Lung Volumes and Capacities Definitions

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What is the role of pulmonary surfactant in the recoil and expansion of the lung?

Increases lung compliance

How would a decrease in functional residual capacity (FRC) affect breathing?

Increase work of breathing

What is the primary reason for dynamic compression of airways during a forced expiration?

Increased alveolar pressure

How would an increase in airway resistance affect the dynamic compliance of the lung?

Decrease dynamic compliance

What contributes to alterations in the work of breathing?

Changes in dynamic compliance and airways resistance

In what physiologic/pathologic condition would you expect an alteration in lung and chest wall compliance?

Asthma exacerbation

What happens to airflow rate at high lung volumes?

It is effort-dependent

In what situation do expiratory efforts merge into an effort-independent curve?

At low lung volumes

What causes decreased peak expiratory flow in obstructive and restrictive diseases?

Foreign bodies or tumors

What type of obstruction is caused by tumors, fat deposits, or weakened pharyngeal muscles?

Variable extra-thoracic obstruction

What determines the movement of lungs according to the text?

Passive mechanisms

What happens to inspiratory and expiratory flow-volume curves in fixed intra-thoracic obstruction?

They shift downward

What is the forced vital capacity?

The largest amount of gas that can be moved into and out of the lungs in 1 minute

How does airway resistance behave?

Is increased following bronchial smooth muscle contraction

What is the function of surfactant lining the alveoli?

Helps prevent alveolar collapse

Where is surfactant produced?

Alveolar type II cells

What is the pressure outside the airway downstream from the equal pressure point?

Less than the driving pressure inside the airway

In obstructive diseases, what factor increases airway resistance?

Respiratory rate

What does TLC stand for in relation to lung volumes?

Total Lung Capacity

Which lung volume is defined as the volume of air remaining in the lungs after a maximal forced expiration?


What is the Forced Expiratory Volume in the 1st second (FEV1) a measure of?

Volume of air that can be expired in 1 second after maximal inhalation

In relation to forced vital capacity (FVC), what do measurements of FEV1/FVC represent?

Fraction of vital capacity that can be expired in 1st second

What does IPP stand for in the context of airflow dynamics?

Equal Pressure Point

What does FEF 25%-75% primarily represent in terms of airways?

Medium-sized airways

During expiration, what happens to intrapleural pressure (IPP)?

It decreases, compressing blood vessels and increasing resistance to blood flow.

What is the primary muscle of inspiration?


What is the result of Expiratory Tension Pneumothorax on intrapleural pressure (IPP)?

IPP is increased, decreasing venous return and cardiac output.

What happens to Alveolar pressure during forced exhalation or positive pressure ventilation?

Alveolar pressure becomes positive due to increased lung compliance.

Which muscle is NOT classified as a muscle of respiration?

Internal Intercostal muscles

'Tripod' Position is commonly observed in individuals with which condition?

Post-exercise recovery

What is the role of the diaphragm during deep inspiration?

It moves downward, increasing thoracic volume for air intake.

How does increased intrathoracic pressure impact cardiac output?

It decreases cardiac output by reducing venous return.

'Thoracic Pump' primarily promotes which physiological process?

'Thoracic Pump' promotes venous return and cardiac output.

Study Notes

Generation of a Pressure Gradient

  • A pressure difference is generated between the atmosphere and alveoli during breathing
  • The diaphragm and intercostal muscles contract to increase intrathoracic volume, making intrapleural pressure (IPP) more negative and expanding the lungs
  • Decreased external pressure dilates the superior vena cava and inferior vena cava, and heart chambers, increasing the pressure gradient for venous return to the right heart
  • During inspiration, the diaphragm descends, causing an increased intra-abdominal pressure, which forces blood flow towards the heart

Pressure-Volume Relationships in the Respiratory System

  • The lung and chest wall have mechanical interactions, with the lung tending to recoil and the chest wall tending to expand
  • The interaction between the lung and chest wall results in a negative intrapleural pressure (IPP) at functional residual capacity (FRC)
  • Pulmonary surfactant and alveolar interdependence play roles in the recoil and expansion of the lung

Airways Resistance

  • Airways resistance is the resistance to airflow in the airways
  • Factors that contribute to airways resistance include airway diameter, length, and friction
  • Airways resistance can be altered by factors such as airway constriction or dilation, and changes in airway length and diameter

Work of Breathing

  • The work of breathing is the energy required to overcome the resistance to airflow in the airways and the elastic resistance of the lung and chest wall
  • Factors that contribute to the work of breathing include airways resistance, lung and chest wall compliance, and respiratory rate
  • The work of breathing can be increased in certain disease states, such as obstructive and restrictive lung diseases

Pressures Involved in Respiration

  • Alveolar pressure is the pressure inside the alveoli and is equal to the intrapulmonary pressure and airway pressure
  • Intrapleural pressure (IPP) is the pressure inside the pleural cavity and is normally negative
  • Transpulmonary pressure is the transmural pressure difference between the alveolar pressure and intrapleural pressure

Muscles of Respiration

  • The muscles of respiration include the diaphragm, external intercostals, scalenes, abdominal muscles, and internal intercostal muscles
  • The diaphragm is the primary muscle of inspiration and accounts for half of the tidal inhalation when upright and up to two-thirds when supine
  • The diaphragm descends during inspiration, increasing the intrathoracic volume and decreasing the intrapleural pressure

Lung Volumes and Capacities

  • Lung volumes and capacities are measured using a spirometer and include vital capacity (VC), total lung capacity (TLC), residual volume (RV), and forced vital capacity (FVC)
  • Forced expiratory volume in the first second (FEV1) is the volume of air that can be expired in one second after maximal inhalation

Flow-Volume Curves

  • Flow-volume curves demonstrate the relationship between airflow and lung volume during forced expiration
  • The curves can be used to diagnose obstructive and restrictive lung diseases
  • Peak expiratory flow is the maximal flow rate that can be attained during forced expiration

Clinical Applications

  • Cardiopulmonary resuscitation (CPR) can be affected by changes in intrathoracic pressure
  • Pneumothorax can cause an increase in intrapleural pressure, leading to decreased venous return and cardiac output
  • Expiratory tension pneumothorax can cause air to enter the pleural cavity during inspiration, but not to leave during expiration, leading to increased intrapleural pressure and decreased venous return.

This quiz covers the definitions and calculations of lung volumes and capacities, including Vital Capacity (VC), Total Lung Capacity (TLC), and Residual Volume (RV). Learn about these important respiratory measurements and their significance in pulmonary function testing.

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