Biomedical subjects

A E Marble

Publications and source records attributed to A E Marble.

At least 19 recordsLinked to original sources

PubMed1992

Image processing system for interpreting motion in American Sign Language.

In this paper, an image processing algorithm is presented for the interpretation of the American Sign Language (ASL), which is one of the sign languages used by the majority of the deaf community. The process involves detection of hand motion, tracking the hand location based on the motion and classification of signs using adaptive clustering of stop positions, simple shape of the trajectory, and matching of the hand shape at the stop position.

Algorithms↗

PubMed1992

Correlation algorithm and sampling techniques for estimating the signal-to-noise ratio of the electrocardiogram.

An algorithm, based on correlation techniques, is proposed for estimating the signal-to-noise ratio of very low frequency signals contaminated by white and flicker noise. Sampling techniques based on converting a single continuous signal into two time series that satisfy the requirements of cross-correlation functions are proposed. The algorithm has been tested on simulated data and the electrocardiogram transduced from ten patients.

Algorithms↗

PubMed1992

Myocardial oxygen consumption and lactate production during antegrade warm blood cardioplegia.

UNLABELLED: Continuous warm blood cardioplegia has recently been recommended as an alternative to multidose cold blood cardioplegia for myocardial protection during coronary bypass operations. Cardioplegia may have to be interrupted in order to provide a bloodless operating field during coronary anastomosis. To determine the effects of ischemia at normothermia on myocardial oxygen consumption and lactate production we randomized 17 dogs to receive either warm blood cardioplegia (37 degrees C) or cold blood cardioplegia combined with systemic and topical cooling. After initiating arrest, cardioplegia was interrupted for periods of 1, 2, 3, 4, 5, 6, and 10 min. Myocardial oxygen debt occurred after 3.5 min of ischemia in the 9 animals receiving warm blood cardioplegia. In contrast, myocardial oxygen consumption never exceeded oxygen availability during cold blood cardioplegia (P less than 0.001). Lactate production increased linearly in both groups but was much greater in those animals receiving warm blood cardioplegia (P less than 0.001). Spontaneous electromechanical activity was much more common during warm blood cardioplegia which required frequent infusions of cardioplegia to maintain cardiac arrest (P less than 0.0003). CONCLUSIONS: (1) Oxygen debt occurred after 3.5 min of warm ischemia; (2) spontaneous electromechanical activity is more common during warm heart protection which necessitates the use of larger volumes of cardioplegia to maintain cardiac arrest.

Animals↗

PubMed1991

Oxygenated cardioplegia ameliorates the adverse effects of small amplitude electrical recording of activity on myocardial metabolic and functional recovery.

UNLABELLED: Small amplitude electrical activity has been recorded from the myocardium during cardioplegic arrest in the absence of electromechanical activity. The presence of persistent electrical activity has been associated with impaired myocardial metabolic and functional recovery. To determine whether or not oxygenated cardioplegia would provide sufficient oxygen to support the increased metabolic activity associated with persistent electrical activity during cardioplegic arrest, we randomized 14 adult mongrel dogs to receive either non-oxygenated or oxygenated cardioplegia during 90 min of ischaemia. Cardiac index (CI), left ventricular stroke work index (LVSWI) and dp/dt were measured before bypass and after 90 min of ischaemia and 45 min of reperfusion. Myocardial oxygen consumption (MVO2) and lactate extraction were measured before and after bypass. Intramyocardial voltage was monitored during cardioplegic arrest, and MVO2 was measured during cardioplegia infusion. The onset of small amplitude electrical activity was associated with a rise in intramyocardial voltage and an increase in MVO2. CI, LVSWI and dp/dt were better preserved in those animals receiving oxygenated cardioplegia. MVO2 and lactate consumption following cardioplegia arrest were also higher in this group. CONCLUSIONS: (1) small amplitude electrical activity during cardioplegic arrest is associated with a rise in MVO2. (2) Oxygenated cardioplegia increases myocardial protection by providing oxygen for the increased metabolic activity associated with the presence of this small amplitude electrical activity.

