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H M Swartz

Publications and source records attributed to H M Swartz.

At least 55 records · Page 3Linked to original sources
PubMed1998

Electron and light microscopy studies on particulate EPR spin probes lithium phthalocyanine, fusinite and synthetic chars.

This is the first detailed study on the morphology of the widely used particulate electron paramagnetic resonance (EPR) probes lithium phthalocyanine (LiPc), methyl-LiPc, methoxy-LiPc, fusinite and synthetic carbon-based chars, by means of both light and electronmicroscopy (LM and EM). The importance of these EPR probes for the measurement of O2/NO has been reported previously. Under LM, LiPc with its distinct crystalline structure differs significantly from the noncrystalline black flakes of both LiPc derivatives, methyl-LiPc and methoxy-LiPc. Unlike the shiny carbon-based synthetic chars, which have no characteristic morphology, fusinite, a fraction of fossilized coal maceral, displays distinctive fine, parallel channels. SEM studies reveal a striated surface and interlocking multilayered structure of LiPc that is markedly different from either the multilayered stacked methyl-LiPc or- botryoidal methoxy-LiPc. The regularly spaced pores and channels of fusinite, a reflection of its plant origin, contrast sharply with the randomly distributed pores of all sizes of the various synthetic chars. Furthermore, the combined results of both LM and EM studies strongly suggest the nonperturbing nature of fusinite and LiPc when they were used as EPR probes to measure oxygen in cells or tissues. We hope that this study, in conjunction with the numerous EPR functional studies of probes reported earlier, provides valuable information for the future development of new particulate EPR spin probes.

Animals↗
PubMed1998

The measurement of oxygen in vivo using EPR techniques.

The measurement of pO2 in vivo using EPR has some features which have already led to very useful applications and this approach is likely to have increasingly wide and effective use. It is based on the effect of oxygen on EPR spectra which provides a sensitive and accurate means to measure pO2 quantitatively. The development of oxygen-sensitive paramagnetic materials which are very stable, combined with instrumental developments, has been crucial to the in vivo applications of this technique. The physical basis and biological applications of in vivo EPR oximetry are reviewed, with particular emphasis on the use of EPR spectroscopy at 1 GHz using particulate paramagnetic materials for the repetitive and non-invasive measurement of pO2 in tissues. In vivo EPR has already produced some very useful results which have contributed significantly to solving important biological problems. The characteristics of EPR oximetry which appear to be especially useful are often complementary to existing techniques for measuring oxygen in tissues. These characteristics include the capability of making repeated measurements from the same site, high sensitivity to low levels of oxygen, and non-invasive options. The existing techniques are especially useful for studies in small animals, where the depth of measurements is not an overriding issue. In larger animals and potentially in human subjects, non-invasive techniques seem to be immediately applicable to study phenomena very near the surface (within 10 mm) while invasive techniques have some very promising uses. The clinical uses of EPR oximetry which seem especially promising and likely to be undertaken in the near future are long-term monitoring of the status and response to treatment of peripheral vascular disease and optimizing cancer therapy by enabling it to be modified on the basis of the pO2 measured in the tumour.

Animals↗
PubMed1998

Effect on regrowth delay in a murine tumor of scheduling split-dose irradiation based on direct pO2 measurements by electron paramagnetic resonance oximetry.

Tumor reoxygenation after irradiation may contribute to a tumor's response to subsequent doses of radiation. The timing of reoxygenation in RIF-1 murine tumors was determined using electron paramagnetic resonance (EPR) oximetry with intratumoral implantation of an oxygen-sensitive paramagnetic material (India ink) to monitor the pO2 in individual murine tumors before, during and after three different irradiation schemes. Radiation was given as a single 20-Gy dose or was split into two 10-Gy doses where the second dose of radiation was delivered at the minimum postirradiation tumor pO2 (24-h interval, hypoxic group) or where the second dose of radiation was delivered after reoxygenation had occurred (72-h interval, oxygenated group). The end point for tumor response was time taken to reach double the volume at the time of treatment. There were significantly longer tumor doubling times in the oxygenated compared to the hypoxic group, indicating that the measured changes in pO2 reflected changes in tumor radiosensitivity. A 24-h interval between doses resulted in a delay of reoxygenation in the tumors, while a 72-h interval resulted in a second cycle of hypoxia/reoxygenation. Our results suggest that repeated direct measurements of pO2 in tumors by EPR oximetry could be useful in timing radiation doses to achieve improved local control of tumors.

