Partial Left Heart Bypass Research Articles

Thoracoabdominal Aortic Replacement Together with Curative Oncological Surgery in Retroperitoneal and Spinal Tumours

Malignancies with an extended encasement or infiltration of the aorta were previously considered inoperable. This series demonstrates replacement and subsequent resection of the thoracoabdominal aorta and its large branches as an adjunct to curative radical retroperitoneal and spinal tumor resection. Five consecutive patients were enrolled between 2016 and 2020, suffering from cancer of unknown primary, pleomorphic carcinoma, chordoma, rhabdoid sarcoma, and endometrial cancer metastasis. Wide surgical resection was the only curative option for these patients. For vascular replacement, extracorporeal membrane oxygenation (ECMO) was used as a partial left-heart bypass. The early technical success rate was 100% for vascular procedures and all patients underwent complete radical tumour resection with negative margins. All patients required surgical revision (liquor leak, n = 2; hematoma, n = 3; bypass revision, n = 1; bleeding, n = 1; biliary leak, n = 1). During follow-up (average 47 months, range 22-70) primary patency rates of aortic reconstructions and arterial bypasses were 100%; no patient suffered from recurrent malignant disease. Thoracoabdominal aortic replacement with rerouting of visceral and renal vessels is feasible in oncologic patients. In highly selected young patients, major vascular surgery can push the limits of oncologic surgery further, allowing a curative approach even in extensive retroperitoneal and spinal malignancies.

Unusual case of successful treatment of a ruptured thoracoabdominal aneurysm in elderly woman

We describe a case of a 76-year-old woman who underwent emergent surgery for ruptured thoracoabdominal aneurysm with the use of partial left heart bypass. Dacron prosthesis was implanted into the thoracic and abdominal aorta (up to its bifurcation), and four visceral arteries were reimplanted into the prosthesis. The procedure of implanting the prosthesis into the thoracic part of the descending aorta was supported by left heart bypass. The patient’s postoperative course was complicated by spinal cord ischaemia-induced lower extremities paraparesis. On the 26th postoperative day, she was referred to the regional neurological rehabilitation centre.

Improvement of PaO2 During One-Lung Ventilation With Partial Left-Heart Bypass in Pediatric Patients Is Caused by Increased Blood Flow to the Dependent Lung

Improvement of PaO2 During One-Lung Ventilation With Partial Left-Heart Bypass in Pediatric Patients Is Caused by Increased Blood Flow to the Dependent Lung

Urgent device retrieval using partial left heart bypass

Percutaneous cardiovascular device implantation plays an important and increasing role in the treatment of congenital heart disease. Device related complications of malposition and embolisation are uncommon and can usually be retrieved by catheter. We present two interesting cases in which migrated devices resulted in thoracic aortic obstruction; both were refractory to percutaneous retrieval. Device retrieval was achieved by thoracotomy and utilising partial left heart bypass because of specific concerns of distal perfusion. Our experience is presented.

Contemporary results of standard open repair of acute traumatic rupture of the thoracic aorta

Open repair of acute traumatic rupture of the thoracic aorta has been the standard of care for the past half century. Traditional criteria of operative success have been patient survival and prevention of spinal cord ischemia. Historical series have reported a variability of surgical results with relation to the variety of operative approaches. This study aims to update the results obtained with a uniform surgical technique based on a systematic utilization of distal perfusion during aortic cross-clamping. During a 35-year period (1974-2009), 138 consecutive patients with an acute traumatic rupture of the thoracic aorta were repaired with a Dacron graft interposition through a standard left thoracotomy. All patients received a method of circulatory support. A passive 9-mm Gott shunt inserted between the ascending and the descending aorta and delivering a median flow of 3 L/min was used in the first 40 cases. A partial left heart bypass realized from the left atrium to the descending aorta and driven with a centrifugal pump was used in the last 98 consecutive cases. A median flow of 4 L/min was recorded. Mean age of the patients was 27 years and 90.6% of them had associated injuries for a calculated mean ISS of 44. Two outcome variables were analyzed: hospital mortality and postoperative spinal cord ischemic injury. Overall hospital mortality is 5% (7/138 patients). This was improved from 7.5% (3/40) in patients perfused with the Gott shunt to 4% (4/98) in patients protected with the left heart bypass and lowered to 1.5% (1/68) in the last 68 patients. Among 134 cases with an intact preoperative spinal cord, one patient (0.7%) developed a new paraplegia due to a nonfunctional Gott shunt. Among 98 patients perfused with a centrifugal pump-driven left heart bypass, none of the 97 patients (0%) with a preoperative intact spinal cord developed a spinal cord ischemic deficit. Conventional open surgical repair of acute traumatic rupture of the thoracic aorta performed with an orderly monitored circulatory support can be accomplished with a very low rate of mortality and spinal cord injury. Compared with the Gott shunt, a left heart bypass propelled with a centrifugal pump is technically a more versatile method of perfusion, and it provides higher hemodynamic performance.

