Annika Rieger

Heart Rate Variability and Blood Pressure during Dynamic and Static Exercise at Similar Heart Rate Levels

Aim was to elucidate autonomic responses to dynamic and static (isometric) exercise of the lower limbs eliciting the same moderate heart rate (HR) response. Method: 23 males performed two kinds of voluntary exercise in a supine position at similar heart rates: static exercise (SE) of the lower limbs (static leg press) and dynamic exercise (DE) of the lower limbs (cycling). Subjective effort, systolic (SBP) and diastolic blood pressure (DBP), mean arterial pressure (MAP), rate pressure product (RPP) and the time between consecutive heart beats (RR-intervals) were measured. Time-domain (SDNN, RMSSD), frequency-domain (power in the low and high frequency band (LFP, HFP)) and geometric measures (SD1, SD2) as well as non-linear measures of regularity (approximate entropy (ApEn), sample entropy (SampEn) and correlation dimension D2) were calculated. Results: Although HR was similar during both exercise conditions (88±10 bpm), subjective effort, SBP, DBP, MAP and RPP were significantly enhanced during SE. HRV indicators representing overall variability (SDNN, SD 2) and vagal modulated variability (RMSSD, HFP, SD 1) were increased. LFP, thought to be modulated by both autonomic branches, tended to be higher during SE. ApEn and SampEn were decreased whereas D2 was enhanced during SE. It can be concluded that autonomic control processes during SE and DE were qualitatively different despite similar heart rate levels. The differences were reflected by blood pressure and HRV indices. HRV-measures indicated a stronger vagal cardiac activity during SE, while blood pressure response indicated a stronger sympathetic efferent activity to the vessels. The elevated vagal cardiac activity during SE might be a response mechanism, compensating a possible co-activation of sympathetic cardiac efferents, as HR and LF/HF was similar and LFP tended to be higher. However, this conclusion must be drawn cautiously as there is no HRV-marker reflecting “pure” sympathetic cardiac activity.

Sample Entropy and Traditional Measures of Heart Rate Dynamics Reveal Different Modes of Cardiovascular Control During Low Intensity Exercise

Abstract: Nonlinear parameters of heart rate vari ability (HRV) have proven their prognostic value in clinical settings, but their physiological background is not very well established. We assessed the effects of low intensity isometric (ISO) and dynamic (DYN) exercise of the lower limbs on heart rate matched intensity on traditional and entropy measures of HRV. Due to changes of afferent feedback under DYN and ISO a distinct autonomic response, mirrored by HRV measures, was hypothesized. Five-minute inter-beat interval measurements of 43 healthy males (26.0 ± 3.1 years) were performed during rest, DYN and ISO in a randomized order. Blood pressures and rate pressure product were higher during ISO vs . DYN ( p < 0.001). HRV indicators SDNN as well as low and high frequency power were significantly higher during ISO ( p < 0.001 for all measures). Compared to DYN, sample entropy (SampEn) was lower during ISO ( p < 0.001). Concluding, contraction mode itself is a significant modulator of the autonomic cardiovascular response to exercise. Compared to DYN, ISO evokes a stronger blood pressure response and an enhanced interplay between both autonomic branches. Non-linear HRV measures indicate a more regular behavior under ISO. Results support the view of the reciprocal antagonism being

Stress Monitoring Based on Stochastic Fuzzy Analysis of Heartbeat Intervals

Quantifying stress levels of an individual based on a mathematical analysis of real-time physiological data measurements is challenging. This study suggests a stochastic fuzzy analysis method to evaluate the short time series of R-R intervals (time intervals between consecutive heart beats) for a quantification of the stress level. The 5-min-long series of R-R intervals recorded under a given stress level are modeled by a stochastic fuzzy system. The stochastic model of heartbeat intervals is individual specific and corresponds to a particular stress level. Once the different heartbeat interval models are available for an individual, an analysis of the given R-R interval series generated under an unknown stress level is performed by a stochastic interpolation of the models. The stress estimation method has been implemented in a mobile telemedical application employing an e-health system for an efficient and cost-effective monitoring of patients while at home or at work. The experiments involve 50 individuals whose stress scores were assessed at different times of the day. The subjective rating scores showed a high correlation with the values predicted by the proposed analysis method.

Effects of breathing patterns and light exercise on linear and nonlinear heart rate variability

Despite their use in cardiac risk stratification, the physiological meaning of nonlinear heart rate variability (HRV) measures is not well understood. The aim of this study was to elucidate effects of breathing frequency, tidal volume, and light exercise on nonlinear HRV and to determine associations with traditional HRV indices. R-R intervals, blood pressure, minute ventilation, breathing frequency, and respiratory gas concentrations were measured in 24 healthy male volunteers during 7 conditions: voluntary breathing at rest, and metronome guided breathing (0.1, 0.2 and 0.4 Hz) during rest, and cycling, respectively. The effect of physical load was significant for heart rate (HR; p < 0.001) and traditional HRV indices SDNN, RMSSD, lnLFP, and lnHFP (p < 0.01 for all). It approached significance for sample entropy (SampEn) and correlation dimension (D2) (p < 0.1 for both), while HRV detrended fluctuation analysis (DFA) measures DFAα1 and DFAα2 were not affected by load condition. Breathing did not affect HR but affected all traditional HRV measures. D2 was not affected by breathing; DFAα1 was moderately affected by breathing; and DFAα2, approximate entropy (ApEn), and SampEn were strongly affected by breathing. DFAα1 was strongly increased, whereas DFAα2, ApEn, and SampEn were decreased by slow breathing. No interaction effect of load and breathing pattern was evident. Correlations to traditional HRV indices were modest (r from -0.14 to -0.67, p < 0.05 to <0.01). In conclusion, while light exercise does not significantly affect short-time HRV nonlinear indices, respiratory activity has to be considered as a potential contributor at rest and during light dynamic exercise.

