Effect of lumbar sympathectomy in distal arterial obstruction.

We developed a model that simulates distal arterial occlusive disease to determine the effects of sympathectomy on certain hemodynamic changes. Two groups of seven dogs each received unilateral distal popliteal artery ligation. Intra-arterial BPs, angiography, pulse volume recordings (PVRs), and photoplethysmograms were taken of the distal hind limb throughout the experiment. After ligation, PVR and distal hind limb pressures were lowered to less than half of the preligation values. Four days after unilateral distal popliteal artery ligation, group 2 dogs received lumbar sympathectomy on the same side as the ligation. One week after sympathectomy, the PVR amplitudes and pressures showed a transient significant rise. Two weeks after sympathectomy, the PVR pressures and amplitudes returned to the previous, diminished postligation values.

Testing and treatment of arterial graft thrombosis.

The in vivo technique of Sauvage et al for determining prosthetic arterial graft thrombogenicity was employed in the sheep carotid model using 4 mm commercial expanded polytetrafluoroethylene (Gore-Tex) grafts. Expanded polytetrafluoroethylene was found to be thrombogenic at 4 hours of low flow in this model. At 24 hours all of these grafts were totally occluded at low flow rates. Intravenous use of ibuprofen (Motrin), a thromboxane inhibitor, in this model markedly reduced occlusion and thrombogenicity at 4 and 24 hours. All grafts were patent at 24 hours when ibuprofen was used.

No change in alpha 1 adrenoceptors in canine femoral arteries after lumbar sympathectomy.

In the dog, alpha 1 adrenoceptors have been identified in the aorta, femoral mesenteric, and renal arteries. The concentration of alpha receptors may be regulated by hormones such as estrogen and progesterone and by drugs such as epinephrine. To assess whether sympathetic denervation, which is known to decrease norepinephrine output, might change the population of alpha 1 receptors in vascular smooth muscle, the femoral artery alpha 1 receptor population was examined 2 weeks after unilateral lumbar sympathectomy. [3H]Prazosin radioligand receptor assay analysis was used to measure the alpha 1 receptor populations. No statistical difference for dissociation constant and receptor density values between sympathectomy and nonsympathectomy femoral artery samples could be detected.

Autonomic control of bronchial blood flow and airway dimensions during strenuous exercise in sheep.

BACKGROUND: During exercise and recovery the transient and steady-state changes in autonomic activity regulating lower airway blood flow and dimensions are unknown. The aim of this study was to define changes in bronchial blood flow (Q(br)) and dimensions during moderate and strenuous exercise, and to analyse the role of vagal and sympathetic nerves. METHODS: Nine ewes (34-44kg) underwent left thoracotomy during general anaesthesia (thiopentone/isoflurane) and either (5 sheep=Group 1) a pulsed Doppler transducer was placed on the bronchial artery, or (4 sheep=Group 2) a pulsed Doppler transducer was placed on the bronchial artery, and transit-time and single crystal sonomicrometers were mounted on the left main bronchus. These measured continuously Q(br), bronchial circumference (Circ(br)) and wall thickness (Th(br)). Aortic pressure (P(a)) and central venous pressure catheters were placed in the superficial cervical artery and vein. Trained sheep exercised on a horizontal treadmill, i.e. Group 1, moderate exercise 2.2mph over 1.6, 6min recovery, for analysis of changes in Q(br) before and after cholinoceptor blockade; Group 2, strenuous exercise 4.4mph over 2, 10min recovery for analysis of changes in Q(br) and airway dimensions, before and after cholinoceptor plus alpha(1)-, alpha(2)-adrenoceptor blockade. beta-adrenoceptor systems were intact. RESULTS: In Group 1 during moderate exercise P(a) and heart rate (HR) rose. Q(br) and blood flow conductance (C(br)) fell immediately to 83% (P<0.001) before returning toward resting levels, but fell when exercise ceased to 89% (P<0.01) before recovering. Prior cholinoceptor blockade abolished the immediate fall in Q(br) and C(br), but not the recovery vasoconstriction. Later in recovery the bronchial bed dilated progressively over 6min (P<0.05). In Group 2 during strenuous exercise P(a) and HR rose substantially. Q(br) and C(br) fell to 68% and 54% (P<0.001), respectively, and there was early vasoconstriction in recovery. Circ(br) fell immediately and remained at 93% (P<0.01), and did not recover fully when exercise ceased. Th(br) did not change during or after exercise. Prior cholinoceptor plus alpha-adrenoceptor block caused P(a) and Q(br) to fall slightly during exercise, but the bronchovascular constriction during and after exercise was abolished, as was circumferential shortening in the airway. CONCLUSIONS: At exercise onset and steady-state, resetting the arterial baroreflex upward in sheep increases parasympathetic cholinergic vasoconstrictor activity and causes bronchial wall and bronchovascular smooth muscle contraction in concert with sympathetic adrenergic constriction of systemic vascular beds. Whether the known sigmoid baroreflex control of tracheal smooth muscle tension at rest is extended to tracheobronchial smooth muscle and its circulation during exercise is yet to be determined.

Effects of graded exercise on bronchial blood flow and airway dimensions in sheep.

