Karin Trimmel

An introduction to heart rate variability: methodological considerations and clinical applications.

Heart rate variability (HRV), the beat-to-beat variation in either heart rate or the duration of the R-R interval, has become a popular clinical and investigational tool (Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology, 1996; Billman, 2011). Indeed, the term “heart rate variability” yields nearly 18,000 “hits” when placed in the pubmed search engine. These temporal fluctuations in heart rate exhibit a marked synchrony with respiration (increasing during inspiration and decreasing during expiration—the so called respiratory sinus arrhythmia) and are widely believed to reflect changes in cardiac autonomic regulation (Billman, 2011). Although the exact contributions of the parasympathetic and the sympathetic divisions of the autonomic nervous system to this variability are controversial and remain the subject of active investigation and debate, a number of time and frequency domain techniques have been developed to provide insight into cardiac autonomic regulation in both health and disease (Billman, 2011). It is the purpose of this book to provide a comprehensive assessment of the strengths and limitations of HRV techniques. Particular emphasis will be placed on the application of HRV techniques in the clinic and on the interaction between prevailing heart rate and HRV. This book contains both state-of-the art review and original research articles that have been grouped into two main sections: Methodological Considerations and Clinical Application. A brief summary of the chapters contained in each section follows below.

Effects of low intensity noise from aircraft or from neighbourhood on cognitive learning and electrophysiological stress responses.

The effects of low intensity noise on cognitive learning and autonomous physiological processes are of high practical relevance but are rarely addressed in empirical investigations. This study investigated the impact of neighbourhood noise (of 45 dB[A], n=20) and of noise coming from passing aircraft (of 48 dB[A] peak amplitude presented once per minute; n=19) during computer based learning of different texts (with three types of text structure, i.e. linear text, hierarchic hypertext, and network hypertext) in relation to a control group (35 dB[A], n=20). Using a between subjects design, reproduction scores, heart rate, and spontaneous skin conductance fluctuations were compared. Results showed impairments of reproduction in both noise conditions. Additionally, whereas in the control group and the neighbourhood noise group scores were better for network hypertext structure than for hierarchic hypertext, no effect of text structure on reproduction appeared in the aircraft noise group. Compared to the control group, for most of the learning period the number of spontaneous skin conductance fluctuations was higher for the aircraft noise group. For the neighbourhood noise group, fluctuations were higher during pre- and post task periods when noise stimulation was still present. Additionally, during the last 5 min of the 15 min learning period, an increased heart rate was found in the aircraft noise group. Data indicate remarkable cognitive and physiological effects of low intensity background noise. Some aspects of reproduction were impaired in the two noise groups. Cognitive learning, as indicated by reproduction scores, was changed structurally in the aircraft noise group and was accompanied by higher sympathetic activity. An additional cardiovascular load appeared for aircraft noise when combined with time pressure as indicated by heart rate for the announced last 5 min of the learning period during aircraft noise with a peak SPL of even 48 dB(A). Attentional mechanisms (attentional control) like being threatened by passing aircraft approaching the airport, higher demands of selective filtering, and difficulties in changing cognitive strategies during noise are discussed as underlying mechanisms.

Treatment of Fear of Flying: Behavioral, Subjective, and Cardiovascular Effects

BACKGROUND Nonaviator fear of flying is a common problem usually managed with behaviorally oriented treatment. The unknown time courses of aspects of anxiety and of physiological response were investigated during a 3-d treatment including flights. METHODS Ratings, heart rate (HR), and heart rate variability (HRV; pNN10, pNN50) of 15 Moderate-Anxious and 9 High-Anxious subjects at critical epochs of treatment and on 2 actual flights, on which 9 Controls participated, were compared. RESULTS All subjects took the flights and displayed a remarkably reduced fear when comparing pre- vs. post-treatment ratings. Repeated ratings showed an increase in relaxation and drops in general somatic and cognitive aspects of anxiety during flights. However, cognitive aspects in High-Anxious did not drop to the level of Controls. Level of anxiety was related to cardiovascular activity almost always during treatment and flights, in particular during takeoffs (average maximum HR of 137 bpm in High-Anxious compared to 118 bpm in Moderate-Anxious and 98 bpm in Controls in the first flight). Moderate-Anxious showed no obvious relationship of cardiovascular response to critical flight epochs, but had the lowest HRV on flights. DISCUSSION Results indicate that anxiety in Moderate-Anxious is related to flight, but not to single critical epochs of flying, contrary to High-Anxious, for which higher ratings on cognitive aspects of anxiety associated with more physiological load at critical epochs were observed. However, HR and ratings showed a remarkable drop in both treatment groups, in particular in perceived physiological symptoms, indicating that the treatment facilitates coping of fear of flying.

