Adaptation To Altitude & Physiology Of Diving

Question 1

What is the difference between hypoxemia and hypoxia?

Answer 1

Hypoxemia is a decrease in arterial PO2, while hypoxia is a decrease in oxygen delivery

Question 2

What are the different causes of hypoxemia?

Answer 2

1) High altitude

2) Hypoventilation

3) Diffusion defect (like in fibrosis)

4) Ventilation perfusion ratio defect

5) Right-to-left shunt

Question 3

How to determine the Alveolar-arterial O2 gradient?

Answer 3

It is determined by PAO2-PaO2 or (PiO2 “inspired O2” - PACO2/R0 - PaO2

• Normal range is 5-10 mmHg
• In healthy older adults it is 15-20 mmHg

Question 4

What are the different uses of the alveolar-arterial oxygen gradient?

Answer 4

1) To measure oxygenation (assessing the functionality of the blood-air barrier)

2) To determine the causes of hypoxemia (intra or extrapulmonary) like is it a embolism or heart failure

Question 5

When does the A-a gradient increases?

Answer 5

1) With age

2) When you inhale a higher concentration of oxygen

3) Right to left shunting

4) When there is fluid in the alveoli (like in congestive heart failure, Acute respiratory distress syndrome, pneumonia)

5) Mismatch between ventilation and perfusion (pulmonary embolism, pneumothorax, Atelectasis, Obstructive lung disease, pulmonary edema, pneumonia)

6) Alveolar hypoventilation (interstitial lung disease, lung fibrosis) They are mostly found with increased CO2 rather than increased A-a oxygen gradient

Question 6

What are the causes of hypoxemia?

Answer 6

Decreased oxygenation of the blood in the lung due to:

1) Extrinsic reasons:

• Lack of oxygen in the atmosphere (high altitude)
• Hypoventilation (NM disorder)

2) Lung diseases

• Hypoventilation ( increased airway resistance, or decreased lung compliance)
• Abnormal alveolar V/Q ratio (increased physiological dead space or increased shunting)
• Decreased respiratory membrane diffusion (like in edema)

3) Venous to arterial shunts like in R-L cardiac shunt

4) Decreased oxygen transport to the tissues by the blood

• Anemia or abnormal Hb
• Circulatory deficiency (general or local)

5) Decreased tissue use of Oxygen

• Deficiency of cellular oxidation enzymes
• Cellular toxicity (cyanide poisoning)
• Vitamin deficiency (vitamin B or beriberi)

Question 7

What happens to the air as we ascend?

Answer 7

The barometric pressure reduces, however oxygen fraction is the same, this will often result in chronic hypoxia from 760 to 43 mmHg in Mount Everest

• As you ascend the arterial oxygen saturation decreases reaching 50% which we can sustain at 20,000 feet but after that we will be unconscious, so we can use 100% which will help us till 45,000 fett

Question 8

How does our respiratory system respond to high altitude?

Answer 8

1) Increased pulmonary ventilation (caused by the stimulation of the arterial chemoreceptors)

2) Decreased oxygen in arterial blood

3) Increased p, respiratory alkalosis (increased ventilation, more breathes, more CO2 excretion, less CO2 in blood, pH increases)

3) Constriction of the pulmonary vessels, increasing the pulmonary resistance and pressure, which will lead to the hypertrophy of the right ventricle

4) The oxygen hemoglobin curve will shift to the right

5) Increased RBC and Hb concentration

6) increased diffusion capacity (due to increased SA, increased Lung volume, and increased pulmonary arterial pressure especially at the apex of the lungs)

7) Increased capillarity (increases systemic capillaries)

8) Changes at cellular level (increased mitochondria and oxidative enzyme systems to use oxygen more effectively)

Question 9

What is the effect of altitude on the PAO2, PACO2 and arterial oxygen saturation?

Answer 9

As we ascend all of those metrics will decrease but breathing pure oxygen will help us maintain a good oxygen saturation till about 45,000 feet

Question 10

What are the different adaptation that occurs in people born at high altitudes?

Answer 10

1) They have a increased chest size compared to body size which aids them in increasing the ratio of ventilation capacity

2) Increased size of the right side of the heart (increasing pulmonary pressure and thus a expanded capillary system)

3) Better delivery of oxygen to the tissues

Question 11

What is the difference between the oxygen-hemoglobin dissociation of blood of natives and sea-level residents?

Answer 11

People living in the mountain have a better arterial oxygen saturation and can withstand lower lower atm pressure and oxygen concentrations

Question 12

What are the causes of chronic mountain sickness?

