Influence of Ultra-Low-Dose and Iterative Reconstructions on the Visualization of Orbital Soft Tissues on Maxillofacial CT

BACKGROUND AND PURPOSE

Dose reduction on CT scans for surgical planning and postoperative evaluation of midface and orbital fractures is an important concern. The purpose of this study was to evaluate the variability of various low-dose and iterative reconstruction techniques on the visualization of orbital soft tissues.

MATERIALS AND METHODS

Contrast-to-noise ratios of the optic nerve and inferior rectus muscle and subjective scores of a human cadaver were calculated from CT with a reference dose protocol (CT dose index volume = 36.69 mGy) and a subsequent series of low-dose protocols (LDPs I-4: CT dose index volume = 4.18, 2.64, 0.99, and 0.53 mGy) with filtered back-projection (FBP) and adaptive statistical iterative reconstruction (ASIR)-50, ASIR-100, and model-based iterative reconstruction. The Dunn Multiple Comparison Test was used to compare each combination of protocols (α = .05).

RESULTS

Compared with the reference dose protocol with FBP, the following statistically significant differences in contrast-to-noise ratios were shown (all, P ≤ .012) for the following: 1) optic nerve: LDP-I with FBP; LDP-II with FBP and ASIR-50; LDP-III with FBP, ASIR-50, and ASIR-100; and LDP-IV with FBP, ASIR-50, and ASIR-100; and 2) inferior rectus muscle: LDP-II with FBP, LDP-III with FBP and ASIR-50, and LDP-IV with FBP, ASIR-50, and ASIR-100. Model-based iterative reconstruction showed the best contrast-to-noise ratio in all images and provided similar subjective scores for LDP-II. ASIR-50 had no remarkable effect, and ASIR-100, a small effect on subjective scores.

CONCLUSIONS

Compared with a reference dose protocol with FBP, model-based iterative reconstruction may show similar diagnostic visibility of orbital soft tissues at a CT dose index volume of 2.64 mGy. Low-dose technology and iterative reconstruction technology may redefine current reference dose levels in maxillofacial CT.

Splanchnic oxygen transport and lactate metabolism during normothermic cardiopulmonary bypass in humans

The effect of normothermic (36.2 degrees C +/- 0.6 degree C) nonpulsatile cardiopulmonary bypass (CPB) on splanchnic (hepatic) blood flow (SBF), splanchnic oxygen transport (DO2spl) and oxygen consumption (VO2spl), splanchnic lactate uptake and gastric mucosal pH (pHi, gastric tonometry) was studied in 12 adults (New York Heart Association class II, ejection fraction > or = 0.4) undergoing coronary artery surgery. SBF was estimated with the constant-infusion indocyanine green (ICG) technique using a hepatic venous catheter. DO2spl, VO2spl, and splanchnic lactate uptake were calculated using the Fick principle after the induction of anesthesia, during aortic cross-clamping, after CPB, and 2 and 7 h after admission to the intensive care unit (ICU). SBF, DO2spl, and VO2spl did not decrease during CPB but increased after ICU admission, whereas pHi decreased 7 h after ICU admission. Initial ICG extraction was 0.78, which decreased to 0.54 during aortic clamping and remained low thereafter. The increased arterial blood lactate concentrations were not associated with a decreased splanchnic lactate uptake. We conclude that normothermic CPB is not associated with deterioration in the global intestinal oxygen supply. The increase of blood lactate levels and the decrease in ICG extraction, as well as in pHi, are consistent with a systemic inflammatory response to CPB.

IMPLICATIONS

This study demonstrated that normothermic cardiopulmonary bypass (at flows > 2.4 L.min-1.m-2) was not associated with deterioration in global intestinal oxygen delivery, which suggests that increased blood lactate concentrations and decreased gastric mucosal pH and indocyanine green extraction are manifestations of a systemic inflammatory response to cardiopulmonary bypass.

Effects of failure of the right side of the heart and increased pulmonary resistance on mechanical circulatory support with use of the miniaturized HIA-VAD displacement pump system

This experimental study was designed to assess the influence of failure of the right side of the heart or pulmonary hypertension, or both, on the performance of a novel miniaturized left ventricular assist device. In small-sized dogs (n = 50) ischemic global left ventricular failure was induced and support was provided by the HIA-VAD displacement pump (stroke volume 10 or 25 ml) installed as a left ventricular assist device. In three groups of animals (n = 10 each) pulmonary hypertension was created before induction of global left ventricular failure. During left ventricular assist device support temporary ischemic failure of the right side of the heart was induced in four groups of animals (n = 10 each). In the group subjected to left ventricular failure, support with the left ventricular assist device, and right ventricular failure during left ventricular assist, left atrial pressure and cardiac index were significantly lower than in the group subjected to left ventricular failure and left ventricular assist alone (2 +/- 6 versus 11 +/- 6 mm Hg and 1.6 +/- 0.4 versus 1.0 +/- 0.4 L/(min/m2), respectively, p < 0.05). In the group subjected to pulmonary hypertension, left ventricular failure, and left ventricular support, left atrial pressure dropped to values near zero but cardiac index remained unaltered as compared with results with the same regimen without pulmonary hypertension. However, when right ventricular failure was added (that is, pulmonary hypertension, left ventricular failure, left ventricular support, and right ventricular failure during support with the left ventricular assist device) left atrial pressure dropped to negative values (p < 0.05) and cardiac index progressively deteriorated. When, in an additional group of dogs, biventricular support was installed in the latter regimen, circulation was initially well supported but oxygenation deteriorated in 60% of cases. We conclude that (1) adequate right ventricular function was indispensable during support with the left ventricular assist device, (2) the combination of pulmonary hypertension and right ventricular failure led to the "low left ventricular assist device output syndrome," and (3) biventricular mechanical support in the presence of pulmonary hypertension may be complicated by the alveolar leakage syndrome.

