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Biomedical subjects

T Farrell

Publications and source records attributed to T Farrell.

At least 73 records · Page 4Linked to original sources
PubMed1991

RR variability and baroreflex sensitivity in patients with ventricular tachycardia associated with normal heart and patients with ischemic heart disease.

Recent studies have suggested that disordered autonomic function, particularly the loss of protective vagal reflexes are associated with an increased incidence of arrhythmic deaths following myocardial infarction (MI). Heart rate variability (HRV) and baroreflex sensitivity (BRS) are measures of myocardial autonomic function and predict arrhythmic deaths post-MI. Patients with ventricular tachycardia associated with a "normal heart" frequently have exercise-induced arrhythmia suggesting that the autonomic nervous system is important in the genesis of this form of ventricular tachycardia (VT). This study examines HRV and BRS in patients with VT associated with a "normal heart" and compares these values to patients post-MI with and without evidence of arrhythmia. Twenty patients with VT associated with a "normal heart," 16 patients with MI but without arrhythmia on follow-up, and 11 patients with MI and VT on follow-up were studied. HRV was measured from 24-hour Holter recordings and BRS was measured from plots of change in systolic blood pressure versus change in heart rate following an intravenous injection of 0.4-0.6 mg phenylephrine. HRV was significantly higher in the patients with VT associated with a normal heart (34.2 +/- 10.8 msec) compared to the patients post-MI, without (23.7 +/- 6.7 msec) and with (14.8 +/- 3.8 msec) arrhythmia (F = 9.2, P less than 0.001) and these differences were unaffected by adjustment for age.(ABSTRACT TRUNCATED AT 250 WORDS)

Autonomic Nervous System↗
PubMed1991

The effect of age on the electrophysiological and autonomic correlates of sudden death after acute myocardial infarction.

To examine the influence of age on the autonomic and electrophysiological correlates of sudden death after myocardial infarction, 223 patients aged less than 60 and 195 patients aged greater than or equal to 60 were followed up for a mena of 790 days. The patients had Holter monitoring and a signal-averaged ECG 5-11 days after infarction. A mean ventricular ectopic beat frequency greater than 10 beats/hour (VE10) was present in 17.0% of young versus 28.2% of old patients (P less than 0.01); a low heart heart variability index in 17.9% of young but in 32.3% of old patients (P less than 0.001) and late potentials in 17.5% but 32% of young and old patients, respectively (P less than 0.01). There was no difference in the incidence of sudden death between young and old patients (3.6% vs 3.1%). However, sudden death accounted for 50%, compared with 24% of all deaths in the young and old groups, respectively (P less than 0.01). Sudden death was more closely associated with low heart rate variability and VE10 in the young than in the older group. The predictive values of a heart rate variability index less than 20 units with VE10 in younger patients were a sensitivity of 50%, a positive predictive accuracy (PPA) of 33% and risk ratio (RR) of 18 (P less than 0.001); these values did not reach significance in older patients (16.7%, 4.3% and 1.4%, respectively.)(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1991

Automatic recognition of ventricular arrhythmias using temporal electrogram analysis.

Future antitachycardia devices must be able to deliver a variety of therapies according to the requirements of the underlying arrhythmia. To ensure that appropriate treatment is prescribed the device must use a detection algorithm that is able to discriminate between multiple arrhythmias. Current criteria such as rate, change of rate, duration at high rate, and high rate stability are inadequate for this purpose. Many algorithms that evaluate the morphology of the endocardial electrogram are of too great a complexity to be incorporated in implantable devices that require real-time analysis without undue power consumption. In this study the sensitivity of a simple morphological technique (temporal electrogram analysis) is examined. The method sets threshold 'rails' above and below the isoelectric line and classifies ECG complexes according to the sequence and duration of rail excursions. A total of 27 ventricular tachyarrhythmias were induced in 25 patients (17 with a history of recurrent arrhythmias and eight undergoing risk stratification postmyocardial infarction). Temporal electrogram analysis (TEA), initially detected the onset of the ventricular arrhythmia in all patients whose surface ECG showed polymorphic or right bundle branch block pattern tachycardia, in 5/8 of cases with left bundle branch block pattern and in 4/5 of patients with concordant complexes across the precordial leads. After minor modifications the overall sensitivity of the method was improved to 95% (26/27 arrhythmias detected). TEA is a technique of low computational demands, which in this study, reliably discriminated between resting sinus rhythm and ventricular arrhythmias.

