Therapeutic delivery of cyclin A2 induces myocardial regeneration and enhances cardiac function in ischemic heart failure

BACKGROUND

Heart failure is a global health concern. As a novel therapeutic strategy, the induction of endogenous myocardial regeneration was investigated by initiating cardiomyocyte mitosis by expressing the cell cycle regulator cyclin A2.

METHODS AND RESULTS

Lewis rats underwent left anterior descending coronary artery ligation followed by peri-infarct intramyocardial delivery of adenoviral vector expressing cyclin A2 (n =32) or empty adeno-null (n =32). Cyclin A2 expression was characterized by Western Blot and immunohistochemistry. Six weeks after surgery, in vivo myocardial function was analyzed using an ascending aortic flow probe and pressure-volume catheter. DNA synthesis was analyzed by proliferating cell nuclear antigen (PCNA), Ki-67, and BrdU. Mitosis was analyzed by phosphohistone-H3 expression. Myofilament density and ventricular geometry were assessed. Cyclin A2 levels peaked at 2 weeks and tapered off by 4 weeks. Borderzone cardiomyocyte cell cycle activation was demonstrated by increased PCNA (40.1+/-2.6 versus 9.3+/-1.1; P<0.0001), Ki-67 (46.3+/-7.2 versus 20.4+/-6.0; P<0.0001), BrdU (44.2+/-13.7 versus 5.2+/-5.2; P<0.05), and phosphohistone-H3 (12.7+/-1.4 versus 0+/-0; P<0.0001) positive cells/hpf. Cyclin A2 hearts demonstrated increased borderzone myofilament density (39.8+/-1.1 versus 31.8+/-1.0 cells/hpf; P=0.0011). Borderzone wall thickness was greater in cyclin A2 hearts (1.7+/-0.4 versus 1.4+/-0.04 mm; P<0.0001). Cyclin A2 animals manifested improved hemodynamics: Pmax (70.6+/-8.9 versus 60.4+/-11.8 mm Hg; P=0.017), max dP/dt (3000+/-588 versus 2500+/-643 mm Hg/sec; P<0.05), preload adjusted maximal power (5.75+/-4.40 versus 2.75+/-0.98 mWatts/microL2; P<0.05), and cardiac output (26.8+/-3.7 versus 22.7+/-2.6 mL/min; P=0.004).

CONCLUSIONS

A therapeutic strategy of cyclin A2 expression via gene transfer induced cardiomyocyte cell cycle activation yielded increased borderzone myofilament density and improved myocardial function. This approach of inducing endogenous myocardial regeneration provides proof-of-concept evidence that cyclin A2 may ultimately serve as an efficient, alternative therapy for heart failure.

Neovasculogenic Therapy to Augment Perfusion and Preserve Viability in Ischemic Cardiomyopathy

BACKGROUND

Ischemic cardiomyopathy is a global health concern with limited therapy. We recently described endogenous revascularization utilizing granulocyte-macrophage colony stimulating factor (GMCSF) to induce endothelial progenitor cell (EPC) production and intramyocardial stromal cell-derived factor-1alpha (SDF) as a specific EPC chemokine. The EPC-mediated neovascularization and enhancement of myocardial function was observed. In this study we examined the regional biologic mechanisms underlying this therapy.

METHODS

Lewis rats underwent left anterior descending coronary artery (LAD) ligation and developed ischemic cardiomyopathy over 6 weeks. Three weeks after ligation, the animals received either subcutaneous GMCSF and intramyocardial SDF injections or saline injections as control. Six weeks after LAD ligation circulating EPC density was studied by flow cytometry. Quadruple immunofluorescent vessel staining for mature, proliferating vasculature was performed. Confocal angiography was utilized to identify fluorescein lectin-lined vessels to assess perfusion. Ischemia reversal was studied by measuring myocardial adenosine triphosphate (ATP) levels. Myocardial viability was assayed by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling detection of apoptosis and quantitation of myofilament density.