Reperfusion after cardioplegic cardiac arrest--effects on intracoronary leucocyte elastase release and oxygen free radical mediated lipid peroxidation

In experimental animal models reperfusion of ischaemic myocardium causes sequestration of leucocytes within the coronary circulation. Leucocytes contribute to postischaemic myocardial injury by releasing proteolytic enzymes and by generating oxygen free radicals. The aim of this study was to investigate whether leucocytes also contribute to myocardial injury following ischaemia and reperfusion associated with cardioplegic cardiac arrest. Therefore, we studied the release of the proteolytic enzyme elastase and oxygen free radical initiated myocardial lipid peroxidation in coronary sinus blood during reperfusion after cardioplegic cardiac arrest. The elastase-alpha-1-proteinase inhibitor complex and malondialdehyde (a byproduct of myocardial lipid peroxidation) were measured in arterial, central venous and coronary sinus blood samples in 19 patients undergoing elective coronary artery bypass grafting before aortic crossclamping and 1, 5, 10 and 20 m in after aortic declamping. Malondialdehyde concentrations did not increase significantly during the study period, whereas elastase concentrations showed a significant increase during cardiopulmonary bypass in arterial, central venous as well as coronary sinus blood. Neither elastase nor malondialdehyde concentrations in coronary sinus blood differed significantly from arterial or central venous blood at any time point measured. Our data demonstrated increased elastase concentrations during cardiopulmonary bypass, but we did not find enhance intracoronary elastase release or myocardial during cardiopulmonary bypass, but we did not find enhanced intracoronary elastase release or myocardial lipid peroxidation. Our data suggest that patients are sufficiently protected from leucocyte mediated ischaemia reperfusion injury during uncomplicated coronary artery bypass grafting with cardioplegic arrest.

Coronary sinus endothelin-1 concentrations after cardioplegic cardiac arrest

BACKGROUND

Data from animal experiments demonstrate that endothelin-1 is released into the coronary circulation during myocardial ischaemia and reperfusion, indicating that endothelin-1 may contribute to the pathophysiology of ischaemia and reperfusion. The aim of this study was to investigate the release of endothelin-1 into the coronary circulation during reperfusion of the human heart after hypothermic cardioplegic cardiac arrest.

METHODS

Endothelin-1 was measured in arterial, central venous and coronary sinus blood in 19 patients undergoing elective uncomplicated coronary artery bypass grafting before aortic crossclamping and 1, 5, 10 and 20 min after aortic declamping.

RESULTS

Endothelin-1 concentrations showed a slight non-significant increase over baseline values 1, 5, 10 and 20 min after aortic declamping. Endothelin-1 concentrations were not significantly higher in coronary sinus blood than in arterial blood at any time point measured, indicating no net release of endothelin-1 by the heart.

CONCLUSIONS

Our results did not demonstrate endothelin-1 release into the coronary circulation after myocardial ischemia and reperfusion associated with hypothermic cardioplegic cardiac arrest.

Diagnosis of congenital pericardial defects, including a pathognomic sign for dangerous apical ventricular herniation, on magnetic resonance imaging

OBJECTIVE

To establish criteria for the accurate diagnosis of different forms of left sided pericardial defects on magnetic resonance imaging. Early detection of a partial apical defect is essential as it is potentially fatal.

DESIGN

Examination of four children with congenital pericardial defects by magnetic resonance imaging, the results being compared with the features on conventional chest radiography and echocardiography and with published data.

RESULTS

Magnetic resonance imaging improved the ability to diagnose and distinguish between complete and partial left sided pericardial defects. A deep myocardial crease was visualised in a patient with apical pericardial defect, indicating the risk of a life threatening ventricular strangulation. A prominent left atrial appendage was, in contrast to many reports, not a reliable sign for partial left sided pericardial defect.

CONCLUSIONS

The various forms of congenital left sided pericardial defects cannot reliably be diagnosed in plain chest radiographs or on echocardiography. Their diagnosis and the distinction between partial and complete defects, however, is of clinical importance and can be accomplished more confidently by magnetic resonance imaging.

