Effects of tracheal bypass breathing on heat balance in rabbits.

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Abstract
Effects of obstruction of the air passage through the nose on hypothalamic temperature (Thy) and heat balance were studied in 37 conscious rabbits using a direct calorimeter. Obstruction was made by forcing the animal to breathe through a tracheal bypass cannula at a calorimeter wall temperature (Tw) of either 17, 22, 26 or 28.degree. C. By bypass breathing Thy and sensible heat loss (HL dry) were increased without a significant change in colonic temperature in a warm environment. At Tw 28.degree. C, Thy in bypass breathing was 39.52 .+-. 0.13.degree. C while that in nose breathing was 39.30 .+-. 0.11.degree. C (P < 0.05). HL dry in bypass breathing was 29.3 .+-. 0.8 W .cntdot. m-2 and nose breathing was 24.8 .+-. 0.6 W .cntdot. m-2 (P < 0.01). Evaporative heat loss (HL wet) was not changed by bypass breathing, although respiratory rate increased. Obstruction of air passing through the nose apparently increased hypothalamic temperature and elicited a thermolytic response through increased sensible heat loss in Tw 28.degree. C environment. Heat production (M) was not suppressed by bypass breathing at Tw 28.degree. C, where value of M was minimum (42.0 .+-. 3.0 W .cntdot. m-2). In 17-26.degree. C range of Tw, heat balance was obtained in nose or bypass breathing. At Tw 28.degree. C, M was higher than HL and a positive shift of heat storage was assumed particularly in nose breathing.

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