Mechanisms by which dopamine alters blood flow distribution during lobar collapse in dogs

Dopamine increases blood flow to a hypoxic left lower lobe in dogs. To elucidate possible mechanisms, left lower lobe collapse was induced in anesthetized dogs, and lobar (QLLL) and total (QT) pulmonary blood flow was measured by electromagnetic flow probes. Dopamine infusion increased mean pulmonary arterial pressure (Ppa), QT, and QLLL. However, the increase in QLLL was double that produced by a similar increase in Ppa without increase in QT (inflation of a Swan-Ganz balloon in right pulmonary artery) or by a similar increase in QT with smaller increase in Ppa (opening of arteriovenous fistulas). QLLL/QT was not changed by opening arteriovenous fistulas, but was increased by Swan-Ganz balloon inflation, and by infusion of dopamine. It is concluded that the increase in QLLL/QT produced by dopamine was due to a decrease in hypoxic vasoconstriction in the lobe secondary to an increase in mixed venous PO2 and to vasoconstriction in the oxygenated lung.     

Treatment of hostile midline back wounds: an extreme approach

The basic principles of successful wound closure remain the same: careful preoperative evaluation, removal of underlying nonviable tissue, and well-vascularized soft-tissue coverage. Many complex or "hostile" back wound closures also require stabilization of the spine and a two-layered wound closure. The use of long arteriovenous fistulas with free tissue transfer provides an additional weapon for the treatment of these complex wounds.     

Fistules pulmonaires artério-veineuses

A case of multiple pulmonary arteriovenous fistulas is reported. Hereditary hemorrhagic telangiectasia is a characteristic associated finding, and in this instance affected 10 members of the patient''s family over four generations. This association suggests that the pulmonary condition in its congenital form is part of a generalized vascular dysplasia. Clinically, the patient experienced increased dyspnea and fatigue but cyanosis and polycythemia were not noted. After surgical excision of the fistula with conservation of as much pulmonary tissue as possible, prompt relief of symptoms was obtained. Furthermore, angiographic studies revealed that the small fistulas in the other lung did not enlarge. The presence of multiple fistulas is not a contraindication to surgery, and such fistulas should be excised to improve the patient''s condition and prevent further complications.     

Effect of cardiac output on gravity-dependent and nondependent inequality in pulmonary blood flow

To examine the effect of cardiac output (CO) on the gravity-nondependent distribution of pulmonary blood flow, 2 X 10(6) 99mTc-labeled albumin microspheres (20 microns) were injected at end expiration into dogs (anesthetized, supine, and breathing room air spontaneously). Two animals were injected at their resting CO, two were injected during increased CO (arteriovenous fistulas induced), and two were injected at low CO (phlebotomy induced). The chest was opened and the lungs were removed, drained of blood, and dried while fully inflated. Single-photon emission-computed tomography was performed on the dry lungs to map the distribution of activity in transverse, coronal, and sagittal slices. The results confirmed the presence of a central-peripheral gravity-nondependent gradient and showed that increases in CO were associated with increases in absolute flow to both the central and peripheral regions of the lung with persistence of the central-peripheral gradient. These observations were further confirmed by direct imaging of midcoronal slices. Examination of the average flow in vertical and horizontal slices showed that, when zone 1 was not present, changes in CO affected all slices uniformly, such that when the CO doubled, the absolute flow in every slice in all three planes also doubled. We conclude that, with the exception of recruitment and derecruitment of vascular channels in the upper regions of the lung (zone 1), when CO changes, the blood flow everywhere in the lung changes uniformly and in proportion to the CO. This uniform increase in blood flow is consistent with the three-dimensional nature and resistive properties of the pulmonary vascular tree.     

Increased cardiac output increases shunt: role of pulmonary edema and perfusion

In low-pressure pulmonary edema increased cardiac output (QT) increases shunt (Qs/QT); we tested whether the mechanism is an increase in extravascular lung water in turn mediated by the accompanying increase in microvascular pressure. In six pentobarbital sodium-anesthetized dogs ventilated with O2 we administered oleic acid into the right atrium. From base line to 2 h post-oleic acid we measured concurrent significant increases in Qs/QT (6-29%, O2 technique) and extravascular thermal volume (ETV, 2.6-7.1 ml/g dry intravascular blood-free lung wt, thermal-green dye indicator technique) that were stable by 90 min. Then, bilateral femoral arteriovenous fistulas were opened and closed in 30-min periods to cause reversible increases in QT and associated Qs/QT. When fistulas were open the time-averaged QT increased from 5.1 to 6.9 min (P less than 0.05), the simultaneous Qs/QT rose from 30.7 to 38.4% (P less than 0.05), but ETV did not increase. We conclude that increasing lung edema does not account for our rise in Qs/QT when QT increased.     

