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Biomedical subjects

E L Fallen

Publications and source records attributed to E L Fallen.

At least 37 records · Page 2Linked to original sources
PubMed1995

Evaluation of the reproducibility and accuracy of apex beat measurement in the detection of echocardiographic left ventricular dilation.

OBJECTIVE: To develop a standardized method for measuring the width of the apex beat and to determine its precision and accuracy in detecting echocardiographically determined left ventricular dilation. DESIGN: In the reproducibility study, two cardiologists blinded to each other's findings measured the apex beat. To determine accuracy, blind, independent assessment of apex beat measurement was compared with left ventricular enlargement determined by echocardiogram. PATIENTS: One hundred and four patients referred for echocardiogram for a wide variety of suspected cardiac abnormalities. MEASUREMENTS: The apex beat was measured with patients in a 45 degrees left lateral decubitus position; medial and lateral aspects of the impulse and the width were identified using electrocardiographic callipers. Echocardiographic left ventricular dilation was defined as a measure exceeding the 95% prediction limits as determined for the patient's age and body surface area. RESULTS: The intraclass correlation measuring agreement on apex beat size between two cardiologists in 13 patients was 0.95. Of the 104 patients, 57 had a measurable apex beat of whom 50 had a technically adequate echocardiogram. The sensitivity of the measurement, using a cut-point of 40 mm, was 0.48 and the specificity 0.96.

Age Factors↗
PubMed1993

Operation Everest II: an indication of deterministic chaos in human heart rate variability at simulated extreme altitude.

It has been shown that fluctuation of human heartbeat intervals (heart rate variability, HRV) reflects variations in autonomic nervous system activity. We studied HRV at simulated altitudes of over 6000 m from Holter electrocardiograms recorded during the Operation Everest II study (Houston et al. 1987). Stationary, approximately 30-min segments of HRV data from six subjects at sea level and over 6000 m were supplied to (1) spectral analysis to evaluate sympathetic and parasympathetic nervous system (SNS, PNS) activity, (2) the analysis of Poincaré section of the phase space trajectory reconstructed on a delayed coordinate system to evaluate whether there was fluctuation with deterministic dynamics, (3) the estimation of the correlation dimension to evaluate a static property of putative attractors, and (4) the analysis of nonlinear predictability of HRV time series which could reflect a dynamic property of the attractor. Unlike HRV at sea level, the recordings at over 6000 m showed a strong periodicity (period of about 20 s) with small cycle-to-cycle perturbation. When this perturbation was expressed on a Poincaré section, it seemed to be likely that the perturbation itself obeyed a deterministic law. The correlation dimensions of these recordings showed low dimensional values (3.5 +/- 0.4, mean +/- SD), whereas those of the isospectral surrogates showed significantly (P < 0.05) higher values (5.3 +/- 0.5) with embedding dimensions of 5.6 +/- 0.9.(ABSTRACT TRUNCATED AT 250 WORDS)

Altitude↗
PubMed1993

Power spectral analysis of heart rate variability: a noninvasive signature of cardiac autonomic function.

Power spectral analysis of short segments of beat-to-beat heart rate variability (PS/HRV) reveals three distinct peaks. In human PS/HRV, the high frequency (HF) band (0.15 to 0.4 Hz) is correlated with respiratory driven vagal efferent input to the sinus node. The low frequency band (LF) 0.06 to 0.15 Hz is believed to be due to baroreceptor mediated blood pressure control. Therefore, PS/HRV represents a noninvasive signature of the balance between sympathetic and parasympathetic components of the autonomic nervous system. This paper reviews the literature on the methodological issues relevant to signal processing, computational, and clinical applications of PS/HRV. Factors affecting the power in the LF and HF bands are examined in healthy controls. Recent work from several laboratories suggests that PS/HRV is a potentially powerful tool for exploring neurocardiac dysfunction in patients with a variety of cardiac and autonomic disorders. Mathematical models which simulate neurocardiac control are examined. Concerns regarding the lack of standardization between different laboratories are expressed. As the PS/HRV attains the status of a clinical diagnostic test, we hope that this review serves as a source of integrated information for researchers in this field.

Adult↗
PubMed1992

Neural regulation of heart rate variability in endurance athletes and sedentary controls.

