title: The ability of the skin to absorb heat; the effect of repeated exposure and age.
abstract: BACKGROUND
  When heat is applied to the skin, it is dissipated due to conductive heat flow in the tissue and the blood. While heat flow has been studied after applying a single heat exposure, the physiology of repeated exposures to local heat has not been well investigated.
  
  
  METHODS
  Twenty male and female subjects in the age range of 20-65 years old participated in a series of experiments during which a thermode was placed on their leg above the quadriceps muscle for 20 minutes, and on 3 sequential days, to see the effect of repeated local heat on skin blood flow, skin temperature, and on caloric transfer from a thermode used to raise skin temperature.
  
  
  RESULTS
  The results of the experiment showed that, for young subjects, to raise skin temperature to 40 degrees C required more than double the calories required in older subjects. Further, in the younger subjects, the blood flow response in the first 20 minutes of heat exposure was over 30% higher than that seen in the older subjects. However, on the 2nd and 3rd day, the blood flow response of the younger subjects, was not significantly different between day 2 and 3, but was significantly less than day 1. There was no statistical difference in the blood flow response between day 1, 2 and 3 in the older subjects. In the younger subjects, in the 2 and 3rd day, the number of calories needed to warm the skin was also significantly less than that seen in the first day.
  
  
  CONCLUSIONS
  In younger subjects but not older subjects, there appears to be some degree of acclimatization with an enhanced blood flow response in the first day that was protective to the skin which was not seen in repeated heat exposure.
authors.affiliation: Department of Physical Therapy, Loma Linda University, Loma Linda, CA 92350, USA. jpetrofsky@llu.edu
authors.forename: Jerrold
authors.initials: J
authors.lastname: Petrofsky
authors.forename: Neha
authors.initials: N
authors.lastname: Goraksh
authors.forename: Faris
authors.initials: F
authors.lastname: Alshammari
authors.forename: Mitali
authors.initials: M
authors.lastname: Mohanan
authors.forename: Janhavi
authors.initials: J
authors.lastname: Soni
authors.forename: Moxi
authors.initials: M
authors.lastname: Trivedi
authors.forename: Haneul
authors.initials: H
authors.lastname: Lee
authors.forename: Akshay N
authors.initials: AN
authors.lastname: Hudlikar
authors.forename: Chia-hao
authors.initials: CH
authors.lastname: Yang
authors.forename: Brindha
authors.initials: B
authors.lastname: Agilan
authors.forename: Nikhila
authors.initials: N
authors.lastname: Pai
authors.forename: Tirupathi
authors.initials: T
authors.lastname: Chindam
authors.forename: Vengatesh
authors.initials: V
authors.lastname: Murugesan
authors.forename: Jong
authors.initials: J
authors.lastname: Eun Yim
authors.forename: Vahishta
authors.initials: V
authors.lastname: Katrak
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000328:Adult; D000367:Age Factors; D000704:Analysis of Variance; D005260:Female; D006358:Hot Temperature; D006801:Humans; D008297:Male; D008875:Middle Aged; D012039:Regional Blood Flow / Q000502:physiology*; D012867:Skin / Q000098:blood supply*; D012879:Skin Physiological Phenomena