A STAT4 variant increases liver fibrosis risk in Caucasian patients with chronic hepatitis B

BACKGROUND

Host genetic modifiers of the natural history of chronic hepatitis B (CHB) remain poorly understood. Recently, a genome-wide association study (GWAS)-identified polymorphism in the STAT4 gene that contributes to the risk for hepatocellular carcinoma (HCC) was shown to be associated with the full spectrum of hepatitis B virus (HBV) outcomes in Asian patients. However, the functional mechanisms for this effect are unknown and the role of the variant in modulating HBV disease in Caucasians has not been investigated.

AIMS

To determine whether STAT4 genetic variation is associated with liver injury in Caucasian patients with CHB and to investigate potential mechanisms mediating this effect.

METHODS

STAT4 rs7574865 was genotyped in 1085 subjects (830 with CHB and 255 healthy controls). STAT4 expression in liver, PBMCs and NK cells, STAT4 phosphorylation and secretion of interferon-gamma (IFN-γ) according to STAT4 genetic variation was examined.

RESULTS

STAT4 rs7574865 genotype was independently associated with hepatic inflammation (OR: 1.42, 95% CI: 1.07-2.06, P = 0.02) and advanced fibrosis (OR: 1.83, 95% CI: 1.19-2.83, P = 0.006). The minor allele frequency of rs7574865 was significantly lower than that in healthy controls. rs7574865 GG risk carriers expressed lower levels of STAT4 in liver, PBMCs and in NK cells, while NK cells from patients with the risk genotype had impaired STAT4 phosphorylation following stimulation with IL-12/IL-18 and a reduction in secretion of IFN-γ.

CONCLUSION

Genetic susceptibility to HBV persistence, hepatic inflammation and fibrosis in Caucasians associates with STAT4 rs7574865 variant. Downstream effects on NK cell function through STAT4 phosphorylation-dependent IFN-γ production likely contribute to these effects.

Non-local means filter denoising for DEXA images

Dual high and low energy images of Dual Energy X-ray Absorptiometry (DEXA) suffer from noises due to the use of weak amount of X-rays. Denoising these DEXA images could be a key process to enhance and improve a Bone Mineral Density (BMD) map which is derived from a pair of high and low energy images. This could further improve the accuracy of diagnosis of bone fractures, osteoporosis, and etc. In this paper, we present a denoising technique for dual high and low energy images of DEXA via non-local means filter (NLMF). The noise of dual DEXA images is modeled based on both source and detector noises of a DEXA system. Then, the parameters of the proposed NLMF are optimized for denoising utilizing the experimental data from uniform phantoms. The optimized NLMF is tested and verified with the DEXA images of the uniform phantoms and real human spine. The quantitative evaluation shows the improvement of Signal-to-Noise Ratio (SNR) for the high and low phantom images on the order of 30.36% and 27.02% and for the high and low real spine images on the order of 22.28% and 33.43%, respectively. Our work suggests that denoising via NLMF could be a key preprocessing process for clinical DEXA imaging.

Conscious or unconscious: The impact of sedation choice on colon adenoma detection

AIM: To determine if anesthesiologist-monitored use of propofol results in improved detection of adenomas when compared with routine conscious sedation.

METHODS: This retrospective study was conducted at two separate hospital-based endoscopy units where approximately 12 000 endoscopic procedures are performed annually, with one endoscopy unit exclusively using anesthesiologist-monitored propofol. Three thousand two hundred and fifty-two patients underwent initial screening or surveillance colonoscopies. Our primary end point was the adenoma detection rate, defined as the number of patients in whom at least one adenoma was found, associated with the type of sedation.

RESULTS: Three thousand two hundred and fifty-two outpatient colonoscopies were performed by five selected endoscopists. At least one adenoma was detected in 27.6% of patients (95% CI = 26.0-29.1) with no difference in the detection rate between the anesthesiologist -propofol and group and the gastroenterologist-midazolam/fentanyl group (28.1% vs 27.1%, P = 0.53).

CONCLUSION: The type of sedation used during co-lonoscopy does not affect the number of patients in whom adenomatous polyps are detected.

