Distal Aortic Flow Research Articles

Partial Left Heart Bypass for Thoracic Aorta Repair

Emergency repair of the torn descending thoracic aorta has been associated with an almost 15% incidence of paraplegia. The literature to date suggests that the incidence of paraplegia is not influenced by mechanical adjuncts to enhance distal aortic perfusion during cross-clamping and therefore, "clamp and sew" has been considered an acceptable technique. The purpose of the present study was to review our experience with repair of descending thoracic aortas using partial left heart bypass and to compare this favorable initial experience with the available data on the use of the heparinless centrifugal pump. A retrospective review of the routine use of partial left heart bypass in 16 consecutive patients with descending thoracic aorta disruptions. Results were compared with similar reports in the recent literature on trauma. A level 1 trauma facility in the Denver, Colo, metropolitan area. All patients with multisystem blunt trauma with a mean injury severity score of 36. Repair of the descending thoracic aorta disruption using partial left heart bypass with a heparinless centrifugal pump. Primary outcome measures were survival and paraplegia; other monitored variables included proximal and distal aortic pressure, flow rates, and oxygen transport. Among the 14 survivors (88%) there were no cases of paraplegia, and intraoperative hemodynamics and oxygen transport were well maintained with partial left heart bypass. This experience is added to the available reported data on the use of the centrifugal pump. In these additional 42 patients, the mortality rate was 7%, with no incidence of paraplegia. This collective experience failed to disclose a single case of paraplegia when partial left heart bypass was employed for repair of descending thoracic aorta. Moreover, the use of partial left heart bypass in this cohort of critically injured patients is associated with survival and perioperative morbidity rates comparable with the best recent reports of emergency thoracic aortic repair.

Fetal O2 consumption in sheep during controlled long-term reductions in umbilical blood flow.

Electromagnetic flow sensors and inflatable occluders were placed on the distal aortas of nine fetal lambs of 111-124 days gestation; indwelling vascular catheters were placed in a lower body artery and vein and the common umbilical vein. After a control period of 7.6 +/- 2.1 (SD) days, distal aortic flow was reduced to about 60% of control flow; placental flow fractions of distal aortic flow were 77 +/- 5%, control; 69 +/- 11% during flow reduction. Duration of the flow reductions was 9.6 +/- 6.5 days. Fetal O2 consumption fell from 6.4 +/- 1.5 to 5.3 +/- 1.1 ml X min-1 X kg-1 (P less than 0.02) as umbilical blood flow was reduced from 202 +/- 47 to 116 +/- 36 ml X min-1 X kg-1 (P less than 0.001). Least-squares polynomial regression analysis showed that O2 consumption was a linear function of umbilical blood flow (P less than 0.01). With regard to long-term fetal O2 consumption, there was no evidence for a margin of safety in fetal umbilical blood flow.

Thrombolysis with recombinant tissue plasminogen activator in atherosclerotic thrombotic occlusion

Human tissue plasminogen activator holds promise for the dissolution of coronary thrombi by intravenous administration and without systemic anticoagulation. Prior animal experiments have been conducted only in vessels without disease. To test the thrombolytic efficacy of recombinant tissue plasminogen activator in the presence of diseased intima, an established model of atherosclerosis was utilized. The aorta of 16 New Zealand white rabbits (2 to 3 kg) was made atherosclerotic by balloon endothelial denudation and concurrent 1% cholesterol feeding for 8 weeks. An aged (24 hour) heterologous (human) clot, labeled with I-125 fibrinogen was injected into the distal aorta and produced thrombotic occlusion. After 1 hour of thrombosis (control period), recombinant tissue plasminogen activator (100,000 IU approximately equal to 1 mg protein, n = 6) or streptokinase (100,000 IU, n = 5) or saline solution (n = 5) was systemically infused over 30 minutes. Serial blood samples, obtained to determine fractional change in blood radioactivity over time, showed a fourfold increase of blood radioactivity after tissue plasminogen activator and streptokinase infusion compared with the control period (47,400 +/- 3,300 [mean +/- standard error] versus 11,800 +/- 300 counts/min, p less than 0.001). Time to 50% of maximal thrombolysis was 41 +/- 14 minutes (+/- standard deviation) for tissue plasminogen activator versus 63 +/- 16 minutes for streptokinase (p less than 0.01). In six of six rabbits receiving tissue plasminogen activator and four of five rabbits receiving streptokinase, reestablishment of distal aortic flow was detected via the indwelling catheter within 25 minutes of drug infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Digital cutaneous fluorometry: Correlation between blood flow and fluorescence

Central to the use of fluorescein in vascular diagnosis is the requirement that the intensity of evoked fluorescence be proportional to blood flow. With the introduction of the digital dermofluorometer, a device that quantitates cutaneous fluorescence, establishment of this relationship has become possible. After experimentally producing measured reductions in the distal aortic flow of eight rabbits, the ratio of fluorescence in the flow-restricted and unrestricted areas was obtained by measuring hind- and forelimb fluorescence. At any time between 20 and 60 minutes following a bolus injection of sodium fluorescein (1 mg/kg body weight), there was a significant linear relationship (p < 0.05, r > 0.75) between residual aortic flow and the ratio of hind-/forelimb fluorescence. Simultaneously obtained plasma fluorescein concentrations decayed rapidly by first-order kinetics with a half-life of 12.5 minutes, regardless of the degree of distal aortic occlusion. The time course of the rise and fall of cutaneous fluorescence was slower than that of the plasma fluorescein concentration, proving that interstitial rather than intravascular fluorescein was responsible for the measured fluorescence. We conclude that the intensity of tissue fluorescence is linearly related to blood flow and that conclusions regarding perfusion may be drawn from relative fluorescence at any time between 20 and 60 minutes following a bolus injection of fluorescein. Furthermore, the passage of fluorescein into the interstitium is dependent on a time-limited diffusion process, which along with flow, establishes the time to peak and the absolute amplitude of the tissue fluorescence curve.

PRECIPITOUS CIRCULATORY COLLAPSE IN THE IMMATURE NEWBORN FROM SHUNTING ACROSS THE DUCTUS ARTERIOSUS

Sudden, unexplained circulatory collapse occurring after successful initial resuscitation of the extremely immature newborn has been attributed to massive intracranial hemorrhage. Our failure to find pathologic confirmation in three such infants led to a prospective attempt to define alternative mechanisms. Ten consecutive infants between 24 and 26 weeks gestation were resuscitated, placed on ventilators and followed serially with aortograms and differential blood gases and blood pressures. Four could not be resuscitated. After initial stabilization of the six remaining infants, leg pressures were higher than arm pressures and aortograms revealed no left to right shunt. Coincidental with rising PaO2 and radiographic evidence of improved lung aeration, leg blood pressures fell to levels equal to or lower than arm pressures in 5/6 infants. Aortograms revealed massive left to right shunts with minimal distal aortic flow. Only 1/5 had a murmur. Intractable aciemia and cardiovascular collapse occurred within 1 to 6 hours of the fall in leg pressures. 4/5 Infants died. Only two had significant intracranial hemorrhage. Sudden massive ductal shunting in the immature newborn can cause precipitous circulatory collapse in the absence of intracranial hemorrhage. The ability of the extremely immature newborn to survive in the extrauterine environment may depend on early closure of this low resistance shunt.