Association between heart rate variability and haemodynamic response to exercise in chronic heart failure.

OBJECTIVES: Heart rate variability (HRV) and haemodynamic response to exercise (i.e. peak cardiac power output) are strong predictors of mortality in heart failure. The present study assessed the relationship between measures of HRV and peak cardiac power output. DESIGN: In a prospective observational study of 33 patients (age 54 ± 16 years) with chronic heart failure with reduced left ventricular ejection fraction (29 ± 11%), measures of the HRV (i.e. R-R interval and standard deviation of normal R-R intervals, SDNN) were recorded in a supine position. All patients underwent maximal graded cardiopulmonary exercise testing with non-invasive (inert gas rebreathing) cardiac output assessment. Cardiac power output, expressed in watts, was calculated as the product of cardiac output and mean arterial blood pressure. RESULTS: The mean RR and SDNN were 837 ± 166 and 96 ± 29 ms, peak exercise cardiac power output 2.28 ± 0.85 watts, cardiac output 10.34 ± 3.14 L/min, mean arterial blood pressure 98 ± 14 mmHg, stroke volume 91.43 ± 40.77 mL/beat, and oxygen consumption 19.0 ± 5.6 mL/kg/min. There was a significant but only moderate relationship between the RR interval and peak exercise cardiac power output (r = 0.43, p = .013), cardiac output (r = 0.35, p = .047), and mean arterial blood pressure (r = 0.45, p = .009). The SDNN correlated with peak cardiac power output (r = 0.42, p = .016), mean arterial blood arterial (r = 0.41, p = .019), and stroke volume (r = 0.35, p = .043). CONCLUSIONS: Moderate strength of the relationship between measures of HRV and cardiac response to exercise suggests that cardiac autonomic function is not good indicator of overall function and pumping capability of the heart in chronic heart failure.

Reproducibility of cardiac power output and other cardiopulmonary exercise indices in patients with chronic heart failure.

Cardiac power output is a direct measure of overall cardiac function that integrates both flow- and pressure-generating capacities of the heart. The present study assessed the reproducibility of cardiac power output and other more commonly reported cardiopulmonary exercise variables in patients with chronic heart failure. Metabolic, ventilatory and non-invasive (inert gas re-breathing) central haemodynamic measurements were undertaken at rest and near-maximal exercise of the modified Bruce protocol in 19 patients with stable chronic heart failure. The same procedure was repeated 7 days later to assess reproducibility. Cardiac power output was calculated as the product of cardiac output and mean arterial pressure. Resting central haemodynamic variables demonstrate low CV (coefficient of variation) (ranging from 3.4% for cardiac output and 5.6% for heart rate). The CV for resting metabolic and ventilatory measurements ranged from 8.2% for respiratory exchange ratio and 14.2% for absolute values of oxygen consumption. The CV of anaerobic threshold, peak oxygen consumption, carbon dioxide production and respiratory exchange ratio ranged from 3.8% (for anaerobic threshold) to 6.4% (for relative peak oxygen consumption), with minute ventilation having a CV of 11.1%. Near-maximal exercise cardiac power output and cardiac output had CVs of 4.1 and 2.2%, respectively. Cardiac power output demonstrates good reproducibility suggesting that there is no need for performing more than one cardiopulmonary exercise test. As a direct measure of cardiac function (dysfunction) and an excellent prognostic marker, it is strongly advised in the assessment of patients with chronic heart failure undergoing cardiopulmonary exercise testing.

Bradykinin type 2 receptor -9/-9 genotype is associated with triceps brachii muscle hypertrophy following strength training in young healthy men.

