R Bruce Light

Hôpital St-Boniface Hospital, Winnipeg, Manitoba, Canada

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Publications (26)111.51 Total impact

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    ABSTRACT: In septic shock, cardiovascular collapse is caused by the release of inflammatory mediators. We previously found that lysozyme (Lzm-S), released from leukocytes, contributed to the myocardial depression and arterial vasodilation that develop in canine models of septic shock. To cause vasodilation, Lzm-S generates hydrogen peroxide (H(2)O(2)) that activates the smooth muscle soluble guanylate cyclase (sGC) pathway, although the mechanism of H(2)O(2) generation is not known. To cause myocardial depression, Lzm-S binds to the endocardial endothelium, resulting in the formation of nitric oxide (NO) and subsequent activation of myocardial sGC, although the initial signaling event is not clear. In this study, we examined whether the myocardial depression produced by Lzm-S was also caused by the generation of H(2)O(2) and whether Lzm-S could intrinsically generate H(2)O(2) as has been described for other protein types. In a canine ventricular trabecular preparation, we found that the peroxidizing agent Aspergillus niger catalase, that would breakdown H(2)O(2), prevented Lzm-S- induced decrease in contraction. We also found that compound I, a species of catalase formed during H(2)O(2) metabolism, could contribute to the NO generation caused by Lzm-S. In tissue-free experiments, we used a fluorometric assay (Ultra Amplex red H(2)O(2) assay) and electrochemical sensor techniques, respectively, to measure H(2)O(2) generation. We found that Lzm-S could generate H(2)O(2) and, furthermore, that this generation could be attenuated by the singlet oxygen quencher sodium azide. This study shows that Lzm-S, a mediator of sepsis, is able to intrinsically generate H(2)O(2). Moreover, this generation may activate H(2)O(2)-dependent pathways leading to cardiovascular collapse in septic shock.
    AJP Heart and Circulatory Physiology 07/2009; 297(3):H930-48. · 4.01 Impact Factor
  • R Bruce Light
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    ABSTRACT: The ability to diagnose and treat infectious diseases and handle infectious disease outbreaks continues to improve. For the most part, the major plagues of antiquity remain historical footnotes, yet, despite many advances, there is clear evidence that major pandemic illness is always just one outbreak away. In addition to the HIV pandemic, the smaller epidemic outbreaks of Legionnaire's disease, hantavirus pulmonary syndrome, and severe acute respiratory syndrome, among many others, points out the potential risk associated with a lack of preplanning and preparedness. Although pandemic influenza is at the top of the list when discussing possible future major infectious disease outbreaks, the truth is that the identity of the next major pandemic pathogen cannot be predicted with any accuracy. We can only hope that general preparedness and the lessons learned from previous outbreaks suffice.
    Critical care clinics 02/2009; 25(1):67-81, viii. · 1.72 Impact Factor
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    ABSTRACT: Blastomycosis is a granulomatous infection caused by the thermally dimorphic fungus, Blastomyces dermatitidis, for which seasonal variation has been proposed. We conducted a retrospective review of medical records of 324 patients with blastomycosis in Manitoba and northwestern Ontario. The average age of patients at the time of diagnosis was 39+/-20 (range, 0-85) years. Symptoms referable to blastomycosis were first noted in the autumn and winter (September to February) by 63% of the patients. The seasonal distribution of cases was different for localized pulmonary infection than the disseminated disease (P<0.0001). For localized lung disease, the peak incidence of symptom onset occurred in the autumn, and lowest incidence in the spring; one half (50%) of the patients with diffuse lung disease had onset of symptoms in the spring months and a few (11%) cases occurred during the summer. We noted a distinct seasonal variation in the clinical presentation of blastomycosis. The observed pattern suggests that summer environmental exposure and acquisition of the infection results in an early (1-6 months) localized pneumonia in the majority of cases, followed by later (4-9 months) reactivation or slow progression of asymptomatic infection resulting in isolated extrapulmonary or disseminated hematogenous disease in the minority.