Answer 12

• It took a while for a person to get sick

1) High mass of RBC (increases the blood viscosity, decreases the blood flow, and decreases oxygen delivery to the tissues

2) Lung hypoxia (this will lead to the constriction of the lung capillaries, increasing the pulmonary arterial pressure, and thus right heart failure might develop

3) Alveolar arterial spasm due to hypoxia, which will increase the pulmonary blood flow shunt

• These causes will ultimately lead to Increased blood viscosity, pulmonary hypertension, and congestive heart failure

Question 13

What are the effects of chronic mountain sickness?

Answer 13

1) High hematocrit

2) Increased pulmonary arterial pressure

3) Enlarged right side of the heart

4) Decreased peripheral arterial pressure

5) Congestive heart failure

6) Death unless moved to a lower altitude

Question 14

What are the effects of acute mountain sickness?

Answer 14

• Few hours to 2 days after ascending

1) Acute cerebral edema (as hypoxia will dilate the cerebral blood vessels increased the filtration which might lead to edema)

2) Acute pulmonary edema (pulmonary htn, pulmonary circulation is engaged with blood and thus edema might develop)

Question 15

What happens to the atm pressure when you deep dive?

Answer 15

The opposite of ascending, where the atmospheric pressure will increase decreasing the lung capacity

Question 16

What happens to the atm pressure when you deep dive?

Answer 16

The opposite of ascending, where the atmospheric pressure will increase decreasing the lung capacity

Question 17

What is boyles law?

Answer 17

• It studies the effect of sea depth on gas volume

As we descend the atm pressure increases which is inversely proportional to the volume of gas, so as we go down the volume of gas decreases

Question 18

What is nitrogen narcosis?

Answer 18

When we dive very deep, nitrogen pressure will be very high and it will dissolve in the fatty substance of the neural membrane, altering the conduction of ions through the membrane reducing its excitability

Question 19

What are the effects of nitrogen narcosis?

Answer 19

• The amount of dissolved nitrogen in the body decreases with depth, where 50% of it dissolves in the fat, which will take several hours to come back to normal when you return to sea level
• Starts under 120 ft and till 250ft
• Joviality and loss of care
• Decreased strength and inability to perform tasks
• Unconsciousness (narcotic)

Question 20

How can we develop oxygen toxicity?

Answer 20

At high pressure, as we descend more the more the amount of oxygen is dissolved in the plasma

Question 21

What are the effect of acute oxygen poisoning?

Answer 21

• Due to the failure of the hemoglobin-oxygen buffering

1) Nausea, muscle twitching, dizziness, vision disturbance, irritability and disorientation

2) Formation of oxygen free radicals which will damage the cell membrane and other cellular metabolic systems

3) Seizures followed by coma

Question 22

What are the effect of chronic oxygen poisoning?

Answer 22

1) Lung airway congestion

2) Pulmonary edema

3) Atelectasis

Question 23

What happens to the level of CO2 in our lungs as we dive?

Answer 23

• CO2 partial pressure in the lungs does not increase as CO2 production remains the same
• However, CO2 can build up in the lungs depressing the respiratory center and leading to respiratory acidosis, lethargy, and narcosis

Question 24

What is the decompression sickness?

Answer 24

• Occurs when the diver comes back to the sea-level very quickly
• Nitrogen bubbles form after some time of diving, which if the diver reaches the surface very quickly will have a very high partial pressure (4065) in the body fluid compared to 760 mmHg from the atmosphere which might cause serious damage

Question 25

What are the effects of decompression sickness?

Answer 25

• Due to the nitrogen bubbles that can plug any blood vessel:

1) Pain in the joints and muscles

2) Nervous system symptoms (dizziness, paralysis, collapse and unconsciousness)

3) Massive numbers of microbubbles can plug the capillaries of the lungs, causing shortness of breath, pulmonary edema, and death in 2% of the cases

• Eliminated by coming to the surface slowly

Question 26

What are some of the preventative measures to minimize the damage while deep diving?

Answer 26

1) Use of hilum in gas mixtures (it has 1/5 of nitrogen narcotic effect, only half of its volume dissolves in the body and it can be removed easily, it has a low density which reduces the work of breathing)

2) Low oxygen concentration is used in the gas mixture to prevent toxicity

Question 27

What is the hyperbaric oxygen therapy?

Answer 27

• Administration of oxygen to the patient at high pressure (2-3 atm pressure), via a mask or intra-tracheal tube
• It can treat:

1) Gas gangrene

2) Arterial gas embolism

3) CO poisoning

4) Osteomyelitis

5) Myocardial infarction

Question 28

What are the complications of the hyperbaric therapy?

Answer 28

1) Trauma to the middle ear

2) Eye and sinus problems

3) Oxygen poisoning in rare and severe cases, leading to seizures, fluid in the lungs, lung failure, etc