The Dartmouth Acoustic Plethysmograph: a Novel Method for Measuring Breathing in Very Small Animals
As genetic modification of brain respiratory control processes becomes more advanced, there is great interest in measuring breathing and the development of respiratory control in neonatal mice and rats to evaluate the roles of the affected processes. Traditional methods for measuring breathing in animals do not work reliably in small rodents for a number of reasons. Head-out and barometric plethysmographic techniques have been used to measure breathing in small animals but each technique has pitfalls and constraints that limit the utility and/or reliability of the measurements. For example, the barometric technique cannot be used when the animal is tested in hyperthermia, a situation of great interest with regards to the influence of temperature upon respiratory control and its interaction with thermal regulation in newborn animals.
A new approach was proposed recently using measurement of acoustic pressure changes caused by breathing inside a resonating cavity. Dartmouth researchers have further developed this approach by designing calibration and methodological techniques to make respiratory measurements practical in neonatal mice as young as post-natal day 5 (body weight ~3 grams) and later with tidal volumes as small as 15-20 microliters. The Dartmouth improvements include a continuous calibration procedure that does not interfere with the ongoing measurement and assures that accurate volume measurements are obtained throughout the experimental procedures. The calibration uses a measured volume change applied to the acoustic chamber while the animal’s breathing changes are recorded. This serves to continuously account for changes in ambient temperature and humidity and alterations in the composition of the inspired gas, for example, and in other factors that influence the measurement. Additionally, we have developed techniques to set the instrument operating point to minimize contamination by ambient environmental acoustic noise at the frequency of the acoustic measurement. The result of these improvements is an approach that permits reliable respiratory measurements to be easily made in neonatal and developing rodents. Such an approach permits the researcher to more accurately and efficiently evaluate the consequences of genetic and other experimental modifications upon the development of respiratory control processes.
This technology is claimed in a pending patent application. We are seeking an industrial partner interested in its commercialization.
(Ref: J413, J416)
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