Fixed Heart Rate Research Articles

PRESCRIBING BLOOD FLOW-RESTRICTED CYCLING USING RPE BALANCES THE PHYSIOLOGICAL AND PERCEPTUAL DEMANDS IN HEALTHY ADULTS

INTRODUCTION Aerobic exercise is commonly prescribed using fixed heart rates or power/speed. These methods may not be suitable when incorporating blood flow restriction (BFR), as this technique can influence these measurements. Prescribing exercise via perception of exertion (RPE), which reflects overall psychophysiological stress, may present an alternative to overcome these issues. Aim: Describe physiological and perceptual responses during fixed-power and fixed-RPE cycling performed with blood flow restriction (BFR_{PWR} and BFR_{RPE}) and without (CON_{PWR} and CON_{RPE}). METHODS Following baseline testing, twelve active males cycled for ten minutes under four conditions. CON_{PWR} was performed first, then the remaining conditions in a randomised and counterbalanced order. BFR_{PWR} and CON_{PWR} were performed at the power equivalent to the first ventilatory threshold (161±38W). CON_{RPE} and BFR_{RPE} were prescribed at the RPE reported during CON_{PWR}. Continuous ventilatory and heart rate measurements were recorded as two-minute averages. Subjective RPE, effort, muscular discomfort, and cuff pain were recorded every two minutes. Blood lactate was measured pre-exercise, post-exercise, and two-minutes post-exercise. RESULTS BFR_{PWR} resulted in the greatest physiological and perceptual responses among all conditions. Power output was lower during BFR_{RPE} (119±48W) than CON_{RPE} (139±47W). Oxygen consumption during BFR_{RPE} (20.8±5.1mL·kg-1·min-1) was lower than CON_{PWR} (25.3±6.0mL·kg-1·min-1, p<0.001) and CON_{RPE} (22.3±5.9mL·kg-1·min-1, p=0.007). Heart rate during CON_{PWR} (143±22beats·min-1) was greater than BFR_{RPE} (133±26beats·min-1, p<0.001) and CON_{RPE} (131±25beats·min-1, p<0.001). Muscular discomfort was not different between BFR_{RPE} (2.5±1.3au) and CON_{PWR}(2.3±1.5au), yet both were greater than CON_{RPE} (p<0.001, 1.8±1.5au). Cuff pain was greater during BFR_{PWR} (3.3±1.7au) than BFR_{RPE} (2.2±1.1au, p<0001). Blood lactate was greater during fixed-power (4.9±3.5mmol·L-1) compared to fixed-RPE trials (3.6±2.7mmol·L-1, p<0.001). CONCLUSIONS BFR_{RPE} caused less discomfort and pain than BFR_{PWR} without compromising physiological stress compared to CON_{RPE}. BFR_{RPE} should be considered when high mechanical loads are contraindicated, or discomfort/pain is undesirable. These findings improve our understanding of aerobic BFR exercise prescription to healthy adults.

In Cardiac Patients Beta-Blockers Attenuate the Decrease in Work Rate during Exercise at a Constant Submaximal Heart Rate.

Exercise prescription based on fixed heart rate (HR) values is not associated with a specific work rate (WR) during prolonged exercise. This phenomenon has never been evaluated in cardiac patients, and might be associated with a slow component of HR kinetics and -adrenergic activity. The aim was to quantify, in cardiac patients, the work rate decrease at a fixed HR, and to test if it would be attenuated by β-blockers. 17 patients with coronary artery disease in stable conditions (69 ± 9 yr) were divided into two groups according to the presence (BB) or absence (no-BB) of a therapy with β-blockers, and performed on a cycle ergometer: an incremental exercise (INCR); a 15-min "HRCLAMPED" exercise, in which WR was continuously adjusted to maintain a constant HR, corresponding to the gas exchange threshold (GET) +15%. HR was determined by the ECG signal, and pulmonary gas exchange was assessed breath-by-breath. During INCR HRpeak was lower in BB vs. no-BB (p < 0.05), whereas no differences were observed for other variables. During HRCLAMPED the decrease in WR needed to maintain HR constant was less pronounced in BB vs. no-BB (-16 ± 10% vs. -27 ± 10, p = 0.04), and was accompanied by a decreased O2 only in no-BB (-13 ± 6%, p < 0.001). The decrease in WR during 15-min exercise at a fixed HR (slightly higher than that at GET) was attenuated in BB, suggesting a potential role by β-adrenergic stimulation. The phenomenon may represent, also in this population, a sign of impaired exercise tolerance, and interferes with aerobic exercise prescription.