RESULTS

The GMCSF/SDF therapy enhanced circulating leukocyte (13.1 +/- 4.5 x 10(6) vs 3.1 +/- 0.5 x 10(6)/cc, p = 0.001, n = 6) and EPC (14.2 +/- 6.6 vs 2.2 +/- 2.1/cc, p = 0.001, n = 6) concentrations. Tetraimmunofluorescent labeling demonstrated enhanced stable vasculature with this therapy (39.2 +/- 8.1 vs 25.4 +/- 5.1%, p = 0.006, n = 7). Enhanced perfusion was shown by confocal microangiography of borderzone lectin-labeled vessels (28.2 +/- 5.4 vs 11.5 +/- 3.0 vessels/high power field [hpf], p = 0.00001, n = 10). Ischemia reversal was demonstrated by enhanced cellular ATP levels in the GMCSF/SDF borderzone myocardium (102.5 +/- 31.0 vs 26.9 +/- 4.1 nmol/g, p = 0.008, n = 5). Borderzone cardiomyocyte viability was noted by decreased apoptosis (3.2 +/- 1.4% vs 5.4 +/- 1.0%, p = 0.004, n = 10) and enhanced cardiomyocyte density (40.0 +/- 5.6 vs 27.0 +/- 6 myofilaments/hpf, p = 0.01, n=10).

CONCLUSIONS

Endogenous revascularization for ischemic cardiomyopathy utilizing GMCSF EPC upregulation and SDF EPC chemokinesis upregulates circulating EPCs, enhances vascular stability, and augments myocardial function by enhancing perfusion, reversing cellular ischemia, and increasing cardiomyocyte viability.

Fructose 1,6-diphosphate administration attenuates post-ischemic ventricular dysfunction

BACKGROUND

Cardiomyocyte energy production during ischemia depends upon anaerobic glycolysis inefficiently yielding two ATP per glucose. Substrate augmentation with fructose 1,6-diphosphate (FDP) bypasses the ATP consuming steps of glucokinase and phosphofructokinase thus yielding four ATP per FDP. This study evaluated the impact of FDP administration on myocardial function after acute ischemia.

METHODS

Male Wistar rats, 250-300 g, underwent 30 min occlusion of the left anterior descending coronary artery followed by 30 min reperfusion. Immediately prior to both ischemia and reperfusion, animals received an intravenous bolus of FDP or saline control. After 30 min reperfusion, myocardial function was evaluated with a left ventricular intracavitary pressure/volume conductance microcatheter. For bioenergetics studies, myocardium was isolated at 5 min of ischemia and assayed for ATP levels.

RESULTS

Compared to controls (n=8), FDP animals (n=8) demonstrated significantly improved maximal left ventricular pressure (100.5+/-5.4 mmHg versus 69.1+/-1.9 mmHg; p<0.0005), dP/dt (5296+/-531 mmHg/s versus 2940+/-175 mmHg/s; p<0.0028), ejection fraction (29.1+/-1.7% versus 20.4+/-1.4%; p<0.0017), and preload adjusted maximal power (59.3+/-5.0 mW/microL(2) versus 44.4+/-4.6 mW/microL(2); p<0.0477). Additionally, significantly enhanced ATP levels were observed in FDP animals (n=5) compared to controls (n=5) (535+/-156 nmol/g ischemic tissue versus 160+/-9.0 nmol/g ischemic tissue; p<0.0369).

CONCLUSIONS

The administration of the glycolytic intermediate, FDP, by intravenous injection, resulted in significantly improved myocardial function after ischemia and improved bioenergetics during ischemia.

Ethyl pyruvate enhances ATP levels, reduces oxidative stress and preserves cardiac function in a rat model of off-pump coronary bypass

BACKGROUND

Off-pump coronary artery bypass grafting is associated with transient periods of myocardial ischemia during revascularization resulting in myocardial contractile dysfunction and oxidative injury. The purpose of this study was to investigate the efficacy of ethyl pyruvate as a myocardial protective agent in a rat model of off-pump coronary artery bypass grafting associated with transient myocardial dysfunction without infarction.

METHODS

Wistar rats were subjected to transient ischemia via 10 min occlusion of the LAD coronary artery followed by 10 min of reperfusion. Animals received an IV bolus of Ringer's solution as a control (n=10) or Ringer's ethyl pyruvate (n=10) immediately before the initiation of ischemia and reperfusion. Myocardial ATP and lipid peroxidation levels were quantified for an estimation of energetics and oxidative stress, respectively. In vivo cardiac function was assessed throughout the ischemia and reperfusion periods.

