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ABSTRACT: We have previously reported a high-spatial-resolution multisite electron paramagnetic resonance (EPR) oximetry method that
is based on consecutive applications of magnetic field gradients with the same direction but different magnitudes. This method
that could be called also two-gradient convolution EPR oximetry has no restrictions for the shape of solid paramagnetic materials
implanted in tissue and is applicable for any particulate EPR oxygen-sensitive matieral with a Lorentzian line shape. To enhance
the utilization of this method, a previously described algorithm was used to develop user-friendly Windows-based software.
Practical conditions of application of the method were established using several different model systems. It has been shown
that the spectral overlap from the adjacent sites can be neglected if the splitting between the corresponding lines exceeds
the largest line width by at least a factor of 1.3. An additional requirement of the method is that the second field gradient
should exceed by at least 30% the value of the first gradient. It was confirmed that the error in line width determination
at L-band is proportional to the noise-to-signal ratio, and does not exceed 1% a noise-to-signal ratio of 0.1 in a typical
in vivo experiment. We demonstrate that the line widths of up to 10 different sites can be determined.
Applied Magnetic Resonance 04/2012; 28(1):69-78. · 0.75 Impact Factor
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ABSTRACT: In vivo electron paramagnetic resonance (EPR) has been very useful for studies in animals, and these results suggest that
there are some very attractive potential applications in human subjects. In this article, we describe our rationale for the
clinical application of in vivo EPR, some of the principal technical challenges, the initial results in human subjects, and
our evaluation of the areas where in vivo EPR is likely to play an important clinical role in the near future. The most obvious
area of very high potential for clinical applications is tissue oximetry, where in vivo EPR can provide repeated and accurate
measurements of tissue pO2, a type of measurement that cannot be obtained by other techniques. Oximetry is capable of providing clinicians with information
that can impact directly on diagnosis and therapy, especially for peripheral vascular disease, oncology, and wound healing.
The other area of great immediate importance is the ability of in vivo EPR to measure clinically significant exposures to
ionizing radiation after the fact, which may occur due to accidents, terrorist activity, or nuclear war. The results obtained
already from human subjects demonstrate the feasibility of the use of in vivo EPR for measurements in human subjects. We anticipate
that in vivo EPR will play a vital role in the clinical management of various pathologies in the years to come.
Applied Magnetic Resonance 04/2012; 30(2):185-199. · 0.75 Impact Factor
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ABSTRACT: Summary The use of 35 GHz microwave frequency has greatly simplified the separation of overlapping signals in dried irradiated fern spores. While in general confirming the conclusions previously drawn from X-band spectra, the use of Q-band has clarified several assignments of radical groups and allowed the recognition of additional radical groups or sub-groups.
07/2009; 27(3):205-210.
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ABSTRACT: In vivo EPR tooth dosimetry is a more challenging problem than in vitro EPR dosimetry because of several potential additional sources of variation associated with measurements that are made in the mouth of a living subject. For in vivo measurement a lower RF frequency is used and, unlike in the in vitro studies, the tooth cannot be processed to optimize the amount and configuration of the enamel that is measured. Additional factors involved with in vivo measurements include the reproducibility of positioning the resonator on the surface of the tooth in the mouth, irregular tooth geometry, and the possible influence of environmental noise. Consequently, in addition to using the theoretical and empirical models developed for analyzing data from measurements of teeth in vitro, other unconventional and more robust methods of dose reconstruction may be needed. The experimental parameter of interest is the peak-to-peak amplitude of the spectrum, which is correlated to the radiation dose through a calibration curve to derive the reconstructed dose. In this study we describe and compare the results from seven types of computations to measure the peak-to-peak amplitude for estimation of the radiation induced signal. The data utilized were from three sets of in vivo measurements of irradiated teeth. Six different teeth with different doses were placed in the mouth of a volunteer in situ and measurements of each tooth were carried out on three different days. The standard error of dose prediction (SEP) is used as a figure of merit for quantifying precision of the reconstruction. We found that many of the methods gave fairly similar results, with the best error of prediction resulting from a computation based on a Lorentzian line model whose center field corresponds to the known parameter of the radiation-induced EPR spectra of teeth, with corrections from a standard sample that was measured as part of the data acquisition scheme. When the results from the three days of measurement were pooled, the SEP decreased dramatically, which suggests that one of the principal sources of variation in the data is the ability to precisely standardize the measurements conditions within the mouth. There are very plausible ways to accomplish improvements in the existing procedures.