Quantifying the impact of heat on human physical work capacity; part IV: interactions between work duration and heat stress severity

High workplace temperatures negatively impact physical work capacity (PWC). Although PWC loss models with heat based on 1-h exposures are available, it is unclear if further adjustments are required to accommodate repeated work/rest cycles over the course of a full work shift. Therefore, we examined the impact of heat stress exposure on human PWC during a simulated work shift consisting of six 1-h work-rest cycles. Nine healthy males completed six 50-min work bouts, separated by 10-min rest intervals and an extended lunch break, on four separate occasions: once in a cool environment (15 °C/50% RH) and in three different air temperature and relative humidity combinations (moderate, 35 °C/50% RH; hot, 40 °C/50% RH; and very hot, 40 °C/70%). To mimic moderate to heavy workload, work was performed on a treadmill at a fixed heart rate of 130 beats·min−1. During each work bout, PWC was quantified as the kilojoules expended above resting levels. Over the shift, work output per cycle decreased, even in the cool climate, with the biggest decrement after the lunch break and meal consumption. Expressing PWC relative to that achieved in the cool environment for the same work duration, there was an additional 5(± 4)%, 7(± 6)%, and 16(± 7)% decrease in PWC when work was performed across a full work shift for the moderate, hot, and very hot condition respectively, compared with 1-h projections. Empirical models to predict PWC based on the level of heat stress (Wet-Bulb Globe Temperature, Universal Thermal Climate Index, Psychrometric Wet-Bulb Temperature, Humidex, and Heat Index) and the number of work cycles performed are presented.

Study to evaluate pulmonary responses of various exercise intensities in young adults using treadmill and ergometer bicycle

Background: Exercise is important for keeping your health in check and is advised for disease prevention, disease diagnosis, and disease rehabilitation. There are several workouts that can be used to enhance exercise performance; however, the threshold differs from individual to individual. Aim and Objective: The objective of this study is to evaluate the pulmonary responses to three different exercise intensities in young, healthy individuals using a treadmill, and a bicycle ergometer at a fixed heart rate value. Materials and Methods: After getting approval from the Institutional Ethics Committee, 130 volunteers were evaluated, and 48 randomly chosen male and female individuals between the ages of 18 and 24 and with a normal BMI were chosen. The selected participants are divided into three groups according to heart rate using the WHO classification and the Karvonen formula for exercise intensity. Sixteen persons in each group begin exercising on a treadmill at speeds of 3, 6, and 7.5 km/h, respectively, with no incline, and on an ergometer bicycle at speeds of 50–60 rpm, 70–80 rpm, and 90–100 rpm, respectively, with no breaking resistance until the predicted goal heart rate is attained. Before and after exercise, pulmonary measures including respiratory rate (RR), tidal volume, minute ventilation (MV), and oxygen saturation level (SPO2) were assessed. The findings were statistically evaluated. Results: RR, TV, and MV are linearly increased with increasing intensity of exercise in ergometer bicycling than treadmill exercise, whereas SPO2 gradually decreased with increasing intensity of exercise; however, more observed in ergometer bicycling than a treadmill. When the difference between pre and post-TV was compared between two modes of exercise, there was a significant increase in TV during ergometer bicycle among all the three groups; however, when post-mean RR, TV, MV, and SPO2 were compared between treadmill and ergometer bicycle exercise, there was statistically insignificant. Conclusion: Each sort of exercise has advantages and disadvantages based on the individual’s needs and physiological condition.

Contribution of fetal magnetic resonance imaging in fetuses with congenital heart disease.

Increasing evidence supports an association among congenital heart disease (CHD), structural brain lesions on neuroimaging, and increased risk of neurodevelopmental delay and other structural anomalies. Fetal MRI has been found to be effective in demonstrating fetal structural and developmental abnormalities. To determine the contribution of fetal MRI to identifying cardiovascular and non-cardiovascular anomalies in fetuses with CHD compared to prenatal US and fetal echocardiography. We performed a retrospective study of fetuses with CHD identified by fetal echocardiography. Exams were performed on 1.5-tesla (T) or 3-T magnets using a balanced turbo field echo sequence triggered by an external electrocardiogram simulator with a fixed heart rate of 140 beats per minute (bpm). Fetal echocardiography was performed by pediatric cardiologists and detailed obstetrical US by maternal-fetal medicine specialists prior to referral to MRI. We compared the sensitivity of fetal MRI and fetal echocardiography for the diagnosis of cardiovascular anomalies, as well as the sensitivity of fetal MRI and referral US for the diagnosis of non-cardiac anomalies. We performed statistical analysis using the McNemar test. We identified 121 anomalies in 31 fetuses. Of these, 73 (60.3%) were cardiovascular and 48 (39.7%) involved other organ systems. Fetal echocardiography was more sensitive for diagnosing cardiovascular anomalies compared to fetal MRI, but the difference was not statistically significant (85.9%, 95% confidence interval [CI] 77.8-94.0% vs. 77.5%, 95% CI 67.7-87.2%, respectively; McNemar test 2.29; P=0.13). The sensitivity of fetal MRI was higher for diagnosing extracardiac anomalies when compared to referral US (84.1%, 95% CI 73.3-94.9% vs. 31.8%, 95% CI 18.1-45.6%, respectively; McNemar test 12.9; P<0.001). The additional information provided by fetal MRI changed prognosis, counseling or management for 10/31 fetuses (32.2%), all in the group of 19 fetuses with anomalies in other organs and systems besides CHD. Fetal MRI performed in a population of fetuses with CHD provided additional information that altered prognosis, counseling or management in approximately one-third of the fetuses, mainly by identifying previously unknown anomalies in other organs and systems.