Animals↗

PubMed1991

Effect of high-volume cardioplegia on small-amplitude electrical activity during cardioplegia arrest.

UNLABELLED: The effects of high-volume cardioplegia on the presence of small-amplitude electrical activity during cardioplegia arrest were investigated in 19 mongrel dogs. The animals were randomly assigned to receive either high-volume crystalloid cardioplegia (HV-plege) or crystalloid cardioplegia guided by continuous electrical monitoring (V-plege). Cardiac index, left ventricular stroke work index dp/dt, and myocardial oxygen consumption were measured before bypass and following 90 min ischemia and 45 min reperfusion. Biopsies were taken for measurement of adenosine triphosphate (ATP) and examination of myocardial ultrastructure. Nine animals received HV-plege, while the remaining 10 animals received cardioplegia guided by voltage criteria. Small-amplitude electrical potentials were recorded within 10-15 min after the infusion of cardioplegia in all animals receiving cardioplegia guided by voltage criteria. Electrical activity, however, was immediately abolished by reinfusion of cardioplegia. HV-plege reduced the incidence of small-amplitude electrical activity during cardioplegia arrest but did not prevent electrical activity. Left ventricular function and myocardial ultrastructure were better preserved when cardioplegia was guided by electrical monitoring. ATP decreased similarly in both groups following cardioplegic arrest, but myocardial oxygen consumption was significantly higher following the arrest in the V-plege group. CONCLUSIONS: HV-plege does not prevent small-amplitude electrical activity and may have adverse effects on myocardial metabolic and functional recovery.

Adenosine Triphosphate↗

PubMed1990

Theoretical model for assessing haemodynamics in arterial networks which include bypass grafts.

The paper presents a theoretical model which can be used to simulate a vascular network which includes loops and bypass grafts, a feature not possible with previous models. Using the linearised Navier-Stokes equations, the linearised equation of a uniform thick-walled viscoelastic tube, and the equation of continuity, the model is applied to a vascular network which includes a bypass graft. This method represents each segment of an artery or graft by a four-terminal-network whose A, B, C, D parameters are functions of the frequency and physical characteristics of the segment. The model predicts the flow and pressure waveforms at any point in the human arterial network very accurately when compared with data obtained from normal patients, patients with arterial stenoses and for hypertensive patients. The model also gives results which are in close agreement with hydraulic experimental data for the input impedance of systems with bypass loops.

Arteries↗

PubMed1990

An adaptive "Wiener" filter for estimating the time-derivative of the left ventricular pressure signal.

This communication presents the development of an optimal digital differentiating filter based on the Wiener theory for estimating the peak derivative of the left ventricular pressure (LVP) signal. The magnitude coherence function is used to estimate the signal and noise spectra. The peak derivative obtained by this method is found to be within 2% of the results obtained by a seven-point second-order data fit and a DFT technique.

Algorithms↗

PubMed1990

A miniature voltmeter for monitoring small amplitude electrical activity in the hypothermic arrested myocardium.

A measurement system which is capable of detecting microfibrillation in the hypothermic, arrested heart has been developed. It is shown that this system can reliably measure microfibrillation signals as low as 10 microV in amplitude. Using this system, it has been shown that even after the heart has been rendered visibly arrested using cold potassium, it may still be producing a low level of electrical activity. It has also been shown that the presence of this microfibrillation during the period of the cold potassium administration and visible arrest, is very highly correlated with the decrease in high energy phosphates (ATP), mitochondrial injury, and a decreased cardiac function post-operatively. Using the information obtained from this first measurement system, a miniature, battery powered voltmeter has been designed and fabricated. This voltmeter has been tested using the initial measurement system as reference and produces the same information concerning the small signal electrical activity (i.e.: same waveform and RMS value). Because this voltmeter is battery powered and is, therefore, completely isolated from all electrical equipment in the operating theatre, it can be used to monitor the presence, or absence, of microfibrillation in the human heart. Of greatest importance, however, is the fact that the voltmeter can serve as a monitoring device which will indicate when the potassium should be administered in order to render the heart both mechanically and electrically arrested.

Animals↗

PubMed1990

Effect of hypothermia and cardioplegia on intramyocardial voltage and myocardial oxygen consumption.

Intramyocardial voltage and myocardial oxygen consumption were measured in the fibrillating heart between the temperatures of 37 degrees C and 25 degrees C and in the arrested heart after infusion of potassium cardioplegic solution in 10 adult mongrel dogs. Electrical activity from the myocardium was recorded using specially designed plunge electrodes, and intramyocardial voltage was monitored by an in-line voltmeter. Myocardial oxygen consumption gradually decreased from 5.8 +/- 0.6 ml O2/min at 37 degrees C to 2.3 +/- 0.5 ml O2/min at 25 degrees C. In contrast, hypothermia did not cause a similar decrease in intramyocardial voltage which remained within a range of 1.8 +/- 0.5 mV to 2.4 +/- 0.5 mV between the temperatures of 37 degrees C and 25 degrees C. The infusion of potassium cardioplegic solution resulted in a dramatic decrease in voltage to 43 +/- 5 microV, and myocardial oxygen consumption fell to 0.5 +/- 0.3 ml O2/min. Our data demonstrated that the mean voltage of the fibrillating heart remains constant between the temperatures 37 degrees C and 25 degrees C and myocardial oxygen consumption decreases with hypothermia, which suggests that voltage does not correlate with the level of myocardial oxygen consumption. Myocardial oxygen consumption and intramyocardial voltage, however, decrease dramatically when cardioplegia is instituted.

Animals↗

PubMed1989

Adaptive numerical smoothing: an efficient method of conditioning physiological signals.

The main aim of the paper is to present a method of reducing the number of necessary operations in the process of numerically smoothing digitised signals, together with increasing the quality of smoothing, using suggestions which are new in the technique of numerical smoothing. The first suggestion consists of an analytical description of the smoothing process and the representation of the input mixture and undergoing smoothing signals by a series of sinc functions. The second proposal consists of using adaptive smoothing, i.e. smoothing with varying step and with some special means for increasing the quality of smoothing. These procedures must be calculated together with the processing and this procedure causes a small delay in the output signal. The approach presented is a deterministic one, i.e. the information about all instantaneous values of the input mixture is used instead of an a priori average information about disturbances. Attention is directed towards disturbances which are associated with physiological signals such as pressure, flow and electrocardiogram waveforms. The paper contains the basic theory and some experimental results which demonstrate the potential of adaptive smoothing.

Electrocardiography↗

PubMed1989

The measurement of afterload, vascular input impedance, and power distribution in aorto-femoral bypass.

The effects of aorto-femoral bypass grafts on the vascular input impedance, and the ratio of pulsatile to total power were studied in eight dogs. Unilateral ileo-femoral stenosis was simulated and comparisons were made between the input impedance and power distribution in healthy and simulated disease situations. Input impedance magnitude spectra and phase were displayed graphically and it was shown that the presence of the simulated disease increases the ratio of pulsatile to total power as measured in the abdominal aorta from 7.5 to 14.8% (p less than 0.05). This suggests that the presence of the stenosis creates an impedance mismatch thus causing reflected waves to propagate proximally towards the heart. It was concluded that the way in which the heart transfers fluid power into the arterial bed was compromised by the presence of the ileo-femoral partial stenoses. It is further suggested that the system described in the paper makes it possible to quantitatively assess afterload, vascular input impedance and cardiovascular power distribution as a quasi-real time diagnostic procedure.

Anastomosis, Surgical↗

PubMed1989

Monitoring the voltage of the myocardium during cardioplegia arrest.

Electrical activity was monitored with specially designed plunge electrodes in 19 animals undergoing 3 h of cardioplegic arrest. Electrical activity was recorded on electromagnetic tape and intramyocardial voltage was monitored with an inline voltmeter. Haemodynamic function was assessed before bypass and following 3 h of ischaemia and 45 min of reperfusion. Intramyocardial voltage during normothermic fibrillation measured 2.4 +/- 0.4 mv. Infusion of cardioplegia initiated a complete electrical arrest in all animals and reduced intramyocardial voltage to 33 +/- 7 mu v. Small amplitude electrical activity was present in 9 of 19 animals. Intramyocardial voltage increased to 108 +/- 12 mu v with the onset of small amplitude electrical activity and spectral analysis of the wave form indicated that the fundamental frequency was in the range of 3.08 Hz. Small amplitude electrical activity during cardioplegic arrest was associated with significant post-arrest depression of left ventricular function. Our data confirms that the presence of small amplitude electrical activity impairs myocardial functional recovery and suggests that continuous intramyocardial voltage monitoring may be used to guide the administration of cardioplegia during cardioplegic arrest.

Adenine Nucleotides↗

PubMed1989

Coupling of cardiac and locomotor rhythms.

The pressure within exercising skeletal muscle rises and falls rhythmically during normal human locomotion, the peak pressure reaching levels that intermittently impede blood flow to the exercising muscle. Speculating that a reciprocal relationship between the timing of peak intramuscular and pulsatile arterial pressures should optimize blood flow through muscle and minimize cardiac load, we tested the hypothesis that heart rate becomes entrained with walking and running cadence at some locomotion speeds, by means of electrocardiography and an accelerometer to provide signals reflecting heart rate and cadence, respectively. In 18 of 25 subjects, 1:1 coupling of heart and step rates was present at one or more speeds on a motorized treadmill, generally at moderate to high exercise intensities. To determine how exercise specific this phenomenon is, and to refute the competing hypothesis that coupling is due to vertical accelerations of the heart during locomotion, we had 12 other subjects cycle on an electronically braked bicycle ergometer. Coupling was found between heart rate and pedaling frequency in 10 of them. Cardiac-locomotor coupling appears to be a normal physiological phenomenon, and its identification provides a fresh perspective from which to study endurance.

Adult↗

PubMed1989

Coupling between cardiac and locomotor rhythms: the phase lag between heart beats and pedal thrusts.

During some rhythmic exercises, the heart and exercise rates may become coupled (be within 1% of each other). If the intraarterial and skeletal intramuscular pressure cycles were reciprocal, blood flow to exercising muscle should be maximized and cardiac load minimized. In this study the authors tested the hypothesis that, while coupling is present, the phase lag between the pedaling and cardiac contraction cycles is consistent and appropriate. Twenty-seven subjects pedaled, at a frequency natural to them, on an electronically braked bicycle ergometer that held the power output constant regardless of pedaling rate. To assess the phase lag between pedal thrust (two per revolution) and heart beat, pedal-gated plots of the electrocardiography signal were generated throughout the most coupled five-minute work load for each of the 9 subjects in whom the rates were within 1% of each other for at least two consecutive four-second samples taken every fifteen seconds. During this interval of thirty-seconds in which the rates were within 1% of each other, the phase lag of most subjects gradually lengthened and shortened and there was considerable variation among subjects, refuting the authors' hypothesis. The results of this study illustrate the importance of beat-by-beat analysis when studying coupling phenomena. The preliminary assumption, that the coupling between cardiac and locomotor rhythms during cycling was on the basis of a single ischemic muscle group, has apparently been disproven.

Adult↗

PubMed1988

The effect of locomotion speed on the anterior tibial intramuscular pressure of normal humans.

We examined the hypothesis that anterior tibial intramuscular pressure increases with the speed of locomotion. A solidstate pressure transducer was placed near the tip of an intramuscular fluid-filled catheter and each of ten normal subjects walked, jogged and ran barefoot, at 1.5, 2.5 and 3.5 m s-1 respectively, on a treadmill to which they had been previously familiarized. The pressure signals during ten gait cycles from each subject were sampled at 600 Hz and were averaged at each speed. The peak pressures increased in magnitude as a function of increasing locomotion speed, while the mean pressure remained constant.

Adult↗

PubMed1988

Transvenous closure of acquired ventricular septal defects.

