Changes In Blood Temperature Research Articles

Origin of temperature changes evoked in the brain by sensory stimulation

Temperature was measured in lateral geniculate nucleus, ventrobasal thalamus and inferior colliculus and at the cerebral arteries which supply these structures in monkeys and cats with chronically implanted thermocouples. Animals were studied when they were conscious and when they were anesthetized, during spontaneously occurring changes in behavior and during the presentation of visual, somesthetic, and auditory stimuli. Parallel low-gain and high-gain recorders allowed absolute temperatures to be determined with an accuracy of 0.05 C and temperature changes of 0.0004 C to be resolved. In confirmation of earlier studies, we found that in behaving animals, large changes in temperature occur in cerebral arterial blood and throughout the brain during feeding, sleeping, and arousal. Brain temperature shifts follow blood temperature shifts. The cerebral arterial blood at the circle of Willis is cooler than the brain. When sensory stimuli are presented, the usual thermal response is a rise in temperature at the cerebral arteries followed by a smaller rise in brain temperature. The changes in cerebral arterial blood temperature following sensory stimulation ranged from 0.003 C to 0.133 C in lightly anesthetized animals. The temperature changes in lateral geniculate, ventrobasal thalamus, or inferior colliculus ranged from 0 to 0.067 C and followed the blood temperature changes by 7 to 71 sec. Changes in brain temperature never occurred without a previous change in blood temperature. Blood temperature responses to sensory stimulation were larger in awake animals and in light anesthesia than in deeply anesthetized animals. Blood temperature rises were associated with peripheral cranial vasoconstriction, suggesting that the initial thermal response to sensory stimulation is peripheral autonomic activity and decreased peripheral heat loss. Other investigators observing brain temperature changes following sensory stimulation did not measure cerebral arterial blood temperature and concluded that the shifts in brain temperature were due to changes in neuronal metabolism or cerebral blood flow. The results of the present study do not support this conclusion. When cerebral arterial blood temperature and brain temperature are monitored simultaneously, it is evident that the changes in brain temperature elicited by sensory stimulation are produced by changes in temperature of the cerebral arterial blood.

Removal of distortion from indicator dilution curves with analog computer.

A method has been developed for characterizing quantitatively, and for removing from indicator dilution curves, the distortion introduced by catheter sampling systems. The method involves a specially constructed cuvette and analog computer analysis of the curves recorded by densitometers placed at the entrance of the catheter and at points downstream. This method of correction of distortion is based on a general theory of function transformation which is applicable to all situations and not upon empirically established constants which are only valid in special situations. The geometry (coiling, bending) of the catheter has been found to affect the distortion. Disruption of the flow pattern by insertion of a braided wire in the lumen causes less variation of the distortion caused by bending and coiling. Distortion was not significantly affected by change in blood temperature in our system.

The use of the thermal dilution principle for measurement of cardiac output in the rat

The thermal dilution principle has been applied to the measurement of cardiac output in small laboratory animals. The circuitry is simple, the components are inexpensive and the performance shows stable, linear characteristics. The volume of injectate need be only 0·05 ml at room temperature (25–27° C). Changes in blood temperature of 0·05°C are easily inscribed as a full scale deflection on a commercial d.c. recorder. Numerous successive determinations of cardiac output may be made with minimal changes in blood volume of the animal. Measurements under controlled conditions did not vary by more than 6 per cent.

Measurement of cardiac output in anaesthetized animals by a thermodilution method.

A method for the determination in anæsthetized dogs of the right and left cardiac outputs has been described; it depends upon accurate and fast recording of the blood temperature changes which occur in the right ventricle and aorta when cold Ringer solution or blood is injected into the inferior vena cava. The curves defining the blood temperature changes are time‐concentration curves, from which the blood flow at the sites of the recording thermocouples can be estimated with an accuracy which is roughly the accuracy of the Fick method. Various errors to which the technique may be subject are considered; attempts have been made to compute their effects quantitatively. The method is here described as the “thermo‐dilution” method.