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Biomedical subjects

S B Colvin

Publications and source records attributed to S B Colvin.

At least 91 records · Page 5Linked to original sources
PubMed1988

Epidural-evoked potentials: a more specific indicator of spinal cord ischemia.

The purpose of this experimental study was to examine the differences between peripheral nerve stimulation and direct spinal stimulation in generating cortical somatosensory-evoked potential (SEP) responses for monitoring spinal cord ischemia during thoracic aorta cross-clamping. Adult mongrel dogs (n = 6) were placed under general anesthesia and a left thoracotomy was performed. A conventional stimulating electrode was placed over the posterior tibial nerve (PN-SEP), and a special bipolar electrode was placed epidurally over the spinal cord at L1-2 (SC-SEP). The aorta was cross-clamped proximal to the left subclavian artery. Stimulations were alternately performed through both electrodes, and SEP responses were continuously monitored. The cross-clamp was released after one hour and the animal was observed for another hour prior to sacrifice. Excellent SEPs were obtained with six stimuli over 3 sec via the SC-SEP stimulus in contrast to the 200 stimulations over 90 sec required for the PN-SEP stimulus. Aortic cross-clamping resulted in a significantly longer mean time to loss of SEPs for SC-SEP (mean +/- SEM, 13.7 +/- 1.0 min for SC-SEP vs 11.3 +/- 0.7 min for PN-SEP, P less than 0.05). Likewise, unclamping of the aorta consistently resulted in a shorter mean time to return of SEPs for SC-SEP compared with PN-SEP. These data indicate that direct epidural stimulation for evoked cortical responses is a more sensitive means of determining the adequacy of posterior spinal cord blood flow as reflected by posterior spinal cord function.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Current concepts of mitral valve reconstruction for mitral insufficiency.

In recent years, there has been a renewed interest in surgical reconstruction of the insufficient mitral valve because of reconfirmation of the limitations of existing prosthetic and bioprosthetic valves. A follow-up study, including late functional data, of 148 patients who underwent mitral valve reconstruction at our institution was combined with a review of the literature to assess the current status of mitral reconstruction. The results indicate that mitral reconstruction by Carpentier techniques is widely applicable, durable, and relatively free of complication. Freedom from late thromboembolic and anticoagulant complications is particularly notable. These factors could prove to justify earlier operative intervention in patients with mitral insufficiency before permanent myocardial damage evolves. As mitral valve reconstruction techniques become more familiar and widely used, mitral reconstruction may become the operative procedure of choice for mitral insufficiency, especially insufficiency due to degenerative disease.

Actuarial Analysis↗
PubMed1988

Percutaneous cardiopulmonary bypass limits myocardial injury from ischemic fibrillation and reperfusion.

Percutaneous implementation of cardiopulmonary bypass (PCPB) with a synchronous pulsatile pump has been shown to be an efficient means of unloading the heart. Therefore, this technique may provide a practical and effective method for treating patients undergoing a major cardiac catastrophe who are unresponsive to the usual resuscitative efforts. We tested whether PCPB could effectively unload the heart and provide myocardial salvage during left anterior descending (LAD) coronary artery occlusion complicated by ventricular fibrillation in the canine model (n = 13). All 13 dogs fibrillated within 20 minutes of LAD occlusion, and none could be successfully resuscitated by manual cardiac compression, sodium bicarbonate administration, antiarrhythmic agent administration, and electrical defibrillation. All 13 dogs were then placed on PCPB by way of the right jugular vein and right femoral artery; in seven, we used a synchronous pulsatile pump and in six a standard roller pump. No vent was placed in the left ventricle. All animals returned to normal sinus rhythm within 20 minutes of institution of PCPB. The LAD snare was released after 2 hours, and all animals were maintained on PCPB during 3 hours of reperfusion. At sacrifice, the area of infarction was determined by staining with triphenyltetrazolium chloride and was expressed as a percentage of the left ventricular area-at-risk for infarction. The tension time index was also measured and expressed as percent change from baseline. The left ventricular area-at-risk for infarction was similar in both groups (31.5% for roller pump vs. 29.2% for pulsatile pump; p greater than 0.05), but the area of infarction as a percentage of the area at risk was significantly smaller in the pulsatile-pump group (22.0%) than in the roller-pump group (35.4%; p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Long-term results of mitral valve reconstruction with Carpentier techniques in 148 patients with mitral insufficiency.