Post infarction ventricular septal defect is an uncommon but frequently fatal complication of myocardial infarction. In this report a method for creating experimental ventricular septal defects is described and the use of a transvenous balloon catheter for closure of septal perforations reported. Ventricular septal defects were created with a specially designed punch in 25 adult mongrel dogs. Severe hemodynamic compromise occurred immediately following septal perforation in 15 animals which failed to permit sufficient time to pass the transvenous balloon catheter. However, passage of the catheter and occlusion of the ventricular septal defect was accomplished in the remaining 10 animals. Perforation of the ventricular septum resulted in a marked left-to-right shunt as indicated by changes in interventricular pressure and a step-up in the right ventricular PO2 saturations. Passage of the double balloon catheter and inflation of the balloons prevented left-to-right shunting and completely occluded the ventricular septal defect. Further refinements of this experimental catheter may result in the development of a balloon catheter that may be used to stabilize patients after spontaneous ventricular perforation, thus allowing them to recover from their infarction and undergo delayed repair of the ventricular septal defect.

Animals↗

PubMed1988

Effect of various low-dose concentrations of verapamil cardioplegia on small-amplitude electrical activity during cardioplegic arrest.

The effect of verapamil cardioplegia on atrioventricular conduction was examined in 19 dogs. During 90 minutes of ischemic arrest, five dogs received multidose potassium cardioplegia, containing 1.2 mg/L of verapamil (group 1), five received potassium cardioplegia containing 600 micrograms/L of verapamil (group 2) and nine animals received cardioplegia containing 300 micrograms/L of verapamil (group 3). Atrioventricular conduction was measured in all groups before bypass, after 90 minutes of ischemia and after 45 minutes of reperfusion. Specially designed plunge electrodes were used to monitor the electrical status of the heart during arrest in group 3 and, in addition, left ventricular function and concentration of high-energy phosphates were determined before and after ischemic arrest. Conduction was prolonged in four group 1 dogs and in two group 2. Atrioventricular conduction was measured in six group 3 dogs; five had prolonged conduction and one experienced second-degree heart block. Small-amplitude electrical potentials were recorded from the myocardium in two of nine dogs in group 3. Persistent electrical activity was associated with continued use of high-energy phosphates and resulted in decreased left ventricular function after 90 minutes of ischemic arrest. Our data indicate that small doses of verapamil will delay atrioventricular conduction and will not prevent small-amplitude electrical activity.

Animals↗

PubMed1987

Effect of force on anastomotic suture line disruption after carotid arteriotomy.

Static and dynamic forces exerted on 6-0 polypropylene suture material after carotid arteriotomy were measured in 22 adult mongrel dogs. Force was measured in 11 normotensive animals (Group I) before and 6 weeks after carotid artery repair. Force was measured in the remaining animals during normotension and induced hypertension before and 6 weeks after operation. The tensile strength of each suture used in the study was measured by the manufacturer. The mean force required to break a 6-0 polypropylene suture measured 436.9 +/- 2 g, whereas knotting of the suture decreased the tensile strength to 316.9 +/- 3.9 g (p less than 0.001). The static and dynamic axial forces exerted on the suture after carotid arteriotomy in Group I was in the range of 26 g and decreased to 18 g at 6 weeks, whereas the 45 degree force exerted during the static dynamic phase measured in the range of 23 g and decreased to 16 g at 6 weeks (not statistically significant). The axial and 45 degree forces exerted on 6-0 polypropylene suture material in Group II under normotensive conditions were in the range of 14 g after carotid arteriotomy and ranged between 12 to 14 g at 6 weeks. Systolic hypertension did not result in a significant increase in axial or 45 degree forces during static or dynamic measurements, both in the range of 15 g after carotid arteriotomy. Measurements were similar at 6 weeks and ranged between 14 and 16 g. Our data indicate that 6-0 polypropylene suture material is an appropriate choice for repair of the carotid artery and that the suture material has sufficient inherent tensile strength to withstand forces generated in the neck region. Furthermore, our data indicate that spontaneous carotid artery suture line disruption is most likely related to damage to the suture strand during carotid artery repair rather than an inherent weakness in the suture material.

Animals↗