Unrestrained acoustic plethysmograph for measuring tidal volume in mice.
Ann Biomed Eng 2006 Sep; 34(9):1494-1499
The traditional method for measurement of tidal volume in unrestrained mice relies on pressure changes induced by a freely respiring animal in a whole body plethysmograph. These changes have been assumed to be the result of thermo-hygrometric differences between respired air and gas within the chamber. It is known, however, that gas compression in the lung can also contribute significantly to changes in plethysmograph pressure. This study describes an acoustic plethysmograph for mice that is capable of measuring the tidal volume time series without the errors associated with the traditional method.The plethysmograph was designed as a resonating cavity at a fixed frequency. It had a sharp resonant peak and was tuned so that changes in body volume produced nearly linear changes in sound amplitude. The plethysmograph was tested with a water filled balloon connected to a syringe pump. The volume of the balloon was varied as a triangle wave with an amplitude of 250 muL. The RMS error between measured and delivered volume was 4.43 muL. A volume step test, performed to assess the response time of the system, showed that the plethysmograph responded in less than one millisecond.
Laboratory-animals; Animals; Animal-studies; Plethysmography; Plethysmographs
Pathology and Physiology Research Branch, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, 1095 Willowdale Road - ms L2101, Morgantown, WV 26505, USA
Annals of Biomedical Engineering