Exam 6 · Week 12 · BIO 280 Pathophysiology
M12 · Respiratory & HEENT
Ventilation versus perfusion, obstructive versus restrictive, and the emergencies that show up as a change in breathing.
▸M12Respiratory & HEENTWeek 12
💡 The one idea
Breathing has two jobs and they fail separately. Ventilation is moving air; perfusion is moving blood past it. Gas exchange needs both, and every respiratory disease breaks one of them.
A pulmonary embolism ventilates without perfusing. A pneumonia perfuses without ventilating.
🪘 Ventilation, perfusion and diffusion
- Ventilation (V) — air reaching the alveoli. Blocked by obstruction, collapse, secretions, or a chest wall that cannot move.
- Perfusion (Q) — blood reaching the capillaries. Blocked by embolism, shock, or destroyed vessels.
- Diffusion — gas crossing the membrane. Impaired by thickened or fluid-filled membranes: pulmonary edema, fibrosis, ARDS.
Dead space = ventilation without perfusion (PE). Shunt = perfusion without ventilation (pneumonia, atelectasis, ARDS).
Hypoxia from a shunt does not correct well with supplemental oxygen, because the oxygen never reaches the blood. That is a diagnostic clue in itself.
The main stimulus to breathe is a rising CO₂. In chronic CO₂ retainers that drive is blunted and low oxygen becomes the stimulus — which is why oxygen is titrated carefully in advanced COPD.
📊 Obstructive vs restrictive
| Obstructive | Restrictive | |
|---|---|---|
| Problem | Air cannot get out | Lungs cannot expand |
| Examples | Asthma, COPD, bronchiectasis, cystic fibrosis | Pulmonary fibrosis, ARDS, obesity, kyphoscoliosis, neuromuscular disease |
| Spirometry | FEV1/FVC low; residual volume high | FEV1/FVC normal or high; all volumes low |
| Feels like | Trouble breathing out; prolonged expiration, wheeze, barrel chest | Trouble breathing in; rapid shallow breaths |
COPD: chronic bronchitis is airway inflammation and mucus — productive cough most days for 3 months in 2 consecutive years. Emphysema is alveolar wall destruction — loss of surface area and elastic recoil, air trapping, barrel chest, pursed-lip breathing.
Asthma is reversible: bronchospasm, inflammation and mucus. Status asthmaticus is an attack unresponsive to treatment.
In a severe asthma attack a silent chest is not improvement — it means too little air is moving to make a sound. That patient is close to respiratory arrest.
🚨 The respiratory emergencies
| Emergency | Recognize it by |
|---|---|
| Pulmonary embolism | Sudden dyspnea, pleuritic chest pain, tachycardia, hypoxia, anxiety. Often normal breath sounds. Usually from a DVT. Virchow triad: stasis, vessel injury, hypercoagulability. |
| Tension pneumothorax | Absent breath sounds on one side, tracheal deviation away from the affected side, JVD, hypotension. Needle decompression, immediately. |
| ARDS | Refractory hypoxemia within <1 week of an
insult (sepsis, trauma, aspiration), bilateral infiltrates, not explained by heart
failure. Oxygen does not fix it. |
| Pulmonary edema | Crackles, frothy pink sputum, severe orthopnea. Usually left-sided heart failure. |
Pneumonia — fever, productive cough, pleuritic pain, crackles, dullness to percussion, raised WBC and an infiltrate on chest X-ray. Aspiration risk rises with impaired swallow, reduced consciousness and tube feeding.
Tuberculosis — airborne; night sweats, weight loss, and a chronic cough that becomes bloody. Requires airborne precautions and a negative-pressure room.
⭐ HEENT
- Otitis media — commoner in children because the eustachian tube is shorter, wider and more horizontal, so it drains badly.
- Sinusitis — facial pain and pressure worse on leaning forward, purulent discharge; most cases are viral.
- Glaucoma — raised intraocular pressure damaging the optic nerve. Open-angle is gradual, painless, and takes peripheral vision first. Closed-angle is sudden, painful, with halos, a fixed mid-dilated pupil and vomiting — an emergency.
- Cataract — clouding of the lens; gradual blurring, glare and poor night vision.
- Macular degeneration — loses central vision, keeps peripheral. The opposite pattern to glaucoma.
- Retinal detachment — floaters, flashes, and a curtain across the visual field. Painless, and an emergency.
- Conductive hearing loss = sound cannot get in (wax, fluid, perforation) and is often fixable. Sensorineural = hair cells or nerve damaged (noise, age, ototoxic drugs) and is usually permanent.
Sudden painless vision loss and sudden painful vision loss are both emergencies — the painless ones (retinal detachment, retinal artery occlusion) are the ones patients wait on.
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