scholarly journals Optimization of oxygen tolerance extension in rats by intermittent exposure

2006 ◽  
Vol 100 (3) ◽  
pp. 869-879 ◽  
Author(s):  
J. M. Clark ◽  
C. J. Lambertsen ◽  
R. Gelfand ◽  
A. B. Troxel
Keyword(s):  
Stress Proteins ◽  
Weighted Average ◽  
Continuous Exposure ◽  
Survival Times ◽  
Direct Evaluation ◽  
Oxygen Tolerance ◽  
Degree Of Protection ◽  
Linear Relationships ◽  
Intermittent Exposure ◽  
Exposure Patterns

Optimization of oxygen tolerance extension by intermittent exposure was studied in groups of 20 rats exposed to systematically varied patterns of alternating oxygen and normoxic breathing periods at 4.0, 2.0, and 1.5 ATA. Oxygen periods of 20, 60, and 120 min were alternated with normoxic intervals that provided oxygen-to-normoxia ratios of 4:1, 2:1, 1:1, and 1:3. In general, median survival times had nearly linear relationships to increasing normoxic intervals with oxygen period held constant. Exceptions occurred at 4.0 and 2.0 ATA where a 5-min normoxic interval was too short for adequate recovery even with a 20-min oxygen period, and an oxygen period of 120 min was too long even with a normoxic interval of 30 min. These exceptions did not occur at 1.5 ATA. Survival time for many intermittent exposure patterns was equivalent to that for continuous exposure to an oxygen pressure definable as a time-weighted average of the alternating oxygen and normoxia periods. However, this predictive method underestimated the degree of protection achieved by several of the intermittent exposure patterns, especially those performed at 4.0 ATA. Results provided guidance for selection of intermittent exposure patterns for direct evaluation in humans breathing oxygen at 2.0 ATA. Definition of intermittent exposure patterns and conditions that produced prominent gains in oxygen tolerance can also facilitate the performance of future experiments designed to study potential mechanisms for oxygen tolerance extension by intermittent exposure. Heat shock and oxidation-specific stress proteins that are induced by exposure to oxidant injury are suggested for emphasis in such investigations.

Spatial assessment of flow and benefit of tropical cyclone hazard mitigation service

2021 ◽  
pp. 030913332110376
Author(s):  
Mingyue Zhao ◽  
Jian Peng ◽  
Hua Zheng ◽  
Gretchen C. Daily ◽  
Yuanxin Liu ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Hazard Mitigation ◽  
Guangdong Province ◽  
Adaptation Strategy ◽  
High Demand ◽  
Economic Interests ◽  
High Exposure ◽  
Degree Of Protection ◽  
Exposure Patterns ◽  
The Pearl River

Ecosystems are employed to effectively protect people and communities in coastal areas from tropical cyclone (TC) hazards. Although a spatially explicit TC hazard mitigation service (TCHMS) is essential for devising adaptation strategy and resilience policy, the process and delivery of this program are unclear. We improved a capacity–exposure–demand conceptual framework using Guangdong Province, China, as a case study area, and spatial analysis was employed to assess the ecosystem service. Under this framework, we assessed “capacity” as the natural potential protection against TC hazards, “exposure” as the need for services, and “demand” as the estimated necessity of protecting coastal populations and economic interests. The analysis results were then used to map the TCHMS flow and benefit gap. The results showed that 21.6% of the whole province had low capacity, 25.3% had high exposure, and 19.3% had high demand. A significantly negative correlation was present between the TCHMS capacity and exposure, and a positive correlation was shown between the exposure and demand. In particular, the TCHMS flow and benefit were sufficient in inland areas but were severely deficient in coastal megacities. In Guangdong Province, the Pearl River Delta, and Chaoshan (CS), 3.3%, 4.0%, and 15.3% of the areas showed high demand–low capacity–high exposure patterns, respectively. Our findings will deepen the scientific understanding of the degree of protection a given ecosystem will provide to communities and infrastructures exposed to TC hazards and will thus provide scientific support for coastal ecosystem planning and management.