Redo Lateral Thoracotomy for Reoperative Descending and Thoracoabdominal Aortic Repair: A Consecutive Series of 60 Patients

Reoperative descending thoracic aorta (DTA) or thoracoabdominal aortic aneurysm (TAAA) surgery is a challenge because of increased risk of lung injury and diffuse bleeding. Sixty patients (34 male, mean age 54.4 years) underwent redo thoracotomy for DTA (22 patients) or extended thoracoabdominal incision for reoperative TAAA (38 patients) from March 1988 to June 2007, after 1.7 +/- 0.9 previous cardioaortic procedures. Forty-one patients were hypertensive (68%), 18 were smokers (30%), 9 had Marfan syndrome (15%), 9 had coronary artery disease (15%), 5 had chronic obstructive pulmonary disease (8%), and 3 had diabetes mellitus (5%). In all, 45% (27 patients) had previous dissection, 30% (18) had atherosclerotic aneurysms, 15% had coarctation surgery (9), and 6 patients had other etiologies. Mean follow-up, 100% complete, was 6.5 years. Hospital mortality for reoperative DTA/TAAA was 13.3% (8 patients). Although 6.3 +/- 2.9 (0 to 14) segmental artery pairs were sacrificed at reoperation-and 6.2 +/- 2.3 (1 to 12) initially-for a total of 10.6 +/- 3.9 (2 to 15) segmental artery pairs sacrificed, only 1 patient had paraplegia (1.6%). Four patients had a 2-day procedure, with 12 to 24 hours of intensive care unit recovery after lysis of extensive adhesions: all survived. Respiratory complications occurred in 13 patients (21.6%), and permanent dialysis was required in 2 (3.3%), but there were no strokes. Adverse outcome-1-year mortality, stroke, permanent dialysis, or paraplegia-occurred in 13 patients (21.6%). Adverse outcome was marginally associated (p < 0.2) with increased age, atherosclerotic aneurysms (33% versus 17% other), TAA incision (30% versus 9%), and greater aneurysm extent, and was significantly associated with perfusion technique (p = 0.02). Adverse outcome occurred in 3 of 4 patients who had clamp-and-sew technique, 6 of 21 using partial cardiopulmonary bypass (28.6%), and 3 of 17 with partial left heart bypass (17.7%), but only 1 of 18 with hypothermic circulatory arrest (5.6%). Reoperative DTA/TAAA repair was significantly safer with hypothermic circulatory arrest rather than partial cardiopulmonary bypass, partial left heart bypass, or clamp-and-sew strategy. A 2-day procedure may be advisable for patients with extensive adhesions.

Technique for repair of suprarenal and thoracoabdominal aortic aneurysms

Suprarenal and thoracoabdominal aortic aneurysms represent significant surgical challenges. For patients with associated aortic dissections, current endovascular technology has not been matured to address branch reconstructions that derive from separate lumens, making open surgical reconstruction the only proven method for repair. The required exposures of the thoracoabdominal aorta are expansive, and the extent of aortic replacement mandates efficient technique. Furthermore, a well-orchestrated team of surgeons, nurses, anesthesiologists, and perfusionists are all integral to achieving good outcomes and keeping operative courses tightly managed. Techniques to address extensive aneurysms of the thoracoabdominal aorta are reviewed in detail here, and videos are provided on The Journal website to show relevant anatomical features.

