Lecture 34: High Altitude

Question 1

Atmospheric pressure progressively ____ as altitude increases

Answer 1

declines

Question 2

At ______ feet above sea level, the atmospheric pressure is only 380 mmHg, which is ___ its normal sea level value

Answer 2

18,000

halfway

Question 3

Since the proportion of O2 and N2 in the air remains the same, the PO2 of inspired air at 18,000 ft altitude is ___% of ____ mm Hg, or ____ mm Hg with anatomic dead space taken into account

Answer 3

21%
380
80

Question 4

At any altitude above 10,000 ft, the arterial PO2 falls into

Answer 4

the steep portion of the O2 Hb dissociation curve below the safety range of the plateau region
As a result, percentage Hb saturation of arterial blood declines with further increases in altitude

Question 5

Ascent to high altitude causes….

thus….

Answer 5

• hypoxic hypoxia (reduced arterial PO2)

- Adjustments must be made to live at high altitudes where the atmos pressure is drastically reduced

Question 6

Acclimation

Answer 6

process of adapting to high altitudes

Question 7

Most common response to high altitude

Answer 7

hyperventilation

Question 8

In high altitude, the PO2 becomes less than 60 mm Hg, which leads to

Answer 8

stimulation of peripheral chemoreceptors, which leads to stimulation of medullary respiratory center, which leads to an increase in the breathing rate

Question 9

Polycythemia

Answer 9

• Adaptive response to high altitude
• Increase in rbc concentration/Hb concentration
• Increase in O2 carrying capacity
• Increase in total O2 content of blood, despite decreased arterial PO2

Question 10

Consequences of polycythemia

Answer 10

An increase in [rbc] leads to an increase in blood viscosity, which leads to an increase in resistance to blood flow, which leads to hypertrophy

Question 11

Hypertrophy

Answer 11

Hypoxemia -> an increase in synthesis of erythropoietin which acts on bone marrow to stimulate rbc production

Question 12

Pulmonary vasoconstriction

Answer 12

• Adaptive response to high altitude
• As pulmonary vascular resistance increase, pulmonary arterial pressure must also increase to keep blood flow constant
• Right ventricle must pump against higher pulmonary pressure
• Hypertrophy may result as a response to the increased afterload

Question 13

Consequence of pulmonary vasoconstriction

Answer 13

-Right sided heart failure

Question 14

Brisket disease

Answer 14

Right sided heart failure due to pulmonary vasoconstriction in cattle
Fluid accumulates in the brisket

Question 15

Increase production of 2,3 DPG due to adaptation to high altitude

Answer 15

• Shift to the right of O2-Hb curve

- Increase in P50

Question 16

Consequence of increased 2,3-DPG due to altitude

Answer 16

Decreased affinity of Hb for O2 in tissues, leading to increased unloading of O2 in tissues

Question 17

Three increases caused by an adaptive response to high altitude

Answer 17

1. Capillary density in tissues - improves gas exchange in blood/tissues
2. Mitochondrial density - enables cells to use O2 more efficiently in ATP synthesis
3. Muscles myoglobin content - myoglobin stores O2 in the muscle, increases the rate of O2 transfer from blood into muscle fibers

Question 18

4 causes of hypoxia

Answer 18

1. Hypoxemia - Decrease in arterial PO2
2. Pulmonary disease
3. Inadequate O2 transport to tissues by blood
4. Inadequate tissue capability of using O2

Question 19

Hypoxemia may be due to

Answer 19

O2 deficiency in the atmosphere

Question 20

Three examples of pulmonary diseases

Answer 20

1. Chronic bronchitis - increased airway resistance
2. Pulmonary fibrosis - decreased pulmonary compliance
3. Pulmonary edema - diminished respiratory membrane diffusion

Question 21

5 examples of inadequate O2 transport to tissues by blood

Answer 21

1. Anemia - not severe at rest. Patients may have difficulty during exercise because limited ability to increase O2 delivery to active tissue
2. CO poisoning
3. General circulatory deficiency - decrease in cardiac output which decreases blood flow to tissues
4. Localized circulatory deficiency (Ischemia) - obstruction of blood flow to tissues
5. Tissue edema - reduces gas transfer between the blood and tissues

Question 22

Inadequate tissue capability of using oxygen

Answer 22

Poisoning of cellular oxidative enzymes

Question 23

Example of inadequate tissue capability of using oxygen

Answer 23

Cyanide poisoning interferes with O2 utilization of tissues.

One cause of hypoxia that does not involve decreased blood flow or decreased O2 content of the blood