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Biomedical subjects

R E Kerber

Publications and source records attributed to R E Kerber.

At least 73 records · Page 4Linked to original sources
PubMed1994

Ascorbyl free radical as a real-time marker of free radical generation in briefly ischemic and reperfused hearts. An electron paramagnetic resonance study.

The role of free radicals in myocardial reperfusion injury remains controversial. We have developed a new method using ascorbyl free radical (AFR) as a real-time, quantitative marker of free radical generation during myocardial reperfusion. A total of 35 dogs were studied. Twelve open-chest dogs underwent either 5 minutes (n = 5) or 20 minutes (n = 7) of coronary artery occlusion and 30 minutes of reperfusion. Seven additional animals undergoing 20 minutes of coronary occlusion also received the antioxidant enzymes superoxide dismutase and catalase, beginning 10 minutes before occlusion through the end of reperfusion. Exogenous ascorbate was infused intravenously, and the concentration of AFR in the great cardiac vein was continuously measured by electron paramagnetic resonance spectroscopy. Preocclusion AFR concentration was similar in the three groups. Upon reperfusion, AFR rose significantly in each animal group (P < .05). However, the AFR rise in the 20-minute-occlusion group, 38 +/- 17%, was significantly greater than in the 5-minute-occlusion group, 27 +/- 14% (P < .002). In addition, in the animals that received superoxide dismutase and catalase, the rise in the AFR was markedly attenuated, 13 +/- 6% (P < .002). Two dogs that received ascorbate but did not undergo coronary artery occlusion/reperfusion sequences showed no change in coronary venous AFR signal, indicating the stability of the signal over time. Five dogs received ascorbate while undergoing interventions to alter coronary venous flow: intravenous saline, dobutamine, dipyridamole, and nitroglycerin. Coronary venous AFR changes were minimal despite large coronary flow alterations, indicating that the AFR signal is independent of changes in coronary venous flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Pediatric defibrillation: current flow is improved by using "adult" electrode paddles.

OBJECTIVE: Current flow, the major determinant of defibrillation success, depends on delivered energy and transthoracic impedance. Previous experimental data suggest that transthoracic impedance is higher using "pediatric" electrode paddles compared to the larger "adult" electrode paddles. There are few data from actual shocks to support the experimental studies. The purpose of this study was to measure transthoracic impedance during actual shock delivery and to determine the optimal electrode paddle size for pediatric defibrillation and cardioversion. METHODS: We prospectively evaluated all shocks of < or = 20 joules given to pediatric patients at the University of Iowa from 1988 to 1992. Data collected included energy selected by the operator, energy delivered by the defibrillator, peak current flow and transthoracic impedance. Data were analyzed by unpaired t test and linear regression. RESULTS: Fifty-five shocks were delivered to 20 patients, age newborn to 8 years. Thirty-seven shocks were given with "pediatric" electrode paddles (surface area 21 cm2) and 18 with "adult" electrode paddles (surface area 83 cm2). Selected energy correlated well with delivered energy (r = .98, P < .0001). Delivered energy using "pediatric" electrodes did not differ from that delivered with "adult" electrodes (8.0 +/- 0.9 joules vs 10.5 +/- 1.2 joules P > .1). However transthoracic impedance was significantly higher with "pediatric" electrodes (78.1 +/- 4.4 ohms vs 54.6 +/- 2.7 ohms P < .0008), resulting in lower peak current flow through "pediatric" electrode paddles (6.2 +/- 0.5 amps vs 8.7 +/- 0.5 amps P < .002). There was no correlation between joules/kg and peak current flow (r = .26, P > .05). CONCLUSION: Use of "pediatric" electrode paddles results in higher transthoracic impedance and thus lower peak current flow. In pediatric defibrillation, larger "adult" electrode paddles should be used as soon as chest size permits (approximately 10 kg). Lower transthoracic impedance results in higher current flow that facilitates cardioversion and defibrillation.