An unusual presentation of pedunculated thrombus in the distal arch of the aorta after splenectomy for B-cell lymphoma

A 59-year-old woman who was asymptomatic after a splenectomy for B-cell lymphoma was found to have a pedunculated mass filling 50% of the aortic lumen within the distal aortic arch on a routine follow-up computed tomographic scan of the chest (A/cover image, and B). She was referred to us with a differential diagnosis of tumor originating from the aortic wall. On transesophageal echocardiogram it seemed to be a solid mass rather than a floating thrombus. With suspicion of malignancy, it was decided to remove the mass surgically. Left thoracotomy was performed, and a 4-cm mass originating from the inner aspect of the distal aortic arch just above the remnant of the ductus arteriosus was excised on partial left heart bypass (C). The histology report showed a cylinder of pale hemorrhagic tissue, 4.0 1.0 0.8 cm, consisting of fibrin thrombus with a few atypical lymphoid cells present at one edge. However, this was insufficient for a firm diagnosis of malignancy. After surgery she received anticoagulant medication for 6 months. She remains well, with no evidence of recurrent thrombus after 3 years of follow-up. Nonaneurysmal aortic arch lesions are a frequent and a stillunderestimated source of stroke and peripheral embolization (in 10% of patients, the source of peripheral embolism cannot be identified). A floating thrombus in an apparently normal aortic arch is considered a life-threatening condition. Although rare, this diagnosis must not be overlooked in the search for etiology of recurrent and disseminated peripheral ischemic events, because of the significant morbidity and mortality related to a delayed diagnosis. Coagulopathies, atherosclerosis, trauma, malignancy, pregnancy, and previous aortic surgery are a few common causes of thrombus formation in this rare condition. There are various treatment options available, such as anticoagulation, balloon thrombectomy, stenting, and surgery. All these therapeutic modalities have their limitations; nonsurgical treatment involves high risk of embolism (reported as a 73% incidence of embolic events for highly mobile aortic thrombi as compared with 12% for immobile ones), ischemia, and stroke, whereas surgery has been reported with high mortality and morbidity. Complicated vascular surgical procedures have been performed for definitive treatment. Primary tumors of the aorta are rare, and only a few cases are reported in the literature; as a result of our suspicion of tumor, we aimed to remove the lesion in a controlled manner under bypass, because no standard approach

Repair of the torn descending thoracic aorta using the centrifugal pump for partial left heart bypass.

To describe the relevant anatomy and sequential technical maneuvers to repair blunt injuries to the descending thoracic aorta with partial left heart bypass. Blunt injury to the descending thoracic aorta remains among the most lethal and morbid of anatomic injuries. Of the techniques of repair which have evolved, "clamp and sew" is simple but has an unacceptable risk of paraplegia. In contrast, partial left heart bypass is more complex but virtually eliminates the risk of paraplegia. We present a detailed management plan for treating blunt injury to the descending thoracic aorta using partial left heart bypass that has evolved over the past 25 years. Preoperative Azā-blockade to reduce the risk of rupture and use of the centrifugal pump to reduce the incidence of paraplegia without the risk of systemic anticoagulation are essential. We present a detailed description of our management of injuries to the descending thoracic aorta. In our experience, no episodes of postoperative paraplegia have occurred with the use of this technique. Blunt injury to the descending thoracic aorta can be safely repaired using partial left heart bypass.

Cerebrovascular complications of aortic arch surgery

Ischemic strokes in the brain and the spinal cord are dreaded complications of aortic arch surgery. The etiology of these strokes is most typically embolic from atheromatous material but compression or dissection of branch vessels or hypoperfusion (particularly of radicular spinal branches) may be associated with increased stroke risk. Various techniques including partial left heart bypass with hypothermic circulatory arrest and retrograde or anterograde cerebral perfusion along with lumbar cerebrospinal fluid drainage may decrease the risk of neurovascular complications of aortic arch or thoracic aortic surgery. The risks of neurovascular complications with endovascular stenting of the aorta are unclear at this time.

Safety of lumbar drains in thoracic aortic operations performed with extracorporeal circulation

