Geriatric men at altitude: hypoxic ventilatory sensitivity and blood dopamine changes

Area of Science:

• Cardiovascular Physiology
• Altitude Physiology
• Neuroendocrinology

Background:

• Short-term high-altitude hypoxia enhances hypoxic ventilatory sensitivity (HVS) in healthy humans.
• Dopamine (DA) is a key neurotransmitter in the carotid body (CB) chemoreceptor response, with its levels potentially influenced by age.
• Peripheral chemoreflexes may be modulated by age-related oscillations in blood DA concentrations.

Purpose of the Study:

• To investigate hypoxic ventilatory responses (HVR) in relation to blood dopamine (DA) and dihydroxyphenylalanine (DOPA) concentrations in young and elderly men during short-term altitude adaptation.
• To assess the influence of age on HVR and associated neurochemical changes at varying altitudes.

Main Methods:

• Nine elderly (61+/-1.4 years) and seven young (23+/-2 years) men were studied at sea level, 2,200 m, and 4,200/5,642 m.
• Hypoxic ventilatory responses (HVR) were measured using isocapnic rebreathing.
• Blood concentrations of DA and DOPA were analyzed at different altitude exposures.

Main Results:

• Elderly men exhibited 47% lower sea-level HVR than young men, with higher blood DOPA (300%) and DA (37%).
• Initial DA and DOPA levels correlated negatively with HVR and positively with age.
• Ascending to 2,200 m doubled HVR slopes in both groups; blood DOPA decreased in the elderly (-22%) and increased in the young (+300%), while DA increased in both.

Conclusions:

• The age-associated relationship between HVR and reciprocal DA/DOPA values suggests decreased DA receptor sensitivity and enhanced DA reuptake during high-altitude adaptation.
• Age significantly modulates the neurochemical and ventilatory responses to hypoxic conditions at altitude.