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Concept: Heart rate

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BACKGROUND: A reduction in maximal stroke volume (SV(max)) and total blood volume (TBV) has been hypothesized to contribute to the decline in maximal oxygen uptake (VO(2)max) with healthy aging. However, these variables have rarely been collected simultaneously in a board age range to support or refute this hypothesis. It is also unclear to what extent scaling size-related cardiovascular determinants of VO(2)max affects the interpretation of age-related differences. METHODS: A retrospective analysis of VO(2)max, maximal cardiac output (Q©max), TBV, and body composition including fat-free mass (FFM) in 95 (51% M) healthy adults ranging from 19-86 years. RESULTS: Absolute and indexed VO(2)max, Q©max, and maximal heart rate decreased in both sexes with age (p ≤ .031). SV(max) declined with age when scaled to total body mass or body surface area (p ≤ .047) but not when expressed in absolute levels (p = .120) or relative to FFM (p = .464). Absolute and indexed TBVs (mL/kg; mL/m(2)) were not significantly affected by age but increased with age in both sexes when scaled to FFM (p ≤ .013). A lower arteriovenous oxygen difference (a-vO(2)diff) contributed to the reduction in VO(2)max with age in treadmill exercisers (p = .004) but not in the entire cohort (p = .128). CONCLUSION: These results suggest (a) a reduction in absolute SV(max), and TBV do not contribute substantially to the age-related reduction in VO(2)max, which instead results from a smaller Q©max due to a lower maximal heart rate, and (b) body composition scaling methods should be used to accurately describe the effect of aging on physical function and cardiovascular variables.

Concepts: Blood, Cardiology, Heart, Affect, Heart rate, Exercise physiology, VO2 max, Blood volume

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Saccharomyces boulardii has been successfully used in the prevention and treatment of antimicrobial-associated diarrhoea in humans. We hypothesised that a viable, dried lyophilised preparation of S boulardii would survive in the gastrointestinal tract of horses with antimicrobial-associated enterocolitis, and significantly decrease the duration of diarrhoea. Twenty-one horses, over one year of age, with antimicrobial-associated diarrhoea of up to 72 hours duration, were consecutively randomised in a controlled prospective study. The treatment group received S boulardii (25 g, orally, every 12 hours) until the cessation of clinical signs. S boulardii was successfully cultured in 58.3 per cent of treatment horses on day 3. No statistically significant differences were found in days to return to normal faecal consistency; resolution of watery diarrhoea; return to normal heart rate, respiratory rate and temperature; resolution of leucopaenia; attitude improvement; appetite improvement; and survival at discharge. This is the first study to demonstrate survival of S boulardii in horses with gastrointestinal illness. Further study of the efficacy and safety of S boulardii in horses with antimicrobial-associated diarrhoea in a larger group is warranted.

Concepts: Statistical significance, Sociology, Gastroenterology, Medical signs, Saccharomyces boulardii, Heart rate, Ronald Fisher, Human gastrointestinal tract

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To investigate the association between resting heart rate and the risk of developing impaired fasting glucose (IFG), diabetes and conversion from IFG to diabetes.

Concepts: Nutrition, Impaired glucose tolerance, The Association, Heart rate, Sunshine pop

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Objective The purpose of this study was to examine the heart rate reserve (HRR) at first and second ventilatory thresholds (VT’s) in postmenopausal women and compare it with optimal intensity range recommended by the ACSM (40-84%HRR). An additional aim was to evaluate whether a higher aerobic power level corresponded to a higher HRR at VT’s. Methods Fifty-eight postmenopausal women participated in this study (aged 48-69). A graded 25Wmin(-2) cycle ergometer (Monark E839) exercise protocol was performed in order to assess aerobic power. The heart rate and gas-exchange variables were measured continuously using a portable gas analyzer system (Cosmed K4b). The first (VT(1)) and the second (VT(2)) VT’s were determined by the time course curves of ventilation and O(2) and CO(2) ventilatory equivalents. A K-means clustering analysis was used in order to identify VO(2max) groups (cut-off of 30.5mlkg(-1)min(-1)) and differences were evaluated by an independent sample t-test. Bland-Altman plots were performed to illustrate the agreement between methods. Results The women’s HRR values at VT(1) were similar to 40%HRR in both VO(2max) groups. At VT(2) both VO(2max) groups exhibited negative differences (P<0.01) for the predicted 84%HRR intensity (-14.46% in the lower VO(2max) group and -16.32% in the higher VO(2max) group). Conclusions An upper limit of 84% overestimates the %HRR value for the second ventilatory threshold, suggesting that the cardiorespiratory target zone for this population should be lower and narrower (40-70%HRR).

Concepts: Pulse, Student's t-test, Heart rate, The Higher, Thresholds, Threshold, Limit superior and limit inferior, K-means clustering

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The aim of this study was to establish the maximal heart rate (HRmax)-age relation with minimal error rate.

