Calculation of coronary vascular resistance.

A conscious, chronically instrumented canine model was used to investigate resistance changes in the distribution of the circumflex coronary artery as the artery was constricted. Several discrete constrictions were studied at two different levels of flow: resting and peak flow reactive hyperaemia. The resistance of the bed downstream from the constriction was calculated by formulae which defined the coronary back pressure as either venous pressure (Pv) or the arterial pressure at which coronary flow ceased (Pc). When Pv was taken as the back pressure, the resistance of the coronary bed during reactive hyperaemia progressively increased as the upstream artery was constricted. When Pc was taken as the back pressure, calculated coronary resistance for reactive hyperaemia showed little change. It is not known if elastic recoil of coronary resistance vessels, consequent to low poststenotic pressure, could occur to the extent required to be the physical basis for the calculated increase in resistance when Pv is taken to be the back pressure. Use of Pc as the back pressure implies that the coronary circulation contains a segment having the hydraulic characteristics of a collapsible tube.

Factors determining delayed peak flow in canine myocardial reactive hyperaemia.

It has been suggested that delayed restoration of flow to the deeper layers of the myocardium is responsible for the gradual rise to peak flow rate characteristic of myocardial hyperaemia (RH). The distribution of coronary flow during RH was studied by injecting radiomicrospheres into the left atrium open chest dog preparations just prior to the end of a 15 s occlusion of the left circumflex branch. The artery was then reoccluded after 1, 2, or 4 s of RH. Myocardium perfused by the left anterior decending branch served as a control; the ratio of endocardial to epicardial (end/epi) perfusion in this bed averaged 1.14. During coronary occlusion and during the first second of RH the end/epi ratio in the hyperaemic zone averaged 50% of control, but rose progressively to equal control at the time of peak flow. Although evanescent subendocardial ischaemia may contribute to the gradual rise to peak flow rate it cannot by itself account for the time course of this response.

Risk assessment in urgent/emergent coronary artery surgery.

A statistical model has been developed to allow for prediction of individual patient prognosis following urgent/emergent coronary artery bypass grafting (CABG). None of the models previously described for use in coronary artery surgery has been tested with a prospective patient series that confirms the true predictive capacity of the model. Ideally, the predictive ability of such models should be validated with prospective trials. To examine the feasibility of statistical modeling in this clinical context, a computerized model based on the theorem of Bayes was developed to predict operative mortality for urgent coronary artery surgery. The presence or absence of 20 risk factors was determined for each of 405 consecutive patients undergoing urgent coronary artery surgery from January 1984 to January 1989. The first 100 patients were used to develop a database for the model, which was then used to prospectively evaluate the remaining 305 patients. There was good agreement between predicted and observed results. Models of this kind are particularly advantageous because of the ability to (1) accommodate multiple risk factors, (2) become tailored to a specific practice, and (3) determine individual rather than group prognosis. Validation with a prospective trial confirms the practical utility of this approach. This model has reliably predicted the risk associated with urgent coronary artery surgery and may provide important clinical information for the management of patients being evaluated for urgent revascularization.

Primary cysts and tumors of the mediastinum.

A retrospective analysis was performed on 230 patients with primary cysts and tumors of the mediastinum seen at our institution from January 1944 to April 1989. We divided these patients into two groups. Group 1 was seen before 1970 and group 2 was seen from January 1970 to April 1989. There was a significant increase in the prevalence of malignancy in group 2 (47.2% versus 17.1%; p less than 0.0001) due to an increase in the number of lymphomas (22.6% versus 3.5%; p less than 0.001) and malignant neurogenic tumors (6.8% versus 1.1%; p = 0.0528). There was a significant increase in the number of malignant tumors in the anterior (59.5% versus 30.9%; p = 0.0022) and paravertebral (28.5% versus 2.8%; p = 0.0027) compartments in group 2. More patients with these tumors were symptomatic in group 2 (63.6% versus 5%; p = 0.0422). There was an increase of ancillary diagnostic studies performed to evaluate these tumors (76.0% versus 34.5%; p = 0.0422). Logistic regression analysis identified date of presentation (p less than 0.005), symptoms (p less than 0.01), size (p less than 0.005), and the anterior mediastinal compartment (p less than 0.005) as preoperative predictors of malignancy. The surgical approach to these tumors included more median sternotomy (30.1% versus 10.7%; p = 0.0008), anterior mediastinotomy, and cervical mediastinoscopy in group 2 (1.1% versus 17.5%; p = 0.0002). Long-term results support surgical resection in benign lesions and an aggressive multimodality approach to malignant lesions.

Three-dimensional image reconstruction for planning of a complex cardiovascular procedure.