Molt-Related Sensitivity of Daphnia pulex in Toxicity Testing

1979 ◽  
Vol 36 (9) ◽  
pp. 1129-1133 ◽  
Author(s):  
David Robert Lee ◽  
Arthur L. Buikema Jr.
Keyword(s):  
Daphnia Pulex ◽  
Toxicity Testing ◽  
Continuous Exposure ◽  
Clean Water ◽  
Survival Times ◽  
Short Term ◽  
Chromium Toxicity ◽  
Short Term Exposure ◽  
Laboratory Cultures ◽  
Cyclic Changes

Continuous and short-term exposures of Daphnia pulex to 0.56 mg Cr/L showed that these animals undergo cyclic changes in susceptibility. Short-term exposure (2 h) followed by transfer to clean water for 22 h resulted in significantly higher mortality for individuals that molted during exposure. Continuous exposure to chromate resulted in significantly shorter mean survival times for animals that had molted < 4 h before being placed in chromate solution. Because laboratory cultures can be synchronized with respect to molting, the effects of cyclic sensitivity can bias bioassay results. By examining the animals at the beginning of the test, the degree of synchrony can be determined and appropriate steps taken. Key words: bioassay, Daphnia pulex, chromium toxicity, molting

Intermittent Exposure to Noise: Effects on Hearing

1983 ◽  
Vol 92 (6) ◽  
pp. 623-628 ◽  
Author(s):  
Joseph Sataloff ◽  
Robert T. Sataloff ◽  
Raymond A. Yerg ◽  
Hyman Menduke ◽  
Robert P. Gore
Keyword(s):  
Hearing Loss ◽  
Noise Exposure ◽  
Continuous Exposure ◽  
Hearing Results ◽  
Noise Effects ◽  
High Frequencies ◽  
Severe Loss ◽  
Intermittent Exposure ◽  
Intense Noise ◽  
Continuous Noise

Most studies of the effects of noise upon hearing have dealt with continuous noise exposure. Previous reports on intermittent exposure to noise concluded that it causes less damage to hearing than does continuous exposure to noise of the same intensity. In this investigation, 12,000 workers were screened to find 295 subjects who met the strict criteria of the study. Most of the subjects were exposed to jackhammer noise at peak levels of 118 dBA. Intermittent exposure to intense noise results in very severe loss in high frequencies but relatively little or no hearing loss in the lower frequencies even after many years of exposure. This differs substantially from the effects of continuous exposure to noise of the same intensity. It remains to be determined whether this pattern of hearing results from intermittent exposure to all sorts of noise or only from the kinds of sources investigated in this study.

Heat shock proteins functioning as molecular chaperones: their roles in normal and stressed cells

1993 ◽  
Vol 339 (1289) ◽  
pp. 327-333 ◽  
Keyword(s):  
Heat Shock ◽  
Heat Shock Proteins ◽  
Molecular Chaperones ◽  
Stress Proteins ◽  
Elevated Temperatures ◽  
Metabolic Stress ◽  
Hsp 70 ◽  
Degree Of Protection ◽  
Stressed Cells ◽  
Shock Proteins

In response to either elevated temperatures or several other metabolic insults, cells from all organisms respond by increasing the expression of so-called heat shock proteins (hsp or stress proteins). In general, the stress response appears to represent a universal cellular defence mechanism. The increased expression and accumulation of the stress proteins provides the cell with an added degree of protection. Studies over the past few years have revealed a role for some of the stress proteins as being intimately involved in protein maturation. Members of the hsp 70 family, distributed throughout various intracellular compartments, interact transiently with other proteins undergoing synthesis, translocation, or higher ordered assembly. Although not yet proven, it has been suggested that members of the hsp 70 family function to slow down or retard the premature folding of proteins in the course of synthesis and translocation. Yet another family of stress proteins, the hsp 60 or GroEL proteins (chaperonins), appear to function as catalysts of protein folding. Here I discuss the role of those stress proteins functioning as molecular chaperones, both within the normal cell and in the cell subjected to metabolic stress.

Analysis of the temperature-dependent temporal pattern of heat-shock-protein synthesis in fish cells

1983 ◽  
Vol 3 (7) ◽  
pp. 647-658 ◽  
Author(s):  
Lashitew Gedamu ◽  
Beverly Culham ◽  
John J. Heikkila
Keyword(s):  
Protein Synthesis ◽  
Heat Shock ◽  
Heat Shock Protein ◽  
Temporal Pattern ◽  
Stress Proteins ◽  
Incubation Temperature ◽  
Stress Protein ◽  
In Vitro Translation ◽  
Continuous Exposure ◽  
Temperature Dependent

Continuous exposure of Chinook salmon embryo cells to an elevated incubation temperature of 24°C induces the transient expression of a set of heat-shock or stress proteins whereas maintenance of the cells at a higher incubation temperature of 28°C produces a continuous synthesis of these stress proteins. In vitro translation studies suggest that the temperature-dependent temporal pattern of stress-protein synthesis is correlated with the levels of stress-protein mRNA. This was verified using a recombinant-DNA probe complementary to the 70K heat-shock-protein mRNA. A transient increase in the level of the fish heat-shock 70K mRNA was observed in RNA samples isolated from cells continuously exposed at 24°C However, a constant increase in the level of this specific mRNA was found in RNA preparations obtained from cells maintained at 28°C Therefore, the temperature-dependent pattern of fish heat-shockprotein synthesis appears to be directly related to the level of heat-shock-protein mRNA.

