Lung Volumes (Exact Values)
| Parameter | Exact Value |
|---|---|
| Tidal Volume (TV) | ~500 mL |
| Inspiratory Reserve Volume (IRV) | 2500–3000 mL |
| Expiratory Reserve Volume (ERV) | 1000–1100 mL |
| Residual Volume (RV) | 1100–1200 mL |
| Inspiratory Capacity (IC) | ~3000–3500 mL |
| Expiratory Capacity (EC) | ~1500–1600 mL |
| Functional Residual Capacity (FRC) | ~2100–2300 mL |
| Vital Capacity (VC) | ~3500–4600 mL |
| Total Lung Capacity (TLC) | ~5000–6000 mL |
Partial Pressure Values
| Location | pO2 (mmHg) | pCO2 (mmHg) |
|---|---|---|
| Atmospheric air | 159 | 0.3 |
| Alveolar air | 104 | 40 |
| Deoxygenated blood (venous) arriving at alveoli | 40 | 45 |
| Oxygenated blood (arterial) leaving alveoli | ~95 | 40 |
| Tissue cells (metabolically active) | ~40 | ~45 |
Gas Transport Percentages
| Gas | Form | Percentage |
|---|---|---|
| O2 | Oxyhaemoglobin | 97% |
| O2 | Dissolved in plasma | 3% |
| CO2 | Bicarbonate ions (HCO3–) | 70% |
| CO2 | Carbaminohaemoglobin | 23% |
| CO2 | Dissolved in plasma | 7% |
Capacity Formulas
- VC = TV + IRV + ERV
- TLC = VC + RV = TV + IRV + ERV + RV
- FRC = ERV + RV
- IC = TV + IRV
- EC = TV + ERV
Key Numbers to Remember
- Haemoglobin carries 4 O2 molecules (4 haem groups per Hb)
- CO2 diffuses ~20× faster than O2 per unit pressure difference (higher solubility)
- Blood transit time through alveolar capillaries: ~0.75 sec at rest; equilibration achieved in ~0.25 sec
- Normal blood pH: 7.35–7.45