USMLE Step 1 Respiratory Physiology Review 62 03 High Altitude Response

USMLE Step 1 Respiratory Physiology Review 62 03 High Altitude Response

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Play USMLE Audio MP3 62 03 High Altitude Response Below

Begin 62 03 High Altitude Response Transcription

Now let’s talk about high altitude response.

When a person goes to a high altitude, what is the immediate effect on arterial oxygen tension?

  • At high altitude, arterial oxygen tension decreases and the person becomes hypoxemic

This is directly a decrease due to a decrease in what other PO2?

  • Alveolar PO2.

The body accommodates for high altitude in six ways. First, what happens to ventilation of the lungs?

  • Ventilation increases, tidal volume increases.

An acute increase in ventilation would be how big?

  •  Ventilation may increase as much as two thirds over normal.

Second, what do kidneys produce more of in high altitudes? It starts with an E.

  • At high altitude, the kidneys produce more erythropoietin

What does increased production erythropoietin directly lead to?

  • More erythrocytes

And what does an increase in erythrocytes lead to?

  • More hemoglobin

Third, an increase in what compound results in a shift to the right of the oxygen dissociation curve?

  • 2,3 diphosphoglycerate

How does this effect hemoglobin?

  • It decreases the affinity of hemoglobin for oxygen

And what does this facilitate?

  • Unloading of oxygen in the tissues

Fourth, what condition will be increased in ventilation cause in the blood? It starts with RA

  • Increased ventilation will cause respiratory alkalosis

And what will the kidneys do in response to this?

  • The kidneys will excrete more bicarbonate

Fifth, how will the pulmonary vessels respond to hypoxemia?

  • There will be pulmonary vasoconstriction which will raise the pulmonary vascular resistance.

What two effects will this have on the heart?

  • There will be an increased work load for the right heart and hypertrophy of the right heart

And finally, sixth, what will the cells of the body create more of? It starts with an M

  • The cells will create more mitochondria.

Student doctor, please pause the tape and summarize the six ways that the body responds to high altitude.

  • Ventilation increases, erythropoietin increases, 2,3 diphosphoglycerate increases, respiratory alkalosis causes kidneys to excrete more bicarbonate, pulmonary vasoconstriction results in right heart hypertrophy and body cells create more mitochondria.

 

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