What you will do: breathe in with both lungs, make the scarring worse with the slider and see how the air you can take in shrinks. In pulmonary fibrosis the lung tissue is scarred and stiff, so the lungs cannot stretch. Done in about 30 minutes: finish the 7-step mission below.
Mission progress: 0 / 7
3D model: Z-Anatomy (CC BY-SA 4.0), based on BodyParts3D © The Database Center for Life Science (CC BY-SA 2.1 Japan); bronchial tree from the Human Reference Atlas (HuBMAP, NIH; CC BY 4.0). Simplified by SciSim. The scarring, color change and shrinking of the fibrotic lungs are made in your browser to show the idea: this is an illustration, not a patient scan.
Task: run the test for a healthy person, for pulmonary fibrosis (restrictive) and for asthma/COPD (obstructive) and press Record each time. Done when the table holds all three kinds. In spirometry you breathe in as far as you can, then blow out as hard and as long as you can into a tube. The machine records the volume of air.
Answer the prediction first.
| # | Lungs | Severity | TLC (L) | FVC (L) | FEV₁ (L) | FEV₁/FVC | FVC, % of normal | Pattern |
|---|
No runs yet. Press Run the test, then Record this run.
Read the graph: the plateau is the biggest volume. In restriction (fibrosis) the volumes are small, but the air still leaves fast, so FEV₁/FVC is normal or high (about 0.80–0.90). In obstruction (asthma/COPD) the air leaves slowly, FEV₁/FVC is below about 0.70, and the lungs trap air (residual volume goes up). Shapes are simplified; values are typical, not a diagnosis. In real patients the ratio is often 0.80–0.90 and does not rise smoothly with severity: the slider draws a small rise only to show the idea (stiff lungs recoil strongly, so the small amount of air leaves fast).
Task: watch oxygen cross the wall between the air and the blood. Predict, then let the scar tissue build up. Done when you have run the animation once and set the exercise slider to hard exercise. The picture is a simplified drawing; the wall is drawn much thicker than real (0.5 µm is far too thin to see).
Answer the prediction first.
| Wall thickness | 0.5 µm (normal) |
|---|---|
| Gas transfer (relative) | 100% of normal |
| Blood passes in | 0.75 s |
| Blood oxygen saturation, healthy | 97% |
| Blood oxygen saturation, fibrosis | 97% |
Fick’s law (the idea): the rate of diffusion is about (area × pressure difference) ÷ wall thickness. A thicker wall and fewer working air sacs mean slower oxygen transfer. At rest the blood spends about 0.75 s in the capillary and there is time; in hard exercise it passes in about 0.25 s, so a scarred lung runs out of time. Saturation values come from a simple illustrative model (not a patient measurement).
Task: inflate both lungs with the pressure slider and compare. Done when you have measured how much pressure +1 liter needs for healthy lungs and for fibrosis (set the severity above 0). Compliance C = ΔV ÷ ΔP tells how easily a lung stretches: a thin balloon has high compliance, a stiff rubber ball low compliance.
Answer the prediction first.
| Healthy | Fibrosis | |
| Volume at this pressure | 2.3 L | 2.3 L |
| Added above resting volume | 0.0 L | 0.0 L |
| Pressure for +1 L | 4.1 cmH₂O | 4.1 cmH₂O |
| Compliance C | 0.20 | 0.20 |
C in liters per cmH₂O, measured near normal breathing.
Why it matters: stiff lungs need much more effort (a bigger pressure change by the breathing muscles) for the same breath, so the person breathes in small, quick breaths. Healthy C ≈ 0.20 L/cmH₂O in this model; at severity 50 it is about 0.11 and at severity 80 about 0.07. Real values vary between people and the curve is simplified.
Task: doctors use a six-minute walk test. In this simplified version six minutes pass in about 30 seconds. Done when both walkers have finished one test at a brisk pace with a severity above 0. The numbers are illustrative, not real patient data.
Answer the prediction first.
| Healthy | Fibrosis | |
| Time | 0:00 of 6:00 | |
| Distance | 0 m | 0 m |
| Breaths per minute | 12 | 12 |
| Blood oxygen (SpO₂) | 97% | 97% |
| Lowest SpO₂ | – | – |
Remember: in clinics a fall to 88% or below on exertion is a recognized warning sign (it is often used when deciding about oxygen treatment). People with fibrosis may have a normal oxygen level at rest and drop only when they move. A pulse oximeter on a finger measures SpO₂. This is a teaching model, not a medical test.
Blow into a new balloon: the first puff is hard, then it stretches and gets easy. Now try a thick, stiff rubber ball with the same effort: hardly any air goes in. Healthy lungs are like the stretchy balloon, with thin walls that give way easily. In pulmonary fibrosis (fibro- = scar tissue) scar tissue builds up in the lung around the tiny air sacs. The lung becomes thick and stiff, like the ball, so less air goes in with each breath, and the scars do not go away.
