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Biomedical subjects

L A Geddes

Publications and source records attributed to L A Geddes.

At least 19 recordsLinked to original sources
PubMed2006

Nonpulsatile and noninvasive transmittance and reflectance tissue-bed oximetry.

A new optical device was developed that measures blood pressure noninvasively, in small human subjects (neonates and premature infants) and small animals (Roeder RAR. Transducer for indirect measurement of blood pressure in small human subjects and animals, Purdue University, BME; 2003.: xi, 50 p.). The ability of this device to measure oxygen saturation enhances its value. The objective of this research was to add the ability to obtain SaO(2) from the same device and to obtain the calibration curve. Another objective was to determine which measurement method (transmittance or reflectance) is preferable. This new oximeter is unlike the conventional pulse oximeter in that it does not require a pulse, making it ideal for measuring oxygen saturation noninvasively in small human subjects with small amplitude pulses or without a pulse. A study was performed in 11 pigs, ranging in weight 20-27 kg. The pig tail was used as the measuring site for %SaO(2) measurements. Arterial blood samples were obtained from the femoral artery and oxygen saturation was measured with a blood-gas analyzer. A small blood-pressure cuff was used to render the optical path bloodless. A comparison of the transmittance and reflectance methods for measuring oxygen saturation was made. %SaO(2) measurements ranged from 4% to 100%. It was found that both the transmittance and reflectance methods can be used to measure %SaO(2) reliably in situations with or without a pulse.

Algorithms↗
PubMed2005

Ventricular fibrillation frequency.

BACKGROUND: Ventricular-fibrillation (VF) wave frequency is known to decrease with prolonged, untreated VF. VF wave frequency is used as an algorithm to identify VF in AEDs and ICDs; yet the nature of the frequency change is not appreciated. METHODS: In this study, anesthetized pigs were used and VF was induced electrically. VF wave frequency was measured each second during VF for periods up to 200 sec. Defibrillation was achieved with transchest electrodes. VF wave frequency was plotted for each second during VF. In 2 animals, CPR was applied and VF wave frequency was measured. RESULTS: In all cases VF wave frequency decreased with increasing duration of VF. At the onset of VF, the VF wave frequency ranged from 5 to 12/sec. A plot of the normalized ratio of VF wave frequency during fibrillation to the VF frequency at induction decreased to between 0.1 and 0.8 of the initial frequency. In one of the animals, VF was initiated, CPR was provided and the VF wave frequency was measured over a 200-second period. Then, the procedure was repeated without CPR. Beyond 130 seconds, the VF frequency with CPR was higher than that without CPR, indicating myocardial oxygenation. CONCLUSION: Those who use VF wave frequency to identify the presence of VF should be aware of the nature of the VF wave frequency decrease with the passage of time.

Animals↗
PubMed2004

Direct-current injury: electrochemical aspects.

Direct-current injuries have occurred to anesthetized patients connected to battery-operated medical devices. This study was designed to document the effects of direct current applied to two electrodes on a tissue surrogate (round steak) at room temperature. Direct current from a 9 V source was applied to a pair of stainless steel electrodes (1.6 cm diameter) spaced 4.3 cm center-to-center. Current flowed for 5 min increments at the first electrode site, 10 min at the second, 15 min at the third, etc. until at the last site, the current flowed for 30 min. In all, 63 measurements were made with the pair of electrodes, which were changed if they became corroded. Lesion appearance, lesion size, pH and resistance were measured. It was found that the pH under the negative electrode became strongly alkaline (pH > 12) and acidic (pH < 5.0) under the positive electrode. The lesion under the negative electrode was red with a dark purplish ring that identified the electrode perimeter. The lesion under the positive electrode was more uniform and gray in appearance. The largest increase in lesion diameter occurred in the first 5 min. In all cases the resistance decreased with the passage of time. At the start of each experiment, both electrodes were shiny. At the end of each experiment the electrodes were different in appearance. The negative electrode retained its original shiny appearance but the positive electrode was pitted and dull in appearance, reflecting the different chemical reactions at each site. The lesions under the negative electrodes were more severe, indicating that alkali is more damaging than the acid environment that was produced electrolytically.

