PK10 Flashcards
1
Q
3 phases of ventilatory control in exercise
A
- 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)
2
Q
What is hyperpnoea?
A
- VA rises in direct proportion to VCO2
- Therefore no fall in PaCO2
3
Q
What is hyperventilation?
A
- After 5x increase in metabolic rate VA rises disproportionately to VCO2
- Therefore fall in PaCO2
4
Q
Factors affecting ventilation at altitude
A
- Hypoxia –> stimulates peripheral chemoreceptors –> hyperventilation
- Blowing off of CO2 (hypocapnia) –> rise in pH (respiratory alkalosis) –> decreases ventilation
5
Q
Calculations indicating it was impossible to climb Everest without supplementary oxygen (PB at summit = 27.5kPa)
A
- 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
6
Q
What limits the length of a snorkel?
A
- 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)
7
Q
Problems of ascent/descent with bodily gases
A
- Gases compress on descent, forcing them into solution
- Gases expand on ascent, possibly causing rupture and them coming out of solution
8
Q
Problems with SCUBA diving
A
- Gas density increases <50m (increased work of breathing)
- Nitrogen narcosis
- Decompression sickness
9
Q
How is gas density increase in SCUBA diving combatted?
A
- Low density heliox (He + O2)
- Trimix (He + O2 + N2)
10
Q
What is nitrogen narcosis?
A
- High fat:water solubility of N2
- Expands lipid component of cell membranes
- General anaesthetic effect
11
Q
How does decompression sickness occur?
A
- 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
12
Q
What can decompression sickness cause?
A
- Pain in regions of joints
- Deafness
- Impaired vision
- Convulsion/unconsciousness/stroke
- Dyspnoea/cough/hyperpnoea
13
Q
Prevention of decompression sickness
A
- Regulate ascent
- Limit dives to <40m
- Use inert carrier less soluble than N2 with greater diffusibility (He)
14
Q
Treatment of decompression sickness
A
High pressure (decompression chamber) –> decompresses bubbles into solution + allows slow equilibration
15
Q
Advantages of liquid respiration
A
- 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