Improvement of steatosis after interferon therapy in HCV genotype 4 is related to weight loss

INTRODUCTION

Hepatic steatosis is common in patients with chronic hepatitis C virus (HCV) infection, and its occurrence may be related to both host and viral factors. Relationship between improvement in steatosis and response to anti-viral treatment remains unclear. This study assessed the factors associated with steatosis in patients infected with genotype 4 HCV, and to correlate degree of changes in steatosis with host factors and response to treatment.

METHODS

Records of 175 patients with chronic genotype 4 HCV infection, who had received interferon and ribavirin combination therapy, were reviewed retrospectively to extract data on body mass index (BMI), presence of diabetes mellitus, and liver histology findings. Paired BMI data and liver biopsies (pre- and 24-weeks post-treatment) were available in 86 patients. Baseline steatosis and its changes (before and after treatment) were the dependent variables in a univariate and multivariate analyses.

RESULTS

Steatosis was found in 88/175 (50.3%) of baseline biopsies. Its presence was related to baseline BMI (r=0.33, P<0.01), but not with viral load, or grade of liver inflammation or fibrosis. On follow up, improvement in steatosis was significantly associated with degree of weight loss but not with response to anti-viral treatment.

CONCLUSION

Steatosis is common in genotype 4 HCV infection, and its presence appears to be related to high BMI, but not to viral load or degree of liver injury.

How common is polycystic ovary syndrome in recurrent miscarriage?

The association between polycystic ovary syndrome (PCOS) and recurrent miscarriage (RM) has been long established, but the relative importance of this condition as a cause of RM is far from clear. Previous studies on the prevalence of PCOS in RM have been hampered by a lack of objective and universally accepted criteria for the diagnosis of PCOS, resulting in considerable controversy. However, the Rotterdam criteria have since been accepted as the gold standard for diagnosis of PCOS, and therefore these criteria have been used to produce a much clearer and more objective assessment of the prevalence of PCOS in RM. Three hundred women with recurrent miscarriage were studied. A diagnosis of PCOS was established via measurement of cycle length and day 21 serum progesterone, determination of the free androgen index and pelvic ultrasonography. All ultrasound reports prior to publication of the Rotterdam criteria were reviewed, ensuring consistency in the diagnosis of a polycystic ovary. Ultrasound scans of 27 patients confirmed polycystic ovaries with a further 10 scans suggestive of polycystic ovaries, but with insufficient information for the Rotterdam criteria to be applied. Hence, 27-37 (9.0-12%) patients presented with ultrasonographic polycystic ovaries. Using the Rotterdam criteria, 25-30 (8.3-10%) patients had PCOS. It is concluded that the prevalence of PCOS in RM is considerably lower than has previously been accepted.

To close or not to close? A systematic review and a meta-analysis of peritoneal non-closure and adhesion formation after caesarean section

Many gynaecologists do not currently close the peritoneum after caesarean section (CS). Recently, several studies examining adhesion formation after repeat CS appear to favour closure of the peritoneum after caesarean section. We performed a systematic review of the current available evidence with regard to the long-term outcome, mainly in terms of adhesion formation after closure versus non-closure of peritoneum during CS. We undertook a literature search between January 1995 and February 2008 using MEDLINE, Pubmed, EMBASE, Cochrane central controlled trials register and Cochrane pregnancy and childbirth group trials register. We also had searched all the references cited in the relevant studies. Both English and non-English language papers were included. Prospective studies which compared peritoneal closure versus non-closure during CS in terms of adhesion formation were included. Studies were included if they had a primary objective to examine adhesion formation in a repeat caesarean section, had a clear study design, had an adhesion scoring system, excluded patients who had adhesions in the primary caesarean section or interim surgeries after the primary caesarean section, and had no usage of anti-adhesion agents in the primary caesarean section. Retrospective studies which were performed by case-notes review alone, were excluded. Eleven studies were identified via our search strategy. Five were retrospective and six were prospective. Out of the eleven studies, three satisfied the inclusion criteria and were included (n=249); two studies were follow-ups of RCTs and one was not randomised. Out of 249 women included in the analysis, 110 had peritoneal closure during CS whereas the other 139 did not have peritoneal closure. Meta-analysis was performed using the two randomised studies plus (i) the unadjusted estimate from the non-randomised study and (ii) the reported adjusted estimate, adjusted for baseline differences in the groups. Non-closure of the peritoneum during CS resulted in a significantly increased likelihood of adhesion formation in both meta-analyses--OR (95% CI): (i) 2.60 (1.48-4.56) and (ii) 4.23 (2.06-8.69). This systematic review has demonstrated that according to current data in the literature, there is some evidence to suggest that non-closure of the peritoneum after caesarean section is associated with more adhesion formation compared to closure.

