Impact of whole body passive heat stress and arterial shear rate modification on radial artery function in young men

Abstract

We sought to determine how whole-body heating acutely influences radial artery function, characterized using flow mediated dilation (FMD) and low-flow mediated constriction (L-FMC), and the mechanistic role of shear rate modification on radial artery functional characteristics during heating. Eleven young healthy men underwent whole-body heating (water-perfused suit) sufficient to raise core temperature +1°C. Trials were repeated with (Heat+WC) and without (Heat) the application of a wrist cuff located distal to the radial artery examined, known to prevent increases in mean and anterograde shear rate but increase retrograde shear. Radial artery characteristics were assessed throughout each trial, with FMD and L-FMC assessed prior to and upon reaching the target core temperature. Heat markedly increased radial artery mean and anterograde shear rate, along with radial artery diameter and blood flow (P<0.05). Heat+WC abolished the heat-induced increase mean and anterograde shear rate (P>0.05), but markedly increased retrograde shear (P<0.05). Concomitantly, increases in radial artery diameter and blood flow were decreased (Heat+WC vs Heat,P<0.05). Heat attenuated FMD (8.6±1.2 vs. 2.2±1.4%, P<0.05), whereas no change in FMD was observed in Heat+WC (7.8±1.2 vs. 10.8±1.2%,P>0.05). In contrast, L-FMC was not different in either trial (P>0.05). In summary, acute whole-body heating markedly elevates radial artery shear rate, diameter and blood flow, and diminishes FMD. However, marked radial artery vasodilation and diminished FMD are absent when these shear rate changes are prevented. Shear rate modifications underpinthe radial artery response to acute whole-body heat-stress, but further endothelial-dependent vasodilation (FMD) is attenuated likely as the vasodilatory range limit is approached.

Impact of acute dynamic exercise and arterial shear rate modification on radial artery low-flow mediated constriction in young men

“…We have previously observed that L-FMC is enhanced immediately (~ 10 min) following a bout of acute dynamic exercise (Elliott et al 2018 ), but it is not known whether this is attributable to an acute enhancement of endothelial function, secondary to changes in the pattern of shear stress (Dawson et al 2012 ). Although we have previously observed that whole-body heating elevated radial artery shear rate, diameter, and blood flow but did not significantly change L-FMC (Alali et al 2020 ). Notably, dynamic exercise with a large muscle mass acutely decreases the conduit artery FMD response for ~ 1 h, although this is not universally observed (Dawson et al 2013 ; Elliott et al 2018 ).…”

“…This may explain the acutely increased radial L-FMC in the immediate post-exercise period (Elliott et al 2018 ). Interestingly, acute whole-body heat stress was also observed to increase radial artery diameter, blood flow and anterograde SR during, however, no significant change in L-FMC was noted (Alali et al 2020 ). However, there are important differences in the hemodynamic, thermoregulatory, and cellular signalling responses to acute exercise and whole-body heating (Cullen et al 2020 ) that may explain the divergent L-FMC results.…”

“…Responses of L-FMC and FMD are presented as relative (%) and absolute (mm). Total vessel reactivity (TVR, %) was calculated using the following equation (Alali et al 2020 ): …”

“…The shear rate area under the curve (SR auc ) and time to peak diameter was calculated from cuff release up to the point of maximum artery dilation. A simple ratio normalization of L-FMC against change in mean SR (difference between baseline SR and SR during L-FMC measurement period; L-FMC-to-∆mean SR ratio, au) and ratio of FMD against SR auc (FMD-to-SR auc ratio, au) were calculated to evaluate role of shear stress in mediating constriction and dilation (Padilla et al 2008 ; Alali et al 2020 ).…”

“…Like FMD, L-FMC is impaired in individuals with cardiovascular disease risk factors and is suggested to provide information that is complimentary to that provided by FMD (Gori et al 2008 , 2012 ). However, while the influence of acute environmental (e.g., heat, hypoxia) and physiological (e.g., exercise, mental stress) stimuli on FMD has been widely studied (Dawson et al 2012 ; Vianna et al 2014 ; Tremblay et al 2019 ; Crandall and Wilson 2011 ), limited work has investigated how such interventions effect L-FMC and the underlying mechanisms (Alali et al 2020 ).…”