Browsing by Author "Poluta, Mladen"

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    Open Access
    Assessment of catheter-manometer systems used for invasive blood pressure measurement
    (1989) Heimann, P A; Murray, W B; Boonzaier, David; Murray, PW le Roux; Poluta, Mladen
    Direct measurement of blood pressure using a fluid-filled catheter and an electromechanical transducer is widely accepted in clinical practice. However, errors associated with the measurement are often not appreciated and these catheter-manometer systems are frequently unable to accurately reproduce applied pressures. To assess the accuracy of catheter-manometer systems used for invasive arterial blood pressure measurements, in vitro and in vivo evaluations were performed. The frequency response (described in terms of damped natural frequency and damping factor) for a variety of cannulae, pressure tubing and stopcocks (and combinations thereof) and their dependence on various parameters (catheter length, lumen diameter, fluid temperature and catheter material) were measured using an hydraulic pressure generator. The design and construction details of the pressure generator are presented. It was found that the damped natural frequency of the catheter-manometer system is directly proportional to lumen diameter of the pressure tubing/catheter. Furthermore, damping factor is inversely related to the damped natural frequency and stiffer catheter material (for identical radius ratios) results in higher damped natural frequency. Catheter length is inversely related to damped natural frequency and the resonant frequency decreases for an increase in fluid operating temperature. It was established that all catheter-manometer systems tested were under-damped (0.15 < β < 0.37) and that the damped natural frequency ranged from 10.5 Hz for 1500 mm to 27.0 Hz for pressure tubing of 300 mm in length. Furthermore, catheter-manometer systems which had pressure tubing in excess of 300 mm in length did not comply with the bandwidth requirements for accurate dynamic blood pressure measurement. For the in vivo assessment of the catheter-manometer system, the blood pressure waveform was analysed in the time and frequency domains. It was established that in 60 percent of the cases, the systolic pressure peak was higher when measured by a narrow bandwidth catheter-manometer system compared to that measured by a wide bandwidth system. Furthermore, values of dp/dt maximum were lower for wide bandwidth catheter-manometer systems than those measured by narrow bandwidth systems for heart rates above 90 beats per minute. In the frequency domain analysis, artifact was sometimes found to occur at frequencies higher than the bandwidth of the catheter-manometer system. This high frequency artifact was found to distort the blood pressure waveform and resulted in false high dp/dt and peak systolic pressures.
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    Computer assisted audiometric evaluation system
    (1991) Weiss, Martin; Poluta, Mladen
    A computer-based audiometric evaluation system has been developed. The system makes use of an IBM PC/XT/AT compatible personal computer to perform pure tone and speech tests and · comprises a plug-in card and custom software. The card contains pure tone and masking noise generators, together with amplifiers for a. set of headphones .and bone conduction transducer, patient and audiologist microphone amplifiers and a hand-held infra-red remote-control unit. A voice-operated gain-adjusting device on the audiologist's microphone eliminates the need for a sound pressure level meter during speech tests. The software-based user-interface makes use.of overlaid pop-up menus, context sensitive assistance.and a text editor on a graphics screen. Pure tone and speech data are acquired and displayed on a dynamic audiogram and speech discrimination gram respectively. This data may be stored and later retrieved from a patient data base. Further audiometric tests may be incorporated at a later stage.
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    The development of a neonatal vital signs database
    (1992) Berelowitz, Jonathan; Poluta, Mladen; Woods, David R; Van der Elst, Clive; Mann, Michael D
    Modern intelligent monitoring systems use digital computer technology to analyze and evaluate physiological vital signs. This analytical and evaluative process is performed by algorithms developed for this purpose. The degree of 'intelligence' of the monitoring system is dependent on the 'sensitivity' and 'specificity' of these algorithms. In order to develop robust and clinically valid algorithms, a database of representative waveforms is required. The aim of this thesis was to create a neonatal vital signs database to be used for this purpose, by means of a computer-based central station. The computer was interfaced to a number of neonatal monitors (Neonatal ICU, Groote Schuur Hospital). The monitors were interrogated to obtain patient condition, ECG waveforms and respiration waveforms using the impedance technique. When possible, percentage oxygen saturation was also captured. The database contains 509 documented clinical records obtained from 35 patients and 20 records containing examples of technical alarm conditions and high frequency noise. Additional patient record data is included. Clinical events recorded include apnoea, bradycardia, periodic breathing tachycardia, tachypnoea and normal traces. These events were recorded against a variety of signal quality conditions that have been characterized in Appendix C. A prototype rate detection algorithm was checked using samples from the database.
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    An investigation into turbine ventilators as a potential environmental control measure to minimise the risk of transmission of tuberculosis - a laboratory and field study
    (2014) Salie, Faatiema; Poluta, Mladen
    TB is an airborne infectious disease which is spread by droplet nuclei, carrying Mycobacterium tuberculosis, in the air. The droplet nuclei small enough to enter human respiratory pathways are 1-5 μm in size and are able to travel long distances (Hodgson, et al., 2009) (WHO, 1999), and can be distributed widely throughout (hospital) buildings (Beggs, Noakes, Sleigh, Fletcher, & Siddiqi, 2003). These droplet nuclei may remain suspended in the air until they are removed by dilution ventilation or other disinfection methods (Parsons, Hussey, Abbott, & de Jager, 2008) (National Department of Health, 2007). Dilution ventilation refers to the dilution of contaminated air with “clean” air (ACGIH, 2005), thereby reducing the concentration of contaminants in the room. One of the recognised approaches for minimising the risk of transmission of TB is to adequately ventilate the contaminated room/space. A higher ventilation rate can provide higher dilution capability, in turn reducing the risk of airborne infections (WHO, 2009). The parameters of concern in ventilation design are ventilation flow rate and airflow pattern in the room (and building). The former reduces contaminant concentration while the latter aims to move uncontaminated air to high risk areas, and contaminated air away from occupied areas, usually to the outside. The shortcomings of conventional natural ventilation strategies are well documented. The aim of this research project is to review and study the effectiveness of natural ventilation design supplemented by a turbine ventilator. The project was divided into two components: a field study and laboratory experiments. In the field study, a turbine ventilator was installed into a bedroom of a low-income house in Pretoria. Tracer gas (concentration decay) tests were performed to determine the ventilation flow rates, mean age of air and air change efficiency of four natural ventilation configurations. These included infiltration/leakage (IL), two cases of single-sided ventilation (SS1 and SS2), and crossventilation (CV). Three baseline (without the turbine ventilator) and three turbine ventilator tests were performed, one each in the morning, noon and afternoon. The tests were performed between February and April 2011 on typical summer days. The turbine ventilator was then tested in a laboratory environment under wind, buoyancy and a combination of wind and buoyancy forces. The wind speeds were low, ranging from 0.0 to 0.5 m/s (0.0 to 1.8 km/h), and the temperature differential tested was in the range of 5.5 to 9.3˚C. The in-duct velocities and centreline velocities were investigated to establish if, under the subjected force(s), a capture envelope described by Dalla Valle’s equation could be measured. This envelope would be used to determine if the turbine ventilator could potentially reduce the concentration of airborne contaminants in the test volume. In the field study baseline tests, IL, SS1, CV and SS2 mean – and range of - ventilation flow rates of 0.6 [0.5 – 0.6], 8.1 [6.8 – 9.3], 16.9 [14.7 – 19.0] and 7.4 [7.0 – 7.9] ACH, respectively, were reported. The baseline tests highlight the potential of cross-ventilation where, by simply opening windows and doors, a ventilation rate exceeding IPC recommendations was obtained. All configurations, save An investigation into turbine venti lators as a potential environmental co ntrol measur e to minimise the risk of transmission on TB Page IV SS1, appear to have approached the fully-mixed case.SS1 also showed the greatest variability in ventilation flow rates. This finding is not unexpected, as air exchange in single-sided ventilation is due to wind pressure fluctuations, which varied across each test. In addition, in all tests it was found that the ventilation flow rate was dependant on the natural ventilation configuration and openable area, and not necessarily environmental conditions. In the turbine ventilator tests, the mean ventilation flow rates for IL, SS1, CV and SS2 were 1.8 [1.6 – 2.1], 5.4 [5.2 – 5.7], 17.7 [16.0 – 18.6] and 9.5 [8.5 – 10.1] ACH, respectively. The mean ventilation flow rate increased in IL and SS2 with the installation of the turbine ventilator, while in SS1 a decrease was reported. The increase in ventilation flow rate in IL was found to be due to natural convection, where the turbine ventilator merely facilitated the exhaustion of warm air. The results of the field study are specific to the environmental conditions at the time of the test, and are not generalizable. In the laboratory experiments, the in-duct velocity increased with an increase in wind speed and temperature differential. For a given temperature differential, an increase in wind speed resulted in a decrease in in-duct velocity. Across all tests, no centreline velocity profile, described by the Dalla Valle equation, could be measured. In the wind speed tests, no capture envelope could be established. This was due to the low wind speed test range, where the resulting centreline velocity was beyond the limit of detection of the thin-film sensors. In the buoyancy forces test, a turbulent region near the base of the turbine ventilator was realised, where the magnitude and direction of the air flowing at 1.5D continuously changed. This turbulent region was again observed in the combined wind and buoyancy forces tests, though the magnitude was smaller and occurrence less frequent. The results of the laboratory experiments are specific to the parameters tested, and are not generalizable. By correlating the field study, laboratory experiments, and previous (similar) studies, it was concluded, that, under the tested conditions, adding a turbine ventilator as a supplement to natural ventilation system will not reduce the concentration of contaminants in the occupied zone in a room.
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    A multi-channel system for use in cardiac electrophysiologic studies
    (1991) Wyatt, Barry Neil; Poluta, Mladen; Millar, Rob Scott
    The location of accessory pathways in Wolff-Parkinson-White syndrome patients is performed manually during open heart surgery at Groote Schuur Hospital, using a hand-held roving electrode. This manual procedure is slow and tedious, prolonging the operation and the time for which the patient remains on cardiac bypass. A multichannel electrogram acquisition and display system with a storage facility would significantly reduce the time taken and improve the reliability of locating the accessory pathways. Having considered a number of currently available cardiac mapping systems it was decided that a new system be developed for specific application within Groote Schuur Hospital. The main design goals of this system are to improve accuracy, increase reliability and enhance the speed of the entire mapping procedure with direct benefit to staff and patients. The system is based on an IBM compatible computer and allows for the acquisition of a maximum of thirty-two electrogram inputs. A typical configuration would acquire twenty epicardial, two references (one each from atrium and ventricle), one roving electrode and two surface lead signals. The epicardial signals are obtained from a custom-built electrode belt which is placed around the heart over the atrioventricular groove. The project includes the development of front-end hardware and software for processing, display and storage of electrogram signals. The relative activation times of the signals are displayed under software control in order to facilitate the location of any accessory pathway(s).
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    Performance and sustainability indicators for Clinical Engineering Services
    (2002) Ngara, Rutendo L; Poluta, Mladen
    In support of the focus on improved performance of health systems¹ this study forms part of an on-going project aimed at establishing indicators for the performance and sustainability of Clinical Engineering Services², as an integral part of cost-effective healthcare service delivery. The study itself develops a working framework for achieving the objectives ofthe project. The general function of a Clinical Engineering Service is to provide a supportive role in the planning, evaluation, procurement, installation, utilisation and maintenance of medical devices (defined as including all medical/surgical devices, equipment and instruments). However, the boundaries of these support roles are not clear and welldefined, as what applies to one country or institution does not necessarily apply to another. Also, a clinical engineering service can range from one isolated but dedicated individual to a fully equipped department with professional and technical/artisan staff, supported by adequate technological and administrative infrastructures, to a shared regional/central resource centre.
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    Ventilation in minibus taxis as a means of airborne infection control
    (2018) Matose, Munyaradzi T; Poluta, Mladen; Douglas, Tania
    Airborne infection control (AIC) measures are used extensively in healthcare settings to curtail the spread of airborne infectious diseases; these measures include administrative, architectural, engineering (e.g. ventilation) and personal protective interventions, serving either to reduce the concentration of airborne infectious particles or to protect individuals from direct exposure to airborne infection. Few such measures are applied in public congregate spaces outside of health facilities, such as those associated with public transport. Limited literature is available on existing AIC measures in the context of public transport modalities. This study explores the role of ventilation as an AIC measure in minibus taxis in Cape Town, South Africa, to determine its potential role in reducing airborne infectious disease transmission. The minibus taxi model chosen for the study was the Toyota Quantum Ses’fikile, which is commonly used in the Cape Town metropole. The Ses’fikile taxi has 6 windows, 2 at the front, 2 in line with the main passenger door and 2 towards the rear of the taxi. Ultrasonic anemometers were placed at key positions throughout the taxi-interior to measure and log airflow patterns, under different widow-open/close configurations and at different taxi speeds. To determine ventilation rates, the configurations were tested in an occupied taxi, with occupants comprising the driver, a researcher, and 14 volunteer participants. This study analysed TB transmission risk using the Issarow equation, a dose-response model. Airflows created by different window configurations produced patterns in airflow direction and velocity. A linear regression model fit to the ventilation data revealed that increasing taxi speed increased ventilation. Ventilation rates were found to depend on interior airflow as a result of the window configuration, as well as on the number of open windows, although the ventilation rate was not highest with the highest number of open windows. The best ventilation rates were found with four open windows, which included the front windows on both sides of the vehicle, and either the middle windows on both sides or the rear windows on both sides. The ventilation rates produced by these configurations at all tested taxi speeds (40 km/h, 80 km/h and 100 km/h) ranged from 108 to 316 L/s and exceeded the World Health Organization recommendation for new healthcare facilities, airborne precaution rooms, and general wards and outpatient departments. TB transmission probabilities in a taxi were dependent on ventilation, occupancy, number of infectors and duration of exposure. The risk of transmission was shown to increase substantially when ventilation rates fell below 50 L/s. In conclusion, minibus taxis were found to provide an effective range of ventilation rates that reduce the risk of TB transmission at varying speeds, however when natural ventilation is not used and with typical high occupancies, the risk posed to all occupants is high. Alternative AIC interventions may have to be considered.