Dolphins,diving &dysrhytmias

Question 1

What are the 4 stages of immersion (in water)?

Answer 1

1. ) Initial responses/sudden death (3-5mins)
   - skin cooling
2. ) Short-term responses (5-30mins)
   - Superficial nerve& muscle cooling
3. )Long term responses( 30min+)
   - Cooling of deep tissues
4. )Post-immersion (during rescue)
   - Collapse of arterial pressure
   - Continued cooling

Question 2

Summarise the cold shock response

Answer 2

• Gasp response
• Hyperventilation
• Peripheral vasoconstriction
• Tachycardia
• Noradrenaline/adrenaline release

Question 3

What drives the cold shock response?

Answer 3

adrenergic-sympathetically driven response

Question 4

What are the acute responses to cold water immersion?

Answer 4

1. )Cold shock response:
   - head out immersion& submersion
2. ) Diving response:
   - Facial submersion

Question 5

Summarise the diving response

Answer 5

• Apnoea
• Bradycardia
• Peripheral vasoconstriction

Question 6

Explain arrhythmias during cold water immersion

Answer 6

• Alternating between periods of Bradycardia& tachycardia because of the conflicting inputs to the heart competing with each other&occasionally one or the other wins so we get alternating periods
• In normal healthy people this is benign

Question 7

What cardiovascular changes occur during the diving response?

Answer 7

• Increased BP

- Decreased peripheral blood flow

Question 8

What does the QT interval approximate to?

Answer 8

-The action potential duration

Question 9

What occurs to the QT interval with a decrease in heart rate

Answer 9

-Prolongs the AP and QT interval

Question 10

What occurs to the QT interval with a increase in heart rate

Answer 10

-Shortens the AP and QT interval

Question 11

Why dont we see a change in the QT interval during the diving response?

Answer 11

-The heart rate changes too fast so the QT interval can’t keep up
(QT interval changes within 30s of a rate change)

Question 12

Do we see a change in the QT interval in the diving response if we wait a little bit longer?

Answer 12

• May see a change in trained divers

- If we wait 3-4mins the QT interval gets longer

Question 13

Explain autonomic conflict that occurs with the diving response

Answer 13

• Parasympathetic stimulation of the SAN causes bradycardia
• Sympathetic activation of the LV causes a decreased APD
• These are conflicting inputs to the heart
• During the 1st minute of facial immersion,something is preventing the action potential (QT) from prolonging

Question 14

Outline autonomic conflict between the diving response and cold water shock response

Answer 14

• The diving response is parasympathetic and vagally mediated; leading to a decreased HR and bradycardia
• The cold-water shock response/ exercise is sympathetic and causes an increased HR and tachycardia
• Results in periods where one or other reflex dominates and alternating periods of tachycardia and bradycardia, which cause arrhtytmias

Question 15

What is long QT syndrome?

Answer 15

• Genetic abnormality in which carriers are characterised by having a prolonged QT interval
• Increased risk of serious cardiac arrhthmias and sudden death

Question 16

How is long QT syndrome diagnosed

Answer 16

• QT prolongation on the ECG
• Unexplained syncope
• family history
• Congenital neural deafness

Question 17

What other situations may trigger autonomic conflict?

Answer 17

• Alarm clock syndrome
• shovelling snow
• Early morning increase in SCD
• CPVT (catecholamines tend to shorten the AP)