Selective brain cooling in goats: effects of exercise and dehydration.

M. A. Baker, M. J. Nijland

Research output: Contribution to journalArticle

24 Scopus citations

Abstract

1. Measurements of brain and central blood temperature (Tbr and Tbl), metabolic rate (MR) and respiratory evaporative heat loss (REHL) were made in trained goats walking on a treadmill at 4.8 km h‐1 at treadmill inclines of 0, 5, 10, 15 and 20% when they were fully hydrated and at 0% when they had been deprived of water for 72 h. 2. In hydrated goats, exercise MR increased progressively with increasing treadmill incline. Both Tbl and Tbr rose during exercise, but Tbl always rose more than Tbr, and selective brain cooling (SBC = Tbl ‐ Tbr) increased linearly with Tbl. Significant linear relationships were also present between REHL and Tbl and between SBC and REHL. Neither the slope of the regression relating SBC to Tbl nor the threshold Tbl for onset of SBC was affected by exercise intensity. Manual occlusion of the angularis oculi veins decreased SBC in a walking goat, while occlusion of the facial veins increased SBC. 3. Dehydrated goats had higher levels of Tbl, Tbr and SBC during exercise, but the relationship between SBC and Tbl was the same in hydrated and dehydrated animals. In dehydrated animals, REHL at a given Tbl was lower and SBC was thus maintained at reduced rates of REHL. 4. It is concluded that SBC is a linear function of body core temperature in exercising goats and REHL appears to be a major factor underlying SBC in exercise. The maintenance of SBC in spite of reduced REHL in dehydrated animals could be a consequence of increased vascular resistance in the facial vein and increased flow of cool nasal venous blood into the cranial cavity.

Original languageEnglish (US)
Pages (from-to)679-692
Number of pages14
JournalThe Journal of Physiology
Volume471
Issue number1
DOIs
StatePublished - Nov 1 1993
Externally publishedYes

ASJC Scopus subject areas

  • Physiology

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