RESULTS

Ethyl pyruvate significantly increased myocardial ATP levels compared to controls (2650+/-759 nmol/g versus 892+/-276 nmol/g, p=0.04). Myocardial oxidative stress was significantly reduced in animals treated with ethyl pyruvate compared to controls (70.4+/-2.6 nmol/g versus 81.8+/-2.4 nmol/g, p=0.04). dP/dt max and cardiac output were significantly greater in the ethyl pyruvate group compared to controls during ischemia and reperfusion.

CONCLUSIONS

Ethyl pyruvate enhances myocardial ATP levels, reduces oxidative stress, and preserves myocardial function in a model of transient ischemia/reperfusion injury not subject to myocardial infarction.

Body mass index and mortality in women: follow-up of the Canadian National Breast Screening Study cohort

OBJECTIVE

The present study was conducted to examine the relationship between obesity and all-cause mortality in women.

STUDY DESIGN AND SETTINGS

The subjects were women enrolled from 1980 to 1985 in a Canadian randomized trial, the National Breast Screening Study (NBSS) to evaluate the efficacy of mammographic screening. Mortality was ascertained by record linkage to the Canadian Mortality Data Base. Hazard ratios (HR) for the association between body mass index (BMI) and all-cause mortality were obtained from Cox proportional hazard regression models.

RESULTS

During an average follow-up period of 16.5 years, 2566 deaths were identified among the 49 165 women, age 40-59 y at enrollment. The risk of all-cause death increased linearly above a BMI of 22 kg/m(2) and the trend was statistically significant. The HR (and 95% confidence intervals) in the various categories of BMI (kg/m(2)) were: BMI<18.5: 1.12 (0.99-1.25); BMI 18.5-21.9: 1.00 (reference); BMI 22-24.9: 1.15 (1.11-1.18); BMI 25.0-27.9: 1.28 (1.24-1.32); BMI 28.0 -29.9: 1.34 (1.29-1.39); BMI 30.0-34.9: 1.30 (1.25,1.35); and BMI > or =35.0: 1.40 (1.33-1.47).

CONCLUSION

This study confirms the association of high BMI with increased all-cause mortality in women.

One year transgene expression with adeno-associated virus cardiac gene transfer

BACKGROUND

Adeno-associated virus (AAV) has shown promise as a vector for cardiac gene transfer given its ability to stably integrate into the host genome and its lack of immune reactivity. This study examined the feasibility of AAV-mediated myocardial gene transfer in mice, the animal which, because of transgenic technology, has become the disease model of choice for cardiovascular research.

METHODS

AAV encoding the cytomegalovirus promoter driven LacZ reporter gene (10(7) LacZ-forming units per animal) or vehicle control was injected into the hearts of young adult C57Bl/6 mice by a transdiaphragmatic approach. At one, two, three, six, and twelve months post-injection, cardiac function was assessed by transthoracic echocardiography and hearts were assayed by X-gal histochemical staining.

RESULTS

Echocardiography revealed normal left ventricular function in both AAV and control groups at all time points. X-gal staining of cryostat sections of hearts revealed uniform LacZ expression at all time points. There were minimal signs of immunologic infiltration by hematoxylin and eosin staining.

CONCLUSIONS

AAV-mediated myocardial gene transfer by transdiaphragmatic injection can be conducted safely and results in long-term expression of the LacZ gene for at least one year without causing significant inflammatory response or adversely affecting LV systolic function.

Creatine phosphate administration preserves myocardial function in a model of off-pump coronary revascularization

AIM

Off pump coronary artery bypass grafting (OPCAB) involves, and is occasionally impaired by obligatory regional myocardial ischemia, particularly with the use of proximal coronary in-flow occlusion techniques. Intracoronary shunts do not guarantee absence of distal ischemia given their small inner diameter and the presence of proximal coronary stenosis. Additional adjunctive measures to provide short-term myocardial protection may facilitate OPCAB. High-energy phosphate supplementation with creatine phosphate prior to ischemia may attenuate ischemic dysfunction.

METHODS

In a rodent model of a transient coronary occlusion and myocardial ischemia, 36 animals underwent preischemic intravenous infusion of either creatine phosphate or saline, 10 minutes of proximal left anterior descending (LAD) occlusion, and 10 minutes of reperfusion. Rats underwent continuous intracavitary pressure monitoring and cellular ATP levels were quantified using a luciferin/luciferase bioluminescence assay.

RESULTS

Within 2 minutes of ischemia onset, creatine phosphate animals exhibited statistically significant greater preservation of myocardial function compared to controls, an augmentation which persisted throughout the duration of ischemia and subsequent reperfusion. Furthermore, significantly greater cellular ATP levels were observed among creatine phosphate treated animals (344+/-55 nMol/g tissue, n=5) compared to control animals (160+/-9 nMol/g tissue, n=5)(p=0.014).

CONCLUSIONS

A strategy of intravenous high-energy phosphate administration successfully prevented ischemic ventricular dysfunction in a rodent model of OPCAB.

Ethyl pyruvate preserves cardiac function and attenuates oxidative injury after prolonged myocardial ischemia

OBJECTIVE

Myocardial injury and dysfunction following ischemia are mediated in part by reactive oxygen species. Pyruvate, a key glycolytic intermediary, is an effective free radical scavenger but unfortunately is limited by aqueous instability. The ester derivative, ethyl pyruvate, is stable in solution and should function as an antioxidant and energy precursor. This study sought to evaluate ethyl pyruvate as a myocardial protective agent in a rat model of ischemia-reperfusion injury.

METHODS

Rats underwent 30-minute ischemia and 30-minute reperfusion of the left anterior descending coronary artery territory. Immediately prior to both ischemia and reperfusion, animals received an intravenous bolus of either ethyl pyruvate (n = 26) or vehicle control (n = 26). Myocardial high-energy phosphate levels were determined by adenosine triphosphate assay, oxidative injury was measured by lipid peroxidation assay, infarct size was quantified by triphenyltetrazolium chloride staining, and cardiac function was assessed in vivo.

RESULTS

Ethyl pyruvate administration significantly increased myocardial adenosine triphosphate levels compared with control (87.6 +/- 29.2 nmol/g vs 10.0 +/- 2.4 nmol/g, P =.03). In ischemic myocardium, ethyl pyruvate reduced oxidative injury compared with control (63.8 +/- 3.3 nmol/g vs 89.5 +/- 3.0 nmol/g, P <.001). Ethyl pyruvate diminished infarct size as a percentage of area at risk (25.3% +/- 1.5% vs 33.6% +/- 2.1%, P =.005). Ethyl pyruvate improved myocardial function compared with control (maximum pressure: 86.6 +/- 2.9 mm Hg vs 73.5 +/- 2.5 mm Hg, P <.001; maximum rate of pressure rise: 3518 +/- 243 mm Hg/s vs 2703 +/- 175 mm Hg/s, P =.005; maximal rate of ventricular systolic volume ejection: 3097 +/- 479 microL/s vs 2120 +/- 287 microL/s, P =.04; ejection fraction: 41.9% +/- 3.8% vs 31.4% +/- 4.1%, P =.03; cardiac output: 26.7 +/- 0.9 mL/min vs 22.7 +/- 1.3 mL/min, P =.01; and end-systolic pressure-volume relationship slope: 1.09 +/- 0.22 vs 0.59 +/- 0.2, P =.02).

CONCLUSIONS

In this study of myocardial ischemia-reperfusion injury, ethyl pyruvate enhanced myocardial adenosine triphosphate levels, attenuated myocardial oxidative injury, decreased infarct size, and preserved cardiac function.

Dimensions underlying legislator support for tobacco control policies

OBJECTIVE

To propose and test a new classification system for characterising legislator support for various tobacco control policies.

DESIGN

Cross sectional study.

SUBJECTS

Federal and provincial legislators in Canada serving as of October 1996 who participated in the Canadian Legislator Study (n = 553; response rate 54%).

MAIN OUTCOME MEASURES

A three factor model (Voters, Tobacco industry, Other interest groups) that assigns nine tobacco control policies according to legislators' hypothesised perceptions of which group is more directly affected by these policies.