BACKGROUND: Bradykinin type 2 receptor (B2BRK) genotype was reported to be associated with changes in the left-ventricular mass as a response to aerobic training, as well as in the regulation of the skeletal muscle performance in both athletes and non-athletes. However, there are no reports on the effect of B2BRK 9-bp polymorphism on the response of the skeletal muscle to strength training, and our aim was to determine the relationship between the B2BRK SNP and triceps brachii functional and morphological adaptation to programmed physical activity in young adults. METHODS: In this 6-week pretest-posttest exercise intervention study, twenty nine healthy young men (21.5 ± 2.7 y, BMI 24.2 ± 3.5 kg/m(2)) were put on a 6-week exercise protocol using an isoacceleration dynamometer (5 times a week, 5 daily sets with 10 maximal elbow extensions, 1 minute rest between sets). Triceps brachii muscle volumes were assessed by using magnetic resonance imaging before and after the strength training. Bradykinin type 2 receptor 9 base pair polymorphism was determined for all participants. RESULTS: Following the elbow extensors training, an average increase in the volume of both triceps brachii was 5.4 ± 3.4% (from 929.5 ± 146.8 cm(3) pre-training to 977.6 ± 140.9 cm(3) after training, p<0.001). Triceps brachii volume increase was significantly larger in individuals homozygous for -9 allele compared to individuals with one or two +9 alleles (-9/-9, 8.5 ± 3.8%; vs. -9/+9 and +9/+9 combined, 4.7 ± 4.5%, p < 0.05). Mean increases in endurance strength in response to training were 48.4 ± 20.2%, but the increases were not dependent on B2BRK genotype (-9/-9, 50.2 ± 19.2%; vs. -9/+9 and +9/+9 combined, 46.8 ± 20.7%, p > 0.05). CONCLUSIONS: We found that muscle morphological response to targeted training - hypertrophy - is related to polymorphisms of B2BRK. However, no significant influence of different B2BRK genotypes on functional muscle properties after strength training in young healthy non athletes was found. This finding could be relevant, not only in predicting individual muscle adaptation capacity to training or sarcopenia related to aging and inactivity, but also in determining new therapeutic strategies targeting genetic control of muscle function, especially for neuromuscular disorders that are characterized by progressive adverse changes in muscle quality, mass, strength and force production (e.g., muscular dystrophy, multiple sclerosis, Parkinson's disease).

Heart rate recovery after submaximal exercise in four different recovery protocols in male athletes and non-athletes.

The effects of different recovery protocols on heart rate recovery (HRR) trend through fitted heart rate (HR) decay curves were assessed. Twenty one trained male athletes and 19 sedentary male students performed a submaximal cycle exercise test on four occasions followed by 5 min: 1) inactive recovery in the upright seated position, 2) active (cycling) recovery in the upright seated position, 3) supine position, and 4) supine position with elevated legs. The HRR was assessed as the difference between the peak exercise HR and the HR recorded following 60 seconds of recovery (HRR60). Additionally the time constant decay was obtained by fitting the 5 minute post-exercise HRR into a first-order exponential curve. Within- subject differences of HRR60 for all recovery protocols in both groups were significant (p < 0. 001) except for the two supine positions (p > 0.05). Values of HRR60 were larger in the group of athletes for all conditions (p < 0.001). The time constant of HR decay showed within-subject differences for all recovery conditions in both groups (p < 0.01) except for the two supine positions (p > 0.05). Between group difference was found for active recovery in the seated position and the supine position with elevated legs (p < 0.05). We conclude that the supine position with or without elevated legs accelerated HRR compared with the two seated positions. Active recovery in the seated upright position was associated with slower HRR compared with inactive recovery in the same position. The HRR in athletes was accelerated in the supine position with elevated legs and with active recovery in the seated position compared with non-athletes. Key pointsIn order to return to a pre-exercise value following exercise, heart rate (HR) is mediated by changes in the autonomic nervous system but the underlying mechanisms governing these changes are not well understood.Even though HRR is slower with active recovery, lactate elimination after high intensity exercise might be more important for athletes than the de-cline of heart rate.Lying supine during recovery after exercise may be an effective means of transiently restoring HR and vagal modulation and a safe position for prevention of syncope.

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.

Resting autonomic modulations and the heart rate response to exercise.

