The ideal theoretical graft oversizing in valve-sparing aortic operations with a standard tubular or a Valsalva graft

Objective: We sought to determine, by a mathematical model, the ideal theoretical degree of ascending aortic graft oversizing needed to obtain normal sinuses dimension in the reimplantation type of valve-sparing aortic operations. Methods: To define a normal-range value, size of sinuses of Valsalva was conventionally expressed as the area surrounding fully opened aortic cusps, the so-called beyond leaflets area (BLA), and measured in 50 healthy subjects. A mathematical relationship between aortic annulus diameter, aortic sinuses diameter and resulting BLA was defined. By simulating intra-operative scenarios, the effect of different degrees of a standard or Valsalva graft oversizing on BLA extension was tested. Results: The same degree of graft oversizing resulted in a bigger beyond leaflets area for the Valsalva graft than for a standard graft. Oversizing degrees exceeding +7 mm for a standard graft and +3 mm for the Valsalva graft resulted in a beyond leaflets area over normal limits. Results were expressed in a visual form as two different normograms, one for the standard graft and one for the Valsalva graft. Conclusions: A less pronounced graft oversizing is needed to achieve normal-range sinuses size when using a Valsalva graft, the ideal theoretical graft oversizing was +7 mm for a standard graft and +3 mm for the Valsalva graft, our normograms can be helpful in selecting a proper graft size when performing a valve-sparing aortic procedure.     

Valsalva prosthesis in aortic valve-sparing operations

Aortic valve-sparing operations have provided very good clinical outcomes. However, the absence of the sinuses of Valsalva might limit valve durability. The Gelweave Valsalva prosthesis, which presents pre-fashioned neo-sinuses, has been designed in order to avoid early leaflets deterioration. We report our results in 63 patients who underwent valve-sparing operations (reimplantation technique) using the Gelweave Valsalva graft. The main indication was ascending aorta aneurysm or annuloaortic ectasia, with or without aortic insufficiency. The operation was performed also in cases of Marfan syndrome, Bicuspid Aortic Valve (BAV), and acute Type A dissection. In-hospital mortality was of 4.7%, and two thirds were acute Type A dissection patients (P=0.01). There were no late deaths. Three years freedom from grade 3-4 AI and freedom from late aortic valve replacement were 91.7+/-4.3% and 93.8+/-5.1%, respectively. Aortic valve-sparing operations show good results in patients electively operated for aortic root ectasia. Aortic cusps repair may lead to late failure. Even if the Gelweave Valsalva prosthesis is easy to implant and it also reproduces pseudosinuses, a long-term follow up is necessary to determine if this graft may reduce leaflets deterioration.     

Aortic repair in Marfan's syndrome: prevention of mechanical leaflets damage

Aortic incompetence in Marfan's syndrome results from distortion or dilatation of the sinuses of Valsalva, annuloaortic ectasia or a combination of these problems. Valve leaflets in these patients are macroscopically normal in spite of aortic insufficiency. Replacement of the ascending aorta, root and aortic valve with a composite graft was, for a long time, the treatment of choice for Marfan patients. Valve-preserving procedures (remodeling or reimplantation) provide the advantages of avoiding the shortcomings of standard surgical techniques, and maintaining the functional integrity of the left ventricular (LV) outflow tract, aortic root and ascending aorta. We developed a modified valve-sparing reimplantation technique for avoiding leaflet damage. This was achieved by leaving a 'cushion' of aortic wall (8--10 mm) that, sewn on the Dacron graft, works as a 'damper' and prevents leaflets injury during the systolic opening of the valve. For final judgment of this operative method long-term results are necessary.     

Analysis of valve motion after the reimplantation type of valve-sparing procedure (David I) with a new aortic root conduit

