Physiology in Medicine: A physiologic approach to prevention and treatment of acute high-altitude illnesses

Abstract

With the growing interest in adventure travel and the increasing ease and affordability of air, rail, and road-based transportation, increasing numbers of individuals are traveling to high altitude. The decline in barometric pressure and ambient oxygen tensions in this environment trigger a series of physiologic responses across organ systems and over a varying time frame that help the individual acclimatize to the low oxygen conditions but occasionally lead to maladaptive responses and one or several forms of acute altitude illness. The goal of this Physiology in Medicine article is to provide information that providers can use when counseling patients who present to primary care or travel medicine clinics seeking advice about how to prevent these problems. After discussing the primary physiologic responses to acute hypoxia from the organ to the molecular level in normal individuals, the review describes the main forms of acute altitude illness--acute mountain sickness, high-altitude cerebral edema, and high-altitude pulmonary edema--and the basic approaches to their prevention and treatment of these problems, with an emphasis throughout on the physiologic basis for the development of these illnesses and their management.

High altitude respiratory physiology and pathophysiology

“…Respiratory acclimatisation occurs more gradually as both the HVR and the hypercapnic respiratory ventilatory response (HCVR) continue to increase over the following days to weeks although the exact mechanism behind these changes remains unclear. Metabolic compensation through renal bicarbonate loss may play a part but the time-course of this process does not match observed changes in ventilation (8,13). An interesting hypothesis explaining why the HVR response has distinct acute and gradual phases relates to cerebral blood flow autoregulation, a well-recognised homeostatic phenomenon that conserves cerebral oxygen delivery (DO2) by increasing blood flow in response to hypoxaemia.…”

“…Classical teaching emphasises the importance of increased oxygen delivery to the peripheral tissues in this process, and indeed respiratory rate, heart rate, cardiac output and red cell mass do all increase as part of an early acclimatisation response (4,8). However it is becoming increasingly clear that changes occur at every stage of the oxygen transport cascade with tissuelevel changes to the microcirculation and mitochondria being important (9,10).…”

Revisión sobre el uso del mate de hoja de coca en la prevención del mal agudo de montaña.

“…2) Farmacológica: La acetazolamida como fármaco de elección y dexametasona son recomendadas para personas con más riesgo de presentar MAM, por ejemplo, personas que ascienden rápido por encima de 3000 msnm y tener antecedentes de MAM en viajes previos (3,4,9).…”

“…De estas personas entre el 25-78% estarían en riesgo de presentar mal agudo de montaña (MAM) dependiendo de factores como la velocidad de ascenso, la altitud del destino final, permanencia en las zonas altas, antecedente de MAM en viajes anteriores, etc. (3)(4)(5).…”

Lower Respiratory Tract Infection: An Unrecognised Risk Factor for High Altitude Pulmonary Edema?

“…It is generally agreed that the cause is pulmonary vasoconstriction causing pulmonary hypertension [1][2][3][4] . Publications on infection as a risk in the development of altitude illnesses are few and conflicting [5,6] .…”