Gaseous Exchange: Hyper- and Hypo-Baric Pressures

Question 1

Regarding breathing at high pressure (true or false):

Increasing pressure leads to increased work of breathing

Answer 1

True. Increasing pressure increases the density of gases. Air at 4 atm is four times as dense as at atmospheric pressure. This leads to increased ventilatory resistance and increased work of breathing.

Question 2

Regarding breathing at high pressure (true or false):

Divers breathing air can suffer from nitrogen narcosis

Answer 2

True. Nitrogen narcosis starts to occur at about 4 atm (30 m). Divers breathe a mixture of helium and oxygen because of its reduced density and to avoid nitrogen narcosis.

Question 3

Regarding breathing at high pressure (true or false):

Inspired oxygen concentration needs to vary with depth

Answer 3

True. In theory, lower concentrations of oxygen are needed, as PIO2 is maintained by high pressure. A concentration of 2.5% oxygen is required at 20 atm pressure to maintain a PIO2 of 50 kPa.

Question 4

Regarding breathing at high pressure (true or false):

Divers can breathe 100% oxygen

Answer 4

False. Breathing 100% oxygen produces oxygen toxicity, convulsions, chest pain and irreversible acute lung injury.

Question 5

Regarding physiological effects of altitude: (true or false)

Inspired PO2 at the summit of Everest is about half the sea level value

Answer 5

False. PIO2 at the summit of Everest is about a quarter of the sea level value. It is about half the sea level value at Everest base camp.

Question 6

Regarding physiological effects of altitude: (true or false)

Mental impairment occurs over 15 000 ft

Answer 6

False. Mental impairment occurs over 20 000 ft.

Question 7

Regarding physiological effects of altitude: (true or false)

Inspired PO2 would be zero at 63 000 ft

Answer 7

True. Also, body water would boil at this altitude.

Question 8

Regarding physiological effects of altitude: (true or false)

Acclimatization to high altitude takes a few hours for most humans

Answer 8

False. Acclimatization occurs over days to weeks.

Question 9

Regarding physiological effects of altitude: (true or false)

Respiration returns to normal within an hour of ascending to high altitude

Answer 9

False. The ascent causes initial hypoxia, but the hypoxic drive is short-lived.

Question 10

Likely symptoms of rapid decompression include the following (true or false):

Neurological damage

Answer 10

True. This damage may be permanent.

Question 11

Likely symptoms of rapid decompression include the following (true or false):

Arterial air embolus

Answer 11

True. This may rupture lung tissue, which can lead to gas bubbles being released into the arterial circulation.

Question 12

Likely symptoms of rapid decompression include the following (true or false):

Barotrauma in air-filled spaces

Answer 12

True. Any air-filled spaces, such as the lungs or ear, can suffer barotrauma.

Question 13

Likely symptoms of rapid decompression include the following (true or false):

Bubbles in cartilage

Answer 13

True. Bubbles can form in vessel poor tissues with avascular narcosis.

Question 14

Likely symptoms of rapid decompression include the following (true or false):

Raised intraocular pressure

Answer 14

False. Possible, but unlikely unless there were gas bubbles in the eye, which is effectively a fluid-filled space.

Question 15

Regarding relevance to anaesthesia (true or false):

Divers may become anaesthetized by nitrogen

Answer 15

True. This can occur when divers breath air below 30 m.

Question 16

Regarding relevance to anaesthesia (true or false):

Patients with hypoxia at sea level may be more vulnerable to desaturation at altitude

Answer 16

True. These patients may require additional oxygen.

Question 17

Regarding relevance to anaesthesia (true or false):

The boiling point of volatile anaesthetic agents reduces at altitude

Answer 17

True. The boiling point of all the volatiles fall, but in practice unaltered vapourizers have been used safely at altitude for many years. The commonest issue being inappropriately light anaesthesia because of inadequate vapourization of volatiles due to low temperature, which accompanies the altitude.

Question 18

Regarding relevance to anaesthesia (true or false):

Hyperbaric oxygen may be administered to a patient suffering from carbon monoxide poisoning

Answer 18

True. The treatment of carbon monoxide poisoning and burns may involve hyperbaric oxygen.

Question 19

Regarding relevance to anaesthesia (true or false):

Nitrous oxide can be used for divers who have returned to the surface

Answer 19

False. This might increase the volume of air bubbles in the tissues.

Question 20

Physiological adaptations to altitude include (true or false):

A shift of the HB dissociation curve to the right

Answer 20

False. The effect is to promote loading of oxygen in the lungs at low PO2. Therefore a leftward shift.

Question 21

Physiological adaptations to altitude include (true or false):

Chronic acidosis

Answer 21

False. Respiratory alkalosis is a response to altitude.

Question 22

Physiological adaptations to altitude include (true or false):

Methaemoglobinaemia

Answer 22

False.

Question 23

Physiological adaptations to altitude include (true or false):

Fetal haemoglobinaemia

Answer 23

False.

Question 24

Physiological adaptations to altitude include (true or false):

Increased red cell mass

Answer 24

True. This is typically a rise of Hb of a gram or so per decilitre.