BACKGROUND: The reimplantation type of valve-sparing procedure does not allow proper reconstruction of the sinuses of Valsalva. We assessed the valve motion after a reimplantation type (David I) of valve-sparing procedure using a new Dacron conduit that incorporates sinuses of Valsalva. METHODS: Nine consecutive patients undergoing an aortic valve-sparing procedure using the new conduit were studied using two-dimensional transesophageal echocardiography shortly (2 +/- 1 months) after operation to determine root distensibility, expressed as percent change in radius and as pressure strain of the elastic modulus. Next, monodimensional view was used to assess valve motion in its various phases (rapid valve opening velocity, slow closing leaflet displacement, rapid valve closing velocity, maximal leaflet displacement, and leaflet displacement before valve closure). Seven healthy individuals served as control subjects. RESULTS: Root distensibility was reduced at the level of the annulus and sinotubular junction but was similar to control subjects at the level of the sinuses (percent change in radius, 4.1% +/- 0.8% versus 4.5% +/- 1.2%; pressure strain of the elastic modulus, 1,286 +/- 674 g/cm2 versus 1,195 +/- 628 g/cm2). Rapid valve opening (69 +/- 34.4 cm/s versus 51 +/- 11.9 cm/s) and closing (47.6 +/- 16 cm/s versus 36.4 +/- 9 cm/s) velocity as well as slow closing leaflet displacement (24% +/- 4.7% versus 22.1% +/- 7.9%), maximal leaflet displacement (20.1 +/- 4 mm versus 22.7 +/- 1.9 mm), and leaflet displacement before valve closure (15.2 +/- 3 mm versus 17.6 +/- 0.8 mm) were similar to control subjects. CONCLUSIONS: The new aortic root conduit used in a reimplantation type of valve-sparing procedure allows the anatomic reconstruction of the aortic root with leaflet motion similar to that of normal subjects.     

Midterm results after aortic valve-sparing operation

OBJECTIVES: We have conducted aortic valve-sparing operation for patients having aortic root dilatation and almost normal aortic valve leaflets since August 1998, and here report midterm results. METHODS: Patients with dilated aortic annulus or Marfan's syndrome were treated with reimplantation, and the remaining patients with remodeling. Either 24 or 26 mm graft was selected based on aortic annular diameter and leaflet size. Aortic valve competence was assessed regularly with echocardiography. RESULTS: Five patients (age: 29 +/- 13 yr), including 4 with Marfan's syndrome, had undergone reimplantation, and 3 (age: 46 +/- 18 yr) remodeling by December 2000. Mean follow-up was 18 (range: 10-32) months, and no postoperative death has occurred and no reintervention has been required thus far. All the patients in the remodeling group showed only a small pressure gradient through the aortic valve and decreased left ventricular diameter. Two in the reimplantation group showed a pressure gradient exceeding 20 mmHg. Two Marfan's syndrome patients in the reimplantation group showed slightly increased diastolic left ventricular diameter and 3 slightly increased systolic left ventricular diameter. Although aortic regurgitation had diminished in all patients by discharge, moderate aortic regurgitation recurred in 1 non-Marfan's syndrome patient in the reimplantation group because of degenerated aortic valve. CONCLUSION: Although postoperative aortic valve function was not perfect in all patients undergoing reimplantation, midterm results after aortic valve-sparing operation were generally satisfactory. Proper selection of patients, procedures, and graft size was thought to be important to ensure a favorable surgical outcome.     

Simple modification of "T. David-V" valve-sparing aortic root replacement to create graft pseudosinuses

The absence of sinuses of Valsalva is postulated to perturb coronary flow patterns and to create abnormal leaflet stresses, which theoretically may limit the long-term durability of valve-sparing aortic root replacement with the original Tirone David-I reimplantation technique with a cylindrical tube graft. David developed the “T. David-V” procedure in 2001; it creates large billowing Dacron pseudosinuses while retaining the reimplantation concept. To illustrate a simple modification of the T. David-V technique, we describe a patient with Marfan's syndrome who underwent valve-sparing aortic root replacement with 1 large and 1 small graft to create pseudosinuses in the Dacron graft, to facilitate suturing the valve inside the graft, and to make the distal graft-to-aorta anastomosis a better size match.     

One-year appraisal of a new aortic root conduit with sinuses of Valsalva.

OBJECTIVES: We evaluate the clinical results 1 year after an anatomic reconstruction of the aortic root in which we used a specifically designed aortic root prosthesis that incorporates the sinuses of Valsalva. MATERIAL AND METHODS: The new aortic Dacron prosthesis has a proximal portion in the Dacron conduit that expands on implantation, creating pseudosinuses. During a 12-month period, 28 patients (mean age 59 +/- 14 years) underwent a Bentall operation (12 cases), a remodeling procedure (7 cases), and a reimplantation procedure (9 cases) with the use of a new aortic root conduit. All patients had aortic root aneurysm with an anatomically normal (for the valve-sparing procedure) or diseased aortic valve (for the Bentall operation). Five patients had aortic dissection and 5 had Marfan disease. The mean follow-up was 6 +/- 3 months. All patients underwent postoperative transesophageal and transthoracic echocardiographic studies. RESULTS: All patients survived and were in good clinical condition at the latest follow-up. Postoperative echocardiography showed a marked reduction in ventricular volumes in all patient groups (P <.0005). In the Bentall group the new prosthesis appeared to reduce the tension on the coronary ostial sutures. In patients undergoing both types of valve-sparing procedures a similar normal anatomy of the aortic root was reconstructed. In the reimplantation group the anulus was smaller than in the remodeling group (P =.01). Patients undergoing the reimplantation procedure had less bleeding and a lower incidence of residual valve insufficiency. CONCLUSIONS: The new aortic root prosthesis allowed the reconstruction of the aortic root anatomy in all types of surgical techniques with low postoperative morbidity.     

Flow patterns in the aortic root and the aorta studied with time-resolved, 3-dimensional, phase-contrast magnetic resonance imaging: implications for aortic valve-sparing surgery

OBJECTIVE: Sparing the aortic valve has become a surgical option for patients who require repair of aortic root ectasia and have normal valve leaflets. Surgical approaches to valve sparing differ with regard to preservation of the native sinuses of Valsalva. The role of the sinuses and the importance of maintaining them remain controversial. METHODS: By using a time-resolved, 3-dimensional, phase-contrast magnetic resonance imaging technique, aortic root and aortic blood velocity data were acquired from 2 patients with Marfan syndrome 6 months after aortic valve-sparing surgery with straight Dacron grafts and contrasted with data from 6 normal volunteers. RESULTS: In normal aortas vortical blood flow became apparent in the individual sinuses after peak systole. The vortices filled the available space behind the valve leaflets and persisted until diastole, expanding and moving inward during aortic valve closure. In contrast, no vortices were observed in the postoperative patients with Marfan syndrome with negligible sinuses. CONCLUSIONS: Changes in supravalvular flow accompany loss of sinus architecture. Whether the presence, size, and velocity of supravalvular vortices affects the function or durability of the preserved aortic valve remains to be studied.     

Valve-sparing aortic root replacement (remodeling/reimplantation) in acute type A dissection

BACKGROUND: High reoperation rates after supracommissural tube graft replacement for acute type A dissection due to sinus of Valsalva dilation have been reported. Valve-sparing operations focusing on the replacement of the sinus of Valsalva are an appealing alternative. The applicability of these techniques in acute type A dissection remains debatable and results are limited. METHODS: From 1992 to 1998, 20 patients with acute type A dissection received a valve-sparing aortic root replacement. Two different types of aortic valve-sparing operations were performed: the remodeling technique in 11 patients and the reimplantation technique in 9 patients. Patients were followed for 26 +/- 18 months. Echocardiographic studies were performed every 6 months. RESULTS: There were 2 early postoperative deaths and no late death, no reoperation, and no thromboembolic events. The latest echocardiographic studies of the 18 survivors showed a competent valve in 12 and a trivial aortic valve insufficiency in 6 patients. The mean aortic valve pressure gradient was 4.3 +/- 1.3 mm Hg. CONCLUSIONS: These midterm results support the surgical strategy of valve-sparing aortic root replacement in patients with acute type A dissection.     

Extensive aneurysms of sinuses of Valsalva precluding valve sparing aortic root reimplantation (David procedure)

A 55-year-old female noticed worsening exertional dyspnoea for two years. She was born with cleft palate and profound deafness. Significant physical findings included dysmorphism with micrognathia and acrocephaly and congenital deafness. Transthoracic echocardiogram revealed aneurysms involving the right and the non-coronary sinuses of Valsalva. Despite that, the native aortic valve retained preserved geometry. Computed tomography (CT)-scan demonstrated multiple aneurysms arising from all three sinuses of Valsalva. This displaced the right ventricle (RV) caudally and indented the RV outflow tract. A valve-sparing root reimplantation was planned. However, intraoperatively the root aneurysms were found to be very extensive such that no healthy tissue remained along the insertion lines of the aortic valve leaflets. The aortic annulus was not dilated (2 cm) and the left ventricular outlow tract was not involved in the disease process. Consequently, despite the presence of macroscopically normal leaflets and relatively undisturbed annular geometry, we were unable to reimplant the native aortic valve and proceeded to a modified Bentall procedure. Histologically, significant medial degeneration with loss of elastin and muscle was identified in the aortic sinus wall. Similar changes were also found affecting the native leaflets coupled with increased fibrous thickening.     