Body Fluids↗
PubMed2002

Electrocardiograms from the turtle to the elephant that illustrate interesting physiological phenomena.

This article describes a collection of ECGs from many species obtained over the past 50 years. Presented are ECGs of species in which the pacemaker is a separate contractile chamber with its own action and recovery potentials. In such species, pacemaker atrial and AV block can be produced. Shortening of the atrial refractory period and the negative inotropic effect can be produced by vagal stimulation. The cardiac electrogram and stroke volume are recorded from the turtle heart. The ECG and respiration were recorded from the snake. ECG records were obtained from the anesthetized and decapitated housefly. ECG records of the rabbit show slowing when the nose encountered irritating vapors. Records from a dog with atrial fibrillation exhibit rhythmic fibrillation frequency changes correlated with respiration. In addition, in a morphinized dog with atrial fibrillation, impulses crossed the AV node only during inspiration. The ECGs of a cow and camel exhibit long P-R intervals and biphasic P waves. Finally the elephant ECG shows a clear U wave following the T wave.

Animals↗
PubMed2002

Electroventilation with monopolar and bipolar intratracheal electrodes.

UNLABELLED: Electroventilation is the technique of producing inspiration with stimuli applied to inspiratory muscles by using strategically placed electrodes on or within the body. We conducted studies using the dog to determine the efficacy of monopolar and bipolar intratracheal electrodes for electroventilation. Bipolar electrodes were able to produce an inspired volume greater than a spontaneous tidal volume in all seven dogs, but monopolar electrodes were able to in only three of seven dogs. The intratracheal electrode has the advantage over body-surface electrodes that less current is required to produce a single tidal volume, and it has the advantage over intraesophageal electrodes that anatomical placement of the electrode is simplified. These experiments demonstrated that a bipolar electrode can be used for electroventilation. IMPLICATIONS: This study demonstrates that electroventilation is possible with intratracheal electrodes, decreasing the current needed to electroventilate by using body-surface electrodes. Two different methods of intratracheal electroventilation can be used: monopolar, in which the return electrode is on the body surface; and bipolar, in which the return electrode is in the trachea.

Animals↗
PubMed2001

Measurement of the direct-current (Faradic) resistance of the electrode-electrolyte interface for commonly used electrode materials.

The direct-current (Faradic) resistance is important because it is the highest impedance that an electrode-electrolyte interface can attain. In this study, the Faradic resistance (Rf) of identical pairs of 0.5 cm2 electrodes of bare and chlorided silver, tin and chlorided tin, nickel-silver, copper, and carbon was measured in contact with 0.9% saline at room temperature. It was found that for positive and negative current flow, the data fit the expression Rf=Rf0 e(-alpha i) (with a high coefficient of determination), where Rf0 is the zero-current Faradic resistance and alpha is a constant that describes the manner in which Rf decreases with increasing current (i). It was found that chlorided silver exhibited the lowest Rf0; removing the chloride deposit increased Rf0 by more than sixfold. Likewise, chloriding tin reduced Rf0 by a factor of about 2. Electrolytically cleaning an electrode reduced Rf0. The highest value for Rf0 was for carbon. This paper concludes with a summary of the data for Rf0 scaled to 1 cm2 electrode area for the electrode materials measured in the present study and data from the published literature.

Biomedical Engineering↗
PubMed2000

Electrophysiological control of ventricular rate during atrial fibrillation.

