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Background: Reverse high-contrast (white-onblack) visual acuity has been shown to improve visual acuity in older patients and patients with pathology under photopic testing. In this study, we investigated whether reverse contrast results in improved visual acuity at mesopic light levels. Methods: Monocular visual acuities (logMAR) were assessed at four different light levels (1 photopic {94 cd/m2} and 3 mesopic {3 cd/m2, 0.75 cd/m2, and 0.38 cd/m2}) in 47 visually normal subjects (27.4±9.3 years). Visual acuity was assessed using an E-ETDRS algorithm, in standard and reverse contrast, at 3 m. Repeated measures ANOVA with post-hoc Tukey testing was used to analyze the data across the light levels. Results: The mean standard contrast visual acuity was -0.07±0.06 under the photopic condition, 0.06±0.08 at 3 cd/m2, 0.17±0.08 at 0.75 cd/m2, and 0.28±0.09 at 0.38 cd/m2. For reverse contrast, it was -0.08±0.06 under the photopic condition, 0.01±0.07 at 3 cd/m2, 0.12±0.08 at 0.75 cd/m2, and 0.22±0.09 at 0.38 cd/m2. There was a significant improvement in visual acuity using reverse contrast under all mesopic light levels (p<0.001), but not under photopic conditions (p=0.15). Conclusions: At mesopic light levels, there were significant differences between standard and reverse contrast. The use of mesopic reverse-contrast visual acuity could be another way to detect subtle changes in visual acuity. Reversecontrast presentations under low lighting conditions may be advantageous for a patient's visual acuity. [ABSTRACT FROM AUTHOR]

During childhood, varying exercise modalities are recommended to stimulate normal growth, development, and health. This project investigated hormonal and metabolic responses triggered by a resistance exercise protocol in lean children (age: 9.3 ± 1.4 y, body fat: 18.3 ± 4.9%), obese children (age: 9.6 ± 1.3 y, body fat: 40.3 ± 5.2%) and lean adults (age: 23.3 ± 2.4 y, body fat: 12.7 ± 2.9%). The protocol consisted of stepping onto a raised platform (height = 20% of stature) while wearing a weighted vest (resistance = 50% of lean body mass). Participants completed 6 sets of 10 repetitions per leg with a 1-min rest period between sets. Blood samples were obtained at rest preexercise, immediately postexercise and 2 times throughout the 1-hr recovery to analyze possible changes in hormones and metabolites. Children-adult differences included a larger exercise-induced norepinephrine increase in adults vs. children and a decrease in glucagon in children but not adults. Similarities between adults and children were observed for GH-IGF-1 axis responses. Metabolically, children presented with lower glycolytic and increased fat metabolism after exercise than adults did. Obesity in childhood negatively influenced GH, insulin, and glucose concentrations. While adults occasionally differed from children, amount of activated lean mass, not maturation, likely drove these dissimilarities. [ABSTRACT FROM AUTHOR]

Cardiovascular (CV) drift, the progressive increase in heart rate (HR) and decrease in stroke volume (SV) during constant rate, moderate intensity exercise, is related to reduced maximal oxygen uptake (V̇O2max) during heat stress. Once it has already occurred, it is unknown whether the detrimental effects of CV drift on V̇O2max can be reversed. This study tested the hypothesis that fan cooling after CV drift has occurred attenuates decrements in V̇O2max associated with CV drift. Eight men completed a control graded exercise test (GXT) in 22°C to measure V̇O2max. Then on separate, counterbalanced occasions, they completed one 15-min (15MIN) and two 45-min bouts (45NF and 45FAN) of cycling in 35°C, 40% RH at 60% V̇O2max, each immediately followed by a GXT to measure V̇O2max. For one of the 45-min trials (45FAN), fan airflow (4.5 m/s) was directed at participants beginning ~5 min before the GXT and continuing throughout the remainder of exercise. The purpose of the separate 15- and 45-min trials was to measure V̇O2max during the same time interval that CV drift occurred. HR increased (13.8% and 11.4%) and SV decreased (14.4% and 14.1%) for 45NF and 45FAN, respectively; trials were not different (all P > 0.05). Despite a decrease in mean skin temperature of ~1°C with fan use, V̇O2max decreased similarly between conditions (17% vs. 15% for 45NF and 45FAN, P = 0.54). Fan cooling after CV drift was insufficient to reverse the negative consequences of CV drift on V̇O2max after prolonged exercise in a hot environment. Abbreviations: 15MIN: 15-min trial; 45FAN: 45-min, fan trial; 45NF: 45-min, no fan trial; ANOVA: Analysis of variance; CV: Cardiovascular; GXT: Graded exercise test; HR: Heart rate; SV: Stroke volume; T̅b: Mean body temperature; Tre: Rectal temperature; T̅sk: Mean skin temperature; V̇O2max: Maximal oxygen uptake [ABSTRACT FROM AUTHOR]

