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Comparison of Respiratory Gated Micro-CT in Mechanically Ventilated and Free-Breathing Rats


N Ford

NL Ford1*, LA McCaig2, JF Lewis2, RA Veldhuizen2, DW Holdsworth2, M Drangova2, (1) University of British Columbia, VANCOUVER, BC, (2) University of Western Ontario, LONDON, ON

SU-C-218-4 Sunday 1:30:00 PM - 2:15:00 PM Room: 218

Purpose:
Lung imaging in preclinical studies can be performed using respiratory-gated micro-computed tomography in mechanically ventilated or free-breathing rodents. In this study, we aim to quantify the differences in lung metrics measured in free-breathing and mechanically ventilated rodents.

Methods:
Male sprague-dawley rats were anaesthetized with ketamine/xylazine and scanned with a retrospective respiratory gating protocol on a GE Locus Ultra micro-CT scanner (80 kVp, 50 mA, 50 s, 0.28 Gy entrance dose). The rats were free-breathing and scanned while externally monitoring the respiration. Each animal was intubated and mechanically ventilated (MV) at 56 bpm, 8 mL/kg and PEEP of 5 cm water and rescanned. Images were reconstructed representing peak inspiration and end expiration with 0.15 mm isotropic voxel spacing. Quantitative image-based measurements of lung volume and air content were used to calculate the functional residual capacity (FRC) and tidal volume. Measured and calculated values were compared (paired t-tests).

Results:
Qualitatively, the images acquired during mechanical ventilation appeared darker in the airspaces and the airways appeared larger. Our image-based measurements showed an increase in lung volume and air content during mechanical ventilation for both respiratory phases (Free 6.9 mL and MV 12.8 mL for peak inspiration and Free 5.6 mL and MV 10.5 mL at end expiration). Comparisons of the functional metrics showed an increase in both FRC and tidal volumes of mechanically ventilated rats (FRC of 3.2 mL for Free and 8.4 mL for MV, tidal volume of 2.7 mL/kg for Free and 6.1 mL/kg for MV).

Conclusions:
Although mechanical ventilation may be useful in promoting consistent respiratory patterns, the amount of air in the lungs is higher than in free-breathing animals. Care should be taken in planning respiratory research to ensure that overinflating the lungs during mechanical ventilation will not compromise the desired measurements or free-breathing animals should be used.

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