There have been few relatively complete follow-up studies of long-term mitral valve function after Carpentier-type surgical reconstruction. Between January 1980 and May 1986, 148 patients underwent Carpentier reconstruction for mitral valve disease (43% degenerative and 30% rheumatic). Operative mortality was 5.4% overall (1.2% for isolated mitral reconstruction), and follow-up (mean, 26 months) was completed for all survivors. Five-year survival from late cardiac death was 90.0%, as was 5-year freedom from postreconstruction mitral valve replacement. Postreconstruction mitral replacement was needed in eight patients, in only five for failure of repair. Follow-up echocardiographic studies on 83.2% (104 of 125) of eligible patients showed 92.3% were free of significant (3+ or 4+) mitral regurgitation. Freedom from mitral valve replacement or recurrent severe (4+) insufficiency was 84.4% at 5 years overall, but was lower for the rheumatic type of mitral disease than for the degenerative type (71.6% vs. 88.3%). At 5 years, 95.2% of patients were free from thromboembolism without the necessity for long-term warfarin (Coumadin) therapy. At follow-up, 95.3% of survivors had improved to New York Heart Association Class I or II. The functional durability of mitral reconstruction and consistently high level of freedom from late endocarditis and thromboembolic and anticoagulant complications support the value of the Carpentier method of mitral reconstruction for mitral insufficiency, especially insufficiency due to degenerative disease.

Adolescent↗
PubMed1987

A comparison of methods for limiting myocardial infarct expansion during acute reperfusion--primary role of unloading.

Current use of angioplasty, thrombolysis, and surgical techniques for prompt reperfusion of an acute myocardial infarction raises questions concerning the optimum reperfusion technique for maximum myocardial salvage. Alterations in the conditions of reperfusion and/or the composition of the initial reperfusate can exert a significant effect on the extent of myocardial salvage. In an effort to define an optimum reperfusion technique, we used 40 dogs in a series of experiments in which the left anterior descending coronary artery (LAD) was snared for 2 hr followed by reperfusion by one of five methods for 4 hr. In addition, in a control group(group I, n = 6) the LAD was occluded for 6 hr without any reperfusion. In group 2 (n = 12), simulating medical reperfusion, reperfusion was achieved by simply releasing the snare for 4 hr. Group 3 dogs (n = 6) were placed on pulsatile left atrial-femoral bypass throughout 4 hr of reperfusion. Group 4 dogs (n = 9) were placed on percutaneous, synchronized pulsatile cardiopulmonary bypass during reperfusion. The procedure in group 5 (n = 7) dogs simulated coronary artery bypass grafting with cardiopulmonary bypass and cold blood, low-Ca++ cardioplegia during reperfusion. Group 6 (n = 6) was treated similarly except that during reperfusion amino acid-enriched cardioplegia was administered by warm induction techniques. At the end of 4 hr of reperfusion, the left ventricular area of infarction was determined by triphenyltetrazolium chloride staining and expressed as a percentage of the left ventricular area at risk for infarction (area of infarction [AI]/area at risk [AR]).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

The atherosclerotic ascending aorta and transverse arch: a new technique to prevent cerebral injury during bypass: experience with 13 patients.

Calcification of the ascending aorta and transverse arch significantly increases morbidity and may compromise the completeness of cardiac surgical procedures. Several stratagems have been suggested to reduce the risk, but for some patients this finding is still associated with a devastating outcome, irrespective of the technique employed. Thirteen patients (7 men and 6 women with a mean age of 66 years) with extensive calcification in the ascending aorta and transverse arch underwent cardiopulmonary bypass (CPB). The presence of calcification was known prior to CPB in 12 patients and noted after cross-clamping of the aorta in 1 patient. Special techniques for cannulation of the ascending aorta or arch were undertaken in 12 patients; 1 patient required groin cannulation. In 12 patients CPB with gradual core cooling to 18 degrees C was done, during which time no manipulation of the aorta was allowed. Circulatory arrest was then initiated for 3.5 to 12 minutes. The aorta was opened widely during this time to remove ulcerated plaques and friable debris, and to locate a safe place for aortic occlusion. All patients recovered without neurological complications. In 1 patient, in whom occipital lobe infarcts developed, calcification was discovered after the aorta had been cross-clamped and necessitated subsequent endarterectomy of the ascending aorta and transverse arch.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

A clinical evaluation of the hypothesis that rupture of the left ventricle following mitral valve replacement can be prevented by preservation of the chordae of the mural leaflet.

