Heat stress in Africa under high intensity climate change.

Extreme weather events are major causes of loss of life and damage infrastructure worldwide. High temperatures cause heat stress on humans, livestock, crops and infrastructure. Heat stress exposure is projected to increase with ongoing climate change. Extremes of temperature are common in Africa and infrastructure is often incapable of providing adequate cooling. We show how easily accessible cooling technology, such as evaporative coolers, prevent heat stress in historic timescales but are unsuitable as a solution under climate change. As temperatures increase, powered cooling, such as air conditioning, is necessary to prevent overheating. This will, in turn, increase demand on already stretched infrastructure. We use high temporal resolution climate model data to estimate the demand for cooling according to two metrics, firstly the apparent temperature and secondly the discomfort index. For each grid cell we calculate the heat stress value and the amount of cooling required to turn a heat stress event into a non heat stress event. We show the increase in demand for cooling in Africa is non uniform and that equatorial countries are exposed to higher heat stress than higher latitude countries. We further show that evaporative coolers are less effective in tropical regions than in the extra tropics. Finally, we show that neither low nor high efficiency coolers are sufficient to return Africa to current levels of heat stress under climate change.

ES cell cycle rates affect gene targeting frequencies.

We have investigated the gene targeting frequency at the hprt locus in a range of embryonic stem cell lines selected for variations in cell cycle parameters. Our results show that targeting frequency varies with cell line by as much as 12-fold between nonisogenic lines and 3-fold between isogenic lines and that a nonisogenic line can support homologous recombination events by up to 21-fold more frequently than an isogenic line. This variation is consistent with both insertion and replacement vectors. These results can be explained by an inverse linear correlation of targeting frequencies with cell doubling times. Additionally, by reducing serum concentration in the culture medium the mean cell doubling time for R1 ES cells can be increased from 11.4 to 15.7 h, with a subsequent 15-fold decrease in gene targeting frequency. This change fits the correlation found for the different nonisogenic cell lines. Our observations have important implications when performing gene targeting experiments and explain some of the variation noted between experiments.

The management of massive lower gastrointestinal bleeding.

To evaluate what has been the most effective surgical treatment for massive lower gastrointestinal bleeding, we reviewed the records of 31 patients who underwent colon resection for hemodynamic instability and/or the need for continued transfusions. These 31 patients underwent either segmental colectomy (21 patients) or subtotal colectomy (10 patients). Resections were performed for diverticular disease (19 patients), angiodysplasia (eight patients), acute ulceration (three patients), and polyps (one patient). The re-bleeding rate (mean follow-up 1 year) for subtotal colectomy was 0 per cent, segmental resection with positive angiography was 14 per cent, and segmental resection with negative angiography was 42 per cent. The complication rate including myocardial infarction, ARDS, pneumonia, and renal failure was highest (83 per cent) in those patients receiving segmental resection with a negative angiogram. The mortality rate was also highest for segmental resection patients with negative angiography (57 per cent). The results of this review suggest that segmental resection should be performed when the bleeding site is identified angiographically. Subtotal colectomy should be reserved for massive bleeding with negative angiography.

Fasted state impedes recovery of porcine hepatic oxygen consumption after warm hepatic ischemia.

The most effective means to prepare the hepatic donor liver for harvest, preservation, and transplantation are not known. Studies have shown that in combination with an injury to the liver, fasting reduces hepatic function. This study randomized 20 market pigs, 20 to 45 kg, to an overnight fast (fed group) or a 42-hour fast (fasted group). Under general anesthetic perfusion of the portal vein and hepatic artery were controlled. Studies were performed at high flow (30 ml/min/kg portal flow and 10 ml/min/kg arterial flow) and after a 90-minute period of warm ischemia (no flow). Flow was restored at 25% of the original (low flow), then increased to 50% of the original (medium flow). After the ischemic insult, the fed group improved hepatic oxygen consumption at a faster rate than the fasted group (p less than 0.05 by ANOVA). In addition, significant differences were noted between the fed and fasted groups in the amount of insulin delivered by the portal venous system to the liver (p less than 0.001 by ANOVA). Hepatic oxygen consumption was related to insulin delivery (r2 = 0.46; p less than 0.001) for both groups. The data suggest that acute changes in the nutritional status of both the donor and the recipient may affect hepatic recovery from ischemia.