Biomedical subjects
Publications and source records attributed to J R Buckley.
We demonstrate the use of a prism-grating sequence to reduce third-order dispersion inside a mode-locked Yb fiber laser. This laser generates pulses as short as 33 fs with extremely clean temporal and spectral profiles. Nanojoule pulse energies are possible.
A series of experiments aimed at determining the maximum pulse energy that can be produced by a femtosecond fiber laser is reported. Exploiting modes of pulse propagation that avoid wave breaking in a Yb fiber laser allows pulse energies up to 14 nJ to be achieved. The pulses can be dechirped to sub-100-fs duration to produce peak powers that reach 100 kW. The limitations to the maximum pulse energy are discussed.
Self-similar propagation of ultrashort, parabolic pulses in a laser resonator is observed theoretically and experimentally. This constitutes a new type of pulse shaping in mode-locked lasers: in contrast to the well-known static (solitonlike) and breathing (dispersion-managed soliton) pulse evolutions, asymptotic solutions to the nonlinear wave equation that governs pulse propagation in most of the laser cavity are observed. Stable self-similar pulses exist with energies much greater than can be tolerated in solitonlike pulse shaping, and this has implications for practical lasers.
Amplification of femtosecond pulses at 1.03 micrometre in a standard Yb-doped single-mode fiber is reported. A pulse energy of 8 nJ and an average power of 400 mW are obtained, limited by available pump power. To our knowledge these are the highest pulse energy and average power obtained from an integrated, single-mode fiber amplifier. After dechirping, 120-fs, 6-nJ pulses are obtained. A practical fiber-based source with performance comparable with that of a bulk solid-state laser is thus demonstrated, and scaling to substantially higher powers will be possible.
We report the generation of 6-nJ chirped pulses from a mode-locked Yb fiber laser at 1.03 micrometre. A linear anomalous-dispersion segment suppresses wave-breaking effects of solitonlike pulse shaping at high energies. The dechirped pulse duration is 50 fs, and the energy is 5 nJ. This laser produces twice the pulse energy and average power, and approximately five times the peak power, of the previous best mode-locked fiber laser. It is to our knowledge the first fiber laser that directly offers performance similar to that of solid-state lasers such as Ti:sapphire.
Experiments were carried out to determine whether the doses of the amino bisphosphonate ibandronate that inhibit bone resorption inhibit soft tissue calcification and death in rats treated with a toxic dose of vitamin D. These studies were prompted by the recent discovery that ibandronate doses that inhibit bone resorption potently inhibit artery calcification induced by treatment with the vitamin K antagonist warfarin. All 16 rats treated with the toxic dose of vitamin D (12.5 mg cholecalciferol x kg(-1)) died by d 6 after the first vitamin D injection (median survival: 4.5 d), whereas the 12 rats treated with vitamin D plus ibandronate (0.25 mg x kg(-1) x d(-1)) were alive and in good health at d 10. Rats treated with vitamin D alone and examined at d 4 had extensive Alizarin red staining for calcification in the aorta, the carotid, hepatic, mesenteric, renal and femoral arteries, kidneys and lungs, whereas rats treated with vitamin D plus ibandronate had no evidence for calcification at any of these tissues when examined at d 7 and 10. Ibandronate treatment also inhibited the dramatic increase in the levels of calcium and phosphate seen in the abdominal aorta, kidneys, lungs and trachea of the vitamin D-treated rats (P < 0.001). Serum calcium levels were, however, not different in rats treated with vitamin D alone (3.4 +/- 0.2 mmol x L(-1)) and in rats treated with vitamin D plus ibandronate (3.5 +/- 0.2 mmol x L(-1)). Treatment with vitamin D alone increased levels of matrix Gla protein, an inhibitor of soft tissue calcification, in the arteries, kidneys, lungs and trachea by 10- to 100-fold, and ibandronate treatment prevented this increase. The importance of these studies in the rat model is that they identify a class of drugs in current clinical use that can be used to treat patients with vitamin D toxicity and that they identify the dose of the drug that is predicted to be effective, namely the dose that inhibits bone resorption. Because there is no other known treatment for vitamin D toxicity, there would seem to be good reason to try bisphosphonates such as ibandronate in future studies aimed at treating patients who have been exposed to toxic levels of vitamin D.
