Intracardiac echocardiography

This article describes currently available intracardiac ultrasound (ICE) technology contrasting it with intravascular ultrasound (IVUS) highlighting their differences. Clinical applications in the electrophysiologic and cardiac catheterization laboratory are discussed and current limitations addressed. Intracardiac echocardiography (ICE) is possible because lower frequency transducers (in contrast to higher frequency IVUS devices) have been miniaturized and mounted onto catheters capable of percutaneous insertion into the heart. These lower frequency transducers are capable of enhanced tissue penetration, permitting high-resolution 2D "whole heart" imaging. Also, with the introduction of the newest phased array transducer, Doppler hemodynamic data in addition to high resolution imaging can also be obtained. ICE facilitates electrophysiologic procedures by guiding transseptal catheterization, enabling endocardial anatomy visualization and targeting of arrhythmogenic substrate, ensuring optimal ablation electrode/tissue contact and promptly diagnosing procedural complications. Promising non-electrophysiologic applications include guidance of percutaneous closure of septal defects, percutaneous mitral balloon valvuloplasty and complex cardiac biopsy. Current limitations include monoplanar imaging, narrow field of view, and relatively large size of the catheter. Intra-cardiac imaging is now a clinical tool and has the potential to play an important role in diagnostic and therapeutic interventional procedures. Further refinement and miniaturization of these transducers, through continued technological progress, will make way for primary operator controlled, integrated ultrasound-guided interventional devices.

Segmenting high-frequency intracardiac ultrasound images of myocardium into infarcted, ischemic, and normal regions

Segmenting abnormal from normal myocardium using high-frequency intracardiac echocardiography (ICE) images presents new challenges for image processing. Gray-level intensity and texture features of ICE images of myocardium with the same structural/perfusion properties differ. This significant limitation conflicts with the fundamental assumption on which existing segmentation techniques are based. This paper describes a new seeded region growing method to overcome the limitations of the existing segmentation techniques. Three criteria are used for region growing control: 1) Each pixel is merged into the globally closest region in the multifeature space. 2) "Geographic similarity" is introduced to overcome the problem that myocardial tissue, despite having the same property (i.e., perfusion status), may be segmented into several different regions using existing segmentation methods. 3) "Equal opportunity competence" criterion is employed making results independent of processing order. This novel segmentation method is applied to in vivo intracardiac ultrasound images using pathology as the reference method for the ground truth. The corresponding results demonstrate that this method is reliable and effective.

Intracardiac echocardiography

This article describes currently available intracardiac ultrasound (ICE) technology contrasting it with intravascular ultrasound (IVUS), highlighting their differences. General and specific clinical applications, limitations and future developments of ICE are addressed. ICE is possible because lower frequency transducers (in contrast to higher frequency IVUS devices) have been miniaturized and mounted onto catheters capable of percutaneous insertion into the heart. Since the recent availability of a steerable, 5.5--10MHz phased-array catheter with full Doppler capability, these lower frequency transducers are not only capable of enhanced penetration, permitting high-resolution two-dimensional (2D) imaging but can also provide haemodynamic data. ICE facilitates electrophysiologic procedures by guiding trans-septal catheterization, enabling endocardial anatomy visualization, ensuring ablation electrode/tissue contact and promptly diagnosing procedural complications. Promising non-electrophysiologic applications include guidance of percutaneous closure of septal defects, percutaneous mitral balloon valvuloplasty and complex cardiac biopsy. Current limitations include monoplanar imaging and narrow field of view. Expanded diagnostic techniques such as tissue Doppler, multiplane, three dimensional (3D) and multimodality imaging represent future refinements. ICE is now a clinical tool. With the introduction of the newest phased-array transducer, with full Doppler capability, ICE has the potential to play an important role in diagnostic and therapeutic interventional procedures. Further refinement and miniaturization hold the key to primary operator controlled, integrated ultrasound-guided interventional devices.

Intracardiac measurement of pre-ejection myocardial velocities estimates the transmural extent of viable myocardium early after reperfusion in acute myocardial infarction

OBJECTIVES

We hypothesized that wall motion velocity during pre-ejection is proportional to the regional content of viable myocardium after reperfusion for acute myocardial infarction (AMI).