A rare left subclavian artery aneurysm associated with a congenital arch anomaly was difficult to visualize using standard radiographic techniques. Three-dimensional computer imaging produced a clear depiction of this unusual anatomy and simplified the preoperative planning.

True emergency coronary artery bypass surgery.

Previous reports of emergency coronary artery bypass grafting often included cases that were not true surgical emergencies, thereby creating inappropriately favorable results. To accurately investigate this important subgroup of patients, we analyzed our recent experience with truly emergent coronary artery bypass grafting. From January 1984 to January 1989, 117 patients underwent true emergency bypass grafting for acute refractory coronary artery ischemia. Clinical deterioration was associated with failure of percutaneous angioplasty in 37 patients and instability during diagnostic catheterization in 13 patients. Refractory ischemia developed in the remaining patients while on the ward or in the intensive care unit. All operations were performed within four hours of surgical consultation, most within one hour. Overall in-hospital operative mortality was 14.5% (17/117), and 76.5% of deaths (13/17) were due to cardiac-related causes. Major morbidity occurred in 35.9% (42/117). Univariate analysis isolated ejection fraction, extent of coronary artery disease, previous myocardial infarction, hypertension, need for inotropic support, use of an intraaortic balloon pump, and cardiopulmonary resuscitation as risk factors for operative mortality. Stepwise multivariate analysis confirmed that previous myocardial infarction, hypertension, cardiopulmonary resuscitation, and reoperation were independently significant risk factors. Age, sex, diabetes, left main disease, and peripheral vascular disease had no significant impact on the prognosis. The 4% operative mortality (2/50) for patients taken directly to the operating room from the catheterization suite was significantly lower than the 22.4% mortality (15/67) associated with emergencies arising on the ward or intensive care unit (p less than 0.01). A logistic risk equation developed from this population accurately modeled operative mortality.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of artificial intelligence for the preoperative diagnosis of pulmonary lesions.

The relatively new field of artificial intelligence has spawned a variety of techniques associated with computer-assisted diagnosis. These techniques have been applied to the diagnosis of pulmonary lesions, but previous reports have focused on medical rather than surgical populations and the results have been evaluated using only retrospective patient surveys. We used a Bayesian algorithm to develop a diagnostic computer model for prospectively evaluating patients undergoing thoracotomy for suspected pulmonary malignancy. Patients who had a preoperative diagnosis were not included. Preoperative clinical and radiographic parameters for 100 consecutive patients were prospectively entered into the diagnostic model, which then categorized the lesion as benign or malignant. The computer predictions agreed with the final histological diagnosis in 95 of the 100 patients. The sensitivity was 96% and the specificity was 89% for this prospective series. These results indicate that the computer-assisted diagnosis of pulmonary lesions may have a role in this clinical setting.

The effect of WR 149024 on survival following hemorrhage in conscious rats.

The effect of WR 149024, an alpha-receptor antagonist, on survival following hemorrhage with no volume replacement therapy, was investigated. WR 149024 (either 5.0 or 50.0 mg/kg) was administered intraperitoneally (i.p.) to conscious rats during exsanguination. Both WR 149024 treatments caused a significant decrease in survival (P less than 0.021), compared with water-injected controls.

Why is Marine combat mortality less than that of the Army?

Data from recent wars indicate that a wounded Marine had a 20% lower risk of dying than an Army soldier. Possible reasons for this difference are (1) Navy care is superior, (2) soldiers sustained more severe wounds, and (3) the services count casualties differently. Injury severity was measured in random samples of Marines and soldiers that were selected from the Wound Data and Munitions Effectiveness Team database. There was no difference in the lethality of injury and the prevalence of lifesaving first aid. Wounded Marines were more likely to wear protective vests, and this decreased Marine mortality in Vietnam. Hospitalized Marines had lower Injury Severity Scores and were less likely to be returned to duty without first being admitted to a medical treatment facility. Lower Marine combat mortality is primarily the result of the fact that a Marine with a minor soft tissue wound was more likely to be hospitalized than was a soldier with a similar injury.

USS Franklin and the USS Stark--recurrent problems in the prevention and treatment of naval battle casualties.

Events such as the Falklands War and naval actions in the Persian Gulf have emphasized the unique nature of battle casualty care on warships. The purpose of this paper is to describe two actions which illustrate the problems that a medical officer may confront when a warship sustains battle damage: that of the USS Franklin in March 1945 and that of the USS Stark in May 1987. Although neither ship was sunk, damage was severe and about one-quarter of each ship's crew became casualties. More than three-quarters of the casualties were killed, death being due to blast, fire and smoke inhalation.