OBJECTIVE: The aim was to examine the cardiac autonomic responses to orthostatic stress and recovery from steady state exercise in endurance trained athletes and sedentary subjects. METHODS: The power spectrum of heart rate variability was measured before and after exercise in 10 male long distance runners and 14 male sedentary control subjects. Both groups were comparable in sex, age, and body mass index. Continuous ECG recordings were obtained during the following physiological manoeuvres: 45 min supine rest state; 10 min standing; 15 min steady state exercise at 50% maximum workload, and 15 min while supine during post-exercise recovery. The resting heart rate of athletes was lower than controls, at 52(SD 4.9) v 67(8.7) beats.min-1, p < 0.001. Power spectrum analysis was performed using autoregressive modelling. RESULTS: The resting high frequency (HF) vagal component was higher in athletes than controls, at 62 (10.7) v 44(22.4) beats.min-1.Hz-1, p < 0.05. The resting low frequency (LF) peak power was significantly reduced in athletes, at 54(9.9) v 70(19.5) in control, p < 0.05. Although no group differences were observed during upright posture or exercise, the LF:HF area ratio had already returned to pre-exercise levels within 5 min of recovery in athletes. Conversely, it required up to 15 min of recovery before a noticeable decrease in the LF:HF area ratio was seen in controls. CONCLUSIONS: These data support the hypothesis that endurance training modifies heart rate control in whole or in part through neurocardiac mechanisms.

Adult↗
PubMed1992

Neurocardiac responses to vagoafferent electrostimulation in humans.

UNLABELLED: To determine if cardiac vagal tone is enhanced by vagal electrostimulation (VES), we examined the heart rate autospectrum (HRA) in eight patients with implanted stimulators for complex partial seizures. In four patients the VES was activated at 30 Hz and 500-msec pulse (HiStim group) compared to 2 Hz and 130-msec pulse for the LoStim group (n = 4). Continuous ECG and respiratory waveforms were recorded for 45 minutes every 8 hours (7-8 AM; 3-4 PM 11-12 PM) during resting supine wakeful epochs both before and 15 days after surgical implantation. From the HRA cardiac sympathovagal balance was expressed as the ratio of the low frequency (LF) power to the high frequency (HF) power. RESULTS: There were no presurgical differences between the groups in heart rate, its variance, or the energies contained in any autospectral band. The LoStim group showed no significant change in heart rate (HR), HF peak power, or LF:HF ratios during 2 weeks of VES. Conversely, in the HiStim group, the LF:HF peak power ratio (an expression of sympathetic dominance) decreased from 2.5 +/- 1.5 preimplant to 1.5 +/- 0.49 (P < 0.02) with VES. During VES there was a significantly higher HF power in the HiStim compared to LoStim group. No diurnal variations in HRA values were seen for either group. CONCLUSIONS: (1) A relationship exists between selective vagal nerve electrostimulation and the HRA; and (2) high stimulation frequency of the vagus nerve in man is associated with sustained augmentation of cardiac vagal tone throughout a 24-hour cycle.

Adult↗
PubMed1992

Effect of vagal nerve electrostimulation on the power spectrum of heart rate variability in man.

The power spectrum of heart rate variability contains low frequency (LF = 0.08-0.12 Hz) and high frequency (HF = 0.18-0.30 Hz) components said to represent neurocardiac rhythms. To verify whether such a relationship exists we report a unique study where the heart rate autospectrum was determined in a 28-year-old epileptic male patient with an implanted vagal electrical stimulator. The stimulator was activated at 20 Hz, 300 microseconds pulse, and 1.25 V. Continuous ECG and respiratory waveform records were obtained over 45 minutes every 8 hours (7-8 AM; 3-4 PM; 11-12 PM) with the stimulator ON, then 24 hours OFF and then 24 hours ON again. The overall LF:HF peak ratio increased from 0.64 to 1.99 (P less than 0.001) after the stimulator was turned OFF. There was a dramatic increase in the LF peak power (greater than 60%) and a corresponding decrease in the HF peak power (greater than 65%) when the stimulator was turned OFF. These values were reversed when the stimulator was turned ON again. In the early morning and late evening hours, there was a significant rightward shift in the LF peak power frequency (average 0.057 to 0.075 Hz) whenever the stimulator was ON. Otherwise, there were no significant circadian variations in any of the autospectral components. The results demonstrate an unequivocal relationship between selective vagal nerve electrostimulation and alterations in the heart rate autospectrum.

