8. A diver breathing air at a depth of 30 metres u

[Editor]

8. A diver breathing air at a depth of 30 metres under water:
a. is exposed to a pressure of about 4 times that at the surface
b. becomes unconscious from nitrogen narcosis
c. has a 2-3 fold increase in the oxygen content of the blood
d. expands more energy on the work of breathing than at the surface for a given ventilation
e. runs the risk of developing gas bubbles in his central nervous system while at this depth

[abanerjeeuk]

8. A diver breathing air at a depth of 30 metres under water:
a. is exposed to a pressure of about 4 times that at the surface
b. becomes unconscious from nitrogen narcosis
c. has a 2-3 fold increase in the oxygen content of the blood
d. expands more energy on the work of breathing than at the surface for a given ventilation
e. runs the risk of developing gas bubbles in his central nervous system while at this depth



Answers:

F F T T T

[aaswani]

(a) is True.

Unconsciousness from nitrogen narcosis occurs at greater depths than this. At this depth, confusion and euphoria may be present. Manual incoordination and coma occur at progressively greater depths.

[aaswani]

(c) is False.

At a depth of 30m, ambient pressure is 4 atm = 405.2kpa

Alveolar gas equation calculates PAO2= PIO2 - PaCO2/R
= 0.21x(405.2-6.3) - 5.3/0.8
= 0.21x 398.9 - 6.625
= 83.769 - 6.625
=77.14 kPa

Therefore as Hb is almost fully saturated with O2 at sea level breathing room air, the increase in oxygen carriage at this depth comes from that dissolved in plasma which can be calculated as:
PaO2 x 0.023 = 77.14 x 0.023 = 1.77ml O2/dL
Therefore, O2 carriage of blood breathing air at this depth only increases by 10%.

[jijindr]

the risk of developing gas bubbles in his central nervous system is during the ascent, so e)F