RESULTS

Based on confirmatory factor analysis, the proposed model had an acceptable fit and showed construct validity. Multivariate analysis indicated that three of the predictors (believing that the government has a role in health promotion, being a non-smoker, and knowledge that there are more tobacco than alcohol caused deaths) were associated with all three factor scales. Several variables were associated with two of the three scales. Some were unique to each scale.

CONCLUSIONS

Based on our analyses, legislator support for tobacco control policies can be grouped according to our a priori factor model. The information gained from this work can help advocates understand how legislators think about different types of tobacco control policies. This could lead to the development of more effective advocacy strategies.

MRI and MRS of Coffin-Lowry syndrome: a case report

MRI and MRS were used to examine the brain and the spine of a Coffin-Lowry syndrome (CLS) patient. There were moderately enlarged lateral and third ventricles and subarachnoid space with prominent Virchow-Robin spaces. MRS of basal ganglia and periventricular white matter was normal.

Effects of partial housing improvement and insecticide spraying on the reinfestation dynamics of Triatoma infestans in rural northwestern Argentina

The long-term effects on domiciliary reinfestation by Triatoma infestans of smoothing the plaster of indoor walls prior to insecticide application (in Amamá village) relative to only insecticide application (in Trinidad-Mercedes villages) were evaluated in rural northwestern Argentina from 1992 to 1997. All domestic and peridomestic areas of each house were sprayed with 2.5% suspension concentrate deltamethrin at 25 mg/m(2) in October 1992, and infestations were assessed by various methods every 6 months. Domiciliary infestation decreased from 72-88% in 1992 to 6-17% in late 1995, to increase moderately thereafter without returning to baseline rates. Peridomestic sites were the first in becoming reinfested, and reached more abundant T. infestans populations than domiciliary areas. Domiciliary infestation rates and bug abundances were not significantly different between communities during surveillance. Domiciliary infestation rates in well-plastered houses were very low (5-9%) and approximately stable until 1996, but in houses with regular or bad plaster they consistently increased from 5 to 19-21% in both communities. Logistic multiple regression analysis showed that the likelihood of domestic infestation assessed through householders' collections was significantly and positively associated with the occurrence of an infested peridomestic site in the respective house, the occurrence of high-density domestic infestations before interventions, and well-plastered walls in 1996. Combining insecticide spraying and partial improvement of walls controlled domestic infestations and transmission of Trypanosoma cruzi effectively, but was not sufficient to eliminate T. infestans from the study area or increase the effectiveness of careful chemical control.

Estimating the effects of successful malarial control programmes on mortality

"This paper proposes a new, empirically based model to measure the expected effects of successful malaria control programmes on human mortality levels and structure.... The model produces a range of estimated death rates. The range depends on uncertainty about the effective success of control measures. A numerical example, based on the data of the Garki project in northern Nigeria, is discussed. Some alternatives to the model are mentioned. Some strengths and weaknesses...are described and evaluated. And some recommendations are offered for the collection and analysis of data in the intersection of malarial epidemiology and demography."

Tobacco commerce on the internet: a threat to comprehensive tobacco control

Although internet use continues to increase and e-commerce sales are expected to exceed US$1 trillion by the end of 2001, there have been few assessments in the literature regarding the implications of this medium for tobacco control efforts. This commentary explores the challenges that the internet may pose to the key components of a comprehensive tobacco control strategy, and pinpoints potential approaches for addressing these challenges. Four key challenges that the internet presents for tobacco control are identified: unrestricted sales to minors; cheaper cigarettes through tax avoidance and smuggling; unfettered advertising, marketing and promotion; and continued normalisation of the tobacco industry and its products. Potential strategies for addressing these challenges include international tobacco control agreements, national and state regulation, and legal remedies.