Radiation Measurements 08/2007; 42(6-7):1089-1098. · 1.18 Impact Factor
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ABSTRACT: The effects of two general anesthetics on skin oxygenation in mice are evaluated by electron paramagnetic resonance oximetry. Up to now no data on the effects of different anesthetics on skin oxygenation could be found. In this study animals were anesthetized with ketamine/xylazine or isoflurane, and partial pressure of oxygen (pO(2)) in the skin, heart rate and hemoglobin oxygen saturation were followed as a function of time and inhaled oxygen concentration. The skin pO(2) significantly increased continuously for about 60 min in mice anesthetized with isoflurane and remained constant after that. During ketamine/xylazine anesthesia, the pO(2) in the skin only slightly decreased. The skin pO(2) increased with higher inspired oxygen concentrations for both anesthetics groups. When breathing 21% oxygen, mice anesthetized with isoflurane had two-fold higher pO(2) in the skin compared to mice anesthetized with ketamine/xylazine. The heart rate was significantly lower in animals anesthetized with ketamine/xylazine, while hemoglobin saturation was almost the same in both groups at all inhaled oxygen concentrations. These results show that the type of anesthesia is an important parameter that needs to be considered in experiments where skin pO(2) is followed.
Skin pharmacology and physiology 02/2007; 20(2):77-84. · 2.92 Impact Factor
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M Dinguizli,
S Jeumont,
N Beghein,
J He,
T Walczak,
P N Lesniewski,
H Hou,
O Y Grinberg,
Artur Sucheta, H M Swartz,
B Gallez
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ABSTRACT: Electron paramagnetic resonance (EPR) oximetry is a powerful technology that allows the monitoring of oxygenation in tissues. The measurement of tissue oxygenation can be achieved using lithium phthalocyanine (LiPc) crystals as oxygen reporters. In order to have biocompatibility for the sensing system and to assure long-term stability in the responsiveness of the system, we developed films of Teflon AF 2400 with embedded LiPc crystals. These systems can be used as retrievable inserts or parts of an implantable resonator or catheter. Atomic force microscopy studies revealed that the surface of the films was regular and planar. The response to oxygen of the sensor (EPR linewidth as a function of pO(2)) remained unchanged after implantation in mice, and was not affected by sterilization or irradiation. The use of resonators, holding LiPc embedded in Teflon AF 2400, implanted in the gastrocnemius muscle of rabbits allowed the monitoring of oxygen during several weeks. Several assays also demonstrated the biocompatibility of the system: (1) no hemolytic effect was noted; (2) no toxicity was found using the systemic injection test of extracts; (3) histological analysis in rabbit muscle in which the films were implanted for 1 week or 3 months was similar to standard polyethylene biocompatible devices. These advanced oxygen sensors are promising tools for future pre-clinical and clinical developments of EPR oximetry. These developments can be applied for other applications of biosensors where there is a need for oxygen permeable membranes.
Biosensors and Bioelectronics 02/2006; 21(7):1015-22. · 5.60 Impact Factor
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ABSTRACT: This article describes an EPR spectrometer specifically designed and constructed for EPR spectroscopy in humans. The spectrometer is based on a permanent magnet, suitable for measurements at 1200 MHz. The magnet has a full 50 cm gap between the poles, which facilitates accurate and comfortable placement of the subject for the EPR measurement at any location on the human body. The bridge includes features to facilitate clinical operations, including an indicator for phasing of the reference arm and a 2 level RF amplifier. Resonators with holders for each type and site of measurement have been developed that comfortably position the resonator and the patient and prevent artifacts due to motion. The initial applications for which the spectrometer has been designed are for oximetry using loops on the surface, oximetry using implanted resonators for measuring deep sites, and measurements in the teeth for determination of exposures to clinically significant doses of ionizing radiation.