Experiences with 14 patients undergoing rupture of the left ventricle following mitral valve replacement over a period of 9 years have been described. Three different types have been recognized. Before 1978, most injuries occurred in the atrioventricular groove, apparently resulting from traction that insidiously avulsed the mitral annulus from the underlying left ventricular muscle. Several changes in operative technique, described in the text, were made to prevent this traction avulsion. Following the adoption of these principles, rupture in the atrioventricular groove virtually disappeared. A second type of injury, strut perforation, has been recognized in only one patient, a small 81-year-old female in whom the prosthesis inserted was too large for the ventricular cavity. Translucent obturators were subsequently developed not only to size the left ventricle but also to note the location of the post of the porcine prosthesis before insertion. Further problems of this type have not been seen. The most puzzling, and currently the most significant, problem is a third type of rupture, the mid-ventricular rupture, suggested as Type III by Miller in 1978 and described in detail by Cobbs in 1977 and 1980. The phenomenon seems to be a true spontaneous rupture of a thin left ventricle, usually occurring in small elderly women with mitral valve disease. If the friability of the left ventricle is transiently increased with potassium cardioplegia, such ventricles may spontaneously rupture following division of the chordae to the annulus of the mural leaflet. If this concept is correct, a rupture in some patients can best be prevented by preserving these chordae. It is well realized, of course, that a fortunate narrative experience of 3 1/2 years does not have any statistical value concerning a complication that occurs in 1 to 2% of operations. The experiences are reported, however, because to our knowledge, the untethered loop hypothesis has not been previously evaluated in a large number of consecutive patients operated on. Future comparison of experiences reported by others should make it possible to determine whether or not this concept is correct.

Aged↗
PubMed1985

Adjunctive left ventricular unloading during myocardial reperfusion plays a major role in minimizing myocardial infarct size.

Although prompt institution of reperfusion following coronary artery occlusion has been shown to limit myocardial infarct size, significant "reperfusion injury" may result. We investigated in a canine model whether maintenance of the left ventricle in an unloaded state during the initial reperfusion period following acute myocardial ischemia would result in greater limitation of infarct size or modify the development of reperfusion injury. Group I (control, n = 6) underwent 6 hours of occlusion of the left anterior descending coronary artery without further intervention. In both Group II (n = 6) and Group III (n = 6), the snare was released after 2 hours and hearts were reperfused for 4 hours. In Group III only, the left ventricle was maintained in an unloaded state throughout the entire reperfusion interval via pulsatile left atrial-femoral artery bypass. The results showed that reperfusion of the left ventricle in an unloaded state resulted in significantly improved limitation of both infarct size (area of infarct/area at risk = 16.6% for Group III versus 72.0% for Group I and 55.4% for Group II, p less than 0.001) and area of microvascular damage (area of microvascular damage/area at risk = 4.8% for Group III versus 30.6% for Group II, p less than 0.001). These results indicate that although myocardial reperfusion of the type provided by thrombolysis and/or angioplasty techniques does result in limitation of infarct size when compared to no reperfusion, this limitation is not optimal unless the left ventricle is unloaded during the initial reperfusion period.

Animals↗
PubMed1985

Experiences with the Carpentier techniques of mitral valve reconstruction in 103 patients (1980-1985).

A total of 103 patients, age range 2 to 77 years, had some type of Carpentier reconstruction for mitral insufficiency. The mitral insufficiency resulted from ruptured chordae in 52, prolapse in 13, rheumatic fever in 16, coronary disease in eight, congenital disease in nine, and endocarditis in five. Multiple abnormalities were usually present. Four patients had severe calcification of the anulus. A reconstruction was accomplished in almost all patients. A ring annuloplasty was performed in all but two small children, but annuloplasty alone was adequate in only 17 patients. Fifty-eight had resection of 1 to 4 cm of diseased mitral leaflet. In 23 patients, chordal transposition or shortening was employed. Aortic leaflet repair was done in 28. Shortened, fused chordae (one to eight) were divided in 13 patients. Additional procedures performed in 28 patients included coronary bypass in 14. A successful repair was accomplished in all but one patient (moderate residual insufficiency). Two late hospital deaths were unrelated to the mitral repair. Following hospital discharge, ring dehiscence necessitated repeat operation in one patient. Thromboembolism produced a permanent minor neurological deficit in only one patient. There have been no late recurrences of insufficiency. Recurrent endocarditis necessitated valve replacement in three patients. A late Doppler evaluation of 95 patients for mitral insufficiency revealed none in 82, a trace in 12, and moderate insufficiency in one. Late catheterization in 16 patients revealed no insufficiency. The data suggest that reconstruction, rather than prosthetic valve replacement, can be successfully performed in over 90% of patients with nonrheumatic, noncalcified mitral valves. A much wider use of the technique seems strongly indicated.

