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Grant Cull, Lin Wang, Simon Thompson; Thigh cuff induced dynamic blood flow autoregulation in the optic nerve head of normal healthy human subjects. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2918.
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© ARVO (1962-2015); The Authors (2016-present)
Dynamic autoregulation (dAR) refers to a transient blood flow (BF) response to the sudden perfusion pressure changes induced by altering either blood pressure (BP) or intraocular pressure. The purpose of the study was to test a group of human subjects with normal vision and to characterize the dAR response in the optic nerve head (ONH) induced by a sudden drop in BP
Thirteen humans with normal vision had BP cuffs placed around the two thighs. A continuous BP measurement was recorded using a Finometer Pro (FMS, The Netherlands) during the experiment. The ONH BF was monitored by a laser speckle flowgraph (NAVI LSFG, Softcare, Japan). The cuffs were inflated and held for 1 minute. After 10 seconds of continuous ONH BF recording the cuffs were released to induce a rapid BP drop (ranging from 5 to 35 mmHg) to evoke the dAR response in ONH. The BF measurements continued for an additional 50 seconds (Fig 1). dAR parameters were extracted from BF recordings, including: 1) Basal BF-before the cuff release; 2) BFmax - maximal BF decrease (%) from basal BF; 3) Tr-the amount of time it took to the maximal BF decrease, 4) Kr-the slope of dAR descending curve. The mean between-eye differences of the parameter were compared (Paired Student T-test). Six of the 13 subjects had completed 3 tests over 3 visits. A repeated measure ANOVA of BFmax, Tr, and Kr was performed on this subset to evaluate the repeatability between tests and individuals
The subjects’ age ranged from 23 to 73 (45 ±14, 3 males and 10 females). The cuff deflation induced a 19.2 ±5.6mmHg BP drop during dAR measurement for OD eyes and 19.8 ±5.3mmHg for OS eyes (OD vs, OS: p=0.5). All four dAR parameters were not significantly different between OD and OS eyes (Table 1). BFmax was not significantly different between tests (p=0.1) but was significantly different between individuals (p=0.02). Both Tr and Kr were not significantly different between tests days (Tr: p=0.8, Kr: p=0.7) or individuals (Tr: p=0.3, Kr: p=0.2)
This method of inducing a sudden BP drop in humans with thigh cuffs permits us to measure the dAR response in the ONH. There is no significant difference between eyes in the dAR parameters or between testing days. Both Tr and Kr statistically appear to be good parameters that likely can be used to evaluate potential autoregulation changes in glaucoma subjects in the future
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