Laparoscopy or laparotomy for distal tubal surgery? A meta-analysis

Of couples with subfertility, 25% have complete or partial blockage of the fallopian tube. Since the advent of in vitro fertilization (IVF), the role of tubal surgery has diminished. However, this type of surgery continues to be undertaken on selected patients with mild tubal disease, and in those with severe tubal disease, in centres where IVF is not available. This systematic review was undertaken to compare pregnancy outcomes after laparoscopic surgery with that of open microsurgical technique. Studies comparing laparoscopic techniques with conventional microsurgery requiring laparotomy for treatment of distal tubal disease were included. The relevant trials were identified from Cochrane Menstrual Disorders and Subfertility Groups of Specialised Register of Controlled Trials (searched up to July 2005). The following strategies were adapted using the OVID platform, MEDLINE (1966 to July 2005), Cochrane Central Register of Control Trials, CENTRAL, and EMBASE (1980 to July 2005). Outcomes analysed were: 'take home baby' rate, intrauterine pregnancy rate and ectopic pregnancy rate per pregnancy. Subgroup analysis was carried out to compare intrauterine pregnancy rate in the laparoscopy and conventional microsurgery groups according to the extent of tubal damage. Six relevant studies were identified. Overall, no significant difference was observed in the intrauterine pregnancy rate between the two groups, combined OR 1.32 (95% confidence interval [CI], 0.58 - 3.02). For patients with mild tubal disease, there was no significant difference in the intrauterine pregnancy rate between treatment and control group, OR 1.06 (95% CI, 0.42 - 2.70). For patients with severe tubal disease, there was a significantly increased intrauterine pregnancy rate in the laparotomy group, OR 0.34 (95% CI, 0.14 - 0.86). Appropriate patient selection is the main factor affecting outcome in terms of fertility. These data do not indicate a significant difference in pregnancy rates between open and laparoscopic techniques for lesser degrees of tubal damage. Other factors, such as costs and hospital stay, will come into the decision making, and are likely to favour laparoscopic techniques. If a decision is made to open the badly damaged tubes of a patient, then an open microsurgical technique should be employed.

An RCT of metformin versus orlistat for the management of obese anovulatory women

BACKGROUND

Treatment of obesity-related anovulation poses a significant clinical challenge. Occasionally, the use of antiobesity medications such as orlistat or insulin sensitizing agents such as metformin is sometimes indicated in these patients. This study aimed to compare the effects of metformin and orlistat for improving ovulation in obese anovulatory women.

METHODS

This was an open-label RCT. A total of 40 women were randomized to receive either metformin (n = 20) or orlistat (n = 20). BMI as well as the androgen profile and the ovulatory status were assessed at baseline and at four weekly intervals for 3 months. Different anthropometric and endocrine parameters were also assessed as possible predictors of ovulation.

RESULTS

There was no significant difference between the two study arms regarding the ovulation rate for metformin and orlistat [40% (n = 8/20) and 25% (n = 5/20), respectively, P = 0.31]. Both arms showed a significant drop in the BMI, testosterone and androstendione concentrations (P < 0.05), but there was no difference between the two arms. Patients who ovulated had significantly lower concentrations of baseline LH, androstendione, dehydroepiandrosterone and free androgen index (P < 0.05). Among these factors, a low baseline LH was found to be the only independent predictor of ovulation (area under curve, 0.85).

CONCLUSIONS

Both metformin and orlistat show a similar effect on weight loss, ovulation rates and androgen concentrations. However, the effects on ovulation rates need to be confirmed in larger studies. The presence of a low baseline serum LH was found to be the most important predictor of ovulation. The study was registered at clinicaltrials.gov. NCT00292799.

Effects of cigarette smoking upon clinical outcomes of assisted reproduction: a meta-analysis

BACKGROUND

The aim of this meta-analysis was to investigate whether any difference exists in success rate of clinical outcomes of assisted reproductive technologies (ART) between women who actively smoke cigarettes at the time of treatment and those who do not.

