A symmetric prescribed breathing cycle with fixed shape, shown at half speed. Real inspiratory and expiratory timing varies. No disease, forced breathing or respiratory-control feedback.
Volume settings illustrate arithmetic, not age-specific normal values or breathing instructions. Stroke changes are not medically predictive.
Chest and alveolus are differently enlarged conceptual sections. Their dimensions and particle counts are not anatomical measurements.
The gas-exchange view is an ongoing direction diagram; gas exchange does not switch off every time airflow pauses.
Volume is not flow: The model prescribes V(t) = Vbase + VT(1 − cos φ)/2, with φ advancing through a cycle. Flow Q = dV/dt. VT is the tidal volume moved per breath. Vbase = 2.5 L is an arbitrary display baseline, not a measured residual volume.
How much air per minute?: Minute ventilation = rate × tidal volume. An illustrative 12 breaths/min × 0.5 L gives 6 L/min. Not all inhaled volume reaches exchange surfaces: conducting airways contain anatomical dead space. This model does not calculate alveolar ventilation or oxygen uptake.
Diffusion has its own variables: Gas transfer depends on partial-pressure gradients, area, barrier thickness and gas properties. The exchange arrows teach direction only; their movement is not a molecule-count, diffusion-rate or oxygen-saturation calculation.
What has been checked
Analytical reference cases, conservation or transition invariants, finite drawing commands, bounded setup parsing, discovery and route integrity are checked automatically. These checks do not establish anatomical fidelity, learner outcomes or browser/device compatibility. Independent subject review, learner trials, comprehensive accessibility review and browser video encoding checks remain pending.
Each source supports the associated claim. Sources do not certify this implementation or its visuals.
About the cover illustration
The topic card uses an AI-generated editorial illustration. It introduces the subject; it is not a validated anatomical reference or a measured landscape. The experiment’s diagrams, readouts and assumptions explain the model separately.