PK10

Question 1

3 phases of ventilatory control in exercise

Answer 1

• Phase 1 (steep immediate increase in V - information from limbs + cortex)
• Phase 2 (sloped/gradual increase in V - information from blood)
• Phase 3 (steady state of high V)

Question 2

What is hyperpnoea?

Answer 2

• VA rises in direct proportion to VCO2
• Therefore no fall in PaCO2

Question 3

What is hyperventilation?

Answer 3

• After 5x increase in metabolic rate VA rises disproportionately to VCO2
• Therefore fall in PaCO2

Question 4

Factors affecting ventilation at altitude

Answer 4

• Hypoxia –> stimulates peripheral chemoreceptors –> hyperventilation
• Blowing off of CO2 (hypocapnia) –> rise in pH (respiratory alkalosis) –> decreases ventilation

Question 5

Calculations indicating it was impossible to climb Everest without supplementary oxygen (PB at summit = 27.5kPa)

Answer 5

• VA 4x that of sea level –> PACO2 = 5/4 = 1.25kPa
• PAO2 = PIO2 - (PACO2 / R)
  > = (0.21 x 27.5) - (1.25 / 0.8)
  > = 5.78 - 1.56
  > = 4.2kPa
• A-a difference (1kPa) –> 4.2 - 1 = 3.2kPa
• PAO2 of 3.2 is incompatible with life

Question 6

What limits the length of a snorkel?

Answer 6

• Dead space (rebreathing problems)
• Resistance (narrow tube –> increased work)
• Maximum inspiratory pressure (intrapulmonary pressure = ambient pressure at surface but pressure on chest wall = pressure exerted by water at depth)

Question 7

Problems of ascent/descent with bodily gases

Answer 7

• Gases compress on descent, forcing them into solution
• Gases expand on ascent, possibly causing rupture and them coming out of solution

Question 8

Problems with SCUBA diving

Answer 8

• Gas density increases <50m (increased work of breathing)
• Nitrogen narcosis
• Decompression sickness

Question 9

How is gas density increase in SCUBA diving combatted?

Answer 9

• Low density heliox (He + O2)
• Trimix (He + O2 + N2)

Question 10

What is nitrogen narcosis?

Answer 10

• High fat:water solubility of N2
• Expands lipid component of cell membranes
• General anaesthetic effect

Question 11

How does decompression sickness occur?

Answer 11

• High PN2 during diving forces it into solution
• Mainly goes to tissues such as fat with relatively high N2 solubility
• Comes out of solution during ascent
• Poor blood flow to adipose tissue + slow diffusion –> long time for N2 to be exhaled
• If ascent too fast, N2 not blown off + comes out of solution, forming bubbles which obstruct circulation

Question 12

What can decompression sickness cause?

Answer 12

• Pain in regions of joints
• Deafness
• Impaired vision
• Convulsion/unconsciousness/stroke
• Dyspnoea/cough/hyperpnoea

Question 13

Prevention of decompression sickness

Answer 13

• Regulate ascent
• Limit dives to <40m
• Use inert carrier less soluble than N2 with greater diffusibility (He)

Question 14

Treatment of decompression sickness

Answer 14

High pressure (decompression chamber) –> decompresses bubbles into solution + allows slow equilibration

Question 15

Advantages of liquid respiration

Answer 15

• No compression by external pressure
• No need to breathe high-pressure gas
• Just ‘dial in’ oxygen-nitrogen mix equal to atmospheric air –> partial pressure fixed at all depths

Question 16

Problems with liquid respiration

Answer 16

• How to circulate liquid
• How to replace lost oxygen + ‘scrub’ excess CO2
• How to evacuate lung after

Question 17

Advantages of liquid ventilation with perfluorocarbons

Answer 17

• Improvement in oxygenation in acute lung injury
• Improvement in lung compliance
• Anti-inflammatory effect
• Alveolar and endobronchial lavage

Question 18

Adverse effects of liquid ventilation with perfluorocarbons

Answer 18

• Pneumothorax
• Circulatory impairment
• Lactic acidosis
• Blocking of the endotracheal tube
• CO2 elimination
• Toxicity
• Interference with radiographic imaging