The long-term biomechanical and viscoelastic performance of repairing anterior cruciate ligament after hemitransection injury in a goat model.

To test the healing of the partially torn anterior cruciate ligament, we transected the posterolateral bundle in 11 adult female goats and tested the ligaments at 12, 24, and 52 weeks and 3 years after surgery. As early as 12 weeks after surgery translucent fibrous tissue covered the wound. The differences in anteroposterior laxity between right and left knees measured at 45 degrees and 90 degrees of flexion were not significantly different at each period. Results of Instron testing of the posterolateral bundle revealed the normalized changes in load-relaxation and Young's modulus were not significantly different at each period, but the ultimate tensile strength and stiffness at 3 years were significantly higher than at 12 weeks (P < 0.05) Failure started at the repair site for the 12-week group, but at 24 and 52 weeks the failure occurred throughout the ligament. At 3 years, the specimens failed with bony avulsion, indicating the repaired tissue was not the weakest link of the bone-ligament-bone complex. This study shows that under favorable conditions, partial anterior cruciate ligament injuries are capable of repair. What is more important, the high ultimate tensile strength and stiffness of the 3-year repaired tissue indicate full structural repair of such an artificial transection injury may be possible.

Biomechanics of patellar tendon autograft for reconstruction of the anterior cruciate ligament in the goat: three-year study.

This study examined the biomechanics of anterior cruciate ligament-patellar tendon autografts for as long as 3 years after surgery. Twenty-seven adult female goats were tested; four served as controls and the others received an autograft to the right knee with each left knee serving as an additional control. The animals with grafts were tested at 0 week (n = 4), 6 weeks (n = 4), 12 weeks (n = 4), 24 weeks (n = 3), 1 year (n = 5), and 3 years (n = 3) after surgery. The anteroposterior laxity of the knee joint, load-relaxation, and structural and material properties of the graft were tested. The anteroposterior laxity was significantly greater than that of the controls for all groups except at 3 years. Load-relaxation was greater than that of the control anterior cruciate ligaments, but in the 1 and 3-year grafts load-relaxation was less than that of the patellar tendons with 5 minutes of sustained loading. Between 12 and 52 weeks, the stiffness and modulus of the grafts increased 3-fold, but the improvement was slow afterward. At 3 years, the strength and stiffness of the grafts were 44 and 49% those of the control ligaments, respectively; the modulus was 37 and 46% that of the control anterior cruciate ligaments and patellar tendons, respectively. The persistent inferior mechanical performance at 3 years suggests that anterior cruciate ligament grafts may never attain normal strength.

Eradication of Brucella ovis from the Falkland Islands 1977-1993.

A campaign to eradicate Brucella ovis from sheep in the Falkland Islands, using a combination of serological tests and culling, was initiated in 1977 and continued until 1993 when, after a total of 65,266 tests had been carried out, the organism had been eradicated from the national flock. The paper discusses the relative values of the serological tests and suggests guidelines for maintaining the flock free of the infection.

Further evaluation of the use of buparvaquone in the infection and treatment method of immunizing cattle against Theileria parva derived from African buffalo (Syncerus caffer).

Three experiments were undertaken to determine the efficacy of different doses of buparvaquone in the infection and treatment immunization of cattle against Theileria parva derived from African buffalo (Syncerus caffer). Two of these experiments also compared buparvaquone with standard doses of long- and short-acting formulations of oxytetracycline. In addition, different dilutions of stabilates were used in the experiments. In the first experiment, a 10(-1.0) dilution of stabilate was used to infect groups of cattle treated with buparvaquone at doses of between 5 and 0.625 mg kg-1 body weight (bwt) on Day 0 after infection. All control cattle developed severe theileriosis and none of the treatment regimes (including those utilizing long-acting oxytetracycline) prevented the development of theileriosis. Treatment with buparvaquone at 2.5 mg kg-1 bwt or oxytetracycline gave the most satisfactory results. In the second experiment when the sporozoite dose was reduced to 10(-2.0) dilution, buparvaquone treatment at 5 and 2.5 mg kg-1 bwt and short- and long-acting formulations of oxytetracycline reduced reactions greatly. While all the oxytetracycline treated animals produced a serological response and were immune to a 50-fold higher challenge with the immunizing stabilate, several animals in the buparvaquone groups did not show a serological response and were not immune to challenge. In the third experiment, groups of cattle were infected with 10(-1.2), 10(-1.4) and 10(-1.6) dilutions of stabilate and were treated with 2.5 mg kg-1 bwt of buparvaquone. No animals developed severe theileriosis and all seroconverted. On homologous challenge, however, two out of 14 cattle showed severe reactions. It was concluded that further work on immunization using buparvaquone treatment at 2.5 mg kg-1 bwt and 10(-1.6) dilution of the stabilate would have to be carried out before such a system could be used in the field.

Immunisation of cattle against theileriosis in Nakuru District of Kenya by infection and treatment and the introduction of unconventional tick control.