Chordae Tendineae↗
PubMed1985

Quantification of pulsatile flow during cardiopulmonary bypass to permit direct comparison of the effectiveness of various types of "pulsatile" and "nonpulsatile" flow.

The relative merits of adding a "pulsatile" component to flow during cardiopulmonary bypass (CPB) has long generated controversy, the resolution of which has been hampered by lack of quantification of the "pulsatility" delivered by different devices. The present experimental series had two goals: to quantify the "pulsatility" of blood flow during CPB in terms of pulse rate and pulsatility index (PI) and to examine which aspects of a "pulsed flow" provide clinical benefits. A flow waveform can be expressed in terms of its baseline rate and its PI, the sum of the square of its harmonics components divided by the square of the mean flow. We used PI to quantify the pulsatility of blood flow in the descending thoracic aorta and used changes in the serum lactate level as an indication of end organ flow. In one experimental series seven adult mongrel dogs were placed on roller pump CPB at a constant flow of 100 ml/kg/min. After a 20-minute stabilization period a roller pump wave and three different pulse shapes (generated by a computer-controlled hydraulic pump) were evaluated for 15 minutes each. The pulse wave shapes were graded, with C being the sharpest and A the least sharp. In a second series six other dogs were placed on CPB and were subjected to roller pump perfusion and three pulse waves of identical shape but at different rates. The results indicated that a combination of a minimum PI of 1.88 and a minimum rate of 80 bpm were necessary to significantly reduce lactate production as compared with roller pump perfusion. Thus the same mean flow can have very different physiologic effects depending on how it is delivered. This quantification method permits direct comparison of different "pulsatile waveforms" and provides a means for identification of optimal pulsatile flow.

Animals↗
PubMed1984

Left ventricular outflow obstruction: a complication of mitral valvuloplasty.

Thirty-two patients with severe mitral regurgitation underwent Carpentier mitral valvuloplasty. Postoperatively, three of these patients developed clinical and echocardiographic evidence of left ventricular outflow tract obstruction. None of these patients had asymmetric septal hypertrophy or preoperative echocardiographic demonstration of systolic anterior motion of the mitral valve. Outflow obstruction postoperatively was caused by systolic anterior motion of the mitral valve. Because this potential complication of Carpentier mitral valvuloplasty produced significant hemodynamic effects in two patients, echocardiography should be routinely performed after this operation.

Echocardiography↗
PubMed1983

Late functional and hemodynamic status of surviving patients following insertion of the left heart assist device.

Since July, 1978, we have inserted a roller pump type of left heart assist device between the left atrium and ascending aorta in 35 patients. There were no significant complications related to use of the device. Seventeen patients recovered sufficiently to have the device removed. There were four early deaths, 60 to 120 days following removal of the device. Three of these patients died of septic complications and one patient died as a result of a cardiac arrest. Of the 13 long-term survivors, seven are working and six are retired. Five patients have mild to moderate cardiac symptoms, whereas eight others are completely asymptomatic. In three patients the ejection fraction was significantly lower than preoperatively; however, in all other patients the ejection fraction either stayed the same or improved postoperatively. We conclude that this type of left heart assist device can provide adequate cardiac support in patients with profound left ventricular dysfunction following cardiac operations. Furthermore, surviving patients generally have satisfactory long-term cardiac function and are leading productive lives.

Adult↗
PubMed1983

The role of the activated clotting time in heparin administration and neutralization for cardiopulmonary bypass.