Magnetic Resonance in Medicine 12/2005; 54(5):1317-20. · 2.96 Impact Factor
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ABSTRACT: EPR has been employed in attempts to understand the basis of specific pathophysiologies in which free radicals have a postulated
role. Examples described include pulmonary free radical damage, free radicals and sickle cell disease, free radicals in amyotrophic
lateral sclerosis, melanin and free radicals and the potential role of oxidative stress in the induction of cancer. The final
section of the chapter describes the use of NMR as the spectroscopic measure of spin-trapped radicals, after they have reacted
further to form diamagnetic species.
12/2004: pages 25-74;
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ABSTRACT: The development of L-band ( ∼ 1.2 GHz) frequency EPR spectrometers has made feasible many in vivo studies in laboratory animals and, recently, in human volunteers. The lower dielectric and eddy current losses that occur at L-band balance the lower Zeeman splitting so useful measurements can be made in conductive aqueous samples. We describe typical resonators used in such studies and provide details on the construction of the spectrometer, including the bridge, the automatic frequency control subsystem, the low-noise high-stability tunable L-band frequency source, as well as the low-frequency components—the signal receiver and the modulation unit. The application of EPR spectroscopy to larger subjects requires special care in the design of an appropriate magnet with sufficient homogeneity and stability, yet with dimensions that allow operation with a wide range of subject sizes. We describe our solution, which involves a permanent magnet, air-core scan coils to provide the field sweep and offset, and field stabilization by means of a field-frequency lock. We also describe the magnetic field modulation system, which operates at 25 kHz to avoid distortion in spectra from materials with narrow lines (such as lithium phthalocyanine). We refer to recent reviews to illustrate the range of in vivo studies and the clinical applications of the type of spectrometer described here.
Review of Scientific Instruments 12/2004; 76(1):013107-013107-6. · 1.37 Impact Factor
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ABSTRACT: Electrochemotherapy is an antitumour treatment that utilises locally delivered electric pulses to increase cytotoxicity of chemotherapeutic drugs. Besides increased drug delivery, application of electric pulses affects tumour blood flow. The aim of this study was to determine tumour blood flow modifying effects of electrochemotherapy with cisplatin, its effects on tumour oxygenation and to determine their relation to antitumour effectiveness. Electrochemotherapy of SA-1 subcutaneous tumours was performed by application of electric pulses to the tumours, following administration of cisplatin. Tumour blood flow modifying effects of electrochemotherapy were determined by measurement of tumour perfusion using the Patent blue staining technique, determination of tumour blood volume, and microvascular permeability using contrast enhanced magnetic resonance imaging, and tumour oxygenation using electron paramagnetic resonance oximetry. Antitumour effectiveness was determined by tumour growth delay and the extent of tumour necrosis and apoptosis. Tumour treatment by electrochemotherapy induced 9.4 days tumour growth delay. Tumour blood flow was reduced instantaneously and persisted for several days. This reduction in tumour blood flow was reflected in reduced tumour oxygenation. The maximal reduction in partial oxygen pressure (pO2) levels was observed at 2 h after the treatment, with steady recovery to the pretreatment level within 48 h. The reduced tumour blood flow and oxygenation correlated well with the extent of tumour necrosis and tumour cells apoptosis induced by electrochemotherapy with cisplatin. Therefore, the data indicate that antitumour effectiveness of electrochemotherapy is not only due to increased cytotoxicity of cisplatin due to electroporation of tumour cells, but also due to anti-vascular effect of electrochemotherapy, which resulted in reduced tumour blood flow and oxygenation.
