Experimental foundation for in vivo measurement of the elasticity of the aorta in computed tomography angiography.

OBJECTIVE: This study was performed to determine the feasibility of measuring the elastic properties of the arterial wall in vivo. To prove this concept, elastic parameters were calculated from an aortic model of elastic behavior similar to a human aorta using computed tomography angiography (CTA) images. METHODS: We first constructed an aortic model from polydimethylsiloxane (PDMS). This model was inserted into a pulsatile flow loop. The model was then placed inside a computed tomography scanner. To estimate the elasticity values, we measured the cross-sectional area and the pressure changes in the model during each phase of the simulated cardiac cycle. A discrete wavelet transform (DWT) algorithm was applied to the CTA data to calculate the geometric changes in the pulsatile model over a simulated cardiac cycle for various pulsatile rates and elasticity values of the PDMS material. The elastic modulus of the aortic model wall was derived from these geometric changes. The elastic moduli derived from the CTA data were compared with those obtained by testing strips of the same PDMS material in a tensile testing machine. Our two aortic models had elastic values at both extremes of those found in normal human aortas. RESULTS: The results show a good comparison between the elastic values derived from the CTA data and those obtained in a tensile testing machine. In addition, the elasticity values were found to be independent of the pulsatile rate for mixing ratios of 6:1 and 9:1 (p = .12 and p = .22, respectively). CONCLUSIONS: The elastic modulus of a pulsatile aortic model may be measured by electrocardiographically-gated multi-detector CTA protocol. This preliminary study suggests the possibility of determining non-invasively the elastic properties of a living, functioning aorta using CTA data.

How should we measure and report elasticity in aortic tissue?

BACKGROUND: Different stress-strain definitions are used in the literature to measure the elastic modulus in aortic tissue. There is no agreement as to which stress-strain definition should be implemented. The purpose of this study is to show how different results are given by the various definitions of stress-strain used and to recommend a specific definition when testing aortic tissues. METHODS: Circumferential specimens from three patients with ascending thoracic aortic aneurysm (ATAA) were obtained from the greater curvature and their tensile properties were tested uniaxially. Three stress definitions (second Piola-Kirchhoff stress, engineering stress and true stress) and four strain definitions (Almansi-Hamel strain, Green-St. Venant strain, engineering strain and true strain) were used to determine the elastic modulus. RESULTS: We found that the Almansi-Hamel strain definition exhibited the highest non-linear stress-strain relation and consequently may overestimate the elastic modulus when using different stress definitions (second Piola-Kirchhoff stress, engineering stress and true stress). The Green-St. Venant strain definition yielded the lowest non-linear stress-strain relation using different definitions of stress, which may underestimate the values of elastic modulus. Engineering stress and strain definitions are only valid for small strains and displacements, which make them impractical when analysing soft tissues. We show that the effect of varying the stress definition on the elastic modulus measurements is significant for maximum elastic modulus but not when calculating the hypertensive elastic modulus. CONCLUSIONS: It is important to consider which stress-strain definition is employed when analysing soft tissues. Although the true stress-true strain definition exhibits a non-linear relation, we favour it in tissue mechanics because it gives more accurate measurements of the material's response using the instantaneous values.

In vitro characterisation of physiological and maximum elastic modulus of ascending thoracic aortic aneurysms using uniaxial tensile testing.