OBJECTIVES: Identify the underlying role of resting heart rate variability (HRV) in the hearts response to graded exercise testing (GXT). METHODS: Resting 5-min HRV and heart rate (HR) measurements were made in 33 volunteers (19 males, median age 34, range 25-63 years and 14 females median age 48, range 21-63 years). Measures of VO2 peak and HR obtained during a maximal GXT and heart rate recovery (HRR) post-GXT were assessed for associations with resting HRV. Differences and effect size (d) for measures of HRV were assessed between groups based on established risk cut-points for resting, exercise and recovery HR responses. RESULTS: Small associations were observed for the majority of resting HRV and GXT HR responses (best r value = -0.27, P > 0.05). Measures of HRV demonstrated moderate associations with HRR (best r value = 0.46, P < 0.05) and were able to predict a negative risk HRR. In contrast to other dependent variables, measures of HRV were consistently able to demonstrate significant and moderate to large (d = 0.9-2.0) differences between groups based on literature defined prognostic HR cut-points. INTERPRETATION: Small associations with HR responses to exercise prevent their accurate prediction from resting HRV. Data support the use of vagally mediated resting HRV in predicting better HRR. Lower resting autonomic modulations underlined high risk resting and exercise HR responses. Resting short-term HRV measurements should be considered when assessing cardiac autonomic health from the HR response before, during and/or after exercise.

Heart rate variability before and after cycle exercise in relation to different body positions.

The purpose of this study was to assess the effect of three different body positions on HRV measures following short-term submaximal exercise. Thirty young healthy males performed submaximal cycling for five minutes on three different occasions. Measures of HRV were obtained from 5-min R to R wave intervals before the exercise (baseline) and during the last five minutes of a 15 min recovery (post-exercise) in three different body positions (seated, supine, supine with elevated legs). Measures of the mean RR normal-to-normal intervals (RRNN), the standard deviation 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 were analyzed. Post-exercise RRNN, RMSSD were significantly higher in the two supine positions (p < 0. 01) compared with seated body position. Post-exercise ln LF was significantly lower in the supine position with elevated legs than in the seated body position (p < 0.05). No significant difference was found among the three different body positions for post-exercise ln HF (p > 0.05). Post-exercise time domain measures of HRV (RRNN, SDNN, RMSSD) were significantly lower compared with baseline values (p < 0.01) regardless body position. Post-exercise ln LF and ln HF in all three positions remained significantly reduced during recovery compared to baseline values (p < 0.01). The present study suggests that 15 minutes following short-term submaximal exercise most of the time and frequency domain HRV measures have not returned to pre-exercise values. Modifications in autonomic cardiac regulation induced by body posture present at rest remained after exercise, but the post-exercise differences among the three positions did not resemble the ones established at rest. Key pointsWhether different body positions may enhance post-exercise recovery of autonomic regulation remains unclear.The absence of restoration of HRV measures after 15 minutes of recovery favor the existence of modifying effects of exercise on mechanisms underlying heart regulation.On the basis of discrepancies in HRV measures in different body positions pre- and post-exercise we argue that the pace of recovery of cardiac autonomic regulation is dependent on body posture.

Motivational interviewing to change quality of life for people with chronic heart failure: a randomised controlled trial.

BACKGROUND: Patients with chronic heart failure have a reduced quality of life due in part to their limited range of physical activity and independence. OBJECTIVES: The paper examines whether a physical activity 'lifestyle' intervention, based on motivational interviewing, will improve quality of life at five months from baseline, compared with conventional treatment. METHODS: Sixty older patients with chronic heart failure were randomly assigned to either a 'standard care', 'motivational interviewing' or 'both' treatment groups for five months in 2002. The primary outcome measures were the Medical Outcomes Short Form-36 Health Survey, the disease-specific Minnesota Living with Heart Failure questionnaire and the Motivation Readiness for Physical Activity scale. RESULTS: There were non-significant differences between the groups at baseline for age, coronary risk factors, severity of chronic heart failure, ejection fraction, specific laboratory tests, length of hospitalisation, medication and social support. Following treatment there was a significant increase (p<0.05) for three of the dimensions of the health survey in the 'motivational interviewing' group. All groups improved their scores (p<0.05) on the heart failure questionnaire. Over the five month period there was a general trend towards improvements in self-efficacy and motivation scores. CONCLUSIONS: This study has demonstrated that a 'motivational interviewing' intervention, incorporating behaviour change principles to promote physical activity, is effective in increasing selected aspects of a general quality of life questionnaire and a disease-specific quality of life questionnaire. Thus a 'motivational interviewing' approach is a viable option compared with traditional exercise programming. It is important to test these motivational interviewing interventions more widely, especially to match individuals to treatments.

Lack of agreement between gas exchange variables measured by two metabolic systems.