Cardiorespiratory Response and Power Output During Submaximal Exercise in Normobaric Versus Hypobaric Hypoxia: A Pilot Study Using a Specific Chamber that Controls Environmental Factors

2021.—Many previous studies have examined hypoxia-induced physiological responses using various conditions, e.g., artificially reduced atmospheric oxygen concentration [normobaric hypoxia (NH) condition] or low barometric pressure at a mountain [hypobaric hypoxia (HH) condition]. However, when comparing the results from these previous studies conducted in artificial NH and HH including real high altitude, we must consider the possibility that environmental factors, such as temperature, humidity, and fraction of inspired carbon dioxide, might affect the physiological responses. Therefore, we examined cardiorespiratory responses and exercise performances during low- to high-intensity exercise at a fixed heart rate (HR) in both NH and HH using a specific chamber where atmospheric oxygen concentration and barometric pressure as well as the abovementioned environmental factors were precisely controlled. Ten well-trained university students (eight males and two females) performed the exercise test consisting of two 20-minute submaximal pedaling at the intensity corresponding to 50% (low) and 70% (high) of their HR reserve, under three conditions [NH (fraction of inspired oxygen, 0.135; barometric pressure, 754 mmHg), HH (fraction of inspired oxygen, 0.209; barometric pressure, 504 mmHg), and normobaric normoxia (NN; fraction of inspired oxygen, 0.209; barometric pressure, 754 mmHg)]. Peripheral oxygen saturation (SpO2) to estimate arterial oxygen saturation and partial pressure of end-tidal carbon dioxide (PETCO2) were monitored throughout the experiment. SpO2, PETCO2, and power output at fixed HRs (i.e., pedaling efficiency) in NH and HH were all significantly lower than those in NN. Moreover, high-intensity exercise in HH induced greater decreases in SpO2 and power output than did high-intensity exercise in NH (NH vs. HH; SpO2, 78.2% - 5.0% vs. 75.1% - 7.1%; power output, 120.7 - 24.9 W vs. 112.4 - 23.2 W, both p &lt; 0.05). However, high-intensity exercise in HH induced greater increases in PETCO2 than did high-intensity exercise in NH (NH vs. HH; 54.2 - 5.9mmHg vs. 57.2 - 3.4 mmHg, p &lt; 0.01). These results suggest that physiological responses and power output at a fixed HR during hypoxic exposure might depend on the method used to generate the hypoxic condition.

Quantifying the impact of heat on human physical work capacity; part III: the impact of solar radiation varies with air temperature, humidity, and clothing coverage

Heat stress decreases human physical work capacity (PWC), but the extent to which solar radiation (SOLAR) compounds this response is not well understood. This study empirically quantified how SOLAR impacts PWC in the heat, considering wide, but controlled, variations in air temperature, humidity, and clothing coverage. We also provide correction equations so PWC can be quantified outdoors using heat stress indices that do not ordinarily account for SOLAR (including the Heat Stress Index, Humidex, and Wet-Bulb Temperature). Fourteen young adult males (7 donning a work coverall, 7 with shorts and trainers) walked for 1 h at a fixed heart rate of 130 beats∙min−1, in seven combinations of air temperature (25 to 45°C) and relative humidity (20 or 80%), with and without SOLAR (800 W/m2 from solar lamps). Cumulative energy expenditure in the heat, relative to the work achieved in a cool reference condition, was used to determine PWC%. Skin temperature was the primary determinant of PWC in the heat. In dry climates with exposed skin (0.3 Clo), SOLAR caused PWC to decrease exponentially with rising air temperature, whereas work coveralls (0.9 Clo) negated this effect. In humid conditions, the SOLAR-induced reduction in PWC was consistent and linear across all levels of air temperature and clothing conditions. Wet-Bulb Globe Temperature and the Universal Thermal Climate Index represented SOLAR correctly and did not require a correction factor. For the Heat Stress Index, Humidex, and Wet-Bulb Temperature, correction factors are provided enabling forecasting of heat effects on work productivity.