A calm breath moves the tidal volume (about 0.5 L in a healthy adult). The biggest breath you can blow out after the deepest breath in is the vital capacity; when it is blown out hard it is called the forced vital capacity (FVC), about 4.6 L. Some air always stays in the lungs, the residual volume (RV), about 1.2 L. Together they make the total lung capacity (TLC) ≈ 5.8 L. FEV₁ is the volume blown out in the first second (about 3.7 L), and the ratio FEV₁/FVC (about 0.80) tells how fast the air leaves.
These are approximate values for a healthy adult; they change with sex, age and height. In this simulator, moderate fibrosis (severity 50) gives FVC ≈ 2.8 L (60% of normal) and TLC ≈ 3.9 L. In one maximal breath the lungs take in 2.1 L instead of 3.5 L.
Stiff lungs. Compliance C = ΔV ÷ ΔP falls from about 0.20 to about 0.11 L per cmH₂O. Each liter needs more pressure, so each breath is smaller (0.42 L instead of 0.50 L) and the breathing rate rises (20 instead of 12 per minute). Thick wall. The wall between air and blood grows from about 0.5 µm to about 1.5 µm, and by Fick’s law the diffusion rate is about (area × pressure difference) ÷ thickness, so oxygen crosses more slowly. In exercise blood rushes past quicker, and the oxygen level in the blood can fall. Open airways. The tubes are not blocked, so the small amount of air leaves quickly: FEV₁/FVC stays normal or even rises (0.85). This is the key difference from asthma and COPD, where narrowed airways slow the air down and FEV₁/FVC falls below about 0.70.
Pulmonary fibrosis (PF) is scarring of the lung tissue: too much collagen builds up in the interstitium, the thin tissue around the alveoli. The walls get thick and stiff, and the scarring is irreversible. Idiopathic pulmonary fibrosis (IPF) is the common form with no known cause; it mostly affects older adults.
A dry, long-lasting cough and shortness of breath, first with effort, then even at rest; fast, shallow breathing; tiredness; in some people, rounded, widened fingertips (clubbing). Crackling sounds in the lungs can be heard with a stethoscope.
A doctor listens to the chest and asks about work, medicines and family; then spirometry (FVC, FEV₁), a gas-transfer test (DLCO), an oxygen level (pulse oximeter, walk test) and a high-resolution CT scan of the chest.
Antifibrotic medicines (pirfenidone, nintedanib) can slow the loss of lung function; they do not reverse the scarring. Other parts of care: oxygen therapy when needed, pulmonary rehabilitation (exercise and breathing training), vaccinations, treating the cause if one is found, and lung transplant for some selected patients.
Educational, not medical advice. This page is a simplified model for learning. Anyone with a long-lasting cough or breathlessness should talk to a doctor or nurse.
Pulmonary fibrosis scars the tissue around the alveoli, the air sacs at the very end of the airways. Know where they are first. Pick Basic (6 labels) or Advanced (10). Switch between the labeled diagram, a blank one, a label quiz and match the jobs. Score 70% or more in the label quiz to finish mission step 6. On a phone, swipe the diagram sideways.
Tap a word, then tap the numbered box it belongs to (on the diagram or in the list below). Tap a filled box to take the word back.
Each line describes the job of one part. Tap a part name, then tap the box next to the job it does. Tap a filled box to take the word back.
Pick Round 1 or Round 2. Each round has 10 questions (at least 4 on reading spirometry values and graphs). Answer, read the explanation, go on. 7 or more right completes the mission.
A two-part print-out: the student worksheet (it includes the rows from your spirometry table if you recorded some) and a separate answer key page for the teacher. Opens in a new window: press Print or save as PDF.
Numbers in the worksheet and its key come from the same model as the simulator (typical adult, severity presets 0, 25, 50 and 80).
A 45-minute lesson for Senior High School biology (grades 9–12; includes data-interpretation skills): how structure (scarred, stiff tissue) changes function (airflow, air volume, gas exchange). The page works on phones, Chromebooks (1366×768) and without WebGL. Students make a result code (under the simulator) that shows time on task, mission steps and quiz score; you can read it at scisim.org/check. Nothing is sent to a server.