OBJECTIVE: Ascending thoracic aortic aneurysms (ATAA) are a life-threatening condition due to the risk of rupture or dissection. This risk is increased in the presence of a bicuspid aortic valve (BAV). The purpose of this study was to provide data on the elastic modulus of aortic wall of ATAA using uniaxial tensile testing in two different areas of the stress-strain relationship: physiological and maximum range of stresses. The influence of tissue location, tissue orientation and valve type on these parameters was investigated. MATERIALS AND METHODS: Tissues freshly excised from ATAA with bicuspid or tricuspid aortic valve were obtained from greater and lesser curvature (GC and LC) and the specimens were tested uniaxially in circumferential (CIRC) and longitudinal (LONG) orientation. Maximum elastic modulus (MEM) was given by the maximum slope of the stress-strain curve before failure. Physiological modulus (PM) was derived from the Laplace law and from ranges of pressure of 80-120 mmHg. Means of each group of specimen were compared using Student's t-test to assess the influence of location, orientation and valve type on each mechanical parameter. RESULTS: PM was found to be significantly lower than the MEM (p < 0.001). The MEM and PM were significantly higher (p < 0.01) in the CIRC (n = 66) than in the LONG orientation (n = 42). The MEM was higher in the circumferential orientation in the BAV group (p < 0.001 in GC and p < 0.05 in LC). MEM and PM in GC specimens were higher in the longitudinal orientation than the LC specimens (p < 0.05). CONCLUSION: This study demonstrates the anisotropy of the aortic wall in ATAA and provides data on the mechanical behaviour in the physiological range of pressure.

The relationship between hand size and difficulty using surgical instruments: a survey of 726 laparoscopic surgeons.

BACKGROUND: Hand size is an important variable to consider when designing hand tools. Laparoscopic surgical instruments have been reported to cause hand and upper extremity discomfort. This study investigates the correlation between surgical glove size, preexisting musculoskeletal problems, and difficulty using laparoscopic instruments. METHODS: Approximately 11,000 questionnaires were sent to SAGES, AAGL, and AWS members. Questions included basic demographic and practice data, surgical glove size, the presence of musculoskeletal problems, and the perceived difficulty using several types laparoscopic instruments. There were 726 responses (from 159 women and 567 men). Subjects were grouped by hand size (Small < or =6.5, Medium 7.0-7.5, Large >7.5; female group only: Small < or =6.0, Medium 6.5, Large >6.5). ANOVA was used to test for differences between groups. RESULTS: The percentage of time subjects reported having difficulty using all laparoscopic instruments was greater for the Small glove size group compared to both the Medium and Large groups ( p < 0.001). In females, the scissors and staplers were more difficult to use for the Small and Medium glove size group compared to the Large group ( p < 0.001). Subjects who reported musculoskeletal problems ( n = 145) performed a significantly greater percent of laparoscopic cases and found the stapler and graspers difficult to use for a greater percentage of time than those not reporting problems ( n = 559). CONCLUSION: Hand size is a significant determinant of difficulty using laparoscopic surgical instruments. Individuals using glove sizes 6.5 or smaller experience significantly more difficulty using common laparoscopic instruments, and in particular laparoscopic staplers. Manufacturers of surgical hand tools should consider hand size when designing future surgical instruments.

Medicina basada en evidencia (MBE). Contras / Evidence based medicine (EBM). Disadvantages

El método de la llamada Medicina Basada en la Evidencia (MBE), se ha convertido en los últimos diez años en el paradigma de investigación clínica en las Ciencias de la Salud. Basada en métodos epidemiológicos y estadísticos, con antecedentes en la agronomía y emparentada filosóficamente con el método hipoteticodeductivo, la MBE sé esta estableciendo como la única doctrina que valide el trabajo científico de los profesionales, despreciando los paradigmas científicos que dieron como resultado los avances sensacionales que la medicina ha experimentado en nuestra generación. Entendemos que la MBE debe suponer una ayuda para a que el fruto de la experiencia se concrete en lo posible de manera sistematica y objetiva en recomendaciones prácticas, no que una conclusión genérica, obtenida de un grupo de pacientes, se convierta en una recomendación de actuación específica sobre un enfermo en concreto. (AU)

Performing laparoscopic surgery is significantly more stressful for the surgeon than open surgery.