BACKGROUND

Pre-ejection wall motion consists of short and fast inward and outward movement towards and away from the center of the left ventricle (LV) and is altered during regional ischemia. This short-lived event can be accurately quantified by Doppler myocardial imaging (DMI).

METHODS

Fourteen open-chest pigs underwent 60 to 120 min of left anterior descending coronary artery occlusion followed by 30 min of reperfusion. The DMI data were collected using a phased-array intracardiac catheter (LV cavity) from ischemic and nonischemic myocardium encompassed within a plane passing through two epicardial bead markers. Peak tissue velocities during isovolumic contraction (IVC) (peak positive and peak negative), ejection (S) and early filling (E) were measured. The cardiac specimen was sliced through the epicardial markers in a plane approximating the ultrasound imaging plane. The transmural extent of necrosis (TEN) (%) was measured by triphenyltetrazolium chloride staining.

RESULTS

During ischemia, positive IVC velocity was zero in ischemic walls with TEN >20%. At reperfusion, positive IVC velocity correlated better with TEN (r = -0.94, p < 0.0001) than it did S (r = -0.70, p < 0.01) and E (r = -0.81, p < 0.01). Differential IVC (the difference between peak positive and peak negative velocity) highly correlated with TEN, during ischemia (r = -0.78, p < 0.001) and during reperfusion (r = -0.93, p < 0.0001).

CONCLUSIONS

Pre-ejection tissue velocity, as measured by intracardiac ultrasound, allows rapid estimation of the transmural extent of viable myocardium after reperfusion for AMI.

Initial experience with a steerable, phased vector array ultrasound catheter in the GI tract

BACKGROUND

EUS requires a significant capital outlay. The ability to perform high-resolution phased array scanning and Doppler interrogation by using a catheter that interfaces with a standard US console could increase the accessibility of EUS. Recently, an electronic phased-array US catheter was developed for intracardiac use. To date, this technology has not been applied to the GI tract. The aim of this study is to determine the feasibility and imaging characteristics of a new phased array scanning US catheter in the GI tract.

METHODS

Swine were placed under general anesthesia. This study used a 100 cm, 10F, torquable catheter with 4-way tip deflection to greater than 90 degrees. The catheter tip houses a phased vector array transducer with variable frequency (5.5-10 MHz) and variable focal distance. It has pulsed/color and power Doppler capability. The probe was passed through a therapeutic flexible sigmoidoscope into the upper GI tract. Acoustic coupling was achieved via a condom filled with water or by gastric water infusion. Needle visualization experiments were performed with a second endoscope (also passed per oral) with a standard EUS-guided fine needle aspiration needle.

RESULTS

Acoustic coupling was easily achieved. Resolution of the GI wall into characteristic layers (esophagus 5, stomach 7) was demonstrated. At 5.5 MHz, tissue resolution and Doppler imaging were excellent to greater than 10 cm from the transducer. A 22-gauge EUS-guided fine needle aspiration needle was easily visualized at depth greater than 4 cm. Flow in gastric, hepatic, and pancreatic parenchymal vessels approximately 1 mm diameter was visualized by using power and color Doppler.

CONCLUSIONS

This 10F array US catheter is capable of high-resolution two-dimensional imaging of the gut wall as well as high-quality Doppler imaging. The Doppler capabilities of this equipment may have new GI applications.

Supplementary eye field: representation of saccades and relationship between neural response fields and elicited eye movements