Child↗
PubMed1994

Is transthoracic impedance arrhythmia specific? Experimental studies.

Transthoracic impedance (TTI) is a major determinant of current flow in defibrillation, and it is therefore important to understand the factors that determine TTI. Our purpose was to evaluate the effect of atrial and ventricular arrhythmias on TTI. In anesthetized, closed-chest dogs we measured TTI by means of a technique previously validated by us, which did not require administration of actual shocks. Measurements were made at baseline (sinus rhythm) and during rapid atrial pacing (atrial fibrillation), rapid ventricular pacing, and electrically induced ventricular fibrillation (VF) with respiration discontinued. TTI was unchanged by rapid atrial or ventricular pacing. When VF was induced and respiration was discontinued, TTI fell immediately from 51.6 +/- 4.3 ohms to 45.6 +/- 4.7 ohms (p < 0.01) and did not change thereafter. The drop in TTI was probably due to respiratory arrest and decreased chest size with full exhalation; when VF was induced but respiration was continued TTI did not change, whereas discontinuing respiration caused TTI to fall even if VF was not induced. We conclude that TTI is not altered by arrhythmias.

Animals↗
PubMed1993

Impact of transesophageal echocardiography on the anticoagulation management of patients admitted with focal cerebral ischemia.

Transesophageal echocardiography (TEE) improves the diagnostic accuracy of transthoracic echocardiography in the identification of potential cardiac sources of embolus. However, there are few studies of the impact of TEE on the medical management of patients with focal cerebral ischemia. The records of 52 consecutive, hospitalized patients undergoing both TEE and transthoracic echocardiography for suspected cardiac source of embolus were reviewed to determine the influence of TEE on the decision to anticoagulate patients. Of 52 patients, 39 had focal cerebral ischemia (transient ischemic attack, n = 9; acute cerebral infarction, n = 30). In 4 of these 39 patients (10%), the TEE results changed the management of anticoagulation. In 19 of 39 patients (49%), the TEE results helped confirm anticoagulation decisions, and in 16 (41%), the results had no effect on anticoagulation decisions, because of overriding clinical information. Ten of the latter 16 patients had TEE evidence for a possible source of an embolus, but were not anticoagulated; 5 of these were poor candidates for long-term anticoagulation, and the others had right-to-left shunting across a patent foramen ovale or an interatrial septal aneurysm. Clinical variables (atrial fibrillation, TEE findings and pre-TEE anticoagulation status) were considered as possible predictors of post-TEE anticoagulation status using logistic regression analysis; the strongest predictor of post-TEE anticoagulation status was pre-TEE anticoagulation status (p < 0.0005). Despite the selection of patients presumed to receive maximal benefit from TEE, this study suggests that TEE findings are not predictive of subsequent anticoagulation management. However, TEE is at least confirmatory of anticoagulation decisions in most cases.

Adult↗
PubMed1993

Validation by high-frequency epicardial echocardiography of a new method of analyzing coronary angiography quantitatively in coronary artery disease.

In coronary atherosclerosis, the arterial lumen size and shape can be markedly irregular, eccentric and variable. Traditional angiographic interpretation, emphasizing percent diameter stenosis, has been criticized as an inadequate descriptor of such diseased arteries. Computerized quantitative angiographic technologies, yielding a true lumen area measurement, may be superior. High-frequency epicardial echocardiography (HFEE) is a technique that allows on-line evaluation of coronary arterial wall and lumen at the time of cardiac surgery. It has been extensively validated and yields accurate measurements of normal and diseased coronary lumen areas. This study compares quantitative coronary angiography (QCA) estimates of lumen area to those obtained by HFEE to determine if the computerized angiographic method more accurately predicts residual luminal area than traditional angiographic percent diameter stenosis measurements. Although actual luminal morphology was quite variable, there was a good correlation between lumen areas determined by HFEE versus QCA: r = 0.85, n = 67, HFEE = 0.8 QCA - 0.1 (HFEE 4.0 +/- 0.30 mm2, mean +/- SEM range 0.3 to 14.0; QCA 5.1 +/- 0.40 mm2, range 0.7 to 11.8). Percent diameter stenosis determined from the angiograms did not correlate well with HFEE or QCA measurements of residual luminal area. Separation of "normal" arterial segments (defined as < 25% diameter stenosis) from "abnormal" segments (> 50% diameter stenosis) by angiography did not agree with lumen areas as defined by either HFEE or QCA. Better separation occurred when QCA-determined luminal areas were used to separate normal from abnormal arterial segments.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Transthoracic defibrillation: effect of dual-pathway sequential pulse shocks and single-pathway biphasic pulse shocks in a canine model.

