Assessment of Thirst

In humans two main techniques have been used to identify the perception of thirst and its alleviation by drinking. The first method is to monitor the volume of drink voluntarily ingested by an individual within an allotted time period and to compare the amount drunk with the volume of fluid required to restore a given water deficit or other imbalance of the body water pools. The other method is to assess the individual's perceived rating of thirst by asking him or her to record on a visual analog scale his or her responses to a series of questions that are thought to relate to the sensation of thirst (Figure 1). The questionnaire technique has the advantages that it allows a series of measurements to be made before, during, and following the period of drinking, and it appears to give an indication of the relative strength of a given stimulus. Although in many studies both methods are used to gauge the sensation of thirst and the responses have been correlated to a number of physiological parameters that are known to influence the drive to drink, it is widely recognized that there is no consistently reliable measure of the thirst sensation.

A more recently introduced technique has been the use of noninvasive methods of imaging to identify the specific regions of the brain that are activated during the genesis and satiation of the thirst response. Different techniques are used to image brain activation. Positron emission tomography and functional magnetic resonance imaging are both being used to visualize brain activation by detecting either temporal changes in blood flow or changes in the chemical composition of regions in the brain that occur when individuals are exposed to specific stimuli. The number of brain regions, their

'How thirsty do you feel now?' (not at all - very thirsty)

'How thirsty do you feel now?' (not at all - very thirsty)

Difference from initial value (0 min) P : <0.05

'How pleasant would it be to drink some water now?' (very unpleasant - very pleasant)

'How pleasant would it be to drink some water now?' (very unpleasant - very pleasant)

'How dry does your mouth feel now?' (not at all - dry)

'How dry does your mouth feel now?' (not at all - dry)

'How would you describe the taste in your mouth?' (normal - very unpleasant)

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