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Biomedical subjects

S K Jones

Publications and source records attributed to S K Jones.

80 records · Page 5Linked to original sources
PubMed1978

Paradoxical sleep and depth perception.

It has been hypothesised that one possible function of paradoxical (REM) sleep is the maintenance of facilitation of co-ordinated eye movements. A prediction from this hypothesis is that binocular depth perception will be more accurate at the end of periods of paradoxical sleep than at the beginning. The results from previous studies are conflicting. Using two groups of eight healthy male volunteers in a two factor repeated measures design, it was found that for a period of paradoxical sleep in the second half of the night only, there was an improvement in binocular depth perception accuracy between the beginning and end of paradoxical sleep. The accuracy at the end of the paradoxical sleep was not significantly different to that on going to bed or on awakening in the morning; the effect was due to a large decrease in accuracy at the start of the REM period. There was no effect of paradoxical sleep on binocular depth perception in the early part of the night. Monocular depth perception accuracy was unaffected by paradoxical sleep.

Adolescent↗
PubMedDate not supplied

The effect of tumour size on ferromagnetic embolization hyperthermia in a rabbit liver tumour model.

OBJECTIVE: Ferromagnetic Embolization Hyperthermia (FEH) consists of arterially embolizing tumours with ferromagnetic particles to cause hysteretic heating upon subsequent exposure to an alternating magnetic field. The objective was to determine the effect of tumour size during FEH using a rabbit liver tumour model. METHOD: Thirty-three rabbits containing implanted hepatic VX2 carcinomas received a hepatic arterial infusion of ferromagnetic particles suspended in lipiodol. Following hysteretic heating, tumour and normal hepatic tissues were chemically analysed for iron content. Tumours were classed as small if their mass was less than the median mass for the whole group of subjects (2.1 g), and as large if their mass was greater than or equal to the median. To control for variability in tumour iron concentration, 13 small tumours were matched to 13 large tumours by iron concentration, and their heating characteristics compared. RESULTS: The heating rate in large tumours (median = 5.0 degrees C/min) was significantly greater than that in the matched small tumours (median = 2.8 degrees C/min), p = 0.006. Regression analysis determined that the slope of the heating rate vs iron concentration curve for large tumours was 1.5 times greater than that for the matched small tumours, p < 0.001. After cessation of heating in large tumours, there was continued heat dissipation into surrounding tissues, which led to anomalous temperature increases. There was an inverse linear relationship between tumour size and tumour iron concentration for a given dose of particles. CONCLUSION: For a given tumour iron concentration, larger tumours heat at a greater rate than small tumours, due to the poorer tissue cooling and better heat conduction in the necrotic regions of large tumours. This warrants further investigation as this finding could confer a significant advantage on FEH over other hyperthermic modalities in the treatment of hepatic malignancies.

Animals↗
PubMedDate not supplied

Treatment of experimental rabbit liver tumours by selectively targeted hyperthermia.

Experimental rabbit liver tumours were preferentially heated to therapeutic temperatures without compromising the surrounding normal hepatic parenchyma. This was achieved by the use of hepatic arterially infused ferromagnetic microspheres that heat as a result of magnetic hysteresis loss when exposed to an alternating magnetic field. Treatment sessions involving a single 20-min exposure to the alternating field resulted in total suppression of tumour growth at 14 days compared to controls, in which tumour sizes increased dramatically over the same period. Histopathological examination of treated tumour sections showed total tumour destruction in some cases. Separate animal groups used to control for the effects of the embolized microspheres alone and for the effect of the applied magnetic field yielded similar tumour growth responses to a control group with no intervention whatsoever. The achievement of positive temperature differentials between tumour and normal liver and the consequent therapeutic responses encourages further development of this technology for the treatment of liver cancer in humans.

Animals↗
PubMedDate not supplied

Magnetically mediated hyperthermia: current status and future directions.

The use of hyperthermia in the treatment of cancers is appealing because, as a physical therapy, hyperthermia would have far fewer restrictive side effects than chemotherapy and radiotherapy, and it could be used in combination with these therapies. However, the currently available modalities of hyperthermia are often limited by their inability to selectively target tumour tissue and, hence, they carry a high risk of collateral organ damage or they deposit heat in a very localized manner which can result in under-treatment of a tumour. Magnetically mediated hyperthermia (MMH) has the potential to address these shortcomings. MMH consists of the localization of magnetic particles or seeds within tumour tissue followed by exposure to an externally applied alternating magnetic field to cause them to heat. Since this concept was introduced (over 40 years ago), MMH has evolved into four general sub-classes: arterial embolization hyperthermia (AEH), direct injection hyperthermia (DIH), intracellular hyperthermia (IH) and interstitial implant hyperthermia (IIH). It is the purpose of this article to review these four sub-classes in terms of experimental or clinical results, advantages, limitations and current status.