One hundred and one cross European-Boran cattle (50 cows and 51 calves), on a farm in Nakuru District, Kenya, were immunised against theileriosis using Theileria parva lawrencei and Theileria parva parva stocks from another district of Kenya. The stabilates used were T.p.lawrencei (Mara III) used at 10(-1.7) dilution and T.p.parva (Kilae) used at 10(-1.0) dilution. The stabilates were combined and inoculated simultaneously with a short-acting formulation of oxytetracycline hydrochloride given intramuscularly at 10 mg kg-1 body weight and was repeated on Day 4 after inoculation of the stabilate. Most of the theileriosis challenge on the farm was thought to be derived directly from the African buffalo (Syncerus caffer). Nine percent of the cattle had significant indirect fluorescent antibody (IFA) titres before the immunisation and 99% after immunisation. The immunised cattle were exposed to tick-borne disease challenge on the farm by withdrawal of acaricide cover. The immunised cattle were divided into five groups plus two susceptible control cows and two calves for each group. Cattle in four of the groups had acaricidal ear tags, each group having a different type, applied to both ears and the fifth group remained untagged. The animals remained without conventional acaricide application for 134 days. Ten out of 20 (50%) non-immunised control cattle became T.p.lawrencei reactors which only one out of 97 (1%) of the immunised cattle reacted. A frequent complication noted was mild infections due to unidentified Theileria sp. which required expert differentiation from T.parva infections. An additional group of ten steers whose tick load was removed by hand at weekly intervals was introduced 79 days after exposure; these had no tick control and four became T.p.lawrencei reactors. Of 12 calves born during the exposure period and without tick control, four became theilerial reactors and one died. The application of acaricidal tags however, reduced tick infestation levels considerably compared with untagged controls but did not prevent transmission of theileriosis with the possible exception of tags on Group 4. A number of transient low grade fevers were noted and attributed to Theileria sp., Ehrlichia bovis, Ehrlichia (Cytoecetes) ondiri and Borrelia theileri infections, none of which were fatal. One immunised animal died of acute dual infection of Babesia bigemina and Borrelia theileri after acaricide control by spraying was re-introduced but no Anaplasma infections were detected. An analysis of the economic effects of immunisation was made.

Computer-controlled muscle paralysis with atracurium in the sheep.

Paralysis was maintained in sheep by computer-controlled infusion of atracurium, using the integrated electromyogram as a measure of neuromuscular transmission. A number of experiments were conducted to ascertain the average infusion rate required to achieve a given level of paralysis for one hour. Each experiment yielded a point on a plot of paralysis versus infusion rate. A dose-response curve based upon a simple model of drug receptor interaction at the neuromuscular junction was fitted to the experimental points by least squares and is able to provide a useful explanation of clinically observed behaviour. The recovery time was also measured in each experiment and plotted against both prior level of paralysis and prior average infusion rate.

Local cerebral blood flow following transient cerebral ischemia. II. Effect of arterial PCO2 on reperfusion following global ischemia.

Following 5 minutes of global ischemia, local cerebral blood flow (LCBF) was shown to have an initial reactive hyperemia that was followed, within the first hour, by persistent hypoperfusion (Part I). Intracranial pressure (ICP) was never elevated during the period of poor reperfusion. These experiments attempted to reverse the state of subnormal LCBF by inducing hypercarbia or hyocarbia or maintaining normocarbia. Although hypocarbia did increase LCBF at several electrode sites, neither the intracerebral steal syndrome nor the "squeeze" syndrome are a dominant consequence of hypercarbia in this model of global ischemia. Hypercarbia was consistently more effective in elevating LCBFs and in recovery of the electrocorticogram. It appears that, in the absence of raised ICP, hypercarbia may be preferred to normal or low PACO2,. Even though hypercarbia was superior to normocarbia or hypocarbia, hypercarbia was not a completely satisfactory regimen for reversing the state of poor reperfusion.

Local cerebral blood flow following transient cerebral ischemia. I. Onset of impaired reperfusion within the first hour following global ischemia.

Using the hydrogen clearance technique, local cerebral blood flow (LCBF) in 22 dogs was estimated at 6 parietal sites prior to and following 5 min of total global ischemia. Ischemia was immediately followed by an initial reactive hyperemia during which the electrocorticogram (ECoG) usually began to recover, and within the first 30 min, most of the LCBF's decreased to subnormal values. This onset of hypoperfusion was accompanied by a concomitant decrease in ECoG activity. Two animals that maintained normal local perfusion after the initial hyperemia recovered ECoG activity quickly. These results suggest that the subsequent poor reperfusion was caused by an increased microvascular resistance rather than by blood aggregates, increased blood viscosity, or a variety of other mechanism which have been proposed. Increased vascular tonus was, at least, partly responsible for the increased vascular resistance. This report supports the hypothesis that impaired reperfusion (which occurs some time after an initial hyperemia) may be responsible for ultimate neuronal death, rather than the period of global ischemic hypoxia per se.

