altitude and diving Flashcards
Acclimatization vs adaptation
acclimatization is a subacute to chronic physiologic process that permits more efficient function at altitude that happens to everyone who goes to high altitude. This includes increased ventilation rate, increased EPO, etc. Adaptation is natural selection that occurs over generations
- Determine the inspired PO2 (PA02) at various barometric pressures and use this to understand the limitations of human travel at high altitude.
Sea level (769 mmHg): 149mmHg PAO2. Denver (630 mmHg): 122 mmHg PAO2. Everest at 27,560 ft (253mmHg) = 35 mmHg PAO2. Arterial O2 saturation on Everest is only 50%
Acute and chronic responses to moderate hypoxia
acute: Increased CO, decreased systemic vascular resistance, increased heart rate and increased ventilation. Chronic: increased ventilation, increased hemoglobin concentration, increased CO2 ventilatory response, increased capillary density and myoglobin amount and affinity for O2 in muscles
effects of hypoxia on systemic/brain and pulmonary vascular beds
systemic/brain: vasodilation due to decreases SVR. Pulmonary: vasoconstriction
At what alveolar O2 pressure does hyperventilation begin
When PAO2 <55mmHg, hyperventilation occurs
Which acute adaptive response to high altitude is most useful
Hyperventilation- lasts for days and weeks, plus a small increase in PaO2 can lead to a significant increase in O2 saturation b/c the oxygen dissociation curve is sigmoidal.
Drug used to prevent high altitude illness
acetazolamide- a diuretic that cuases metabolic acidosis through renal bicarbonate loss. This acidosis triggers increased ventilation to lower arterial PaCO2, thus PaO2 increases.
Which conditions make traveling to high altitude difficult
Conditions that limit the ability to increase ventilation such as pulmonary fibrosis, COPD, obesity, etc. Diseases that cause lower PaO2 at rest such as lung disease (not asthma), CHF, hypoventilation. Existing pulm HTN or Left heart failure also bad
Chronic changes in red cell, Hb %, plasma volume and blood volume at high altitude
Hemoglobin and red cell mass are increased, while plasma volume is decreased and overall blood volume increases.
Changes in hemoglobin and oxygen dissociation curve with high altitude (long term)
Structural changes in hemoglobin increase its affinity for O2, so there is a leftward shift in the O2-Hb dissociation curve due to respiratory alkalosis. At any PaO2, Hb saturation is increased
Describe ventilatory rates in an acclimatized person vs person just arriving at altitude
In persons that have acclimatized to high altitude, the ventilatory responses to both hypoxia and to higher PaCO2 are exaggerated. The acclimatized person’s ventilatory rate will increase when PaO2 falls below 63mmH whereas the un-acclimatized person’s Ve will increased when PaO2 falls below 55mmHg.
A-a gradient and hypoxia
In severe hypoxia, the O2 concentration gradient btw pulmonary capillaries and alveoli is small, so the driving force for diffusion is smaller and diffusion may be limited. This is even worse at a higher CO when RBCs travel faster through lung capillaries. During exercise at extreme high altitude, the A-a gradient may be increased even in the abscence of any lung disease
List illnesses associated with exposure to high altitude
Acute mountain sickness, high altitude pulmonary edema (HAPE), high altitude cerebral edema (HACE) and chronic mountain sickness
Describe acute mountain sickness manifestations
AMS is manifest as headache (near universal), nausea, malaise, insomnia, and anorexia. It is almost universal above 18,000ft.
Acute mountain sickness mechanism
Increased brain volume in response to hypoxia, possibly due to cerebral edema and/or increased cerebral blood flow and intravascular volume.
Acute mountain sickness treatment
oral dexamethasone (a corticosteroid that blunts hypoxic induction of brain vessel permeability by altering gene expression) OR oral acetazolamide (a diuretic that causes a metabolic acidosis) are best as prevention. Ibuprofen, acclimatization, dexamethasone and acetazolamide may help with treatment
High Altitude Cerebral Edema (HACE) manifestation
ataxia, confusion/combativeness, hallucinations, and coma
HACE treatment
Oxygen, descent, mechanical ventilation (for coma), followed by IV dexamethasone
High Altitude Pulmonary Edema (HAPE) manifestation
Cough, shortness of breath, fatigue. Hypoxia, lung rales and infiltrates on CXR. Pulmonary hypertension (in response to acute hypoxia), increased pulmonary arterial pressure
Is HAPE cardiogenic or non?
HAPE is a noncardiogenic pulmonary edema (diuretics to decrease intravascular volume won’t help).
What does pulmonary hypertension in HAPE lead to
Uneven vasoconstriction throughout th elung leading to scattered lung capillary breakdown with blood leakage into alveoli
Treatment of HAPE and prevention
Immediate descent to lower altitude, oxygen, vasodilators such as nifedipine (lower pulmonary artery pressures). Prevention involves pulmonary vasodilators such as nifedipine and tadalafil, Salmeterol is a bronchodilator that increases clearance of water out of alveoli,
Chronic mountain sickness manifestation
Polycythemia and pulmonary hypertension, with increased risk of stroke and heart failure. Increases risk of low infant birth weight and preeclampsia
Who gets chronic mountain sickness
People who live above 10,000 ft who are not as well adapted