Adult↗
PubMed1990

Circadian rhythm of heart rate variability after acute myocardial infarction and its influence on the prognostic value of heart rate variability.

This study examined heart rate (HR) variability in patients surviving acute myocardial infarction (AMI) to find the optimum time and duration of recording of the ambulatory electrocardiogram for the prediction of the risk of sudden cardiac death, or serious arrhythmic events, or both. Twenty patients (group I) who initially survived an AMI but later experienced serious events (death or symptomatic sustained ventricular tachycardia) during a 6-month follow-up were compared with 20 patients (group II) who remained free of complications for greater than 6 months after discharge. Groups I and II were matched with regard to age, gender, infarct site, ejection fraction, and beta-blocker treatment. HR variability was assessed in the 24-hour electrocardiograms recorded during the first 2 weeks after an AMI and in various portions of the complete 24-hour recording, with both the beginning and the length of the analyzed portion varied by 20 minutes (a total of 5,113 possibilities). The maximum reduction of HR variability in group I patients was systematically found when assessing HR variability in recordings starting approximately at 6 A.M. and lasting for approximately 8 hours. In the low-risk patient, the diurnal rhythm of HR variability is more marked than in the high-risk patient and the long-term components of HR variability due to the diurnal variation must be included in the measurement of HR variability when using it as a long-term predictor of risk from arrhythmic events after an AMI.

Circadian Rhythm↗
PubMed1989

Long-term spectral analysis of heart rate variability--an algorithm based on segmental frequency distributions of beat-to-beat intervals.

Reduced heart rate variability has been reported as a predictor of long-term mortality in recent myocardial infarction patients. However, it has not been systematically investigated whether the reduction in heart rate variability in those post myocardial infarction patients who later suffer death or severe arrhythmias is caused by a reduction of short-term variability of heart rate (such as respiratory arrhythmia) or whether the differences in long term variability (such as diurnal rhythm) are involved. In order to perform such an evaluation, a new algorithm has been developed which permits different wavelength components (including the long-term components due to diurnal rhythm) of heart rate variability to be approximated. In general, the method uses segmental frequency distributions of durations of intervals between successive normal cardiac beats. To assess the spectral components of heart rate variability, a scale of wavelength limits is used and for each limit of this scale, the algorithm excludes the rate changes of wavelength longer than the given bound. The method was applied to the analysis of electrocardiograms recorded in 14 post myocardial infarction patients who later suffered death or ventricular tachycardia, and in 14 other randomly selected patients with an uncomplicated course following acute myocardial infarction. The rate variability spectra obtained for both groups of patients were compared statistically and the results showed that the groups of positive and negative cases were most significantly distinguished when including both short- and long-term components of heart rate variability. Separate evaluation of different wavelength components showed that the very long-term components of heart rate variability were more powerful in distinguishing between positive and negative cases than the short term components.

Algorithms↗
PubMed1989

Heart rate variability in relation to prognosis after myocardial infarction: selection of optimal processing techniques.