Потенциальная роль бенфотиамина в лечении диабетической автономной нейропатии сердца

Актуальность. Диабетическая нейропатия сердца — серьезное осложнение сахарного диабета, связанное с примерно пятикратным повышением риска сердечно-сосудистой смертности. Автономная нейропатия сердца проявляется широким спектром, начиная от тахикардии покоя и фиксированного сердцебиения до развития бессимптомного инфаркта миокарда. Значение диабетической автономной нейропатии сердца до конца не выяснено, также не существует единого алгоритма лечения. Цель: исследовать влияние бенфотиамина на состояние вариабельности ритма сердца, корригированный интервал QT, дисперсию QT и пространственный угол QRS-T у больных сахарным диабетом 2-го типа и автономной нейропатией. Материалы и методы. Тридцать два пациента с сахарным диабетом 2-го типа и функциональной стадией автономной нейропатии сердца были распределены в две группы лечения: контрольную (n = 15), получавшую стандартную сахароснижающую терапию, и группу 2 (n = 17) — бенфотиамин 300 мг/сут в дополнение к традиционной терапии в течение трех месяцев. Результаты. Установлено, что назначение бенфотиамина вызывало увеличение процента последовательных интервалов NN, разница между которыми превышает 50 мс, — pNN50 (Δ% = + 45,90 ± 7,91 %, р &lt; 0,05), высокочастотной компоненты вариабельности ритма сердца во время активного (Δ % = + 25,80 ± 5,58 %, p &lt; 0,05) и пассивного периодов суток (Δ% = +21,10 ± 4,17 %, р &lt; 0,05), способствовало уменьшению корригированного интервала QT (Δ% = –7,30 ± 1,36 %, p &lt; 0,01), дисперсии QT (Δ% = –27,7 ± 9,0 %, p &lt; 0,01) и пространственного угла QRS-T (Δ% = –24,4 ± 10,2 %, p &lt; 0,01). Выводы. Положительное влияние бенфотиамина свидетельствует о целесообразности его назначения пациентам с сахарным диабетом 2-го типа и функциональной стадией автономной нейропатии сердца.

Aerobic fitness as a parameter of importance for labour loss in the heat

ObjectivesTo derive an empirical model for the impact of aerobic fitness (maximal oxygen consumption; V̇O2max in mL∙kg−1∙min−1) on physical work capacity (PWC) in the heat. DesignProspective, repeated measures. MethodsTotal work completed during 1 h of treadmill walking at a fixed heart rate of 130 b∙min−1 was assessed in 19 young adult males across a variety of warm and hot climate types, characterised by wet-bulb globe temperatures (WBGT) ranging from 12 to 40 °C. For data presentation and obtaining initial parameter estimates for modelling, participants were grouped into low (n = 6, 74 trials), moderate (n = 8, 76 trials), and high (n = 5, 29 trials) fitness, with group mean V̇O2max 42, 52, and 64 mL∙kg−1∙min−1, respectively. For the heated conditions (WBGT 18 to 40 °C), we calculated PWC% by expressing total energy expenditure (kJ above resting) in each trial relative to that achieved in a cool reference condition (WBGT = 12 °C = 100% PWC). ResultsThe relative reduction in energy expenditure (PWC%) caused by heat was significantly smaller by up to 16% for the fit participants compared to those with lower aerobic capacity. V̇O2max also modulated the relationship between sweat rate and body temperature changes to increasing WBGT. Including individual V̇O2max data in the PWC prediction model increased the predicting power by 4%. ConclusionsIncorporating individual V̇O2max improved the predictive power of the heat stress index WBGT for Physical Work Capacity in the heat. The largest impact of V̇O2max on PWC was observed at a WBGT between 25 and 35 °C.

Cardiorespiratory Response and Power Output During Submaximal Exercise in Normobaric Versus Hypobaric Hypoxia: A Pilot Study Using a Specific Chamber that Controls Environmental Factors.

