Updated: 11/17/2017

Response to High Altitude

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Overview
 
  • High altitude ↓ atmospheric pressure (Patm) and ↓ alveolar PO2
  • Ventilation
    • ↓ alveolar PO2↑ respiratory rate (hyperventilation)
      • ↓ alveolar PO2 stimulates peripheral chemoreceptors in aortic bodies and carotid bodies to instruct medullary inspiration center to increase respiratory rate
  • Arterial blood
    • ↑ ventilation rate → ↑ PaO2 and ↓ PaCO2 respiratory alkalosis
      • CO2 + H2O  H2CO3  H+ + HCO3-
        • ↓ CO2 shifts equilibrium left
          • ↓ H+↑ pH
    • respiratory alkalosis ↑ renal HCO3- excretion
      • carbonic anhydrase inhibitors (e.g., acetazolamide) ↑ renal HCO3- excretion and create a metabolic acidosis, which can be used to "acclimate" someone going to a higher altitude because they will naturally increase ventilation to compensate for metabolic acidosis
  • Pulmonary blood flow
    • ↓ alveolar PO2 hypoxic vasoconstriction of pulmonary vasculature ↑ pulmonary vasculature resistance ↑ pulmonary arterial pressure
      • pulmonary arterial pressure increases to maintain a constant blood flow
        • right ventricle pumps against ↑ pulmonary arterial pressure (↑ afterload)
          • chronic hypoxic vasoconstriction of pulmonary vasculature causes cor pulmunale (right ventricular hypertrophy (RVH))
  • Cerebral blood flow 
    • primarily controlled by PCO2
      • ↓ PCO2 → vasoconstriction
      • therapeutic hyperventilation (↓ PCO2→ ↓ intracranial pressure by decreasing cerebral perfusion
        • used in cases of cerebral edema
        • effect is usually only temporary
    • PO2 can have effects during severe hypoxic events
      • ↓ PO2 → vasodilation and ↑ cerebral perfusion pressure
  • Cellular changes
    • chronic hypoxia ↑ erythropoietin → ↑ hemoglobin concentration and ↑ hematocrit
      • synthesis of erythropoietin in kidneys
        • erythropoietin acts on bone marrow to stimulate RBC synthesis
      • ↑ hemoglobin concentration↑ O2 carrying capacity and ↑ total O2 content
    • ↑ mitochondria
  • Oxygen-hemoglobin dissocation curve
    • ↑ 2,3-BPG shifts to right
      • ↓ hemoglobin affinity for O2 ↑ O2 unloading
 

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Questions (2)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
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(M1.PL.4695) A healthy 20-year-old male college student attempts to climb Mount Everest and travels to the Tibetan plateau by plane. Upon landing, he feels increasingly dizzy and fatigued. He notices that he is breathing faster than usual. What is the initial stimulus for the most likely acid-base disorder? Review Topic

QID: 107937
1

Hypoxic pulmonary vasodilation

8%

(9/120)

2

Decreased partial pressure of alveolar oxygen

58%

(69/120)

3

Increasing arterial partial pressure of carbon dioxide

25%

(30/120)

4

Worsened diffusion limitation of oxygen

6%

(7/120)

5

Undiagnosed atrial septal defect

1%

(1/120)

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(M1.PL.117) A 31-year-old female with a history of anxiety has a panic attack marked by dizziness, weakness, and blurred vision. Which of the following most likely accounts for the patient’s symptoms? Review Topic

QID: 100920
1

Oxygen toxicity

23%

(3/13)

2

Increased arterial CO2

38%

(5/13)

3

Decreased cerebral blood flow

38%

(5/13)

4

Decreased respiratory rate

0%

(0/13)

5

Carotid artery obstruction

0%

(0/13)

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