METHODS

An intensive computerized search was conducted on published literature from eight databases, using search terms related to smoking, assisted reproduction and outcome measures. Eligible studies compared outcomes of ART between cigarette smoking patients and a control group of non-smoking patients and reported on live birth rate per cycle, clinical pregnancy rate per cycle, ectopic pregnancy rate per pregnancy or spontaneous miscarriage rate per pregnancy, and 21 studies were included in the meta-analyses. Pooled odds ratios (OR) and 95% confidence intervals (CI) were calculated for the data, and statistical heterogeneity was tested for using chi(2) and I(2) values. A systematic review examined the effect of smoking upon fertilization rates across 17 studies.

RESULTS

Smoking patients demonstrated significantly lower odds of live birth per cycle (OR 0.54, 95% CI 0.30-0.99), significantly lower odds of clinical pregnancy per cycle (OR 0.56, 95% CI 0.43-0.73), significantly higher odds of spontaneous miscarriage (OR 2.65, 95% CI 1.33-5.30) and significantly higher odds of ectopic pregnancy (OR 15.69, 95% CI 2.87-85.76). A systematic literature review revealed that fertilization rates were not significantly different between smoking and non-smoking groups in most studies.

CONCLUSIONS

This meta-analysis provides compelling evidence for a significant negative effect of cigarette smoking upon clinical outcomes of ART and should be presented to infertility patients who smoke cigarettes in order to optimize success rates.

Randomized controlled trial comparing laparoscopic ovarian diathermy with clomiphene citrate as a first-line method of ovulation induction in women with polycystic ovary syndrome

BACKGROUND

Laparoscopic ovarian diathermy (LOD) is currently accepted as a successful second-line treatment for ovulation induction (OI) in clomiphene citrate (CC)-resistant women with polycystic ovary syndrome (PCOS). The aim of this study was to test the hypothesis that LOD may be superior to CC as a first-line treatment.

METHODS

The study included 72 anovulatory women with PCOS who were randomized to LOD (n = 36) or CC (n = 36). Women who remained anovulatory after LOD were offered CC. Similarly, women receiving CC who failed to ovulate or conceive were offered LOD. Pregnancy rates were compared between the two groups using chi(2) and odds ratio with 95% confidence interval (OR, 95% CI).

RESULTS

After randomization, six women conceived before starting treatment and another patient postponed treatment. The remaining 65 women received the treatment (33 underwent LOD and 32 received CC). After the primary treatment, more pregnancies (44%) occurred in women receiving CC than in those undergoing LOD (27%), although the difference did not reach statistical significance [P = 0.13, OR 2.1 (0.7 - 5.8)]. After adding the second treatment, the pregnancy rate was still higher, but to a less extent, in the CC group [63% versus 52%, P = 0.2, OR 1.6 (0.6 - 4.2)].

CONCLUSIONS

LOD is not superior to CC as a first-line method of OI in women with PCOS. The trial is registered with ClinicalTrials.gov with an identifier number NCT00220545.

Effect of increased body mass index on oocyte and embryo quality in IVF patients

Obesity may have an adverse effect on the outcome of IVF/intracytoplasmic sperm injection (ICSI) treatment. In this study, the effects of increased body mass index (BMI) on oocyte and embryo quality during IVF cycles were studied. A retrospective analysis of 426 IVF/ICSI cycles was performed. Cycles were classified according to the BMI: normal BMI (19-24.9 kg/m(2)), overweight (25-29.9 kg/m(2)) and obese (> or = 30 kg/m(2)). Cycles were further stratified based on age (group 1, < 35 years; group 2, > or = 35 years). Markers of oocyte quality (number of oocytes inseminated and fertilization rate) and embryo quality (utilization rate, number of embryos discarded and cryopreserved, and mean embryo grade) were examined. In group 1, obesity had a significant adverse effect on the mean embryo grade (P = 0.02), the embryo utilization rate (P = 0.01), number of embryos discarded (P = 0.007) and cryopreserved (P < 0.05). In group 2, there was no difference in markers of embryo quality between the three BMI ranks. Obesity did not have any significant effect on markers of oocyte quality or clinical pregnancy rates. In conclusion, obesity may adversely affect embryo quality in young women (<35 years) undergoing IVF/ICSI, while the oocyte quality is not affected.

