Q.103 Consider a healthy person with the following lung volumes:
Residual volume = 900 mL
Expiratory reserve volume = 800 mL
Tidal volume = 200 mL
If the Total lung capacity is 5500 mL, then the Inspiratory reserve volume of the
person is _____ mL. (Answer in integer)

Inspiratory reserve volume (IRV) is calculated as 3600 mL using the total lung capacity (TLC) formula.

Lung Volume Definitions

Total lung capacity represents the maximum air volume the lungs hold after full inspiration, summing all lung volumes: TLC = IRV + tidal volume (TV) + expiratory reserve volume (ERV) + residual volume (RV).

Residual volume is air remaining after maximal exhalation (900 mL here). Expiratory reserve volume is additional air exhaled post-normal expiration (800 mL), and tidal volume is air moved in quiet breathing (200 mL).

Step-by-Step Calculation

Rearrange TLC formula for IRV: IRV = TLC – (RV + ERV + TV).

Substitute values: IRV = 5500 – (900 + 800 + 200) = 5500 – 1900 = 3600 mL.

This aligns with typical healthy adult IRV ranges of 1900-3300 mL, though values vary by individual factors like age and size.

Introduction to Lung Volumes for CSIR NET

To calculate inspiratory reserve volume accurately, understand key spirometry terms essential for CSIR NET life sciences exams. Total lung capacity (TLC) is the sum of inspiratory reserve volume (IRV), tidal volume (TV), expiratory reserve volume (ERV), and residual volume (RV), helping diagnose respiratory health.

Key Lung Volumes Explained

• Residual volume (RV): Air left after maximal exhalation (900 mL), preventing alveolar collapse (~1-1.2 L normal).
• Expiratory reserve volume (ERV): Extra air exhaled beyond TV (800 mL, normal 700-1200 mL).
• Tidal volume (TV): Normal breath volume (200 mL, typically ~500 mL).
• Inspiratory reserve volume (IRV): Maximum extra inhalation beyond TV (target value here).

How to Calculate Inspiratory Reserve Volume

Use TLC formula: IRV = TLC – RV – ERV – TV.

For given values (TLC=5500 mL, RV=900 mL, ERV=800 mL, TV=200 mL): IRV = 5500 – 900 – 800 – 200 = 3600 mL.

Verify: Vital capacity (VC = IRV + TV + ERV) = 3600 + 200 + 800 = 4600 mL; TLC = VC + RV confirms 5500 mL.

Clinical Relevance

These calculations aid pulmonary function tests (PFTs) for conditions like COPD, where RV/TLC rises above 25-35%.

Practice for CSIR NET by memorizing: TLC ~6 L, IRV ~3 L in healthy adults.