Term
| What happens to FRC, TLC, VC, Vt, Ve, RR and Vd/Vt during gestation? |
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Definition
Remember, barrel chested anatomy alters respiratory space.
1) FRC decreases 10-25%
2) TLC decreases slightly
3) VC does not change
4) Vt increases
5) Ve increases (due to Vt)
6) RR doesn't change
7) Vd/Vt doesn't change |
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Term
| Why does alveolar ventilation increase during pregnancy? |
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Definition
Vt increases without a change in RR, leading to increased Ve.
Since Vd/Vt does not change, the increased Ve leads to increased alveolar ventilation. |
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Term
| What are the most pronounced alterations in respiratory physiology in pregnancy? |
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Definition
1) Increased respiratory drive
- Progesterone stimulates center directly and increases sensitivity to PCO2.
2) Increased Ve (increased Vt without change in RR) |
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Term
| Why is their a primary respiratory alkalosis in pregnancy, despite increased PCO2 production due to an increased metabolic rate? |
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Definition
| Increase in Ve over-compensates for increased PCO2 (respiratory center is also more sensitive to PCO2) producing a primary respiratory alkalosis with renal compensation. |
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Term
| What happens to PaO2 in pregnancy? |
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Definition
| Increased alveolar ventilation due to increased Ve leads to decreased PaCO2, which leads to an increased PaO2 according to the alveolar air equation. |
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Term
| Why do you see dyspnea with mild exertion during pregnancy? |
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Definition
Not entirely clear.
1) Progesterone-induced hyperventilation?
2) Mechanical load imposed by uterus |
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Term
| How can you distinguish between normal dyspnea in pregnancy and a pathological process? |
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Definition
| Sudden onset with a cough, sputum or tachypnea are clues towards pathology. |
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Term
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Definition
Increased total pressure surrounding chest
1) Increases PACO2 and PAO2 (Boyle's law)
2) Increases O2, CO2 and nitrogen in blood and tissues (Henry's law)
3) Compression of chest decreases FRC and TLC |
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Term
| Why can't you breath through a tube over 1m deep under water? |
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Definition
| Respiratory muscles cannot overcome extra-thoracic pressure exerted by depth to inflate compressed lungs. |
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Term
| Why do breath-hold divers sometimes lose consciousness upon ascent? |
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Definition
Hypoxemia as volume of thoracic cavity increases and partial pressure of O2 plummets
**Mechanical damage is rare!** |
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Term
| Why do breath-hold divers hyperventilate before diving? |
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Definition
To inhibit the desire to breath.
1) Hyperventilation increases PO2 and decreases PCO2.
2) When diver descends, both PAO2 and PACO2 will increase, causing more O2 to diffuse from alveolar gas into capillary blood (PaO2 decreases) and CO2 buildup in the respiratory system (PaCO2 increases)
3) CO2 buildup produces respiratory acidosis, which signals central PCO2 receptors to induce ventilation.
**start with the least PCO2 possible** |
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Term
| What are 3 important complications of diving? |
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Definition
1) Barotrauma
- increased pressure during dive damages lung with alveolar rupture, pneumothorax or alveolar hemorrhage.
2) Decompression illness
- During ascent, gas pressure and solubility rapidly decreases, causing N bubbles to form in vessels and tissue
**Immediate re-compression with assistance of 100% O2 to aid reabsorption of O2**
3) Nitrogen Narcosis
- At high ambient pressures, very high PN2 can alter CNS function and cause euphoria, amnesia and irrational behavior. |
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Term
| Why do you need supplemental oxygen at high altitudes? |
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Definition
1) Fall in barometric pressure causes PAO2 and PaO2 to fall, which stimulates chemoreceptors (carotid body) to increase Ve, PaCO2 to fall and arterial pH to rise (alkalosis)
2) Compensation is not enough
This is why you need supplemental oxygen! |
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Term
| What physiological changes take place after acute hypobaric hypoxia to reduce the gradient between PiO2 and tissue PO2 at high altitudes in order to optimize O2 utilization? |
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Definition
Acclimatization via HIF-1-alpha.
Different from adaptation that occurs over generations of people in a given area. |
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Term
A new mountain climber reaches 13000 ft and presents with headache, dizziness, dyspnea at rest, weakness and nausea.
What is going on and how can it be prevented/treated? |
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Definition
Acute Mountain sickness
1) Hypoxia-induced cerebral vasodilation, leading to hyper-perfusion and edema (people with less space for CSF are at higher risk- "tight fit")
2) Prevention
- Slow ascent
- Treat with dexamethasone (corticosteroid) to reduce edema and acetazolamide to prevent alkalosis and reduce edema with sodium wasting.
- drugs work as prophylaxis.
**Only acetazolamide accelerates acclimatization in addition to improving symptoms. |
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Term
| What drugs should be given prophylactically to prevent acute mountain sickness? |
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Definition
1) Dexamethasone steroids to prevent edema
2) Acetazolamide to prevent edema, alkalosis and to ACCELERATE ACCLIMATIZATION |
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Term
| Why do you see Cheyne-Stokes respirations during sleep at high altitudes? |
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Definition
1) Overstimulation of carotid body causes hyperpnea following by compensatory apnea
2) Compensatory apnea sometimes wakes up from non-REM sleep. |
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Term
Why can you see high altitude pulmonary edema (HAPE)?
How can you prophylactically prevent it? How do you treat? |
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Definition
HAPE can occur within 2-4 days of rapid ascents (most common cause of high altitude disease-related death).
1) Males in the cold who are vigorously exerting themselves present with elevated pulmonary artery pressures due to inadequate eNO and overproduction of endothelin (PATCHY edema results from regional over-perfusion).
2) Give beta-agonists that increase Na channel expression in lung epithelium.
- Also prevent progression with slow ascents
2) Treat with Hyperbaric oxygen chamber, supplemental oxygen, PDE-5i, Nifedipine and beta-agonists. |
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Term
A young man who recently started building a house on a mountain top presents with dyspnea at rest, cough, and production of frothy sputum.
What genetic predispositions might this man have to lead to this condition? |
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Definition
This sounds like High Altitude PE.
1) Sodium channel mutations on type II pneumocytes that transport fluid out of the alveolar space.
Impaired sodium channel function makes it difficult for sodium (and water) to transverse alveolar space and be absorbed in blood.
2) Polymorphisms in eNOS, ACE and leukocyte antigens are also associated. |
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Term
| Why might you give someone a beta agonist before they plan on spending a week on a mountain top? |
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Definition
| Increase sodium channel expression in type II pneumocytes to increase sodium (and water) that can pass through alveolar space into blood, thereby preventing High Altitude PE. |
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