The purpose of this study was to assess the agreement and consistency between gas exchange variables measured by two online metabolic systems during an incremental exercise test. After obtaining local ethics approval and informed consent, 15 healthy subjects performed an incremental exercise test to volitional fatigue using the Bruce protocol. The Innocor (Innovision, Denmark) and CardiO2 (Medical Graphics, USA) systems were placed in series, with the Innocor mouthpiece attached to the pneumotach of the CardiO2. Metabolic data were analysed during the last 30 seconds of each stage and at peak exercise. There were non- significant differences (p > 0.05) between the two systems in estimation of oxygen consumption (VO2) and in minute ventilation (VE). Mean Cronbach's alpha for VO2 and VE were 0.88 and 0.92. The Bland-Altman analysis revealed that limits of agreement were -0.52 to 0.55 l.min(-1) for VO2, and -8.74 to 10.66 l.min(-1) for VE. Carbon dioxide production (VCO2) and consequently respiratory exchange ratio (RER) measured by the Innocor were significantly lower (p < 0.05) through all stages. The CardiO2 measured fraction of expired carbon dioxide (FeCO2) significantly higher (p < 0.05). The limits of agreement for VO2 and VE are wide and unacceptable in cardio-pulmonary exercise testing. The Innocor reported VCO2 systematically lower. Therefore the Innocor and CardiO2 metabolic systems cannot be used interchangeably without affecting the diagnosis of an individual patient. Results from the present study support previous suggestion that considerable care is needed when comparing metabolic data obtained from different automated metabolic systems. Key pointsThere is general concern regarding the limited knowledge available about the accuracy of a number of commercially available systems.Demonstrated limits of agreement between key gas exchange variables (oxygen consumption and minute ventilation) as measured by the two metabolic systems were wide and unacceptable in cardio-pulmonary exercise testing.Considerable care is needed when comparing metabolic data obtained from different automated metabolic systems.

The impact of short term supervised and home-based walking programmes on heart rate variability in patients with peripheral arterial disease.

The aims of the study were to determine whether heart rate variability (HRV) measured at rest and during exercise could be altered by an exercise training programme designed to increase walking performance in patients with peripheral arterial disease. Forty-four volunteers were randomised into 12 weeks of either: supervised walking training twice weekly for 30 min at 75% VO2peak (SU), home-based walking training sessions: twice weekly, 30 min per week (HB) or no exercise (CT). HRV measures were calculated from a 5-min resting ECG. Each patient then underwent maximal, graded exercise treadmill testing. All measures were repeated after 12 weeks. The SU group showed significantly (p < 0.001) increased maximal walking time (MWT) but no change in VO2peak. There were no statistically significant changes in any of the measures of HRV in any group. Effect sizes for change in HRV measures were all very small and in some cases negative. Improved walking performance was not accompanied by central cardiorespiratory or neuroregulatory adaptations in the present study. The lack of any change in HRV was possibly due to either the low intensity or discontinuous nature of exercise undertaken. Key pointsIt is known that exercise can positively influence heart rate variability in some cardiac patients.It is known that exercise can increase walking performance in peripheral vascular disease patients.Exercise training improved walking performance in peripheral vascular disease patients but HRV was unaltered.This may be due to low overall physiological demands on the cardiovascular system or the intermittent nature of the exercise.

Acute changes in arterial stiffness following exercise in people with metabolic syndrome.

BACKGROUND: This study aims to examine the changes in arterial stiffness immediately following sub-maximal exercise in people with metabolic syndrome. METHODS: Ninety-four adult participants (19-80 years) with metabolic syndrome gave written consent and were measured for arterial stiffness using a SphygmoCor (SCOR-PVx, Version 8.0, Atcor Medical Private Ltd, USA) immediately before and within 5-10min after an incremental shuttle walk test. The arterial stiffness measures used were pulse wave velocity (PWV), aortic pulse pressure (PP), augmentation pressure, augmentation index (AI), subendocardial viability ratio (SEVR) and ejection duration (ED). RESULTS: There was a significant increase (p<0.05) in most of the arterial stiffness variables following exercise. Exercise capacity had a strong inverse correlation with arterial stiffness and age (p<0.01). CONCLUSION: Age influences arterial stiffness. Exercise capacity is inversely related to arterial stiffness and age in people with metabolic syndrome. Exercise induced changes in arterial stiffness measured using pulse wave analysis is an important tool that provides further evidence in studying cardiovascular risk in metabolic syndrome.