| Time | Step | What students do | Go to |
|---|---|---|---|
| 0–5 min | Hook and predict | Show the Lung Lab on the board. Students answer the prediction, then press Max breath. | Lung Lab |
| 5–15 min | Explore | Pairs try Mild, Moderate and Severe. They write down air inhaled in a max breath (healthy vs fibrosis) and describe how the lungs look and move. | Lung Lab |
| 15–27 min | Spirometry lab | Record a healthy, a fibrosis and an asthma/COPD run. Students fill the data table and work out which pattern is restrictive and which is obstructive. | Spirometry |
| 27–35 min | Why? Alveolus and compliance | The thick wall slows oxygen (Fick); stiff lungs need more pressure. Do one of the two labs, or split the class. | Alveolus / Compliance |
| 35–42 min | Walk test or label lab | Walk test: does oxygen fall below 88%? Or label the airway diagram. | Walk test / Label lab |
| 42–45 min | Exit ticket and result code | Exit ticket: students write two sentences (why is FEV₁/FVC not low in pulmonary fibrosis?), make their result code and submit it with a photo or PDF of the data table. The 10-question quiz round fits as homework or extra time. | Quiz |
See the six misconceptions below; each is answered on the page.
| Sev. | Grade | FVC (L) | TLC (L), % of 5.8 | FEV₁ (L), % of 3.68 | FEV₁/FVC | Calm breath (L) | Breaths/min | C (L/cmH₂O) | SpO₂ rest / brisk walk | 6-min walk (m) |
|---|---|---|---|---|---|---|---|---|---|---|
| 0 | normal range | 4.6 | 5.8 (100%) | 3.68 (100%) | 0.80 | 0.50 | 12 | 0.20 | 97% / 96% | 564 m |
| 25 | mild | 3.6 | 4.7 (82%) | 2.96 (80%) | 0.83 | 0.46 | 16 | 0.15 | 97% / 95% | 501 m |
| 50 | moderate | 2.8 | 3.9 (67%) | 2.35 (64%) | 0.85 | 0.42 | 20 | 0.11 | 96% / 92% | 437 m |
| 80 | severe | 2.0 | 3.1 (53%) | 1.77 (48%) | 0.88 | 0.38 | 25 | 0.07 | 95% / 86% | 361 m |
| 100 | severe | 1.7 | 2.7 (46%) | 1.49 (40%) | 0.90 | 0.35 | 28 | 0.06 | 94% / 79% | 310 m |
Healthy reference: TV 0.5, IRV 3.0, ERV 1.1, RV 1.2 L (IC 3.5, VC 4.6, FRC 2.3, TLC 5.8 L), FEV₁/FVC 0.80, 12 breaths/min, C 0.20 L/cmH₂O. Restrictive: FVC % predicted = 100 − 0.96 s + 0.0032 s²; RV = 1.2 (1 − 0.0015 s); FEV₁/FVC = 0.80 + 0.001 s. The obstructive example uses the same slider: FEV₁/FVC = 0.80 − 0.005 s, RV rises (air trapping). Walk-test and oxygen values are illustrative.
| # | Question | Correct answer |
|---|---|---|
| 1 | What is pulmonary fibrosis? | Scarring (extra collagen) in the lung tissue around the air sacs, which makes the lungs thick and stiff |
| 2 | Where does the scarring of pulmonary fibrosis build up? | In the thin tissue between the air sacs (alveoli) and the blood capillaries |
| 3 | Why does a thicker alveolar wall make it harder to get oxygen into the blood? | Oxygen has a longer way to diffuse, and the rate of diffusion is proportional to 1 / thickness (Fick’s law) |
| 4 | A patient’s FVC is 2.3 L (predicted 4.6 L) and FEV₁/FVC is 0.86. Which pattern fits? | Restrictive, as in pulmonary fibrosis |
| 5 | A person blows out 3.0 L in total (FVC) and 1.5 L of it in the first second (FEV₁). What is FEV₁/FVC and what does it suggest? | 0.50: obstruction (slow emptying) |
| 6 | Which breathing pattern is typical for a person with moderate pulmonary fibrosis at rest? | Fast and shallow |
| 7 | On a volume–time graph of a forced breath, how does the curve of a person with pulmonary fibrosis compare with a healthy person’s? | It levels off at a lower volume (smaller FVC) but still rises steeply |
| 8 | What can antifibrotic medicines such as pirfenidone and nintedanib do? | Slow down the loss of lung function; they do not remove scars that already formed |
| 9 | A person’s FEV₁ is 2.4 L and the predicted value for them is 3.7 L. What is FEV₁ as a percentage of predicted? | About 65% |
| 10 | Lung compliance is C = ΔV / ΔP. A stiff, fibrotic lung has… | low compliance: a big pressure change gives only a small volume change |
| 11 | Which result shows a RESTRICTIVE pattern best? | Low total lung capacity and low FVC, with a normal or high FEV₁/FVC |
| 12 | The healthy FVC is 4.6 L. A patient with fibrosis has an FVC of 2.8 L. About what percent of normal is that? | About 61% |
| 13 | Why is FEV₁/FVC NOT low in pulmonary fibrosis? | The airways are open, so air leaves quickly; FEV₁ and FVC both fall together and their ratio stays normal or rises |
| 14 | A forced-breath curve levels off at 3.0 L, and 2.55 L has been blown out after 1 second. What is FEV₁/FVC? | 0.85 |
| 15 | On a pressure–volume graph, the curve of fibrotic lungs compared with healthy lungs is… | flatter and lower: more pressure is needed for the same volume |
| 16 | Which of these is a known cause or risk factor for pulmonary fibrosis? | Breathing in asbestos or silica dust over many years |
| 17 | If an alveolar wall becomes 3 times thicker and nothing else changes, the diffusion of oxygen through it becomes about… | one third as fast |
| 18 | Which of these lung diseases is OBSTRUCTIVE rather than restrictive? | Asthma |
| 19 | During a walking test the blood oxygen saturation (SpO₂) of a patient falls from 95% to 86%. What does this tell us? | Oxygen drops with effort: a warning sign (88% or lower is often used as a limit) when doctors decide about oxygen treatment |
| 20 | Which is a general part of care for people with pulmonary fibrosis (not a cure)? | Pulmonary rehabilitation, vaccinations and, when needed, oxygen therapy |
The worksheet answer key is on the second page of the worksheet (open it in the worksheet section).
