A 30-year-old woman who normally resides in Florida (elevation near sea level) plans to travel to La Paz, Bolivia (elevation 3,600 m [11,900 ft]) for a week-long business trip. Medical history is unremarkable. Which of the following physiologic changes are expected during the patient's week in La Paz?

Question

A 30-year-old woman who normally resides in Florida (elevation near sea level) plans to travel to La Paz, Bolivia (elevation 3,600 m [11,900 ft]) for a week-long business trip. Medical history is unremarkable. Which of the following physiologic changes are expected during the patient's week in La Paz?
A 30-year-old woman who normally resides in Florida (elevation near sea level) plans to travel to La Paz, Bolivia (elevation 3,600 m [11,900 ft]) for a week-long business trip. Medical history is unremarkable. Which of the following physiologic changes are expected during the patient's week in La Paz? A) A B) B C) C D) D E) E

Quizplus · Accepted Answer

11ec160b_3cde_5dca_9249_057664ec8fac_MD0001_00 The decreased atmospheric pressure at high altitude (eg, >2,500 m [~8,000 ft]) reduces the partial pressure of inspired oxygen (PiO₂). Such an environment stimulates an array of physiologic responses aimed at maintaining adequate O₂ delivery to the tissues. The initial responses to high altitude include: Peripheral chemoreceptors in the aorta and carotid body stimulate hyperventilation in an effort to increase arterial oxygenation (PaO₂). The hyperventilation also increases CO₂ removal to decrease PaCO₂ and cause respiratory alkalosis. The alkalosis initially shifts the hemoglobin dissociation curve to the left to increase O₂ uptake in the lungs. Hypoxic pulmonary vasoconstriction occurs to minimize ventilation-perfusion mismatching and optimize pulmonary O₂ uptake. This leads to increased pulmonary vascular resistance, which increases pulmonary arterial pressure. Sympathetic activity is increased, leading to increased heart rate and cardiac output. Despite the drop in PaCO₂ (which encourages cerebral vasoconstriction), reduced PaO₂ and marked tissue hypoxia lead to overall cerebral vasodilation to increase cerebral blood flow. Additional responses occur over the next 24-48 hours: The kidneys increase HCO₃⁻ excretion (compensatory metabolic acidosis), which decreases blood pH. Because central chemoreceptors inhibit ventilation when pH gets too high, the HCO₃⁻ excretion allows for additional hyperventilation. Hypoxemia suppresses aldosterone activity, which together with increased HCO₃⁻ excretion results in diuresis and total body volume loss. The reduced plasma volume increases hematocrit and also reduces cardiac preload to decrease myocardial O₂ demand. There is a resulting decrease in stroke volume, but cardiac output remains slightly increased from baseline due to increased heart rate. Red blood cells increase production of 2,3-biphosphoglycerate to shift the hemoglobin dissociation curve back to the right and facilitate O₂ unloading in the tissues. In addition, the kidneys increase secretion of erythropoietin. There is also upregulation of hypoxia inducible factor (HIF) in cells throughout the body. HIF stimulates erythropoiesis as well as increased angiogenesis in skeletal muscle and other tissues to improve O₂ delivery. Individuals who remain at high altitude for an extended period will experience the full benefit of increased erythropoietin secretion and upregulation of HIF, as secondary polycythemia (increased O₂ carrying capacity) and angiogenesis are maximized after several weeks. Educational objective: An array of physiologic responses takes place to maintain adequate O₂ delivery to the tissues in the hypoxic environment at high altitude. These include hypoxic pulmonary vasoconstriction (increased pulmonary vascular resistance), increased sympathetic activity to increase cardiac output, and aldosterone suppression to reduce plasma volume. __________ References: Human responses to extreme altitudes. (http://www.ncbi.nlm.nih.gov/pubmed/21672720)

A 30-Year-Old Woman Who Normally Resides in Florida (Elevation near Sea