Altitude Physiology

Question 1

how might someone present with altitude sickness?

Answer 1

headache

dyspnoea

inability to perform activity due to dyspnoea

pulmonary oedema

Question 2

what is the reason for the main physiological effects of altitude?

Answer 2

they are due to a decrease in barometic pressure

Question 3

what composit of air changes at high altitudes?

Answer 3

air composition stays the exact same, but hte pressure of O2 in the air falls

Question 4

what are some acute effects of high altitude?

Answer 4

• Respiratory: Rate of Ventilation increases by 65%, PACO2 and PaCO2 decrease
• Cardiovascular: Pulmonary hypertension, Increased Heart rate and Cardiac output
• Acid-base status: Respiratory alkalosis
• CNS: Drowsiness, decreased manual dexterity, judgement and memory, euphoria. Coma at > 23,000 feet

Question 5

What are some symptoms and signs of acute mountain sickness?

Answer 5

A small percentage of people who ascend rapidly to high altitudes become acutely sick & can die if not given oxygen or removed to a low altitude

• Dyspnoea, palpitations, fatigue, muscular weakness, drowsiness, sleeplessness, dizziness, headache, nausea, anorexia, decreased visual acuity,
• Cerebral oedema (HACE): local dilation of cerebral blood vessels
• Pulmonary hypertension & pulmonary oedema (HAPE): vasoconstriction of pulmonary arterioles.

Question 6

how do we treat acute mountain sickness?

Answer 6

• Descent
• Dexamethasone, Nifedipine
• Gamow bag (Gam-off)
• Prophylactic Acetazolamide

Acetazolamide inhibits renal CA leading to increased bicarbonate excretion

Question 7

what are some chronic effects of altitude ?

Answer 7

• Respiratory: Ventilation increases further to 300-500% of sea-level values and PaCO2 decreases further
• Cardiovascular: Cardiac output and heart rate return towards normal but not pulmonary arterial pressure. There is increased tissue vascularity, erythropoietin, HCT [to 60-65%], haemoglobin (to 22 g/dl), Blood Volume (by 20-30%) and diffusing capacity
• Acid-base: Renal compensation i.e. increased renal HCO3- excretion
• Cellular: Increased tissue oxidative enzymes and mitochondria

Death Zone: > 26,000 ft or <356 mmHg : No acclimatization possible

Question 8

what are the 5 acclimatization factors?

Answer 8

• increased pulmonary ventilation -
  
  • -Arterial chemoreceptors (carotid & aortic bodies)
• Alkalosis effect on brainstem respiratory centre
• Kidney response ( reduce H+ excretion; increase HCO3 excretion)
• increased numbers of RBC
• increased diffusing capacity of the lung

Blood volume; lung volume; pulmonary artery bp

• Increased threefold from 21ml/mmHg/min
• Due to increased capillary,& alveolar-capillary interface surface area. Blood in greater number of alveolar capillaries.
• increased vascularity of peripheral tissues - increased angiogenesis
• increased ability of tissue cells to use oxygen
  *

Question 9

what are some effects of chronic mountain sickness?

Answer 9

• Excessive increase in HCT (Polycythemia HCT >55%)
• Severe pulmonary hypertension
• Right heart failure
• Peripheral arterial pressure falls

Death

Question 10

What are the three main causes of chronic mountain sickness?

Answer 10

increased blood viscosity causing decreased tissue blood flow

pulmonary arteriole vasoconstriction due to hypoxia in all alveoli - cuases increased pulmonary arterial pressure

pulmonary shunt blood flow due to alverolar arteriolar spasm diversion of blood through non-alveolar vessels