To determine whether dual-pathway sequential shocks and single-pathway biphasic shocks improved the efficacy of transthoracic defibrillation, we delivered single or sequential truncated waveform shocks of variable duration, voltage, and direction (polarity) to three groups of closed-chest dogs. Dual-pathway sequential shocks were assessed in group 1 (eight animals), biphasic shocks with a single pathway were compared in 11 dogs (group 2), and the effect of varying the duration of the biphasic shocks was assessed in group 3 (four animals). There was no improvement in success rates of the intervention shocks compared with a standard single "control" shock at any energy level. In this experimental model unidirectional or biphasic sequential shocks given over single or dual pathways were not superior to standard single-pulse transthoracic defibrillation.

Analysis of Variance↗
PubMed1993

Lidocaine and dextran sulfate inhibit leukocyte accumulation but not postischemic contractile dysfunction in a canine model.

Leukocytes have been implicated as a possible factor in the pathogenesis of postischemic contractile dysfunction, probably through the release of oxygen free radicals. Lidocaine and dextran sulfate are known to inhibit leukocyte adherence to endothelial cells in vitro and in vivo. In an acute open-chest canine model both agents were found to inhibit the augmented accumulation of indium-111-labeled leukocytes in briefly ischemic and subsequently reperfused myocardium. Pharmacologic inhibition of leukocyte accumulation by lidocaine and dextran sulfate, however, was not associated with improvement in postischemic contractile dysfunction.

Animals↗
PubMed1993

Cardiac geometry and mass changes associated with pacing-induced cardiomyopathy in the dog.

We evaluated the effects of chronic rapid pacing (240 beats/min) on ventricular geometry and function and on cardiac mass in a canine model. Forty dogs were studied by two-dimensional echocardiography before and after 45 days of pacing. Compared with sham-operated control animals, the paced animals had significant increases in end-diastolic and end-systolic volume and a decrease in ejection fraction. The increase in ventricular volume was primarily the result of dilation of the short axis of the ventricular lumen, without significant changes in the long-axis dimension. Paced animals had biatrial hypertrophy but no change in ventricular or total cardiac mass.

Animals↗
PubMed1993

Electrical treatment of cardiac arrhythmias: defibrillation and cardioversion.

The passage of electrical current across the chest and heart to terminate ventricular fibrillation (defibrillation) or organized supraventricular or ventricular arrhythmias (cardioversion) is effective and safe. This paper reviews the physiology, techniques, and rationale for defibrillation and cardioversion. New developments and future directions are discussed. Rapid defibrillation is the most important factor in survival of out-of-hospital ventricular fibrillation.

Electric Countershock↗
PubMed1992

Variable morphology of coronary atherosclerosis: characterization of atherosclerotic plaque and residual arterial lumen size and shape by epicardial echocardiography.

