Brain, balance and walking

Abstract

Purpose: Falls and mobility problems are common causes of morbidity and death in elderly people, yet their causes are poorly understood. Slowing of gait is a prominent feature of human aging, even in the absence of specific diseases, and it is strongly associated with falls, dementia, and mortality. At the same time, gait and balance are dependent upon the brain's ability to maintain cerebral perfusion during standing and walking. The concept of cerebrovascular reserve has emerged as a potential biomarker for a syndrome of slow gait speed, and as an indicator of both functional decline and fall risk. Cerebrovascular reserve is brain's ability to maintain perfusion during physical activities, and to redistribute blood supply to areas with high energy demands. However, the relationship between cerebral hemodynamics, cardiovascular control, and locomotion control for standing and walking is not well understood, and has not been adequately studied. Method: Cardiovascular risk factors alter brain perfusion regulation and accelerate the effects of aging on gait and balance. Hypertension and diabetes are the most prevalent risk factors. Hypertension affects more than a third of world's population. Among those who are 65 years and older, almost 75% have hypertension 1,2 and 26% have diabetes 3. Cerebromicrovascular disease associated with hypertension, diabetes, and other cardiovascular risk factors, including age, is linked with regional hypoperfusion, white matter hyperintensities (WMHs), and brain volume loss on MRI, as well as with neuronal degeneration, slower gait speed, and cognitive decline in elderly people 4-9. Metabolic syn drome, hypertension, and stroke were each independently associated with cognitive and functional decline later in life 10.The Honolulu Aging study shows that high systolic BP (120-140 and >140 mmHg) in midlife increases the risk of late-life dementia 11. Both diseases have been associated with syncope (fainting) or orthostatic hypotension (blood pressure decline during standing) that account for up to 6% of hospital admissions. Up to 58% of those with dementia experienced a systolic BP decrease of ≥10 mmHg in later life 11. By the age of 70, half of the population has experienced syncope or a fall at least once. With increasing age, the frequency and severity of syncope events increases, further elevating the risk for injurious falls 12. Results & Discussion: Diabetes is associated with regional hypoperfusion 13,14, gray matter atrophy and peripheral neuropathy, slower gait speed, and worse functional outcomes. In diabetic subjects, slower walking correlates with worse perfusion in the brain and more brain volume loss. Furthermore, diabetic subjects with peripheral neuropathy that have slower and less steady gaits and increased risk of falling are dependent upon gray matter volume in the cerebellum and other brain regions to maintain balance 15. Furthermore, the presence of WMHs in diabetic and hypertensive subjects worsens dynamic balance parameters 16. In summary, cardiovascular risk factors accelerate brain aging and further aggravate the impact of aging on locomotion and balance, therefore increasing the risks for falls and fall related injuries.