Pulmonary Function Flashcards

Introduction

• The respiratory system's functions include:
  • Supplying oxygen (O_2) during inhalation.
  • Removing carbon dioxide (CO_2) during exhalation.
  • Adjusting the acid-base balance (pH) by removing acid-forming CO_2.
• Oxygen is essential for cellular metabolism, so the pulmonary system's capacity to supply air is crucial for determining work capacity and metabolism limits.
• Measuring lung volumes and airflow rates are important for assessing a person's health and lung capacity.
• Lung capacity is restricted by the size of the thoracic cavity and varies with size and age.
  • Taller individuals typically have larger lungs.
  • Lung capacity decreases with age due to loss of elasticity and reduced efficiency of respiratory muscles.

Pulmonary Volumes

• Tidal Volume (TV): The amount of air involved in a normal inhalation and exhalation.
  • Average tidal volume is 500 mL, but can be lower due to shallow breathing.
• Minute Respiratory Volume (MRV): The amount of air inhaled and exhaled in one minute.
  • Calculated by multiplying tidal volume by the number of respirations per minute.
  • Average respiratory rate: 12 to 20 breaths per minute.
  • Example: If TV = 500 mL and respiratory rate = 12 breaths/minute, MRV = 6000 mL or 6 liters per minute.
    MRV = TV \,\times\, Respiratory Rate
• Inspiratory Reserve Volume (IRV): The amount of air, beyond tidal volume, that can be inhaled with the deepest possible inhalation.
  • Normal range: 2000 to 3000 mL.
• Expiratory Reserve Volume (ERV): The amount of air, beyond tidal volume, that can be expelled with the most forceful exhalation.
  • Normal range: 1000 to 1500 mL.
• Residual Volume (RV): The amount of air remaining in the lungs after the most forceful exhalation.
  • Average range: 1000 to 1500 mL.
  • Ensures some air remains in the lungs for continuous gas exchange.
• Alveolar Ventilation: It is the amount of air that reaches the alveoli and participates in gas exchange.
  • Around 350 to 400 mL of a 500 mL tidal volume reaches the alveoli.
  • The remaining 100 to 150 mL is the anatomic dead space, which is air within the respiratory passages.

Pulmonary Dead Space

• Gas exchange occurs in the smaller, thin-walled terminal parts of the bronchial tree, starting with the respiratory bronchioles.
• The anatomical dead space includes the remaining part of the respiratory system (including the entire upper division).
  • It is ventilated but does not participate directly in gas exchange.
• Physiological dead space: Volume of non-functioning alveoli that reduces gas exchange; this is not normal.
• Causes of increased physiological dead space: bronchitis, pneumonia, tuberculosis, emphysema, asthma, pulmonary edema, and a collapsed lung.

Pulmonary Capacities

• Lung capacities are combinations of two or more lung volumes.
• Inspiratory Capacity (IC): Tidal volume plus inspiratory reserve volume.
  • Approximately 3500 mL (500 mL + 3000 mL).
    IC = TV + IRV
• Functional Residual Capacity (FRC): Expiratory reserve volume plus residual volume.
  • Volume remaining in the lungs after a normal tidal volume is expired.
  • Approximately 2400 mL (1200 mL + 1200 mL).
    FRC = ERV + RV
• Vital Capacity (VC): Inspiratory capacity plus expiratory reserve volume.
  • Approximately 4700 mL (3500 mL + 1200 mL).
  • Volume that can be expired after maximal inspiration.
  • Increases with body size, male gender, and physical conditioning; decreases with age.
• Total Lung Capacity (TLC): Sum of all lung volumes: vital capacity plus residual volume.
  • Approximately 5900 mL (4700 mL + 1200 mL).
    TLC = VC + RV
    TLC = IRV + TV + ERV + RV
• Expiratory Capacity (EC): Tidal Volume plus Expiratory Reserve Volume.
  EC = TV + ERV
• Tiffneau Index: Proportion of vital capacity expired in the first second of forced expiration (FEV1/VC).
  • Also known as the bronchial permeability index.
  • Normally over 80%.
    Tiffneau \, Index = \frac{FEV1}{VC} \,(\%)