Background The safety of cerebrospinal fluid (CSF) drainage in thoracic aortic surgery using extracorporeal circulation (ECC) with systemic heparinization has not been established. Methods Four hundred thirty-two patients had descending thoracic or thoracoabdominal aortic repair between 1993 and 2002. One hundred sixty-two of those patients (age range, 67 ± 13 years) had repairs performed with ECC, systemic anticoagulation, and lumbar CSF drainage. Repairs performed without CSF drainage, without ECC, or by stent graft (n = 53) were excluded. The CSF catheters were inserted at L3 to L5. Cerebrospinal fluid was drained to maintain pressures of 10 to 12 mm Hg. In the absence of neurologic deficit or coagulopathy, the catheters were capped at 24 hours and removed at 48 hours. Cerebrospinal fluid drainage was continued beyond 24 hours for delayed onset paraparesis. Results Cerebrospinal fluid drains were used in 135 thoracoabdominal aortic aneurysms (extent I, n = 63; extent II, n = 25; extent III, n = 39; extent IV, n = 8) and 27 descending thoracic aortic repairs (aneurysm, n = 24; traumatic aortic injury, n = 2; aortic coarctation, n = 1). Partial left heart bypass was used in 132 patients, full cardiopulmonary bypass without deep hypothermic circulatory arrest in 5, and cardiopulmonary bypass with adjunctive deep hypothermic circulatory arrest in 25. Time between catheter insertion and anticoagulation was 153 ± 60 minutes. Heparin achieved an average maximum activated clotting time of 528 ± 192 seconds. Average ECC time was 114 ± 77 minutes. Average deep hypothermic circulatory arrest time was 40 ± 12 minutes. Mortality was 14.1% (23 of 162), and permanent paraplegia was 4.9% (8 of 162). No epidural or spinal hematoma was observed. Six (3.7%) patients had catheter-related complications (temporary abducens nerve palsy [n = 1]; retained catheter fragments [n = 2]; retained catheter fragment and meningitis [n = 1]; isolated meningitis [n = 1]; and spinal headache [n = 1]). Conclusions The CSF drainage in thoracic aortic surgery using ECC with full anticoagulation did not result in hemorrhagic complications. The permanent paraplegia rate in this complex patient population consisting of combined distal arch, thoracoabdominal aortic procedures were low, and lumbar CSF catheter-related complications had no permanent sequelae.

Delayed paraplegia after thoracic and thoracoabdominal aneurysm repair: a continuing risk

BackgroundParaplegia or paraparesis after otherwise successful thoracic or thoracoabdominal aortic reconstruction is a devastating complication for patient and physician. Interventions for its prevention have focused primarily on the intraoperative period. We have recently noted a significant incidence of delayed-onset neurologic deficit. MethodsWe reviewed our most recent 5-year experience with thoracic and thoracoabdominal reconstruction to examine the incidence of and potential contributors to delayed paraplegia or paraparesis. ResultsBetween June 1996 and June 2001, 60 patients (29 men, 31 women) underwent repair of isolated thoracic (n = 26) or thoracoabdominal aortic aneurysm (Crawford I, n = 7; Crawford II, n = 14; Crawford III, n = 12; Crawford IV, n = 1) by the cardiac and vascular surgical services collaboratively. Repair was performed endovascularly in 6, and open with either circulatory arrest in 12, partial left heart bypass in 37, or partial femorofemoral bypass in 5. Operative mortality was 9.3% (5 of 54 patients) for open repair and 0% for endovascular repair. Paraplegia or paraparesis occurred in 6 (10%) patients of which 83.3% (5 of 6) were delayed in onset. All patients with delayed paraplegia or paraparesis had degenerative aneurysms of Crawford extent II (n = 3) or III (n = 2), had intraoperative left heart bypass, and had perioperative spinal drainage. Delayed paraplegia or paraparesis occurred up to 27 days postoperatively, and was associated with a documented episode of hypotension in 60% (3 of 5) of patients. ConclusionsImprovements in intraoperative management may have reduced immediate paraplegia or paraparesis among vulnerable patients only to leave them at risk of delayed-onset deficit. Postoperative care, including assiduous attention to avoidance of even transient hypotension, must be tailored to this patient population.

Extracorporeal Circulation Induced Microvascular Perfusion Injury of the Small Bowel

Gastrointestinal complications following cardiopulmonary bypass (CPB) are relatively uncommon, but are associated with a high mortality rate. Impairment of bowel perfusion during and following CPB may serve as a trigger for the development of multiorgan failure. The aim of our study was the development of a new animal model allowing quantitative analysis of small bowel microcirculation during and after CPB. Twelve Landrace pigs served as laboratory animals. A 15-cm loop of the terminal ileum was exteriorized for microscopic observation. In 6 animals, a normothermic, partial left heart bypass (pLHB) was established for 2 h with a flow rate of 2,000 ml/min. Arterioles, collecting venules and the capillaries of the small bowel were recorded for the analysis of the microcirculation. All parameters were recorded prior to, during pLHB and up to 2 h after weaning off the bypass. Six sham operated animals served as controls. Despite unchanged hemodynamics, pLHB leads to microvascular perfusion disturbances of the small bowel. In pLHB animals, blood cell velocity in postcapillary venules (30–70 µm) was significantly decreased during and following bypass. Capillary density was also reduced during bypass and decreased even further after pLHB to only 30% of the control values. With this new large animal model for quantitative assessment of microvascular perfusion of the small bowel during CPB, it could be clearly demonstrated that partial normothermic left heart bypass leads to a significant disturbance of the small bowel microcirculation even under stable hemodynamic conditions.