Purpose: To quantify the impact of a 14-day bovine colostrum (BC) supplementation on intestinal cell damage following exercise in a hot and humid environment.Methods: Ten male participants (20 ± 2 years, VO2max 55.80 ± 3.79 mL kg-1 min-1, 11.81 ± 2.71% body fat) ran for 46 ± 7.75 min at 95% of ventiliatory threshold in 40 °C and 50% RH following a 14-day double-blinded supplementation with either BC or placebo (Plac). Core temperature, skin temperature, heart rate, and rating of perceived exertion were recorded every 5 min during exercise. Blood was taken pre, post, 1 h, and 4 h post exercise. Intestinal cell damage was assessed via intestinal fatty acid binding protein (I-FABP).Results: I-FABP concentrations were similar between conditions at all time points [pre 989.39 ± 490.88 pg ml-1 (BC) 851.35 ± 450.71 pg ml-1 (Plac) post 1505.10 ± 788.63 pg ml-1 (BC) 1267.12 ± 521.51 pg ml-1 (Plac) 1-h, 1087.77 ± 397.06 pg ml-1 (BC) 997.25 ± 524.74 pg ml-1 (Plac) 4-h, 511.35 ± 243.10 pg ml-1 (BC) 501.46 ± 222.54 pg ml-1 (Plac)]. I-FABP was elevated pre to post exercise for both BC (162 ± 50%) and Plac (162 ± 56%) (p < 0.05). BC had no effect on mean body temperature [beginning 36.11 ± 0.30 °C, ending: 39.52 ± 0.28 °C (BC); beginning:35.96 ± 0.43 °C, ending:39.42 ± 0.38 °C (Plac)].Conclusions: While BC supplementation may protect against enterocyte damage during exercise in thermonuetral environments, our data suggest that BC supplementation may not be an effective technique for preventing enterocyte damage during exercise when core temperature exceeds 39 °C. [ABSTRACT FROM AUTHOR]

Dofetilide Effect on f Waves in AF Introduction The electrocardiogram (ECG) fibrillatory (f) wave characteristics in atrial fibrillation (AF) could provide important information regarding the efficacy of antiarrhythmic drug therapy. Methods and Results To measure the effects of dofetilide on the surface ECG f wave characteristics in patients with persistent AF, baseline and post-drug (2 hours after first dose and after multiple doses) ECGs in 31 patients with persistent AF admitted for dofetilide loading were evaluated. A QRST template subtraction algorithm was used to yield an atrial ECG. Fast Fourier transform analysis was performed to evaluate the maximum organizational index (OI), the dominant frequency (DF) in the lead with max OI, the median DF for all leads, and the vector magnitude f wave amplitude. Dofetilide reduced DF in the lead with the max OI (6.32 ± 0.98 Hz at baseline vs. 4.83 ± 0.63 Hz after final dose, P < 0.0001) and median DF (6.46 ± 0.87 Hz vs. 4.92 ± 0.62 Hz, P < 0.0001). Dofetilide also increased the maximum OI from 0.52 ± 0.11 at baseline to 0.59 ± 0.11 after final dose (P = 0.02). Of the 29 patients with long-term follow-up, the 22 (76%) with recurrent AF on dofetilide had a lower baseline DF in the lead with the max OI (6.01 ± 1.08 vs. 6.89 ± 0.46; P = 0.05). The change in DF after dofetilide did not correlate with the change in QTc interval. Conclusions The standard ECG can be used to assess atrial rate in AF. This may be useful to assess antiarrhythmic drug effects for treatment of AF. [ABSTRACT FROM AUTHOR]