Global stability, local stability and permanence in model food webs

The dynamical theory of food webs has been based typically on local stability analysis. The relevance of local stability to food web properties has been questioned because local stability holds only in the immediate vicinity of the equilibrium and provides no information about the size of the basin of attraction. Local stability does not guarantee persistence of food webs in stochastic environments. Moreover, local stability excludes more complex dynamics such as periodic and chaotic behaviors, which may allow persistence. Global stability and permanence could be better criteria of community persistence. Our simulation analysis suggests that these three stability measures are qualitatively consistent in that all three predict decreasing stability with increasing complexity. Some new predictions on how stability depends on food web configurations are generated here: a consumer-victim link has a smaller effect on the probabilities of stability, as measured by all three stability criteria, than a pair of recipient-controlled and donor-controlled links; a recipient-controlled link has a larger effect on the probabilities of local stability and permanence than a donor-controlled link, while they have the same effect on the probability of global stability; food webs with equal proportions of donor-controlled and recipient-controlled links are less stable than those with different proportions.

Modeling household transmission of American trypanosomiasis

American trypanosomiasis, or Chagas disease, caused by the protozoan parasite Trypanosoma cruzi and transmitted by blood-feeding triatomine bugs, is a chronic, frequently fatal infection that is common in Latin America. Neither adequate drugs nor a vaccine is available. A mathematical model calibrated to detailed household data from three villages in northwest Argentina shows that householders could greatly reduce the risk of human infection by excluding domestic animals, especially infected dogs, from bedrooms; removing potential refuges for bugs from walls and ceilings; and using domestically applied insecticides. Low-cost, locally practicable environmental management combined with intermittent use of insecticides can sustainably control transmission of T. cruzi to humans in rural Argentina and probably elsewhere.

Transient dynamics and food-web complexity in the Lotka-Volterra cascade model

How does the long-term behaviour near equilibrium of model food webs correlate with their short-term transient dynamics? Here, simulations of the Lotka -Volterra cascade model of food webs provide the first evidence to answer this question. Transient behaviour is measured by resilience, reactivity, the maximum amplification of a perturbation and the time at which the maximum amplification occurs. Model food webs with a higher probability of local asymptotic stability may be less resilient and may have a larger transient growth of perturbations. Given a fixed connectance, the sizes and durations of transient responses to perturbations increase with the number of species. Given a fixed number of species, as connectance increases, the sizes and durations of transient responses to perturbations may increase or decrease depending on the type of link that is varied. Reactivity is more sensitive to changes in the number of donor-controlled links than to changes in the number of recipient-controlled links, while resilience is more sensitive to changes in the number of recipient-controlled links than to changes in the number of donor-controlled links. Transient behaviour is likely to be one of the important factors affecting the persistence of ecological communities.

Combined endovascular treatment of dissecting vertebral artery aneurysms by using stents and coils

OBJECT

With the recent development and refinement of endovascular stents, the significant potential for these devices in the treatment of wide-necked dissecting and fusiform aneurysms has become apparent. In this article the authors report on the use of stents and coils to treat dissecting and fusiform vertebral artery (VA) aneurysms.

METHODS

Eight consecutive patients harboring eight dissecting aneurysms and one fusiform aneurysm of the VA were succesfully treated using a procedure in which the authors inserted an intravascular stent and secondary endosaccular coils when needed. In all but one patient complete aneurysm occlusion was achieved, and in all cases there was no neurological complication. Follow-up angiography examinations were performed in all patients (mean duration of follow-up angiography review 13.1 months, range 3-42 months). The patients remained stable throughout the clinical follow-up period (mean 14.1 months, range 4-42 months). No rebleeding was recorded.

CONCLUSIONS

At present this combined approach represents a reliable and safe alternative for the treatment of VA dissecting aneurysms, especially in patients who cannot tolerate occlusion tests.

Heterogeneity among smokers and non-smokers in attitudes and behaviour regarding smoking and smoking restrictions

OBJECTIVE

To determine if smokers and non-smokers cluster into meaningful, discrete subgroups with distinguishable attitudes and behaviours regarding smoking and smoking restrictions.

DESIGN

Qualitative research with 45 smokers guided development of questionnaire items applied in a population based telephone survey of 432 current smokers and 1332 non-smokers in Ontario, Canada.

METHODS

Cluster analysis of questionnaire items used to categorise adult smokers and non-smokers; comparison of clusters on sociodemographic characteristics and composite knowledge and attitude scores.