The impact of obesity on female reproductive function

Obesity may be described as the new worldwide epidemic, and its serious impact on morbidity and mortality are well known. As more and more women become obese, the reproductive problems associated with obesity present an ever-growing challenge to physicians involved in their fertility care. The spectrum of reproductive problems associated with obesity encompasses a wide range of disorders including infertility problems, miscarriage and pregnancy complications. In this review, we aim to discuss the impact of obesity on the various aspects of female reproductive function with focus on the clinical aspects of fertility problems in obese women. We finally comment on the available therapeutic options available to this group of women.

Randomized controlled trial of three doses of letrozole for ovulation induction in patients with unexplained infertility

The aromatase inhibitor letrozole is a novel agent that can be used as an alternative to clomiphene citrate for ovulation induction in patients with unexplained infertility. The dose of letrozole used has varied between studies, and this study aimed to compare the three most commonly used doses: 2.5, 5 and 7.5 mg. A total of 179 patients were randomly recruited in this prospective study with 58, 61 and 60 patients in each dosage group respectively. This study reports a significantly higher (P < 0.05) number of follicles (total, > 14 mm and > or = 18 mm) on the day of administration of human chorionic gonadotrophin in the 7.5 mg group, associated with significantly fewer (P < 0.05) days of stimulation. However the pregnancy and miscarriage rates were similar in the three groups. In conclusion, it seems that the use of higher doses of letrozole offers no advantage in terms of pregnancy rates over the lower (2.5 mg) dose.

Impact of high body mass index on endometrial morphology and function in the peri-implantation period in women with recurrent miscarriage

There is evidence that women with a high body mass index may have a higher risk of miscarriage. It is not known if this is due to an endometrial or embryo defect. The aim of this retrospective study was to examine markers of endometrial function in overweight and obese women with recurrent unexplained miscarriage. A total of 136 women were included in the study and classified according to their body mass index (BMI) into two groups, normal BMI (< 25 kg/m(2), n = 70) and high BMI (> or = 25 kg/m(2), n = 66). Endometrial morphology was examined in all patients. A subgroup of 28 patients was examined for endometrial oestrogen and progesterone receptors in different components of the endometrium, and in a further subgroup of 28 patients, endometrial glandular leukaemia inhibitory factor and leukocyte populations were examined. A modest increase in the BMI (30.4 +/- 0.71 kg/m(2)) does not have a significant impact on endometrial steroid receptors, leukocyte populations or endometrial morphology. However, there was a significant negative correlation between endometrial glandular leukaemia inhibitory factor concentrations and the BMI (r = -0.4, P = 0.02), warranting further investigation in prospective studies that include patients with higher BMI levels.

Fluid and pharmacological agents for adhesion prevention after gynaecological surgery

BACKGROUND

Pelvic surgery is associated with high rates of both de novo adhesion formation and adhesion reformation. Since subsequent fertility is reduced with increasing severity of periadnexal adhesions, pelvic adhesions will remain a clinical problem in infertility patients. Steroids, antihistamines and heparin were amongst the first substances to be advocated for adhesion prevention. More recently icodextrin 4%, hyaluronic acid agents and SprayGel have been used. This review aims to evaluate the role of fluid and pharmacological agents in the prevention of adhesions in fertility-conserving gynaecological surgery.

OBJECTIVES

To investigate fluid and pharmacological agents for adhesion prevention when used as adjuvants during pelvic surgery.

SEARCH STRATEGY

This review has drawn on the search strategy developed for the Menstrual Disorders and Subfertility Group. The following databases were searched: the Cochrane Menstrual Disorders and Subfertility Group Specialised Register, Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE and EMBASE.

SELECTION CRITERIA

Randomised controlled trials investigating the use of fluid and pharmacological agents to prevent adhesion formation after fertility-conserving gynaecological surgery.

DATA COLLECTION AND ANALYSIS

Data extraction and analysis was performed independently by two authors (Metwally M and Watson A). Two-by-two tables were generated for dichotomous outcomes and expressed as odds ratios (OR) with 95% confidence intervals (CI). For continuous outcomes a standardised mean difference was used.

