Oxygen transport during steady-state submaximal exercise in chronic hypoxia

Area of Science:

• Physiology
• Altitude Medicine
• Exercise Science

Background:

• Arterial oxygen delivery initially decreases upon arrival at high altitude during exercise.
• With acclimatization, increased arterial oxygen content is accompanied by reduced blood flow.

Purpose of the Study:

• To evaluate factors influencing oxygen delivery during prolonged submaximal exercise after acclimatization at 4,300 m.
• To understand the physiological adaptations to high altitude exercise.

Main Methods:

• Seven men performed 45-minute steady-state submaximal exercise at sea level, acute high altitude (4,300 m), and after 21 days of acclimatization.
• Measurements included oxygen uptake, cardiac output, leg blood flow, arterial oxygen saturation, hemoglobin concentration, and vascular resistance.

Main Results:

• Oxygen uptake remained constant during exercise at both altitudes.
• After acclimatization, cardiac output and leg blood flow decreased, while hemoglobin and arterial oxygen saturation increased.
• Total body and leg oxygen delivery remained unchanged post-acclimatization, despite increased vascular resistance and norepinephrine levels.

Conclusions:

• Total body and leg oxygen delivery decrease upon arrival at high altitude and remain unchanged with acclimatization.
• This stability is achieved through a balance of reduced cardiac output and leg blood flow, alongside increased arterial oxygen content.
• Increased vascular resistance and norepinephrine contribute to maintaining oxygen delivery during acclimatized high-altitude exercise.