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
QUESTIONS 1 of 3 1 2 3 Previous Next Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (M1.PL.17.4695) 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? QID: 107937 Type & Select Correct Answer 1 Hypoxic pulmonary vasodilation 5% (11/202) 2 Decreased partial pressure of alveolar oxygen 68% (138/202) 3 Increasing arterial partial pressure of carbon dioxide 19% (39/202) 4 Worsened diffusion limitation of oxygen 3% (7/202) 5 Undiagnosed atrial septal defect 0% (1/202) M 1 Question Complexity C Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 2 Review Tested Concept Review Full Topic (M1.PL.13.117) 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? QID: 100920 Type & Select Correct Answer 1 Oxygen toxicity 7% (5/70) 2 Increased arterial CO2 14% (10/70) 3 Decreased cerebral blood flow 79% (55/70) 4 Decreased respiratory rate 0% (0/70) 5 Carotid artery obstruction 0% (0/70) M 1 Question Complexity D Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic