Characterisation of regional myocardial dynamics during mechanical alternans in heart of anaesthetised pig.

OBJECTIVE: The aim was to investigate the behaviour of regional myocardium during mechanical alternans in a multidirectional manner. METHODS: Mechanical alternans was induced in 12 anaesthetised open chested pigs by rapid atrial pacing. In contrast to previous studies, regional mechanical activity was simultaneously assessed at up to three different sites on the left ventricle using epicardial measuring devices able to provide multidirectional information on segment motion. Pressure-length loops were plotted to assess different patterns of segmental motion. The integral of pressure and length was calculated to obtain a regional work index for each beat. RESULTS: Pressure-length loops revealed profound abnormalities in segment motion and work index during regional mechanical alternans. Myocardial segments either performed alternate amounts of positive work on each beat or alternate amounts of positive and negative work on each beat. Alternating segments contracted out of phase with each other and were occasionally stretched during systole. CONCLUSIONS: The spatio-temporal heterogeneity of regional mechanical behaviour is greatly increased during mechanical alternans.

Mechanically induced changes in action potential duration and left ventricular segment length in acute regional ischaemia in the in situ porcine heart.

OBJECTIVE: The electrophysiological events accompanying early ischaemia are important. The aim of this study was to investigate mechano-electric feedback in acute regional myocardial ischaemia in the intact heart in situ by measuring the change in action potential duration in response to increased ventricular loading imposed by transient aortic occlusion. METHODS: 11 landrace pigs were anaesthetised and their hearts exposed. A pneumatically operated blood pressure clamp was placed around the aorta. Monophasic action potentials and an index of segment motion were recorded from the epicardium in and around the ischaemic area produced by a snare placed around a coronary artery. Ventricular and systemic arterial pressures were measured. An initial aortic clamp was performed during which control recordings were taken. The coronary artery was then tied and the aorta clamped for 5-10 s every 5 min for the duration of the 30 min tie. Recordings were taken from the ischaemic area and non-ischaemic areas. RESULTS: Aortic clamp before ischaemia increased intraventricular diastolic and systolic pressure and reduced action potential duration in all the areas studied (p < 0.001). During acute regional myocardial ischaemia aortic clamping resulted in significantly more shortening of the action potential in the ischaemic area after 10 min of ischaemia than in the control area (5 ms v 10 ms, p = 0.008). Over the following 20 min the degree of shortening decreased. The greater shortening at 10 min could not be attributed to changes in the end diastolic segment length or peak ventricular pressure and could thus represent a change in the expression of mechano-electric feedback by ischaemic myocardium rather than a change in loading conditions. CONCLUSIONS: During the first 30 min following a coronary artery occlusion mechano-electric feedback in the ischaemic myocardium varies with time.

The effects of baclofen on gamma motoneurones supplying gastrocnemius muscle in the rabbit.

The effect of baclofen on gamma motoneurones supplying gastrocnemius medialis muscle in the rabbit has been investigated. Baclofen was found to decrease the frequency of firing of tonic gamma motoneurones, and in some cells to inhibit the tonic discharge altogether. Baclofen also increased the regularity of tonic gamma motoneurone discharge. The drug was found to raise the threshold for firing of gamma motoneurones in response to electrical stimulation of the sural nerve, indicating a depression of reflex transmission between the sural nerve and the motoneurones. The results are discussed and brief consideration given to the possible consequences of these results for the action of the drug in human spasticity.

Core course in leadership and management skills for allied health professionals.

This article describes the two major purposes of a core course for allied health professionals developed at the University of North Carolina. The purposes of the course are to equip practitioners with practical skills necessary for effective management and to bridge the gap between didactic and clinical knowledge. Emphasizing leadership and management skills, the course has four major sections: Current Health Care Issues, Management and Administrative Skills and Issues, Professional Development Skills, and Clinical Education. Classroom formats, student assignments, and relevant readings are suggested, and participant reactions to the course are described.

A minority recruitment and retention model for a Department of Medical Allied Health Professions.

A model for the recruitment and retention of minority students for a department of medical allied health professionals has been developed. The model includes four major components: recruitment, admissions, support systems, and career realization. Suggestions for implementation and coordination of model activities revolve around the services of a minority student advocate whose job description is provided. Specific criteria for evaluation and the time table for implementation of the model are suggested. The model has implications for improving the potential for a positive experience for minority allied health students who apply to and enroll in majority campuses of higher education.

How do skilled nursing rehabilitation managers track efficiency and costs?

Financial and efficiency indicators have not been used extensively by skilled nursing (SNF) rehabilitation managers, but may prove useful in the prospective payment system (PPS)-dominated long-term care (LTC) environment. The purpose of this pilot study was to demonstrate a method for measuring the extent of SNF rehabilitation managers' use of volume, revenue, cost, and manpower indicators; and whether usages differ among occupational, physical, and speech therapy managers. The subjects were 74 occupational, 75 physical, and 72 speech therapy managers employed by a multinational health care corporation. A total of 221 Likert scale surveys were mailed to SNF rehabilitation managers to obtain data on use of 32 efficiency and financial indicators. The 32 indicators were in four categories: visit volume, revenue, costs, and manpower utilization. Twelve indicators were used regularly by at least 60% and three were used regularly by 85-100% of respondents. The response rate was 17.89%. Chi-square analyses were performed for therapy discipline and response frequency. None was significant at 0.05. Three of the payermix indicators demonstrated post-hoc significance in "regular" or "sometimes" use by the physical therapy managers. The results show discipline-specific differences among LTC rehabilitation managers in the extents of efficiency and financial indicator usage for decision making. Suggestions for future use of the survey instrument are provided. The method proved useful for demonstrating differences in the combinations and degrees of use of the 32 indicators. The results point to a need to educate SNF rehabilitation managers in cost-monitoring techniques. Recommendations for cost monitoring are provided.