Sensitivity of HRV parameters including pNNxx proven by short-term exposure to 2700 m altitude

Analysis of heart rate variability (HRV) is increasingly applied in research and intervention. However, the sensitivity of the variety of HRV parameters for changes in cardiovascular reactivity remains unclear. This study investigated effect sizes of HRV parameters in an experimental field study, exposing persons to 2700 m altitude. Parameters analyzed were mean heart rate (HR), atrioventricular conduction time, SDNNi, rMSSD, pNN50, pNNxx (xx = pNN05, pNN10, pNN20, pNN25, pNN30, pNN40), LF, HF, LFnu, LF/HF ratio, and Total Power, as well as ratings of arousal and mood. Forty-five persons were taken to the Dachstein mountain by cable car. HRV parameters of 40 min epochs and ratings at 170 m and 2700 m were compared. At altitude, HR increased and HRV decreased in all parameters. Although moods were not changed, test persons experienced higher arousal at altitude. Besides for HR, analysis revealed the highest effect size for SDNNi, followed by pNN20 and pNN25 and was much lower for HF. As pNNxx parameters were highly correlated with HF, they are discussed to reflect vagal activity. Moreover, pNNxx parameters are clearly defined, whereas HF is susceptible to variations in computation; thus pNNxx parameters seem preferable due to higher effect sizes and better comparability.

Lateralization of language function in epilepsy patients: A high-density scalp-derived event-related potentials (ERP) study

OBJECTIVES Language functional magnetic resonance imaging (fMRI) represents the clinical standard for language lateralization assessment in presurgical epilepsy evaluation, but still many patients experience postoperative language deficits. Event-related potentials (ERPs), especially the negative component around and after 400ms, are related to language processing and could therefore represent a complementary method of language lateralization assessment. METHODS Scalp EEG was recorded from 64 locations in 36 epilepsy patients and 37 controls during three visually presented language tasks: A short-term language memory task (differentiation memorized vs. unknown words), a phonological task (detection of rhymes in word pairs), and a semantic decision task (differentiation words vs. pseudowords). ERPs were analyzed in the 300ms-800ms epoch. Language fMRI was routinely obtained in patients. RESULTS ERPs were significantly more negative over the left compared to the right hemisphere in all three tasks in patients and controls. Laterality indices showed highest concordance with fMRI for the Word/Pseudoword Task. CONCLUSIONS ERPs of language processing were lateralized to the left hemisphere in the majority of epilepsy patients and controls. In patients, single-subject laterality indices showed high concordance with fMRI results. SIGNIFICANCE Results indicate that scalp-derived ERPs are a promising tool to investigate lateralization of language function in epilepsy patients.

Activations in temporal areas using visual and auditory naming stimuli: A language fMRI study in temporal lobe epilepsy

OBJECTIVE Verbal fluency functional MRI (fMRI) is used for predicting language deficits after anterior temporal lobe resection (ATLR) for temporal lobe epilepsy (TLE), but primarily engages frontal lobe areas. In this observational study we investigated fMRI paradigms using visual and auditory stimuli, which predominately involve language areas resected during ATLR. METHODS Twenty-three controls and 33 patients (20 left (LTLE), 13 right (RTLE)) were assessed using three fMRI paradigms: verbal fluency, auditory naming with a contrast of auditory reversed speech; picture naming with a contrast of scrambled pictures and blurred faces. RESULTS Group analysis showed bilateral temporal activations for auditory naming and picture naming. Correcting for auditory and visual input (by subtracting activations resulting from auditory reversed speech and blurred pictures/scrambled faces respectively) resulted in left-lateralised activations for patients and controls, which was more pronounced for LTLE compared to RTLE patients. Individual subject activations at a threshold of T>2.5, extent >10 voxels, showed that verbal fluency activated predominantly the left inferior frontal gyrus (IFG) in 90% of LTLE, 92% of RTLE, and 65% of controls, compared to right IFG activations in only 15% of LTLE and RTLE and 26% of controls. Middle temporal (MTG) or superior temporal gyrus (STG) activations were seen on the left in 30% of LTLE, 23% of RTLE, and 52% of controls, and on the right in 15% of LTLE, 15% of RTLE, and 35% of controls. Auditory naming activated temporal areas more frequently than did verbal fluency (LTLE: 93%/73%; RTLE: 92%/58%; controls: 82%/70% (left/right)). Controlling for auditory input resulted in predominantly left-sided temporal activations. Picture naming resulted in temporal lobe activations less frequently than did auditory naming (LTLE 65%/55%; RTLE 53%/46%; controls 52%/35% (left/right)). Controlling for visual input had left-lateralising effects. CONCLUSION Auditory and picture naming activated temporal lobe structures, which are resected during ATLR, more frequently than did verbal fluency. Controlling for auditory and visual input resulted in more left-lateralised activations. We hypothesise that these paradigms may be more predictive of postoperative language decline than verbal fluency fMRI.