Takezawa, Toshihiro, Shohei Dobashi, and Katsuhiro Koyama. Cardiorespiratory response and power output during submaximal exercise in normobaric versus hypobaric hypoxia: a pilot study using a specific chamber that controls environmental factors. High Alt Med Biol. 22: 201-208, 2021. Background: Many previous studies have examined hypoxia-induced physiological responses using various conditions, e.g., artificially reduced atmospheric oxygen concentration [normobaric hypoxia (NH) condition] or low barometric pressure at a mountain [hypobaric hypoxia (HH) condition]. However, when comparing the results from these previous studies conducted in artificial NH and HH including real high altitude, we must consider the possibility that environmental factors, such as temperature, humidity, and fraction of inspired carbon dioxide, might affect the physiological responses. Therefore, we examined cardiorespiratory responses and exercise performances during low- to high-intensity exercise at a fixed heart rate (HR) in both NH and HH using a specific chamber where atmospheric oxygen concentration and barometric pressure as well as the abovementioned environmental factors were precisely controlled. Methods: Ten well-trained university students (eight males and two females) performed the exercise test consisting of two 20-minute submaximal pedaling at the intensity corresponding to 50% (low) and 70% (high) of their HR reserve, under three conditions [NH (fraction of inspired oxygen, 0.135; barometric pressure, 754 mmHg), HH (fraction of inspired oxygen, 0.209; barometric pressure, 504 mmHg), and normobaric normoxia (NN; fraction of inspired oxygen, 0.209; barometric pressure, 754 mmHg)]. Peripheral oxygen saturation (SpO2) to estimate arterial oxygen saturation and partial pressure of end-tidal carbon dioxide (PETCO2) were monitored throughout the experiment. Results: SpO2, PETCO2, and power output at fixed HRs (i.e., pedaling efficiency) in NH and HH were all significantly lower than those in NN. Moreover, high-intensity exercise in HH induced greater decreases in SpO2 and power output than did high-intensity exercise in NH (NH vs. HH; SpO2, 78.2% ± 5.0% vs. 75.1% ± 7.1%; power output, 120.7 ± 24.9 W vs. 112.4 ± 23.2 W, both p < 0.05). However, high-intensity exercise in HH induced greater increases in PETCO2 than did high-intensity exercise in NH (NH vs. HH; 54.2 ± 5.9 mmHg vs. 57.2 ± 3.4 mmHg, p < 0.01). Conclusions: These results suggest that physiological responses and power output at a fixed HR during hypoxic exposure might depend on the method used to generate the hypoxic condition.

Adaptation of ventricular repolarization duration and dispersion during changes in heart rate induced by atrial stimulation.

BackgroundThe duration of ventricular repolarization (VR) and its spatial and temporal heterogeneity are central elements in arrhythmogenesis. We studied the adaptation of VR duration and dispersion and their relationship in healthy human subjects during atrial pacing.MethodsPatients 20‐50 years of age who were scheduled for ablation of supraventricular tachycardia without preexcitation but otherwise healthy were eligible. Vectorcardiography recordings with Frank leads were used for data collection. Incremental atrial pacing from a coronary sinus electrode was performed by decrements of 10ms/cycle from just above sinus rate, and then kept at a fixed heart rate (HR) just below the Wenckebach rate for ≥5min and then stopped. VR duration was measured as QT and VR dispersion as T area, T amplitude and ventricular gradient. The primary measure (T90 End) was the time to reach 90% change from baseline to the steady state value during and after pacing.ResultsA complete study protocol was accomplished in 9 individuals (6 women). VR duration displayed a monophasic adaptation during HR acceleration lasting on average 20s. The median (Q1‐Q3) T90 End for QT was 85s (51‐104), a delay by a factor >4. All dispersion measures displayed a tri‐phasic response pattern during HR acceleration and T90 End was 3‐5 times shorter than for VR duration.ConclusionsEven during close to “physiological” conditions, complex and differing response patterns in VR duration and dispersion measures followed changes in HR. Extended knowledge about these responses in disease conditions might assist in risk evaluation and finding therapeutic alternatives.

ON VENTRICLE PUMPING EFFICIENCY IN MIXED AORTIC VALVE DISEASE AND A NEED FOR NEW PARAMETERS

Aortic stenosis (AS) and aortic regurgitation (AR) are frequently encountered in both pediatric and adult populations. Data on combined AS and AR are however scarce and little is known regarding how to better evaluate patients with mixed aortic valve disease (MAVD). The specific objective of this work is to evaluate in silico the combined volume and pressure overloads on the left ventricle (LV) using a newly developed non-invasive parameter inspired by classical thermodynamic concepts: LV efficiency. A mathematical model has been developed to simulate several combinations of MAVD. We have developed a new non-invasive parameter, LV efficiency, combining the effects of AS and AR on LV function: ELV=(1-Rf)*(Psys/(Psys+TPGmean)), where Rf is the regurgitant fraction, Psys is the systolic arterial pressure and TPGmean is the mean transvalvular pressure gradient. The LV efficiency was evaluated for AS valve effective orifice areas ranging from 0.6 to 3.5 cmˆ2 combined with AR valve effective orifice areas ranging 0 to 0.7 cmˆ2. The simulations have been performed for four different stroke volumes: 50, 60, 70 and 80 ml with a fixed heart rate of 70 bpm and systolic pressure of 120 mmHg. The effect of heart rate (60, 70, 80 and 90 bpm) and systolic pressure (120 and 140 mmHg) on LV efficiency was also evaluated at a fixed stroke volume of 70 ml. Our results show that LV efficiency has a strong nonlinear power law relationship with LV stroke work (Rˆ2=0.81). In healthy simulated cases, LV efficiency was higher than 90%. Very severe cases (severe AS + severe AR) led to LV efficiencies below 20%. Cases with moderate MAVD display a wide variation in LV efficiencies ranging from 61.71% down to 34.36%. Those values were found to be equivalent to LV efficiencies corresponding to severe pure AS simulated cases. We have introduced a new patient-specific non-invasive parameter capable of capturing the combined pressure and volume overloads supported by the LV. This parameter has the potential to unify the decision-making process in patients with aortic valve disease.