Automatic analysis of heart rate variability from Holter recordings may be invalidated by beat recognition errors and recording artefact, necessitating filtering and editing of the computer-recognized RR interval sequence. Two new methods for heart rate variability analysis have been developed, based on an estimation of the width of the main peak of the frequency distribution curve of the computer-recognized normal-to-normal beat sequence. These methods are independent of a low level of recognition error and artefact, thus removing the need for operator-dependent, time-consuming editing. The value of the new methods (heart variability indices 1 and 2) in identifying patients with serious events (death and symptomatic, sustained documented ventricular tachycardia) during a 6-month follow-up after acute myocardial infarction was assessed in a case-control study comparing 20 patients who had experienced such events (Group I) with 20 patients who, following admission with acute myocardial infarction, had remained free of complications for greater than 6 months after discharge (Group II). Group II was selected to match Group I with regard to age, sex, infarct site, ejection fraction, and beta-blocker treatment. Analysis of the unfiltered computer-recognized normal-to-normal interval sequence showed that heart rate variability indices 1 and 2 were significantly lower (P less than 0.005, P less than 0.002) in those who had experienced events compared with those free from complications. Two other methods of expressing heart rate variability, including the standard deviation method, in combination with four different data-filtering techniques, gave less significant distinction between those with and without events during follow-up. It is concluded that using the methods described, reduced heart rate variability in patients at risk from death or sustained ventricular tachycardia after acute myocardial infarction can be detected automatically from unfiltered Holter tape recordings even in the presence of a low level of beat recognition error and recording artefact.

Aged↗
PubMed1988

Abdominal pain.

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Abdomen↗
PubMed1984

Vocational training.

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Costs and Cost Analysis↗
PubMed1984

Awareness of the response after feedback training for changes in heart rate and sudomotor laterality.

What is the relation between the ability to control visceral responding on a biofeedback task and the ability to report behaviors actually contributing to this performance? Subjects received biofeedback training for unidentified visceral responses and then gave written reports about what they had done to control the feedback displays. Independent judges were given these reports and, on the basis of knowledge about activities known to contribute to visceral activity, were asked to determine the visceral responses for which the subjects had been trained. The reports of subjects who succeeded at bidirectional control of heart rate (Experiment 1) or sudomotor laterality (Experiment 2) showed awareness of behaviors related to feedback as assessed by this procedure, whereas the reports of subjects who failed at bidirectional control did not. Subsequent experiments indicated that these results did not depend on a learning strategy that might have been specific to the initial studies. These findings call into question the view that people are unaware of what they have done to produce the response after training on biofeedback tasks. Earlier studies reporting lack of awareness in biofeedback are discussed in light of factors that affect the measurement of biofeedback learning and response awareness.

Adolescent↗
PubMed1982

Drill and fill.

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Dental Care↗
PubMed1982

Potential pitfalls in the evaluation of the usefulness of hemodialysis for the removal of lithium.

A 50-year old female who was comatose from an overdose of lithium was treated with hemodialysis. Serum lithium concentrations declined 47% during a 3-h hemodialysis but increased afterwards, peaking 8 h after hemodialysis was stopped. Hemodialysis clearances were estimated by equations using extraction ratios of lithium from whole blood, serum, and red cells, and flows of whole blood, serum or red cells. The amount of lithium removed was calculated from these clearances as well as measured directly in the dialysate. Errors were introduced into the calculation of the amount of lithium removed by hemodialysis unless whole blood concentrations of lithium and whole blood flows were used. These arose because extraction of lithium from serum (0.7 +/- 0.3, mean +/- SD) was greater than that from whole blood (0.49 +/- 0.06) or from red blood cells (0.18 +/- 0.12). Despite the rapid decrease in serum concentrations of lithium during hemodialysis and rebound afterwards, the patient's neurologic status did not change concurrently. The patient did not regain consciousness until lithium concentrations fell to less than 0.4 meq/L in serum and 0.1 meq/L in cerebrospinal fluid. The lack of parallel change in serum concentrations and coma probably reflects the lag time in equilibration between lithium concentrations in serum and brain.

Female↗
PubMed1978

Functional classification of undernourished populations in the Republic of El Salvador. Methodological development.

Typical government nutrition programmes usually lack precise information on the size of groups that could benefit from interventions, on the different types of potential beneficiaries and their location, and on socio-economic and cultural characteristics through which they could readily be identified. In the functional classification approach to the definition of nutritional problems, detailed information on human behaviour and social constraints is collected at family and community levels. The data are then interpreted in general terms in order to understand how these factors contribute to inadequate levels of nutrition within larger groups. This new approach should enable more effective measures for reducing the numbers of those living under conditions of deprivation to be presented to planners and decision makers.

El Salvador↗