Gavin Sandercock

A Quantitative Systematic Review of Normal Values for Short-Term Heart Rate Variability in Healthy Adults

Heart rate variability (HRV) is a known risk factor for mortality in both healthy and patient populations. There are currently no normative data for short‐term measures of HRV. A thorough review of short‐term HRV data published since 1996 was therefore performed. Data from studies published after the 1996 Task Force report (i.e., between January 1997 and September 2008) and reporting short‐term measures of HRV obtained in normally healthy individuals were collated and factors underlying discrepant values were identified. Forty‐four studies met the pre‐set inclusion criteria involving 21,438 participants. Values for short‐term HRV measures from the literature were lower than Task Force norms. A degree of homogeneity for common measures of HRV in healthy adults was shown across studies. A number of studies demonstrate large interindividual variations (up to 260,000%), particularly for spectral measures. A number of methodological discrepancies underlined disparate values. These include a systematic failure within the literature (a) to recognize the importance of RR data recognition/editing procedures and (b) to question disparate HRV values observed in normally healthy individuals. A need for large‐scale population studies and a review of the Task Force recommendations for short‐term HRV that covers the full‐age spectrum were identified. Data presented should be used to quantify reference ranges for short‐term measures of HRV in healthy adult populations but should be undertaken with reference to methodological factors underlying disparate values. Recommendations for the measurement of HRV require updating to include current technologies. (PACE 2010; 1407–1417)

Effects of Exercise on Heart Rate Variability: Inferences from Meta-Analysis

INTRODUCTION Chronic exercise training produces a resting bradycardia that is thought to be due partly to enhanced vagal modulation. PURPOSE The aim of the present study was to determine the effects of exercise training on heart rate and measures of heart rate variability associated with vagal cardiac modulation and to quantify the relationship between changes in these measures. METHODS A random effects model of effect size (d) for change in high frequency (HF) power and RR interval was calculated. Within-group heterogeneity was assessed using the Q statistic. Where heterogenous effects were found, subgroup analyses were performed using the between-group Q statistic. RESULTS A meta-analysis of 13 studies measuring HF (N=322 cases) produced an overall effect size of d=0.48 (C.I. 0.26-0.70, P=0.00003). Twelve studies (298 cases) reported a change in RR interval with an overall effect size of d=0.75 (C.I. 0.51-0.96, P<0.00001). Effect sizes for RR interval data were significantly heterogenous. Subgroup analysis revealed significantly smaller responses of RR interval to training in older subjects (P<0.1). Effect sizes for change in HF were homogenous, although a trend toward an attenuated response to training was exhibited in older subjects (P>0.10). Linear, quadratic, and cubic fits all revealed weak (P>0.05) relationships between effect sizes for change in HF and RR interval. DISCUSSION Exercise training results in significant increases in RR interval and HF power. These changes are influenced by study population age. The smaller effect size for HF and weak relationship between HF and RR interval suggest factors additional to increased vagal modulation are responsible for training bradycardia.

Validity and Reliability of Short-Term Heart-Rate Variability from the Polar S810

PURPOSE : To assess the validity and the reliability of short-term resting heart-rate variability (HRV) measures obtained using the Polar S810 heart-rate monitor and accompanying software. METHODS : Measures of HRV were obtained from 5-min R to R wave (RR) interval data for 19 males and 14 females during 10 min of quiet rest on three separate occasions at 1-wk intervals using the Polar S810. Criterion measures of HRV were obtained simultaneously using the CardioPerfect (CP; Medical Graphics Corporation, St Paul, MN) 12-lead ECG module. Measures of validity of the Polar S810 were estimated by regression analysis, and measures of reliability of both devices were estimated by analysis of change scores. Measures of the SD of normal-to-normal intervals (SDNN), the root mean square of successive differences (RMSSD), and the low-frequency (LF) and the high-frequency (HF) spectral power and their ratio (LF/HF) were analyzed after log transformation, whereas mean RR and LF and HF in normalized units were analyzed without transformation. RESULTS : There were marginal differences between the Polar and the CP mean measures of HRV, and the uncertainty in the differences was small. The Polar S810 demonstrated high correlations (0.85-0.99) with CP for all measures of HRV indicating good to near-perfect validity. Except for the low- and the high-frequency normalized units, Polar S810 did not add any substantial technical error to the within-subject variability in the repeated measurements of HRV. CONCLUSION : HRV measures obtained with the Polar S810 and accompanying software have no appreciable bias or additional random error in comparison with criterion measures, but the measures are inherently unreliable over a 1-wk interval. Reliability of HRV from longer (e.g., 10 min) and/or consecutive 5-min RR recordings needs to be investigated with the Polar and criterion instruments.

The Role of Heart Rate Variability in Prognosis for Different Modes of Death in Chronic Heart Failure

Classic risk factors for mortality due to chronic heart failure (CHF), such as low left ventricular ejection fraction, NYHA functional stage, and increased heart rate perform well in the prediction of death from pump failure. The prediction of sudden cardiac death (SCD) remains somewhat problematic. Numerous studies have analyzed the potential contribution heart rate variability (HRV) can make to risk assessment in CHF. The aim of this review was to summarize the literature and identify the role HRV might play in identifying mode of death, as well as overall mortality risk. In studies where all‐cause mortality or cardiac events were the clinical end point(s), global and slow oscillatory measures of HRV were the strongest risk predictors. In the fewer studies that used SCD as an end point, the strongest risk factors were HRV measures of short‐term oscillations and sympathovagal interaction. We concluded from these findings that different HRV measurements predict different modes of death in CHF. Additionally, further studies using short‐term analysis of HRV and non‐linear analyses are warranted. Furthermore, studies with multiple end points, which clearly delineate pump failure from SCD, may be useful to identify more clearly the role HRV measures can play in the prediction of SCD.