Errors of Fixed QT Heart Rate Corrections Used in the Assessment of Drug-Induced QTc Changes.

The accuracy of studies of drug-induced QTc changes depends, among others, on the accuracy of heart rate correction of QT interval. It has been recognized that when a drug leads to substantial heart rate changes, fixed universal corrections cannot be used and that alternative methods such as subject-specific corrections established for each study participant need to be considered. Nevertheless, the maximum heart rate change that permits use of fixed correction with reasonable accuracy has not been systematically investigated. We have therefore used full QT/heart-rate profiles of 751 healthy subjects (mean age 34.2 ± 9.6, range 18–61 years, 335 females) and compared their subject-specific corrections with 6 fixed corrections, namely Bazett, Fridericia, Framingham, Hodges, Rautaharju, and Sarma formulae. The comparison was based on statistical modeling experiments which simulated clinical studies of N = 10 or N = 50 female or male subjects. The experiments compared errors of ΔQTc intervals calculated as differences between QTc intervals at an initial heart rate (in the range of 40 to 120 beats per minute, bpm) and after a heart rate change (in the range from −20 to +20 bpm). The experiments also investigated errors due to spontaneous heart rate fluctuation and due to omission of correction for QT/RR hysteresis. In each experiment, the absolute value of the single-sided 90th percentile most remote from zero was used as the error estimate. Each experiment was repeated 10,000 times with random selection of modeled study group. From these repetitions, median and upper 80th percentile was derived and graphically displayed for all different combinations of initial heart rate and heart rate change. The results showed that Fridericia formula might be reasonable (with estimated errors of ΔQTc below 8 ms) in large studies if the heart rate does not change more than ± 10 bpm and that the errors by fixed corrections and the errors due to omission of QR/RR hysteresis are additive. Additionally, the results suggest that the variability introduced into QTc data by not correcting for the underlying heart rate accurately might have a greater impact in smaller studies. The errors by Framingham formula were practically the same as with the Fridericia formula. Other investigated fixed heart rate corrections led to larger ΔQTc errors.

Impact of Fan Use on Physical Work Capacity in Extreme Heat

Emerging evidence suggests that electric fan use can reduce thermoregulatory and cardiovascular strain at air temperatures as high as 42°C during rest. However, there is a dearth of empirical evidence relating to the safety limits for fan use at various combinations of air temperatures and humidity, and how their use impacts physical work capacity (PWC). PURPOSE: The aim of the current study is to provide new threshold limit values for electric fan use during physical work. METHODS: Sixteen young adult males (heterogenous in fitness and anthropological characteristics) performed ~20 trials, consisting of 1 hour of treadmill walking at a fixed heart rate of 130 beats·min-1. The first experimental trial was conducted in a reference environment with no heat-stress (15°C, 50% rh). The remaining trials were conducted at the same fixed heart rate for a maximum of 1 hour at 30-50°C at various humidities. Each experimental trial was conducted with and without electric fans. The PWC in each heat-stress trial was defined as the total energy expended during 1 hour of treadmill walking and was expressed relative (%) to that expended during the reference condition. The study cohort was split into two subgroups with one group performing trials in minimal clothing (shorts only) whilst the second group undertook trials wearing protective clothing covering the legs, torso and arms (e.g. coveralls). RESULTS: Based on individual responses to fan exposure during moderate to heavy work undertaken wearing minimal clothing, forced convection was always beneficial at air temperatures ≤34°C. Between 34 and 43°C, a consistent fan benefit was only observed between 40 and 60% relative humidity, with lowered PWC above and below. In contrast, when protective clothing was worn, the beneficial impact of fans between 34 and 43°C was eroded with negligible effects on PWC observed. PWC was consistently impaired by fan use at air temperatures >43°C. CONCLUSION: These empirical data will facilitate the formulation of comprehensive threshold limit values for fan use during physical work based on biophysical parameters. Funding was provided by ‘Heat-Shield’, European Union's Horizon 2020 research and innovation programme under the Grant agreement no. 668786.