    Medical Mycology 12/2008; 46(8):835-41. · 1.98 Impact Factor
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    ABSTRACT: In septic shock, systemic vasodilation and myocardial depression contribute to the systemic hypotension observed. Both components can be attributed to the effects of mediators that are released as part of the inflammatory response. We previously found that lysozyme (Lzm-S), released from leukocytes, contributed to the myocardial depression that develops in a canine model of septic shock. Lzm-S binds to the endocardial endothelium, resulting in the production of nitric oxide (NO), which, in turn, activates the myocardial soluble guanylate cyclase (sGC) pathway. In the present study, we determined whether Lzm-S might also play a role in the systemic vasodilation that occurs in septic shock. In a phenylephrine-contracted canine carotid artery ring preparation, we found that both canine and human Lzm-S, at concentrations similar to those found in sepsis, produced vasorelaxation. This decrease in force could not be prevented by inhibitors of NO synthase, prostaglandin synthesis, or potassium channel inhibitors and was not dependent on the presence of the vascular endothelium. However, inhibitors of the sGC pathway prevented the vasodilatory activity of Lzm-S. In addition, Aspergillus niger catalase, which breaks down H(2)O(2), as well as hydroxyl radical scavengers, which included hydroquinone and mannitol, prevented the effect of Lzm-S. Electrochemical sensors corroborated that Lzm-S caused H(2)O(2) release from the carotid artery preparation. In conclusion, these results support the notion that when Lzm-S interacts with the arterial vasculature, this interaction results in the formation of H(2)O(2), which, in turn, activates the sGC pathway to cause relaxation. Lzm-S may contribute to the vasodilation that occurs in septic shock.
    AJP Heart and Circulatory Physiology 05/2008; 294(4):H1724-35. · 4.01 Impact Factor
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    ABSTRACT: Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) are important causes of morbidity and mortality, with mortality rates approaching 62%. HAP and VAP are the second most common cause of nosocomial infection overall, but are the most common cause documented in the intensive care unit setting. In addition, HAP and VAP produce the highest mortality associated with nosocomial infection. As a result, evidence-based guidelines were prepared detailing the epidemiology, microbial etiology, risk factors and clinical manifestations of HAP and VAP. Furthermore, an approach based on the available data, expert opinion and current practice for the provision of care within the Canadian health care system was used to determine risk stratification schemas to enable appropriate diagnosis, antimicrobial management and nonantimicrobial management of HAP and VAP. Finally, prevention and risk-reduction strategies to reduce the risk of acquiring these infections were collated. Future initiatives to enhance more rapid diagnosis and to effect better treatment for resistant pathogens are necessary to reduce morbidity and improve survival.
    The Canadian journal of infectious diseases & medical microbiology = Journal canadien des maladies infectieuses et de la microbiologie medicale / AMMI Canada 02/2008; 19(1):19-53. · 1.02 Impact Factor
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    ABSTRACT: Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) are important causes of morbidity and mortality, with mortality rates approaching 62%. HAP and VAP are the second most common cause of nosocomial infection overall, but are the most common cause documented in the intensive care unit setting. In addition, HAP and VAP produce the highest mortality associated with nosocomial infection. As a result, evidence-based guidelines were prepared detailing the epidemiology, microbial etiology, risk factors and clinical manifestations of HAP and VAP. Furthermore, an approach based on the available data, expert opinion and current practice for the provision of care within the Canadian health care system was used to determine risk stratification schemas to enable appropriate diagnosis, antimicrobial management and nonantimicrobial management of HAP and VAP. Finally, prevention and risk-reduction strategies to reduce the risk of acquiring these infections were collated. Future initiatives to e
    The Canadian journal of infectious diseases \& medical microbiology = Journal canadien des maladies infectieuses et de la microbiologie m\'edicale / AMMI Canada. 01/2008; 19:19-53.
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    ABSTRACT: We previously showed that lysozyme (Lzm-S), derived from leukocytes, caused myocardial depression in canine sepsis by binding to the endocardial endothelium to release nitric oxide (NO). NO then diffuses to adjacent myocytes to activate the cGMP pathway. In a canine right ventricular trabecular (RVT) preparation, Lzm-S also decreased the inotropic response to field stimulation (FSR) during which the sympathetic and parasympathetic nerves were simulated to measure the adrenergic response. In the present study, we determined whether the pathway by which Lzm-S decreased FSR was different from the pathway by which Lzm-S reduced steady-state (SS) contraction. Furthermore, we determined whether the decrease in FSR was due to a decrease in sympathetic stimulation or enhanced parasympathetic signaling. In the RVT preparation, we found that the inhibitory effect of Lzm-S on FSR was prevented by NO synthase (NOS) inhibitors. A cGMP inhibitor also blocked the depressant activity of Lzm-S. However, in contrast to the Lzm-S-induced decline in SS contraction, chemical removal of the endocardial endothelium by Triton X-100 to eliminate endothelial NO release did not prevent the decrease in FSR. An inhibitory G protein was involved in the effect of Lzm-S, since FSR could be restored by treatment with pertussis toxin. Atropine prevented the Lzm-S-induced decline in FSR, whereas beta(1)- and beta(2)-adrenoceptor function was not impaired by Lzm-S. These results indicate that the Lzm-S-induced decrease in FSR results from a nonendothelial release of NO. NO then acts through inhibitory G protein to enhance parasympathetic signaling.
    AJP Heart and Circulatory Physiology 12/2007; 293(5):H3140-9. · 4.01 Impact Factor
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    ABSTRACT: Cardiovascular dysfunction in septic shock (SS) is ascribed to the release of inflammatory mediators. Norepinephrine (NE) is often administered to treat low MAP in SS. We recently found that lysozyme c (Lzm-S) released from leukocytes was a mediator of myocardial depression in an Escherichia coil model of SS in dogs. This effect can be blocked in an in vitro preparation by chitobiose, a competitive inhibitor of Lzm-S. In the present study, we examined whether chitobiose treatment can reverse myocardial depression and obviate NE requirements in two respective canine E. coli preparations. In a 6-h study, we administered chitobiose after 3.5 h of E. coli bacteremia and compared stroke work (SW) and MAP at 6 h with a sepsis control group. In a 12-h study, we determined whether chitobiose treatment can reduce the need for NE requirements during 12 h of bacteremia. In the latter study, either chitobiose or NE was given when MAP decreased approximately 20% from the presepsis value in respective groups. In anesthetized, mechanically ventilated dogs, we monitored hemodynamic parameters during continuous E. coli infusion. In the 6-h study, chitobiose improved SW and MAP at the 6-h period as compared with the nontreated sepsis group. In the 12-h study, SW and MAP increased after chitobiose without the necessity of NE administration. These results suggest that inhibitors of Lzm-S such as chitobiose may improve myocardial depression and reduce the need for NE requirements in SS.
    Shock 10/2007; 29(6):681-7. · 2.61 Impact Factor
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    ABSTRACT: Inflammatory mediators have been implicated as a cause of reversible myocardial depression in septic shock. We previously reported that the release of lysozyme-c (Lmz-S) from leukocytes from the spleen or other organs contributes to myocardial dysfunction in Escherichia coli septic shock in dogs by binding to a cardiac membrane glycoprotein. However, the mechanism by which Lzm-S causes this depression has not been elucidated. In the present study, we tested the hypothesis that the binding of Lzm-S to a membrane glycoprotein causes myocardial depression by the formation of nitric oxide (NO). NO generation then activates soluble guanylyl cyclase and increases cyclic guanosine monophosphate (cGMP), which in turn triggers contractile impairment via activation of cGMP-dependent protein kinase (PKG). We examined these possibilities in a right ventricular trabecular preparation in which isometric contraction was used to measure cardiac contractility. We found that Lzm-S's depressant effect could be prevented by the non-specific NO synthase (NOS) inhibitor N(G)-monomethyl-l-arginine (l-NMMA). A guanylyl cyclase inhibitor (ODQ) and a PKG inhibitor (Rp-8-Br-cGMP) also attenuated Lzm-S's depressant effect as did chemical denudation of the endocardial endothelium (EE) with Triton X-100 (0.5%). In EE tissue, we further showed that Lzm-S caused NO release with use of 4,5 diaminofluorescein, a fluorescent dye that binds to NO. The present study shows that the binding of Lzm-S to EE generates NO, and that NO then activates the myocardial guanosine 3',5' monophosphate pathway leading to cardiac depression in sepsis.
    Journal of Molecular and Cellular Cardiology 11/2005; 39(4):615-25. · 5.15 Impact Factor
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    ABSTRACT: In sepsis, reversible myocardial depression has been ascribed to the release of mediators of inflammation. We previously found that lysozyme released from leukocytes from the spleen and other organs mediated myocardial depression in an Escherichia coli model of septic shock in dogs. We hypothesize that lysozyme binds to or cleaves a cardiac surface membrane N-glycoprotein to cause depression. The objectives of the present study were: 1) to determine whether the binding of lysozyme is reversible; 2) to assess the N-glycan structure to which lysozyme binds; 3) to examine whether nonenzymatic proteins, termed lectins, with a binding specificity similar to that of lysozyme could also cause depression; and 4) to assess whether the membrane to which lysozyme binds is affected by the enzymes protease type XIV and collagenase A, that are used to prepare single cell myocyte experiments. We measured isometric contraction in a right ventricular trabecular preparation. We found that lysozyme binds in a reversible manner to the Man beta(1-4) GlcNAc beta(1-4)GlcNAc moiety in the tri-mannosyl core structure of high mannose/hybrid and tri-antennary carbohydrate classes where GlcNAc is N-acetylglucosamine and Man is mannose. Lectins with a specificity similar to that of lysozyme also caused depression, and lysozyme's depressant activity was eliminated by protease type XIV and collagenase A. These results indicate that lysozyme reversibly binds to a membrane glycoprotein to cause myocardial depression in sepsis. We further localize its binding site to a variant of the chitotriose structure in the tri-mannosyl core of the membrane glycoprotein.