The functional organization of the low-threshold supplementary eye field (SEF) was studied by analyzing presaccadic activity, electrically elicited saccades, and the relationship between them. Response-field optimal vectors, defined as the visual field coordinates or saccadic eye-movement dimensions evoking the highest neural discharge, were quantitatively estimated for 160 SEF neurons by systematically varying peripheral target location relative to a central fixation point and then fitting the responses to Gaussian functions. Saccades were electrically elicited at 109 SEF sites by microstimulation (70 ms, 10-100 microA) during central fixation. The distribution of response fields and elicited saccades indicated a complete representation of all contralateral saccades in SEF. Elicited saccade polar directions ranged between 97 and 262 degrees (data from left hemispheres were transformed to a right-hemisphere convention), and amplitudes ranged between 1.8 and 26.9 degrees. Response-field optimal vectors (right hemisphere transformed) were nearly all contralateral as well; the directions of 115/119 visual response fields and 80/84 movement response fields ranged between 90 and 279 degrees, and response-field eccentricities ranged between 5 and 50 degrees. Response-field directions for the visual and movement activity of visuomovement neurons were strongly correlated (r = 0.95). When neural activity and elicited saccades obtained at exactly the same sites were compared, response fields were highly predictive of elicited saccade dimensions. Response-field direction was highly correlated with the direction of saccades elicited at the recording site (r = 0.92, n = 77). Similarly, response-field eccentricity predicted the size of subsequent electrically elicited saccades (r = 0.49, n = 60). However, elicited saccades were generally smaller than response-field eccentricities and consistently more horizontal when response fields were nearly vertical. The polar direction of response fields and elicited saccades remained constant perpendicular to the cortical surface, indicating a columnar organization of saccade direction. Saccade direction progressively shifted across SEF; however, these orderly shifts were more indicative of a hypercolumnar organization rather than a single global topography. No systematic organization for saccade amplitude was evident. We conclude that saccades are represented in SEF by congruent visual receptive fields, presaccadic movement fields, and efferent mappings. Thus SEF specifies saccade vectors as bursts of activity by local groups of neurons with appropriate projections to downstream oculomotor structures. In this respect, SEF is organized like the superior colliculus and the frontal eye field even though SEF lacks an overall global saccade topography. We contend that all specialized oculomotor functions of SEF must operate within the context of this fundamental organization.

Intracardiac echocardiography: newest technology

Intracardiac echocardiography, defined as ultra-sonographic navigation and visualization within large blood-filled cavities or vessels of the cardio-vascular system, has recently undergone refinement as a clinical tool through technologic advances in transducer miniaturization. Intra-cardiac ultra-sound catheters image at lower frequencies than current conventional intravascular ultrasound catheters used for intracoronary imaging. The lower imaging frequency enables greater tissue penetration, permitting whole-heart evaluation from a right-sided catheter position. Newer devices are steerable, have variable imaging frequency (5.5 to 10 MHz), and full Doppler capability (pulsed, continuous wave, and tissue Doppler). These advances have made intracardiac high-resolution imaging as well as hemodynamic assessment possible. A historical perspective, current capabilities and limitations, and potential clinical and research applications of this new imaging technique are discussed.

Personal ultrasound imager: abdominal aortic aneurysm screening

BACKGROUND

Miniaturized ultrasonographic machines (2.5-MHz curved-array transducer connected to a compact 2.6-kg console), termed personal ultrasound imagers (PUIs), may enable detection of occult abdominal aortic aneurysms (AAAs).

OBJECTIVES

Our goals were to determine whether a PUI is capable of screening for AAAs and to compare the results with an established screening examination with standard echocardiography (SE).

METHODS

One hundred twenty-five patients (aged >70 years) with hypertension who were referred for transthoracic echocardiography were enrolled. After SE, a focused screening with a PUI examination was performed by a blinded sonographer. An AAA was defined as a focal enlargement of the aorta >30 mm. Results and the length of time to image the aorta were compared for both tests.

RESULTS

We studied 64 men and 61 women (aged 76.8 +/- 5 years; mean blood pressures: systolic 145.7 +/- 18 and diastolic 78.6 +/- 10; body surface area 1.9 +/- 0.2 m(2)). The mean time for SE was 2.9 +/- 1.5 minutes and for the PUI examination was 4.6 +/- 2.3 minutes. By using SE as the gold standard, the sensitivity and specificity of the PUI were 91% and 96%, respectively. The positive predictive value of the PUI was 71%, and the negative predictive value was 99%.

CONCLUSION

A PUI can be used to screen for occult AAAs as an extension of the physical examination. Results are comparable to an established screening strategy that uses more expensive, nonportable echocardiographic equipment.

Application of a continuous regression model of restenosis to saphenous vein grafts after successful percutaneous transluminal coronary angioplasty or directional coronary atherectomy

OBJECTIVES

To evaluate a quantitative model of restenosis in patients with vein graft disease undergoing percutaneous transluminal coronary angioplasty (PTCA) or directional coronary atherectomy (DCA).