Interventional neuroradiology.

A wide variety of diseases affecting the central nervous system and head and neck can be treated using interventional neuroradiologic techniques. These new treatments have depended on advances in radiologic imaging, catheter technology, and the development of new embolic agents. These procedures may be an adjunct to other therapy, palliative or curative. Diseases for which interventional neuroradiologic techniques have been major advances in treatment include cerebral aneurysms, vasospasm after subarachnoid hemorrhage, cerebral arteriovenous malformations, dural arteriovenous fistulas, dural sinus thrombosis, atherosclerosis, scalp arteriovenous fistulas, carotid-cavernous fistulas, and stroke. This field is rapidly evolving as advances are made in catheter technology and new embolic agents are developed.     

Cleft palate fistulas: a multivariate statistical analysis of prevalence, etiology, and surgical management

A retrospective, multivariate statistical analysis of 129 consecutive nonsyndromic patients undergoing cleft palate repair was performed to document the incidence of postoperative fistulas, to determine their cause, and to review methods of surgical management. Nasal-alveolar fistulas and/or anterior palatal fistulas that were intentionally not repaired were excluded from study. Cleft palate fistulas (CPFs) occurred in 30 of 129 patients (23 percent), although nearly a half were 1 to 2 mm in size. Extent of clefting, as estimated by the Veau classification, was significantly more severe in those patients who developed cleft palate fistula. Type of palate closure also influenced the frequency of cleft palate fistula. Forty-three percent of patients undergoing Wardill-type closures developed cleft palate fistula versus 10, 22, and 0 percent for Furlow, von Langenbeck, and Dorrance style closures, respectively. The fistula rate was similar in patients with (30 percent) and without (25 percent) intravelar veloplasty. Age at palate closure did not significantly affect the rate of fistulization; however, the surgeon performing the initial closure did not have an effect. Thirty-seven percent of patients developed recurrent cleft palate fistulas following initial fistula repair. Recurrence of cleft palate fistulas was not influenced by severity of cleft or type of original palate repair. Following end-stage management, a second cleft palate fistula recurrence occurred in 25 percent of patients. Continued open discussion of results of cleft palate repair is recommended.     

Analysis of pharyngocutaneous fistula following free jejunal transfer for total laryngopharyngectomy

The development of a pharyngocutaneous fistula is the most common and troublesome complication in the early postoperative period following free jejunal transfer for total laryngopharyngectomy. However, many aspects of this complication remain unclear. In this study, the authors analyzed their experience with the pharyngocutaneous fistula formation following free jejunal transfers to evaluate its clinical behavior, determine the significance of the anastomotic technique used, and evaluate the role of preoperative radiation therapy on its formation and management. Of 168 patients who underwent free jejunal transfers following total laryngopharyngectomy at the authors' institution between July of 1988 and March of 2000, 23 patients (13.7 percent) with postoperative fistulas were identified. The mean onset of fistula formation was 16 days. Of the 23 fistulas, 13 (56.5 percent) occurred at the proximal and 10 (43.5 percent) at the distal anastomoses. Whereas the majority of the proximal fistulas (69.2 percent) developed near the mesenteric side of the jejunal flap, most of the distal fistulas (90 percent) were located anteriorly. The incidence of proximal fistula formation was higher in patients with a single-layer repair than in patients with a two-layer repair of a proximal anastomosis (80 percent versus 38.5 percent, p = 0.09). The incidence of fistula formation was greater in patients who received preoperative radiation therapy than in those who did not (16.3 percent versus 11.4 percent, p = 0.36). In addition, whereas a majority of fistulas (80 percent) occurred at the proximal anastomosis in patients who did not receive preoperative radiation therapy, most fistulas (61.5 percent) occurred at the distal anastomosis in patients who did receive radiation therapy (p = 0.09). The fistulas closed spontaneously in 15 patients (65 percent). On average, spontaneous closure occurred in 7.4 weeks. Proximal fistulas had a significantly higher rate of spontaneous closure compared with distal fistulas (85 percent versus 40 percent, p = 0.04). The rate of spontaneous fistula closure was higher in patients who had not received preoperative radiation therapy than in those who had (90 percent versus 46 percent, p = 0.07). Surgical closure of the fistula was required in five patients. The fistulas were not repaired in three patients because of recurrent tumor. Twenty patients (87 percent) resumed oral feeding after the closure of the fistula, with 17 (85 percent) of 20 patients tolerating a regular diet and three (15 percent) of 20 a liquid diet only.In conclusion, most fistulas occur at the proximal anastomosis and near the mesenteric side of the jejunal flap, and the use of a two-layer anastomotic technique seems to be associated with a lower incidence of fistula formation at the proximal suture line. Most fistulas close spontaneously, especially ones that occur proximally. Preoperative radiotherapy does seem to increase the risk of fistula formation, especially at the distal anastomotic site and make subsequent resolution of the fistulas more difficult. Most patients are able to resume oral feeding once the fistula is closed.     