MAIN RESULTS

There is no evidence of benefit from the use of steroids, dextran or other pharmacological agents in any of the outcomes. The use of hyaluronic acid agents may decrease adhesion formation (OR 0.31, 95% CI 0.19 to 0.51) and prevent the deterioration of pre-existing adhesions (OR 0.28 (95% CI 0.12 to 0.66). There is insufficient evidence for the use of icodextrin 4% or SprayGel as adhesion-preventing agents. None of the studied agents has been shown to improve the pregnancy rate when used as an adjunct during pelvic surgery.

AUTHORS' CONCLUSIONS

The current evidence for the use of fluid and pharmacological agents for the prevention of adhesions is limited. There is no evidence on any benefit for improving pregnancy outcomes when pharmacological and fluid agents are used as an adjunct during pelvic surgery. There is insufficient evidence for the use of the following agents: steroids, icodextrin 4%, SprayGel and dextran in improving adhesions following surgery. There is some evidence that hyaluronic acid agents may decrease the proportion of adhesions and prevent the deterioration of pre existing adhesions. However, due to the limited number of studies available, this evidence should be interpreted with caution and further studies are needed.

Enriched Gas Pressure Cycling Process For Depleted Heavy Oil Reservoirs

Abstract

The majority of Canadian heavy oil reservoirs cannot be exploited, after primary production, by thermal recovery as formations are thin or bottom water exists. Thermal process applications to these reservoirs are not promising due to excessive heat losses to the surrounding formations. Solvent vapour extraction process (VAPEX) and other similar processes are faced with major problems, mainly reservoir depletion, existence of channels "wormholes" following primary production and high costs of new horizontal wells, facilities and solvent.

The proposed process is based on pressure cycling of depleted heavy oil reservoirs. It involves injection of natural gas with a specified concentration of vapourized propane into a number of wells for a period of time to pressurize the producing channels connected with injection wells and surrounding reservoir volume. After reaching a pressure target, injection is terminated and the blowdown phase is started. Production is continued until most of the effects of the injection phase are diminished, then the cycle is repeated a number of times. The composition of the injected enriched gas is selected based on the expected reservoir pressure range during the pressurizing phase to achieve high solubility of propane in oil. The process involves relatively low injection rates and to be operated at low pressures and has the potential for low injectant losses and effective oil recovery.

This paper reviews the proposed enriched gas pressure cycling process and discusses the various mechanisms controlling it. The process appears to be a viable improved recovery method for depleted heavy oil reservoirs if appropriate reservoir conditions can be achieved. Incremental recovery is expected to be dependent on the target application, process design and number of cycles. The process appears to have many attractive features. It is designed to utilize reservoir conditions created by primary recovery. It requires no new wells, utilizes existing wells, requires reasonable volumes of solvent, requires no water treating or major facilities and the associated risk with its application is minimal.

Introduction

The observed primary production of many heavy oil reservoirs in Alberta and Saskatchewan such as Lindbergh, Frog Lake and many Lloydminister fields, has been significantly higher than predicted by Darcy flow models. Many of these reservoirs produced over 10% of the original-oil-in-place (OOIP) during primary and many of them are currently depleted or approaching depletion. However, at the termination of primary recovery production, 80 to 90% of the OOIP remains in the reservoirs. An economically viable post-primary improved oil recovery process would add substantially to heavy oil reserves.

The most efficient method of increasing heavy oil mobility has been reservoir heating by thermal recovery methods, based mainly on steam or air injection. However, the majority of Canadian heavy oil reservoirs cannot be exploited economically after the primary production phase by thermal recovery as formations are thin or bottomwater exists. Over 80% of Canadian heavy oil reservoirs are less than 6.0 m thick(1). Applications of steam processes to these reservoirs, including the steam assisted gravity drainage process (SAGD), are not promising due to excessive heat losses to surrounding formations.

Determination of the maximum product yield from glucoamylase-producing Aspergillus niger grown in the recycling fermentor

Aspergillus niger has been grown in glucose- and maltose-limited recycling cultures to determine the maximum growth yield, the maximum product yield for glucoamylase production, and the maintenance requirements at very slow specific growth rates. Using the linear equation for substrate utilization, and using the experimental data from both recycling experiments, both the maximum growth yield, Yxsm, and the maximum product yield, Ypsm, could be determined. The values estimated were 157 g biomass per mol maltose for Yxsm and 100 g protein per mol maltose for Ypsm. Expressed on a C1-basis these values are 0.52 and 0.36 C-mole per C-mol for respectively Yxsm and Ypsm. The found value for Ypsm is half the value found for alkaline serine protease production in Bacillus licheniformis, and it can be concluded that formation of extracellular protein is more energy consuming in filamentous fungi than in prokaryotic organisms. Maintenance requirements are no significant factor during growth of Aspergillus niger, and reported maintenance requirements are most probably due to differentiation.