Humans↗
PubMedDate not supplied

Hepatic clearance of arterially infused ferromagnetic particles.

OBJECTIVE: Arterial embolization hyperthermia (AEH) consists of arterially embolizing tumours with ferromagnetic particles that generate hysteretic heating on exposure to an alternating magnetic field. It was the objective of this study to determine if such particles are cleared from the liver. METHOD: A lobe of normal liver in three pigs was arterially embolized with 300 mg of gamma-Fe2O3 particles (150 nm) suspended in lipiodol. The same liver lobe of three other pigs was embolized with 300 mg of ferromagnetic polymer matrix-encapsulated microspheres (32 microm) suspended in 1% tween-water. Samples of liver and blood were obtained before infusion, and at 60 min and 28 days after arterial infusion. At 28 days, samples of lung and other abdominal viscera were also obtained. The tissue samples were chemically analysed for iron content, and submitted to histopathological examination. RESULTS: There was no significant reduction in the hepatic iron concentration in either treatment group 28 days after infusion. Both types of particles illicited an immunogenic response and were extensively phagocytosed in the liver. The particle/lipiodol suspension caused extensive necrosis of liver, while the microsphere/tween-water suspension was well tolerated. Small amounts of both types of ferromagnetic particles embolized in the lungs, but there was no evidence of embolization into other organs. There were no haematological or biochemical changes and all subjects experienced uneventful 28-day survivals. CONCLUSION: This study has shown that, although arterially infused ferromagnetic particles were extensively phagocytosed, there was no significant hepatic clearance 28 days after infusion. It also determined that the suspension of 150 nm ferromagnetic particles in lipiodol was too vaso-occlusive for use in hepatic tissue. However, the suspension of 32 microm microspheres containing ferromagnetic particles in tween-water was safe and well tolerated.

Animals↗
PubMedDate not supplied

In vitro and in vivo responses of doxorubicin ion exchange microspheres to hyperthermia.

The utility of microspheres as targeted drug delivery agents is addressed with reference to using heat during formulation and to administration in combination with hyperthermia. It was demonstrated that rate of loading of the drug doxorubicin onto resin microspheres is enhanced under conditions of elevated temperature but this was shown to increase the incidence of microsphere aggregation. Total amount of drug loaded was related to time rather than temperature such that low temperature loading for up to 24 h produced optimum quality injectates. However, release of doxorubicin from microspheres was significantly increased during elevations of temperature to 43 degrees C. Thus, during hyperthermia doxorubicin release can be increased to provide periods of high drug availability targeted to tumour tissue for concomitant thermochemotherapy with microspheres. The therapeutic benefit derived from this combined therapy was assessed in 20 rabbits with VX2 carcinoma implanted in the liver. Hyperthermia was delivered by 2450 MHz microwave applicator to the exteriorized liver at 43 degrees C for 30 min, while chemotherapy was administered by intratumoural injection of doxorubicin microspheres (2.3 mg) into each tumour. Both hyperthermia and chemotherapy alone significantly reduced the size of tumours 10 days following treatment (p less than 0.01). However, in animals treated with both modalities, the size of tumours was significantly less than either treatment alone (p less than 0.05). These results provide a strong rationale for combining hyperthermia with targeted chemotherapy using microspheres.

Animals↗
PubMedDate not supplied

Treatment of experimental Pneumocystis carinii pneumonia with 1,3-di(4-imidazolino-2-methoxyphenoxy)propane lactate.

An analogue of pentamidine, 1,3-di(4-imidazolino-2-methoxyphenoxy)propane (DMP) lactate, was tested against rat Pneumocystis carinii pneumonia (PCP). The drug was found to be highly active in the treatment of rat PCP at a dose of 1.75 mg/kg (parent molecule) when administered by intravenous (i.v.) injection (daily for 2 wk). The compound was also active against PCP when given orally, however, significantly higher doses of DMP were necessary when compared to the i.v. dosing regimen. Prophylactic doses (i.v.) of the drug also proved highly effective in preventing PCP.

Administration, Oral↗