BACKGROUND

A quantitative relationship between acute gain and late loss has been developed to describe the late changes in lumen dimension after native vessel coronary intervention. This same relationship may also be seen after treatment of saphenous vein graft disease.

METHODS

Patients with native coronary artery stenoses (CAVEAT-I) or saphenous vein graft lesions (CAVEAT-II) were randomized to either DCA or PTCA, and data from these trials were analyzed retrospectively. Angiographic results of the target lesions were reviewed, and each lesion was assessed for vessel caliber and reference diameter, absolute minimal lumen diameter, percent diameter stenosis, percent stenosis of the cross-sectional area, acute gain and late loss. Linear regression models were used to determine late loss and to detect differences in angiographic outcomes.

RESULTS

Vein grafts had significantly larger reference vessel diameters than native coronary arteries; they also had significantly more acute gain and more late loss. Directional coronary atherectomy was associated with a larger acute gain in both studies. Patients undergoing DCA also experienced greater late loss although the effect was statistically significant only in the CAVEAT-I study. After adjusting for the acute gain, the treatment effect on late loss became nonsignificant in both studies.

CONCLUSIONS

In patients undergoing DCA or PTCA of saphenous vein graft narrowings, the relationship between late loss and acute gain is also demonstrated, similar to the device-independent relationships seen in native coronary lesions. In CAVEAT-II, larger degrees of acute gain were also associated with higher degrees of late lumen loss.

Depletion of bovine CD8+ T cells with chCC63, a chimaeric mouse-bovine antibody

In order to investigate the role of T cells in immune responses to infectious pathogens, depletion of individual T cell subsets using monoclonal antibodies (mAbs) is commonly undertaken. Since most mAbs are of murine origin, such depletion studies in cattle are restricted by the bovine anti-mouse antibody (BAMA) response to the mouse mAbs used for the depletions. In this study, we describe the use of antibody engineering to overcome the BAMA response. The variable region cDNA from CC63, a monoclonal mouse anti-bovine CD8 antibody, has been expressed in conjunction with bovine constant region genes to produce a mouse-bovine chimaeric antibody (chCC63). Characterisation of chCC63 showed that the antibody contained a bovine constant region and specifically bound bovine CD8+ T cells. Furthermore, chCC63 blocked the binding of the original mouse antibody, CC63, and mediated complement-dependent lysis of bovine CD8+ cells in vitro. In vivo, chCC63 depleted calves of CD8+ T cells as effectively as CC63 and provoked a BAMA response that was about one-tenth of that seen with the mouse antibody.

Fixed left ventricular outflow tract obstruction in presumed hypertrophic obstructive cardiomyopathy: implications for therapy

BACKGROUND

A subset of patients presenting with a presumed diagnosis of hypertrophic obstructive cardiomyopathy (HOCM) have a fixed left ventricular outflow tract (LVOT) obstruction. Recognition of this pathophysiologic abnormality is important in choosing therapy.

METHODS

Of patients referred for treatment of HOCM, 4 had fixed LVOT obstruction. Clinical and echocardiographic data and surgical findings were reviewed.

RESULTS

In the 4 patients with clinical features consistent with HOCM or HOCM-like conditions, echocardiography showed fixed LVOT obstruction with an early-peaking LVOT Doppler signal or absence of severe systolic anterior motion of the mitral valve. The causes of fixed obstruction included accessory mitral tissue with associated fibrous ring (1 patient), fixed subaortic tunnel stenosis (2 patients), and a discreet subaortic ridge (1 patient). After surgical relief of the fixed LVOT obstruction, all patients had relief of the ventricular outflow tract gradient.

CONCLUSIONS

Not all patients with a presumed diagnosis of HOCM have isolated dynamic LVOT obstruction but may have isolated or additional fixed obstruction. Careful two-dimensional and Doppler echocardiography are needed to identify this subset of patients who are best treated surgically.

