Compliance of lungs, Respiratory Work, and Pneumothorax.

Mechanism of breathing
Muscle contraction and relaxation function to bring air in and out of the respiratory system.

During normal breathing, contraction of the diaphragm and external intercostals increases the volume of the thoracic cavity. ?!?!?!?!? which decreases the intrathoracic and intrapleural pressures and works in inspiration. Relaxation has the opposite effect in expiration.

!!!!!!!important graphs!!!! compare inspiration and expiration, pressure in visceral pleura, parietal pleura, and pleural fluid

''exhalation works because of elasticity. lungs will recoil. when intraalveolar space decreases, air from higher pressure goes to lower pressure, lungs will recoil, visceral and parietal pleura will be pulled back.''

During exercise and respiratory distress, other muscles are also used – scalene and sternocleidomastoid (inspiration), internal intercostal and abdominal (expiration).

Lung compliance
Compliance is a description of the ability of the lungs and chest wall to distend. This is about elasticity of lung tissue but also non-elastic resistance (friction of parietal and visceral pleura, see slides, look up why airway resistance increases going from bigger to smaller curves. Gotta explain these two resistances, don't start to draw the weird graph because even professor dont ask about it. But wait, the triangle includes respiratory work. Includes elastic, viscous, and air resistance work. But the graph is in the Constanzo textbook around 202. It is much easier to explain with words - the graph does not give you anything. Muscles are not part of the respiratory system for this purpose). It inherently decreases with increasing stiffness, but also depends on physical circumstances:

C = V/P

For Compliance C (mL/mm Hg), Volume V (mL), Pressure P (mm Hg)

Plotting V vs P can give the slope (a measure of compliance).

Inspiration and expiration follow different pathways on this plot, since it takes work to overcome surface tension during inspiration but not during expiration.

Respiratory work includes the work needed to overcome


 * Elastic forces in lungs
 * Viscosity of surfactant
 * Airway resistance

Pneumothorax
If air is introduced into the intrapleural space, the pressure there will increase to the level of the surroundings. The lungs will then collapse, and the chest wall will go outward.

[look at slides, make sure to include all the points mentioned]