1. Bohr Effect and Exercise Physiology During exercise, working muscles produce CO2 and lactic acid (lowering blood pH) and generate heat. These conditions shift the O2–Hb dissociation curve to the right, meaning haemoglobin releases more O2 per unit time to active muscles. This is the physiological basis of the increased O2 delivery during exercise. Athletes also develop increased 2,3-BPG levels with training, enhancing this right-shift adaptation.
2. High-Altitude Acclimatisation At altitude, pO2 is reduced. The body responds with: (a) hyperventilation (to raise alveolar pO2), (b) increased RBC production (polycythaemia, to increase O2-carrying capacity), and (c) increased 2,3-BPG (right-shifted curve for better tissue O2 release). HbF in fetuses has a left-shifted curve to extract O2 efficiently from maternal blood at the placenta.
3. Emphysema and Spirometry Emphysema destroys alveolar elastic tissue → loss of elastic recoil → air trapping. Clinically: RV ↑, TLC ↑, FRC ↑, VC ↓, FEV1 ↓. The barrel chest results from chronically hyperinflated lungs repositioning the rib cage permanently outward. Treatment focuses on bronchodilators and supplemental O2.
4. Respiratory Acidosis and CO2 Retention Hypoventilation (e.g., opiate overdose, COPD exacerbation) → CO2 retention → blood pH falls (respiratory acidosis). CO2 crosses the blood-brain barrier, acidifies CSF, and stimulates medullary chemoreceptors. The kidney compensates over hours by retaining HCO3– (metabolic compensation). Clinically, arterial blood gas shows: pH < 7.35, pCO2 > 45 mmHg.
5. Pneumothorax A penetrating chest wound or spontaneous rupture allows air into the intrapleural space, equalising intrapleural pressure with atmospheric. The lung on the affected side collapses (atelectasis) because the negative intrapleural suction that maintained inflation is lost. Immediate life-threatening if tension pneumothorax develops (air enters but cannot escape, compressing mediastinum).
6. Occupational Lung Disease Silicosis (stone cutters, miners) and asbestosis (construction, insulation workers) cause irreversible restrictive lung disease through fibrosis. Increased diffusion membrane thickness by Fick's Law reduces gas exchange efficiency. Prevention through dust masks is the key public health intervention.
7. CO Poisoning Carbon monoxide (CO) binds haemoglobin at the haem iron with approximately 250 times greater affinity than O2, forming carboxyhaemoglobin (HbCO). This (a) prevents O2 loading and (b) left-shifts the remaining oxyhemoglobin curve, further impeding O2 delivery. Treatment: 100% O2 (to out-compete CO by mass action).