Fanning as an alternative to air conditioning – A sustainable solution for reducing indoor occupational heat stress

We assessed whether increasing airflow with an electric fan is similarly effective as decreasing air temperature with air cooling (AC) in preventing heat-related reductions in productivity, and elevations in body temperatures and discomfort in a warm/humid indoor environment. In 48 experimental trials, we compared the reduction in the human heat stress response of sixteen participants during 135 min of intermittent arm ergometry at a fixed heart rate of 110 beats min−1, from a simulated tropical environment (HOT; 30 °C, 70%RH; wind < 0.2 m s−1) to that observed with either a, (i) 7 °C reduction in air temperature (AC; 23 °C, 70%RH, wind < 0.2 m s−1); or (ii) facilitated airflow (FAN; 30 °C, 70%RH, wind = 4.2 m s−1). Cumulative work was similarly improved (+11%) by FAN compared to AC. Likewise, reductions in rectal temperature, thermal sensation, and thermal discomfort were similar with the two different cooling strategies. Sweat losses in the FAN trial were higher compared to AC but lower than HOT without fanning. In conclusion, fanning offers an effective method for alleviating thermal stress and preventing productivity losses for workers exposed to environmental heat. Moving air instead of chilling it may require a little more sweating, but it can save electricity and hence lower greenhouse gas emissions compared to AC.

Cardiac autonomic neuropathy: Risk factors, diagnosis and treatment.

Cardiac autonomic neuropathy (CAN) is a serious complication of diabetes mellitus (DM) that is strongly associated with approximately five-fold increased risk of cardiovascular mortality. CAN manifests in a spectrum of things, ranging from resting tachycardia and fixed heart rate (HR) to development of “silent” myocardial infarction. Clinical correlates or risk markers for CAN are age, DM duration, glycemic control, hypertension, and dyslipidemia (DLP), development of other microvascular complications. Established risk factors for CAN are poor glycemic control in type 1 DM and a combination of hypertension, DLP, obesity, and unsatisfactory glycemic control in type 2 DM. Symptomatic manifestations of CAN include sinus tachycardia, exercise intolerance, orthostatic hypotension (OH), abnormal blood pressure (BP) regulation, dizziness, presyncope and syncope, intraoperative cardiovascular instability, asymptomatic myocardial ischemia and infarction. Methods of CAN assessment in clinical practice include assessment of symptoms and signs, cardiovascular reflex tests based on HR and BP, short-term electrocardiography (ECG), QT interval prolongation, HR variability (24 h, classic 24 h Holter ECG), ambulatory BP monitoring, HR turbulence, baroreflex sensitivity, muscle sympathetic nerve activity, catecholamine assessment and cardiovascular sympathetic tests, heart sympathetic imaging. Although it is common complication, the significance of CAN has not been fully appreciated and there are no unified treatment algorithms for today. Treatment is based on early diagnosis, life style changes, optimization of glycemic control and management of cardiovascular risk factors. Pathogenetic treatment of CAN includes: Balanced diet and physical activity; optimization of glycemic control; treatment of DLP; antioxidants, first of all α-lipoic acid (ALA), aldose reductase inhibitors, acetyl-L-carnitine; vitamins, first of all fat-soluble vitamin B1; correction of vascular endothelial dysfunction; prevention and treatment of thrombosis; in severe cases-treatment of OH. The promising methods include prescription of prostacyclin analogues, thromboxane A2 blockers and drugs that contribute into strengthening and/or normalization of Na+, K+-ATPase (phosphodiesterase inhibitor), ALA, dihomo-γ-linolenic acid (DGLA), ω-3 polyunsaturated fatty acids (ω-3 PUFAs), and the simultaneous prescription of ALA, ω-3 PUFAs and DGLA, but the future investigations are needed. Development of OH is associated with severe or advanced CAN and prescription of nonpharmacological and pharmacological, in the foreground midodrine and fludrocortisone acetate, treatment methods are necessary.

