REGRESSION TO THE MEAN: METHODOLOGICAL ISSUES FOR EVALUATION OF HEART RATE VARIABILITY VARIABLES FOR STRESS ASSESSMENT

There is now a substantial body of evidence linking the baseline level of heart rate variability (HRV) with the magnitude of stress-induced reduction in respiratory sinus arrhythmia. However, it remains to be proved to what extent these interindividual differences in stress responses may be attributed to the statistical phenomenon of regression to the mean (RTM). We sought to test the hypothesis that the statistical artifact RTM explains pan of the baseline effect. Heart rate recording was carried out in 1156 volunteers. To obtain an estimate of the stress response. 148 persons were randomly selected. Participants were monitored on a rest day and just before an academic examination for state anxiety and HRV. Participants were divided into quartiles according to baseline HRV levels and were compared for response to academic stress. We observed a significant reduction in HRV in subjects with a high baseline HRV (> 75th percentile), while a significant increase was found in the group with low baseline HRV. Regression analysis demonstrated that the value of baseline HRV correlated with the magnitude of stress reaction consistent with the RTM model. Baseline-adjusted ANCOVA does not reveal significant intergroup differences in the changes hi heart rate (HR) and HRV from rest to exam. RTM-adjusted estimates confirmed an exam effect for HR and HRV. The results of our study strongly support RTM as the source of variability of stress-related changes in HRV.

Interindividual variability in HRV reactivity: autonomic flexibility or regression to the mean?

ObjectiveThere is now a substantial body of evidence linking the baseline level of heart rate variability (HRV) with the magnitude of stress-induced reduction in respiratory sinus arrhythmia. However, it remains to be proved to what extent these interindividual differences in stress responses may be attributed to the statistical phenomenon of regression to the mean (RTM). We sought to test the hypothesis that the statistical artifact RTM explains part of the baseline effect.ApproachHeart rate recording was carried out in 1,156 volunteers. To obtain an estimate of the stress response, 148 persons were randomly selected. Participants were monitored on a rest day and just before an academic examination for state anxiety and HRV. Participants were divided into quartiles according to baseline HRV levels and were compared for response to academic stress.Main resultsWe observed a significant reduction in HRV in subjects with a high baseline HRV (> 75th percentile), while a significant increase was found in the group with low baseline HRV. Regression analysis demonstrated that the value of baseline HRV correlated with the magnitude of stress reaction consistent with the RTM model. Baseline-adjusted ANCOVA does not reveal significant intergroup differences in the changes in heart rate (HR) and HRV from rest to exam. RTM-adjusted estimates confirmed an exam effect for HR and HRV.SignificanceThe results of our study strongly support RTM as the source of variability of stress-related changes in HRV.

Activity pattern and energy expenditure due to physical activity before and during pregnancy in healthy Swedish women

Human pregnancy is associated with increased requirements for dietary energy and this increase may be partly offset by reductions in physical activity during gestation. Studies in well-nourished women have shown that the physical activity level (PAL), obtained as the total energy expenditure (TEE) divided by the BMR, decreases in late pregnancy. However, it is not known if this decrease is really caused by reductions in physical activity or if it is the result of decreases in energy expenditure/BMR (the so-called metabolic equivalent, MET) for many activities in late pregnancy. In the present study activity pattern, TEE and BMR were assessed in twenty-three healthy Swedish women before pregnancy as well as in gestational weeks 14 and 32. Activity pattern was assessed using a questionnaire and heart rate recording. TEE was assessed using the doubly labelled water method and BMR was measured by means of indirect calorimetry. When compared to the pre-pregnant value, there was little change in the PAL in gestational week 14 but it was significantly reduced in gestational week 32. Results obtained by means of the questionnaire and by heart rate recording showed that the activity pattern was largely unaffected by pregnancy. The findings support the following conclusion: in a population of well-nourished women where the activity pattern is maintained during pregnancy, the increase in BMR represents approximately the main part of the pregnancy-induced increase in TEE, at least until gestational week 32.

Effekte der Entwicklungsqualität auf die Herzfrequenz, die Aktivitäts- und Ruhezeiten und deren Rhythmizität sowie auf die Wachstumsleistung der Milchrindkälber während der Aufzucht in Gruppenhaltung mit Tränkeautomatenfütterung

Title of the paper: Effects of development quality on heart rate, activity and resting times and their diurnal rhythmicity and on growth of group housed feeder-fed dairy calves To characterize the rhythmicity of physiological variables in dairy calves of different developmental quality and fitness (groups by hemoglobin content of blood) at early gowth (71 German Holstein Friesian, 6 German Red Pied, 36 male and 41 female) long term heart rate recordings were taken at 5, 15, 40 and 60 days of age using Polar Sport Tester, from which the number and duration of activity (ZDA) and resting times (ZDR) and the total daily activity (GZA) and resting time (GZR) could be established. For these periods characteristic heart rate values were calculated (HFA and HFR) and they were analysed for daytime periods of three hours duration at different life ages. Mean HFA and HFR were significantly different between calves of group HbG1, HbG2 and HbG3 at 5 days and 15 days of age and ZDA was significantly different at 5 and 60 days of age. HF and the increase of HF (HFA-HFR) were significantly smaller at 15 days then at 5 days of age. Mean ZDA and GZA and ZDR were greater and the GZR was smaller at 40 and 60 days then at 5 and 15 days of age. Changes of the variables by 40 and 60 days of life took place with different degrees in calves of the three groups. Deviation of HFA and HFR from the mean of the individual daytime heart rate recording showed a rhythmicity that has been affected by feed access of the calves at the feed supply station. Means of ZDA and ZDR were significantly different between daytime periods of three hours duration at the age points. Results show effects of development quality on physiological variables of calves and on the rhythmicity of the variables and what changes occur with advanced development and adaptation of the animals.

Heart rate recording method validated by whole body indirect calorimetry in 10-yr-old children

The aim of the study was to validate the heart rate (HR) recording method against whole body indirect calorimetry in prepubertal children. Nineteen 10.5-yr-old healthy children (10 boys, 9 girls) participated in this study. HR and energy expenditure (EE) were recorded through laboratory tests. Individual relationships between HR and EE were computed (equation established in laboratory). Several models were tested and validated from 24-h measurements of EE and HR by whole body indirect calorimetry. The best fit was obtained with individual polynomial relationships. Mean differences between predicted (equation established in laboratory) and measured total daily EE averaged 7.6 +/- 20.1%. The causes of the differences and the means of improving the accuracy of the prediction equation are discussed.