Cold-induced Vasodilation in Humans

Cold-induced vasodilation (CIVD) is a peripheral thermoregulatory response characterized by cyclical increases in blood flow to the extremities during cold exposure. Although CIVD has been studied for nearly a century, its underlying mechanisms, sources of inter-individual variability, and functional relevance for performance and injury prevention are not completely understood. This dissertation advances the scientific understanding of CIVD through a comprehensive and integrative approach that combines controlled experimental studies, a clinical case report, and the first meta-analysis of the CIVD literature. Across a series of experimental investigations, this work demonstrates that CIVD is not impaired by repeated intraday cold-water immersions of the hand, suggesting resilience of the response in operational and occupational settings where repeated cold exposure is common. When anthropometric variables were carefully controlled, body dimensions, particularly surface-to-mass ratio and hand and finger morphology, emerged as primary determinants of CIVD characteristics, whereas sex alone exerted minimal influence. These findings highlight the importance of an anthropometric matched study group when evaluating sex differences in CIVD. This dissertation further establishes CIVD as a functionally meaningful response. Stronger CIVD and faster rewarming were associated with improved preservation and restoration of manual dexterity and tactile sensitivity following cold exposure. The rewarming phase, which has often been neglected in prior studies, provided valuable insight into peripheral vascular recovery and sensorimotor function. A case study of a U.S. Marine who sustained second-degree frostbite revealed a delayed CIVD response following injury, suggesting that altered vasomotor control may persist after cold injury and potentially increase susceptibility to future damage. These findings emphasize the need for further longitudinal research in cold-injured populations. The accompanying meta-analysis synthesizes data from 80 studies spanning more than three decades and demonstrates that CIVD timing and magnitude are influenced by environmental (e.g., water and air temperature), procedural (e.g., immersion depth, prewarming), and personal factors (e.g., body size, age, sex, ethnicity, and acclimatization). Finger temperature responses were found to be strongly dependent on water temperature. Evidence from the narrative synthesis suggests that CIVD may be mediated by impaired noradrenaline transmission at arterio-venous anastomoses or nitric oxide-related mechanisms, although further mechanistic studies are required. The review also highlights the underrepresentation of women and older adults in CIVD research and calls for more inclusive future investigations. Finally, this dissertation proposes a standardized operating procedure (SOP) for CIVD assessment, developed through systematic evaluation of the existing literature. This SOP provides guidance on participant preparation, instrumentation, immersion protocols, outcome definitions, and recovery measurements, thereby enhancing methodological consistency, reproducibility, and cross-study comparability. In summary, this dissertation demonstrates that CIVD is a multifaceted physiological response governed by the interaction of local vascular control, systemic thermoregulation, and individual morphology. By clarifying the physiological, functional, and methodological determinants of CIVD, this work provides a foundation for improved assessment of cold tolerance, performance, and injury risk in military, occupational, and environmental contexts.