Respiartoty System Lec 3 Flashcards
What’s the district difference between PA and AP chest?
PA = less mag of heart whereas in AP the heart is magnified more ass it is further away from IR
What should a chest X-ray look like?
Inspiration = 10 ribs above diaphragm w
Spinous process centred between medial ends of clavicle
Trachea shown with air, lung vascularity
Why does the expansion of the chest cause the lungs to expand?
Due to the pleural linkage
The chest wall and the lungs are covered in parietal and visceral pleura, and the lungs are always held in close apposition with the chest wall at all times due to the cohesive forces of these pleural membranes and fluid.
Thus, when the chest expands, the lungs will also follow as they are linked (respectively)
Explain the role of the pleural membranes in generating the pleural linkage (the mechanics) and how it allows for ventilation
The parietal pleura is attached to interior of thoracic cavity (ie. lines rib cage and diaphragm), and this forms 2 completely seperate sacs with one on each side of the midline
The visceral pleura is the coat of membrane for the lungs
The space between the 2 membranes referred to as pleural cavity has intrapleural fluid (20-30 mL) and this reduces friction and the membranes can glide amongst each other easily as the lungs expand and contract - pleural fluid bond
How does a collapsed lung occur?
If negative intrapleural pressure is lost, the elastic recoil of the lung will be the driving force and THEREFORE COLLAPSED LUNG
REMEMBER = you usually only get one collapsed lung because we have two sets of pleural cavities (pleural membrane sets) on each side of the midline
Collapsed lung = atelectasis
Explain the mechanics of a pneumothorax presence
Air enters pleural space and increases intrapleural pressure towards atmospherical pressure causes collapsed lung
Explain what’s traumatic or spontaneous PT
It can be traumatic or spontaneous
- open PT (air coming from outside through chest walls) (eg. A gun shot wound opening)
- closed PT (air coming from lungs)( eg. Due to cancer of Cystic fibrosis)
- COPD major cause of spontaneous PT (70% cases)
What’s tension PT
Opening that allows air to enter pleural cavity functions as a one way valve, causing more air to be trapped
This will displace organs (esp. heart)
What’s a treatment done for a pneumothorax?
Chest drain with direction flow valve (or drain under water)
Remove the air from pleural cavity and lung will reinflate
Explain the mechanics of ventilation (inspiration)
Inspiration begins with contraction of respiratory muscles (the diaphragm and external intercostal muscles) (occurs every inspiration)
- this increases intra thoracic volume
- which reduces pressure inside lungs to less than ATmospheric Pressure
Air is then drawn into airways
Action of accessory respiration muscles further enlarge TC ONLY DURING FORCEFUL INSPIRATION
The mechanics of ventilation (inspiration) can be defined mathematically
Using Boyle’s law
Volume is inversely proportional to pressure (1/P)
Meaning, during inspiration VOL INCREASES, so the P out > P in
Which causes air to flow into lungs as P is lower.
Vice versa for expiration
So the intraalveolar P decreases by 1 usit from AP (759 during inspiration) and then increases by 1 unit during expiration. Pleural cavity pressure decreases to 754 during inspiration and increases back to 756 during expiration
What causes expiration?
The elastic recoil of the alveoli
What’s the atmospheric pressure?
Force of air put on objects
It’s 760 mmHg at sea level and decreased with altitudes above
What’s intra alveolar pressure?
Intrapulmonary pressure is pressure in alveoli
760 mmHg like atmosphere outside
What’s intrapleural pressure?
Pressure within pleural cavity.
Around 756 mmHg at rest. Referred to as -4 as it is 4 units below 760 in atmosphere
Thus, there’s a slight vacuum