British Journal of Cancer 11/2002; 87(9):1047-54. · 5.04 Impact Factor
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ABSTRACT: We describe a new method to enhance the spatial resolution of multi-site electron paramagnetic resonance (EPR) oximetry. The method is suitable for any shape (density distribution function) of a solid paramagnetic material implanted in tissue. It corrects distortions of lineshapes caused by the gradient and thus overcomes limitations of previous multi-site EPR oximetry methods that restricted the ratio of the particle size to the distance between sites. The new method is based on consecutive applications of magnetic field gradients with the same direction but with a different magnitude and uses a convolution-based fitting algorithm to derive Lorentzian EPR linewidths of each individual peak of the EPR spectrum. The method is applicable for any particulate EPR oxygen sensitive materials whose EPR spectra can be approximated by a Lorentzian function or a superposition of Lorentzian functions. By incorporating this model of the lineshape in the data processing, we are able to decrease significantly the number of parameters needed for the calculations and to recover the oxygen concentration, even from quite noisy spectra. We (i) describe our method and the data-processing algorithm, (ii) demonstrate our approach in model and in vivo experiments, and (iii) discuss the limitations.
Journal of Magnetic Resonance 11/2001; 152(2):247-58. · 2.14 Impact Factor
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ABSTRACT: Ketamine-xylazine is a commonly used anesthetic for laboratory rats. Previous results showed that rats anesthetized with ketamine-xylazine can have a much lower cerebral partial pressure of oxygen (P(t)O(2)), compared to unanesthetized and isoflurane anesthetized rats. The underlying mechanisms for the P(t)O(2) reduction need to be elucidated. In this study, we measured regional cerebral blood flow (CBF) using nuclear magnetic resonance (NMR) perfusion imaging and cortical P(t)O(2) using electron paramagnetic resonance (EPR) oximetry in the forebrain of rats under isoflurane, ketamine, ketamine-xylazine and isoflurane-xylazine anesthesia. The results show that in ventilated rats ketamine at a dose of 50 mg/kg does not induce significant changes in CBF, compared to isoflurane. Ketamine-xylazine in combination causes 25-65% reductions in forebrain CBF in a region-dependent manner. Adding xylazine to isoflurane anesthesia results in similar regional reductions in CBF. EPR oximetry measurements show ketamine increases cortical P(t)O(2) while xylazine decreases cortical P(t)O(2). The xylazine induced reduction in CBF could explain the reduced brain oxygenation observed in ketamine-xylazine anesthetized rats.
Brain Research 10/2001; 913(2):174-9. · 2.73 Impact Factor
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ABSTRACT: EPR oximetry using paramagnetic particles relies on the measurement of the EPR linewidth, which is directly related to the pO2. It was previously found that some of the paramagnetic materials with optimal EPR spectroscopic properties in vitro may lose their responsiveness to oxygen in tissues (change of the calibration curve of the EPR linewidth as a function of the pO2). We hypothesized that coating paramagnetic particle materials could improve the stability of response, as well as the biocompatibility. In this study, very thin films holding paramagnetic materials were prepared with different biopolymers (cellulose acetate, cellulose triacetate, cellulose nitrate, silicone, and polyurethane) that already are accepted for clinical applications. Their performance was evaluated in EPR oximetry by measuring the stability of the calibration curves (EPR linewidth as a function of pO2) after a prolonged period in an aqueous environment (1 week in saline) or in vivo (implantation for 3 weeks under the skin of mice). We found that one type of silicone film was able to stabilize the responsiveness of an intrinsically unstable carbon material (a wood char).
Magnetic Resonance in Medicine 10/2001; 46(3):610-4. · 2.96 Impact Factor
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ABSTRACT: Although many aspects of firefly bioluminescence are understood, the mechanism by which adult fireflies produce light as discrete rapid flashes is not. Here we examine the most postulated theory, that flashing is controlled by gating oxygen access to the light-emitting cells (photocytes). According to this theory, the dark state represents repression of bioluminescence by limiting oxygen, which is required for bioluminescence; relief from this repression by transiently allowing oxygen access to the photocytes allows the flash. We show that normobaric hyperoxia releases the repression of light emission in the dark state of both spontaneously flashing and non-flashing fireflies, causing continual glowing, and we measure the kinetics of this process. Secondly, we determine the length of the barriers to oxygen diffusion to the photocytes in the aqueous and gas phases. Thirdly, we provide constraints upon the distance between any gas-phase gating structure(s) and the photocytes. We conclude from these data that the flash of the adult firefly is controlled by gating of oxygen to the photocytes, and demonstrate that this control mechanism is likely to act by modulating the levels of fluid in the tracheoles supplying photocytes, providing a variable barrier to oxygen diffusion.