BACKGROUND: The awkward visual and physical interface of video-endoscopic surgery (VES) has been shown to increase the physical workload of the surgeon, yet there is a lack of objective information on the mental effort and stress demanded by VES techniques. This study addresses the hypothesis that VES is more stressful than open surgery using an ergonomic analysis of surgical tasks in a laboratory setting. METHODS: A portable ergonomic work station was developed using a software Virtual Instrument (VI) interfaced with electronic hardware to compare the mental workload of 28 surgeons. The task was knot tying. The independent variable was work condition: rest, open technique, or VES technique. Dependent variables were tonic skin conductance level (SCL), electrooculogram (EOG), and subjective reports of concentration (CON) and stress (STR). Statistical analysis used nonparametric methods. RESULTS: Subjects tied fewer knots using the VES technique (p < 0.05). The SCL increased progressively from rest to the open task to the VES task (p < 0.05), correlating with the subjects' reported increase in mental stress level (p < 0.05). Eye blinks decreased from rest to the open task (p < 0.05), consistent with the subjects' reported increase in level of mental concentration. From the open to the VES task, eye blinks increased (p < 0.05), as would be expected given the greater demands of the VES task. Experienced subjects demonstrated less variability in SCL levels across tasks. CONCLUSIONS: VES technique requires greater concentration and places greater mental stress on surgeons than to open surgery. More experience with VES may decrease this effect. Studies are needed to improve the human-technology interface the stress.

Intra-aneurysmal pressure after incomplete endovascular exclusion.

PURPOSE: An endoleak results from the incomplete endovascular exclusion of an aneurysm. We developed an experimental model to analyze hemodynamic changes within the aneurysm sac in the presence of an endoleak, with and without a simulated open collateral branch. METHODS: With a latex aneurysm model connected to a pulsatile pump, pressures were measured simultaneously within the system (systemic pressure) and the aneurysm sac (intrasac pressure). The experiments were performed without endoleak (control group) and after creating a 3.5-mm (group 1), 4.5-mm (group 2), and 6-mm (group 3) diameter orifice in the endograft, simulating an endoleak. Pressures were also registered with and without a patent aneurysm side branch. RESULTS: In each endoleak group, the intrasac diastolic pressure (DP) and mean pressure (MP) were significantly higher than the systemic DP and MP (P =.01, P =.006, and P =.001, respectively), although the pressure curve was damped. The presence of an open side branch significantly reduced the intrasac DP and MP. CONCLUSION: In this model, intrasac pressures were significantly higher than systemic pressures in the presence of all endoleaks, even the smallest ones. Intrasac pressures higher than systemic pressure may pose a high risk for aneurysm rupture. Although patent side branches significantly reduce these pressures, the aggressive management of an endoleak should be pursued.

The effect of laparoscopic instrument working angle on surgeons' upper extremity workload.

BACKGROUND: Laparoscopic surgery may be kinder to the patient, but it is more demanding on the surgeon. Fixed trocar positions often require the surgeon to work with instruments at awkward angles to their body. We studied the effect of horizontal and vertical laparoscopic instrument working angle on the surgeon's thumb, forearm, and shoulder muscle work. METHODS: Electronyographic (EMG) signals were collected from the thenar compartment (TH), flexor digitorum superficialis (FDS), and deltoid (DEL) muscles of the dominant arm of eighth surgeons while they were closing a standard pistol-grip disposable laparoscopic grasper against a fixed resistance of 3 N. With the aid of a special testing bench, the instruments' position was randomly changed among 15 degrees, 45 degrees, and 75 degrees of horizontal angulation relative to the surgeons' sagital plane, and 15 degrees, 45 degrees, and 75 degrees degrees of vertical angulation relative to a horizontal plane. EMG signals were rectified and smoothed using analogue circuitry and digitally sampled at l0 Hz using a National Instruments DAQCard-700 connected to a Macintosh PowerBook 5300c running LabVIEW software. Statistical analysis was carried out by analysis of variance (ANOVA). RESULTS: The effects of vertical and horizontal working angles on the muscle effort were as follows: TH (horizontal, N.S.; vertical, N.S.), FDS (horizontal, p 45 degrees to the surgeon's sagital plane significantly increases the workload of the flexor digitorium superficialis and deltoid muscles. The deltoid muscle is also adversely affected by vertical angulation of the instrument. The instrument working angle has no effect on the thenar muscles. Whenever possible, laparoscopic surgeons should strive to place their instruments and trocars so as to minimize extreme horizontal or vertical displacement of their hands away from a resting position of comfort.

