Respiratory sinus arrhythmia during exercise in aerobically trained and untrained men.

Respiratory sinus arrhythmia (RSA) was examined in aerobically trained (AT) and untrained (NT) college-aged males during 12 periods consisting of a 3-min sitting baseline, six common 3-min absolute exercise stages, and five 3-min recovery stages that followed voluntary exhaustion to determine the relationship of work and training status to parasympathetic influence upon the heart. RSA systematically decreased during absolute exercise, was observed at heart rates (HR) above 100 beats x min(-1), and progressively increased during recovery. Additionally, independent of work stages, comparative regression analyses were conducted for both the exercise and recovery phases, separately, in which HR was regressed on RSA, as well as RSA on % VO2max, to contrast the obtained relationships for the AT and NT. No differences were revealed as a function of endurance training status as the slopes and intercepts obtained for the two groups from each of these analyses were similar. The within-subject correlations between RSA and % VO2max, calculated for each of the individuals across all 12 periods, were consistently negative. Between-subjects correlations of RSA with RR and tidal volume were predominantly nonsignificant, indicating that RSA, as measured here, is independent of individual differences in ventilatory activity and, as such, can be compared between groups during exercise. The findings demonstrate that RSA is detectable during both exercise and recovery, even at HR beyond 100 beats x min(-1), and reveals a similar relationship to HR and metabolic state in both aerobically trained and untrained populations.

Role of aerobic capacity and body mass index in the age-associated decline in heart rate variability.

The extent to which age-associated changes in aerobic capacity and body composition modulate the age-associated decline in heart rate variability (HRV) is unknown. We therefore measured HRV, peak O2 consumption (VO2peak) during treadmill testing, and relative weight (body mass index; BMI) in 164 healthy normotensive adults (75 men, age 20-87 yr) from the Baltimore Longitudinal Study on Aging. Two components of HRV, respiratory sinus arrhythmia (RSA; 0.12-0.40 Hz) and 0.10-Hz variability (0.06-0.10 Hz), were extracted from 8-min electrocardiogram recordings in the supine, seated, and standing postures. RSA, 0.10-Hz variability, and VO2peak varied inversely with age; BMI was unrelated to age. Age contributed 15.5-21.1% independent variance to RSA and 13.2-17.3% independent variance to 0.10-Hz HRV. VO2peak did not contribute significantly to RSA or 0.10-Hz HRV beyond the effect of age in any posture. There were no consistent independent contributions of BMI to HRV. Thus, in this population-based sample, age-associated changes in aerobic capacity and relative body weight do not provide the primary explanation for the decline in HRV observed with advancing age.

Psychophysiology and adaptive automation.

Adaptive automation is an approach to automation design where tasks are dynamically allocated between the human operator and computer systems. Psychophysiology has two complementary roles in research on adaptive automation: first, to provide information about the effects of different forms of automation thus promoting the development of effective adaptive logic; and second, psychophysiology may yield information about the operator that can be integrated with performance measurement and operator modelling to aid in the regulation of automation. This review discusses the basic tenets of adaptive automation and the role of psychophysiological measures in the study of adaptive automation. Empirical results from studies of flight simulation are presented. Psychophysiological measures may prove especially useful in the prevention of performance deterioration in underload conditions that may accompany automation. Individual differences and the potential for learned responses require research to understand their influence on adaptive algorithms. Adaptive automation represents a unique domain for the application of psychophysiology in the work environment.

Data-dependent filter characteristics of peak-valley respiratory sinus arrhythmia estimation: a cautionary note.

Filter characteristics of the peak-valley respiratory sinus arrhythmia estimation method are described. To identify filter characteristics of this method, models were generated that combined signals of different frequencies with trends of varying slopes. These models simulate the influence of trend and changing respiratory frequency on the accuracy of peak-valley estimates. The transfer function of the peak-valley method, unlike that of other time domain filters, is not solely dependent upon signal frequency. Two factors interact to determine the relative accuracy of the peak-valley method: (a) slope of the signal component and (b) slope of the underlying trend. Combinations of these factors may result in significant distortion to the input signal. The direction of error is a function of the direction of the trend (i.e., overestimation with deceleration and underestimation with acceleration). In many situations when respiratory sinus arrhythmia amplitude is low in special populations (e.g., cardiovascular disorders, high-risk infants, or human fetuses) or under conditions that greatly reduce respiratory sinus arrhythmia amplitude (e.g., exercise, drugs, pharmacological manipulations), use of the peak-valley method may result in significant measurement error. The use of this method to evaluate respiratory sinus arrhythmia over short epochs (i.e., less than 2 min) or to quantify changes in respiratory sinus arrhythmia due to discrete stimulation (e.g., breath by breath) may result in inconsistent measurement error. Recommendations are made for detrending heart rate data prior to application of the peak-valley method.

