Spleen reactivity during incremental ascent to altitude

Area of Science:

• Human physiology
• Altitude medicine
• Cardiovascular research

Background:

• The spleen stores red blood cells, releasing them during physiological stress to enhance oxygen transport.
• While the spleen's role in acute hypoxia is known, its function during high-altitude ascent remains unstudied.
• Understanding spleen response to altitude is crucial for acclimatization and managing hypoxia-related conditions.

Purpose of the Study:

• To investigate the spleen's volume and red blood cell mobilization capacity during ascent to high altitude.
• To assess the spleen's response to acute stressors (exercise and phenylephrine) at varying altitudes.
• To determine if the spleen contributes to acclimatization to chronic hypoxia.

Main Methods:

• Twelve participants underwent handgrip exercise at 1,045m, 3,440m, and 4,240m.
• Eight participants received phenylephrine infusion at each altitude.
• Spleen volume was measured via ultrasound, and hematocrit was analyzed from blood samples before and after stimuli.

Main Results:

• Resting spleen volume did not change with altitude.
• At low altitude, handgrip induced spleen contraction and increased hematocrit, but this response was absent at high altitudes.
• Phenylephrine caused spleen contraction at all altitudes, yet only increased hematocrit at low altitude.

Conclusions:

• The human spleen does not appear to contribute to acclimatization to chronic hypoxia at high altitude.
• The spleen's response to acute sympathoexcitation is altered at altitude, with a dampened reflex response to exercise.
• These findings suggest a reduced role for spleen-derived red blood cells in oxygen delivery during high-altitude exposure.