One stage carotid artery resection: reconstruction in radiated head and neck carcinoma.

PURPOSE: Management of the carotid artery involved with metastatic squamous cell carcinoma continues to be a topic of much discussion. Early reports, for the most part, focused on the sequel of ligation and the development of various tests to predict patient tolerance for the procedure. More recent alternatives have described resection reconstruction in multistage procedures. By using immediate reconstruction with autogenous arterial grafting, carotid artery resection can be accomplished in patients with radiation failure in a single stage. This technique can be used without the addition of myocutaneous flaps, controlled fistulas, or intracranial surgery advocated for usage with alternative techniques. PATIENTS AND METHODS: Immediate reconstruction after resection of the carotid artery with superficial femoral arterial graft is described. RESULTS: In a series of 18 high-risk patients with radiation failure, the artery was successfully resected and reconstructed in 1 stage without any neurologic or vascular complications. The technique has been associated with prolonged survival in selected patients. CONCLUSION: Carotid artery resection and immediate reconstruction can be performed in high-risk radiation failure patients with acceptable complications, and is associated with prolonged survival in selected cases.

An ergonomic evaluation of surgeons' axial skeletal and upper extremity movements during laparoscopic and open surgery.

BACKGROUND: Many surgeons have complained of fatigue and musculoskeletal pain after laparoscopic surgery. We evaluated differences in surgeons' axial skeletal and upper extremity movements during laparoscopic and open operations. METHODS: Five surgeons were videotaped performing 16 operations (8 laparoscopic and 8 open) to record their neck, trunk, shoulder, elbow, and wrist movements during the first hour of surgery. We also compared postprocedural complaints of pain, stiffness, or numbness between the two groups. RESULTS: Compared with surgeons performing open surgery, surgeons performing laparoscopic surgery exhibited less lateral neck flexion; less trunk flexion; more internal rotation of the shoulders; more elbow flexion; more wrist supination and wrist ulnar and radial deviation. There was a trend of more shoulder stiffness after laparoscopic operations than after open operations. CONCLUSIONS: Laparoscopic surgery involves a more static posture of the neck and trunk, but more frequent awkward movements of the upper extremities than open surgery. Ergonomic changes in the operating room environment and instrument design could ease the physical stress imposed on surgeons during laparoscopic operations.

A virtual instrument ergonomics workstation for measuring the mental workload of performing video-endoscopic surgery.

The visual and physical interface imposed on the surgeon by video-endoscopic surgery (VES) increases the surgeon's mental workload. Ergonomic studies are needed to develop ways to reduce this workload. We used virtual instrumentation to devise a portable ergonomic workstation to compare the surgeon's mental workloads during simulated open surgery and VES. The system measures palmar tonic skin conductance level (SCL) and electrooculogram (EOG) and frontalis electrical activity to monitor mental stress and concentration levels. We used the system at a national surgery conference on volunteer subjects during a rest period and as they performed simulated surgery, consisting of typing knots using open and VES techniques. The subjects were asked to self-rate their levels of mental concentration and stress during these activities and reported that both progressively increased from rest to the open surgery task to the VES task. The subjects tied fewer knots during the VES than the open task, consistent with the increased demands of the VES task. The SCL progressively increased from rest to the open task to the VES task, correlating with the subjects' reported increase in mental stress level. Eye blinks and low frequency EOG activity decreased from rest to the open task, consistent with the subjects' reported increase in mental concentration level. From the open to the VES task, eye blinks and EOG activity increased, as expected given the greater demands of the VES task. High frequency frontalis activity merits further study as another indicator of the subjects' levels of mental concentration and stress.