Feasibility study: transesophageal echocardiography with a 10F (3.2-mm), multifrequency (5.5- to 10-MHz) ultrasound catheter in a small rabbit model

Transesophageal echocardiography (TEE) is useful in children with congenital heart defects. However, because of available probe size (>/=7 mm diameter), its use is limited to patients weighing more than 3 kg. The aim of this study was to determine the feasibility of TEE in a small animal model by using a 10F (3.2-mm) intravascular ultrasound tipped catheter with a monoplane (longitudinal) 5.5- to 10-MHz phased vector array transducer. Ten New Zealand White rabbits (400 to 3400 g; mean 1580 g) underwent TEE. With animals under general sedation, the probe was blindly introduced into the esophagus. All intracardiac and extracardiac structures were examined, and the images were stored and independently reviewed. All pertinent intracardiac and extracardiac structures were identified except in the 3 smallest rabbits (400 to 600 g). Doppler hemodynamics and color Doppler were possible in each animal. Frequency agility (5.5 to 10 MHz) facilitated optimization of image resolution and penetration. Certain transgastric, 4-chamber, and short-axis views were limited because of the monoplane array. No overt adverse effects were associated with the procedure. Diagnostic TEE can be performed in a small animal model with a 10F, 5.5- to 10-MHz phased vector array ultrasound catheter. Our study suggests that this system has potential in performing diagnostic TEE safely in small, even premature, neonates.

Determinants of infarct size after thrombolytic treatment in acute myocardial infarction

Both experimental and single-center clinical studies have shown that myocardium at risk, residual collateral flow, and duration of coronary occlusion are important determinants of final infarct size. The purpose of this study was to replicate these results on a multicenter basis to demonstrate that perfusion imaging using different camera and computer systems can provide reliable assessments of myocardium at risk and collateral flow. Sequential tomographic myocardial perfusion imaging with technetium-99 (Tc-99m) sestamibi was performed in 74 patients with first time myocardial infarction, who were enrolled in a multicenter, randomized, double-blind, placebo-controlled pilot study of poloxamer 188 as ancillary therapy to thrombolysis. All patients underwent thrombolysis within 6 hours of the onset of chest pain. Tc-99m sestamibi was injected intravenously at the initiation of thrombolytic therapy, and tomographic imaging was performed 1 to 6 hours later to assess myocardium at risk. Collateral flow was estimated noninvasively from the acute sestamibi images by 3 methods that assess the severity of the perfusion defect. Final infarct size was determined at hospital discharge by a second sestamibi study. Myocardium at risk (r = 0.61, p <0.0001) and radionuclide estimates of collateral flow (r = 0.58 to 0.66, all p <0.0001) were significantly associated with final infarct size. These associations were independent of the treatment center. On a multivariate basis, myocardium at risk (p = 0.003), the radionuclide estimate of collateral flow (p = 0.03), and treatment arm (p = 0.04) were all independent determinants of infarct size. Time to thrombolytic therapy showed only a trend (p = 0.10). The treatment center was not significant (p = 0.42). Myocardium at risk and collateral flow are important determinants of infarct size that are independent of treatment center. Tomographic imaging with Tc-99m sestamibi can provide noninvasive assessments of these parameters in multicenter trials of thrombolytic therapy.

Intracardiac Doppler hemodynamics and flow: new vector, phased-array ultrasound-tipped catheter

Comprehensive intracardiac Doppler examination under simultaneous direct ultrasound visualization has not been previously possible. This human feasibility study demonstrates that a new 10Fr, 3.2-mm diameter, 5.5- to 10-MHz frequency agile, phased, vector array, ultrasound-tipped catheter with 4-way tip articulation provides diagnostic, high-quality, intracardiac Doppler signals using pulsed and continuous-wave, color flow, and tissue Doppler.

Clinical assessment and management of mitral stenosis

There have been significant advances in the diagnosis and treatment of the patient with mitral stenosis over the past two decades. Two-dimensional and Doppler echocardiography have supplanted the cardiac catheterization laboratory in the diagnosis and determination of the hemodynamic severity of the stenotic mitral valve. The development of a catheter-based approach for splitting fused commissures has led to earlier indications for intervention. It is likely that with the resurgence of rheumatic fever as well as influx of immigrant populations, the incidence of mitral stenosis may increase in the twenty-first century. It is thus important for the clinician to have a complete understanding of the evaluation and treatment options for the patient with mitral stenosis in the modern-day era.

