Franke Warren D, Allbee Kelly A, Spencer Seldon E
Department of Health and Human Performance, Iowa State University, Ames, Iowa 50011, USA.
Gerontology. 2006;52(5):282-9. doi: 10.1159/000094609.
Animal models suggest that aging negatively affects the cerebral blood flow (CBF) response to a hypotensive challenge while research with humans suggests that chronic physical activity may positively affect age-associated alterations in CBF. The extent to which chronic exercise affects the CBF responses to orthostatic stress in older subjects is unknown.
The purpose of this study was to determine the extent to which differences in age and cardiovascular fitness, reflective of differences in chronic exercise training, affect cerebral blood flow responses to severe orthostatic stress.
Subjects were divided into four groups: old fit (OF; 72 +/- 2 year-olds; 38.7 +/- 1.6 ml.kg(-1).min(-1)), old unfit (OU; 71 +/- 1 year-olds; 27.7 +/- 2.9 ml.kg(-1).min(-1)), young fit (YF; 23 +/- 0.5 year-olds; 56.1 +/- 1.8 ml.kg(-1).min(-1)) and young unfit (YU; 23 +/- 1 year-olds; 41.1 +/- 1.6 ml.kg(-1).min(-1)). Fitness was quantified with maximal graded exercise testing. Middle cerebral artery blood flow velocity (CBF velocity; transcranial Doppler) responses to graded orthostatic stress (lower body negative pressure) to presyncope were assessed.
Orthostatic tolerance did not differ between groups (p = 0.633). The groups differed in fitness (YF >YU = OF >OU; p < 0.001) but not in either resting CBF velocity (p = 0.364) or pulsatility index (PI; p = 0.251). CBF velocity decreased below rest in the last completed stage of submaximal LBNP (p < 0.001) but did not differ between groups (p = 0.182). PI did not change with submaximal LBNP within groups. At presyncope, mean CBF velocity decreased below that of the last completed stage of LBNP in all groups (p < 0.001) while the PI increased in the young fit group only (p < 0.001).
Marked differences in age and fitness did not affect cerebral blood flow responses to severe orthostatic stress. While severe orthostatic stress can compromise CBF velocity in all age groups, older adults appear to autoregulate CBF as well as much younger subjects.
动物模型表明，衰老对低血压刺激时的脑血流量（CBF）反应产生负面影响，而针对人类的研究表明，长期体育活动可能对与年龄相关的CBF变化产生积极影响。长期运动对老年受试者直立位应激时CBF反应的影响程度尚不清楚。
本研究旨在确定年龄和心血管健康状况的差异（反映长期运动训练的差异）在多大程度上影响对严重直立位应激的脑血流量反应。
受试者分为四组：老年健康组（OF；72±2岁；38.7±1.6 ml·kg⁻¹·min⁻¹）、老年非健康组（OU；71±1岁；27.7±2.9 ml·kg⁻¹·min⁻¹）、青年健康组（YF；23±0.5岁；56.1±1.8 ml·kg⁻¹·min⁻¹）和青年非健康组（YU；23±1岁；41.1±1.6 ml·kg⁻¹·min⁻¹）。通过最大分级运动试验对健康状况进行量化。评估大脑中动脉血流速度（CBF速度；经颅多普勒）对分级直立位应激（下体负压）直至接近晕厥时的反应。
直立位耐受性在各组之间无差异（p = 0.633）。各组在健康状况方面存在差异（YF>YU = OF>OU；p < 0.001），但静息CBF速度（p = 0.364）或搏动指数（PI；p = 0.251）无差异。在次最大下体负压（LBNP）的最后完成阶段，CBF速度降至静息水平以下（p < 0.001），但各组之间无差异（p = 0.182）。各组内PI在次最大LBNP时无变化。在接近晕厥时,所有组的平均CBF速度均降至LBNP最后完成阶段以下（p < 0.001），而仅青年健康组的PI升高（p < 0.001）。
年龄和健康状况的显著差异并未影响对严重直立位应激的脑血流量反应。虽然严重直立位应激会损害所有年龄组的CBF速度，但老年人似乎与年轻得多的受试者一样能自动调节CBF。
