Acute alterations in stroke volume during exercise at 3,100 m altitude

Area of Science:

• Physiology
• Altitude Medicine
• Cardiovascular Exercise

Background:

• Chronic exposure to high altitude (3,100 m) can alter cardiovascular responses during exercise.
• Understanding these adaptations is crucial for athletes and individuals living at altitude.

Purpose of the Study:

• To investigate the acute effects of breathing 60% oxygen on cardiac output and stroke volume during upright submaximal and maximal exercise after 3 weeks at altitude.

Main Methods:

• Three healthy subjects were exposed to 3,100 m for 3 weeks.
• Cardiac output was measured during submaximal exercise under two conditions: breathing ambient air and breathing 60% oxygen.
• The conditions were alternated within a single 30-minute testing period.
• Cardiac output was also measured during maximal exercise in two subjects.

Main Results:

• Breathing 60% oxygen during exercise resulted in an immediate bradycardia (slowing of heart rate).
• Stroke volume increased by approximately 16% during submaximal exercise and 10% during maximal exercise when breathing 60% oxygen.
• Cardiac output levels were minimally affected by the high oxygen inspirate.

Conclusions:

• Acute administration of high oxygen during exercise at altitude significantly increases stroke volume.
• The findings suggest that reduced myocardial contractility due to myocardial hypoxia may contribute to decreased exercise stroke volume observed with chronic altitude exposure.