Protective effects of various preservation solutions on cultured endothelial cells

Vascular endothelium represents the first target in organ preservation and plays an important role in reperfusion injury. Bovine aortic endothelial cells were cultivated and the most commonly used preservation solutions, such as University of Wisconsin HTK (Brettschneider's histidine-tryptophane-ketoglutarate), and Euro-Collins solutions were tested on the endothelial monolayer. In addition, one group of cultivated cells was preserved with cold saline solution, and endothelial monolayers grown in culture medium were used as controls. The quality of preservation was assessed after 24, 48, and 72 hours of cold storage. Reperfusion was simulated and its effects were observed by reincubation in culture medium at 37 degrees C for 6 hours. The total number of cells, cell viability (determined using trypan blue exclusion), and morphologic alterations were determined. Prostacyclin release was evaluated as a biochemical marker. University of Wisconsin solution maintains more than 99% cell viability after rewarming after both 24 and 48 hours of cold storage. After 72 hours, 86.7% of cells were still viable. Preservation with HTK and Euro-Collins solution allowed cell survival for only 24 hours (96.7%, HTK; 49.9%, Euro-Collins), with no viable cells seen after 48 hours. The cold saline-preserved sample showed 57.8% viable cells after 24 hours and 29.7% after 48 hours. No viable cells were detectable after 72 hours. Light microscopy revealed several patterns of both structural damage and intracellular change (nucleus and cytoplasm) in the endothelial monolayer after preservation with HTK, Euro-Collins solution, and cold saline solution. No morphologic alterations were seen in the University of Wisconsin solution group for as long as 72 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac troponin T: a new marker of myocardial tissue damage in bypass surgery

The purpose of this study was to evaluate cardiac troponin T (TnT) in the diagnosis of minor perioperative myocardial tissue damage and small myocardial infarctions during aortocoronary bypass surgery. In 15 patients without enzymatic or electrocardiographic signs of perioperative myocardial ischemia (group 1, uncomplicated bypass surgery), TnT did not exceed 3.55 micrograms/L. In 3 patients with perioperative non-Q-wave infarctions (group 2), TnT was significantly higher than in group 1 patients. In all 3 patients, TnT peak concentrations exceeded 3.5 micrograms/L. Thirteen patients (group 3, borderline cases) showed either signs of perioperative myocardial ischemia by creatine kinase isoenzyme MB (CKMB) activity levels (CKMB > 20 U/L on the first postoperative day, 3 patients) or by electrocardiography (new ST-T segment alterations, 10 patients). TnT concentrations were comparable to group 1 patients and indicated uncomplicated bypass surgery in all 3 patients with solely elevated CKMB activities. On the other hand, TnT concentrations in 3 patients with electrocardiographic signs of perioperative myocardial ischemia were significantly higher than in uncomplicated patients (group 1) with peak values exceeding 3.5 micrograms/L. Thus, TnT indicated perioperative non-Q-wave infarctions not detected by CKMB activity in these 3 patients. These results are in accordance with findings in nonsurgical patients. They suggest a higher sensitivity and specificity of cardiac TnT compared to CKMB activity in the diagnosis of small perioperative myocardial infarctions after bypass surgery.

Repeated endomyocardial biopsy without complication in an infant after heart transplantation

Endomyocardial biopsy is necessary for accurate diagnosis of rejection after heart transplantation. This case illustrates the safe use of repeated endomyocardial biopsies in an infant after heart transplantation.

Nutritional management of the heart transplant recipient

From July 1982 through February 1985, 52 patients underwent an orthotopic heart transplantation at the Texas Heart Institute. Immunosuppressive therapy consisted of cyclosporine and corticosteroids. Compromised preoperative nutritional status did not preclude acceptance into the heart transplant program. However, nutritional assessment provided a means of identifying patients who may benefit from preoperative nutritional support. The goal of postoperative nutritional therapy was to provide adequate nutrients to promote rapid wound healing and minimize complications associated with suboptimal nutritional status.

Cardiac transplantation: current results at the Texas heart institute

The first series of cardiac transplants at the Texas Heart Institute began in May of 1968 but was discontinued because of the complications of infection and rejection. A second series of cardiac transplants was initiated in July of 1982 after the introduction of the immunosuppressant drug, cyclosporine. By August of 1984, 30 patients had undergone orthotopic cardiac transplantation for end-stage cardiac disease. Of the patients in this series, four have died of rejection, two of infectious complications, and one of an unknown cause. The remainder have all returned to Class I New York Heart Association (NYHA) cardiac status. All patients were reviewed in detail for suitability of cardiac transplantation and presented to a cardiac transplant review board. All transplanted patients were functional Class IV. Donor hearts were obtained locally or by long-distance procurement. Ten of the hearts were obtained from an average distance of 250 miles from Houston. Donors ranged in age from 16 to 37 years. Requirements were normal cardiac function with minimal use of inotropic support, no history of cardiac disease, absence of cardiac arrest and absence of active infection. Although only one of the patients in the initial group of transplants survived 1 year, to date there have been 11 survivors for more than 1 year in the current series. Advances in cardiac transplantation have resulted in an improved prognosis for the terminal cardiomyopathic patients requiring transplantation. The use of cyclosporine, an immunosuppressant that spares the nonspecific immune system, has been helpful in allowing patients to survive infections. The use of the drug must be carefully monitored, however, because of its numerous toxicities.