Delayed operative intervention in the management of traumatic descending thoracic aortic rupture

Background Outcomes may be improved by purposefully delaying surgical intervention of the traumatically ruptured descending thoracic aorta. Methods Fifty-seven patient records identified through the Trauma Registry of a level 1 trauma center between January 1993 and April 2002 were retrospectively analyzed between groups who underwent “clamp-and-sew” versus partial left heart bypass repair techniques and between emergent versus delayed repair. Results Thirty-two (56%) of 57 patients were male. The mean age among survivors and nonsurvivors was 41 ± 18 (range 13 to 70) and 52 ± 23 (range 18 to 92; p = 0.04) years, and Injury Severity Score was 31 ± 13 (range 17 to 75) and 40 ± 16 (range 16 to 75; p = 0.04) points, respectively. Thirty-one (54%) underwent surgical intervention, 20 (35%) died during their initial resuscitation, and 6 (11%) were managed nonoperatively. Seventeen (55%) were repaired using partial left heart bypass and 14 (45%) using the clamp technique. Twenty-one (68%) had emergent repair and 10 (32%) had delayed repair. The rates of paraplegia, renal failure, and mortality were 12% (2 of 17), 0%, and 24% (4 of 17) in the bypass group, 0% ( p = 0.29), 0%, and 36% (5 of 14, p = 0.36) in the clamp group, 9.5% (2 of 21), 0%, and 38% (8 of 21) in the emergent group (<24 hours after admission), and 0% ( p = 0.45), 0%, and 10% (1 of 10, p = 0.12) in the delayed group (>24 hours after admission), respectively. Mean clamp times for the bypass and clamp groups were 44 ± 18 (21 to 90) and 30 ± 10 (14 to 52) minutes, respectively ( p = 0.02). Overall operative mortality was 29% (9 of 31). Conclusions Purposefully delaying surgical intervention in selected cases of descending thoracic aortic rupture and using the clamp technique does not increase mortality or morbidity over immediate operation and use of partial left hear bypass.

Dopexamine attenuates microvascular perfusion injury of the small bowel in pigs induced by extracorporeal circulation

Cardio-thoracic surgery with the use of extracorporeal circulation may lead to an impairment of splanchnic perfusion. The aim of this study was to investigate the effect of dopexamine on gastrointestinal microvascular perfusion failure due to extracorporeal circulation. Twenty landrace pigs served as laboratory animals. A loop of the terminal ileum was exteriorized for microscopic observation. In 13 animals a partial left-heart bypass (pLHB), with a non-pulsatile pump flow of approximately 50% of the cardiac output, was established for 2 h. Seven animals received a continuous i.v. infusion of 3 micrograms kg-1 min-1 dopexamine from the beginning of pLHB to the end of the experiment. Seven sham-operated animals served as controls. The microcirculatory network was analysed by means of intra-vital microscopy prior to, during pLHB, and 2 h after bypass. Despite normal haemodynamics measured by arterial pressure and cardiac output, pLHB led to significant impairment of microvascular perfusion characterized by arteriolar vasoconstriction, reduction of functional capillary density (FCD) to 30% 2 h after weaning off bypass and diminished blood-cell velocities in submucous venules. Dopexamine attenuated this perfusion impairment, preventing arteriolar vasoconstriction. FCD remained normal. Our data demonstrate that treatment with the vasoactive drug dopexamine leads to a significant reduction of the perfusion injury of the small bowel.

Oxygenator support for partial left-heart bypass

Partial left-heart bypass provides circulatory support and distal perfusion for repair of thoracic and thoracoabdominal aortic disease without requiring full anticoagulation. Unfortunately some patients, such as those with significant lung contusion in the setting of trauma or those with severe chronic obstructive pulmonary disease and degenerative aneurysms, do not tolerate single-lung ventilation. We have recently modified our left-heart bypass circuit in selected cases to provide supplementary oxygenation, making this technique more broadly applicable.

Bypass Techniques for Descending Thoracic Aortic Surgery

The conduct of partial left heart bypass or partial car diopulmonary bypass (CPB) during surgery involving the descending thoracic aorta or thoracoabdominal aorta is one of the most unappreciated and misunder stood extracorporeal circulation procedures in cardio vascular surgery. It is different from conventional CPB, and although some uninitiated practitioners consider it simpler, it is in fact more complicated than conven tional CPB and involves different concepts. It requires expertise and skill in regulating the flow, pressure, and oxygenation of blood going to both the proximal and distal parts of the body and management of the special bypass or shunt procedures used, specialized monitor ing, and knowledge about the protection and preserva tion of organs both proximal and distal to the aortic clamping. It demands exquisite communication and un derstanding of the unique problems faced by the sur geon, anesthesiologist, and perfusionist.

