The effects of a novel "fluid loading" strategy on cardiovascular and haematological responses to orthostatic stress.

Water drinking reduces the occurrence of syncope in healthy volunteers but the effects of hyperhydration are unknown. This study assessed the effects of combined creatine (Cr) and glycerol (Gly) induced hyperhydration on the cardiovascular and haematological responses to postural change. Subjects in all trials lay supine for 30 min before being tilted head-up to 70 degrees for a further 30 min or until the limit of their tolerance. Following 2 baseline trials, 19 subjects were matched for body mass and assigned to ingest either 20 g Cr and 2 g Gly kg(-1) body mass (BM) plus 2 l of water or 2 l of water alone (Pl) each day for 6 days and once more 5 h prior to the experimental trial. Subjects ingested 500 ml of water prior to all trials to ensure euhydration. During baseline trials, 3 subjects in the Cr/Gly group and 2 in the Pl group experienced presyncope during head-up tilt. Following Cr/Gly supplementation, BM increased by (mean +/- S.D.) 0.9 +/- 0.3 and total body water (TBW) increased by 0.7 +/- 0.2 l with no change in the Pl group. Cr/Gly supplementation resulted in a significant increase in systolic (11 mmHg) and diastolic (7 mmHg) blood pressure during head-up tilt with no change following Pl supplementation. Cr/Gly. Following Cr/Gly supplementation the number of subjects who became presyncopal was reduced from 3 to 1, with no change in the Pl group. These data suggest that hyperhydration mediated by Cr and Gly can enhance orthostatic tolerance in healthy individuals.

Visual acuity loss in patients with age-related macular degeneration measured using a novel high-pass letter chart.

BACKGROUND/AIMS: Conventional Logarithm of the Minimum Angle of Resolution (logMAR) acuity is the current gold standard for assessing visual function in age-related macular degeneration (AMD). However, visual acuity (VA) often remains 'normal' when measured with these charts, even with advanced retinal changes. We wished to investigate how VA measurements with the Moorfields Acuity Chart (MAC), which employs high-pass filtered letters, compares to conventional letter charts in subjects with AMD. METHODS: Monocular best-corrected VA measurements and test-retest variability (TRV) were compared for conventional and MAC charts in 38 normal observers (mean age 52.1 years) and 80 patients (mean age 80.6 years) with varying degrees of acuity loss owing to AMD. Methods of Bland-Altman and ordinary least-squares regression were employed for data analysis. RESULTS: A proportional bias was confirmed between conventional and MAC measurements (r(2)=0.133, p=0.001) such that MAC acuity was -0.45 logMAR 'worse' at the 0.00 logMAR acuity level, but only -0.26 logMAR 'worse' at the 1.00 logMAR level. The mean bias was much smaller in the normal subject group (-0.16 logMAR). Similar TRV (ranging from ±0.09 to ±0.12 logMAR) was found for both charts in both subject groups. CONCLUSIONS: VA measurements with the MAC chart appear to be more sensitive to functional loss in AMD compared with conventional letter charts, with similar TRV. Simulations indicate this may be because the high-pass filtered letters are more vulnerable to undersampling as a result of retinal cell loss in the disease process.