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Biomedical subjects

S G Brooks

Publications and source records attributed to S G Brooks.

17 recordsLinked to original sources
PubMed1994

Percutaneous laser recanalisation of femoropopliteal occlusions using continuous wave Nd-YAG laser and sapphire contact probe delivery system.

A conventional continuous wave Nd-YAG medical laser system delivered by transparent sapphire tipped optical fibres was used for percutaneous recanalisation of 32 chronic femoropopliteal occlusions in 27 patients (19 men, eight women; median age 68 years, range 46-83 years). Twenty-four patients had severe intermittent claudication and three had critical ischaemia. The median occlusion length was 8 cm (range 3-35 cm) and lesions were not negotiable by guidewire. Laser energy was delivered at powers of 10-15 Watts using intermittent 1 second emissions (mean total energy 315 Joules, range 30-1015]). The sapphire tips used were 1.8 to 3.0 mm diameter. After laser recanalisation adjunctive balloon dilatation was necessary to widen the resulting lumen. All patients received anti-platelet therapy. Initial clinical success was achieved in 22 limbs (69%) with symptomatic relief and increase in mean (+/- S.D.) ankle-brachial pressure ratio from 0.52 (+/- 0.25) to 0.80 (+/- 0.21) [Mann-Whitney U, p < 0.001]. Recanalisation was unsuccessful in all calcified lesions (four cases). There was a high incidence of vessel perforation (28%) and wall dissection (25%). Emergency surgery was not required after failed procedures. The median follow-up was 12 months (range 6-20 months). By 6 months, 15 of 22 successfully recanalised lesions (68%) had reoccluded. The cumulative primary patency at 1 year was only 12%. These disappointing results do not support routine use of this system. Clearly, modifications of the laser/delivery system or the technique, or both, are required. The aim should be to achieve sole laser recanalisation without concomitant balloon dilatation.

Aged↗
PubMed1992

Exogenous chromophores for the argon and Nd:YAG lasers: a potential application to laser-tissue interactions.

Chromophore dyes can be employed to modify laser-tissue interaction. A number of dyes have been investigated for their effect on the absorption and transmission of argon and Nd:YAG laser energy by vascular tissue in vitro. Three histological dyes have been assessed as potential chromophores for the argon laser and four infrared dyes for the Nd:YAG. Segments of porcine coronary artery to which dye had been applied were lased (1,064 nm, 2.5 W, 83 W/cm2, 60 s and 488/514 nm, 400 mW, 10.5 W/cm2, 60s) and the tissue temperature measured remotely using an infrared thermometer. In addition, energy transmission was measured with a photodiode and tissue morphological changes assessed histologically. All three argon dyes significantly increased energy absorption (typically 60 degrees C v. 20 degrees C at 60 s, P less than 0.001, 2-way ANOVA). Three of the four infrared dyes behaved similarly (40-70 degrees C v. 20 degrees C, P less than 0.001). All dyes significantly increased the initial rate of rise in tissue temperature during lasing. A reduction in energy transmission was observed for each of the Argon dyes but not for the Nd:YAG dyes. Histological evidence of thermal damage in control tissue first occurred for the argon and Nd:YAG lasers at 800 mW and 7.5 W without chromophore and at 400 mW and 2.5 W with the chromophore, respectively. A number of effective chromophores have therefore been identified at each wavelength.

Absorption↗
PubMed1991

Alternative technique for repair of sinus venosus atrial septal defect.

A technique is described for closure of a sinus venosus atrial septal defect using a single patch held in place by sutures placed from outside the right atrium and underneath the superior vena cava. The superior vena cava does not require enlargement and potential damage to the artery to the sinoatrial node is avoided.

Adolescent↗
PubMed1991

Isotope limb blood flow measurement in patients undergoing peripheral laser angioplasty.

