Regarding the subdivisions of total lung capacity (TLC), all of the following statements are correct EXCEPT:

Explanation

## Lung Volume Subdivisions and Their Relationships ### Correct Statements (Options 0, 1, 2) **Key Point:** Residual volume (RV) cannot be measured by simple spirometry because it represents air that remains in the lungs even after maximal expiration. Gas dilution techniques (helium dilution, nitrogen washout) or body plethysmography are required [cite:Guyton & Hall 14e Ch 39]. **Key Point:** Functional residual capacity (FRC) = ERV + RV. This is the volume of air remaining in the lungs at the end of normal expiration and is clinically important because it prevents airway collapse [cite:West's Respiratory Physiology 11e Ch 2]. **Key Point:** Vital capacity (VC) = IRV + TV + ERV. This is the maximum volume of air that can be expelled after maximal inspiration and is a key spirometric measurement [cite:Guyton & Hall 14e Ch 39]. ### Incorrect Statement (Option 3) — THE ANSWER **High-Yield:** Inspiratory capacity (IC) = IRV + TV, NOT TV + ERV. IC represents the maximum amount of air that can be inhaled from functional residual capacity (FRC). It does NOT include expiratory reserve volume (ERV), which is part of the expiratory phase [cite:West's Respiratory Physiology 11e Ch 2]. ### Lung Volume Relationships Table | Volume/Capacity | Components | Normal Value (Adult Male) | | --- | --- | --- | | Tidal Volume (TV) | Single breath at rest | 500 mL | | Inspiratory Reserve Volume (IRV) | Maximum inhalation from TV | 3100 mL | | Expiratory Reserve Volume (ERV) | Maximum exhalation from FRC | 1200 mL | | Residual Volume (RV) | Air remaining after maximal expiration | 1200 mL | | **Inspiratory Capacity (IC)** | **IRV + TV** | **3600 mL** | | **Functional Residual Capacity (FRC)** | **ERV + RV** | **2400 mL** | | **Vital Capacity (VC)** | **IRV + TV + ERV** | **4800 mL** | | **Total Lung Capacity (TLC)** | **IRV + TV + ERV + RV** | **6000 mL** | **Clinical Pearl:** IC is measured during spirometry as the maximum inspiration from FRC. Reduced IC suggests inspiratory muscle weakness or restrictive disease [cite:Harrison 21e Ch 246]. **Mnemonic:** **TIRE-RV** = Tidal, Inspiratory Reserve, Expiratory Reserve, Residual Volume (the four primary subdivisions that sum to TLC).