Adult↗
PubMed1991

Diurnal variations of neurocardiac rhythms in acute myocardial infarction.

To determine the diurnal pattern of cardiac autonomic tone in acute myocardial infarction (AMI), this study examined the power spectrum of heart rate (HR) variability in 24 patients during a single 24-hour segment within 4 days of AMI. Patients were nonrandomly allocated to a group (n = 14) without autonomic drugs and to a group (n = 10) already receiving beta blockers at the time of AMI. With use of autoregressive modeling, the power spectrum of HR variability was computed from continuous 1-hour electrocardiographic segments recorded at equally spaced intervals; 7 to 8 A.M., 3 to 4 P.M., and 11 to 12 P.M. All patients were supine, awake and pain free during recordings. There were no differences in HR, HR variance or the low-frequency peak power (0.06 to 0.1 Hz) from one temporal sequence to another. For the patients not taking beta blockers, the high-frequency peak power (0.2 to 0.36 Hz) or vagal component increased significantly from 3 P.M. to 11 P.M. (28 +/- 11 to 45 +/- 20 beats/min2.Hz-1, p less than 0.01). There was a significant decrease in the low- to high-frequency peak power and area ratios from 3 P.M. to 11 P.M. All power spectral parameters in the patients taking beta blockers remained unchanged over 24 hours. There was significantly heightened vagal modulation of sinus node activity in those receiving beta blockers, especially at 7 A.M. and 3 P.M. The data suggest that under steady-state wakeful conditions in the early recovery phase after an AMI, vagal tone is more pronounced during the late evening hours with a possible shift to relative sympathetic dominance during early morning and midafternoon hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗
PubMed1991

Report of the Canadian Cardiovascular Society's consensus conference on the Management of the Postmyocardial Infarction Patient.

In October 1989, the Canadian Cardiovascular Society announced a program to achieve consensus on important issues in the care of patients with cardiovascular disease. This report on the management of the postmyocardial infarction patient represents the first in a series of these consensus conferences. The process for establishing consensus recommendations involved several steps. A primary panel of 11 experts from various fields was selected to review the available clinical evidence and to make a list of recommendations about management decisions in the postmyocardial infarction period. The initial report was distributed to a secondary panel of 16 reviewers* representing allied health care constituencies from across Canada. On the basis of the critical reviews and feedback from these reviewers, a revised report was distributed to all members (over 800) of the Canadian Cardiovascular Society for further review and feedback. This iterative approach resulted in a penultimate report that was presented at a plenary session of the annual scientific meeting of the Canadian Cardiovascular Society on Oct. 18, 1990, in Halifax, NS. On the basis of discussion and feedback from this symposium, the consensus review was completed.

Canada↗
PubMed1991

Effects of steady state exercise on the power spectrum of heart rate variability.

The effects of steady state exercise on the power spectrum of heart rate variability were studied in 19 healthy subjects. Continuous ECG signals were recorded during 1) 15 min of rest in the supine state, 2) 10 min of standing, 3) 10 min of steady state exercise at 50% of maximum predicted power output on a cycle ergometer, and 4) 15 min of post-exercise recovery in the supine state. Autoregressive modeling was used to determine the power spectrum of heart rate variability. While orthostatic stress produced a significant 51% increase in the ratio of low to high frequency peak spectral power, steady state exercise caused a significant suppression of both low and high frequency components. The low frequency peak power rose to significantly high levels throughout 15 min of the post-exercise recovery period. There was a significant leftward shift in the frequency of the low frequency peak with exercise and a rightward shift during the recovery supine state. These results suggest that neuroregulatory control of heart rate plays a major role in adaptive responses to orthostatic stress and post-exercise recovery, while humoral factors are probably more important in maintaining heart rate during steady state exercise.

Adult↗
PubMed1988

A controlled trial of digoxin in congestive heart failure.