Bioenergetic consequences of glucoamylase production in carbon-limited chemostat cultures of Aspergillus niger

Aspergillus niger has been grown in glucose- and maltose-limited continuous cultures to determine the bioenergetic consequences of the production of the extracellular enzyme glucoamylase. Growth yields (g biomass per mol substrate) were high, indicating that growth was very efficient and protein production for biomass was not exceedingly energy consuming. It has been found that the energy costs for the production of this extracellular enzyme is very high. Depending on the efficiency of energy conservation the glucoamylase protein yield on ATP is between 1.3 and 2.6 g protein per mol ATP, which is equal or less than 10% of the theoretical maximum of 25.5. These high energy costs most probably have to be invested in the process of excretion. A comparison between an industrial over-producing strain and the wild type Aspergillus niger showed that this over-producing strain most probably is a regulatory mutant. Two regions of specific growth rates could be determined (one at specific growth rates lower and one at specific growth rates higher than 0.1 h-1), which are characterized by differences in mycelium morphology and a significant deviation from linearity in the linear equation for substrate utilization. Analysis of the region of specific growth rates higher than 0.1 h-1 yielded maintenance requirements of virtual zero. It has been concluded that for a good analysis of the growth behaviour of filamentour fungi the linear equation for substrate utilization is not suitable, since it contains no term for the process of differentiation.

Effect Of Gaseous Additives On Steam Processes For Lindbergh Field, Alberta

Abstract

Performance Of steam stimulation or steam flooding processes can be improved by the use of an appropriate gaseous additive such as carbon dioxide or methane. Several beneficial effects are postulated such as improving steam injectivity, increasing the size of the heated areas and providing additional drive energy which is likely to increase production rate. The over-all effect of these mechanisms on performance is difficult to predict.

A laboratory program for the Lindbergh Field (Cummings Formation) was conducted to investigate the effect of carbon dioxide and methane on the performance of steam processes and investigate the differences in performance between simultaneous injection of steam and a gaseous additive and injection of a gas slug prior to steam injection. A total of eight coreflood tests were carried out, employing core and fluids from the Cummings zone of the Lindbergh Field. In addition, a validated numerical model was used to evaluate the impact of adding non-condensible gases to steam under various conditions.

Results indicate that the presence of a non-condensible gas improved steam injectivity. Injectivity improvement was most pronounced when a gas slug was injected prior to steam injection, but the presence of a non-condensible gas with steam did not improve recovery and resulted in much higher residual oil saturation compared to steam injection alone. Results from numerical simulation work supported these observations.

Introduction

PanCanadian Petroleum Limited has a significant land position in the Lindbergh Field located near the town of Elk Point in northeastern Alberta. Formations of the Upper Mannville Group in this field are generally unconsolidated sands and contain heavy oil of 12 to 14 °C API. The Cummings formation, at a depth of about 600 m. contains the majority of the Upper Mannville oil in place and is considered to have good potential under primary and thermal recovery. Its thickness varies up to 20 m.

The main purpose of the work reported in this paper was to evaluate the effect of gaseous additives on the performance of steam stimulation and steamflooding processes for the Cummings Formation. It should be noted that the over-all effect of gaseous additives on these processes is difficult to predict. Several potentially beneficial mechanisms could be assumed such as improving injectivity, increasing the heated volume, reducing interfacial tension between oil and water, providing additional reservoir energy by solution gas mechanisms, etc. But, gaseous additives could also have detrimental effects due to the presence of a free gas saturation and the associated effect of reducing relative permeability to oil.

Limited field tests have been reported to date on the effect of gaseous additives on steam processes. Moreover, the published laboratory and simulation studies have led to some conflicting results. Additional investigation was necessary for the Cummings formation.

Literature Review

Meldau(1) reported the results of air-steam stimulation field tests in Paris Valley, California. The addition of air to steam nearly doubled oil production. He attributed this to several mechanisms including displacement of residual oil by trapped gas, gas drive and increased reservoir pressure.