Measurement of intracellular gamma-interferon, interleukin-4, and interleukin-10 levels in patients following laparoscopic cholecystectomy.

Major surgery suppresses intracellular T-cell cytokine production. Laparoscopic surgery has been reported to have no effect on in vitro lymphocyte reactivity, but its effects on intracellular cytokine production are unknown. This study measured T-cell intracellular gamma-interferon, interleukin-4 (IL-4), and interleukin-10 (IL-10), along with serum interleukin-6 (IL-6) and cortisol levels, immediately before and 1 day after laparoscopic cholecystectomy in a cohort of six Air Force and veteran patients. Stimulated intracellular levels of gamma-interferon were slightly, but not significantly, elevated during the postoperative period in all T-cell subsets. There were no postoperative changes in stimulated IL-4 or IL-10 levels. Postoperative serum IL-6 levels, but not serum cortisol levels, were significantly elevated compared to preoperative values. In conclusion, laparoscopic surgery causes slight trauma but has no effect on T-cell intracellular interferon, IL-4, and IL-10 responses.

Surgical reconstruction of the extracranial vertebral artery: management and outcome.

PURPOSE: The purpose of this study was to identify the risk and outcome of reconstruction of the extracranial vertebral artery (ECVA). METHOD: The study was conducted as a retrospective review of 369 consecutive ECVA reconstructions. RESULTS: The clinical presentations consisted of hemispheric symptoms alone in 4% of the cases, hemispheric and vertebrobasilar symptoms in 30%, and vertebrobasilar symptoms alone in 60%. The cause of the lesion was atherosclerosis (n = 300), extrinsic compression (n = 42), dissection (n = 7), radiation arteritis (n = 5), intimal hyperplasia (n = 3), fibromuscular dysplasia (n = 2), previous surgical ligation (n = 3), aneurysm (n = 2), and other (n = 5). All the patients underwent preoperative arteriography. There were 252 proximal ECVA reconstructions (218 transpositions, 42 bypass grafting procedures, and two other) and 117 distal ECVA reconstructions (85 bypass grafting procedures, 25 transpositions, and seven other). In 83 patients, the ECVA operation was performed concomitant with a carotid or supraaortic trunk reconstruction. This series was analyzed in two separate sets: before 1991 (n = 215), when changes in indications and management were occurring; and after 1991 (n = 154), when we acquired a dedicated anesthesia team and digital arteriography in the operating room and established uniform protocols for the management of ECVA disease. The stroke, death, and stroke/death rates for the period before 1991 were, respectively, 4. 1%, 3.2% and 5.1%. The stroke, death, and stroke/death rates for the period after 1991 were, respectively, 1.9%, 0.6% and 1.9%. The patency rate at 5 years was 80%. The survival rate at 5 years was 70%. Most of the deaths during the follow-up period were caused by cardiac disease. Among the survivors, the protection rate from stroke was 97%. CONCLUSION: The changes in operative selection and management have improved the results of ECVA reconstruction. The data reported for ECVA reconstruction in patients who underwent operation since 1991 reflect the outcome of ECVA reconstruction today. In our experience, a reconstruction of the ECVA is less risky than a carotid reconstruction.

A virtual instrument ergonomics workstation to measure surgeons' physical stress.

Videoendoscopic (VES) instruments have poor force transmission properties and often require surgeons to employ awkward hand and arm positions. In order to compare the physical workload of laparoscopic surgery to open surgery, we collected long-duration EMG records from the thumb (thenar compartment) of six surgeons performing suturing and knot tying in a training box using both open and VES techniques. EMG signals were acquired using a LabVIEW Virtual Instrument and analyzed using a Modified Exposure Variation Analysis (MEVA) algorithm. Standard EMG indices and the MEVA analysis demonstrated significantly greater amplitude and duration of EMG signals using VES technique compared to open technique. Our results suggest that the use VES techniques requires a greater intensity of physical effort than open surgery techniques.