Search PubMed⌕ Search

Biomedical subjects

S Naimi

Publications and source records attributed to S Naimi.

31 records · Page 2Linked to original sources
PubMed1978

Sequential unipolar strength-interval curves and conduction times during myocardial ischemia and reperfusion in the dog.

Computerized techniques were employed to generate alternating anodal and cathodal or sequential anodal strength-interval curves during and following 15-minute coronary artery ligations in 14 anesthetized dogs. The right atrium was paced at 2.5 Hz, and unipolar ventricular strength-interval curves with simultaneous conduction times were recorded every 45-120 seconds during ischemia and reperfusion. Within 1--2 minutes of ligation, anodal midcurve and late diastolic thresholds fell sharply, and cathodal thresholds fell slightly or changed little. After 5 minutes of ischemia, anodal thresholds remained low, cathodal thresholds rose, and conduction times increased. At 10--15 minutes of ligation, if the ischemic zone was small, anodal thresholds were low, often approaching cathodal values, and conduction returned toward control values. When the ischemic zone was large, unipolar thresholds and conduction times increased late during the ligation period. Throughout the course of ischemia, the falling limb of the strength-interval curve shifted progressively to the left indicating shorter refractory periods. Following abrupt reperfusion, anodal phase 3 dips promptly reappeared; refractory periods returned toward control, and supernormal conduction was noted. By 3--5 minutes of reperfusion, the falling limb of the strength-interval curve had shifted to the right of control and conduction times increased. Thus, vulnerability to arrhythmias during early ischemia (i.e., 5 minutes) is characterized by low anodal midcurves and late diastolic thresholds, short refractory periods, and slow conduction. During the first minute of reperfusion, anodal excitability is increased during the early dip and conduction times are supernormal. Increases in anodal excitability correlate better with the peak incidence of early ligation and reperfusion arrhythmias than do changes in cathodal excitability.

Animals↗
PubMed1977

Dispersion of effective refractory period during abrupt reperfusion of ischemic myocardium in dogs.

Dispersion of the effective refractory period was measured in anesthetized dogs using a computerized system and bipolar epicardial electrodes or, alternatively, transmural plunge electrodes. Measurements were made at 1 minute intervals during short (5 minute) and long (15 minute) periods of coronary arterial ligation and for 3 to 5 minutes after release of the ligatures. Both transepicardial and transmural temporal dispersion of refractoriness correlated well with the increased vulnerability to spontaneous ventricular fibrillation during short periods of ligation and the relative electrical stability observed toward the end of the longer periods of ligation. During reperfusion, transmural dispersion increased somewhat after ligature release in the longer-term experiments but the increase did not appear adequate to explain the associated large incidence of spontaneous arrhythmias after release. Effective refractory periods measured at one nonischemic and five ischemic electrode sites at intervals as short as 20 seconds revealed abrupt shortening of the refractory period at all ischemic sites during the 1st minute of reperfusion, resulting in a large but short-lived electrical gradient between the ischemic and nonischemic myocardium. This increased dispersion between the ischemic and nonischemic myocardium occurred at a time of maximal vulnerability to reperfusion arrhythmias. However, this increased dispersion was greater after the 5 minute than after the 15 minute periods of ligation and thus does not fully explain the greater incidence of reperfusion arrhythmias after ligature release in the longer-term studies. Although arrhythmias of acute ischemia are associated with increased dispersion of refractoriness within theischemic segment and reperfusion arrhythmias with dispersion between ischemic and nonischemic segments, other electrophysiologic alterations probably play an important role in the genesis of the arrhythmias of reperfusion.

Animals↗
PubMed1971

Effect of free fatty acid mobilization on the electrophoretic mobility of alpha-lipoproteins in the dog.

Dogs were given infusions of norepinephrine and subsequent additional infusions of propranolol and nicotinic acid over a 4-hr period. Under different physiological conditions, alpha-lipoproteins of three different electrophoretic mobilities were identified by means of paper electrophoresis; they were designated alpha-lipoproteins X, Y, and Z. During norepinephrine infusion, alpha-lipoprotein Y fell from 45% (of all lipoproteins) to 14%. There was a reciprocal rise in alpha-lipoprotein Z. On the other hand, alpha-lipoprotein X was not significantly changed. There was evidence that alpha-lipoprotein Y was progressively transformed into alpha-lipoprotein Z by increasing plasma FFA concentrations. The percentages of both alpha-lipoproteins Y and Z returned to original values after the dogs were given either nicotinic acid or propranolol. The alterations in the alpha-lipoprotein peaks Y and Z were rapid, being noted within 5 min of change in plasma FFA concentration. However, there appeared to be a threshold of plasma FFA concentration of 1200 micro Eq/liter, below which no changes in alpha-lipoproteins were noted. It was concluded that alpha-lipoprotein Y is rapidly, progressively, but reversibly transformed into alpha-lipoprotein Z by binding to plasma FFA above a threshold level of 1200 micro Eq/liter. However, alpha-lipoprotein X does not appear to be involved in the binding of plasma FFA.

Animals↗
PubMedDate not supplied

Evaluation of a new method for cardiovascular reasoning.

OBJECTIVE: Evaluate the accuracy of the detailed diagnostic reasoning of the Heart Failure Program incorporating a new mechanism to handle temporal relationships and severity constraints. DESIGN: Tools were developed to summarize diagnoses and automatically generate evaluation forms. Five expert cardiologists were asked to review the reasoning of the program, with two analyzing each case. Cases were gathered retrospectively for diversity and difficulty and 26 randomly selected cases were evaluated. The underlying issues were identified and classified. RESULTS: Both reviewers rated the first diagnosis correct in 25% of the cases and at least one rated it wrong in 10%. Analyzing the detailed reasoning, 137 issues were raised, about 5.3 per case. Of these, 53% were possible concerns raised by one reviewer. Of the 5.3 issues per case, 2.5 were attributable to controversies, misunderstandings, or mistakes; 1 was due to the overly simplistic representation of the summaries; and 1.8 were issues related to the program. CONCLUSION: Overall, the program is capable of providing high-quality detailed diagnostic hypotheses for complex cardiovascular cases. The results highlight several issues: 1) the difficulty of effectively summarizing hypotheses, 2) the nature of a physician's causal explanation, and 3) some problems in evaluating detailed diagnostic reasoning. The mistakes the program made imply that some additional refinement is needed but that the reasoning mechanisms developed can support the appropriate reasoning. The appropriate next step is a prospective evaluation addressing the program's usefulness.

Aged↗