Influence of steroids on microvascular perfusion injury of the bowel induced by extracorporeal circulation

Background. Extracorporeal circulation is associated with gastrointestinal complications. By means of intravital microscopic methods, we investigated whether preoperative treatment with steroids can attenuate the impairment of the bowel microcirculation. Methods. In 20 pigs, a partial left heart bypass (pLHB) was established. A loop of the terminal ileum was exteriorized for intravital-microscopic observation. Seven sham-operated animals served as controls. In 13 animals, pLHB was established for 2 hours with a flow rate of 2,000 mL per minute; 7 of the animals received 20 mg/kg body weight prednisolone preoperatively. The microcirculatory network was analyzed before, during pLHB, and 2 hours after bypass. Results. Despite unchanged macro-hemodynamics, pLHB resulted in a significant microvascular perfusion injury of the small bowel. Arteriolar vasoconstriction and a reduction of perfused capillaries per unit area (functional capillary density) to 30% of prebypass values could be found. Blood cell velocities were reduced in submucuous collecting venules. In the steroid-treated animals, the functional capillary density remained normal. In addition, arteriolar vasoconstriction could be prevented. Conclusions. Treatment with prednisolone largely prevents the microcirculatory alterations in the small bowel induced by extracorporeal circulation.

Perioperative Management of Calves Undergoing Implantation of a Left Ventricular Assist Device

To describe perioperative management of calves that underwent left lateral thoracotomy, aortic cross-clamping, partial left heart bypass and implantation of a left ventricular assist device. A total of 43 healthy castrated male calves, weighing 121 +/- 24 kg. Diazepam (mean +/- SD, 0.26 +/- 0.07 mg/kg), ketamine (5.9 +/- 2.17 mg/kg) and isoflurane were used in the anesthetic management of calves undergoing implantation of a left ventricular assist device in the descending thoracic aorta. Other adjunctive agents administered were fentanyl (11 +/- 5.4 microg/kg), lidocaine (4.9 +/- 3.19 mg/kg), bupivacaine (0.75%) and butorphanol (0.49 +/- 0.13 mg/kg). None of the calves regurgitated at induction or during intubation. A tube was used to drain the rumen and prevent bloat during the procedure. Partial left heart bypass was used to perfuse the caudal half of the body during the period of aortic cross clamp and device implantation. Initial mean systemic blood pressure was 96 +/- 25 mm Hg, and pressures measured in the auricular artery increased during aortic cross-clamping and bypass. Vasoconstrictor therapy was required to treat caudal arterial hypotension during the procedure in 9 calves. Mean systemic arterial pressures returned to baseline values by the end of the anesthetic period. Initial mean pulmonary arterial pressures (PAP) were 22 +/- 3 mm Hg. A significant but transient increase in pulmonary arterial pressure occurred after both heparin and protamine administration. The described anesthetic protocol was effective for thoracotomy and implantation of an intra-aortic left ventricular assist device in normal calves. Partial left ventricular bypass was a useful adjunct during the period of aortic cross clamp. The doses of heparin and protamine administered were effective. Responsibility to monitor oxygenation of the cranial half of the animal continues during the bypass period as hypoxemia due to pulmonary dysfunction will not be detected by the perfusionist.

Afferent and efferent nerve activity of arterial baroreceptor reflex under nonpulsatile systemic circulation.

We studied the changes in arterial baroreceptor reflex (ABR) afferent activity and efferent activity induced by nonpulsatile systemic circulation (NC) during total left heart bypass (TLHB) in rabbits. To evaluate the influence of the circuit priming fluid and exposure to NC, we directly measured aortic depressor nerve activity (ADNA) (n = 5) and renal sympathetic nerve activity (RSNA) (n = 5) before the start of partial left heart bypass (PLHB) (Before), after PHLB (After), and 5 min after the start of TLHB (During THLB) while maintaining the mean aortic pressure. The circuit priming fluid did not affect the ABR. ADNA exhibited periodic discharge at Before and After, but at During THLB, this periodic discharge transformed into a continuous discharge, and ADNA increased significantly. However, there were no significant differences in RSNA. Our results suggested that in the acute phase under NC, the ABR differed from that under natural circulation.