Precise guidelines for heparin administration and neutralization during cardiopulmonary bypass (CPB) are not established. To a large extent, the uncertainty originates from a disparity between the heparin dosage, the plasma heparin concentration, and the clinical heparin effect. We investigated these relationships in 44 consecutive patients at New York University Medical Center. Following serial loading doses of heparin (2 and 4 mg/kg) there was a wide variation in both the measured clinical heparin effect (activated clotting time--ACT) and the plasma heparin concentration. When the Act was compared to the heparin concentration, there was no linear relationship noted after heparin does commonly employed for CPB. The calculated heparin sensitivity varied over a fourfold range and was not related to the baseline antithrombin III activity. At the completion of CPB, heparin was neutralized with a 2 mg/kg protamine dose regardless of the total heparin dose. Heparin levels fell from 4.17 +/- 1.29 to 0.19 +/- 0.20 units/ml. Additional protamine was given to 49% of the patients as the ACT had not returned to pre-heparin levels. The total protamine dose rarely exceeded 3 mg/kg. This technique resulted in the administration of 30% to 50% less protamine than predicted by other commonly used protocols. In the subsequent 4 hours after protamine administration, heparin levels remained insignificant. Mild heparin rebound was found in two patients (4.5%) but was not associated with excessive bleeding. Following bypass a comparison of heparin levels and ACTs demonstrated the ACT to be a poor indicator of residual circulating heparin. These data show: (1) that neither the heparin dosage nor the plasma heparin concentration can accurately predict the magnitude of the clinical heparin effect in patients undergoing CPB and emphasize the importance of the ACT as the best available measurement of safe anticoagulation, (2) heparin "rebound" was not clinically significant, and (3) heparin was neutralized with 2 to 3 mg/kg protamine in virtually all patients, regardless of the total heparin dose.

Adult↗
PubMed1983

Aneurysms of the descending aorta. Surgical experience in 48 patients.

Uniformity of opinion does not exist concerning an optimal surgical strategy for descending aortic aneurysms. In order to assess the impact of surgical technique on operative mortality, morbidity, late outcome, we reviewed 48 consecutive patients operated upon from 1976 to 1980. Average age was 61 years, and 37 patients (77%) were men. The average interval of aortic occlusion in the Gott shunt group was 48 minutes, which was significantly longer than that of patients operated upon without shunts (30 minutes). No patient in the Gott shunt group had postoperative paraplegia, but it was noted in two patients (18%) treated without a shunt. Operative deaths in patients with Gott shunts were caused by cardiac (two patients), neurologic (one patient), pulmonary (one patient), and abdominal (two patients) factors. A pulmonary embolus caused the single postoperative death in the "no shunt" group, and another patient died intraoperatively. A group of seven patients were treated by temporary femoral vein--femoral artery bypass because of extensive aneurysmal disease, advanced associated major systemic disorders, or anticipated excessive hemorrhage when the aneurysm was opened. All patients survived free of neurologic sequela, but one developed a reversible intraoperative coagulopathy. This study underscores the safety and usefulness of the femoral vein--femoral artery bypass in treating certain descending thoracic aneurysms and reinforces the importance of several technical guidelines concerning the proper insertion and use of the Gott shunt. These guidelines would have significantly reduced the observed operative morbidity and mortality.

Adult↗
PubMed1982

Cardiac tamponade secondary to chylopericardium following cardiac surgery: case report and review of the literature.

Only four instances of isolated chylopericardium following cardiac operation have been reported previously. We encountered this complication in a young patient who was operated on for infundibular pulmonary stenosis. The etiology appears to be related to a combination of intraoperative lymphatic injury and catheter-related subclavian vein thrombosis, the latter potentially elevating pressure within the thoracic duct and thereby resulting in an accumulation of chyle within the pericardial space. Therapy for this problem usually includes partial pericardiectomy with or without ligation of the thoracic duct.

Adult↗
PubMed1982

Long-term survival with partial left heart bypass following perioperative myocardial infarction and shock.

During the period from July 1, 1978 to Dec. 31, 1980, we employed a partial left heart bypass (left atrium to ascending aorta) in 16 patients who could not be weaned from cardiopulmonary bypass with inotropic agents and the intra-aortic balloon pump. Flow rates up to 3,500 ml/min could be obtained with this device. Eight of the 16 patients survived and left the hospital. One patient died of a cardiac arrest 4 months postoperatively and one has recurrent angina and moderate congestive heart failure 24 months postoperatively. Six patients are well 5 to 17 months after discharge. Seven of the eight deaths were characterized by progressive myocardial failure. One patient died of ventricular fibrillation 18 hours after discontinuation of the left heart bypass. All survivors had significant improvement in ventricular function 12 to 24 hours afer institution of the left heart bypass, which was continued for 16 to 68 hours. These results indicate that early institution of left heart bypass in seriously ill patients can provide satisfactory long-term results.

Aged↗