RESULTS

Smokers clustered in three groups. "Reluctant" smokers (16%) show more concern about other people discovering that they smoke, but parallel "easygoing" smokers (42%) in supporting restrictions on smoking and not smoking around others. "Adamant" smokers (42%) feel restrictions have gone too far, and are less likely to accommodate non-smokers. Significant gradients across categories in the expected direction were observed with respect to smoking status, stage of change, knowledge, and attitude scores, and predicted compliance with restrictions, validating the proposed typology. Non-smokers also clustered into three groups, of which the "adamant" non-smokers (45%) are the least favourably disposed to smoking. "Unempowered" non-smokers (34%) also oppose smoking, but tend not to act on it. "Laissez-faire" non-smokers (21%) are less opposed to smoking in both attitude and behaviour. A significant gradient across categories in the expected direction was observed with respect to composite scores regarding knowledge of the health effects of active and passive smoking and a composite score on support for restrictions on smoking in public places.

CONCLUSION

Recognition and consideration of the types of smokers and non-smokers in the population and their distinguishing characteristics could inform the development of tobacco control policies and programmes and suggest strategies to assist implementation.

Dynamic optimization of a linear-quadratic model with incomplete repair and volume-dependent sensitivity and repopulation

PURPOSE

The linear-quadratic model typically assumes that tumor sensitivity and repopulation are constant over the time course of radiotherapy. However, evidence suggests that the growth fraction increases and the cell-loss factor decreases as the tumor shrinks. We investigate whether this evolution in tumor geometry, as well as the irregular time intervals between fractions in conventional hyperfractionation schemes, can be exploited by fractionation schedules that employ time-varying fraction sizes.

METHODS

We construct a mathematical model of a spherical tumor with a hypoxic core and a viable rim, which is most appropriate for a prevascular tumor, and is only a caricature of a vascularized tumor. This model is embedded into the traditional linear-quadratic model by assuming instantaneous reoxygenation. Dynamic programming is used to numerically compute the fractionation regimen that maximizes the tumor-control probability (TCP) subject to constraints on the biologically effective dose of the early and late tissues.

RESULTS

In several numerical examples that employ five or 10 fractions per week on a 1-cm or 5-cm diameter tumor, optimally varying the fraction sizes increases the TCP significantly. The optimal regimen incorporates large Friday (afternoon, if 10 fractions per week) fractions that are escalated throughout the course of treatment, and larger afternoon fractions than morning fractions.

CONCLUSION

Numerical results suggest that a significant increase in tumor cure can be achieved by allowing the fraction sizes to vary throughout the course of treatment. Several strategies deserve further investigation: using larger fractions before overnight and weekend breaks, and escalating the dose (particularly on Friday afternoons) throughout the course of treatment.

The effectiveness of midazolam as a single pharmacologic agent to facilitate endotracheal intubation by paramedics

OBJECTIVE

Endotracheal intubation (ETI) remains the "gold standard" for securing a patient's airway. In recent years, the use of pharmacologic agents to assist paramedics achieve successful intubation of problematic airways has become more common. This study was done to determine the efficacy of intravenous midazolam, a short-acting benzodiazepine, as a drug to facilitate intubation in patients resistant to conventional ETI.

METHODS

This retrospective observational study reviewed the 22-month experience of a suburban municipal EMS system after midazolam was introduced as an agent to be used for systemic sedation to facilitate ETI. All calls where midazolam was used were reviewed on a monthly basis by investigators via retrospective review of the prehospital care reports.

RESULTS

During the study period 13,212 emergency responses occurred, resulting in 154 ETIs by paramedics. Midazolam was used to facilitate 20 (13%) of these ETIs. "Clenched teeth" and failed conventional intubation were the most commonly cited indications for facilitated intubation. Eleven patients had medical complaints and nine were trauma patients. Successful ETI with midazolam was achieved in 17 of 20 (85%) cases. In 85% (15 of 17) of these cases, a single dose of midazolam was sufficient for ETI [mean dose 3.6 mg (SD 1.1 mg)]. The three patients with failed ETI received multiple doses of midazolam [mean dose 5.0 mg (SD 2.0 mg)].

CONCLUSION

The prehospital use of single-dose IV midazolam is generally effective in accomplishing facilitated ETI in patients resistant to conventional (nonpharmacologic) ETI.