Measuring Tidal Volume with Diaphragm Movement and Chest Circumference

Abstract

Objective: The movement of the diaphragm plays an important role in respiration. In this study, we proposed and validated a new method for estimating the volume of a single ventilation (representing the tidal volume [VT]) from the vertical distance of diaphragmatic movement and thoracic circumference. Method: Diaphragm excursion (DE) was measured in healthy adult subjects via ultrasound, and the thoracic cavity volume change was estimated based on DE and thoracic circumference. Moreover, we measured the VT obtained by an expiratory gas analyzer and examined the relationships between DE and thoracic volume change (TVC) and between DE and VT. Results: The results showed that a correlation (ρ = 0.609) existed between DE and VT, and an even higher correlation existed between TVC and VT. TVC correlated better with the product of thoracic circumference squared and DE (ρ = 0.839) than with the product of thoracic circumference and DE as an alternative index (ρ = 0.746). Conclusion: Our findings demonstrate that, taking into account body size in addition to DE, changes in thoracic cavity volume are useful predictors of VT and provide an alternative measure for assessing the respiratory function, which will improve clinical and research practice in respiratory care.