Validity of thoracic respiratory inductive plethysmography in high body mass index subjects

•Respiratory inductive plethysmography was evaluated in high BMI subjects.•A non-negligible negative bias was linked with increased BMI values.•Vt values determined by RIP are slightly lowered by increase of ribcage perimeter.•Lowering of Vt values obtained by RIP is partially due to viscoelasticity of fat tissue.

We aim to evaluate thoracic respiratory inductive plethysmography (RIP) in high body mass index (BMI) subjects with a pneumotachometer (PT) as a reference. We simultaneously evaluated spontaneous breathing by RIP and PT in 10 low and 10 high BMI subjects at rest and in moderate exercise. We then recorded RIP amplitude with different excursions mimicking respiratory thoracic deformation, with different sizes of RIP belts surrounding cylinders of different perimeters with or without deformable foam simulating adipose tissue. RIP responses correlated with PT values in low and high BMI groups for inspiratory time (r = 0.86 and r = 0.91, respectively), expiratory time (r = 0.96 and r = 0.91, respectively) and amplitude (r = 0.82 for both) but with a bias (−0.23 ± 0.25 L) for high BMI subjects. ANOVA revealed the effects of perimeter and simulated adiposity (p < 0.001 for both). We concluded that thoracic perimeter and deformity of adipose tissue are responsible for biases in RIP response in high BMI subjects.