Journal of Experimental Biology 09/2001; 204(Pt 16):2795-801. · 3.00 Impact Factor
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ABSTRACT: Vinblastine (VLB) previously has been shown to perturb tumor blood flow, but the effect of these perturbations on tissue oxygenation is not known. The recent development of electron paramagnetic resonance (EPR) oximetry now has made it feasible to measure the effects of changes of perfusion on the pO(2) in tumors and normal tissues as a function of time and dose. We measured changes in tumor perfusion by Patent blue staining, tumor blood volume and microvascular permeability by contrast-enhanced magnetic resonance imaging, and tumor oxygenation by EPR in s.c. SA-1 murine tumors. We found that treatment with VLB induced dose-dependent reduction in tumor perfusion. One hour after i.p. treatment of mice with 2.5 mg/kg VLB, tumor perfusion was reduced to 20% of the pretreatment value and returned to close to original values within 48 h. A transient tumor blood flow-modifying effect of VLB was demonstrated also by contrast-enhanced magnetic resonance imaging; reduction of tumor blood volume and microvascular permeability was found. Reduced tumor oxygenation was found as measured by EPR oximetry, with the same time course of changes in tumor blood flow. Tumor oxygenation was reduced to 50% of pretreatment value 1 h after the treatment with 2.5 mg/kg VLB and returned to pretreatment levels within 24 h after the treatment. Although the directions of the changes in perfusion and oxygenation were similar, they were quantitatively different. Reduction in oxygenation of normal tissues, muscle, and subcutis also occurred but was smaller and returned to pretreatment values more quickly compared to the changes induced in the tumors. In conclusion, the present study demonstrates that VLB causes a profound reduction in tumor blood flow and oxygenation, which may have implications in controlling side effects of therapy and the planning of combined treatment with VLB, either with other chemotherapeutic drugs or with radiotherapy.
Cancer Research 06/2001; 61(10):4266-71. · 7.86 Impact Factor
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ABSTRACT: Endogenous reductants such as hydrogen sulfide and alkylthiols provided free radical scavenging systems during the early evolution of life. The development of oxygenic photosynthesis spectacularly increased oxygen levels, and ancient life forms were obliged to develop additional antioxidative systems. We develop here the hypothesis of how "prototypical" bioluminescent reactions had a plausible role as an ancient defense against oxygen toxicity through their "futile" consumption of oxygen. As oxygen concentrations increased, sufficient light would have been emitted from such systems for detection by primitive photosensors, and evolutionary pressures could then act upon the light emitting characteristics of such systems independently of their use as futile consumers of oxygen. Finally, an example of survival of this ancient mechanism in present-day bioluminescent bacteria (in the Euprymna scolopes-Vibrio fischeri mutualism) is discussed. Once increasing ambient oxygen levels reached sufficiently high levels, the use of "futile" oxygen consumption became too bioenergetically costly, so that from this time the evolution of bioluminescence via this role was made impossible, and other mechanisms must be developed to account for the evolution of bioluminescence by a wide range of organisms that patently occurred after this (e.g., by insects).
Journal of Molecular Evolution 05/2001; 52(4):321-32. · 2.27 Impact Factor
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ABSTRACT: The efficacy of radiation treatment depends upon local oxygen concentration. We postulated that the variability in responsiveness of tumor xenografts to a fixed dose of radioimmunotherapy might be related to the tumor pO2 at the time that radioimmunotherapy was administered. We evaluated the growth of xenografts of CALU-3 tumors, a non-small cell lung carcinoma, in response to an 8.9-MBq dose of 131I-RS-7-anti-EGP-1 and correlated tumor growth rate with initial tumor pO2 measured by EPR oximetry. The greatest growth delay in response to radioimmunotherapy had the highest initial pO2, and the fastest-growing tumors had the lowest initial pO2. We then determined the dynamic effect of radioimmunotherapy on tumor pO2 by serial measurements of pO2 for 35 days after radioimmunotherapy. This information could be important for ascertaining the likelihood that a tumor will respond to additional doses as part of a multiple dose scheme. Serial tumor pO2 measurements may help identify a window of opportunity when the surviving tumor regions will be responsive to a second round of radioimmunotherapy or a second therapeutic modality such as chemotherapy or an anti-vascular agent. After radioimmunotherapy, there was an increase in tumor pO2 followed by a decrease below initial levels in most mice. Thus defined times may exist when a tumor is more or less radiosensitive after radioimmunotherapy.
