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Biomedical subjects

A Parkin

Publications and source records attributed to A Parkin.

At least 19 recordsLinked to original sources
PubMed1992

An analysis of a radionuclide technique used to measure reactive hyperaemia in limbs.

A radionuclide technique (PT) for measuring the blood flow to a limb during reactive hyperaemia is described and analysed. Patients are positioned with lower limbs within the field of view of the gamma camera and pneumatic cuffs are placed below the knees to isolate the blood and induce a hyperaemic response. The remaining blood pool is labelled with 99Tcm-human serum albumin. Following release of the occlusion the rate of inflow to the limb of the radionuclide is measured and hyperaemic flow then determined, during the initial phase of the hyperaemia. The results may be analysed using a single compartment to represent the vascular pool in the lower limb. During the initial phase, activity entered the pool at a constant rate from which the blood flow may be calculated. Results were obtained in a group of 20 normal control volunteers and 20 patients with occlusive arterial disease. They indicate that following release of the cuff the blood flow rises rapidly (within 1-2 s) to a constant value which is maintained for at least 10-12 s in normal subjects and a longer period in arteriopaths. The mean flow in the normal group was 14.4 ml/100 ml min-1 and in the arteriopathic group was 4.6 ml/100 ml min-1. The constant flow measured by PT during the initial phase of reactive hyperaemia appears to differ from the results of venous occlusion plethysmography and washout of a freely diffusible tracer and possible reasons for these differences are discussed.

Adult↗
PubMed1992

Hepatic perfusion index: a multicentre trial.

The reproducibility and accuracy of the hepatic perfusion index (HPI) was examined by consideration of in vitro and in vivo factors. A phantom was used to simulate liver blood flow and data acquired on nine gamma cameras. Dynamic hepatic scintigraphy was undertaken on 28 patients at two centres and values obtained for the HPI. Results from the phantom study showed good agreement between the nine cameras and also with the HPI values predicted from the measured phantom flow rates. The results of the patient study indicated a high degree of conformity between observers (r = 0.95, S.E = 0.03) but poorer correlation between the HPI values from the two centres (r = 0.67, S.E. = 0.09). These results imply that centres wishing to use HPI clinically should establish their own range of normality.

Blood Flow Velocity↗
PubMed1991

24-hour survival of autotransfused red cells in elective aortic surgery: a comparison of two intraoperative autotransfusion systems.

Twelve patients undergoing elective aortic surgery had intraoperative autotransfusion using either the Haemonetics Cell Saver or the Solcotrans device. The 24-h post-transfusion survival of the patients' preoperative red cells, labelled with indium-111, was compared with the survival of salvaged red cells labelled with chromium-51. A correction coefficient for the instability of the indium-111 label was calculated from the study of red cell survival in six healthy volunteers. There was no significant difference in the volume of circulating red cells measured using each isotope, indicating that extensive early destruction of the autotransfused red cells does not occur. The percentage survival of autotransfused red cells at 24 h was similar to that of the red cells that had not undergone salvage. Both devices were comparable with respect to the effects of cell salvage on the 24-h survival rate of autotransfused red cells.

Aortic Diseases↗
PubMed1991

The effect of cyclosporin on lower limb blood flow in renal transplant recipients.

We investigated the effect of electively converting stable renal allograft recipients from cyclosporin A (CyA) to prednisolone and azathioprine on limb blood. We used a non-invasive method designed to measure the hyperaemic blood flow to the lower limb following a standard ischaemic insult. The hyperaemic blood flow was greater during CyA therapy--median 14 ml/100 ml tissue per minute (95% confidence limits 10.5-16.5)--than that after conversion--median 11 ml/100 ml tissue per minute (8.3-13.8; P less than 0.01). By increasing peripheral vascular resistance and reducing limb blood flow, CyA may have caused an increase in the degree of ischaemia, so resulting in a greater hyperaemic response.

Adult↗
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↗
PubMed1991

Comparing subjective and objective assessments of the severity of vibration induced white finger.

The present staging of the disease severity of vibration induced white finger (VWF) is based on the patients' symptoms. Forty patients, with a history of VWF, with disease severity stage III or stage IV, on the Taylor-Pelmear scale, were investigated. Total, reactive hyperaemic blood flow to the hands was measured using an isotope limb blood flow (ILBF) technique. Skin blood flow patterns were assessed using a cold provocation test, followed by thermographic assessment of hand rewarming. Thermographic abnormalities were detected in 39 patients (97%). Decreased post-occlusive, reactive hyperaemic blood flow occurred in 29 patients (73%). There was no difference in skin blood flow patterns or in total hand blood flow between the stage III and stage IV groups. Reduction of postocclusive reactive hyperaemic blood flow may be indicative of occlusive lesions of the digital vessels. We conclude that the classification of the severity of VWF using subjective assessment, needs to be augmented by objective evidence of altered blood flow.

Adult↗
PubMed1991

Synthesis and antiviral activity of 9-alkoxypurines. 2. 9-(2,3-Dihydroxypropoxy)-, 9-(3,4-dihydroxybutoxy)-, and 9-(1,4-dihydroxybut-2-oxy)purines.