Baroreflex Response and AF Dominant Frequency. Introduction: Parasympathetic stimulation is known to promote atrial fibrillation (AF) through shortening of atrial refractory periods. We hypothesized that baroreflex-mediated parasympathetic stimulation via phenylephrine (PE) infusion would increase AF rate as measured by dominant frequency (DF). Methods and Results: The protocol was performed in 27 patients (24 M, 59 ± 1 years old) prior to AF ablation. For 10 patients in AF, PE was infused until systolic blood pressure increased ≥30 mmHg. Electrograms were recorded in the left atrium before and after PE. DFs of each recording were calculated offline. Atrial effective refractory periods (ERPs) were measured before and after PE in 11 patients who were in sinus rhythm during the procedure. DFs were also measured in 6 patients in AF before and after complete parasympathetic blockade with atropine (0.04 mg/kg). PE resulted in increased RR intervals during sinus rhythm (1,170 ± 77 to 1,282 ± 85 ms, P = 0.03) and AF (743 ± 32 to 826 ± 30 ms, P = 0.03), consistent with parasympathetic effect on the sinus and AV nodes, respectively. DFs were decreased by PE in the left atrium (6.2 ± 0.2 to 6.0 ± 0.2 Hz, P = 0.004). Correspondingly, atrial ERPs significantly increased from 218 ± 13 to 232 ± 11 ms (P = 0.04). Atropine resulted in a decreasing trend in DF in the left atrium (5.9 ± 0.1 to 5.8 ± 0.1 Hz, P = 0.07). Conclusions: Despite baroreflex-mediated parasympathetic effect, PE produced a slowing of AF along with lengthening of ERP, while parasympathetic blockade also slowed DF. It is therefore likely that the direct and indirect adrenergic effects of PE on atrial electrophysiology are more prominent than its parasympathetic effects. (J Cardiovasc Electrophysiol, Vol. 23 pp. 1045-1050, October 2012) [ABSTRACT FROM AUTHOR]

Atrial Fibrillatory Wave Characteristics . Introduction: Fibrillatory waves on the surface ECG have been scrutinized to allow inferences about underlying mechanisms and pathophysiology, based on the premise that fibrillatory waves do not vary “randomly” but provide a consistent reflection of the underlying state of the atria in an individual patient. This premise is untested. Methods and Results: Ten standard ECGs were recorded over a 24-hour period in each of 20 clinically stable inpatients with atrial fibrillation. After QRS-T cancellation, the remainder fibrillatory waves were analyzed. Interpatient versus intrapatient differences in fibrillatory wave characteristics were evaluated by analysis of variance (ANOVA). The fibrillatory wave peak-to-peak amplitude of all the patients ranged from 0.06 to 0.35 mV, whereas 1 SD of the amplitude for each patient ranged from 0.004 to 0.053 mV. Short-term peak frequencies of all the patients ranged from 4.6 to 8.0 Hz, whereas 1 SD for each patient varied from 0.2 to 0.5 Hz. For these and all other parameters tested, interpatient differences were significantly greater compared to intrapatient differences (P < 0.0001). Conclusion: Fibrillatory wave characteristics are repeatable from ECG to ECG over 24 hours for clinically stable patients, whereas substantial differences are present between patients. Further study of the relationship of such characteristics to pathophysiology and management decisions is valid and warranted. (J Cardiovasc Electrophysiol, Vol. 15, pp. 911-917, August 2004) [ABSTRACT FROM AUTHOR]