Atmospheric pressure = 760 mmHg = 1 atm
Intrapulmonary pressure – the pressure in the alveoli
– rises and falls with the phases of breathing
Intrapleural pressure – the pressure in the pleural cavity
– always about 4 mmHg less than intrapulmonary pressure
due to the strong adhesive force between the parietal and visceral
pleura
– the amount of pleural fluid in the pleural cavity must remain minimal in
order for the negative intrapleural pressure to be maintained
(active pumping of the pleural fluid into the lymphatics)
Transpulmonary pressure – the difference between the intrapulmonary and intrapleural
pressures
– keeps the air spaces of the lung open and prevent the lungs from
collapsing
Pneumothorax and Haemothorax
1. Pneumothorax
- presence of air in the pleural cavity
- spontaneous pneumothorax
caused by rupture of a small bleb
often occur in tall, thin men who smoke where mechanical stresses at the apex weaken the lung tissue
chronic obstructive pulmonary disease, cystic fibrosis, necrotizing pneumonia and AIDS patients with pneumocytis carinii infection
- traumatic pneumothorax
internal trauma such as rib fracture
external trauma such as stab wound or bullet wound
invasive or therapeutic procedures (iatrogenic pneumothorax)
- tension pneumothorax
air accumulates in the pleural cavity more rapidly than it can be evacuated
lung collapses
can also shift the mediastinum and severely impede venous return and cardiac ouput
2. Haemothorax
- presence of blood in the pleural cavity
- chest trauma where virtually every blood vessel in the chest can bleed into the pleural space
When air or fluid enters the pleural cavity:
visceral and parietal pleura are separated, disrupting the negative pressure that prevents the lungs from collapsing
compresses the lungs
Thus, lungs collapse.
Sources:
mcb.berkeley.edu/courses/mcb136/topic/Respiration/SlideSet1/Resp1.pdf
www.teleflexmedical.com/ucd/normal_anatomy_physiology.pdf
(Posted by: Vivian)
No comments:
Post a Comment