Pulmonary Function Measurements


In a biological process exchange of gases, take place. Diaphragm acts as physiological pump, it creates alternative positive and negative pressure inside the sealed chamber named Thoracic Cavity. Lungs are the elastic bags. They cause the air to be sucked in and out of lungs within the chamber. Lungs are connected to external air through nasal cavity. A common pathway between lungs and nasal cavity carries air to lungs and food to stomach. During inhalation muscles are contracted, ribs are lifted and increases lung volume. During exhalation, reverse will happen, the muscles are relaxed and lung volume decreases.

Three basic types of pulmonary functions namely ventilation, distribution and diffusion.

  • Ventilation

    Ventilation determines the ability of the body to displace air volume and the rate at which displacement occurs. Spirometers are used to measure the volume displacement and amount of gas at a specific time. Patient takes deep breath and exhales rapidly. It is known as forced vital capacity that gives an indication about how much air the lungs can hold and how freely air can flow.

  • Distribution

    Distribution determines the degree of lung obstruction for the airflow. It also tells about the residual volume (RV). RV is the amount of air that is not removed due to patient’s effort. Pneumotachometers are used to measure rate of volume of inspired gas.

  • Diffusion

    Diffusion is the methodology used to identify the rate at which gas is exchanged with blood stream using gas analyzers.

Respiratory Volume

  1. Tidal Volume(TV)

    During each breath volume of gas inhaled or exhaled is known as tidal volume.

  2. Minute Volume (MV)

    During quiet breathing, volume of gas exchanges per minute. Value is equal to Tidal Volume multiplied with breathing rate.

  3. Inspiratory Reserve Volume (IRV)

    A person breathing at rest has normal inspiration and expiration. However, when the same person does exercise he will inhale more. This additional amount of air is Inspiratory reserve volume which is around 3000 ml.

  4. Expiratory Reserve Volume (ERV)

    Additional amount of air a person exhales is expiratory reserve volume.

  5. Residual Volume (RV)

    The amount of air left in the lungs after maximum expiration is residual volume.

Respiratory Capacities

Capacities: When two or more volumes are combined it is capacities.

  1. Total Lung Capacity (TLC)

    The final total amount of air inside lungs.

  2. Vital Capacity (VC)

    The amount of air a person can breathe in and breathe out.

  3. Dead Space

    It is the functional volume in the lung, that does not participate in gas exchange.

  4. Functional Residual Capacity (FRC)

    After normal exhalation volume of gas in lungs.

  5. Inspiratory Capacity (IC)

    The maximum volume that is inhaled from resting end position.

pulmonary function measurements

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