The purpose of this study was to evaluate the in vivo characteristics of coronary atherosclerosis by using high frequency epicardial echocardiography. High frequency epicardial echocardiography was used to evaluate residual lumen and wall morphology at the sites of maximal coronary atherosclerosis in 26 patients undergoing coronary artery bypass grafting. The maximal/minimal wall thickness ratio was 3.1 +/- 0.2 (mean +/- SEM) with a large range (1.3 to 7.5). Portions of the wall were normal in 16 of 31 lesions; the percent normal circumference ranged from 9% to 85%. Maximal/minimal lumen diameter ratio was 1.5 +/- 0.1 (range 1.1 to 2.9). The shape of the residual coronary lumen was noncircular in 16 lesions: oval in 13 and complex in 3. The residual coronary lumen was eccentrically placed within six arteries. These data emphasize the variability of residual lumen and wall geometry in atherosclerosis.

Coronary Artery Bypass↗
PubMed1992

Transthoracic defibrillation: effect of sternotomy on chest impedance.

The purpose of this study was to determine the effect of sternotomy on transthoracic impedance, a major determinant of current flow and defibrillation success. Transthoracic impedance was determined by using a validated test-pulse technique that does not require actual shocks. Seventeen patients undergoing median sternotomy were studied prospectively. Transthoracic impedance was determined before operation, 3 to 5 days after operation and (in eight patients) greater than or equal to 1 month after operation. When measured using paddle electrodes placed in the standard apex-right parasternal defibrillating position, transthoracic impedance declined after sternotomy in all patients, from 77 +/- 18 to 59 +/- 17 omega (p less than 0.01); smaller declines were demonstrated by using other electrode positions. Transthoracic impedance remained below the preoperative level in the eight patients who underwent a second set of measurements at least 1 month after operation. Six normal subjects not undergoing sternotomy underwent serial transthoracic impedance measurements at least 5 days apart; mean transthoracic impedance did not change. It is concluded that transthoracic impedance declines after sternotomy. At any operator-selected energy level a higher current flow will result after sternotomy; this may facilitate postoperative defibrillation.

Cardiography, Impedance↗
PubMed1992

Ventricular tachycardia rate and morphology determine energy and current requirements for transthoracic cardioversion.

BACKGROUND: The electrical current and energy required to terminate ventricular tachyarrhythmias are known to vary by arrhythmia: Ventricular tachycardia (VT) is generally considered to require less energy than ventricular fibrillation (VF). The hypothesis of our study was that current requirements for transthoracic termination of VT are further determined by VT rate and QRS complex morphology. METHODS AND RESULTS: We prospectively studied 203 patients who received a total of 569 shocks for VT or VF by following a current-based protocol. This protocol recommended shocks for VT beginning at 18 A (70 +/- 22 J) and shocks for VF beginning at 25 or 30 A (137 +/- 52 J or 221 +/- 70 J). The ventricular tachyarrhythmias were subclassified as monomorphic VT (MVT): uniform QRS complex morphology on surface electrocardiogram and heart rate greater than 100 beats per minute; polymorphic VT (PVT): nonuniform QRS complex morphology and heart rate less than or equal to 300 beats per minute; or VF: nonuniform QRS complex morphology and heart rate greater than 300 beats per minute. We found that shocks of 18 A and 25 A for terminating MVT had success rates of 69% and 82%, respectively, whereas such low-current shocks were less successful for PVT (33% at 18 A) and for VF (19% at 18 A, 53% at 25 A). High-current shocks of 35 A and 40 A were equally successful for the three ventricular tachyarrhythmias. Subdividing MVT revealed that slower MVT (heart rate less than 200 beats per minute) had a significantly better success rate with low-current shocks of 18 A and 25 A than did faster MVT (greater than 200 beats per minute) (89% versus 72% success, p less than 0.01). Bundle branch block morphology, QRS axis, and duration of ventricular tachyarrhythmia did not alter current requirements. CONCLUSIONS: Heart rate and electrocardiographic degree of organization of ventricular tachycardia are important determinants of transthoracic energy and current requirements for cardioversion and defibrillation. Transthoracic termination of MVT requires relatively low current or energy, but PVT behaves more like VF and requires higher electrical current or energy.

Electric Countershock↗
PubMed1991

Effect of nisoldipine on hemodynamic responses to defibrillation.

