Respiratory Physiology & Neurobiology · Sep 23, 2019
Reduced cerebrovascular and cardioventilatory responses to intermittent hypoxia in elderly
By Liu X, Chen X, Kline G et al.
BACKGROUND: The impact of aging on cerebrovascular function and tissue oxygenation during graded hypoxemia is incompletely known. This study compared the age effect on these variables during cyclic hypoxemia-reoxygenation. METHODS: Hypoxia-induced changes in arterial (SaO₂) and cerebral tissue (ScO₂) O₂ saturation, middle cerebral arterial flow velocity (VMCA), estimated cerebral vascular conductance (CVC), heart rate (HR) and ventilation were compared between 12 elderly (71 ± 2 yr, 7 women) and 13 young (24 ± 3 yr, 5 women) adults during the first and fifth 5-min exposures to 10% O₂. RESULTS: Although pre-hypoxia SaO₂ did not differ between the groups, ScO₂ was lower (P < 0.05) in the elderly (68.4 ± 1.2%) than young (73.8 ± 0.9%) adults, commensurate with a lower resting VMCA (P < 0.05). SaO₂ fell less sharply (P < 0.05) in the elderly subjects during the first and fifth hypoxia exposures. Moreover, the responses of ScO₂, VMCA, CVC, HR and breathing frequency to hypoxia were attenuated in the elderly subjects. Systolic and diastolic arterial pressures fell by 2-6 mmHg during hypoxia in both young and elderly. Thus, hypoxemia developed more gradually in elderly than young adults during normobaric hypoxia, concordant with a reduced metabolic demand in the elderly. CONCLUSIONS: The elderly adults safely tolerated cyclic, moderate hypoxemia which lowered SaO₂ by 20-25%, despite dampening of cerebrovascular and cardiac responses to hypoxemia.