Tri-axial high-resolution acceleration for oxygen uptake estimation: Validation of a multi-sensor device and a novel analysis method.

We validated a multi-sensor chest-strap against indirect calorimetry and further introduced the total-acceleration-variability (TAV) method for analyzing high-resolution accelerometer data. Linear regression models were developed to predict oxygen uptake from the TAV-processed multi-sensor data. Individual correlations between observed and TAV-predicted oxygen uptake (V̇O2) were strong (mean r = 0.94) and bias low (1.5 mL·min(-1)·kg(-1), p < 0.01; 95% confidence interval: 8.7 mL·min(-1)·kg(-1); -5.8 mL·min(-1)·kg(-1)); however, caution should be taken when a single-model value is used as a surrogate for V̇O2.

Stress and fitness monitoring embedded on a modern telematics platform.

Lack of regular physical activity and high stress levels are the leading causes of several illnesses. There is thus a real need for a personal low-cost and mobile monitoring solution over extended periods to prevent health risks. Based on the above fact, this article presents a system capable of estimating and monitoring both stress and fitness levels without a physical consultation of a medical specialist. The system consists of three main subcomponents: a mobile real-time acquisition of physiological as well as subjective data, an expert model for stress and fitness estimations based on physiological signals collected from wireless vital sensors, and a secure and scalable telematics platform on which the entire system is embedded. Features and tasks performed by the telematics platform will be presented. The experimental part of the work involved a representative number of subjects. Results for 110 subjects whose fitness levels were assessed at different periods of the year and 50 individuals whose stress scores were assessed at different times of the day showed a high correlation of the estimated values with the true ones. The application of such a low-cost monitoring system will improve the quality of service in preventive medicine.

24-Hour ambulatory monitoring of complex physiological parameters with a wireless health system: Feasibility, user compliance and application

In this paper, the feasibility of a wireless health system will be presented. The developed system is based on a sensor electronic module, a smartphone and a process management system that handles expert models for individual health estimation and delivers results from the primary data. The system was evaluated with experiments on N = 128 volunteers who were monitored in real-world settings. Ecological momentary assessment was triggered automatically by the smartphone several times per day. All participants confirmed the feasibility and ease of use of the developed system.

Psychophysiologic stress reduction in surgery

We read with interest the paper entitled Effects of Intraoperative Breaks on Mental and Somatic Operator Fatigue. This paper describes a randomized clinical trial authored by Engelmann and colleagues, who noted that ‘‘work breaks during complex laparoscopic surgery can reduce psychological stress and preserve performance without prolongation of the operation time compared with the traditional work scheme’’ [1]. Similar to the working group of Ure, our research team conducted a psychophysiologic study including 25 surgeons, who accomplished 51 surgeries. The volunteers were monitored over the period of 1 working day with a real-time working telemedical system [2]. The strain markers in our study included heart rate (HR), breathing rate (BR), skin temperature (ST), and three self-report questionnaires answered on a mobile phone before and after each surgery. After the procedures, intraoperative function (primary surgeon, first assistant surgeon), level of complication, and application of lead aprons were documented on the mobile phone. Our results clearly indicated that the function during surgery and the wearing of lead aprons had an impact on the intraoperative stress of the surgeon. Surgeons in the function of primary operator showed higher levels of HR, BR, and ST than they experienced in their role as first assistant surgeon. Furthermore, an additional increase in load was documented during operations with lead aprons. The answers given in the self-report questionnaires supported the findings. The primary surgeons evaluated the intraoperative stress significantly higher than the first assistant surgeons, and the application of lead aprons also resulted in higher stress levels. For this reason, we suggest that apart from consideration of intraoperative work breaks within one surgery, careful preoperative planning of consecutive surgeries that allows for both an alternation of intraoperative functions and a rotative system for the application of lead aprons should be taken into account.

Comment on "Cytokines and oxidative stress status following a handball game in elite male players".

In a well-conducted study, Marin et al. [1] reported significant alterations of oxidative stress biomarkers, antioxidant capacity, and indices of muscular damage in elite handball players after a friendly match. The authors were surprised by the marked increase of muscular damage indirectly assessed by serum creatine kinase (CK) in experienced players, which increased from about 80 U/L at baseline to 150 U/L 24 hours after game. However, average CK values reported here are quite low in comparison to reference values of athletic populations [2] and do not exceed reference values used in clinical practice [3, 4]. Although containing lots of eccentric exercises like abrupt stopping or landing after jumping and the risk of muscle injury due to direct contact with other players, the average 24-hour postmatch value reported by Marin and colleagues reached only 20% of the upper reference level of swimmers. Swimmers generally exhibit low CK levels because of the non-weight-bearing, noncontact, and concentric nature of their sport [2, 5, 6]. We investigated twenty-one elite handball players to obtain representative values during a regular play-off season and found 12-hour postmatch CK values of 347 U/L (SEM: 43 U/L) and values of 255 U/L (SEM: 38 U/L) during a normal training week (60 hours after match). The relatively low values reported by Marin et al. are due to the study design, which included the abstinence from handball training and games before a friendly match for 2 and 4 days, respectively. Furthermore, serum CK is not always an (indirect) marker of muscular damage, but rather reflects increased rates of muscle turnover, stimulated by muscle use [6–8]. Thus, a 2-fold and even higher increase in response to exercise is not surprising [6, 9, 10].