Breathing compliance Flashcards
Examples of obstructive and restrictive diseases
obstructive: bronchitis, asthma, emphysema. Restrictive: pulmonary fibrosis
Describe muscles involved in inspiration
Diaphragm (moves down with contraction), external intercostals (move the rib cageforward and outwards with contraction). Sternocleidomastoid and scalenes are silent during normal breathing, but are accessory muscles when ventilation of respiratory load is increased (ie. during exercise). They elevate the rib cage
Describe muscles involved in expiration.
None during quiet breathing. Some during forced expiration and exercise (ie. Muscles in abdominal wall push the diaphragm upwards and internal intercostals may pull ribs inward/downward)
Describe how the status of the inspiratory muscles during disease can impact breathing
Patients with obstructive diseases breathe at higher lung volumes and the diaphragm is more contracted/reduced in length. This results in a decreased maximum force produced
Define intrapleural pressure and its role in lung expansion during inspiration
Pressure in the intrapleural space btw the lung and chest cavity. The source of this pressure is the intrinsic elastic properties of the lung and chest wall, PLUS the lung and chest wall deviate from their intrinisic equilibrium positions so there is a negative pressure that glues the lung to the chest cavity.
What are typical values for intrapleural pressure?
PIP is -5cm-H2O at the end of expiration. -30cm-H2O at the end of inspiration
Describe air flow during inspiration and expiration
Inspiration: lung pressure becomes negative relative to mouth pressure, so air flows into the lung. Expiration: lung pressure becomes positive relative to mouth pressure, so air flows out of the lung
Which pulmonary force is the driving force for changing lung volume during breathing
Transpulmonary pressure (= lung pressure - intrapleural pressure). During inspiration, transpulmonary and intrapleural pressure become more negative, but IP negative pressure happens more quickly. This causes the lung pressure to transiently achieve negative values
Describe the contribution of elastic recoil pressure to expiration
The inherent tendency of the lung to recoil back toward its intrinsic equilibrium position produces a transient positive pressure inside of lung, often referred to as a lung’s elastic recoil pressure.
Describe the importance of lung and chest wall compliance on breathing
Compliance, C, provides a measure of the elastic properties of the lung (C= ∆V/∆P). Compliance is high at the resting lung volume, and it decreases at high volumes, making expansion more difficult. Compliance is inversely proportional to elasticity of lung: highly compliant lungs have lost elasticity.
What is hysteresis
A property where compliance of lung differs during inspiration and expiration, with a greater
change in transpulmonary pressure being required to effect a given volume change during inspiration
How does fibrosis effect compliance
infiltration of connective tissue, is associated with
low lung compliance, making inspiration difficult
how does emphysema effect compliance
caused by the loss of elastic tissue, which results in high lung compliance. This makes expiration difficult
Causes of reduced chest wall compliance
old age, obesity and scar tissue. These reduce tidal volume which reduces air flow