Reaction of alkenoxyamines (3,5) or (R,S)-, (R)-, and (S)-hydroxy-protected derivatives of hydroxyalkoxyamines (20a,b, 37a-c) with 4,6-dichloro-2,5-diformamidopyrimidine (4) and cyclization of the resultant 6-[(alkenoxy)amino]-and 6-(alkoxyamino)pyrimidines (6,7,21a,b, 38a,b,c) by heating with diethoxymethyl acetate afforded 9-alkenoxy- and 9-alkoxy-6-chloropurines (9,10,22a,b, 39a-c, 40a). These were subsequently converted to 9-(2,3-dihydroxypropoxy), 9-(3,4-dihydroxybutoxy), and 9-(1,4-dihydroxybut-2-oxy) derivatives of guanine and 2-aminopurine (13-16, 25-28, 41a-c, 42a). A 2-amino-6-methoxypurine derivative (17) was also prepared. The racemic guanine derivative 13 showed potent and selective activity against herpes simplex virus types 1 and 2 (HSV-1 and HSV-2), but was less active against varicella zoster virus (VZV). Its antiviral activity is attributable to the S isomer (28), which was found to be more active than acyclovir against HSV-1 and HSV-2 and about 4 times less active than acyclovir against VZV. The S enantiomer of 9-(1,4-dihydroxybut-2-oxy)guanine (41c) also showed noteworthy antiviral activity in cell culture. Although this acyclonucleoside (41c) is only weakly active against HSV-1 and inactive against HSV-2, it is about twice as active as acyclovir against VZV.

Antiviral Agents↗
PubMed1991

Radionuclide limb blood flow in peripheral vascular disease: a review of 1100 measurements.

Radionuclide limb blood flow measurements using 99Tcm-labelled human serum albumin and a gamma camera have been performed on normal volunteers and on patients with suspected or confirmed peripheral arterial disease. The normal range of flow was found to be 10.0-22.3 ml per 100 ml tissue per min. Flow in the symptomatic legs of patients with arterial disease varied from 9.0 ml per 100 ml tissue per min in mild claudication to less than 1.0 ml per 100 ml tissue per min in rest pain. The technique has been used as an initial screening procedure, to resolve diagnostic problems, to measure objectively the treatment response and to assess patients with critical ischaemia. The results of 1100 measurements are reported and the clinical utility in routine vascular surgical practice is discussed.

Adult↗
PubMed1990

Dual tracer technique to measure salvaged red cell survival following autotransfusion in aortic surgery.

The survival of autotransfused red cells was measured for two salvage devices used in 12 elective aortic reconstructions. Six patients underwent cell salvage with the Solco-trans device and six with the Haemonetics cell saver. A double tracer technique was used to take account of post-operative blood loss and fluid replacement. Comparison was made with the results of a group of normal volunteers. A comparison was made of the labelling efficiency of damaged and undamaged red cells using chromium to check that red cells damaged during autotransfusion can be labelled. No significant difference was seen. There was no significant difference in red cell survival between the volunteer group and either of the two salvage device groups. These results suggest that red cell survival is not compromised by the autotransfusion process using these two devices.

Aortic Diseases↗
PubMed1990

The application of isotope limb blood flow measurement to diagnostic problems in vascular surgery.

A new method of limb blood flow measurement has been developed; normal flow is 10-22 ml/100 ml of tissue/min and flow to limbs with claudication is 1.8-2.3. Does this technique help to deal with diagnostic problems in vascular surgery? Twenty-five patients presented with exercise-induced leg pain. Twelve had a convincing history of claudication but seven of these had palpable pedal pulses, the other five had normal Doppler ratios. Of 13 with a poor history six had absent pulses; of the other seven with palpable pulses, two had abnormal and five had normal Doppler ratios. All 25 patients have had blood flow to both legs measured. For the five with a poor history, palpable pulses and normal Doppler ratios: (Table: see text). Twelve had reduced flows consistent with claudication (less than 8 ml/100 ml of tissue/min); 10 of these have undergone arteriography which demonstrated significant vascular disease, one had surgery to rheumatoid toes deferred and one refused further investigation. Of 13 with normal flows nine have been found to have significant orthopaedic problems affecting spine, hips or knees, the other four have all had normal arteriograms. In every case the history, signs or Doppler ratios were potentially misleading, but all cases of significant arterial disease were detected. It is cheap, readily available and effectively selected cases for referral or arteriography.

Gamma Cameras↗
PubMed1989

Limb volume measurements in peripheral arterial disease.

A simple method for measuring limb volumes of patients with peripheral arterial disease undergoing limb blood flow measurement is described. The device uses the change in surface level of water in a cylindrical reservoir to generate a voltage which is amplified and converted to a volume. The plethysmograph is stable and accurate over a wide range of limb volumes. For patients with leg ulcers or gangrene, where water immersion is not possible, a geometrical model has been developed which allows the volume to be calculated from a series of six external measurements. Comparison with measured volumes in 46 patients has shown this model to be accurate with a mean error of 3.3%. It provides a convenient alternative to direct measurement in these patients.

Blood Volume↗
PubMed1989

Working memory, comprehension ability and the resolution of text anomaly.

This article examines possible working memory deficits in 7-8-year-olds who are accurate readers but relatively poor comprehenders. In Expt 1, poor comprehenders scored below good comprehenders on a non-linguistic test of working memory (reading series of digits and recalling the last digit in each series) on the more taxing items. Experiment 2 examined the relationship between working memory and text comprehension using an anomaly resolution task. Good and poor comprehenders heard stories describing an adult's anomalous emotional response to a child's action, some of which contained information to resolve the anomaly. The load on working memory imposed by the need to integrate the resolution with the anomaly was varied in two ways: the resolution was presented immediately next to, or two sentences distant from, the anomaly, and appeared either before or after the anomaly. Poor comprehenders were worse than good ones at anomaly resolution only when the anomalous and resolving information were separated. The results support the hypothesis that text processing is influenced by working memory demands and suggest that children's comprehension is related to the efficiency of a general non-linguistic working memory system.

Attention↗