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Effects of varying body temperature in whole body

plethysmographySteve Smith

Safety PharmacologyAstraZeneca Pharmaceuticals

April-September 2009

Disclaimer: The contents of this presentation are meant to give an overview of some of the work conducted by Steven Smith during his six month Drexel University co-op

experience at AstraZeneca. The materials presented have not yet been published and as such they have not been peer reviewed.

What is whole body plethysmography at AstraZeneca?• Whole body plethysmography used as a means to

measure respiratory parameters (tidal volume, respiratory rate, etc.) in rats during safety pharmacology studies at AstraZeneca

• Measurements based on pressure deflections within plethysmography chamber (see appendix slides for schematic of system)

• The primary cause of deflections is due to heating and humidification of inspired air by the animal

• The increase in pressure not accurate representation of tidal volume. Thus, correction factors employed

• Two methods to calculating correction factors: Drorbaugh & Fenn or Epstein & Epstein

Drorbaugh & Fenn vs Epstein and Epstein

• Both methods utilize environmental factors such as ambient temperature/humidity, pressure, and animal’s body temperature to calculate correction factor

• Principle difference =>Epstein & Epstein incorporates a nasal temperature correction factor into equation

• Supporting evidence that one method is more valid over the other

– Epstein et al. (1980)

– Fleming et al. (1983)

– Jacky (1980)

– Stahel and Nicol (1988)

– Stephenson and Gucciardi (2002)

Purpose of the Study

• During plethysmography studies, animal’s body temperature is sometimes assumed to remain 37.5 C.

• Deviations from this default temperature theoretically produce changes in tidal volume using either method

• How much would a deviation from the “default” value of 37.5 C affect the tidal volume (and thus the minute volume) calculations?

Methods• Orally administered compounds known to affect

either body temperature, tidal volume, or both.

• For this presentation, focus is on baclofen, known to affect both temperature and respiration

• Recorded respiratory changes in WBP using default body temperature

• Retroactively replaced default body temperatures in WBP software with “actual” body temps (temps recorded simultaneously with DSI telemetry)

• The corrected body temps allowed comparison of tidal/minute volume using both approaches to correction factor calculation

Study Design

• 8 telemetered male Han Wistar rats used in the study

• 1 hour acclimation period beginning at approximately the same time everyday (8:55 AM +/- 10 minutes)

• A 30 min. baseline period preceded dosing

• On each experimental day, 2 animals each received either vehicle (water), 3 mg/kg, 10 mg/kg or 30 mg/kg.

• Body temperature, tidal volume, minute volume and respiratory rate were sampled for a 30 minute baseline pre-dose period and at 30 minute intervals for 4 hours post dose on each experimental day.

• Animals crossed over (4 study days per compound) with at least 72 hours between doses

Body temperatures

Respiratory rate dose response

Tidal volume dose response

Tidal volume dose response as percent baseline

Minute volume dose response

Minute volume dose response as percent baseline

Percent difference of methods

Correlation between ΔT from 37.5 C and % difference in methods

D&F y=(14.4 ± 1.1) x+(5.1 ± 0.5) r2=0.83

E&E y=(11.5 ± 1) x + (3.8 ± 0.4) r2 =0.80

D&F y=(8.7 ± 0.8) x+(3.0 ± 0.3) r2=0. 78

E&E y=(10.4 ± 0.9) x + (3.7 ± 0.4) r2 =0.79

Conclusions

• Cannot assume body temps do not change over time or treatment

• Statistical significance of minute volume varies depending on body temperature used

• Respiratory measurements dependent on accuracy of temp for most valid result

Acknowledgments

Thank you to Maneesha Altekar, Herb Barthlow, Russ Bialecki,

Bob Caccese, Pam Campbell, Tish Cheatham, Dave Lengel, Dennis Litwin, Frank McGrath, Jen

Stevenson, and Andy Zuvich.

ReferencesEpstein, M.A.F. and R.A. Epstein. A theoretical analysis of the barometric method for measurement of tidal volume. Respir. Physiol. 32: 105-120, 1978.

Fleming, P.J., M.R.Levine, A.L.Goncalves and S. Woollard. Barometric plethysmograph: advantages and limitations in recording infant respiration. J.Appl.Physiol. 66(6): 1924-1931, 1983.

Jacky, J.P. Barometric measurement of tidal volume: effects of pattern and nasal temperature. J.Appl.Physiol. 49(2): 319-325, 1983.

Stahel, C.D. and S.C. Nicol. Comparison of barometric and pneumotachographic measurements of resting ventilation in the little penguin. Comp. Biochem. Physiol. 89a(3):387-390, 1988.

Stephenson, R. and E.J.Gucciardi. Theoretical and practical considerations in the application of whole body plethysmography to sleep research. Eur. J. Appl. Physiol. 87:207-219, 2002

Additional Slides/Appendix

Schematic of whole body plethysmography system

Vacuum

Compressed air flowing through chamber at constant rate

SMALL pressure deflections

Vacuum

Temperature/Humidity

EMMS Software

Vacuum

Correlation between ΔT from 37.5 C and % difference in methods-with variability

D&F y=(14.4 ± 1.1) x+(5.1 ± 0.5) r2=0.83

E&E y=(11.5 ± 1) x + (3.8 ± 0.4) r2 =0.80

D&F y=(8.7 ± 0.8) x+(3.0 ± 0.3) r2=0. 78

E&E y=(10.4 ± 0.9) x + (3.7 ± 0.4) r2 =0.79

Contact information:sbs34@drexel.edu