Intermittent Exposure to Cigarette Smoke Increases Lung Tumors and the Severity of Emphysema More than Continuous Exposure

2018 ◽  
Vol 59 (2) ◽  
pp. 179-188 ◽  
Author(s):  
Naofumi Kameyama ◽  
Shotaro Chubachi ◽  
Ahmed E. Hegab ◽  
Hiroyuki Yasuda ◽  
Shizuko Kagawa ◽  
...  
Keyword(s):  
Cigarette Smoke ◽  
Lung Tumors ◽  
Continuous Exposure ◽  
Intermittent Exposure

scholarly journals Intra-Articular Slow-Release Triamcinolone Acetonide from Polyesteramide Microspheres as a Treatment for Osteoarthritis

Pharmaceutics ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 372
Author(s):  
Anna Tellegen ◽  
Martijn Beukers ◽  
Imke Rudnik-Jansen ◽  
Nicolien van Klaveren ◽  
Kan Loi How ◽  
...  
Keyword(s):  
Triamcinolone Acetonide ◽  
Articular Chondrocytes ◽  
Inflammatory Marker ◽  
Local Drug Delivery ◽  
Radiographic Examination ◽  
Continuous Exposure ◽  
Proof Of Concept ◽  
Intermittent Exposure ◽  
Continuous Presence ◽  
Fluid Levels

Osteoarthritis (OA) is a common cause of pain and disability. Local corticosteroid injections are effective in treating OA pain and inflammation but are short-acting. Prolonged intra-articular (IA) corticosteroid exposure may even lead to cartilage deterioration. The aim of this prospective study was to assess safety and provide proof-of-concept of IA-applied biodegradable polyesteramide-based microspheres (PEAMs) gradually releasing triamcinolone acetonide (TA). Mimicking continuous exposure associated with local drug delivery in canine articular chondrocytes cultured in the continuous presence of TA tissue regeneration was not affected, whereas intermittent exposure reduced proteoglycan production. In this respect, TA-PEAMs administered IA in a proof-of-concept study in 12 client-owned dogs with established OA also showed safety by radiographic examination, without changes in OA severity and in glycosaminoglycan synovial fluid levels. Treatment also resulted in clinical improvement in 10 out of 11 dogs during the two-month follow-up period, which persisted in 6 out of 10 dogs after 6 months, based on objective gait analysis and owner questionnaires. Synovial prostaglandin E2, a pro-inflammatory marker, was decreased two months after treatment. This study showed safety and proof-of-concept of IA-administered TA-PEAMs in dogs with OA, as a first step towards translation into the veterinary and human clinic.

Effects of intermittent hypoxia on structural vascular adaptation in chick embryos

1988 ◽  
Vol 254 (6) ◽  
pp. H1194-H1199
Author(s):  
T. H. Adair ◽  
J. P. Montani ◽  
A. C. Guyton
Keyword(s):  
Intermittent Hypoxia ◽  
Vascular System ◽  
Average Concentration ◽  
Whole Body ◽  
Control Group ◽  
Continuous Exposure ◽  
Chick Embryos ◽  
Low Oxygen ◽  
Intermittent Exposure ◽  
Tissue Cells

We explored whether the blood vascular system of the chick embryo adapts its structure to meet the maximum or average oxygen needs of the tissue cells. Chick embryos were grown in continuous 12% oxygen, continuous 16% oxygen, and intermittent 12% oxygen in which the embryos were exposed to 12% oxygen for 4 h each day. Control groups were grown in room air. Measurements of structural vascular resistance (SVR), i.e., the resistance of the maximally dilated vasculature, were used to estimate the whole body vascularity of the 14- or 15-day-old embryos. Continuous exposure to 12% oxygen decreased SVR by 63.1 +/- 1.2 (SE) %, and intermittent exposure to 12% oxygen decreased SVR by 55.6 +/- 0.5% when compared with a 15-day-old normoxic control group. Based on studies with continuous exposure to different levels of low oxygen, it was predicted that exposure to 19.5% oxygen, the average concentration for the intermittent hypoxia group, would decrease SVR by 15.0 +/- 0.3%. These results indicate that intermittent hypoxia at 12% oxygen was approximately 90% as effective as continuous hypoxia at the same level in decreasing SVR and about four times more effective than 19.5% continuous oxygen. Therefore, the results support the hypothesis that the blood vascular system adapts its structure to meet almost entirely the maximum oxygen needs of the tissue cells.