Vital Capacity

• Predicted vital capacities can be estimated using equations based on height and age.
• Vital capacities are also dependent on factors besides age and height.
• 80% of the calculated values are considered normal.
  • Male: V.C. = 0.052H – 0.022A – 3.60
  • Female: V.C. = 0.041H – 0.018A – 2.69
    • VC = Vital Capacity in liters
    • H = Height in centimeters
    • A = Age in years

Functional Residual Capacity (FRC) Measurement

• Helium dilution method: Subject breathes a known amount of helium added to a spirometer.
• Helium is insoluble in blood, so its concentration in the lungs equals that in the spirometer after a few breaths.
• The initial amount of helium and its concentration in the lungs are used to calculate lung volume. C1 \times V1 = C2 \times (V1 + V_2)
  • C_1 = known concentration of an inert gas
  • C_2 = new concentration of the gas
  • V_1 = known volume of a box
  • V_2 = lung volume

Maximum Pulmonary Volumes and Capacities

• Measurements indicating the upper limit of work a person can do based on their respiratory system capabilities.
• Forced Vital Capacity (FVC): Maximal amount of air a person can forcibly exhale after a maximal inhalation.
• Forced Expiratory Volume (FEV): Percentage of FVC that a person forcibly expels in 1, 2, and 3 seconds (FEV1.0, FEV2.0, FEV3.0).
• Maximal Voluntary Ventilation (MVV): Maximum ventilated flow per minute; the volume of air circulated within one minute by forced breathing.
  • Average normal values: Female: 100-120 L/min, Male: 110-130 L/min

Spirogram

• A spirometer measures the volume of air a person inhales (inspires) and exhales (expires).
• A bell spirometer consists of a double-walled cylinder with an inverted bell filled with oxygen-enriched air immersed in water to form a seal.
• A pulley connects the bell to a recording pen that writes on a drum rotating at a constant speed.
• During inspiration, air is removed from the bell and the pen rises, recording inspired volume. As expired air enters the bell, the pen falls, recording expired volume.
• The spirogram is the resultant record of volume change vs. time.

Correct Measurement - Preparation

• To avoid:
  • Alcohol consumption 4 hours before.
  • Heavy meals 2 hours before.
  • Smoking an hour before.
  • Intense exercise 30 minutes before.

Correct Measurement - Posture

• Upright sitting: Sitting straight is important; standing is better than supine lying.
• Feet flat on the floor with legs uncrossed: Avoid using abdominal muscles for leg position.
• Loosen tight-fitting clothing.
• Dentures normally left in: Maintain mouth structure unless dentures are very loose.
• Use a chair with arms: Prevent swaying or fainting during maximal exhalation.

Clinical Significance of Ventilatory Function Tests

• Help doctors:
  • Determine the degree of impairment of ventilatory function in restrictive or obstructive syndromes.
  • Diagnose lung diseases like asthma or chronic obstructive pulmonary disease (COPD).
  • Evaluate a person's ventilatory function before surgical intervention.
  • Monitor respiratory function of individuals exposed to respiratory toxins (e.g., asbestos, dust, silicon).
  • Monitor the effectiveness of treatment for various lung diseases.

Types of Respiratory Dysfunction

• Obstructive Ventilatory Dysfunction (OVD):
  • Reduced FEV (< 80% of ideal).
  • Reduced Tiffneau index (< 70-80%).
  • Normal VC.
• Restrictive Ventilatory Dysfunctions (RVD):
  • Reduced VC (< 80% of ideal).
  • Normal or increased Tiffneau index (> 70-80%).
• Mixed Ventilatory Dysfunctions:
  • VC < 80%.
  • Tiffneau index < 70%.