Pulmonary fibrosis (PF) is scarring of the lung tissue. Too much collagen builds up in the thin tissue around the air sacs (the interstitium), so the walls become thick and stiff. The scarring is permanent. In idiopathic pulmonary fibrosis (IPF) no cause is found; it mostly affects older adults.
Key takeaway: PF is permanent scarring that makes the lungs stiff.Scarred lungs are stiff, so they stretch less (low compliance, C = ΔV/ΔP). The breathing muscles must make a much larger pressure change to get the same volume, so each breath is smaller. The total lung capacity and the forced vital capacity are reduced; in this simulator, FVC is about 60% of normal at severity 50.
Key takeaway: stiffness limits the volume of air the lungs can hold.In spirometry you breathe in as far as you can and blow out as hard and as long as you can. The total volume blown out is the forced vital capacity (FVC). The volume blown out in the first second is FEV1 (forced expiratory volume in 1 second). A healthy adult has an FVC near 4.6 L and an FEV1 near 3.7 L (typical values; they depend on sex, age and height).
Key takeaway: FVC = how much air; FEV1 = how fast it comes out.In fibrosis the airways are open, so the small amount of air that the lungs hold leaves quickly: FEV1 and FVC fall together and the ratio stays about 0.80 or rises to 0.85–0.90. In asthma and COPD the airways are narrowed, so the air leaves slowly, FEV1 falls much more than FVC and the ratio drops below about 0.70.
Key takeaway: restrictive = small lungs, normal or high ratio; obstructive = low ratio.Compliance is how easily the lungs stretch: C = change in volume divided by change in pressure (ΔV/ΔP), in liters per cmH2O. Healthy lungs are about 0.20 L/cmH2O in this model. Scarred, stiff lungs have a lower compliance, for example about 0.11 at severity 50.
Key takeaway: low compliance = stiff lungs.The scarred alveolar wall is thicker, so oxygen crosses more slowly (Fick’s law: rate is about area × pressure difference ÷ thickness). At rest the blood spends about 0.75 s in the capillary, which is enough time. In exercise the blood passes faster and there is not enough time, so the blood oxygen (SpO2) can fall. In this model the values are illustrative.
Key takeaway: a slow barrier plus fast blood flow means low oxygen during effort.Known causes and risk factors include long-term exposure to asbestos, silica or coal dust, some medicines (for example bleomycin, amiodarone and nitrofurantoin), radiation to the chest, autoimmune diseases such as rheumatoid arthritis or scleroderma, and hypersensitivity pneumonitis. For many people, the cause is not found (idiopathic). Older age, a history of smoking, reflux and genes are associated with IPF.
Key takeaway: many causes, and often no known cause.The scarring cannot be reversed. Antifibrotic medicines (pirfenidone and nintedanib) can slow the decline in lung function. Oxygen therapy, pulmonary rehabilitation, vaccination and, for selected patients, a lung transplant are other parts of care. Talk to a doctor: this page is educational and is not medical advice.
Key takeaway: treatment slows the disease; it does not remove scars.The simulator uses approximate textbook values for a typical healthy adult (TV 0.5 L, IRV 3.0 L, ERV 1.1 L, RV 1.2 L, TLC 5.8 L, FEV1/FVC 0.80) and a simple model in which the severity slider sets the FVC as a percentage of normal (mild about 70–80%, moderate 50–69%, severe below 50%). The 3D scarring is drawn in your browser and is not a patient scan, and the oxygen and walk-test values are illustrative. Real people vary a lot.
Key takeaway: a teaching model, not a diagnosis.