Biomedical subjects
Publications and source records attributed to M A Tooley.
MultiMed is a telemedicine and tele-education project to extend access to a sophisticated medical simulation facility in Bristol. It will allow remote users to undertake simulated medical scenarios and to access a reference database, for a comprehensive remote learning experience. The first phase will focus on the area of anaesthesia and all remote users will be based in the UK.
A randomized double-blind study was carried out on 20 patients after coronary artery bypass surgery to investigate the effects of graded doses of dopexamine hydrochloride or placebo on systemic haemodynamic responses and renal vascular resistance index (RVRI) measured using Doppler ultrasound. Pre-operatively, all patients had good left ventricular function and normal renal function. Eleven were allocated randomly to receive incremental infusions of dopexamine 0.5, 1, 2, and 4 micrograms kg-1 min-1 for 40 min each, and nine received corresponding infusions of placebo. One patient was withdrawn from the dopexamine group because of tachycardia. In the remaining 19, heart rate (HR) and cardiac index (CI) were significantly (P < 0.05) increased from base-line with dopexamine: the HR values with dopexamine differed significantly from those with placebo at the 2 and 4 micrograms kg-1 min-1 dose and at 4 micrograms kg-1 min-1 for CI. Systemic vascular resistance index (SVRI) fell significantly in both groups: the reduction was significantly greater with dopexamine 4 micrograms kg-1 min-1 than with the corresponding infusion of placebo. RVRI increased and urine output decreased significantly during the infusions in both groups, but with no significant difference between groups. There were no changes in systemic arterial pressures, pulmonary artery occlusion pressures, stroke volume index or left ventricular stroke work index. Where changes from base-line occurred in either group, they had not returned to base-line within 40 min of stopping the infusions (except perhaps for CI in the dopexamine group). Dopexamine appears to offer no particular protection to the renal vascular bed.
We have studied the effects of propofol, as the sole agent, at blood concentrations of 1-10 micrograms ml-1, on the first 100 ms of the auditory evoked response (AER) in 41 women before gynaecological surgery. AER were recorded with the patients awake and then after 30 min of one of seven stepped infusion regimens. Each patient was studied at only one blood concentration. The recordings were edited and processed off-line by coherent signal averaging, to obtain reliable estimates of each AER. We measured standard features, such as amplitudes and latencies of brainstem wave V and the mid-latency waves Na, Pa and Nb. In addition, we studied several composite indices, intended to give a more global characterization of the AER. We derived relationships between the doses and blood concentrations of propofol, features of the AER and response to eyelash stimulus and venepuncture. Nb latency was better than either concentration or dose rate of propofol in providing a confident explanation of the likelihood of eyelash response (which parallels the response to command). A cut-off value of 53 ms had a sensitivity of 100%, a specificity of 96% and an overall correctness of 98% as a discriminator of eyelash response vs no response. Several alternative AER-derived indices provided more than 90% correctness in discrimination, as did a dose rate of propofol of 6.3-7.8 mg kg-1 h-1 or a blood concentration of 2.9 micrograms ml-1. We conclude that the concentration and dose of propofol were good discriminators of response to venepuncture, while the latency of the Na wave was the most successful of the AER features.
All patients discharged from a general intensive care unit over a 4.5 year period were sent a questionnaire 3 months after discharge which investigated aspects of their health and physical abilities. Replies were compared on the basis of age, diagnosis and sickness severity on admission. Five hundred and four questionnaires were analysed. Overall, 47% of patients described their health as good/very good, 42% as fair and 11% as poor/very poor. Activity level, compared to that before their admission, was unchanged in 59%, worse in 33% and improved in 8% of patients. There were no differences in health status or changes in activity with age, diagnosis or severity of sickness. Patients aged 76 years or older were more likely to perceive their health as 'better than average' than younger patients (p < 0.01). Eight percent of patients would be unwilling to undergo intensive care again. An unacceptable health status after intensive care cannot be predicted in any group of patients.
We have used Median Power Frequency (MPF) to study changes in the electroencephalogram during propofol infusions in 52 women about to undergo gynaecological surgery. Patients were allocated to receive propofol by one of nine different manually-controlled infusion schemes designed to achieve and maintain a stable blood propofol concentration between 1.0 and 6.0 micrograms ml-1, covering a range of states between conscious sedation and full anaesthesia. We recorded the changes in MPF and the response to clinical signs of loss of consciousness at these different doses and concentrations of propofol. Using probit analysis, we derived MPF values corresponding to 50% and 95% suppression of response to verbal (9.3 Hz and 6.8 Hz), eyelash (8.9 Hz and 6.7 Hz) and venepuncture (5.7 Hz and 3.0 Hz) stimuli. Likewise, we obtained dose and concentration requirements for propofol to suppress these stimuli. The mean (95% confidence intervals) ED50 (5.8 (3.5-6.8) mg kg-1 h-1) and ED95 (8.3 (7.1-16.9) mg kg-1 h-1) propofol doses for suppression of consciousness were similar to the values for suppression of the eyelash reflex (6.2 (5.3-6.8) mg kg-1 h-1 and 8.6 (7.8-10.8) mg kg-1 h-1, respectively). The EC50 for loss of consciousness was a propofol concentration of 2.3 (1.8-2.7) micrograms ml-1 and for 50% suppression of MPF was 3.1 (2.7-3.5) micrograms ml-1. The dose required for 50% suppression of MPF was 7.1 (6.2-8.0) mg kg-1 h-1. After 30 min, at blood propofol concentrations > 4.0 micrograms ml-1, consistent with stable anaesthesia, the mean MPF was 5.6 (4.5-6.3) Hz.