Dosage patterns of non-depolarizing neuromuscular blockers in the sheep.

Eighty per cent paralysis was induced and maintained for 90 minute in the sheep by computer-controlled injection of gallamine, pancuronium, alcuronium or d-tubocurarine, using the integrated electromyogram as a measure of neuromuscular transmission. The dosage pattern consisted of a loading phase before any IEMG depression was detected, an onset phase during which a moderate amount of drug was required to achieve increasing paralysis, and a maintenance phase during which a substantially constant and relatively low infusion rate was required. The steady state rates of infusion in microgram/kg/min during "maintenance" was found to be 6.0 for gallamine, 0.15 for pancuronium, 0.2 for alcuronium and 0.5 for d-tubocurarine.

Reversal of non-depolarizing block by neostigmine.

Paralysis was maintained in the sheep for 30 or 90 minutes by computer-controlled injection of gallamine, pancuronium, alcuronium or d-tubocurarine, using the integrated electromyogram as a measure of neuromuscular transmission. Neostigmine was given and the recovery time measured. In all trials the recovery rise time was no longer than two minutes, but varied between one and two minutes.

D-tubocurarine requirement during hypothermia.

The effect of hypothermia on the action of d-tubocurarine (d-TC) was studied under carefully controlled experimental conditions. It was found that with computer controlled infusion, 60% less d-TC was required to sustain 75% muscle paralysis in cats, during steady-state, in vivo, when the temperature was changed from 37 degrees C to 30 degrees C. The corresponding relaxant consumption rates were 0.136 +/- 0.025 and 0.055 +/- 0.012 mg/kg/1/2 hr respectively. When there was no temperature change the maintenance dosage of d-TC remained constant for up to four hours denoting the equilibrium phase of the relaxant kinetics. Temperature transitions introduced dynamic changes in these kinetics and altered the constancy of the maintenance dosage.

Derivation of reliable electromyograms and their relation to tension in mammalian skeletal muscles during synchronous stimulation.

There exists a good correlation between the measured electrical activities and isometric twitch tension in the cat soleus muscle during synchronous stimulation. For an unbiased sampling of electrical activities by averaging a number of electromyograms over the muscle concerned, a relation of the form E = 0.98T + 5.35 has been established. It is hoped that this relation will prove valuable in clinical application where EMGs are used. Electrode types for EMG pick-up differ in terms of the signal recorded due to the difference in the spatial and temporal addition of individual motor unit firing and the constructional difference of the electrodes. Fine wire pairs are the best for linearity and ease of application. Whe surface electrodes are used because of their non-invasive nature, care must be exercised to established the exact relation between EMG and tension. EMG recordings from different sites within a muscle show considerable variation. A more reliable measure can be obtained by external averaging of multiple pairs of electrodes.

Local cerebral blood flow and the electrocorticogram during sodium nitroprusside hypotension.

Changes in local cerebral blood flow during sodium nitroprusside hypotension were measured using the hydrogen electrode technique. At mean arterial pressures from 90% to 50% of control values, local cerebral blood flow showed a significant decrease by 20%. When blood pressure was reduced below 50%, the local cerebral blood flow increased significantly and approached control levels. It is suggested that the flow increase may be due to local hypoxia. Associated with this increase were electrocorticogram changes indicative of hypoxia. The significant decrease in mean local cerebral blood flow and the large range of flows seen during mild hypotension indicate that autoregulation is impaired. During hypotension, intracranial pressure increased by, at most, 3 mm Hg. Cardiac output was usually unaffected and was never decreased by more than 20%.

Intra-ocular pressure during retrobulbar injection.

It was found that the use of retrobulbar injections can cause quite large transient rises in intra-ocular pressure which can be significantly reduced by using local anaesthetic in the injected saline, and by injecting in small steps, typically 0.2 to 0.3 mls/kg body weight at 1 minute intervals for a total of not more than ten steps. After a moderate retrobulbar injection, the intra-ocular pressure was found to return to near normal in a few minutes, but with some decrease in anterior chamber volume.

Computer controlled muscle relaxation: a comparison of four muscle relaxants in the sheep.

Computer control of anaesthesia has been extended to include muscle relaxant drugs. Injection of d-tubocurarine, gallamine, alcuronium or pancuronium was controlled by computer to reduce the integrated electromyogram to a preset level (40 per cent of control) for one hour. A programmed level of muscle paralysis is therefore possible for use in physiological and pharmacological experiments, and in clinical practice where precise control of the degree of paralysis together with minimal dosage is advantageous.

Computer controlled studies in surface cooling hypothermia: the effect of carbon dioxide on brain temperature.

A computer controlled ventilation system was employed to maintain a constant end-expired CO2 percentage (FECO2) during a series of studies on young dogs aimed at measuring brain temperature differences during surface cooling hypothermia. The conclusion is that an FECO2 of six per cent or more is desirable if brain temperature differences are to be minimized. Additional experiments showed that ethyl alcohol and sodium nitroprusside infusions during cooling did not decrease brain temperature differences.