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Respiratory frequency of mice at rest and after exercise
Ajit Kale*, Stephanie Praster, Wade Thomas*, Ivo Amende, and Thomas G. Hampton;
Mouse Specifics, Inc. and *The CuraVita Corporation, Boston, MA.
Web published: March 1, 2002
Abstract
Conventional methods for characterizing respiratory function in mice require restraint, anesthetic, or surgery. We developed a rapid non-invasive screening system comprising of custom-designed housing, a digital capture device, and time-domain and frequency-domain software for monitoring and measuring respiratory frequency in conscious mice. With a growing interest in mouse models for evaluating the effects of environmental toxins1 and exploring cytokine involvement in asthma2 and genes affecting cystic fibrosis3,4, the method we describe should accelerate identification of genes and drugs important to respiratory health.
Methods
Figure 1.One gray-scale image from movie of rib-cage displacement in mouse.
Figure 2.Breathing pattern in conscious mouse at rest.
Male C3H/He (n=4, age 24 weeks) were obtained from The Jackson Laboratory. Imaging was performed in a custom-built mouse enclosure with a high-speed digital capture device to monitor rib-cage displacement coincident with breathing. Mice were exercised and gait dynamics monitored using the The CuraVitaTM Gait Imaging system. Neither restraint nor anesthetic was required. Baseline recordings were performed after the mice walked at 20 cm/s for 2 min. Treadmill speed was increased to 35 cm/s for 2 min. Recordings were immediately repeated. e-MOUSETM peak detection algorithms were used to interpret the signals.5
Results
Effects of Exercise.
Rest (n=4)
Exercise (n=4)
Breath frequency (bpm)
216 ± 19
291 ± 23*
Stride frequency (strides/min)
182 ± 18
294 ± 21*
*P<0.05 via Student's 2-tail paired t-test.
Discussion
We show that breathing frequency in C3H/He male mice is approximately 220 bpm after slow walking, and increases about 40% after exercise. Respiratory frequency may be strain and gender dependent, with smaller lung size possibly requiring a faster respiratory rate.6 Respiratory frequency in mice has been shown to be altered by gene expression7, environmental toxins1, and administration of drugs8. Exercise tests for mice are being increasingly utilized to investigate cardiopulmonary, metabolic, and skeletal muscle function. Yet, clear physiological end-points for submaximal and maximal exercise are not well defined. The baseline values we recorded non-invasively are in agreement with data measured with invasive systems.6 Interestingly, these early data seem to indicate that breathing frequency has a correlation with stride frequency, an observation consistent with galloping ponies9, but not running humans.10 A greater reliance on breathing frequency to maintain minute ventilation when the upper limbs are actively loaded during exercise may contribute to these phenomena.11
References
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