Animals↗
PubMed1997

MRI contrast enhanced study of cartilage proteoglycan degradation in the rabbit knee.

Early degeneration of cartilage is accompanied by a loss of proteoglycans and consequent changes in the content of water. Conventional magnetic resonance imaging (MRI) cannot reliably detect this change, since the relaxation properties of the cartilage are dominated by its collagen content. The applicability of a positively charged nitroxide as an MRI contrast agent in detection of the content of the negatively charged proteoglycans within the cartilage was investigated. The results from both MRI and electron paramagnetic resonance (EPR) spectroscopy indicate that the accumulation of the contrast agent reflects the amount of proteoglycans within the cartilage, presumably due to the electrostatic interactions between the negatively charged proteoglycans and the positively charged nitroxide. Such a contrast agent could be useful in the detection and study of early stages of the degeneration of joints.

Animals↗
PubMed1997

Gloxy: an oxygen-sensitive coal for accurate measurement of low oxygen tensions in biological systems.

This paper describes the characteristics of a new oxygen sensitive, paramagnetic material that has some significant advantages for measurements of tissue pO2 by in vivo EPR. This paramagnetic component of Welsh coal, termed "gloxy" was found to have valuable EPR features that allow accurate measurement of low oxygen tensions in vivo; these include large oxygen-dependent changes in linewidth, a high number of paramagnetic spin centers (resulting in high signal amplitude), and stability in tissue allowing repeated pO2 measurements to be made in vivo with high precision. Renal pO2 was measured deep in the medulla region of isolated perfused kidneys and found to be lower than that in the cortex (1.7 +/- 0.05 and 7.1 +/- 0.3 mm Hg, respectively). The quality of the EPR signal obtained from the renal outer medulla and also from tumors in mice was such that the pO2 measurements were obtained with a precision of +/-3% of the measured pO2 (Kidney: 1.7 +/- 0.05 mmHg; Tumor: 1.37 +/- 0.04 mmHg). In vitro tests on the viability of cells and in vivo studies using Gloxy demonstrate the stability and inertness of this oxygen-sensitive material.

Animals↗
PubMed1997

Reduction of carcinogenic chromium(VI) on the skin of living rats.

The reduction of chromate (Cr(VI)) on the skin of living rats was investigated using the technique of in vivo electron paramagnetic resonance (EPR) spectroscopy with a surface coil resonator. Topical application of aqueous solution of Cr(VI) on the skin of rats generated the transient species, Cr(V). Partial removal of the stratum corneum increased the rates of formation and decay of Cr(V), as well as Cr(V) signal intensity. The results demonstrate that skin represents one route for chromium to enter into animals and humans. The generation of reactive Cr(V) species in the reduction of Cr(VI) by the skin may play an important role in the mechanism of Cr(VI)-induced skin cancer. These findings indicate the potential for in vivo EPR spectroscopy for studying the metabolism of paramagnetic reactive species in chemical and biochemical reactions occurring in/on the skin of both small and large animals, and possibly humans.

Animals↗
PubMed1997

Myocardial oxygen tension in isolated erythrocyte-perfused rat hearts and comparison with crystalloid media.

