Keywords: Heat loss; Insulation; Meadow voles; Pelage; Rodentia; Thermoregulation; White-footed mice 相似文献
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1.
Objective
Safety concerns about the Riata ICD shock lead were recently raised, with insulation failure due to conductor externalisation. Its incidence and presentation were assessed, and predictors of insulation failure and lead survival of the Riata 1580–1582 were studied, retrospectively, before the official recall.Methods
All 374 patients at the Erasmus Medical Center between July 2003 and December 2007 with a 1580, 1581 or 1582 shock lead.Results
The majority of the patients were male (78 %), with a median age of 60 years (IQR 52–70); primary prevention in 61 %. Median follow-up was 60.3 months (IQR 35.5–73.2), with 117 (31 %) patients dying. Electrical abnormalities (mainly noise, 65 %) were observed in 20/257 patients (7.8 %). Definite conductor externalisation was confirmed with fluoroscopy or chest X-ray in 16 patients, and in one after extraction. One patient presented with a drop in the high-voltage impedance trend with a short circuit of the ICD system during defibrillation testing, and needed to be shocked externally. In 8 more patients, conductor externalisation was found during an elective procedure. No predictors of externalisation could be found, except for the use of single coil (p = 0.02). Median time to conductor externalisation was 5 years (IQR 3.1–6.2). Lead externalisation was observed in 5.4 % (95 % CI 3.1–9.3) at 5 years and 22.7 % (95 % CI 13.6–36.6) at 8 years.Conclusion
A high incidence of insulation defects associated with conductor externalisation in the Riata ICD lead family is observed. The mode of presentation is diverse. This type of insulation failure can lead to failure of therapy delivery. 相似文献2.
Exertion-induced fatigue and thermoregulation in the cold 总被引:1,自引:0,他引:1
Young AJ Castellani JW 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2001,128(4):793-776
Cold exposure facilitates body heat loss which can reduce body temperature, unless mitigated by enhanced heat conservation or increased heat production. When behavioral strategies inadequately defend body temperature, vasomotor and thermogenic responses are elicited, both of which are modulated if not mediated by sympathetic nervous activation. Both exercise and shivering increase metabolic heat production which helps offset body heat losses in the cold. However, exercise also increases peripheral blood flow, in turn facilitating heat loss, an effect that can persist for some time after exercise ceases. Whether exercise alleviates or exacerbates heat debt during cold exposure depends on the heat transfer coefficient of the environment, mode of activity and exercise intensity. Prolonged exhaustive exercise leading to energy substrate depletion could compromise maintenance of thermal balance in the cold simply by precluding continuation of further exercise and the associated thermogenesis. Hypoglycemia impairs shivering, but this appears to be centrally mediated, rather than a limitation to peripheral energy metabolism. Research is equivocal regarding the importance of muscle glycogen depletion in explaining shivering impairments. Recent research suggests that when acute exercise leads to fatigue without depleting energy stores, vasoconstrictor responses to cold are impaired, thus body heat conservation becomes degraded. Fatigue that was induced by chronic overexertion sustained over many weeks, appeared to delay the onset of shivering until body temperature fell lower than when subjects were rested, as well as impair vasoconstrictor responses. When heavy physical activity is coupled with underfeeding for prolonged periods, the resulting negative energy balance leads to loss of body mass, and the corresponding reduction in tissue insulation, in turn, compromises thermal balance by facilitating conductive transfer of body heat from core to shell. The possibility that impairments in thermoregulatory responses to cold associated with exertional fatigue are mediated by blunted sympathetic nervous responsiveness to cold is suggested by some experimental observations and merits further study. 相似文献
3.
太湖流域湖西区城市化空间过程及其生态效应 总被引:5,自引:1,他引:4
我国快速推进的城市化进程正对周围生态系统造成现实或潜在的威胁.基于RS和GIS技术,从镇域尺度探讨1984~2004年太湖流域城市化空间过程及其生态效应.(1)城镇用地轴向扩展明显:沿路三级邻域带R1、R2、R3在1984~2004年期间新增城镇用地面积累积平均百分比分别为88.24%、90.23%、94.68%.(2)城镇用地扩展形态指数MFD与城镇公路连接数UR存在关系:UR=UR3时,扩展形态指数MFD>=1.5;UR=UR1时,1.250高值区占全区面积的66.33%,形成两核两带:两核位于溧阳经济开发区和镇江谏壁镇-丹徒镇附近;两带分别是两核连线地带和溧阳城区-宜兴新街镇附件一带. 相似文献
4.