Left Ventricular Assist Device as a Bridge to Recovery for Patients With Advanced Heart Failure.

BACKGROUND: Left ventricular assist devices (LVADs) have been used as an effective therapeutic option in patients with advanced heart failure, either as a bridge to transplantation, as destination therapy, or in some patients, as a bridge to recovery. OBJECTIVES: This study evaluated whether patients undergoing an LVAD bridge-to-recovery protocol can achieve cardiac and physical functional capacities equivalent to those of healthy controls. METHODS: Fifty-eight male patients-18 implanted with a continuous-flow LVAD, 16 patients with LVAD explanted (recovered patients), and 24 heart transplant candidates (HTx)-and 97 healthy controls performed a maximal graded cardiopulmonary exercise test with continuous measurements of respiratory gas exchange and noninvasive (rebreathing) hemodynamic data. Cardiac function was represented by peak exercise cardiac power output (mean arterial blood pressure × cardiac output) and functional capacity by peak exercise O2 consumption. RESULTS: All patients demonstrated a significant exertional effort as demonstrated with the mean peak exercise respiratory exchange ratio >1.10. Peak exercise cardiac power output was significantly higher in healthy controls and explanted LVAD patients compared with other patients (healthy 5.35 ± 0.95 W; explanted 3.45 ± 0.72 W; LVAD implanted 2.37 ± 0.68 W; and HTx 1.31 ± 0.31 W; p < 0.05), as was peak O2 consumption (healthy 36.4 ± 10.3 ml/kg/min; explanted 29.8 ± 5.9 ml/kg/min; implanted 20.5 ± 4.3 ml/kg/min; and HTx 12.0 ± 2.2 ml/kg/min; p < 0.05). In the LVAD explanted group, 38% of the patients achieved peak cardiac power output and 69% achieved peak O2 consumption within the ranges of healthy controls. CONCLUSIONS: The authors have shown that a substantial number of patients who recovered sufficiently to allow explantation of their LVAD can even achieve cardiac and physical functional capacities nearly equivalent to those of healthy controls.

Physiological range of peak cardiac power output in healthy adults.

AIMS: The purpose of this study was to indicate the normal range for peak cardiac power output (CPO(peak)) in healthy adults and to explore age- and sex-related variations of this parameter. METHODS AND RESULTS: Using the non-invasive exponential CO(2) rebreathing technique [J.G. Defares, J Appl Physiol13 (1958) 159], cardiac output was measured at an exercise intensity determined to coincide with > or =95% of peak oxygen consumption in 102 healthy adults (mean +/- SD, age 43 +/- 13 years, body mass 74 +/- 13 kg). Peak cardiac power was then computed from measurements of peak cardiac output (Q(Tpeak)) and peak mean arterial pressure (MAP(peak)) using the equation described by Cooke et al. [Heart79 (1998) 289]. Peak oxygen consumption in the study population was 2.42 (+/-0.74) l min(-1) and subjects achieved 101 +/- 7% of this value during the measurement of . was 17.3 (+/-4) l min(-1), and CPO(peak) was computed as 4.5 (+/-1.2) W. CPO(peak) ranged from 3.11 to 7.94 W in men and 2.53 to 5.57 W in women. Additionally, ageing appears to be associated with a significant loss of peak cardiac power in men that is not apparent in women. CONCLUSION: Although the sample size remains moderate, the CPO values attained were normally distributed and these values provide a useful indication of the normal range for CPO(peak) in healthy adults.

Professional roles and communications in clinical placements: a qualitative study of nursing students' perceptions and some models for practice.

