This question is quite an important one for two reasons. First, there is a substantial difference in weight between the obese subjects vs. the lean control group. For instance, obese mice can weigh 50g or more, while their age-matched control group can typically weigh 30g. While there is this significant difference in the weight between both groups, there may not be a large difference in the actual size of the subjects’ lungs.
A recent study performed by Dr. Guivarchis et al.¹, highlights the harmful effects of ventilating obese subjects with a tidal volume based on actual weight vs ideal weight using the flexiVent system. In this study, the effects of two hours of mechanical ventilation in a diet-induced obese mice model, with tidal volume calculated on either the actual body weight or the ideal body weight (based on the mean weight of control mice) were demonstrated. Their findings indicate that in comparison to lean control subjects, mechanically ventilating obese subjects with a tidal volume based on actual body weight is harmful.
They observed a noticeable variation in lung mechanics and associated lung inflammation in obese mice ventilated with a tidal volume based on actual body weight. In contrast, obese mice ventilated with a tidal volume calculated using the ideal body weight had lung mechanics and inflammation parameters close to the lean control group.
Therefore, when studies involve the assessment of obese mice, SCIREQ recommends entering the average weight of the lean control group rather than using the actual weight of the obese subjects.
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