Impedance cardiography has been used increasingly to measure human physiological responses to emotional and mentally engaging stimuli. The validity of large-scale ensemble averaging of ambulatory impedance cardiograms was evaluated for preejection period (PEP), interbeat interval, and dZ/dt(min) amplitude. We tested whether the average of “classical” 60-sec ensemble averages across periods with fixed activity, posture, physical load, social situation, and location could be accurately estimated from a single large-scale ensemble average spanning these entire periods. Impedance and electrocardiograms were recorded for about 24-h from 21 subjects. Recordings were scored by seven raters, using both methods for each subject. Good agreement (average intraclass correlation coefficient was .91) between both ensemble averaging methods was found for all three cardiac function measures. The results indicate that for unambiguous ambulatory impedance cardiograms, large-scale ensemble averaging is valid, which makes measuring prolonged changes in cardiac sympathetic activity by measuring ambulatory PEP feasible even in large epidemiological samples.

Background Previous studies on dental anxiety have examined the psychophysiological responses evoked in dentally anxious subjects by dental-related stimuli, but not during a real-life dental examination, which was achieved in the present study. Methods The heart rate, skin conductance level, and heart rate variability of 25 subjects with dental anxiety and 25 healthy controls were examined. Anxiety was determined by the Modified Dental Anxiety Scale and the Dental Anxiety Scale–Revised. The psychophysiological reactions of the two groups were compared during exposure to dental-related pictures, dental-related sounds, and an actual examination in a dental surgery. Results All the dental-related stimuli provoked an increase in heart rate, i.e. visual stimuli (p<0.001; 95% CI 0.98–3.95 bpm), auditory stimuli (p<0.001; 95% CI 1.34–4.99 bpm), and a dental examination (p<0.001; 95% CI 1.26–5.39 bpm). Dental-related pictures provoked inferior skin conductance level changes compared to dental-related sounds and the dental examination (visual modality vs auditory p<0.001; 95% CI 0.039–0.152; visual modality vs examination p<0.001; 95% CI 0.083–0.275). Heart rate variability manifested in a complex pattern of responses to the dental examination. However, when exposed to all three dental-related stimuli presentation conditions, the heart rate (F = 0.352, p = 0.556), skin conductance level (F = 0.009, p = 0.926), and heart rate variability parameters of subjects with dental anxiety did not differ in comparison to the healthy controls. Conclusions This pilot study represents an evaluation of psychophysiological reactions during a real-life dental examination compared to single modality stimuli, and shows that a real-life dental examination provokes an increase in heart rate, heart rate variability and skin conductance level. Additionally, autonomic responses did not differ between the experimental and control groups. The key issue for future studies is the effect of real-life situations on the physiological and psychological state of the subjects, which should be considered when planning new research and studied in depth.