BACKGROUND: Research evidence suggests that clinical placements are important to both the perceptions and outcomes of nurse education. Nevertheless, despite this knowledge, research also indicates that many students receive negative experiences whilst attending these 'remote' settings, sometimes resulting in missed opportunities for learning and negative impressions of potential places of employment. OBJECTIVE: In this context, this study investigates the experiences and perceptions of students relating to their clinical placements and, in particular, their views on professional structuring. Specifically it addresses the roles of, and communications between, the key academics, clinical professionals and institutions responsible for their organization. METHODS: Focus group discussions with students (n=7) and an interview survey of ex-students (n=30) each from two British universities in Southeast England. FINDINGS: The research highlights the diverse experiences that student receive on clinical placements, as well as their own suggestions for improvements. Student informed models of worst, minimum, current and best practice are then presented, as well as a cross-setting evaluation feedback model. These highlight responsibilities and communications across health professionals and educational sites. The models include an emphasis on the roles of ward managers, mentors, link tutors and more generally on shared but clearly delineated institutional responsibility for quality assurance mechanisms. They offer the opportunity to improve educational practice in clinically-based education and concurrently to improve student experiences and outcomes. CONCLUSIONS: Clinical placements are designed to provide practical learning through a 'slice of practice life'. However, it is necessary to maximize this learning experience. Placements certainly need not be the worst slice.

Working in London hospitals: perceptions of place in nursing students' employment considerations.

During the past decade, a distinct body of research has started to investigate the dynamics between nursing and place. However, despite attention being paid to a wide-range of nursing subjects, few studies have engaged with the important topic of labour force recruitment. In this context, this study uses a combined questionnaire (n=650), interview (n=30) and focus group (n=7) survey of London-based students, and investigates the complex mix of experiences and perceptions that result in hospitals having varying degrees of popularity as potential workplaces. The findings suggest experiences and perceptions of institutions-often gained on clinical placements-to be important, particularly relating to feeling valued, the quality of patient care, clinical and educational opportunities and team cohesion. These are often combined with experiences and perceptions of locality, relating to factors such as cost of living, travel considerations and sense of personnel safety. The study demonstrates that place is relevant to employment decision-making on multiple scales from wards to regions. Furthermore, that perceptions of potential workplaces result from engagements with complex mixes of cultural, economic and physical features, many of which are the consequences of management. It is argued that in order to effectively unpack workplaces, geographical research of nursing labour may benefit from researching simultaneously both 'inside' institutions, focusing on their dominant cultures of production and sub-cultures, and 'outside', focusing on their local urban or rural contexts.

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.

The reliability of short-term measurements of heart rate variability.

Short-term assessment of heart rate variability (HRV) is a non-invasive technique to examine ANS function. Within the literature, HRV is commonly referred to as a reliable measurement technique. The aim of this review was to assess the accuracy of this description based upon a comprehensive review of the available data concerning reliability of short-term HRV measures. Reviewing only studies using appropriate statistical analyses, it was determined that reliability coefficients for HRV measures were highly varied. Coefficients of variation ranged from <1% to >100%. Similar variation was found in studies using the intraclass correlation coefficient values, and limits of agreement. Reliability coefficients reported displayed some distinct patterns. Firstly, where measurements were made during interventions such as tilt or pharmacological stimulation, reliability was poorer than when HRV was measured at rest. Secondly, clinical populations displayed poorer reliability than healthy subjects. There was little effect of test-retest duration on reliability and although no single HRV measurement appeared less reliable than another, there was evidence that optimal data collection conditions for specific frequency domain measures exist. Describing HRV as a reliable measurement technique appears to be a gross oversimplification, as results of reliability studies are heterogeneous, and dependent on a number of factors. Further studies are required, particularly in clinical populations to assess HRV reliability. Authors should refer to coefficients from similar populations measured under similar conditions when making future sample size calculations.

Urinary iodine excretion and thyroid function status in school age children of hilly and plain regions of Eastern Nepal.