Deficits in smooth-pursuit eye movements after muscimol inactivation within the primate's frontal eye field

To evaluate smooth-pursuit (SP) function in the primate frontal eye field (FEF), microinjections of muscimol, a gamma-aminobutyric acid (GABA) agonist, were used to reversibly deactivate physiologically characterized sites in FEF. SP was severely impaired by deactivation at sites in the FEF's smooth eye movement region (FEFsem) located in the fundus and posterior bank of the macaque monkey's arcuate sulcus. These SP deficits were apparent immediately after the muscimol injection and persisted for several hours but recovered by the next day. SP was most drastically and consistently impaired for directions similar to the injected site's elicited smooth eye movement direction or to the optimal SP direction for its neuronal responses. Targets moving in these directions, usually ipsilateral to the injected hemisphere, were tracked primarily with saccades after the muscimol injection, the peak SP velocity being only 10-30% of preinjection velocity. SP in other directions, including contralateral, was less strongly affected. Initial SP acceleration in response to target motion onset was also significantly diminished, generally by approximately the same proportion as peak SP velocity. In contrast, saccades were largely unaffected by muscimol injections in FEFsem; nor was there an immediate effect on SP when control sites in the saccadic region of FEF (FEFsac) were deactivated, although a SP deficit often appeared 30-60 min after FEFsac injections, possibly reflecting diffusion of muscimol into neighboring FEFsem. These reversible SP deficits produced by muscimol inactivation within FEFsem are similar to permanent deficits caused by large aspiration lesions of FEF and indicate that inclusion of FEFsem is the critical factor determining whether FEF lesions impair SP. The severity of the reversible deficits found here indicates how extremely critical FEFsem is for normal highgain SP.

Newer advances in the diagnosis and treatment of mitral stenosis

There have been significant changes in presentation, diagnosis, and therapy of patients with mitral stenosis. Both the prevalence of mitral stenosis, as well as the type of patient now with mitral stenosis, have changed significantly over the past few decades. In patients with mitral stenosis two-dimensional and Doppler echocardiography have become the diagnostic modalities of choice. The advent of percutaneous mitral balloon valvotomy now provides a nonsurgical approach for the treatment of selected patients with mitral stenosis.

Suppression of task-related saccades by electrical stimulation in the primate's frontal eye field

Patients with frontal lobe damage have difficulty suppressing reflexive saccades to salient visual stimuli, indicating that frontal lobe neocortex helps to suppress saccades as well as to produce them. In the present study, a role for the frontal eye field (FEF) in suppressing saccades was demonstrated in macaque monkeys by application of intracortical microstimulation during the performance of a visually guided saccade task, a memory prosaccade task, and a memory antisaccade task. A train of low-intensity (20-50 microA) electrical pulses was applied simultaneously with the disappearance of a central fixation target, which was always the cue to initiate a saccade. Trials with and without stimulation were compared, and significantly longer saccade latencies on stimulation trials were considered evidence of suppression. Low-intensity stimulation suppressed task-related saccades at 30 of 77 sites tested. In many cases saccades were suppressed throughout the microstimulation period (usually 450 ms) and then executed shortly after the train ended. Memory-guided saccades were most dramatically suppressed and were often rendered hypometric, whereas visually guided saccades were less severely suppressed by stimulation. At 18 FEF sites, the suppression of saccades was the only observable effect of electrical stimulation. Contraversive saccades were usually more strongly suppressed than ipsiversive ones, and cells recorded at such purely suppressive sites commonly had either foveal receptive fields or postsaccadic responses. At 12 other FEF sites at which saccadic eye movements were elicited at low thresholds, task-related saccades whose vectors differed from that of the electrically elicited saccade were suppressed by electrical stimulation. Such suppression at saccade sites was observed even with currents below the threshold for eliciting saccades. Pure suppression sites tended to be located near or in the fundus, deeper in the anterior bank of the arcuate than elicited saccade sites. Stimulation in the prefrontal association cortex anterior to FEF did not suppress saccades, nor did stimulation in premotor cortex posterior to FEF. These findings indicate that the primate FEF can help orchestrate saccadic eye movements by suppressing inappropriate saccade vectors as well as by selecting, specifying, and triggering appropriate saccades. We hypothesize that saccades could be suppressed both through local FEF interactions and through FEF projections to subcortical regions involved in maintaining fixation.

