science of submersion

Question 1

what is the diving reflex

Answer 1

a natural CNS reflex that stops you inhaling and decreases your heart rate

Question 2

what causes skin wrinkling

Answer 2

• hypertonic swelling/ oedema with water entering through the skin
• nerve control causing sympathetic vasoconstriction

Question 3

what is the pathaway of the diving reflex

Answer 3

1. cold water trigger on your face
2. detected by the sensory arm of the trigeminal nerve
3. directly simulates the vagus nere to increase firing
4. this slows down heart rate
5. brainstem has respiratory centre so this is also inhibited

Question 4

what are the 2 difference pathways in the driving reflex

Answer 4

• afferent pathway: trigeminal to pons
• efferent pathway: brainstem via vagus nerve to heart

Question 5

what is the sympathetic gasp reflex in cold water immersion

Answer 5

• sudden cooling of peripheries causes sudden gasp
• then leads to hyperventilation

Question 6

what type of response is the gasp reflex

Answer 6

a sympathetic response, antagonised the by diving reflex

Question 7

what physiological changes occur from the gasp reflex

Answer 7

• cold water will increase heart rate, vasoconstriction and hypertension etc

Question 8

why is there reduced cerebral blood flow in cold water immersion

Answer 8

• blowing off lots of CO2 in hyperventilation which is a potent vasodilator
• body is going into alkalosis
• Co2 is no longer present so you get vasoconstriction

Question 9

what are the overtime responses to cold water immersion

Answer 9

• fewer gasps but still hyperventilation
• reduction in cerebral blood flow
• peripheral hypothermia
• severe hypothermia

Question 10

what causes severe hypothermia in cold water immersion

Answer 10

• feedback loops to the brain are altered
• you can’t stop the hypothermic effects
• decreasing consciousness

Question 11

why do you get arrhythmias in cold water immersion

Answer 11

• gets mixed response with acetylcholine slowing down the heart and adrenaline increasing it for the sympathetic response
• causes uncontrolled heart muscles

Question 12

what factors increase the risk of drowning in cold water immersion

Answer 12

• loss of consciousness
• peripheries too cold to swim
• gasping causing water aspiration
• decreased responses so you can’t keep your head above the water

Question 13

what are the physiological affects of hypothermia

Answer 13

• metabolic rate decline
• depressed myocardial contraction
• left shift of O2 dissociation curve
• vasoconstriction
• VQ mismatch
• increased blood viscosity

Question 14

how does heat loss happen in cold water

Answer 14

heat loss from convection, rapidly decreasing temperature. need to decrease evaporation when out of water

Question 15

what is the mechanism for autonomic conflict

Answer 15

• diving reflex causes parasympathetic stimulation
• cold shock response causes sympathetic stimulation

Question 16

what are important treatment approaches for cold water immersion

Answer 16

• need to measure core temperature
• minimise evaporation and convection then warm up
• heat gain wont be quick until vasoconstriction
• ECG conduction changes
• need to reverse
  alkalosis
• enzymes need optimal levels to work at so drugs wont have an effect

Question 17

how does breath hold diving work

Answer 17

• cant drive inspiration - high CO2
• blowing off co2 reduces the need for inspiration
  0 decrease the amount of air in the lungs allows easier decent
• rapid decent causes lung stretch so you don’t feel the need to breath