L11 physiology

Lung Volumes and Capacities

• Lung volumes and capacities are subdivisions of the total lung volume at maximal inspiration.
• A spirometer records lung volumes and capacities.

Learning Objectives

• Describe lung volumes and capacities
• Explain FEV1 and FVC (and their importance)
• List obstructive and restrictive respiratory diseases

Spirometer

• Records lung volumes and capacities
• Measures breathing

Lung Volumes and Capacities

• The total lung volume is subdivided into volumes and capacities.

Lungs Volumes and Capacities

• Key volumes include: Inspiratory reserve volume, Expiratory reserve volume, Tidal volume, Residual volume.
• Key capacities include: Inspiratory capacity, Vital capacity, Functional residual capacity, Total lung capacity.

Lungs Volumes

• Tidal volume (TV): Amount of air breathed in or out during a quiet respiration. Normal value: 500 ml
• Inspiratory reserve volume (IRV): Maximum amount of air inspired after a normal inspiration. Normal value: 3000 ml
• Expiratory reserve volume (ERV): Maximum amount of air expired after a normal expiration. Normal value: 1100 ml
• Residual volume (RV): Amount of air remaining in the lungs after a maximal expiration. Normal value: 1200 ml

Lung Capacities

• Inspiratory capacity (TV + IRV): Maximum volume of air that can be inspired after a normal expiration. Normal value: 3500 ml
• Vital capacity (TV+IRV+ERV): Maximum volume of air that can be forcefully expelled from the lungs following a maximum inspiration. Normal value: 4600 ml
• Functional residual capacity (RV+ERV): Volume of air remaining in the lungs at the end of a normal expiration. Normal value: 2300 ml
• Total lung capacity (TV+IRV+ERV+RV): Volume of air contained in the lungs at the end of a maximal inspiration. Normal value: 6000 ml

Expiratory Flow Rate

• Also known as peak expiratory flow rate (PEFR).
• Recorded using a peak flow meter where the subject exhales maximally for 10 milliseconds.
• Expressed for one minute.
• Normal value: 400 L/minute.
• PEFR measures air flow obstruction in larger airways (e.g., asthma).

Forced Vital Capacity (FVC)

• Total volume of air exhaled forcefully from total lung capacity.
• Most of the FVC is exhaled in <3 seconds, but it can be prolonged in obstructive diseases.
• Measured in liters (L).

Forced Expiratory Volume (FEV₁)

• When forced vital capacity is measured in the first second, it's known as FEV1
• Normal subjects expire 85% in 1 second and 97% in 3 seconds
• FEV₁ measurement is useful for detecting obstructive and restrictive pulmonary diseases.
• In obstructive pulmonary disease, FEV₁ is reduced.
• In restrictive pulmonary disease, FVC is reduced.

Respiratory Diseases

• Obstructive: Asthma, COPD (Chronic bronchitis & Emphysema), Cystic fibrosis
• Restrictive: Interstitial lung fibrosis, heart failure, lung edema, Pulmonary tuberculosis, pneumonia, pneumothorax, extreme obesity, pregnancy

Learning Resources

• Textbook: Hall, John E. Guyton and Hall textbook of medical physiology, 14th edition, 2021, Chapter 38, 491-501
• Website: https://www-clinicalkey-com.gmulibrary.com/#!/content/book/3-s2.0-B9780323597128000382?indexOverride=GLOBAL
• Powerpoint presentation in Moodle

Test your knowledge on lung volumes and capacities with this quiz. Explore essential concepts such as FEV1, FVC, and the distinctions between obstructive and restrictive respiratory diseases. Assess your understanding of how a spirometer measures these vital parameters.