Thirteen anesthetized canine subjects (17-29 kg) were used to demonstrate that mild cervical left vagal stimulation could control ventricular rate effectively during atrial fibrillation (AF). Two studies are presented. The first study used six subjects to demonstrate the inverse relationship between (manually applied) left vagal stimulation and ventricular excitation (R wave) rate during AF. As left vagal stimulation frequency was increased, ventricular excitation rate decreased. In these studies, a left vagal stimulus frequency of 0-10 per second reduced the ventricular excitation rate from > 200/min to < 50/min. The decreasing ventricular excitation rate with increasing left vagal stimulation frequency was universal, occurring in all 26 trials with the six subjects. This fundamental principle was used to construct an automatic controller for use in the second study, in which seven subjects were used to demonstrate that ventricular rate can be brought to and maintained within a targeted range with the use of an automatic (closed-loop) controller. A 45-minute record of automatic ventricular rate control is presented. Similar records were obtained in all seven subjects.

Animals↗
PubMed2000

Burst pressure of canine carotid arteries.

The burst pressure was measured on 40 freshly excised, unstretched carotid arteries derived from dogs ranging in weight from 20-25 kg. Each carotid artery specimen was tied to the nozzle of a high-pressure nitrogen tank and regulator. The pressure was slowly increased until the artery burst. The burst pressure ranged from 2400 to 6500 mmHg, a value well above typical mammalian systolic pressure.

Animals↗
PubMed1999

Compliance, elastic modulus, and burst pressure of small-intestine submucosa (SIS), small-diameter vascular grafts.

Small-intestine submucosa (SIS) is cell-free collagen, 100 mu thick, derived from the small intestine. It has been used as a vascular graft and has the highly desirable property of remodeling itself to become host tissue. To date there has been limited reporting on its preimplantation mechanical properties as a vascular graft. In this study, compliance, elastic modulus, and burst pressure have been measured on 5- and 8-mm SIS grafts. The compliance (percent of diameter increase for a pressure rise from 80 to 120 mmHg) was 4.6% av (range 2.9 to 8.6%) for the 5-mm grafts. For the 8-mm graft, the increase in diameter for the same pressure rise was 8.7% av (range 7.2 to 9.5%). The modulus of elasticity (E) increased exponentially with increasing pressure according to E = E(o)e(alphaP), where Eo is the zero-pressure modulus and alpha is the exponent that describes the rate of increase in E with pressure; the units for E, Eo, and P are g/cm2. The mean value for Eo was 4106 (g/cm2 range 1348-5601). The mean value for alpha was 0.0059 (range 0.0028-0.0125). At 100 mmHg, the mean value for E was 8.91 x 10(3) g/cm2 (range 1.02-8.80 x 10(3)). The mean burst pressure for 5.5-mm grafts was 3517 mm Hg (range 2069-4654). In terms of preimplant compliance, the small-diameter SIS graft is about (1/2) as compliant as the dog carotid artery, about four times more compliant than a typical vein graft, and more than an order of magnitude more compliant than synthetic vascular grafts.

Animals↗
PubMed1998

Success--failure diagram for defibrillation.

A new method for presenting defibrillation threshold data (current, voltage or energy) is presented in the form of a success--failure diagram, the y-axis of which is the shock strength employed. A vertical line divides the successful shocks from the unsuccessful shocks for each shock strength. The diagram shows clearly how many shocks have been given at each strength and how the success for defibrillation increases with increasing shock strength.

Arrhythmias, Cardiac↗
PubMed1997

Calcification potential of small intestinal submucosa in a rat subcutaneous model.

Glutaraldehyde treatment of collagen biomaterials promotes calcification, poor host-tissue incorporation, and ultimately mechanical failure of bioprotheses. Porcine small-intestinal submucosa (SIS) is a biomaterial which has been investigated for several applications including arterial and venous grafts and repair of tendon, ligament, body wall, and urinary bladder defects. The calcification potential of peracetic acid (PAA)-sterilized SIS was studied. Four test samples, (1) native (cleaned, untreated) SIS, (2) SIS sterilized with 0.1% PAA, (3) SIS treated with 0.25% glutaraldehyde for 20 min, and (4) commercially available glutaraldehyde-preserved porcine bioprosthetic heart valve cusp segments (GPV), were each implanted subcutaneously in each of 24 weanling rats. Six rats were euthanatized at 1, 2, 4, and 8 weeks. Evaluation of calcium concentration by atomic absorption spectroscopy and extent of mineralization and fibrosis by light microscopy were performed. Atomic absorption revealed no calcification in native or peracetic acid-treated SIS at any time point compared with preimplant calcium concentration. Statistically significant (P < 0.0001) calcification occurred in glutaraldehyde-treated materials (SIS and GPV) at each evaluation as compared to native and peracetic acid-treated samples. Histopathology indicated native and peracetic acid-treated SIS showed no implant mineralization (P < 0.0001) and little peri-implant fibrosis (P < 0.0001). Results suggested that native and peracetic acid-treated SIS have a low calcification potential and further study of this biomaterial is warranted.