Effects of acute and chronic hypercapnia on oxygen tolerance in rats

1981 ◽  
Vol 50 (5) ◽  
pp. 1036-1044 ◽  
Author(s):  
J. M. Clark
Keyword(s):  
Protective Effect ◽  
Survival Times ◽  
Brain Oxygenation ◽  
Oxygen Tolerance ◽  
Significant Amelioration ◽  
Cerebral Vasodilation

Groups of 16-52 normal or CO2-adapted rats were exposed top 100% O2 or to O2 with 60 Torr PICO2 (O2-CO2) at pressures of 1.0, 1.5, 2.0, 3.0, and 4.0 ATA. Exposure durations for 50% mortality (LD50) in normal rats at 4.0, 3.0, 2.0, 1.5, and 1.0 ATA O2 were 6.3, 9.3, 17.2, 27.4, and 76.1 h, respectively. Corresponding LD50 values for normal rats exposed to O2-CO2 were 2.0, 2.9, 16.3, 24.8, and 74.8 h. Survival times of CO2-adapted rats exposed to O2 were nearly identical to those of normal rats. LD50 values for CO2-adapted rat exposed to O2-CO2 were 4.1, 7.5, 17.9, 23.6, and 65.4 h, respectively. These data confirm acceleration of O2 intoxication by acute hypercapnia at 4.0 and 3.0 ATA, but they show less prominent effects at 2.0, 1.5, and 1.0 ATA. Hypercapnia adaptation clearly has a protective effect in rats exposed to O2-CO2 at 4.0 and 3.0 ATA. At 2.0, 1.5, and 1.0 ATA, where acute hypercapnia has less effect, the effects of CO2 adaptation are also less prominent. The observed changes in oxygen tolerance can be explained by cerebral vasodilation with increased brain oxygenation in acute hypercapnia and by significant amelioration of this response during chronic hypercapnia.

Online Exposure for Spider Phobia: Continuous Versus Intermittent Exposure

2011 ◽  
Vol 28 (3) ◽  
pp. 143-155 ◽  
Author(s):  
Allison J. Matthews ◽  
Zee H. Wong ◽  
Joel D. Scanlan ◽  
Ken C. Kirkby
Keyword(s):  
Post Treatment ◽  
Spider Phobia ◽  
Continuous Exposure ◽  
Exposure Treatment ◽  
Spider Fear ◽  
Treatment Assessment ◽  
Home Based ◽  
Intermittent Exposure ◽  
Distress Scale

AbstractBackground: The aim of this research was to evaluate an online exposure treatment for spider phobia (www.feardrop.com) and to investigate the effects of intermittent versus continuous exposure.Methods: Spider phobic participants (N = 23) completed two 14-minute stages of laboratory-based online exposure. In the first of these stages exposure was either continuous or intermittent (alternating fearrelevant and -irrelevant images). One week later, participants commenced a sixstage home-based graded online exposure task, which was undertaken over 30 days. Subjective Units of Distress Scale (SUDS) ratings were taken throughout all exposure stages. Spider fear was assessed prior to treatment, and at 1-week and 1-month post treatment.Results: Habituation was observed across each stage for both the laboratory and home-based tasks and generalisation of habituation was found between stages. Habituation was not impaired in the alternating fear-relevant and -irrelevant image condition, though subjects experienced less summed anxiety. Adherence rates were low in home-based online exposure. However, participants who completed 30-days post-treatment assessment (n = 14) showed a significant reduction in spider fear as measured by the Fear of Spiders Questionnaire (FSQ).Conclusions: Online exposure produces habituation and generalisation of habituation to spider images as well as longer-term reductions in spider fear. Alternating fear-relevant and -irrelevant exposure is feasible in online exposure and may lead to habituation with less summed anxiety that has implications for tolerability and acceptability. Measures to increase adherence rates and hence dosage delivered are a key consideration for further online exposure research.

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