Laparoscopic resection for diverticular disease

PURPOSE

The role of laparoscopic surgery in treatment of patients with diverticulitis is unclear. A retrospective comparison of laparoscopic with conventional surgery for patients with chronic diverticulitis was performed to assess morbidity, recovery from surgery, and cost.

METHODS

Records of patients undergoing elective resection for uncomplicated diverticulitis from 1992 to 1994 at a single institution were reviewed. Laparoscopic resection involved complete intracorporeal dissection, bowel division, and anastomosis with extracorporeal placement of an anvil.

RESULTS

Sigmoid and left colon resections were performed laparoscopically in 25 patients and by open technique in 17 patients by two independent operating teams. No significant differences existed in age, gender, weight, comorbidities, or operations performed. In the laparoscopic group, three operations were converted to open laparotomy (12 percent) because of unclear anatomy. Major complications occurred in two patients who underwent laparoscopic resection, both requiring laparotomy, and in one patient in the conventional surgery group who underwent computed tomographic-guided drainage of an abscess. Patients who underwent laparoscopic resection tolerated a regular diet sooner than patients who underwent conventional surgery (3.2 +/- 0.9 vs. 5.7 +/- 1.1 days; P < 0.001) and were discharged from the hospital earlier (4.2 +/- 1.1 vs. 6.8 +/- 1.1 days; P < 0.001). Overall costs were higher in the laparoscopic group than the open surgery group ($10,230 +/- 49.1 vs. $7,068 +/- 37.1; P < 0.001) because of a significantly longer total operating room time (397 +/- 9.1 vs. 115 +/- 5.1 min; P < 0.001). Follow-up studies with a mean of one year revealed two port site infections in the laparoscopic group and one wound infection in the open group. Of patients undergoing conventional resection, one patient experienced a postoperative bowel obstruction that was managed nonoperatively, and, in one patient, an incarcerated incisional hernia developed that required urgent laparotomy.

CONCLUSIONS

Laparoscopic resection in patients with chronic diverticulitis is safe, with faster recovery and shorter hospital stay compared with conventional open surgery. Higher cost of operating room usage time makes the laparoscopic technique difficult to justify economically. Simplification of operating room use and better case selection may improve cost-effectiveness of the laparoscopic approach.

Neurons in the supplementary eye field of rhesus monkeys code visual targets and saccadic eye movements in an oculocentric coordinate system

1. We investigated whether neurons in the supplementary eye field (SEF) of macaque monkeys code saccadic eye movements in oculocentric coordinates (relative to the current direction of fixation) or in craniocentric coordinates (relative to the head). Craniocentric coding in SEF had been previously suggested by the convergent appearance of electrically elicited saccades originating at different orbital positions. 2. We primarily studied SEF neurons that started responding before the beginning of saccades because such presaccadic activity is likely related to saccade generation and metrics. Using a memory-saccade task, we classified the presaccadic activity of each neuron as either purely visual related, purely movement related, or both visual and movement related. 3. We then mapped the response fields (receptive fields and movement fields) of SEF neurons from different orbital positions. When mapped relative to a central fixation point, the strongest responses for a given SEF neuron invariably occurred for a particular polar direction with fairly symmetrical declines for departures from that direction. When tested using other fixation point locations, their strongest responses almost always continued to occur for stimuli having the same polar direction relative to each fixation point tested, and thus they appeared to code both stimulus direction and saccade direction in an oculocentric coordinate system. 4. The effect of eye position on SEF presaccadic activity was quantified in two ways by computing, for each neuron, 1) an "intersection distance," the eccentricity of the point where extensions of the neuron's optimal polar directions measured at two eccentric orbital positions converged, and 2) an "orbital perturbation index" such that an index of 0 corresponded to no change in the neuron's optimal polar direction across different orbital positions (i.e., perfectly oculocentric response fields) and an index of 1 corresponded to optimal polar directions that converged to the same craniocentric goal regardless of initial eye position (i.e., perfectly craniocentric response fields). For neurons with both visual and movement responses, these measures were calculated separately for each type of activity using tasks that temporally separated the visual cue presentation and the saccade to it. 5. Almost all of the intersection distances were well beyond the oculomotor range (+/- 50 degrees) of the monkey (38/39 for movement activity and 62/66 for visual activity). The median intersection distance for visual activity was very large (274 degrees), and the median for movement activity was slightly divergent (beyond infinity). Thus SEF neurons rarely showed a conspicuous convergence of response field direction. 6. Likewise, the mean orbital perturbation indexes were very small (-0.04 +/- 0.21, mean +/- SD, for movement activity and 0.09 +/- 0.15 for visual activity), also indicating that SEF neurons code stimuli and saccades in an oculocentric manner. 7. For neurons with both visual and movement activities, the orbital perturbation indexes of the two activities were not significantly correlated (r = 0.16), even though their characteristic directions (optimal polar direction estimated from the center of the screen) were almost the same (circular correlation, r+ = 0.97). The lack of a significant correlation between the visual and movement activity orbital perturbation indexes is consistent with the hypothesis that most of the variation in this index represents statistically independent errors of measurement. Conversely, the strong covariation of visual and movement activity characteristic directions indicates that directional preference is a fundamental functional property of SEF presaccadic activity.(ABSTRACT TRUNCATED)