Modified surgical technique for treating hepatic echinococcosis]

The authors present modified operational technique in hepatic echinococcosis. Echinococcus in 14 patients was removed by either peri-cystic excision or hepatic lobe excision with the closure of blood inflow into the liver by construction the blood vessels in hepato-duodenal ligament for 20 minutes. All patients survived. Biliary fistulas lasting for a few days up to 3 weeks were the only complications encountered. Presented modified operational technique of surgery is safe; it shortens the duration of surgery and prevents major intraoperative haemorrhages.     

Repair of pharyngocutaneous fistulas with the submental artery island flap

Pharyngocutaneous fistulas after total laryngectomy are difficult to manage and are a cause for significant morbidity to the patient. When fistulas fail to close with conservative measures, debridement and flap closure are indicated. Although a number of techniques to repair pharyngocutaneous fistulas are described, each of these procedures has its drawbacks. The authors have used the submental island flap to close postoperative pharyngocutaneous fistulas in nine male patients during the past 4 years. The mean patient age was 65 years (range, 57 to 75 years). The submental island flap is based on the submental artery, a branch of the facial artery. The inner aspect of the fistula was initially formed using hinge flaps on the skin around the fistula. Once a watertight closure of inner side was created, the skin defect was closed with the submental island flap. The maximum flap size was 6 x 3 cm and the minimum size was 4 x 2 cm (average, 4.8 x 2.7 cm) in this series. Direct closure was achieved at all donor sites. Patients were followed for 6 months to 4 years. No major complication was noted in the postoperative period. All patients have successfully recovered their swallowing function. The submental island flap is safe, rapid, and simple to elevate and leaves minimal donor-site morbidity. The authors believe that this technique is a good alternative in the reconstruction of pharyngocutaneous fistulas. Application of the technique and results are discussed.     

Arteriovenous fistulas after replantation surgery

The delayed appearance of congenital arteriovenous fistula precipitated by local trauma is a rare event. However, these reports may provide some insight into pathogenetic mechanisms responsible for the opening of subclinical arteriovenous communications. This case of multiple arteriovenous fistulas in a previously "normal" hand followed a sharp, incomplete amputation at the wrist level with replantation.     

A validated patient-specific FSI model for vascular access in haemodialysis

The flow rate inside arteriovenous fistulas is many times higher than physiological flow and is accompanied by high wall shear stress resulting in low patency rates. A fluid–structure interaction finite element model is developed to analyse the blood flow and vessel mechanics to elucidate the mechanisms that can lead to failure. The simulations are validated against flow measurements obtained from magnetic resonance imaging data.     

Surgical closures of oropharyngocutaneous fistulas

Of the 146 patients undergoing surgery for oropharyngeal cancer in our institution, 12 (8.2 percent) developed fistulas. As a first line of therapy, conservative measures were used, which consisted of debridement, Xeroform gauze packing, and nasogastric feeding. Seven fistulas closed after conservative treatment. Of the five patients who required surgery for fistula closure, three had large (more than 20 mm) and two had mid-size (5- to 20-mm) fistulas. In all cases, internal flaps were prepared from the healthy viable tissues surrounding the fistula, and sternocleidomastoid-trapezius-platysma myocutaneous flaps were used for external closure. None of the closures failed, and we obtained good functional and aesthetic results.     