A technique of isotope limb blood flow (ILBF) measurement employing Technetium-labelled human albumin and a gamma camera, was used to assess limb perfusion in 19 patients undergoing percutaneous laser angioplasty, both before and one month after treatment. Twenty-three limbs with femoro-popliteal occlusions ranging in length from 3-35 cm (median 8 cm) were recanalized using an Nd-YAG laser and sapphire tipped optical fibre. Primary angiographic success was achieved in 19 lesions of which 6 re-occluded within the first month, and 13 remained patent with relief of symptoms. Clinically successful procedures were associated with a large increase in ILBF. However, normal blood flow was restored in only 54% of limbs. There was a slight decrease in limb perfusion after failed laser angioplasty but this was not statistically significant in this small series. Furthermore, there was no clinically apparent circulatory compromise, or need for urgent surgical bypass in failed cases. We conclude that ILBF is a useful means of assessing patients undergoing laser angioplasty, particularly for detecting small flow changes in patients who are unable to complete a standard exercise test. Its use can be recommended for assessing blood flow changes following other forms of limb revascularization.

Aged↗
PubMed1990

Thermal characteristics of sapphire contact probe delivery systems for laser angioplasty.

Contact probes made from synthetic sapphire crystal, designed for general laser surgery, are currently being evaluated for use in laser angioplasty. Their mode of action and safety in the context of arterial recanalisation is unknown, particularly with respect to the degree of probe and catheter heating. Infrared thermal imaging was used to investigate the surface temperature rise of various rounded sapphire probes during emission of continuous wave Nd-YAG (1,064 nm) laser energy. Catheter safety was addressed by analyzing the temperature of the metal interface between the optical fiber and sapphire, as well as the catheter proximal to this junction. Transmission of Nd-YAG energy through each probe was also measured. Five rounded probes of 1.8-3.0 mm diameter (three supplied by Surgical Laser Technologies [SLT], two by Living Technology [LT]), along with their respective optical catheters, were compared. There was a large temperature gradient between the front and rim of the probes. The maximum surface temperature rise of the sapphire (at 20 W, 5-second exposure) was 314-339 degrees C (SLT) and 90-108 degrees C (LT) [P less than 0.001, 3-way ANOVA]. The reason for this difference may be related to "crazing" of the front surface of the SLT sapphires. At all energy levels sapphire temperatures were considerably lower than attained by metal laser thermal angioplasty probes. Forward transmission was slightly higher in the SLT probes (75-85%) than the LT sapphires (54-69%). With fiber perfusion at 2 ml/minute, a minor degree of heating of the metal sapphire holders was recorded (maximum rise 35 degrees C), but heating of the catheter proximal to this was negligible. Therefore, it would appear that the risk of tip detachment or arterial injury due to heating of the connecting metal interface is extremely low. Without perfusion, however, there was a greater degree of interface heating in the LT delivery system suggestive of more laser backscattering by these sapphires compared with the SLT probes [P less than 0.001, one-way ANOVA]. The SLT system is, therefore, potentially safer in this respect. These results suggest that some degree of surface heating of contact probes due to energy absorption within the sapphire does occur, but is localised to the front of the probe. This effect may contribute to the process of arterial recanalisation with this device. However, variation in the thermal and optical properties of sapphires from different sources has been demonstrated. The influence of these properties on plaque ablation, and ultimately the clinical performance of different contact probe systems, requires further investigation.

Humans↗
PubMed1990

Aneurysm formation after dynamic catheter assisted balloon angioplasty.

A male patient underwent recanalisation of a symptomatic popliteal artery occlusion using a dynamic angioplasty catheter, followed by balloon dilatation. A small subintimal dissection lead to an acute reocclusion. Repeat balloon angioplasty reopened the occlusion but was complicated by a distal embolus which was successfully treated by thrombolytic therapy followed by oral anticoagulation. Angiography 9 months later, demonstrated an aneurysm at the site of initial dissection. The artery remained patent and the patient free of claudication. A causal relationship between dynamic angioplasty and subsequent aneurysm formation is suggested and the possible predisposing factors discussed.

Aneurysm↗
PubMed1990

Experimental analysis of sapphire contact probes for Nd-YAG laser angioplasty.

