What is Chest Wall Compliance?
Chest wall compliance, also known as thoracic compliance, measures how easily the thoracic cage can expand and contract during breathing. It involves the ribs, sternum, spine, muscles, and connective tissues. High compliance means less effort is needed to breathe, while low compliance increases the work for respiratory muscles. Compliance and airway resistance are key factors in breathing mechanics. Chest wall compliance and lung compliance together determine total respiratory system compliance. The natural balance between the chest wall's outward recoil and the lungs' inward recoil sets the functional residual capacity (FRC).
The Physiological Decline of Chest Wall Compliance with Age
Chest wall compliance normally decreases with age, particularly after 50, making the chest wall stiffer. This is due to several structural and muscular changes.
Structural changes include:
- Costal cartilage stiffens due to calcification, limiting rib cage movement.
- Thoracic vertebrae changes, potentially from osteoporosis, can cause kyphosis, reducing chest wall mobility.
- Rib-vertebral joints undergo changes that add to the rib cage's rigidity.
Muscular changes include:
- Respiratory muscles, like the diaphragm and intercostals, weaken with age.
- Connective tissues in the chest wall become less elastic.
Comparison: Chest Wall Compliance vs. Lung Compliance
Unlike chest wall compliance, lung compliance typically increases with age. This difference is important for understanding how the aging respiratory system works.
| Feature | Chest Wall Compliance | Lung Compliance |
|---|---|---|
| Trend with Age | Decreases (stiffer). | Increases (less elastic). |
| Reason for Change | Cartilage calcification, joint stiffening, osteoporosis, muscle weakening. | Loss of elastic fibers in lung tissue. |
| Effect on Breathing | Harder to expand the chest for inspiration. | Expiration is less efficient, can cause air trapping. |
| Overall Impact | Increases the work of breathing against outward expansion. | Raises residual volume and functional residual capacity. |
Consequences for Respiratory Function
The aging respiratory system faces increased demands from decreased chest wall compliance and increased lung compliance. Breathing requires more effort, and air can become trapped in the lungs. While the body adapts, this reduced capacity makes older adults more susceptible during illness.
Key consequences:
- Increased work of breathing: More muscle effort is needed to expand the stiff chest wall.
- Reduced vital capacity (VC): The maximum amount of air exhaled after a full breath decreases.
- Increased residual volume (RV): More air remains in the lungs after a full exhale.
- Altered breathing: Breathing may become faster and shallower.
- Respiratory muscle fatigue: Extra effort can lead to faster fatigue of breathing muscles.
Measuring Chest Wall Compliance
Measuring chest wall compliance in awake individuals is tricky because it requires relaxed respiratory muscles. Methods include:
- Using an esophageal balloon to estimate intrapleural pressure, allowing calculation of lung and chest wall compliance based on volume changes.
- Applying external pressure to the chest and abdomen to assess mechanical properties.
Potential Strategies and Management
Although age-related changes are natural, lifestyle and interventions can help maintain respiratory health:
- Regular exercise: Helps keep respiratory muscles strong and improves cardiorespiratory fitness.
- Breathing exercises: Techniques like pursed-lip or diaphragmatic breathing can improve efficiency.
- Posture: Addressing poor posture or kyphosis through therapy or exercise can improve chest wall movement.
- Managing conditions: Treating skeletal conditions like osteoporosis supports better respiratory function.
Conclusion
In conclusion, chest wall compliance decreases with age due to structural changes like cartilage stiffening, altered joints, and weakened muscles. This, combined with increased lung compliance, makes breathing harder and changes lung function. While aging is a factor, maintaining an active lifestyle, practicing breathing exercises, and managing health conditions can support respiratory well-being throughout life. Understanding these age-related shifts is important for health management in older adults.
What are the main anatomical reasons behind decreased chest wall compliance with age?
The decrease is primarily due to calcification of costal cartilages, which makes the rib cage more rigid, and age-related osteoporosis, which can cause kyphosis and restrict spinal and rib cage mobility. Weakening of the intercostal muscles and connective tissues also contributes.
Does lung compliance also decrease with age?
No, lung compliance and chest wall compliance change in opposite directions with age. While the chest wall becomes stiffer (less compliant), the lungs themselves become more compliant due to a loss of elastic fibers, a condition sometimes called “senile emphysema”.
What is the practical effect of decreased chest wall compliance on breathing?
The primary effect is an increase in the work of breathing. More muscular effort is needed to expand the stiffer chest wall during inhalation, which can lead to respiratory muscle fatigue, especially during illness or increased physical demand.
How does reduced chest wall compliance affect lung volumes?
Decreased chest wall compliance contributes to a reduction in total lung capacity (TLC) and vital capacity (VC). However, because of the concurrent increase in lung compliance, residual volume (RV) and functional residual capacity (FRC) typically increase, leading to trapped air.
Can exercise help improve age-related chest wall compliance?
While exercise cannot reverse the structural changes like cartilage calcification, it can help maintain respiratory muscle strength and overall cardiorespiratory fitness. This can help compensate for the increased work of breathing caused by a stiffer chest wall, making breathing more efficient.
What is the difference between static and dynamic chest wall compliance?
Static chest wall compliance is measured when there is no airflow and all respiratory muscles are relaxed, reflecting the intrinsic elastic properties of the chest wall. Dynamic compliance is measured during breathing and also accounts for airway resistance.
How does obesity affect chest wall compliance?
Obesity decreases chest wall compliance by adding a load of adipose tissue, which makes the chest wall harder to expand. This can combine with age-related stiffening to further increase the work of breathing.