RASA1: variable phenotype with capillary and arteriovenous malformations

Capillary malformation-arteriovenous malformation (CM-AVM) is a newly discovered hereditary disorder. Its defining features are atypical cutaneous multifocal capillary malformations often in association with high-flow lesions: cutaneous, subcutaneous, intramuscular, intraosseous and cerebral arteriovenous malformations and arteriovenous fistulas. Some patients have Parkes Weber syndrome - a large congenital cutaneous vascular stain in an extremity, with bony and soft tissue hypertrophy and microscopic arteriovenous shunting. In the past, arteriovenous malformations and arteriovenous fistulas had been considered non-hereditary. A classical genetic approach was used to identify the locus. Candidate gene screening pinpointed mutations in RASA1 (p120-RASGAP) - a RasGTPase. RASA1 reverts active GTP-bound Ras into inactive GDP-bound form. Murine Rasa1 knockout and tetraploid-aggregated embryos with RNA interference exhibited abnormal vascular development. Lack of RASA1 activity caused inhibition of cell motility, possibly through p190-RhoGAP. Thus, RASA1 defects probably cause abnormal angiogenic remodeling of the primary capillary plexus that cannot be compensated for by other RasGAPs: RASA2, RASAL and NF1. Signaling pathways involving RASA1 might offer novel targets for treatment of high-flow vascular anomalies.     

Ventilatory responses to increased blood flow and decreased lung volume in awake dogs

The effect of decreased lung volume on ventilatory responses to arteriovenous fistula-induced increased cardiac output was studied in four chronic awake dogs. Lung volume decreases were imposed by application of continuous negative-pressure breathing of -10 cmH2O to the trachea. The animals were surgically prepared with chronic tracheostomy, indwelling carotid artery catheter, and bilateral arteriovenous femoral shunts. Control arteriovenous blood flow was 0.5 l/min, and test flow level was 2.0 l/min. Arterial blood CO2 tension (PaCO2) was continuously monitored using an indwelling Teflon membrane mass spectrometer catheter, and inhaled CO2 was given to maintain isocapnia throughout. Increased fistula flow alone led to a mean 52% increase in cardiac output (CO), whereas mean systemic arterial blood pressure (Psa) fell 4% (P less than 0.01). Negative-pressure breathing alone raised Psa by 3% (P less than 0.005) without a significant change in CO. Expired minute ventilation (VE) increased by 27% (P less than 0.005) from control in both of these conditions separately. Combined increased flow and negative pressure led to a 50% increase in CO and 56% increase in VE (P less than 0.0025) without any significant change in Psa. Effects of decreased lung volume and increased CO appeared to be additive with respect to ventilation and to occur under conditions of constant PaCO2 and Psa. Because both decreased lung volume and increased CO occur during normal exercise, these results suggest that mechanisms other than chemical regulation may play an important role in the control of breathing and contribute new insights into the isocapnic exercise hyperpnea phenomenon.     

Ulceration of the hand secondary to a radial arteriovenous fistula: a model for varicose ulceration.

A patient in whom a radial arteriovenous fistula was constructed in preparation for haemodialysis subsequently developed ulceration on the dorsum of the hand. The lesion failed to heal despite antibiotic treatment, and so the fistula was closed. The lesion healed within three weeks. Subsequent construction of a fistula at the right wrist was followed 12 months later by the development of similar ulceration of the right hand. This complication of arteriovenous fistulas is similar to varicose ulceration of the leg and provides a unique opportunity to study the effects of sustained venous hypertension on the skin.     

Direct demonstration of 25- and 50-microm arteriovenous pathways in healthy human and baboon lungs

Postmortem microsphere studies in adult human lungs have demonstrated the existence of intrapulmonary arteriovenous pathways using nonphysiological conditions. The aim of the current study was to determine whether large diameter (>25 and 50 microm) intrapulmonary arteriovenous pathways are functional in human and baboon lungs under physiological perfusion and ventilation pressures. We used fresh healthy human donor lungs obtained for transplantation and fresh lungs from baboons (Papio c. anubis). Lungs were ventilated with room air by using a peak inflation pressure of 15 cm H(2)O and a positive end-expiratory pressure of 5 cm H(2)O. Lungs were perfused between 10 and 20 cm H(2)O by using a phosphate-buffered saline solution with 5% albumin. We infused a mixture of 25- and 50-microm microspheres (0.5 and 1 million total for baboons and human studies, respectively) into the pulmonary artery and collected the entire pulmonary venous outflow. Under these conditions, evidence of intrapulmonary arteriovenous anastomoses was found in baboon (n = 3/4) and human (n = 4/6) lungs. In those lungs showing evidence of arteriovenous pathways, 50-microm microspheres were always able to traverse the pulmonary circulation, and the fraction of transpulmonary passage ranged from 0.0003 to 0.42%. These data show that intrapulmonary arteriovenous pathways >50 microm in diameter are functional under physiological ventilation and perfusion pressures in the isolated lung. These pathways provide an alternative conduit for pulmonary blood flow that likely bypasses the areas of gas exchange at the capillary-alveolar interface that could compromise both gas exchange and the ability of the lung to filter out microemboli.