Pulmonary Compliance and Work of Breathing

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Questions and Answers

Which condition is associated with increased lung compliance?

Myositis

Old age (correct)

Kyphosis

Obesity

What primarily contributes to the work of breathing during expiration?

Passive elastic recoil of the lungs (correct)

Increased airway resistance

Compliance changes in the thorax

Active muscular contraction

Which of the following factors decreases lung compliance?

Athletic training

Emphysema

Scoliosis (correct)

Increased surface tension

What percentage of total body energy expenditure does the work of breathing account for at rest?

1-2% Signup and view all the answers

Which work of breathing is defined as the effort to expand the lung against its elastic recoil?

Compliance work Signup and view all the answers

What is the primary effect of bronchodilation on airflow resistance?

Decreases resistance to airflow Signup and view all the answers

Which system primarily mediates bronchoconstriction in the respiratory system?

Parasympathetic nervous system Signup and view all the answers

What does the term 'compliance' refer to in pulmonary mechanics?

The change in volume per unit change in pressure Signup and view all the answers

Which of the following factors is known to decrease lung compliance?

Pulmonary congestion Signup and view all the answers

How does increased work of breathing typically manifest?

Strain on respiratory muscles Signup and view all the answers

What physiological changes occur in compliance with aging?

Compliance increases slightly Signup and view all the answers

Which receptors are primarily involved in bronchial muscle contraction during bronchoconstriction?

Muscarinic receptors Signup and view all the answers

What is the primary role of surfactant in the lungs?

To decrease surface tension in alveoli Signup and view all the answers

What is the definition of pulmonary compliance?

The ability of the lung to expand with pressure changes. Signup and view all the answers

What is the normal value for lung compliance?

200 ml/cm H2O Signup and view all the answers

Which of the following factors does NOT affect lung compliance?

Airway resistance Signup and view all the answers

In which type of lung condition is lung compliance typically decreased?

Restrictive lung diseases Signup and view all the answers

What is the formula for lung compliance?

C = ∆V / ∆P Signup and view all the answers

How does surface tension in the alveoli affect lung compliance?

It decreases compliance by increasing lung stiffness. Signup and view all the answers

During which part of the breathing cycle is decreased surface tension likely to increase lung compliance?

During expiration. Signup and view all the answers

What does the hysteresis loop in the dynamic lung pressure-volume curve indicate?

The same pressure results in different volumes during inflation and deflation. Signup and view all the answers

Study Notes

Pulmonary Compliance and Work of Breathing

Pulmonary compliance is the change in lung volume per unit pressure change.
Normal lung compliance for the lungs alone is 200 ml/cm H2O.
Normal lung and chest wall compliance combined is 100 ml/cm H2O.
Compliance is lower during deflation than inflation, this is called hysteresis.
Factors decreasing compliance include: decreased surfactant, pulmonary congestion, pulmonary fibrosis, pulmonary edema, and chest wall issues (e.g., kyphosis, scoliosis, obesity).
Factors increasing compliance include old age and emphysema.

Work of Breathing

Work of breathing is the effort needed to overcome resistance to move air in and out of the lungs.
During normal breathing, work is primarily done during inspiration. Exhalation is passive.
At rest, work of breathing represents 1-2% of total body energy.
During heavy exercise, work of breathing represents 3-5% of total body energy.
Work of breathing can be divided into three parts: compliance work, tissue resistance work and airway resistance work.
Compliance work is 65% of the total work of breathing and is required to expand the lungs against their elastic recoil tendency.
Tissue resistance work is 7% of the total work of breathing and is required to overcome the resistance of non-elastic lung and chest wall tissue components.
Airway resistance work is 28% of the total work of breathing and is required to overcome resistance to airflow during breathing.

Factors Affecting Airway Resistance

Airway resistance is inversely proportional to the fourth power of the radius. Thus a decrease in radius significantly increases airway resistance.
Airway resistance is inversely proportional to the number of airways. Thus an increase in the number of airways decreases airway resistance.
Larger airways (e.g., medium sized bronchi) have higher resistance compared to smaller ones (e.g., terminal bronchioles) due to having a smaller radius and a lower number of airways.
Factors affecting airway resistance include lung volume, airway radius, and airway number.

Factors Affecting Bronchial Diameter

Bronchodilation (decreased resistance):
- Sympathetic nervous system (releases noradrenaline) acting on beta-2 adrenergic receptors.
- Adrenaline from adrenal medulla acting on beta-2 adrenergic receptors.
Bronchoconstriction (increased resistance):
- Parasympathetic nervous system (releases acetylcholine) acting on muscarinic receptors.
- Histamine, Leukotrienes, Cold air, increased PCO2, and dust/gas irritation.

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Description

This quiz covers the critical concepts of pulmonary compliance and the work of breathing essential for understanding respiratory mechanics. Explore factors influencing compliance and methods to calculate the effort required for breathing during different activities. Perfect for students studying respiratory physiology.