Hair is considered to be a basic mammalian feature that provides protection and insulation, promoting energy conservation
and survival. To quantify the functional significance of mammalian pelage, we tested the short-term experimental effects of
fur removal in a natural population of the California vole, Microtus californicus, in winter. The daily energy expenditure (DEE) of seven voles was directly measured in the field using stable isotopes, first
with the animals in their natural condition and then again after experimental removal of pelage by shaving. The initial mean±SD
DEE of 96.0±23.1 kJ/day increased by only about 10%, to 106.3±21.4 kJ/day, following shaving. The voles showed a body mass
loss of 5%, about half of which was due to fur removal. Comparing slightly larger samples of all animals whose local survival
could be documented, we found 100% survival over the 5 initial days of the experimental manipulation in 16 control animals
and nine shaved animals; over the following 3 weeks the survival of shaved mice did not differ significantly from that of
controls. We were surprised that the average increase in energy expenditure of voles without fur was so modest, though the
range of individual values was great, and likewise we were surprised that shaved voles survived as well as they did. M.
californicus survives naturally in winter under conditions of social aggregation that include huddling together of individuals in nests;
this situation probably provided our experimentally shaved voles an opportunity to minimize the energetic disadvantages of
pelage loss. They may also have employed a variety of compensatory physiological and behavioral responses, including reduction
in activity time and food intake, and perhaps a related small decline in body mass. Our limited sample sizes made it difficult
to detect subtle differences that may have been biologically significant in the system we studied. Nonetheless, we can reaffirm
that fur has an insulative value that promotes energy economy and survival. However, we also conclude that mammalian physiology
and behavior are sufficiently complex and flexible that a variety of responses can be deployed to promote survival under unusual
circumstances such as those of our experimental test.
Received: 29 March 1999 / Accepted: 3 September 1999 相似文献
5.
Mark C. Mainwaring D. Charles Deeming Chris I. Jones Ian R. Hartley 《Ecology and evolution》2014,4(6):851-861
Nest construction is taxonomically widespread, yet our understanding of adaptive intraspecific variation in nest design remains poor. Nest characteristics are expected to vary adaptively in response to predictable variation in spring temperatures over large spatial scales, yet such variation in nest design remains largely overlooked, particularly amongst open‐cup‐nesting birds. Here, we systematically examined the effects of latitudinal variation in spring temperatures and precipitation on the morphology, volume, composition, and insulatory properties of open‐cup‐nesting Common Blackbirds’ Turdus merula nests to test the hypothesis that birds living in cooler environments at more northerly latitudes would build better insulated nests than conspecifics living in warmer environments at more southerly latitudes. As spring temperatures increased with decreasing latitude, the external diameter of nests decreased. However, as nest wall thickness also decreased, there was no variation in the diameter of the internal nest cups. Only the mass of dry grasses within nests decreased with warmer temperatures at lower latitudes. The insulatory properties of nests declined with warmer temperatures at lower latitudes and nests containing greater amounts of dry grasses had higher insulatory properties. The insulatory properties of nests decreased with warmer temperatures at lower latitudes, via changes in morphology (wall thickness) and composition (dry grasses). Meanwhile, spring precipitation did not vary with latitude, and none of the nest characteristics varied with spring precipitation. This suggests that Common Blackbirds nesting at higher latitudes were building nests with thicker walls in order to counteract the cooler temperatures. We have provided evidence that the nest construction behavior of open‐cup‐nesting birds systematically varies in response to large‐scale spatial variation in spring temperatures. 相似文献
6.
Morten Klamer Elisabeth Morsing Thor Husemoen 《International biodeterioration & biodegradation》2004,54(4):317
Commercially available paper, flax, glass wool and rock wool insulation materials were tested for sensitivity to moisture and the ability of fungi to grow on them under different moisture regimes. Three levels of moisture were used, ambient, simulated rain and water holding capacity. After wetting, the materials were inoculated with a mixture of fungi and incubated at 26°C in boxes with high moisture levels for 4 weeks. The greatest degree of fungal growth was observed on paper and flax insulation materials initially conditioned to ambient moisture levels. Paper and flax insulation were strongly affected by moisture, with all treatments showing losses in dry mass of approx. 20%, except for paper subjected to simulated rain treatment in which the loss was 39%. Glass and rock wools were not sensitive to moisture and were resistant to fungal degradation, showing only traces of fungal growth and minimal loss in dry mass over 4 weeks. 相似文献
7.
Beef cattle grazing semi-arid foothill range of the Northern Rockies during winter may be exposed to cold temperatures and high winds while grazing pastures with low nutritional value. We refined a simple thermal balance equation to model heat exchange of free-ranging cattle. We account for the complex interactions between animal behavior and the changing natural environment by applying the components of the model to a rotating ellipsoid representing a cow at different orientations to the sun and wind. Correlation coefficients (r) between predicted standard operative temperature and measured surface temperature ranged from 0.82 on an individual basis to 0.88 on a herd average basis, indicating the model successfully quantifies heat exchanges of cattle exposed to cold conditions in the field. 相似文献
8.