A comparison of survival at different degrees of hemorrhagic shock in germ-free and germ-bearing rats

We have previously reported superior survival after one level of hemorrhagic shock in germ-free (GF) rats compared with germ-bearing (GB) rats. The objective of this study was to determine the effect of the GF state on survival at different degrees of hemorrhagic shock. GF and GB rats were bled to a mean arterial blood pressure of 30 mmHg. Shock was terminated after 10, 20, 40, or 80% of the maximum shed blood volume was reabsorbed spontaneously. Both shock time and time to decompensation were significantly longer in GF rats (p < .05). Comparative survival was greater for GF rats at most levels of shock (p < .01). This superiority in survival was greatest at moderate shock levels and decreased at severe shock levels. There may be several reasons for the increased tolerance of GF animals to hemorrhagic shock such as metabolic or immunologic variations. It is hard to avoid the fact, however, that the most notable difference between the GF and GB rat is the presence or absence of bacteria.

Topography of projections to posterior cortical areas from the macaque frontal eye fields

Frontal eye field (FEF) projections to posterior cortical areas were mapped by autoradiography of tritiated amino acids (Leu, Pro) in six macaque monkeys. In three monkeys, the large saccade part of the FEF (IFEF) was identified by microstimulation and injected with tracers. In a fourth monkey, the small saccade part of the FEF (sFEF) was identified by microstimulation and injected with tracer. Tracer injections were placed into the sFEF region of two other monkeys using anatomical landmarks. The IFEF and sFEF generally had distinct and largely segregated projections to posterior cortical areas, and the overall pattern of labeling in visual areas with established topology indicates that IFEF neurons preferentially project to areas having large and eccentric receptive fields, whereas sFEF neurons project to areas having smaller, more centrally located fields. The terminal fields from the sFEF were more widespread than those from IFEF. Projections from sFEF terminated in the lateral intraparietal area (LIP), the ventral intraparietal area (VIP), and the parietal part of visual area V3A, in the fundus of the superior temporal visual area (FST), the middle temporal area (MT), the medial superior temporal area (MST), the temporal part of visual area V4, the inferior temporal area (IT), and the temporal-occipital area (TEO) and in occipital visual areas V2, V3, and V4. Projections from IFEF terminated in parietal areas 7a, LIP, and VIP and the medial part of parietal area PE; in temporal areas MST and the superior temporal polysensory area (STP); and in occipital area V2 and posterior cingulate area 23b. Projections from IFEF and sFEF appeared to terminate in different parts of common target areas in MST, LIP, and V2. The topography of IFEF and sFEF projections to LIP suggests that this posterior eye field may also be organized by saccade amplitude. Most terminal labeling from FEF injections was bilaminar to layers I and V/VI, but labeling in area LIP, area MT, the medial part of area PE, and area 23b was columnar-form to all layers.