Lecture 7 The Dive Response

What does local or peripheral (external) cooling need?

Shunting of blood and an appropriate response from the heart

What happens to aquatic animals when they submerge?

Dive response: Breathing ceases, heart rate slows, and blood flow to peripheral tissues is reduced

What protects an animal from immediate asphyxiation during forced submergence?

• Sequesters blood oxygen for the brain and heart while allowing peripheral tissues to become anaerobic

• Decrease in peripheral blood is in direct conflict with the exercise response needed for muscle metabolism

Scholander’s forced dives

He held animals under, noted:

• “Diving Response” consisted of 3 key physiological reflexes

  • apnea - cessation of breathing

  • bradycardia - slow heart rate

  • peripheral vasoconstriction - narrowing of blood vessels in extremities

• Conclusion: during a dive, the animal turns itself into a heart-lung-brain machine

Do free diving penguins show bradycardia?

No, not normal diving, but involves tachycardia (fast) - tested in Humboldt

In some cases, they can - constant argument, no natural data, all forced

Why does bradycardia occur?

Blood doesn’t need to pump fast as it’s only going to the brain and lungs, not the rest of the body - beats fast uses more oxygen

Why tachycardia at the surface?

Heart rate goes up and beats hard and fast to reoxygenate the whole body

Oxygen has to go from the lungs to the rest of the body

Blue Whales

• Use huge amounts of energy to feed

• HR increases during lunge - step function

• Dive response - heart rates down to 2 beats per minute

What does bradycardia depend on?

Dive duration, e.g. seals don’t use step function

Dalton’s law

• Total pressure exerted is equal to the sum of the partial pressures of the individual gases

• Going down the water column, as the water pressure increases, so does the pressure of the gases in the lungs

What happens to the body at higher pressure?

Makes gases move into the body tissues (equilibration), and be more soluble

What happens the deeper you are?

More nitrogen in your body’s tissues, accumulates over time until equilibrium

Function of time and depth

Why can large amounts of nitrogen be problematic on the way back to the surface?

It expands out in bubbles to the rest of the body (Decompression Sickness, DCS)

DSC/ the bends

Results from the formation of bubbles in the tissues or circulation as a result of inadequate elimination of inert gas after a dive

How do diving animals avoid the bends?

• Only get it if your lungs are open to the rest of your body

• Dive with little air in their lungs - exhale before descent

• Collapsed lung - does not impart gases to the body

• Chest-wall collapse seen in seals, deeper depth = deeper collapse

What’s the disadvantage of tracheal compression?

Delays alveolar collapse during deep diving

What do penguins do to prevent the bends?

• Inhale

• Good vaso-constriction, that has little to no leakage

• Nitrogen only gets into a small amount of blood, so accumulates more slowly in the body tissues

• Vasoconstriction opens at the surface and dilutes the nitrogen in the brain with the blood from the rest of the body, stopping buildup

Another way diving animals avoid the bends?

Slow ascent

Methods used by animals to avoid the bends?

1. Lung collapse

2. Good vaso-constriction

3. Exhale - little air in lungs

4. Return to the surface slowly

Does it ever go wrong?

Yes - gas bubble lesions seen in stranded cetaceans

14 beaked whales in the Canary Islands near a naval exercise site (fear from sonar exposure) caused an accelerated ascent rate or a physical effect from the sonar