CC 1 - Exercise Associated Hyponatremia

Question 1

Normal plasma [Na+] range?

Answer 1

135-145 mEq/L

Question 2

Effect of prolonged endurance on the body?

Answer 2

Creates a state of dynamic and continous homeostatic imbalance and the body struggles to maintain homeostasis under that kind of stress

Question 3

Definition of exercise associated hyponatremia (EAH)?

Answer 3

Occurrence of hyponatremia in individuals engaged in prolonged physical activity and is defined by a plasma [Na+] below the normal reference range of the lab performing the test (for most labs, this is <135 mmol/L)

Question 4

Can EHA occur both during and after physical activity?

Answer 4

YUP

Question 5

Common length of exercise for EAH to occur?

Answer 5

Longer than 4 hours

Question 6

Physiology of hyponatremia?

Answer 6

Drop of [Na+] outside the brain due to dilution from retained water or due to increased losses in urine and/or sweat => water moves into the brain due to osmosis => cerebral edema where brain occupies the space with the cerebrospinal fluid was => compression of cerebral blood vessels => cerebral ischemia => death

Question 7

What happens during cerebral edema once the brain has reached the limits of the skull? Consequence?

Answer 7

Herniation through cerebellum and spinal cord => compression of respiratory centers => respiratory arrest

Question 8

2 potential causes of death due to EAH?

Answer 8

1. Cerebral ischemia

2. Respiratory arrest

Question 9

Can’t the brain just adapt to cerebral edema with water/Na+ moving out of it?

Answer 9

Yes, but that takes 24-48 hours so not fast enough to adapt to the edema

Question 10

Effect of hyponatremia on lungs?

Answer 10

Pulmonary edema

Question 11

What % of marathon runners become hyponatremic? More males or females?

Answer 11

15%

More females

Question 12

Why is EAH a modern disease?

Answer 12

Because marathons become popular

Question 13

Is EAH the most common life threatening manifestation of fluid dysregulation during prolonged endurance exercise?

Answer 13

YUP

Question 14

2 types of hyponatremia? Which is more common?

Answer 14

1. Dilution (2/3rds)

2. Depletion (1/3rd)

Question 15

Treatment for depletion hyponatremia?

Answer 15

Saline IV

Question 16

How do we know EAH is due to water intoxication and not excessive sweat loss?

Answer 16

Studies done measuring body weight and hyponatremia is associated with overhydration and high body weight + normalizing sodium after endurance makes patients excrete water

Question 17

If your water homeostasis in normal during endurance, are you supposed to gain or lose weight?

Answer 17

Loose 2kg in lean body mass due to muscle metabolism

Question 18

Is there also sodium depletion in EAH?

Answer 18

A little, but that is not the source of the issue

Question 19

When does thirst begin? Describe it. What to note?

Answer 19

When AVP is causing maximal urine concentration, thirst starts and increases in linear proportion to increases in plasma osmolarity

Note: PERCEPTIBLE thirst does not begin until a higher plasma osmolarity is reached

Question 20

What is the osmotic threshold for thirst?

Answer 20

5-10 mOsm/kg H2O higher than that of AVP secretion

Question 21

In what way was EAH mismanaged?

Answer 21

Marathon runners were advised to drink as much as possible, even when they were not thirsty

Question 22

Max volume of kidney excretion a day?

Answer 22

18-24 L = 700 mL-1L/hour = 14.2 mL/min

Question 23

What is the most important hormone in the body? Why?

Answer 23

AVP - it controls body water, which is the largest component of our body

Question 24

Why does maximal urine excretion decrease during exercise?

Answer 24

Because AVP secretion is stimulated by many factors that occur during exercise:

1. Hypovolemia due to sweating
2. Nausea
3. Hypoxia
4. Hypoglycemia
5. Stress
6. Physical activity

Question 25

Describe the relationship between AVP and urine concentration.

Answer 25

Linear relationship

Question 26

Describe the relationship between urine osmolarity and urine volume.

Answer 26

Exponential and inverse, meaning that a low levels of AVP there are greater effects on the amount of water you excrete

Question 27

Describe how exercise increases AVP secretion?

Answer 27

AVP increases in relation to work intensity

Question 28

Based on EAH findings, what are the new recommendations regarding endurance exercise and hydration?

Answer 28

1. Drink only to thirst, no forced hydration

OR

1. Take USATF sweat test to gauge true fluid requirements
2. Decrease water/sport drink stops at endurance events
3. Point of care electrolyte testing at medical tent

Question 29

Should you drink ahead of your thirst to prevent dehydration? Explain.

Answer 29

NOOO

Thirst is there to prevent dehydration, that is how mammals have evolved

Question 30

6 risk factors for EAH?

Answer 30

1. Weight gain
2. Race time >4h
3. Low or high BMI

Univariate:

4. Female
5. Consumption of over 3L of fluids
6. Consumption of fluids every mile

Question 31

Why does increased race time increase EAH risk?

Answer 31

Because more opportunities to drink more water

Question 32

What is the myth around sports drinks?

Answer 32

They replete electrolytes - which they BARELY do. They barely protect from hyponatremia because they do not have that much Na+

Question 33

What is the best drink to avoid EAH after a race?

Answer 33

Bloody mary: Na+ rich to replete osmolarity and alcohol to increase urine output by inhibiting AVP secretion

Question 34

Normal sweat osmolarity?

Answer 34

30-60 mmol/L

Question 35

How does alcohol affect urine output?

Answer 35

It increases it independently of the volume ingested because it inhibits AVP secretion by the posterior pituitary