The Clamping of End-Tidal Carbon Dioxide Does Not Influence Cognitive Function Performance During Moderate Hyperthermia With or Without Skin Temperature Manipulation

• Published in: Frontiers in psychology Vol. 12; p. 788027
• Main Authors: Schultz Martins, Ricardo, Wallace, Phillip J, Steele, Scott W, Scott, Jake S, Taber, Michael J, Hartley, Geoffrey L, Cheung, Stephen S
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Media S.A 22.12.2021
• Subjects: clamping; cognitive function; end-tidal carbon dioxide; isocapnia; middle cerebral artery velocity; passive hyperthermia; Psychology; cognitive function; working memory; passive hyperthermia; clamping; middle cerebral artery velocity; end-tidal carbon dioxide; isocapnia; executive function
• ISSN: 1664-1078; 1664-1078
• DOI: 10.3389/fpsyg.2021.788027

Increases in body temperature from heat stress (i.e., hyperthermia) generally impairs cognitive function across a range of domains and complexities, but the relative contribution from skin versus core temperature changes remains unclear. Hyperthermia also elicits a hyperventilatory response that decreases the partial pressure of end-tidal carbon dioxide (P CO ) and subsequently cerebral blood flow that may influence cognitive function. We studied the role of skin and core temperature along with P CO on cognitive function across a range of domains. Eleven males completed a randomized, single-blinded protocol consisting of poikilocapnia (POIKI, no P CO control) or isocapnia (ISO, P CO maintained at baseline levels) during passive heating using a water-perfused suit (water temperature ~ 49°C) while middle cerebral artery velocity (MCA ) was measured continuously as an index of cerebral blood flow. Cognitive testing was completed at baseline, neutral core-hot skin (37.0 ± 0.2°C-37.4 ± 0.3°C), hot core-hot skin (38.6 ± 0.3°C-38.7 ± 0.2°C), and hot core-cooled skin (38.5 ± 0.3°C-34.7 ± 0.6°C). The cognitive test battery consisted of a detection task (psychomotor processing), 2-back task (working memory), set-shifting and Groton Maze Learning Task (executive function). At hot core-hot skin, poikilocapnia led to significant (both  < 0.05) decreases in P CO (∆-21%) and MCA (∆-26%) from baseline, while isocapnia clamped P CO (∆ + 4% from baseline) leading to a significantly (  = 0.023) higher MCA (∆-18% from baseline) compared to poikilocapnia. There were no significant differences in errors made on any task (all  > 0.05) irrespective of skin temperature or P CO manipulation. We conclude that neither skin temperature nor P CO maintenance significantly alter cognitive function during passive hyperthermia.