Effect of Age on the Changes of Extracranial Circulation During Hypoxia

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Abstract
In 68 healthy older men (mean age 59.5 years), the peak amplitude of impedance plethysmographic pulse tracings from the forehead increased significantly during hypoxia (breathing a 10 per cent O2, 90 per cent nitrogen mixture), while there was no significant change in a group of 58 healthy young men (mean age 23.4 years). The height of the dicrotic notch increased in the older men and decreased in the younger men. In both groups, the cycle length decreased, and the relative peak time increased significantly during hypoxia. The absolute peak time decreased in the older group and did not change in the younger group. The amplitude changes in hypoxia were related to the decrease of arterial oxygen saturation in the older, but not in the younger, men. It is suggested that hypoxia is a stronger stimulus for the reaction of extracranial circulation in older subjects.