Effects of carbamazepine and lamotrigine on functional magnetic resonance imaging cognitive networks

To investigate the effects of sodium channel–blocking antiepileptic drugs (AEDs) on functional magnetic resonance imaging (fMRI) language network activations in patients with focal epilepsy.

Acoustic Noise Alters Selective Attention Processes as Indicated by Direct Current (DC) Brain Potential Changes

Acoustic environmental noise, even of low to moderate intensity, is known to adversely affect information processing in animals and humans via attention mechanisms. In particular, facilitation and inhibition of information processing are basic functions of selective attention. Such mechanisms can be investigated by analyzing brain potentials under conditions of externally directed attention (intake of environmental information) versus internally directed attention (rejection of environmental stimuli and focusing on memory/planning processes). This study investigated brain direct current (DC) potential shifts—which are discussed to represent different states of cortical activation—of tasks that require intake and rejection of environmental information under noise. It was hypothesized that without background noise rejection tasks would show more positive DC potential changes compared to intake tasks and that under noise both kinds of tasks would show positive DC shifts as an expression of cortical inhibition caused by noise. DC potential shifts during intake and rejection tasks were analyzed at 16 standard locations in 45 persons during irrelevant speech or white noise vs. control condition. Without noise, rejection tasks were associated with more positive DC potential changes compared to intake tasks. During background noise, however, this difference disappeared and both kinds of tasks led to positive DC shifts. Results suggest—besides some limitations—that noise modulates selective attention mechanisms by switching to an environmental information processing and noise rejection mode, which could represent a suggested “attention shift”. Implications for fMRI studies as well as for public health in learning and performance environments including susceptible persons are discussed.

Left temporal lobe language network connectivity in temporal lobe epilepsy

Impairment of naming function is a critical problem for temporal lobe epilepsy patients, yet the neural correlates of the disruption of temporal lobe language networks are poorly understood. Using functional MRI, we investigated the activation and task-related functional connectivity of left temporal lobe language networks and their relation to clinical naming performance and disease characteristics. We studied 59 adult patients with temporal lobe epilepsy (35 left temporal lobe epilepsy) and 32 healthy controls with auditory and visual naming functional MRI tasks. Time series of activation maxima in the left posterior inferior temporal lobe were extracted to create a psychophysiological interaction regressor for subsequent seed-based whole-brain task-related functional connectivity analyses. Correlational analyses were performed to assess the association of functional MRI activation and functional connectivity with clinical naming scores, age of onset of epilepsy, and duration of epilepsy. Auditory naming elicited activation in the left posterior inferior temporal gyrus and visual naming in the left fusiform gyrus across all groups. Activations in the left inferior temporal gyrus, left thalamus and left supplementary motor region during auditory naming as well as left fusiform activations during picture naming correlated with better clinical naming performance. Functional connectivity analyses indicated coupling of left posterior inferior temporal regions to bilateral anterior and posterior temporal lobe regions and the bilateral inferior precentral gyrus as well as contralateral occipital cortex. Stronger functional connectivity was associated with better clinical naming performance in all groups. In patients with left temporal lobe epilepsy only, functional connectivity increased with later age of onset of epilepsy and shorter disease duration. This suggests that onset of seizures early in life and prolonged disease duration lead to disrupted recruitment of temporal lobe networks ipsilateral to the seizure focus, which might account for naming deficits in temporal lobe epilepsy.

Rating Comfort and Every-Day Mood States (TRIM-S): Comparing Likert Scales with Visual Analog Scales (VAS) and Relations to Cardiovascular Response

Objective: A direct comparison of different kinds of scale formats of ratings of comfort and of mood states as well as their relation to the cardiovascular response was the objective. It was expected that activation-related scales are associated with physiological measures and that comfort scales and ratings of mood states would give complementary information on the impact of environmental conditions.