An audiovisual teaching model of the muscle spindle.

Students in biology and medicine often have difficulty in visualizing the structure, function and disease of complex integrated body systems. One example in neurophysiology is the muscle spindle and Golgi tendon organ. A model is described which demonstrates the properties of these two muscle receptors. The model combines mechanical elements, which can change their length to represent muscle contraction, with an electronic representation of the passage of action potentials along 'nerves', indicated by light-emitting diodes and loudspeakers. The model has been in use for some years as a supplement to conventional teaching methods. In a recent questionnaire about the model, a group of medical students responded favourably. We suggest that models such as this are valuable teaching aids.

Regional electromechanical alternans in anesthetized pig hearts: modulation by mechanoelectric feedback.

Electrical and mechanical alternans have often been found to coexist. However, the factors controlling their interdependence are not known. In this study we measure regional electrical and mechanical activity during mechanical alternans to investigate this relationship. Mechanical alternans was induced by rapid atrial pacing in 18 anesthetized, open-chest pigs. Regional segmental contraction and monophasic action potential were measured in three areas of left ventricle using epicardial tripodal strain gauges and suction electrodes. Electrical alternans always accompanied pulsus alternans. The phase of electrical alternans was not related to any measure of regional mechanical activity but did show a constant discordant relation to peak ventricular pressure. This suggested that mechanically dependent changes in action potential duration (mechanoelectric feedback) may be important in modulation electrical alternans. In support of this, pulsus alternans simulated by clamping the proximal aorta on alternate beats was associated with electrical alternans comparable to that produced with rapid atrial pacing. Mechanoelectric feedback modulates regional electrophysiology in the intact heart and may be important in the generation of electrical alternans.

Regional alternans in relaxation and the onset of pulsus alternans in the heart of the anaesthetized pig.

1. The factors leading to the alternation in myocardial contractility believed primarily responsible for pulsus alternans are not known. We examine regional and global contraction patterns in the in situ heart at stimulation rates just below the threshold for pulsus alternans to determine if events occurring in the transition to alternans can give clues to cellular mechanisms. 2. Twelve pigs were anaesthetized, the chest wall removed and regional contraction measured in three areas of the left ventricle using tripodal strain gauges. We analysed regional and global dynamics during right atrial pacing at cycle lengths 50-150 ms greater than the threshold for pulsus alternans. 3. At pacing cycle lengths 50 ms greater than that required to produce pulsus alternans seven of twelve pigs showed alternans in the maximum rate of ventricular pressure decay but none showed alternans in the maximum rate of pressure rise. Pigs showing alternans in global relaxation were more likely to show alternans in regional contracility (P < 0.05). 4. Twenty-six of the thirty-six areas sampled showed alternans in end-diastolic length at pacing rates below the threshold for pulsus alternans. In fifteen of these areas alternation in end-diastolic length occurred in the absence of alternans in measures of contractility. 5. Alternans in global measures of relaxation may simply be a manifestation of regional alternans in contractility. It is therefore not appropriate, from global haemodynamic data, to suppose that alternans in relaxation is the primary abnormality in the generation of pulsus alternans.(ABSTRACT TRUNCATED AT 250 WORDS)

Contribution to heart rate variability by mechanoelectric feedback. Stretch of the sinoatrial node reduces heart rate variability.

BACKGROUND: Heart rate variability is an important prognostic indicator for sudden death. An increased risk of sudden death and arrhythmia is associated with reduced heart rate variability in heart failure. In heart failure, there is also dilatation of the atria, which raises the prospect that there could be some physiological basis to possibly link heart rate variability with atrial dilatation. We therefore investigated whether sustained atrial stretch could modulate heart rate variability directly. METHODS AND RESULTS: Pigs were anesthetized and their hearts exposed. A specially built device stretched the sinoatrial node before and after vagal section and then after administration of propranolol. Stretch of the sinoatrial node decreases heart rate variability in the following ways: The standard deviation of the beat-to-beat interval decreases (4.2 to 2.6 ms; P = .004), and the high-frequency components are reduced (control, 6.5 +/- 2.2 ms2, during stretch, 1.4 +/- 0.3 ms2, P = .003). After section of both vagi, the high-frequency components are reduced by stretch of the sinoatrial node (2.8 +/- 0.9 ms2 for control versus 1.2 +/- 0.3 ms2 during stretch; P = .05). Similarly, after both vagal section and beta-blockade, stretch of the sinoatrial node reduces the high-frequency components (10.6 +/- 3.5 ms2 for control verses 3.0 +/- 1.5 ms2 during stretch; P = .01). CONCLUSIONS: We conclude that stretch of the sinoatrial node reduces high-frequency heart rate variability. This may account in part for the reduced heart rate variability seen in clinical conditions in which the right atrium is dilated, such as congestive cardiac failure.