Comparison of distensibility of the aortic root and cusp motion after aortic root replacement with two reimplantation techniques: Valsalva graft versus tube graft

The aim of this study is to evaluate distensibility of the aortic root and function of the aortic cusp after aortic root replacement using valve sparing procedure. Between October 1999 and August 2006, valve sparing aortic root replacements were performed in 39 patients who had annuloaortic ectasia (AAE) and aortic valve regurgitation. Reimplantation type of valve-sparing procedure was performed with a tube graft (n=12) or a Valsalva graft (n=27). Echocardiographic studies were performed six months after the operation comparing Valsalva graft (Group V, n=15), tube graft (Group T, n=5), and normal control (Group C, n=5). Percent changes in radius (PCR) of the aortic root were measured as indices of distensibility. Rapid valve opening velocity (RVOV/HR (mm/s/min)) and rapid valve closing velocity (RVCV/HR (mm/s/min)) of the aortic cusp were analyzed in each group. Root distensibility of sinus in Group T (1.9+/-1.1) was significantly smaller than Group C (7.2+/-1.8) (P=0.003). RVOV/HR in Group T was highest among the three groups (T: 48.2+/-6.2, V: 36.2+/-11.9, C: 33.7+/-9.6). RVCV/HR showed no difference among the three groups (T: 26.1+/-6.7, V: 40.7+/-16.6, C: 28.4+/-16.3). In conclusion, sinus distensibility of the Valsalva graft was well preserved and valve-opening characteristics with the Valsalva graft were identical to normal.     

Valve-sparing aortic root replacement

The aortic root has a unique 3-dimensional configuration and the distinctive function of supporting the aortic valve and blood vessels. The sinuses of Valsalva are crucial to create appropriate eddy currents that are important in initiating and coordinating aortic valve closure and promoting coronary artery blood flow. Most aneurysms in the aortic root are associated with degenerative changes in the elastic media rather than atherosclerosis. Valve-sparing root repair has become widely accepted, although the Bentall procedure remains the gold standard. Because reimplantation using the Valsalva graft allows root geometry to be retained and theoretically and practically prevents recurrent aortic valve regurgitation, it is considered the most reliable and preferred technique among various valve-sparing aortic root repair procedures.     

Aortic prosthetic ring annuloplasty: a useful adjunct to a standardized aortic valve-sparing procedure?

OBJECTIVE: Dilation of aortic annulus, sinuses of Valsalva, and sinotubular junction (STJ) diameters are the characteristic lesions of aortic root aneurysm. The remodeling technique reduces STJ diameter and creates three neosinuses of Valsalva. Alternatively, the reimplantation technique reduces both annulus and STJ diameters to the detriment of aortic root dynamics. Although the remodeling technique is recognized as the most physiological valve-sparing procedure, aortic annulus dilation may jeopardize its results. A standardized approach that combines an external subvalvular aortic prosthetic ring annuloplasty with the remodeling technique is suggested. METHODS: Eighty-three patients underwent an elective aortic root remodeling procedure, either isolated (group 1, n=34) or combined with an external subvalvular aortic prosthetic ring annuloplasty (group 2, n=49). Preoperative aortic regurgitation was 1.59+/-1.1 (group 1) and 1.97+/-1.3 (group 2) (NS). The aortic annulus was more dilated in group 2 than in group 1 (27+/-2.77 mm vs 26.4+/-2.3 mm, p<0.01). Residual aortic regurgitation > or =grade II was the conversion criteria for aortic valve replacement. RESULTS: Operative mortality was 3.6% (n=3). Intraoperative conversion for valve replacement was 32.7% in group 1 (n=11) versus 4.2% in group 2 (n=2) (p<0.001). In group 1, preoperative annulus diameter was larger for converted than for valve-spared patients (27.6+/-1.7 mm vs 25.2+/-1.5 mm, p<0.02). In group 2, implanted aortic ring significantly reduced annulus diameter (20.6+/-1.8 mm) without significant aortic valve gradient (8.3+/-3 mmHg). Follow-up was 17.2+/-13.4 months (group 1) and 10.41+/-7.95 months (group 2). Reoperation for recurrent aortic regurgitation was 13% in group 1 (n=3) versus 4.2% in group 2 (n=2). Echocardiographic follow-up found residual aortic regurgitation < or =grade I in 17 patients in group 1 (90%) versus 43 patients in group 2 (95.5%) and of grade II in two patients in group 1 (10%) and two patients in group 2 (4.5%). CONCLUSION: The addition of external aortic prosthetic ring annuloplasty improves the remodeling technique's operative reproducibility and short-term results. Therefore, its use as a systematical adjunct to the remodeling procedure is suggested. However, further long-term evaluation comparing this valve-sparing procedure to composite graft replacement should define the best surgical strategy for aortic root aneurysm.     