Associations between habitual school-day breakfast consumption, body mass index, physical activity and cardiorespiratory fitness in English schoolchildren

Objectives:The aim of this study was to assess associations between habitual school-day breakfast consumption, body mass index (BMI), physical activity (PA) and cardiorespiratory fitness (CRF).Methods:BMI, PA and CRF were measured in 4326 schoolchildren aged 10–16 years. Participants were classified as obese or non-obese, as having low or high PA and CRF. Habitual school-day breakfast consumption was assessed by a questionnaire and classified as never, sometimes or always.Results:Participants who sometimes ate breakfast were more likely to be obese than those who always did (P<0.05). Boys who never ate breakfast were more likely to have low PA odds ratio (OR) 2.17, 95% CI 1.48–3.18) and low CRF (OR 2.02, 95% CI 1.40–2.93) than those who always did. Compared with those who always did so, girls were more likely to have low PA if they sometimes (OR 1.39, 95% CI 1.13–1.70) or never (1.48 95% CI 1.06–2.05) ate breakfast, but the likelihood of low CRF was not different between groups.Conclusions:Habitual breakfast consumption is associated with healthy BMI and higher PA levels in schoolchildren. In boys, regularly eating breakfast is also associated with higher levels of CRF. The higher PA observed in habitual breakfast eaters may explain the higher CRF values observed. These positive health behaviours and outcomes support the encouragement of regular breakfast eating in this age group.

Physical activity levels of children living in different built environments

OBJECTIVE To review the available literature assessing differences in physical activity levels of children living in different built environments classified according to land use within developed countries. METHODS A systematic review of published literature up to March 2009. Online searches of five databases yielded 18 studies which met inclusion criteria. Studies provided data on n=129446, 5-18 years old (n=117544 from the United States). RESULTS From 13 assessments of differences in physical activity between rural and urban children one showed that rural children were significantly more active than urban children. In studies where the built environment was sub-divided further, suburban and small town children showed the highest levels of physical activity, followed by rural, then urban children. Differences in types of physical activity undertaken were evident, showing that rural children spent more time outdoors, involved in unstructured play compared with urban children. These findings were mainly restricted to children <13 years old. CONCLUSIONS The literature does not show major differences in the physical activity levels between children from rural or urban areas. Where studied, the suburban built environment appears most conducive to promoting physical activity. Further research should use at least a trilateral division of the built environment and should also account for socioeconomic status, racial factors and seasonal effects.

The use of heart rate variability measures to assess autonomic control during exercise

Heart rate variability (HRV) is a non‐invasive indicator of cardiac autonomic modulation at rest. During rhythmic exercise, global HRV decreases as a function of exercise intensity. Measures reflecting sympathovagal interactions at rest do not behave as expected during exercise. This makes interpretation of HRV measures difficult, especially at higher exercise intensities. This problem is further confounded by the occurrence of non‐neural oscillations in the high‐frequency band due to increased respiratory effort.

Ten-year secular changes in muscular fitness in English children

1.Faculty of Life Sciences, London Metropolitan University, London, UK2.Department of Biological Sciences, University of Essex, Colchester, UK3.Centre for Research in Human Development, Concordia University, Montreal, QC, CanadaCorrespondenceDD Cohen, Faculty of Life Sciences, London Metro-politan University, London, UK.Tel: +44 207 133 4687 |Fax: +44 0207 133 4149 |Email: d.cohen@londonmet.ac.ukReceived8 October 2010; revised 25 February 2011;accepted 8 April 2011.DOI:10.1111/j.1651-2227.2011.02318.x

The Great Outdoors: how a green exercise environment can benefit all

The studies of human and environment interactions usually consider the extremes of environment on individuals or how humans affect the environment. It is well known that physical activity improves both physiological and psychological well-being, but further evidence is required to ascertain how different environments influence and shape health. This review considers the declining levels of physical activity, particularly in the Western world, and how the environment may help motivate and facilitate physical activity. It also addresses the additional physiological and mental health benefits that appear to occur when exercise is performed in an outdoor environment. However, people’s connectedness to nature appears to be changing and this has important implications as to how humans are now interacting with nature. Barriers exist, and it is important that these are considered when discussing how to make exercise in the outdoors accessible and beneficial for all. The synergistic combination of exercise and exposure to nature and thus the ‘great outdoors’ could be used as a powerful tool to help fight the growing incidence of both physical inactivity and non-communicable disease.

Randomized controlled trial of supervised exercise to evaluate changes in cardiac function in patients with peripheral atherosclerotic disease

Introduction:  Peripheral atherosclerotic disease (PAD) is a condition characterized by low functional capacity which is associated with impaired free living, ambulation and low exercise tolerance. The purpose of this randomized controlled study was to evaluate whether changes in maximal walking time are associated with adaptations in cardiovascular function following supervised exercise.