Doucette LI Geiser F 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2008,151(4):615-620
Many birds living in regions with seasonal fluctuations in ambient temperatures (Ta) typically respond to cold by increasing insulation and adjusting metabolic rate. Seasonal variation in thermal physiology has not been studied for the Caprimulgiformes, an order of birds that generally have basal metabolic rates (BMR) lower than predicted for their body mass. We measured the metabolic rate and thermal conductance of Australian owlet-nightjars (Aegotheles cristatus) during summer and winter using open-flow respirometry. Within the thermoneutral zone (TNZ; 31.3 to 34.8 °C), there was no seasonal difference in BMR or thermal conductance (C), but body temperature was higher in summer- (38.2 ± 0.3 °C) than winter-acclimatized (37.1 ± 0.5 °C) birds. Below the TNZ, resting metabolic rate (RMR) increased linearly with decreasing Ta, and RMR and C were higher for summer- than winter-acclimatized birds. The mean mass-specific BMR of owlet-nightjars (1.27 mL O2 g− 1 h− 1) was close to the allometrically predicted value for a 45 g Caprimulgiformes, but well below that predicted for birds overall. These results suggest that owlet-nightjars increase plumage insulation to cope with low winter Ta, which is reflected in the seasonal difference in RMR and C below the TNZ, rather than adjusting BMR. 相似文献
9.
Elke Schleucher Philip C. Withers 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2001,129(4):316-827
Wet thermal conductance is an important thermoregulatory parameter for birds and mammals. It is generally calculated as C(wet) (ml O2 g(-1) h(-1) degrees C(-1)) = VO2/(T(b)-T(a)), where VO2 is metabolic rate measured in ml O2 g(-1) h(-1), T(b) is body and T(a) is ambient temperature measured in degrees C. Minimum C(wet) is measured at T(a) at or below the lower critical temperature (T(lc)) of the thermoneutral zone, and is strongly influenced by time of day (rest or activity phase) and body mass [J. Aschoff, Comp. Biochem. Physiol. 69A (1981) 611]. Allometric analyses indicate differences in C(wet) for passerine and non-passerine birds, in their rest and active phases (Aschoff, 1981). The allometric slope for non-passerine rest-phase (-0.583) is lower than that for non-passerine active-phase (-0.484), and passerine rest-phase (-0.461) and active-phase (-0.463), although none of these slopes are significantly different. This different-sloped relationship for non-passerine rest-phase C(wet) extrapolates to lower-than-expected values at high body mass, and so this allometric relationship may be inappropriate for predictive purposes. Consequently, we have reanalysed Aschoff's (1981) data, as well as more recent compilations, to determine a more useful allometric relationship for C(wet) of non-passerine rest-phase birds. Re-analyses of minimum thermal conductance data from Drent and Stonehouse [Comp. Biochem. Physiol. 40A (1971) 689], Aschoff (1981) and Gavrilov and Dolnik [Acta XVIII Congressus Internationalis Ornithologici Moscow (1982) 421] indicate that the most appropriate regressions for predicting C(wet) (ml O2 g(-1) h(-1) degrees C(-1)) of birds from body mass (M; g) are the pooled regressions for non-passerine and passerine birds, in the active (alpha) and resting (rho) phases, using data tabulated by Aschoff (1981): alpha, C(wet)=0.994M(-0.509); rho, C(wet)=0.702M(-0.519). C(wet) is approximately 40% higher in the active phase than the rest phase. Regressions of various data sets for C(wet) of birds and mammals indicate a similar slope of approximately -0.5 for the allometric relationship, but significantly higher elevations for mammals compared to birds. The approximately 50% higher C(wet) for mammals than birds indicates a better physical insulation for birds than mammals of the same body mass. The general scaling of C(wet) with M(-0.5) indicates that (T(b)-T(lc)) should scale with M(0.22), if mass-specific metabolic rate scales with M(-0.28) [Reynolds and Lee, Am. Nat. 147 (1996) 735]. The observed scaling for (T(b)-T(lc)) of M(0.183) (calculated from Gavrilov and Dolnik, 1985) is consistent with this expectation. 相似文献
10.
- (1) We measured the thermal conductance of dorsal pelage from meadow voles (Microtus pennsylvanicus) and white-footed mice (Peromyscus leucopus) during summer and winter.
(2) Thermal conductance was lower in the winter pelage of both species, but the seasonal change was greater in meadow voles.
(3) The form of wind speed dependence was determined by fitting a nonlinear curve of the form a+buc to data recorded at five wind speeds. The most appropriate exponent c was between 0.908 and 0.987, depending on species and season. These values are common and suggest that thermal and dynamic forces are important.