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This Article Full Text Full Text (PDF) All Versions of this Article: 93/10/1104    most recent expphysiol.2008.042580v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Lucas, R. A. I. Articles by Ainslie, P. N. PubMed PubMed Citation Articles by Lucas, R. A. I. Articles by Ainslie, P. N. Related Collections Human, Environmental & Exercise

¹ Department of Physiology² School of Physical Education, University of Otago, Dunedin, New Zealand

We tested the hypothesis that older adults, relative to younger adults, would be more prone to critical reductions in cerebral blood flow and oxygenation upon standing during passive heat stress. Six older (70 ± 4 years, mean ± S.D.) and six younger males (29 ± 4 years) were heated (oesophageal temperature raised 0.5°C) in a water-perfused suit. Blood flow velocity in the middle cerebral artery (MCAv), cerebral oxygenation, mean arterial pressure (MAP) and end-tidal partial pressure of carbon dioxide () were measured continuously before and during 3 min standing in each thermal state. At supine normothermic baseline, MCAv was 47% lower in older participants (P < 0.001), whilst MAP and cerebral oxygenation were similar between groups (P > 0.05). Heating lowered the supine MAP more in younger adults, and elevated heart rate only in this group. Upon initial standing in normothermia, older participants had a greater drop in MCAv (P < 0.05 versus young), a lesser drop in MAP (24 and 42% in older and younger participants, respectively), but slower recovery of MAP (27.3 ± 6.8 versus 18.6 ± 4.7 s, mean ± S.D., P = 0.004); heating did not exacerbate any postural responses in either age group. During the last minute of standing, MCAv and were lower in older participants, though age differences were not evident in cerebral oxygenation (normothermic or heated). Thus, independent of heat stress, in addition to lower resting MCAv, there are further age-related reductions in MCAv and slower corrections of MAP following standing. However, these asymptomatic changes seem to represent a physiologically acceptable insult which can be well tolerated in otherwise healthy older participants even during heat stress.

(Received 5 March 2008; accepted after revision 30 May 2008; first published online 30 May 2008)
Corresponding author P. N. Ainslie: Department of Physiology, University of Otago, Dunedin 9054, New Zealand.  Email: philip.ainslie{at}stonebow.otago.ac.nz