Animals↗
PubMed1997

Ventricular defibrillating threshold: strength-duration and percent-success curves.

The term defibrillation threshold is usually understood to mean the shock intensity just enough to defibrillate a specified cardiac chamber (atria or ventricles). With the advent of so many different types of defibrillator, it is important to be able to specify the defibrillation threshold, which has frequently been described by the classical strength-duration curve. Another method of representing defibrillation plots the percent-successful defibrillation against shock-strength area. The mechanism of defibrillation is discussed, and the concepts of the strength-duration curve and percent-success against shock-strength curves are compared. Because defibrillation is associated with a time-varying spectrum of cellular excitability, a given shock strength will not always achieve defibrillation, and this produces the sigmoid shape for the curve that relates percent-successful defibrillation to shock strength. Therefore it is important to recognise two concepts: first, there is a family of strength-duration curves for defibrillation, each curve representing a given percent-successful defibrillation, and, secondly, there is a family of percent-success against shock-strength curves, one for each pulse duration. Canine ventricular defibrillation data are used to bring these two concepts together. Most importantly, the concepts adduced in the paper apply to transventricular, intracardiac and transchest defibrillation; the only difference in these applications is a scale factor that represents electrode location with respect to the heart.

Animals↗
PubMed1997

Preimplant atrial defibrillation testing with a temporary catheter in sheep.

Prior to implantation of an atrial defibrillator, its effectiveness should be tested in each patient. A new catheter design for temporary use with electrodes for atrial defibrillation, electrogram sensing, and pacing was tested in this study. Atrial defibrillation thresholds defined using this temporary catheter were compared to the ones defined by catheters intended for chronic use with an implantable atrial defibrillator. Atrial defibrillation threshold was determined in six sheep using both types of catheters. Each animal was subjected to studies on 2 consecutive days. On the first day, shocks were applied between two of the temporary catheters. On the following day, permanent leads were inserted and atrial defibrillation threshold was redetermined. In both cases, defibrillation electrodes were positioned in the same heart location with one electrode in the distal coronary sinus and the second electrode in the right atrium. Atrial defibrillation threshold was obtained using 10 V increments or decrements to determine the lowest shock intensity needed to defibrillate the atria. Threshold was defined as the shock intensity at which 20 shock percent success was at or between 15% and 85%. Statistical analysis showed no significant difference (P < 0.05) between atrial defibrillation threshold energy (0.53 J vs 0.55 J), voltage (122 V vs 120 V) or current (2.2 A vs 2.6 A) measured with the temporary catheters and the permanent leads, respectively. These data indicate that temporary catheters can be used for efficacy testing prior to implant of an atrial defibrillator, and that they predict atrial defibrillation threshold adequately for chronic leads.

Animals↗
PubMed1997

The paradox in using electrically stimulated skeletal muscle to pump blood.

For over four decades, various methods have been described for the use of electrically stimulated skeletal muscle to pump blood. To date, there has been no way of predicting the efficacy or long-term pumping capabilities of these methods. This article reviews the basic physiological properties of skeletal muscle and relates them to the blood pumping task and illustrates the paradox, namely a high preload is needed for a forceful contraction, but a high prolonged preload produces muscle ischemia and early fatigue. However, the high preload is only required just before muscle contraction. Two methods are described to attain the high preload and high muscle capillary blood flow.