In Vitro Evaluation of a Novel Autologous Aortic Valve (Biovalve) With a Pulsatile Circulation Circuit

We have used in‐body tissue architecture technology to develop an autologous valved conduit with intact sinuses of Valsalva (biovalve). In this study, we fabricated three different forms of biovalves and evaluated their function in vitro using a mock circulation model to determine the optimal biovalve form for aortic valve replacement. A cylindrical mold for biovalve organization was placed in a dorsal subcutaneous pouch of a goat, and the implant that was encapsulated with connective tissue was extracted 2 months later. The cylindrical mold was removed to obtain the biovalve (16 mm inside diameter) that consisted of pure connective tissue. The biovalve was connected to a pulsatile mock circulation system in the aortic valve position. The function of the three biovalves (biovalve A: normal leaflets with the sinuses of Valsalva; biovalve B: extended leaflets with the sinuses of Valsalva; biovalve C: extended leaflets without the sinuses of Valsalva) was examined under pulsatile flow conditions using saline. In addition, the mock circuit was operated continuously for 40 days to evaluate the durability of biovalve C. The regurgitation rate (expressed as a percent of the mean aortic flow rate during diastole) was 46% for biovalve A but only 3% for biovalves B and C. The durability test demonstrated that even after biovalve C pulsated more than four million times (heart rate, 70 bpm; mean flow rate, 5.0 L/min; mean aortic pressure, 92 mm Hg), stable continuous operation was possible without excessive reduction of the flow rate or bursting. The developed biovalve demonstrated good function and durability in this initial in vitro study.     

Time-resolved three-dimensional magnetic resonance velocity mapping of aortic flow in healthy volunteers and patients after valve-sparing aortic root replacement

OBJECTIVE: To provide more complete characterization of ascending aortic blood flow, including vortex formation behind the valve cusps, in healthy subjects and patients after valve-sparing aortic root replacement (David reimplantation). METHODS: Time-resolved 3-dimensional magnetic resonance imaging velocity mapping was performed to analyze pulsatile blood flow by using encoded 3-directional vector fields in the thoracic aortas of 10 volunteers and 12 patients after David reimplantation using a cylindrical tube graft (T. David I) and two versions of neosinus recreation (T. David-V and T. David-V-S mod ). Aortic flow was evaluated by using 3-dimensional time-resolved particle traces and velocity vector fields reformatted onto 2-dimensional planes. Semiquantitative data were derived by using a blinded grading system (0-3: 0, none; 1, minimal; 2, medium; 3, prominent) to analyze the systolic vortex formation behind the cusps, as well as retrograde and helical flow in the ascending aorta. RESULTS: Systolic vortices were seen in both coronary sinuses of all volunteers (greater in the left sinus [2.5 +/- 0.5] than the right [1.8 +/- 0.8]) but in only 4 of 10 noncoronary sinuses (0.7 +/- 0.9). Comparable coronary vortices were detected in all operated patients. Vorticity was minimal in the noncoronary cusp in T. David-I repairs (0.7 +/- 0.7) but was prominent in T. David-V noncoronary graft pseudosinuses (1.5 +/- 0.6; P = .035). Retrograde flow (P = .001) and helicity (P = .028) were found in all patients but were not distinguishable from normal values in the T. David-V-S mod patients. CONCLUSIONS: Coronary cusp vorticity was preserved after David reimplantation, regardless of neosinus creation. Increased retrograde flow and helicity were more prominent in T. David-V patients. These novel magnetic resonance imaging methods can assess the clinical implications of altered aortic flow dynamics in patients undergoing various types of valve-sparing aortic root replacement.     

