The relationship of vascular anatomy to thermal physiology: linking anatomical and imaging studies to in vivo non‐invasive infrared thermography of free‐ranging birds

Abstract

Vertebrates use the blood vascular system to moderate the temperature of specific anatomical regions. However, in many groups, such as birds, fundamental thermoregulatory mechanisms—the actual link between physiological function (heating and cooling) and the underlying vascular “plumbing”—have largely remained obscure, challenging our understanding of issues ranging from organismal responses to climate change to the human health consequences of vascular disease. In vivo physiological testing typically involves highly invasive procedures that may impose confounding artifacts due to stress responses mediated by the sympathetic nervous system. Fortunately, high‐resolution infrared (IR) thermal imaging provides a non‐invasive means of in vivo physiological measurement of surface temperatures in free‐ranging, normally behaving animals. In our study, thermal imaging was used to document heat maps of freely ranging birds (e.g., vultures, pelicans) in South Carolina and Florida. Quantitative thermographic data were analyzed to assess sites of heat exchange. Thermal data were compared to existing and new anatomical data based on microCT scanning of radio‐opaque (barium‐latex) vascular injections on legally obtained cadaveric bird specimens. Specific regions of the head where vascular devices in birds are suspected to be important for shedding heat as well as for cooling venous blood destined for the brain and eye were analyzed for anatomical and physiological correlations. This study seeks to establish the mechanistic links that ultimately allow birds to manage thermal stressors. Thermal images of investigated sites of thermal exchange indicated heat flow was found to correspond to the location of known blood vessels. These blood vessels were discernable in times of both heating and cooling. For example, in pelicans, the location of the ophthalmic rete corresponds to the location of a cool spot located behind the eye. Blood vessels in the pelican's pouch correspond to a streak of high temperature in the pouch. These results indicate that blood vessels play an active role in the thermophysiology of free‐ranging and unstressed birds and that the details of thermoregulatory mechanisms are discernable with non‐invasive methods.Support or Funding InformationUnited States National Science Foundation (IOB‐0517257, IOS‐1050154), Ohio University Heritage College of Osteopathic Medicine, Ohio University Research Committee, Natural Sciences and Engineering Research Council of Canada, and the National Geographic Society.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.