Because of conflicting results from studies examining the usefulness of digoxin in congestive heart failure (CHF) patients in sinus rhythm, a cross-over trial was conducted in which 20 patients received 7 weeks of digoxin titrated to a level of 1.54 to 2.56 nmol/liter and 7 weeks of matched placebo. The order of treatments was determined by random allocation and patients, clinicians and research staff were blind to allocation. In patients with deteriorating condition, the treatment period was terminated and outcome measures were obtained. If deterioration occurred during the first period, the patient was crossed over without the code being broken. Seven patients required premature termination of study periods because of increasing symptoms of CHF. All 7 were taking placebo at the time (p = 0.016). Small differences in dyspnea (p = 0.044), walking test score (p = 0.055), clinical assessment of CHF (p = 0.036) and ejection fraction (p = 0.004) favored the digoxin treatment group. Patients with more severe CHF were more likely to benefit from digoxin administration. It was concluded that oral digoxin, in doses titrated to produce a serum level of 1.54 to 2.56 nmol/liter, improved quality of life and functional exercise capacity in some patients with CHF in sinus rhythm.

Aged↗
PubMed1988

Microcomputerized on-line evaluation of heart rate variability power spectra in humans.

The heart rate variability power spectra is computed using an on-line microcomputer system. In normal subjects (n = 10), standing and post-exercise states demonstrated statistically significant increases (p less than 0.05) in the peak power at 0.1 Hz. During exercise, the peak power at 0.1 Hz was reduced significantly (p less than 0.05). In patients with myocardial infarction, either the peak at 0.1 Hz or the peak associated with breathing frequency was augmented. Our system is mobile and is useful especially when on-line heart rate variability power spectra are required in experimental or clinical situations.

Adult↗
PubMed1988

Spectral analysis of heart rate variability following human heart transplantation: evidence for functional reinnervation.

To determine the status of innervation in long-term human donor allografts, the power spectrum of heart rate variability was analysed in 9 post-transplant patients and 7 healthy control subjects. The mean post-transplant follow-up was 17.8 months (range: 2-37 months). Continuous ECG signals were recorded throughout a 15-min rest period. An R-R interval tachogram was generated and an autoregressive model using linear predictive coding, was applied to the heart rate variability data. In 8 transplant patients the frequency oscillations were irregular, broad based and widely dispersed from 0 to 1 Hz. The patterns resembled white noise and were consistent with dissociation of the donor allograft from the recipient's central nervous system. In contrast, one patient displayed a heart rate variability spectrum indistinguishable from that of control subjects. This pattern contained two distinct spectral bands; one corresponding to the patient's respiratory rate at 0.2 Hz and a low frequency Mayer wave at 0.1 Hz. Atropine abolished the respiratory (vagal) peak. Except for this patient's post-transplant time (33 months compared to the group mean of 17.6 months), there were no clinical characteristics which distinguished this patient from the others. While the mean heart rate for the remaining 8 allografts was significantly higher than controls (95.3 vs 64.5 bt/min; P less than 0.001) the standard deviation of heart rate variability for the 8 patients was significantly narrower than controls (0.7 vs 4.86; P less than 0.01). The variance of heart rate for the patient with the normal power spectrum was fourfold greater than the mean SD of the other transplant patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Power spectrum of heart rate variability: a non-invasive test of integrated neurocardiac function.

Under steady state conditions, frequency specific oscillations in the heart rate record reflect beat-to-beat autonomic control of sinus node activity. Using an autoregressive model, samples (2.5 min) of continuous ECG records were analyzed in 36 healthy young adults during supine rest (45 min), orthostatic stress and controlled respiration. In the supine state, constancy of heart rate was achieved (mean HR 62.8 bt/min +/- 4.88 SD). However, the 0.1 Hz peak spectral power varied considerably: average coefficient of variation was 34% compared to only 8% for heart rate. When breathing rates were synchronized to a metronome there was a small insignificant decrease in the peak power at 0.1 Hz compared to spontaneous respiration. Standing produced a significant increase in the peak power at 0.1 Hz especially during synchronized breathing. There was a maximum increase in the low frequency (0.1 Hz) peak power of 40 (bt/min)2. Hz-1 at a controlled breathing frequency of 0.25 Hz in the standing compared to supine position. The data show that reproducibility of the power spectrum heart rate variability is best achieved at controlled but physiologic respiratory rates and, preferably, in the upright position.