A study to evaluate cardiovascular responses by using treadmill and ergometer bicycle exercise in young adults

BACKGROUND AND OBJECTIVE: Exercise is inevitable to keep good health status, advised for health promotion, diagnosis of diseases, and rehabilitation. Different types of exercise are performed as exercise tolerance, but tolerance is not same for every individual. Thus, the objective of this study is to evaluate the cardiovascular responses for three different intensities of exercise using treadmill and bicycle ergometer at fixed heart rate (HR) value in young healthy adults. METHODS: After obtaining the ethical clearance from the Institutional Ethical Committee, a total of 130 participants were screened and 48 randomly selected male and female individuals with age group of 18–24 years and with normal body mass index. Selected participants are divided into three groups according to HR using WHO classification and Karvonen formula of exercise intensity. Sixteen individuals in each group start exercising for treadmill exercise at 3, 6, and 7.5 k/h, respectively, with zero inclination and for ergometer bicycle exercise at pedal frequency 50–60, 70–80, and 90–100 rpm, respectively, with 0 kg breaking resistance until calculated target HR is achieved. Cardiovascular parameters such as (systolic blood pressure [SBP], diastolic blood pressure [DBP], and rate pressure product [RPP]) pre- and post-exercise were recorded, and data are subjected to statistical analysis in both modes of exercise. RESULTS: SBP and RPP are linearly increased with increasing intensity of exercise and more observed in ergometer bicycling than treadmill exercise. Postexercise mean DBP among the three intensities of exercise: in mild exercise, there was negligible change in case of treadmill exercise and a higher mean DBP was recorded in case of ergometer bicycle exercise; in moderate exercise, value was slightly lower in treadmill exercise and slightly higher in ergometer bicycle exercise, but in severe exercise, mean DBP decreased in both treadmill as well as in ergometer bicycle exercise. CONCLUSION: Each mode of exercise has its own advantage and disadvantage depends on individual's physical condition and requirement.

Cardiac action potential repolarization revisited: early repolarization shows all-or-none behaviour.

In healthy mammalian hearts the action potential (AP) waveform initiates and modulates each contraction, or heartbeat. As a result, AP height and duration are key physiological variables. In addition, rate-dependent changes in ventricular AP duration (APD), and variations in APD at a fixed heart rate are both reliable biomarkers of electrophysiological stability. Present guidelines for the likelihood that candidate drugs will increase arrhythmias rely on small changes in APD and Q-T intervals as criteria for safety pharmacology decisions. However, both of these measurements correspond to the final repolarization of the AP. Emerging clinical evidence draws attention to the early repolarization phase of the action potential (and the J-wave of the ECG) as an additional important biomarker for arrhythmogenesis. Here we provide a mechanistic background to this early repolarization syndrome by summarizing the evidence that both the initial depolarization and repolarization phases of the cardiac action potential can exhibit distinct time- and voltage-dependent thresholds, and also demonstrating that both can show regenerative all-or-none behaviour. An important consequence of this is that not all of the dynamics of action potential repolarization in human ventricle can be captured by data from single myocytes when these results are expressed as 'repolarization reserve'. For example, the complex pattern of cell-to-cell current flow that is responsible for AP conduction (propagation) within the mammalian myocardium can change APD and the Q-T interval of the electrocardiogram alter APD stability, and modulate responsiveness to pharmacological agents (such as Class III anti-arrhythmic drugs).

Perceived Exertion is Lower in Running than Walking at the Same Heart Rate and Lactate Level

The purpose of this study was to examine perceived effort at various intensities in human walking and running. Fifteen male subjects participated in this study. Two progressive protocols were randomized, starting at a treadmill speed of 3 Metabolic Equivalents (METs) to Measure Ratings of Perceived Exertion (RPE), Heart Rate (HR) and blood lactate concentration. From these data, RPE was estimated at an intensity corresponding to Fixed Heart Rate (FHR; 120, 130, 140, 150 bpm) and Fixed Blood Lactate Concentrations (FBLCs; 2 and 3 mM) from the individual regression line.

Vernakalant does not alter early repolarization or contractility in normal and electrically remodelled atria.

Besides the inhibition of the sodium inward current, vernakalant also inhibits the ultra rapid rectifier (IKur) and transient outward current (Ito). Inhibition of these currents increases contractility in canine atrial myocytes and goat atria. We investigated the effect of vernakalant on early repolarization and contractility in normal and electrically remodelled atria. Goats were implanted a pressure catheter, piezoelectric crystals, and electrodes to obtain atrial contractility and effective refractory period (ERP). The active component in pressure distance loops was used to compute the atrial work index (AWI). Experiments were performed in normal and electrically remodelled atria at clinically relevant plasma levels of vernakalant. As a positive control, the Ito/IKur blocker AVE0118 was investigated. Monophasic action potentials were recorded in anaesthetized goats and in explanted hearts to determine changes in action potential morphology. Vernakalant did not affect atrial work loops during sinus rhythm. Likewise vernakalant did not increase atrial fractional shortening or AWI during pacing with fixed heart rate and AV-delay. In contrast, AVE0118 did increase AWI, with a positive force frequency relation. Both in normal and remodelled atria, vernakalant strongly increased ERP but did not prolong early repolarization. In goat atria, vernakalant does not have an atrial positive inotropic effect and does not affect early repolarization. At high rates vernakalant may even have a negative inotropic effect.