Animals↗
PubMed1996

Maintenance of atrial fibrillation in anesthetized and unanesthetized sheep using cholinergic drive.

Atrial fibrillation (AF) was induced electrically and the duration of AF was measured in six isoflurane-anesthetized sheep (weight range 54.5-72.7 kg), and in five unanesthetized sheep (weight range 60-75 kg). In the anesthetized sheep, AF was induced by direct electrical stimulation of the right atrium with a catheter electrode and the duration of AF was determined. Intravenous neostigmine (10 micrograms/kg IV) was administered and the duration of AF was again measured. Then cholinergic drive was increased by bilateral electrical vagal stimulation; AF was induced and the duration of AF was measured. In the anesthetized animals with no neostigmine or vagal stimulation, 34% of the episodes of AF lasted 10 seconds, 11% lasted 20 seconds, and only 1% lasted 200 seconds. However, in one anesthetized animal AF was sustained for 4,800 seconds with no drug or vagal support. The administration of neostigmine alone in 3 anesthetized animals more than doubled the average duration of AF. In the animals with vagal stimulation (after neostigmine), AF persisted throughout stimulation, but ceased shortly after vagal stimulation was terminated at 2,220, 4,500, and 3,840 seconds. The AF frequency ranged from 325-750/min. The unanesthetized sheep were lightly sedated with a small dose (200 micrograms/kg IM) of xylazine to make them less sensitive to environmental noise; then AF was induced and its duration was timed. After these measurements, neostigmine was administered (30 micrograms/kg IM) and cholinergic drive was produced reflexly by intravenous injection of 60-2,000 micrograms of phenylephrine. AF was electrically induced at the time of maximum reflex slowing in heart rate. For the control (no drug) studies, 64% of the AF episodes lasted 10 seconds, 20% lasted 20 seconds, and only 2% of the episodes lasted as long as 140 seconds. When phenylephrine was injected after neostigmine to provide increased cholinergic drive, the duration of fibrillation depended on the dose of phenylephrine. In a 60-kg sheep, the duration of AF increased from 1 second with an intravenous dose of 60 micrograms to 700 seconds with an intravenous dose of 2,000 micrograms. However, there was a considerable range in responsiveness to the reflex cholinergic drive provided by the intravenous phenylephrine; for example a single intravenous 500-micrograms dose produced AF ranging from 190-540 seconds among the sheep. The duration of AF was most controllable in the anesthetized sheep, following neostigmine administration and with bilateral vagal stimulation. In the unanesthetized sheep, AF could generally be sustained for more than the duration of the half-life (about 4 minutes) of phenylephrine following neostigmine. However, there was a large variation in the duration of AF among the animals for the same dose of phenylephrine. This study identifies two methods (direct vagal stimulation and reflex vagal stimulation) for providing the cholinergic drive needed to sustain AF in the adult sheep. The duration of AF is sufficiently long to enable the measurement of electrical atrial defibrillation threshold.

Anesthesia, General↗
PubMed1995

Mechanical properties of xenogeneic small-intestinal submucosa when used as an aortic graft in the dog.

Small-intestinal submucosa (SIS) has been shown to induce tissue remodelling in vivo when used as a vascular graft. The present study investigated in physical and mechanical properties of remodeled aortic grafts derived from xenogeneic SIS material. Eight infrarenal aortic grafts were implanted in mongrel dogs. The grafts were explanted at 1 or 2 months and tested for compliance and hoop mechanical properties. The morphologic changes within the grafts were also characterized. The remodeling process produced graft structures which were significantly stronger than both the normal artery (P = .012) and the original SIS graft (P = .0001), and the compliance of these structures was one third that of normal artery and similar to the original SIS grafts. The remodeled grafts were > 10 times the thickness of the implanted SIS. Immunohistochemical analysis of remodeled tissues suggest that the SIS material was degraded and resorbed over time. The remodeling process transformed a material which was physically and mechanically quite different from normal aorta into a blood conduit which had the physical and mechanical properties needed to function in this mammalian arterial system.

Animals↗