Sequences of ventricular fibrillation-defibrillation cause transient hypertension; we hypothesized that this "adrenergic overshoot" might be blunted by the functional antiadrenergic effect of the calcium channel blocking drug nisoldipine, with a potentially beneficial reduction in myocardial oxygen requirements. However, other calcium channel blocking drugs have been shown to reduce shock success for defibrillation, a deleterious effect. Thus the purposes of this study were to assess the effect of nisoldipine on the hemodynamic responses to the sequences of ventricular fibrillation-defibrillation, and its effect on the energy requirements for defibrillation. In 16 dogs we administered intravenous nisoldipine (1 microgram/kg bolus followed by an infusion of 0.075 to 0.50 microgram/kg/min) to lower mean blood pressure 10% and 20% below baseline. Ventricular fibrillation was induced electrically, and shocks of varying energy levels (30, 50, and 100 joules) were administered to determine defibrillation energy requirements. Heart rates and blood pressures were recorded up to 3 minutes after each shock to determine hemodynamic responses. Measurements were made before nisoldipine administration and again at the two levels of drug-induced blood pressure decline. We found that the usual systolic blood pressure "overshoot" after defibrillation (typically maximum at 15 to 30 seconds after shocks) was significantly blunted after nisoldipine administration (p less than 0.05). Heart rate slowing after defibrillation (a cholinergic response) was not affected. Nisoldipine did not alter shock success rates, which varied from 12 +/- 7%SE at 30 joules to 68 +/- 12% at 100 joules. Thus nisoldipine blunted the "adrenergic overshoot" of systolic blood pressure following defibrillation, a potentially beneficial effect, without altering the energy requirements for transthoracic defibrillation.

Animals↗
PubMed1991

Coronary arterial remodeling studied by high-frequency epicardial echocardiography: an early compensatory mechanism in patients with obstructive coronary atherosclerosis.

Coronary arterial remodeling is a compensatory mechanism that may limit the adverse effects of coronary obstructive lesions by expansion of the entire vascular segment. To determine if this compensatory anatomic change occurs in patients, high-frequency epicardial echocardiography using a 12 MHz transducer was performed during open heart surgery in 33 patients (10 with normal coronary arteries undergoing valvular surgery and 23 with coronary atherosclerosis). From stop-frame videotape high-frequency epicardial echocardiographic images, cross-sectional measurements of luminal area and total arterial area (lumen, intima, media and dense adventitia) were made in the patients with atherosclerosis at the site of arterial lesions and from the most proximal portion of the same artery. Remodeling was defined as enlargement of the total arterial area. In normal arteries measurements were made from proximal and midarterial locations. In the patients with normal coronary arteries, total arterial area, as determined by high-frequency echocardiography, decreased from the proximal site to the midportion of the artery (from 10.4 +/- 0.9 to 8.4 +/- 1.0 mm2, p less than 0.05); luminal area also decreased (from 6.0 +/- 0.6 to 4.5 +/- 0.7 mm2, p less than 0.05). In patients with coronary arterial lesions, luminal area also decreased from the proximal site to the arterial lesion site (from 5.3 +/- 0.6 to 2.3 +/- 0.3 mm2, p less than 0.05), but total arterial area increased (from 11.6 +/- 1.0 to 13.0 +/- 1.0 mm2, p less than 0.05). Of the 25 coronary arteries evaluated, only 4 had angiographic evidence of coronary collateral formation. These data indicate that coronary arterial remodeling is an important compensatory mechanism in obstructive coronary disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Surgical Procedures↗
PubMed1991

Free radicals from plastic syringes.

We have found that disposable sterile plastic syringes can leach free radicals into the fluids they hold. The free radical we observe appears to be a nitroxide (aminoxyl radical) because in aqueous solution it produces a 1:1:1 three line spectrum with a hyperfine splitting constant of 16.9 G.

Electron Spin Resonance Spectroscopy↗