Question

  5. Often the lungs of premature infants have not matured to the point where they are
producing adequate surfactant. Why might this be a problem?

Experiment: Investigating Intrapleural Pressure

1. Describe what happens to air flow when one lung is “collapsed”.

2. What clinical term is used to describe the condition of:

1. a collapsed lung?
   

2. air in the pleural cavity?

3. Why does air enter the pleural cavity when the valve is open?

4. Why does the lung collapse when the valve is opened? (What forces are causing this to happen?)  

      5. Does the lung reinflate once the valve is closed? What must be done in order for the
lung to reinflate?

     6. A patient is brought to the emergency room with a stab wound to the right side of the
chest and a collapsed lung. Why is only one lung deflated with the knife wound?

Answer 1

Answer 5 -

1. The alveoli in the human lungs are lined by fluid.
2. Therefore the alveoli have high surface tension.
3. This surface tension has the tendency to collapse the alveoli.
4. Therefore, if this surface tension in not reduces there work of breathing increases and can lead to fatigue after some time.
5. Therefore, specialized cells in the lung called the type II pneumocytes to produce surfactants
6. Thes surfactants are a group of phospholipids and proteins
7. They along with calcium spread over the liquid lining of the alveoli and reduce the surface tension.
8. A human being starts producing surfactant by 24 - 28 weeks of gestation.
9. When a premature baby is born, its lungs are deficient in surfactants.
10. As a result, the increase in surface tension prevents the lung from expanding.
11. This decrease lung compliance ( in other words, resist change in its shape)
12. As the lung is not aerated, it receives less amount of oxygen and that causes vasoconstriction of the pulmonary vessels.
13. This results in lung ischemia. This leads to damage of the epithelial lining, edema, and protein accumulation.
14. This leads to hyaline membrane formation.

The following things happen to airflow when the lung collapses:

1. Collapse lung is an airless lung.
2. The collapse can occur due to a variety of reasons
   1. Fibrosis
   2. Surfactant deficiency
   3. Relaxation collapse - this seen with pneumothorax and pleural effusions.
3. Due to the collapse in the lung, the lung's compliance decrease.
4. It becomes difficult to inflate the lung.
5. The airways also narrow.
6. As the airways resistance is inversely proportional to the fourth power of the radius. There is a profound increase in airway resistance.
7. This reduces the airflow
8. Plus secretions built up in the collapsed part of the lung.
9. These secretions have the potential of eliciting bronchoconstriction.
10. All of these factors together cause hypoxia.
11. Hypoxia causes vasoconstriction of the pulmonary vasculature.
12. So there is not air reach the pulmonary capillaries and the pulmonary capillaries are constricted. This leads to ventilation/perfusion mismatch and shunt formation.
13. The shunt is that part of the cardiac output that doesn't get oxygenated.
14. The overall the patient develops hypoxia and needs supplemental oxygen.

A collapsed lung is called atelectasis

The air in the pleural cavity is called - pneumothorax

Answer 3:

Air enters the pleural cavity because -

1. The pleural cavity consists of two-layer of pleural
2. The visceral pleural which adherent to the lungs
3. The parietal pleura is adherent to the thoracic cavity.
4. The lung has the tendency to contract and collapse towards the hilum. This is because of the elastic components of the lung tissue.
5. The thoracic wall and the muscle attached to it have a tendency to move the thorax outwards.
6. Plus the lymphatics in the pleural cavity keep pumping the fluid out of the pleural cavity.
7. The pull of the thorax is slight higher than that of the lung.
8. The net effect the intrapleural pressure is negative ( irrespective of the phase of respiration)
9. This pressure is negative in comparision to the atmospheric pressure.
10. So if there is a breach in the thoracic wall, or and alveoli burst open, Air moves from positive pressure to negative pressure.
11. This causes the intrapleural pressure to become less negative and more positive.
12. This causes air to accumulate in the pleural cavity.

The lung collapses when the air enters because:

1. The lung has the tendency to collapse towards the hilum
2. this is because of the elastic tissue of the lungs and the surface tension of the alveoli.
3. The thorax wall has a tendency to move outside.
4. These opposing forces create negative pressure.
5. When air leaks into the pleural cavity, these opposing forces are uncoupled.
6. The elastic recoil of the lung ( which was so far prevented from collapsing due to the negative intrapleural pressure) acts unrestricted.
7. This causes the lung to collapse

Yes, the lung reinflates after the valve is closed.

• if the valve is closed the air leak is stopped.
• This allows the air inside the pleural cavity to be absorbed into the blood vessels
• the air absorption takes place at the rate of 1.25% of the volume of the hemithorax
• this process of air absorption can be hastened by giving 100% oxygen.
• It reduces the partial pressure of nitrogen in the pleural capillaries
• This promotes air absorption into the pleural capillaries

Only one lung deflated because,

1. this is because the patient was stabbed only one side.
2. Therefore only the right side lung collapsed.
3. The two lungs don't are independent of each other.
4. Unilateral traumatic injuries dont spread to the other side.