BACKGROUND: Iodine deficiency is a major public health problem in many developing countries including Nepal. The present study was designed to investigate the urinary iodine excretion (UIE), thyroid function status and household salt iodine content (SIC) in school-aged children (SAC) and to establish the relationships between these factors. METHODS: A community-based cross sectional study was conducted in selected schools of two districts, Tehrathum and Morang, lying in the hill and plain region of eastern Nepal respectively. A total of 640 SAC, (Tehrathum n = 274 and Morang n = 366) aged 6-11 years, were assessed for UIE and household SIC. Among the 640 children, 155 consented to blood samples (Tehrathum n = 78 and Morang n = 77) to test for serum thyroglobulin (Tg), thyroid stimulating hormone (TSH), free triiodothyronine (fT3) and free thyroxine (fT4). UIE was measured by ammonium persulfate digestion method. SIC was measured by iodometric titration method and Tg, TSH, fT4 and fT3 were measured by immunoassay based kit method. RESULTS: In Tehrathum and Morang, 9.5 and 7.7% of SAC had UIE values of UIE <100 µg/L while 59.5 and 41% had iodine nutrition values of >299 µg/L, with median UIE of 345.65 and 270.36 µg/L respectively. The overall medians were as follows, Tg 14.29 µg/L, fT3 3.94 pmol/L, fT4 16.25 pmol/L and TSH 3.61 mIU/L. There was a negative correlation between UIE and Tg (r = -0.236, p = 0.003) and a positive correlation between UIE and SIC (r = 0.349, p < 0.0001). We found 19.5%, n = 15 and 16.7%, n = 13 subclinical hypothyroid cases in Morang and Tehrathum respectively. Iodometric titration showed only 6.4% (n = 41) of the samples had household SIC <15 ppm. Multivariate analysis revealed that use of packaged salt by SAC of Tehrathum district correlated with higher UIE values. CONCLUSIONS: Our focused data suggests that collaborative universal salt iodization (USI) programs are improving the health of children in the Tehrathum and Morang districts of Nepal. We also found that excessive iodine in a large portion of the study groups is a substantial concern and iodine intervention programs need to deal with both deficient and excessive iodine scenarios that can both be present simultaneously in study populations.

Changes in serum biochemical responses during cardiac rehabilitation.

PURPOSE: The objective of the study was to establish the difference in the exercise response profile of the enzymes lactate dehydrogenase (LDH), lactate dehydrogenase isoenzyme 1 (LDH-1), creatine kinase (CK), and creatine kinase polypeptide subunit MB (CK-MB) after a 12-wk cardiac rehabilitation exercise program. METHODS: Nineteen male nonblockade recent postmyocardial infarction patients (PMIP), aged 60.7 +/- 6.5 yr, performed a graded exercise test on a motorized treadmill until volitional cessation or reaching any of the American College of Sports Medicine criteria. After this, a 12-wk exercise-based cardiac rehabilitation program was adopted at a frequency of 3x wk-1. Each subject was then retested using the same protocol and intensity. Blood samples were collected by venipuncture from the antecubital vein into Vacutainer tubes preexercise, immediately, postexercise, and 24 h later. The blood samples were then centrifuged to obtain serum before being transported to the laboratory for enzymatic analysis by conventional methods. RESULTS: a) a 12-wk cardiac rehabilitation exercise program had no influence on the serum activities of enzymes at rest; b) the same exercise reduced the enzyme activity level after training; and c) LDH and CK values returned to normal faster after the program. CONCLUSIONS: These findings provide further evidence for the benefits of exercise-based cardiac rehabilitation and demonstrate that an exercise test provokes a temporary serum enzyme response, which does not reflect myocardial damage.

Household salt iodine content estimation with the use of rapid test kits and iodometric titration methods.

BACKGROUND: Universal salt iodization remains the best strategy for controlling iodine deficiency disorders in Nepal. AIMS: This study was designed to study the salt types and the household salt iodine content of school aged children in the hilly and the plain districts of eastern Nepal. MATERIAL AND METHODS: This cross-sectional study was carried out on school children of seven randomly chosen schools from four districts, namely, Sunsari, Dhankuta, Sankhuwasabha and Tehrathum of eastern Nepal. The school children were requested to bring two teaspoonfuls (approx. 12-15 g) of the salt which was consumed in their households, in a tightly sealed plastic pouch. The salt types were categorized, and the salt iodine content was estimated by using rapid test kits and iodometric titrations. The association of the salt iodine content of the different districts were tested by using the Chi-square test. The sensitivity, specificity, positive predictive values, and negative predictive values of the rapid test kits were compared with the iodometric titrations. RESULTS: Our study showed that mean±SD values of the salt iodine content in the four districts, namely, Sunsari, Dhankuta, Sankhuwasabha and Tehrathum were 34.2±17.9, 33.2±14.5, 27.4±15.1 and 48.4±15.6 parts per million (ppm). There were 270 (38.2%) households which consumed crystal salt and 437(61.8%) of the households consumed packet salts. CONCLUSIONS: Our study recommends a regular monitoring of the salt iodization programs in these regions. More families should be made aware of the need to ensure that each individual consumes iodized salt.