In-vitro and in-vivo validation of Cosmed Q-box system

Abstract

Introduction: Whole-body plethysmograpyh is the measurement of intrathoracic gasvolume and volume change. It is an important diagnostic tool in the definition of restrictive lung diseases and of abnormally increased lung volumes in obstructive lung diseases. The usefulness of any diagnostic tool depends on the combination of accuracy, reproducibility and stability. We conducted a validation study of the Cosmed Q-box system including both in-vitro and in-vivo testing.

Methods: Three equal Q-box systems were used in this study. All measurements were done without any added volume, with 20 L and 50 L added volume. Weight was adjusted in software to compensate for added volume.

In-vitro Simulated TGV tests were performed using an Erlenmeyer Flask as described in ERS/ATS Workshop Report, with 5 measurements per device.

In-vivo 15 healthy subjects (3 F/12 M, age 42.5±9.2) performed standard measurements in each of the 3 boxes, in random order.

Results: In-vitro ANOVA testing did not show any significant differences between the 3 devices. Relative difference to the flask volume was -0.49% (±1.23%). Adding extra volume did not differ the results.

In-vivo ANOVA testing did not show any significant differences between the 3 devices, while Intra class correlation showed very good consistency between the 3 devices (ICC of 0.982 for FRC, 0.997 for VC and 0.967 for TLC (all p<0.001)). Coefficient of variation was 3.7% for FRC, 1.7% for VC, 3.9% for TLC. Bland and Altman plots showed no systematic error between devices. Adding extra volume did not differ the results.

Discussion: We found good accuracy, inter-device reproducibility and no significant difference between devices. Devices are interchangeable in clinical or research setting.