Concepts: Regression analysis, Heart rate, Minimal

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Pre-exercise nutritional practices for active females exercising for mood, cognitive and appetite benefits are not well established. Results from an initial field pilot study showed that higher energy intake at breakfast was associated with lower fatigue and higher overall mood and alertness post-exercise (all p < 0.05). In a follow-up, randomised, controlled trial, 24 active women completed three trials in a balanced, cross-over design. At 0815 h participants completed baseline cognitive tasks, mood and appetite visual analogue scales (VAS) and were administered a cereal breakfast (providing 118 or 236 kcal) or no breakfast. After 45 min, they completed a 30 min run at 65% heart rate reserve (HRR). Parameters were re-assessed immediately after exercise, then hourly until lunch (~1240 h), immediately post-lunch and at 1500 and 1900 h via a mobile phone. Breakfast enhanced feelings of relaxation before lunch (p < 0.05, d > 0.40), though breakfast was detrimental for working memory mid-afternoon (p = 0.019, d = 0.37) and mental fatigue and tension later in the day (all p < 0.05, d > 0.038). Breakfast was also beneficial for appetite control before lunch irrespective of size (all p < 0.05, d > 0.43). These data provide information on pre-exercise nutritional practices for active females and suggest that a small breakfast eaten prior to exercise can benefit post-exercise mood and subjective appetite ratings.

Concepts: Clinical trial, Obesity, Eating, Pulse, Weight loss, Heart rate, Mobile phone, Exercise intolerance

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Daphnia magna heartbeat is myogenic-originating within the animal’s heart. However, the mechanism for this myogenic automaticity is unknown. The mechanism underlying the automaticity of vertebrate myogenic hearts involves cells (pacemaker cells), which have a distinct set of ion channels that include hyperpolarization activated cyclic nucleotide-gated (HCN) and T-type calcium ion channels. We hypothesized that these ion channels also underlie the automatic myogenic heartbeat of Daphnia magna. The drugs, ZD7288 and mibefradil dihydrochloride, block HCN and T-type calcium ion channels respectively. Application of these drugs, in separate experiments, show that they inhibit the heartbeat of Daphnia magna in a dose-dependent manner. Calculation of the percent difference between the heart rate of pretreatment (before drug application) and heart rate following drug application (post-treatment) allowed us to graph a dose-response curve for both ZD7288 and mibefradil, revealing that ZD7288 produces a greater effect on decreasing heart rate. This indicates the HCN ion channels play a foremost role in generating Daphnia magna heartbeat. Our results show conclusively that HCN and T-type calcium ion channels underlie the automatic myogenic heartbeat in Daphnia magna-and suggest a conserved mechanism for generating myogenic heartbeat within the animal kingdom. Thus, Daphnia magna represents a credible model system for further exploration of cardiac physiology.

Concepts: Pharmacology, Bone, Heart, Action potential, Sodium, Heart rate, Potassium, Cardiac pacemaker

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<b>Objective:</b> Mental stress is detrimental to cardiovascular health, being a risk factor for coronary heart disease and a trigger for cardiac events. However, it is not currently routinely assessed. The aim of this study was to identify features of the photoplethysmogram (PPG) pulse wave which are indicative of mental stress. <b>Approach:</b> A numerical model of pulse wave propagation was used to simulate blood pressure signals, from which simulated PPG pulse waves were estimated using a transfer function. Pulse waves were simulated at six levels of stress by changing the model input parameters both simultaneously and individually, in accordance with haemodynamic changes associated with stress. 32 feature measurements were extracted from pulse waves at three measurement sites: the brachial, radial and temporal arteries. Features which changed significantly with stress were identified using the Mann-Kendall monotonic trend test. <b>Main results:</b> 17 features exhibited significant trends with stress in measurements from at least one site. Three features showed significant trends at all three sites: the time from pulse onset to peak, the time from the dicrotic notch to pulse end, and the pulse rate. More features showed significant trends at the radial artery (15) than the brachial (8) or temporal (7) arteries. Most features were influenced by multiple input parameters. <b>Significance:</b> The features identified in this study could be used to monitor stress in healthcare and consumer devices. Measurements at the radial artery may provide superior performance than the brachial or temporal arteries. <i>In-vivo</i> studies are required to confirm these observations. .

Concepts: Blood, Heart, Blood pressure, Artery, Pulse, Heart rate, Brachial artery, Radial artery

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Little is known about whether levels of physical fitness, which is related to adiposity and physical activity (PA), have changed in children, particularly the progressive increase in childhood obesity levels. We aimed to examine the time trends in resting pulse rate (a marker of physical fitness) among UK children, in order to better understand the trends in levels of physical fitness in recent decades.

Concepts: Obesity, Physical exercise, Exercise, Pulse, Childhood, Heart rate, Radial artery, Palpation

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Active flight requires the ability to efficiently fuel bursts of costly locomotion while maximizing energy conservation during non-flying times. We took a multi-faceted approach to estimate how fruit-eating bats (Uroderma bilobatum) manage a high-energy lifestyle fueled primarily by fig juice. Miniaturized heart rate telemetry shows that they use a novel, cyclic, bradycardic state that reduces daily energetic expenditure by 10% and counteracts heart rates as high as 900 bpm during flight. Uroderma bilobatum support flight with some of the fastest metabolic incorporation rates and dynamic circulating cortisol in vertebrates. These bats will exchange fat reserves within 24 hr, meaning that they must survive on the food of the day and are at daily risk of starvation. Energetic flexibly in U. bilobatum highlights the fundamental role of ecological pressures on integrative energetic networks and the still poorly understood energetic strategies of animals in the tropics.

Concepts: Biodiversity, Metabolism, Energy, Muscle, Heart rate, Conservation of energy, Bradycardia, Energy conservation