Physiology of Hot Flashes
Despite their prevalence and impact on women’s lives, the underlying physiology
of hotflashes is not well understood. Leading models of hotflashes point to a
dysregulation of the thermoregulatory system. This system maintains core body
temperature within a“thermoneutral zone” by utilizing heat dissipation (e.g.,
sweating) and heat conservation (e.g., shivering) processes. In women with hot
flashes, there are data indicating that this thermoneutral zone appears to be quite
narrow, with small changes in core body temperature able to trigger dramatic heat
dissipation responses in the form of a hotflash (Freedman 2001 ). However, the
hypothalamic–pituitary–gonadal (HPG) axis is also likely at play. Notably, hot
flashes occur when women are transitioning through menopause, a time marked by
dramatic changes in the HPG axis; suppression of the HPG axis can trigger hot
flashes (Freedman 1998 , 2001 ); and exogenous administration of estrogen can
effectively treat hotflashes (Nelson 2004 ). Finally, other systems linked to hot
flashes include central serotonergic and adrenergic systems (estrogen, serotonin,
and norepinephrine; Freedman 2005 ; Quan et al. 1991 ; Berendsen 2000 ;
Kronenberg 1990 ); hypothalamic, insula, and anterior cingulate activation
(Freedman et al. 2006 ; Freedman 2001 ); peripheral autonomic function (heart rate
variability; Thurston et al. 2010 ,2012a; de Zambotti et al. 2013 ); and vascular
endothelial function (flow-mediated dilation; Thurston et al.2008c; Bechlioulis
et al. 2010 ). Thus, although there is a general understanding of the physiology of
hotflashes, much remains to be learned.
Measuring Hot Flashes
Hotflashes can be measured in several ways, including by self-report and physi-
ologic measures. Self-report measures of hotflashes include questionnaires, diaries
completed at the end of the day or at the time of the hotflashes (paper and
electronic), and electronic event markers on a range of devices typically activated at
the time of the hotflash. Physiologic indices of hotflashes that have been evaluated
includedfinger and core temperature (Tataryn et al. 1981 ), skin bloodflow and
water evaporation (Frödin et al. 1985 ), heart rate and respiratory exchange ratio
(Freedman 2000 ), skin conductance levels (SCL; Tataryn et al. 1981 ; de Bakker
and Everaerd 1996 ; Freedman 1989 ; Hanisch et al. 2007 ; Carpenter et al. 2012 ;
Carpenter et al. 1999 ), and hygrometry (a measure of humidity; Freedman and
Wasson 2007 ). However, SCL sampled sternally has been the most common and
widely used physiologic hotflash measure. Below, we provide a brief overview of
commonly employed self-report and SCL hotflash measurements, including their
respective advantages and challenges.
11 Hot Flashes: Phenomenology and Measurement 235