The present experiments were carried out to test the hypothesis that arterial calcification is linked to bone resorption by determining whether the selective inhibition of bone resorption with osteoprotegerin will inhibit arterial calcification. In the first test, arterial calcification was induced by treating 22-day-old male rats with warfarin, a procedure that inhibits the gamma-carboxylation of matrix Gla protein and causes extensive calcification of the arterial media. Compared with rats treated for 1 week with warfarin alone, rats treated with warfarin plus osteoprotegerin at a dose of 1 mg/kg per day had dramatically reduced alizarin red staining for calcification in the aorta and in the carotid, hepatic, mesenteric, renal, and femoral arteries, and they had 90% lower levels of calcium and phosphate in the abdominal aorta (P<0.001) and in tracheal ring cartilage (P<0.01). More rapid arterial calcification was induced by treating 49-day-old male rats with toxic doses of vitamin D. Treatment for 96 hours with vitamin D caused widespread alizarin red staining for calcification in the aorta and the femoral, mesenteric, hepatic, renal, and carotid arteries, and osteoprotegerin completely prevented calcification in each of these arteries and reduced the levels of calcium and phosphate in the abdominal aorta to control levels (P<0.001). Treatment with vitamin D also caused extensive calcification in the lungs, trachea, kidneys, stomach, and small intestine, and treatment with osteoprotegerin reduced or prevented calcification in each of these sites. Measurement of serum levels of cross-linked N-teleopeptides showed that osteoprotegerin dramatically reduced bone resorption activity in each of these experiments (P<0.001). Therefore, we conclude that doses of osteoprotegerin that inhibit bone resorption are able to potently inhibit the calcification of arteries that is induced by warfarin treatment and by vitamin D treatment. These results support the hypothesis that arterial calcification is linked to bone resorption.
This comparative prospective study of mammalian bites attending one urban Accident and Emergency department before the implementation of the Dangerous Dogs Act 1991 and again 2 years later, was to see the effect of the Act on the pattern of injury. The study comprised a simple questionnaire detailing the injury, the implicated species, and the treatment or referral if applicable. In both groups studied (before and after implementation of the Act) 134 consecutive bites were recorded, contributing 1.2 per cent and 1.23 per cent of total attendances during these respective periods. Dogs were found to bite most commonly: in the pre-legislative group 73.9 per cent were due to dog bites and in the post-legislation group 73.1 per cent. In both groups studied, human bites occurred as the second most common mammalian bite; 17.9 per cent in the pre-legislation group and 12.7 per cent in the post-legislation group. Human bites were as common as those from the most implicated breed of dog. In general human bites were found to require more active treatment and specialist referral. The study demonstrates the vast majority of such injuries are treated within Emergency departments. This study also shows how dangerous breeds compare with others that bite, demonstrating that these breeds contribute to only a small proportion of these injuries. This comparative study clearly demonstrates little impact on rate of attendances for such injuries since the introduction of the 1991 Act. If legislation aims to reduce and prevent injury from animal bites, in its present form it does little to protect the public; this study suggests a wider control of the dog population may be required.
External fixation of comminuted upper femoral fractures has not been studied widely. The minority of such fractures which cannot be fixed internally due to clinical and anatomical problems are generally treated in traction. Early external fixators were not sufficiently robust to hold these fractures and pin site problems are more common in femoral fixation than in the tibia. A study was undertaken including all patients with comminuted upper femoral fractures who were too unwell or otherwise unsuitable for internal fixation. The long-term results were comparable, if not superior to traction, and patient comfort and mobilization were much improved.
Over a 14-month period, 100 consecutive cases of intertrochanteric fracture were randomly allocated to be treated by either Pugh nail-plate or Dynamic Hip Screw (DHS) fixation. Although there were 11 cases of malreduction and/or suboptimal positioning of the fixation device in the femoral head, only two of these gave long-term problems. Despite the difference in configuration of the devices and a considerable disparity in price, patient satisfaction and the incidence of untoward radiological features at an average of 6 months after surgery were similar in the two groups. A trifin-ended device would thus appear to be a reliable alternative to the more commonly used hip screw systems for intertrochanteric fracture.
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Sixty patients underwent arthroscopy of the knee as day cases using a local anaesthetic technique. This provided satisfactory operating conditions and high patient acceptability.
Forty-six patients requiring arthroscopic surgery following diagnostic arthroscopy under local anaesthetic infiltration had this tried under the same anaesthetic (four patients had to be converted to a general anaesthetic to complete the procedure). Local infiltration provides good anaesthesia for arthroscopic surgery, except in those with an acutely locked knee or a painful collateral ligament.
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