ISSN:
1432-2013
Keywords:
Nasal and lingual blood flow
;
Hypothalamus-temperature regulation
;
Regional vasomotor differentiation
;
Panting
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract 1. Nasal and lingual blood flow were synchronously recorded with respiratory rate and arterial blood pressure in 14 anesthetized spontaneously breathing dogs in which blood temperature was raised by radiant heat. The blood flow responses of the infraorbital and sphenopalatine arteries to increasing heat load were characterized by a continuous increase which resulted from significant decreases in local vascular resistances. The final values during panting exceeded the resting values by 3 times. In contrast, lingual blood flow remained nearly unaffected as long as panting did not occur. With the onset of panting, lingual blood flow increased in close correlation with the increase in respiratory rate. This increase also resulted from a significant decrease in local vascular resistance. 2. The preoptic-anterior hypothalamic region was heated with a water perfused thermode in 10 other dogs at normal (38.4°C) and elevated (39.4°C) blood temperature. Hypothalamic heating at a normal blood temperature induced vasodilatation only in the nasal vessels, while lingual blood flow and respiratory rate were nearly unaffected. However, in animals at an elevated blood temperature hypothalamic heating stimulated the full heat defense response, i.e. a marked increase in both nasal and lingual blood flow associated with polypnea. 3. The results suggest that under normal conditions, in which the dog is breathing with the mouth closed, the graded enhancement of convective heat transfer to the respiratory mucous surfaces of the nose enables a continuous control of evaporative heat loss from these surfaces. During panting, when the dog is breathing with the mouth opened, the additional increase of heat transfer to the surface of the protruded tongue further increases the efficiency of evaporative heat loss. In addition the results confirm the hypothesis that the upper brainstem coordinates the differential patterns of circulatory adjustments in evaporative tissues.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00583710
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