Adult↗
PubMed1987

Heart rate variability power spectrogram as a potential noninvasive signature of cardiac regulatory system response, mechanisms, and disorders.

This paper attempts to provide evidence that the heart rate variability power spectrum (HRVPS) reflects the presence of neural control of cardiac regulation. A normal individual is seen to have a characteristic HRVPS (comprising a 0.1-Hz peak and a respiratory peak at 0.25-0.34 Hz), which is altered in a predictable manner in response to orthostatic stress and exercise, while in two patients with autonomic neuropathy, the HRVPS failed to demonstrate such a characteristic alteration in response to orthostatic stress. Postinfarct HRVPS signatures were studied in two patients with anterior and inferior infarcts so as to lend insight using non-invasive means into both the healing process and the dominant deliterious sympathetic or protective vagal tone due to the infarct. When subjects with transplanted hearts were studied, their HRVPS did not exhibit the characteristic pattern of a normal individual; rather, the HRVPS energy was spread over a wider and higher frequency range. However, one of the transplanted patients surprisingly but consistently revealed the characteristic HRVPS; the post-transplant time at the time of the study was 33 months and the patient had the typically high resting heart rate of a transplant recipient but a wide standard deviation like that of a normal individual. This could be the first noninvasively demonstrated evidence in humans of reinnervation of a transplanted heart. Thus, the HRVPS constitutes a simple non-invasive method to assess cardiac neuroregulatory response and disorders and it is proposed that it be referred to as the heart rate variability cardiogram (HRVC).

Adult↗
PubMed1987

Intrinsic indices of the left ventricle as a blood pump in normal and infarcted left ventricles.

To assess the left ventricle as a blood pump, data are collected from contrast angiograms and analysed by computer, using two-dimensional finite element analysis, to provide instantaneous distributions of intra-LV flow and differential pressure during the diastolic and ejection phases. Characteristic indices are derived for normal and infarcted LVs, and for cases before and after administration of nitroglycerin. These indices may be used to assess the degree and nature of dysfunction in coronary artery disease.

Biomedical Engineering↗
PubMed1985

The 6-minute walk: a new measure of exercise capacity in patients with chronic heart failure.

Cycle and treadmill exercise tests are unsuitable for elderly, frail and severely limited patients with heart failure and may not reflect capacity to undertake day-to-day activities. Walking tests have proved useful as measures of outcome for patients with chronic lung disease. To investigate the potential value of the 6-minute walk as an objective measure of exercise capacity in patients with chronic heart failure, the test was administered six times over 12 weeks to 18 patients with chronic heart failure and 25 with chronic lung disease. The subjects also underwent cycle ergometer testing, and their functional status was evaluated by means of conventional measures. The walking test proved highly acceptable to the patients, and stable, reproducible results were achieved after the first two walks. The results correlated with the conventional measures of functional status and exercise capacity. The authors conclude that the 6-minute walk is a useful measure of functional exercise capacity and a suitable measure of outcome for clinical trials in patients with chronic heart failure.

Aged↗
PubMed1985

The effect of afterload on the cardiodepressor reflex response to coronary artery occlusion in dogs.

The acute hemodynamic responses to anterior and posterior wall ischemia were examined at different afterloads in 30 open-chest anaesthetized dogs. Regional and global left ventricular responses to acute ischemia were also measured before and following bilateral cervical vagotomy in 18 dogs. As the preocclusion afterload (mean aortic pressure) was progressively raised with intravenous methoxamine, a significant decrease in stroke volume occurred following circumflex artery occlusion, whereas no change in stroke volume occurred following occlusion of the left anterior descending artery. Bilateral cervical vagotomy completely inhibited the decrease in stroke volume during circumflex occlusion at high afterload. Vagotomy had no effect on the hemodynamic response to acute anterior wall ischemia. Reversible cold vagal block in paced hearts at high afterload unmasked compensatory inotropy in the nonischemic anterior myocardial segment during circumflex occlusion. Restoring vagal tone by rewarming attenuated the fractional shortening of the nonischemic segment. The results indicate that a relationship exists between myocardial wall tension and reflex cardioinhibition during acute posterior wall but not anterior wall ischemia in dogs.

Animals↗