Research methods for measurement of heart rate and respiration.

Strategies for heart rate and respiration quantification are dependent upon a knowledge of physiology and statistics. To develop appropriate and sensitive psychophysiological measures, it is necessary to understand the neural control of the autonomic nervous system and the statistical characteristics of physiological data. Moreover, it is proposed that inferences derived from physiological measures are dependent upon a statistical interaction between the characteristics of the physiological data and the measurement techniques. The steps required to analyze heart rate and respiration data are presented, ranging from data acquisition and editing to data analysis and physiological inference. A variety of techniques are described and contrasted with recommendations for future research.

Cardiac vagal tone predicts outcome in neurosurgical patients.

OBJECTIVE: To evaluate the relationship between presurgical levels of cardiac vagal tone and outcome in neurosurgical patients. DESIGN: Prospective series. SETTING: Respiratory ICU in a university hospital. PATIENTS: Fifty-one adults admitted to the respiratory ICU between 1982 and 1985. Forty-two patients were scheduled for elective neurosurgery, and nine patients suffered from head trauma. INTERVENTIONS: Ten minutes of electrocardiographic (EKG) data were recorded before medical intervention. Neurosurgical patients scheduled for surgery had EKG data recorded 24 hrs before their operation. Trauma patients had EKG data recorded immediately after arrival in the respiratory ICU. MEASUREMENTS AND MAIN RESULTS: Cardiac vagal tone was evaluated using a vagal tone index, quantified from the EKG. Cardiac vagal tone monitored before surgical intervention significantly distinguished between the outcome groups only for the elective neurosurgical patients. Age, gender, heart rate, Glasgow Coma Scale scores, and tumor location, size, and malignancy were not related to outcome in the elective neurosurgery group. However, within the trauma group, low Glasgow Coma Scale scores were significantly related to poor outcome. CONCLUSIONS: Cardiac vagal tone may offer important predictive value by alerting the physician to the functional consequence of head injury. Information relating to autonomic nervous system functioning, such as the vagal tone index used in this study, may provide additional information that will complement the computed tomography scan results. This study demonstrates that the vagal tone index is a predictive factor that may be efficiently extracted from the heart rate pattern routinely monitored in ICUs.

Frequency-specific amplification of heart rate rhythms using oscillatory tilt.

Heart rate rhythms have been demonstrated to parallel specific psychological processes. Efficient experimental control of the amplitude of these rhythms would allow evaluation of bidirectional psychophysiological hypotheses. This experiment was performed to examine the specificity of the heart rate rhythm response to oscillatory head-up tilt. Seventy-one adults (36 male, 35 female) aged 18-30 were positioned on a tilt-table and oscillated at 0.08 Hz with a maximum tilt angle of +21 degrees for a 10-min period. Heart period, heart period variability at 0.08 Hz (i.e., Traube-Hering-Mayer (THM) variance), and respiratory sinus arrhythmia (quantified using vagal tone, V) were measured. For a subset of 21 subjects, continuous measures were derived to examine the response to onset of oscillatory tilt. Respiratory activity was also measured in these subjects. There was a significant increase in the amplitude of the THM variance during tilt stimulation. Tilt did not significantly change heart period, V, or respiration frequency. Following cessation of tilt, THM variance returned to baseline levels, heart period lengthened for males, and V increased for both sexes. Subjects with higher amplitude baseline V were characterized by more rapid THM variance response to tilt. Results suggest that parasympathetic tone moderates the THM variance increase elicited by low-frequency oscillatory tilt.

Vagal mediation of the effect of alcohol on heart rate.

Alcohol (0.5 g/kg bodyweight) was administered in two sessions and placebo in a third session to normal, healthy social drinkers. A control group was administered a mixer (i.e., no alcohol) for each of the three sessions. The heart rate and vagal tone index (V) response patterns were different to alcohol than to the mixer or placebo. The treatments did not differentially influence pulse transit time. The results indicated that the acute effect of a moderate dose of alcohol on the heart is parasympathetically (i.e., vagally) mediated and has no significant direct sympathetic component.

The effects of mentally handicapped children on families--a conceptual review.

Recent research which examines the effects of mentally handicapped children upon families is reviewed. The studies are grouped into three categories based on the underlying conceptions which appear to guide them. The first category examines which families are most vulnerable to the presumed stress of a mentally handicapped child. The second category emphasises the material and practical problems families experience. The third category stresses the competence of families and describes the resources used to develop coping strategies. Links are drawn between these three categories and to parallel developments in related areas, and implications for future research are discussed.