Which of the following changes in the lungs occurs under the ...

[lracut11]

Which of the following changes in the lungs occurs under the influence of general anesthesia? I. decreased chest wall elastance II. increased pleural pressure III. decreased muscle tone IV. decreased chest wall compliance
 
  A. I only
  B. II, III only
  C. I, II, III only
  D. II, III, IV only

Question 2

At which of the following points along the ventilatory cycle is alveolar pressure equal to atmospheric pressure; therefore, transpulmonary pressure equals pleural pressure? I. during inspiration II. at end-inspiration III. during expiration IV. at FRC
 
  A. I only
  B. II only
  C. I, III only
  D. II, IV only

[meganmoser117]

Answer to Question 1

ANS: B
A. Incorrect response: See explanation B.
B. Correct response: The effect of general anesthesia or mechanical ventilation on regional pleural pressure in humans is not well described, though it is known that muscle tone decreases during anesthesia, increasing chest wall elastance and thus increasing pleural pressure. This effect helps explain the diminished FRC and eventual development of atelectasis in the dependent regions of normal subjects undergoing prolonged mechanical ventilation for elective surgery.
C. Incorrect response: See explanation B.
D. Incorrect response: See explanation B.

Answer to Question 2

ANS: D
A. Incorrect response: See explanation D.
B. Incorrect response: See explanation D.
C. Incorrect response: See explanation D.
D. Correct response: Regional lung inflation depends on the local transpulmonary pressure, which is the difference between the pressure in the alveoli and pressure at the pleural surface. That is,
Ptranspulmonary = Ppleural Palveolar
At FRC and at end-inspiration, alveolar pressure equals atmospheric pressure. Therefore transpulmonary pressure equals pleural pressure.

[lracut11]

Excellent

[yeungji]

TYSM