Pulmonary 9 - Lecture 31

Question 1

What is the affect of High Altitude on

1. Barometric pressure
2. PO2

Answer 1

Both decrease!!

Question 2

What is the PiO2 at a Barometric Pressure of 255 mmHg (high altitude)?

What is the PAO2?

Answer 2

PiO2: 0.21 x (255-47mmHg) = 44 mmHg

PCO2 = 40 mmHg, respiratory ratio = 1

PalveolarO2 = 43 – 40/1 = 3 mmHg !

Question 3

How is acclimatization achieved at high altitudes where the PO2 is low?

Answer 3

Acclimitization via Hyperventilation

• 5 fold increase in PO2!

PalveolarO2 = 43 – 8/1 = 35 mmHg

Question 4

How do people achieve hyperventilation in high altitudes with PaCO2 of 33 mmHg?

Answer 4

HYPOXIC STIMULATION of peripheral chemoreceptors

Question 5

What happens initially at high altitudes due to hyperventilation?

Answer 5

Respiratory Alkalosis due to low PaCO2 and high pH

• this initially inhibits further ventilation, but is adjusted within several days & hyperventilation is further increased

Question 6

How does Polycythemia normalize O2 concentration? How is polycythemia achieved?

Answer 6

1. Increases RBC concentration
   - via erythropoietin from Kidney (takes days/weeks)
2. Increase Hb/O2 carrying capacity
   - although Saturation may decrease, the total Oxygen per dL of blood is relatively high due to the increased Hematocrit

(higher Hb = more Oxygen can build up)

Question 7

What are the normal Hb, SO, and Oxygen content per ml/dl

Answer 7

normal Hb = 15 g/dL
SO = 95%
19.1 mL O2/dl

Question 8

What is the only blood at high altitude that has relatively similar PO2 to sea level?

Answer 8

Mixed Venous Blood!

• only 7 mmHg difference

Question 9

What is the initial affect of 2,3- DPG because of high altitudes? What is the secondary affect?

Answer 9

1. RIGHTWARD shift of O2 binding curve
   - O2 dissociates easier
2. LEFTWARD shift once alkalosis occurs, due to hyperventilation (low CO2 - better loading of Oxygen)

Question 10

What is the affect of alveolar hypoxia on Pulmonary Vasculature? (2 clinical correlates)

Answer 10

1. Pulmonary Vasocontriction
2. Pulmonary Edema
3. Right Heart Hypertrophy

Question 11

Because the air is less dense at high altitudes, what happens to the breathing capacity?

Answer 11

Maximal Breathing Capacity Increases

Question 12

What is Acute Mountain Sickness? What 2 clinical cases can this progress into?

Answer 12

1. Headache, fatigue, dizziness, nausea
2. Pulmonary Edema
3. Cerebral Edema

Question 13

What is Chronic Mountain Disease?

Answer 13

Polycethemia, Fatigue, Reduced Exercise TOlerance, Hypoxemia

Question 14

What is the increase in pressure for every 10 m/33ft depth increase ?

Answer 14

Pressure doubles!

• lung is compressed, so volume decreases (breathing is reduced)

Question 15

What is the primary and secondary responses of the DIVING REFLEX? What is it induced by?

Answer 15

INDUCED BY APNEA

1. Primary - Peripheral Vasoconstriction due to Sympathetic Activity
   = initial hypertension
2. Secondary - Vagal induced Bradycardia & reduction of CARDIAC OUTPUT

= slow HR to spare oxygen

Question 16

What is the primary purpose of Bradycardia within the context of the diving reflex?

Answer 16

Slow HR = decrease CO and decrease Oxygen Use

Question 17

What are the 3 important affects of the diving reflex?

Answer 17

1. Sympathetic Peripheral Vasoconstriction = increase BP
2. Decrease HR (vagally induced bradycardia)
   - O2 saturation is maintained
3. Increase Hb by splenic contraction

Question 18

What is the pO2 that hypoxic loss of consciousness occurs at?

Answer 18

PO2 of 20-25 mmHg

Question 19

How does Hyperventilation lead to LOC? What input is overridden?

Answer 19

1. Reduces CO2 drive to breath (low CO2 = less of a stimulus to increase ventilation)
2. Weak Respiratory Stimulus from Hypoxia is OVERRIDDEN voluntarily by low CO2

(the low CO2 has a greater affect than the low O2)

Question 20

How does Ascent Blackout occur?

Answer 20

Reduction of Water Pressure & Gas Pressure causes a decrease in pO2 content

(due to lower pressure = lower O2 partial pressure)

• need to slowly ascend to avoid LOC at 20-25 mmHg of PO2

Question 21

How does carbohydrate depletion lead to Hypoxic Loss of Consciousness?

Answer 21

Less CO2 produced by metabolism

• reduces CO2 drive to breath

Question 22

What are the 3 reasons that LOC can occur in Breath Holders?

Answer 22

1. Hyperventilation - low CO2
2. Ascent Blackout - low PO2
3. Carbohydrate Depletion - Low CO2

1 and 3 have a common theme = LOW CO2! = loss of CO2 drive to breath

Question 23

What is the affect of barotrauma of descent?(2) Why does this happen?

Answer 23

1. Lung Edema
2. Damage
   - Atelectasis
   - Capillary Rupture

Pressures redistribute & increase in certain areas
ex: Capillary Hydrostatic pressure increases and causes pulmonary edema

Pressures redistribute because LUNG VOLUME redistributes (occurs at low PRESSURES
ex: submerging head underwater)

Question 24

What is maintained in Barotrauma of Descent & what is lost?

Answer 24

1. Compression of lung
2. Redistribution of blood volume

LOST:

1. Atelectasis
2. Edema
3. Capillary Rupture

Question 25

What is Decompression Sickness?

Answer 25

Nitrogen content increases in the tissues as the pressure increases (when diving) - since more Nitrogen pushed into the tissues, the blood needs time to equilibrate since it is poorly soluble Nitrogen Diffuses out as you ascend to lower pressures - causes the formation of NITROGEN BUBBLES - can function like emboli and lead to pain in joints etc..

Question 26

What is Inert Gas Narcosis?

Answer 26

High levels of N2 in the blood due to diving to HIGH PRESSURES at 50 m: EUPHORIA at deeper levels: Loss of Coordination/Coma

Question 27

What affects to N2 and O2 have at high pressures?

Answer 27

N2 and O2 affect the CNS O2 affects the Lung

Question 28

What is the affect of oxygen toxicity in the CNS? (Hyperbaric O2) In the lung? What levels must it reach to cause damage in the lung?

Answer 28

1. Vomiting, Dizziness, Vision Impairment, seizures - HIGH LEVELS OF OXYGEN 2. Must reach FiO2 > 0.4 - 0.5 Damage of endothelial cells of pulmonary capillaries Substernal pain during breathing Impaired gas exchange Reduction of vital capacity Atelectasis Retrolental fibroplasia in premature infants  fibrotic tissue due to increased O2

Question 29

What is Hyperbaric O2 therapy used for?

Answer 29

1. CO poisoning 2. Anemic Crisis 3. Gas Gangrene (anaerobic bacteria) 4. Impaired bone/wound healing - use dissolved Oxygen for CO poisoning

Question 30

What is the most important problem at high altitude? How can this be resolved?

Answer 30

Low PO2 - HYPERVENTILATION

Question 31

How does high altitude lead to the formation of Pulmonary Vasoconstriction, Right Heart Hypertrophy, and Pulmonary Edema?

Answer 31

via ALVEOLAR HYPOXIA

Question 32

What is the main purpose of the Diving Response?

Answer 32

SPARE OXYGEN