Radiation Research 04/2001; 155(3):466-73. · 2.68 Impact Factor
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ABSTRACT: Numerical simulations of oxygen diffusion from the capillaries in tumor tissue were used to predict the capillary oxygen supply within and near hypoxic regions of the RIF-1 tumor. A finite element method to simulate the oxygen distribution from a histology section is presented, along with a method to iteratively estimate capillary oxygen concentrations. Pathological structural data for these simulations came from sections of the tumor stained with hematoxylin and eosin and were used to define the capillary positions and shapes, while overlapping regions of low oxygen concentration were defined by the hypoxia marker pimonidazole. These simulations were used to calculate spatial maps of the oxygen concentration and were tested for their ability to reproduce Eppendorf pO(2) histograms from the same tumor line. This simulation study predicted that capillary oxygen concentrations ranged from zero to above 20 microM, with a dominant peak in the hypoxic regions showing 78% of capillaries with less than 1 microM oxygen concentration, compared to only 12% in the non-hypoxic regions. The results were not highly sensitive to the metabolic oxygen consumption rate, within the range of 2 to 16 microM/s. This numerical method for oxygen capillary simulation is readily adaptable to histology sections and provides a method to examine the heterogeneity of oxygen within the capillaries and throughout the tumor tissue section being examined.
Radiation Research 02/2001; 155(1 Pt 1):15-25. · 2.68 Impact Factor
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ABSTRACT: Factors regulating cerebral tissue PO2 (PtO2) are complex. With the increased use of clinical PtO2 monitors, it has become important to elucidate these mechanisms. The authors are investigating a new methodology (electron paramagnetic resonance oximetry) for use in monitoring cerebral PtO2 in awake animals over time courses of weeks. The authors used this to study cerebral PtO2 in rats during chronic acclimation to hypoxia predicting that such acclimation would cause an increase in PtO2 because of increases that occur in capillary density and oxygen carrying capacity. The average PtO2 between 7 and 21 days was increased by 228% over controls.
Journal of Cerebral Blood Flow & Metabolism 01/2001; 20(12):1632-5. · 5.01 Impact Factor
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ABSTRACT: We describe the development and use of a direct kinetic technique to determine the time taken for oxygen to diffuse from the external environment into the light-producing cells (photocytes) in the prothorax of bioluminescent larvae of Pyrearinus termitilluminans. This was achieved by measuring the time course of the pseudoflash induced through sequential anoxia followed by normoxia. We have also determined the separate times taken for this oxygen diffusion in gaseous and tissue (predominantly aqueous) phases by using helium and nitrogen as the carrier gas. Of the total time taken for diffusion, that in the gas phase required 613+/-136 ms (mean +/- s.e. m., N=5) whilst that in the aqueous phase required 1313+/-187 ms. These values imply pathlengths of diffusion in the gaseous and aqueous phases of 4.80x10(-)(3)+/-0.53x10(-)(3) and 8. 89x10(-)(5)+/-0.61x10(-)(5 )m, respectively. In addition, the pathlength of gas-phase diffusion was used to derive a parameter relating to the tortuosity of the tracheal system. These values, together with those obtained upon bioluminescent oxygen consumption, have been used to model oxygen supply to the photocyte. From these studies, it would also appear that the modulation of tracheolar fluid levels might be a significant mechanism of control of tissue oxygen levels in at least some insects.
Journal of Experimental Biology 09/2000; 203(Pt 16):2479-84. · 3.00 Impact Factor