Early valve failure after aortic valve-sparing root reconstruction.

Aortic valve-sparing root reconstructive surgery has been widely adopted to improve the patient's quality of life. We experienced a patient who required reoperation for progressive aortic regurgitation 17 months after the initial operation of valve-sparing root reconstruction with the reimplantation method in acute aortic dissection. In this study, we were concerned with valve durability because of the absence of sinuses of Valsalva in the new aortic root and the need for careful follow-up after this procedure.     

A technique to reposition sinotubular junction in aortic valve reimplantation procedures with the De Paulis Valsalva graft.

Sinotubular junction reconstruction in reimplantation type of valve-sparing aortic procedure can present some problem when a Valsalva graft is used. Since in the Valsalva graft the sinotubular junction height is predetermined, correct matching with native commissures height can be difficult. We propose a method by which it is possible to create a new sinotubular junction in Valsalva graft without altering its original configuration.     

Aortic valve-sparing operation and a total arch replacement by an elephant trunk method for Marfan’s syndrome with aortic regurgitation and a DeBakey type IIIb dissection

A 35 year-old male with Marfan's syndrome was referred with a fortuitous echographic finding of an abdominal aorta flap. Transthoracic echocardiography showed moderate aortic regurgitation and an aneurysm in the sinus of Valsalva. Computed tomography demonstrated an aneurysm in the sinus of Valsalva 60 mm in size and a DeBakey type IIIb dissection extending from the left subclavian artery to the right common iliac artery. An aortic valve-sparing operation (reimplantation), total aortic arch replacement and the elephant trunk method were used in this patient. An aortic valve-sparing operation is preferable because the patient is young, and has no need for anticoagulant therapy after surgery. The extent of the aortic reconstruction, including the intact aortic arch, was appropriate to prohibit future dilatation of the aortic arch and retrograde dissection from a DeBakey type IIIb dissection. (Jpn J Thorac Cardiovasc Surg 2005;53: 657–660)     

Aortic valve-sparing operation and a total arch replacement by an elephant trunk method for Marfan's syndrome with aortic regurgitation and a DeBakey type IIIb dissection.

A 35 year-old male with Marfan's syndrome was referred with a fortuitous echographic finding of an abdominal aorta flap. Transthoracic echocardiography showed moderate aortic regurgitation and an aneurysm in the sinus of Valsalva. Computed tomography demonstrated an aneurysm in the sinus of Valsalva 60 mm in size and a DeBakey type IIIb dissection extending from the left subclavian artery to the right common iliac artery. An aortic valve-sparing operation (reimplantation), total aortic arch replacement and the elephant trunk method were used in this patient. An aortic valve-sparing operation is preferable because the patient is young, and has no need for anticoagulant therapy after surgery. The extent of the aortic reconstruction, including the intact aortic arch, was appropriate to prohibit future dilatation of the aortic arch and retrograde dissection from a DeBakey type IIIb dissection.     

Opening and closing characteristics of the aortic valve after valve-sparing procedures using a new aortic root conduit

BACKGROUND: The durability of aortic valve-sparing procedures is negatively affected by increased leaflet stress in the absence of normally shaped sinuses of Valsalva. We compared valve motion after remodeling procedures using a standard conduit and a specifically designed aortic root conduit. METHODS: Echocardiographic studies of the aortic valve dynamics were performed in 14 patients after remodeling of the aortic root (7 standard conduits, group A; 7 new conduits, group B) and in 7 controls (group C). Opening and closing leaflet velocities and percent of slow closing leaflet displacement were measured. Root distensibility and the pressure strain of the elastic modulus were measured at all root levels. RESULTS: Root distensibility and the pressure strain of the elastic modulus were different in group A and B only at the sinuses (p < 0.001). Opening and closing leaflet velocities were not different among groups. Slow closing leaflet displacement was markedly more evident in group B patients (24.2%+/-1.9% versus 2.5%+/-1.9% in group A, p < 0.001) and similar to controls (22.1%+/-7.9%). CONCLUSIONS: The new conduit guarantees dynamic features of the aortic valve leaflets superior to those obtained with standard conduits and more similar to normal subjects.