Laser angioplasty may offer percutaneous recanalization of occluded vessels where conventional guidewire and balloon techniques fail. Metal laser thermal angioplasty probes may, however, cause excessive thermal damage due to high tip temperatures (greater than 400.C). Therefore, contact probes made from artificial sapphire crystal designed for general laser surgery are currently being evaluated for use in laser angioplasty with continuous wave Nd-YAG energy. The sapphire modifies the laser energy in various ways, and this paper examines the physical characteristics of five types of rounded sapphire probe (SMTR, MTR, MTRL, OS, LT) and how these properties are affected by clinical usage. The laser beam profile emitted by these probes demonstrates a focal spot 1-2 mm in front of the tip. However, the forward transmission of Nd-YAG energy through the sapphires varied (SMTR, 85%; MTR, 83%; MTRL, 75%; OS, 54%; LT, 69%). Probe heating occurs owing to energy absorption within the sapphire. The surface temperature of the sapphires was measured in air by infrared thermography and the hottest region within the probes localized by an isothermographic technique. At energy settings used clinically (20 J, 10 watts for 2 s) the SMTR, MTR, and MTRL probes exhibited higher temperature rises (94-112.C) than the OS and LT probes (30.C), and heating was localized to the front surface of the former probes. Peak sapphire temperatures remained lower than those of metal probes even at higher energies. After clinical use, the MTR probe demonstrated reduced transmission, beam defocusing, and increased heating, due to surface pitting. Thus, recanalization with sapphire probes occurs by a combination of photothermal and contact thermal effects that are localized to the probe tip and may reduce the degree of thermal injury associated with metal probes. Understanding these basic properties is important to the application and development of contact probes for laser recanalization.

Aluminum↗
PubMed1989

An automated high-performance liquid chromatographic trace enrichment method for the determination of metoclopramide in serum and its application to a bioequivalence human volunteer study.

An automated trace enrichment method for metoclopramide is described. Serum was injected on to a short column packed with PLRP-S 100A (a polymeric reversed-phase material). The unwanted components were washed off with borate buffer (pH 9.8) before switching to a Spherisorb ODS column for the separation. The limit of detection in serum samples was 2 ng/ml. The method was used in a pharmacokinetic study to compare the biovailability of two formulations of the drug.

Adult↗
PubMed1984

Pharmacokinetics of an oral frusemide/amiloride combination tablet.

A randomized four-way crossover study was carried out in 12 healthy volunteers to investigate the pharmacokinetics of a new oral combination of frusemide (40 mg) and amiloride (5 mg), formulated as a single tablet. The experimental design of this bioequivalence study used commercially-available 40 mg frusemide tablets and 5 mg amiloride tablets as reference drugs, administered either separately or concomitantly. From a statistical analysis of plasma levels of frusemide and amiloride, no significant differences between the reference drugs alone and the combination tablet were seen in peak plasma levels, mean times to peak or mean areas under the plasma concentration-time curves (AUCs). The ratio of AUCs of the combination tablet to the reference drugs approached a limiting value many hours prior to complete elimination of the drug and hence reliable bioavailability comparisons were possible with blood sampling up to 24 hours post-dose.

Administration, Oral↗
PubMedDate not supplied

Comparison of the pharmacokinetics of porcine calcitonin in saline and in gelatin diluents in healthy volunteers.

A randomised 2-way crossover study was carried out in nine healthy male volunteers to compare the pharmacokinetics of porcine calcitonin (pCT) following i.m. administration of 160 i.u. of pCT in physiological saline or in a solution of hydrolysed gelatin. A new radioimmunoassay for pCT is described. It employs an antiserum raised in a guinea pig and a labelled tracer prepared from highly purified pCT. While comparable mean areas under the serum concentration-time curve for both dosage forms indicate equivalent bioavailability, the serum pCT profiles were different; peak pCT levels of 8.3 +/- 0.8 ng ml-1 (s.e.m.) occurred at 13 +/- 2 min (s.e.m.) with peak levels of 4.8 +/- 0.5 ng ml-1 (s.e.m.) when the gelatin diluent was used. The hypocalcaemic effects produced by the two preparations of pCT were of short duration (less than 1 h) and of a similar magnitude (-0.08 to -0.12 mmol.l-1). Comparable degrees of hypophosphataemia (-0.11 to -0.15 mmol.l-1) were observed 20 min post-injection. The administration of pCT in gelatin and saline diluents resulted in markedly different pharmacokinetic profiles. Whether there are therapeutic advantages in the use of either diluent remains to be investigated.

Adult↗