Exercise stimulus-response relationships for airway blood supply and dimensions have not been described in mammalian species. These relationships are vital for postulates concerning integrated reflex factors normally controlling the airways and which may underlie the asthma syndromes of exercise. This study defines airways stimulus-response relationships in exercising sheep. Ewes between 35 and 40kg were instrumented at left thoracotomy under thiopentone/isoflurane general anaesthesia. Pulsed Doppler ultrasonic transducers were mounted on the bronchial artery, and transit-time plus single-crystal sonomicrometers on the left main bronchus. These recorded simultaneously and continuously bronchial blood flow (Q(br)) and conductance (C(br)), bronchial circumference (Circ(br)) and wall thickness (Th(br)). In Protocol 1 (P1), four sheep ran duplicate 5min protocols on a horizontal treadmill at continuous step-up-and-down speeds of 1min duration, namely, 0.8, 1.6, 2.2, 1.6 and 0.8mph (moderate exercise), followed by 10min recovery. In P2, four sheep ran duplicate 2min protocols at constant 4mph (strenuous exercise), and in P3, one sheep ran duplicate protocols each of 3min at 2.2, 4.4 and 6mph (severe exercise). Regression analysis and repeated measures ANOVA were used to assess differences between times, runs and exercise intensity. In P1, airway effects were directly related to graded exercise effort sustained over 5min. Peak effects occurred at 2.2mph, except for Th(br). Heart rate and P(a) rose (to 156% and 111% of resting, respectively), and Q(br) and C(br) fell (to 83% and 75%; both P<0.001). Circ(br) fell to 96% (P=0.02), and Th(br) rose at low speeds early and late, and thinned at the highest speed. In P2 and P3 for all variables the steady-state effects were systematically greater than for P1 (4.4mph: C(br) to 43%, Circ(br) to 93%; 6.6mph: C(br) to 25%, Circ(br) to 82%). There was no significant recovery hyperaemia, but there was residual post-exercise bronchoconstriction. The exercise stimulus-response relationships from rest to a maximal 6mph for sheep airway circumference and its bronchial circulation are inverse and functionally constrictor.

Platelet function and coagulation parameters in sheep during experimental vascular surgery.

Various clotting parameters (prothrombin time, activated coagulation time, activated partial thromboplastin time, platelet counts, and platelet aggregation) were obtained from unanesthetized sheep and from sheep at various times during 5 hours of vascular surgery. The values obtained were not influenced by anesthesia and surgery and were consistent between sheep. Ovine platelets were less prone to aggregate in the presence of collagen, epinephrine, and ristocetin than those of man. Platelet aggregation induced by adenosine diphosphate was similar to that seen in man. Based on these parameters, the sheep would seem to be a reasonable model for experimental vascular surgery when results are to be applied to man.

Potency of isoflurane and nitrous oxide in conventional swine.

The minimum alveolar concentration (MAC) of isoflurane in oxygen (O2) was determined to be 1.55 +/- 0.08 (SEM) volumes % in twelve pigs (Sus scrofa). Values for isoflurane MAC in the presence of 50% (I-50%N2O) and 66% (I-66%N2O) nitrous oxide were determined in nine and six of these same animals, respectively, and equalled 1.03 +/- 0.05 vol % for I-50%N2O and 0.95 +/- 0.07 vol % for I-66%N2O. Animals respired spontaneously and arterial blood pressure (AP), heart rate (HR), rectal body temperature, and arterial blood gases (PO2, PCO2, and pH) were recorded throughout the study period. These parameters were within normal limits near MAC for all three gas combinations. The MAC for isoflurane in swine was similar to that for other animals and, man and the use of this agent was associated with rapid and uneventful anesthetic induction and recovery. The addition of 50% and 66% nitrous oxide (N2O) reduced the isoflurane MAC by 30% and 42%, respectively.

Anesthetic, preoperative and postoperative considerations for liver transplantation in swine.

Perioperative care and anesthetic management of donor and recipient animals are crucial factors in studies involving experimental liver transplantation in the pig. Prevention of unacceptably high morbidity and mortality in the transplant recipients requires meticulous attention to anesthesia, preoperative and postoperative care. Liver transplant surgeries were performed using 15 pairs of pigs. Six of the transplant recipients were anesthetized with halothane plus 50% nitrous oxide (N2O) and oxygen (O2), and nine with isoflurane plus 50% N2O in O2. Arterial blood pressure, total anesthetic time, time of interruption of vena cava blood flow, and fluids administered, as well as length of survival were among the parameters measured and compared for the two groups. No deaths were attributed to either anesthetic technique. However, the isoflurane group had slightly higher blood pressure intraoperatively, better long range survival, and relatively rapid recoveries when compared to the halothane group. Because of these findings and the reported low rate of isoflurane metabolism and low resultant potential for formation of toxic metabolites when compared to halothane metabolism, we have elected to use the isoflurane-50% N2O regimen for this procedure.

Orthotopic porcine liver transplantation: operative technique.

Considerable interest in experimental liver transplantation has been generated recently due to improvements in the results of clinical liver transplantation efforts. An operative technique for orthotopic porcine liver transplantation is presented which represents modifications of and improvements to previously published techniques. Salient features of the technique include (1) use of a diaphragmatic cuff for the suprahepatic inferior vena cava anastomosis, (2) use of a splenojugular shunt, (3) omission of caval shunts, and (4) use of isoflurane as the primary anesthetic agent. This operative technique has provided excellent survival rates in our transplanted animals.