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In this paper we present a detailed analysis of the use of the APACHE II (acute physiological and chronic health evaluation) scoring system on all of the patients admitted to the general intensive care unit at the Bristol Royal Infirmary over a 20-month period. The 6-month survival of 691 adult medical and surgical patients following intensive care was recorded and this data was analysed with admission and daily APACHE II scores using a relational database. Our data confirms the relationship between admission APACHE II scores and outcome, with mean scores decreasing as duration of survival increases. We also demonstrate that the best day one scores are approximately 50% less than the admission score, irrespective of outcome, indicating the benefit of intensive care. By contrast, however, the scores on day one have either not improved or have worsened since admission, reflecting the importance of the pre-morbid health status of the patient in determining outcome from intensive care.
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New implantable devices are now available that can offer different therapies for different arrhythmias but they need a method of discriminating between these rhythms. Heart rate analysis is predominantly used to discern between sinus rhythm (SR) and pathological tachycardias but this may be of limited value when the rates of the rhythms are similar. An enhanced form of Gradient Pattern Detection (GPD) has been developed using an 8-bit microcomputer that can distinguish between SR and up to three other arrhythmias in real time. This is a method based on electrogram morphology where each rhythm's specific electrogram is classified by a sequence of gradient 'zones'. The microprocessor of the computer is of similar processing power to ones used in current pacemakers. Five patients with multiple arrhythmias were studied. Four had ventricular tachycardia (VT) and one had three conduction patterns during supraventricular tachycardia (SVT). Bipolar endocardial right ventricular electrograms were recorded during SR and tachycardia in all patients. The computer would first 'learn' about each different rhythm by a semi-automatic means. Once all the rhythms were learned the program would enter the GPD analysis phase. The computer would output a series of real-time rhythm specific marker codes onto a chart recorder as it recognized each rhythm. Sixteen different arrhythmias (13 VT, 3 SVT) were examined for this study. All rhythms (including SR) were distinguished from each other except in the case of one patient with six VTs where two VTs had identical shapes and therefore could not be detected apart. The method would be a useful addition to heart rate analysis for future generations of microprocessor assisted pacemakers.
Pacemaker recognition of pathological tachycardia relies on heart rate analysis. This can lead to misdiagnosis when sinus tachycardia exceeds the preset tachycardia response trigger rate. We have explored a method for automatic tachycardia diagnosis by analysis of bipolar endocardial electrogram morphology. Electrograms were recorded from 11 patients (pts) during sinus rhythm and during a total of 20 abnormal rhythms: retrograde atrial depolarization from ventricular pacing in six patients; atrioventricular reentry tachycardia in five patients with intermittent left bundle branch block in one of those; AV nodal reentry tachycardia in five patients and ventricular tachycardia in three patients. Posture and respiration were varied during all rhythms except ventricular tachycardia. The electrograms were then digitized and converted to a form in which the amplitudes were proportional to the rates of change of the original electrogram (equivalent to a first time derivative); the derived signal was then analyzed by a new gradient pattern detection (GPD) program. Analysis of the processed atrial signals by GPD resulted in automatic recognition of abnormal rhythms from sinus rhythm in all cases except for one patient's retrograde atrial depolarization. At the ventricular level, GPD successfully distinguished all abnormal rhythms from sinus rhythm including recognition of left bundle branch block and varying degrees of preexcitation. Respiratory and postural variation did not affect the recognition process. We conclude that electrogram GPD has successfully and automatically detected a variety of arrhythmias which can be treated by implantable pulse generators and may, therefore, be a useful adjunct to heart rate analysis in future generations of such antitachycardia pacemakers.
An instrument for monitoring the frequency components contained in the electroencephalogram is described. The technique uses the fast Fourier transform which is implemented in a microprocessor controlled 'black box'. The control and display of the data are organised by a conventional microcomputer. The system is designed for use by practising anaesthetists in a district general hospital environment and is, therefore, inexpensive and simple to operate. The operation of the equipment is described and some limited results from early clinical trials are presented.
A microcomputer system for the measurement of parameters of ventilation and blood pressure in the spontaneously breathing anaesthetized patient is described. The system continuously calculates minute volume, respiratory frequency, and mean end tidal carbon dioxide concentration. Additionally four cardiovascular parameters are measured. The inputs are obtained from a wet-wedge spirometer, a capnograph and a blood pressure monitor. The methods of computer calculation are described in detail. The computer-generated results are compared with those obtained by manual calculation. The system described has the capacity to record and display a wide variety of further measurements made during anaesthesia. This system provides invaluable information for research and teaching, but may also be useful during routine anaesthesia.