The isolated heart, typically perfused with crystalloid media equilibrated with >/=95% O2 to ensure adequate myocardial oxygen tension, is commonly used to study cardiac function. When hemoglobin is available for oxygen transport, equilibration with 21% O2 is considered adequate to meet metabolic demands. This study presents the measurement of myocardial pO2 in isolated hearts perfused with an erythrocyte suspension. Baseline myocardial pO2 in erythrocyte-perfused hearts was 16.4+/-3.5 mmHg (mean+/-s.e.). When compared to previous measurements of myocardial pO2 in isolated hearts perfused with crystalloid media, the use of erythrocyte suspensions resulted in a 10-fold lower level of myocardial pO2, while avoiding very low and high values. The standard use of 95% oxygen with crystalloid results in myocardial levels of oxygen far above those usually found in the presence of hemoglobin and room air.

Animals↗
PubMed1997

Myocardial oxygen tension and capillary density in the isolated perfused rat heart during pharmacological intervention.

Oxygen is essential for normal cardiac function and plays an important role in cardiac regulation. Electron paramagnetic resonance (EPR) oximetry appears to have some significant advantages for measuring oxygen tension (pO2) in the beating heart. This study presents the serial measurement of myocardial pO2 by EPR oximetry in the isolated crystalloid perfused heart during treatment with different cardioactive drugs: dobutamine, metoprolol, verapamil, vasopressin, and N omega-Nitro-L-Arginine Methyl Ester (L-NAME). Baseline myocardial pO2 was 176 +/- 14 mmHg (mean +/- S.E.). Myocardial capillary density in the intact contracting heart was calculated to be 2300 +/- 100 mm-2, using local myocardial pO2 and a cylindrical model for oxygen diffusion in tissue. Each drug had characteristic effects on myocardial pO2, myocardial oxygen consumption (MVO2), and capillary density. Metoprolol and verapamil increased myocardial pO2 by 51% and 18%, respectively, dobutamine decreased myocardial pO2 by 84% while vasopressin and L-NAME had no significant effect on myocardial pO2. Metoprolol and verpamil decreased MVO2 by 9% and 56%, respectively, while dobutamine increased MVO2 by 59%. A quantitative comparison of effects on the capillary bed based on changes in myocardial pO2 and MVO2 was made. Metoprolol and verapamil had opposite effects on the capillary bed. Verapamil decreased myocardial capillary density by 39%, while capillary density increased by 10% (n.s.) with metoprolol. Data following perfusion without drug is also presented. We conclude that: 1) The application of EPR oximetry with LiPc provides dynamic evaluation of local myocardial pO2 in the contracting heart. 2) Using a cylindrical model of oxygen delivery and diffusion in tissue, these data may be used to describe the changes of capillary density during pharmacological interventions.

Adrenergic beta-Agonists↗
PubMed1997

Histological assessment of rodent CNS tissues to EPR oximetry probe material.

The effects of the paramagnetic oxygen sensing material, lithium phthalocyanine (LiPc) and fusinite were assessed in the brain of Mongolian gerbils and the spinal columns of rats respectively, to determine if there are histologically discernible changes in the tissue surrounding the probe material. This information is essential for the evaluation of the role of EPR oximetry in the measurements of pO2 in the CNS; the technique has great potential value for such measurements because it reports on the pO2 accurately and sensitively and, after the initial placement, measurements can be made repeatedly without invasive procedures or anesthesia. Histologic assessments demonstrated the inert nature of both the fusinite and LiPc EPR probes in rodent CNS tissue over relatively long (2 month) time periods. The fusinite suspensions and LiPc crystals (size range of approximately 100-200 microns) remained well localized to the point of injection and created mild acute tissue reaction on implantation (which appeared to resolve quickly) and virtually no tissue reaction at later times. The majority of the implanted fusinite and LiPc material was present extracellularly in the brain and spinal cord. MRI provided an accurate, noninvasive assessment of probe placement and was able to investigate pathologic effects (hemorrhage, edema, necrosis) associated with the probe placement and treatment effects.

Animals↗