stage 3, HR increased, but remained significantly lower than the initial values. The overall HRV according to SDNN and TP decreased, reaching baseline values. Concentrations of salivary lactoferrin during cooling in Stage 2 tended to increase, which was also maintained in Step 3 after cooling. Correlation analysis in the entire sample (n=15) revealed a positive correlation between SDNN and Tear in Stage 2 (r s =0.56, P=0.035). In Stage 2, the change in Tskin was significantly correlated with the salivary lactoferrin level (r s =-0.73, P=0.003); this relationship was also found in Stage 3 (r s =-0.65, P=0.015). Conclusion: The successful return of body temperature after general cooling occurs under the condition of increasing the overall HRV, enhancing vagal influences on the heart rhythm, HF and VLF components of HRV during cooling. An increase in the level of salivary lactoferrin, while maintaining vagal reserves of the vegetative regulation of heart rhythm against a decrease in skin temperature during general cooling, as well as a decrease in the level of lactoferrin against the background of recovery of body temperature after cooling, at least 10 minutes, can be regarded as an adaptive response of the body to exposure to cold temperature with minimal ri...