JSIM and CRM are synergistic for modeling breath‐dependent drift when tidal volume is derived from pulmonary airflow measures

In spirometry, pulmonary functions are measured, visualized, and calculated. With each inspiration and expiration, airflow can be measured directly with a pneumotachometer. The volume, V, is then calculated as the integral of flow. Expired volume is typically greater than inspired volume due to warming and humidification, causing ‘breath dependent drift’ of the volume. Some educational spirometry equipment provides two correction options: simply zeroing after every respiratory cycle, or use of volume correction ratios (V = ∫ F dt (inspiring), V = ∫ F/k dt (expiring) where k >1.0). For this study in a physiology lab course, multidisciplinary teams of biology and engineering students used JSIM software to correct the drift. First, a linear regression curve was fit to the drift. The slope was used to calculate a volume correction that was subtracted from the integral of flow. Second, considering that flow should integrate to zero over one breathing period (V = ∫ (F + ΔF) 1 dt) and flow is a periodic signal, a Fourier Series was used to derive a correction. To help frame thinking about mathematical models for theoretical explanations of the drift, a CRM model describing the relationship between conceptual understanding (C), reasoning (R) and the nature and quality of the representation mode (M) was used. JSIM software facilitated CRM as students modeled and processed the pulmonary airflow signal to calculate tidal volumes.