    Intensive Care Medicine 02/2005; 31(1):129-37. · 5.26 Impact Factor
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    ABSTRACT: Reversible myocardial depression in sepsis has been ascribed to the release of inflammatory mediators. We recently found that lysozyme c (Lzm-S), consistent with that originating from the spleen, was a mediator of myocardial depression in an Escherichia coli model of septic shock in dogs. We further showed in a right ventricular trabecular (RVT) preparation that Lzm-S's depressant activity could be blocked by N,N',N" triacetylglucosamine (TAC), a competitive inhibitor of Lzm-S. We hypothesized that Lzm-S binds to or cleaves a cardiac membrane glycoprotein, thereby interfering with myocardial contraction in sepsis. In the present study, we examined whether TAC could prevent myocardial depression in an in vivo preparation and whether other related N-acetylglucosamine (NAG) structures could also inhibit Lzm-S's effect in RVT. Randomized experimental study. University laboratory. Anesthetized, mechanically ventilated dogs. We produced sepsis by infusion of E. coli over an approximately 6-hr period. We examined the effect of TAC on stroke work, our primary index of myocardial function, when treatment was administered before sepsis (pretreatment) and after 1.5 hrs (early treatment study) and 3.5 hrs of sepsis (late treatment study; LTS). In the pretreatment study and early treatment study, myocardial depression would have not yet occurred but would have already been present in the late treatment study. In RVT, we assessed the effect of other NAG oligosaccharides and variants to the NAG structure on Lzm-S's depressant activity. In pretreatment and the early treatment study, TAC prevented the reduction in stroke work observed in nontreated septic groups but did not reverse the reduction found in the late treatment study. In RVT, of the compounds tested, only N,N'-diacetylglucosamine showed an inhibitory effect. We found that TAC, a competitive inhibitor of Lzm-S, prevented myocardial depression in experimental sepsis. Only specific NAG structures are inhibitory to Lzm-S's depressant activity. TAC may be useful in attenuating cardiovascular collapse in sepsis.
    Critical Care Medicine 02/2004; 32(1):184-93. · 6.12 Impact Factor
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    ABSTRACT: In the multinational PROWESS trial, drotrecogin alfa (activated) significantly reduced mortality rate in patients with severe sepsis compared with placebo. The use of large multiple-center trials can potentially complicate interpretation of results in severe sepsis populations because of variability in medical attitudes and practices and the frequency of confounding events such as protocol violations. The objective of this study was to perform a blinded, critical, integrated review of data from the 1,690 severe sepsis patients from 164 medical centers enrolled in the PROWESS trial using a Clinical Evaluation Committee. Blinded, critical, integrated review of data. Participating sites. The 1,690 severe sepsis patients from 164 medical centers enrolled in the PROWESS trial. We performed analyses of the optimal cohort, defined as patients who had full compliance with the protocol, had evidence of an infection, and received adequate anti-infective therapy. We also performed other analyses, including significant underlying disorders, life support measures, and causes of death. The optimal cohort of 81.4% of the intention-to-treat population [drotrecogin alfa (activated), n = 695; placebo, n = 680] had similar baseline severity of illness between the two groups, a similar pharmacodynamic effect, and a relative risk of death estimate consistent with that observed in the overall PROWESS trial (0.83, 95% confidence interval 0.69-0.99 vs. 0.806, 95% confidence interval 0.69-0.94). A beneficial effect of drotrecogin alfa (activated) similarly was observed in patients with significant underlying disorders (0.73, 95% confidence interval 0.57-0.93) who were more severely ill and had a higher percentage of patients forgoing life-sustaining therapy. In contrast with the original investigator determinations, a benefit associated with drotrecogin alfa (activated) treatment in urinary tract infection adjudicated by the Clinical Evaluation Committee was observed. The survival benefit associated with drotrecogin alfa (activated) use was consistent with the results of the overall trial regardless of whether patients met criteria of the optimal cohort or had a significant underlying disorder.
    Critical Care Medicine 10/2003; 31(9):2291-301. · 6.12 Impact Factor
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    ABSTRACT: The objective of the present study was to identify the nature of a filterable cardiodepressant substance (FCS) that contributes to myocardial dysfunction in a canine model of Escherichia coli septic shock. In a previous study, it was found that FCS increased in plasma after 4 h of bacteremia (Am J Physiol 1993;264:H1402) in which FCS was identified by a bioassay that included a right ventricular trabecular (RVT) preparation. In that study, FCS was only partially identified by pore filtration techniques and was found to be a protein of molecular weight between 10 and 30 K. In the present study, FCS was further purified by size exclusion high-pressure liquid chromatography, until a single band was identified on one-dimensional gel electrophoresis. This band was then subjected to tandem mass spectrometry and protein-sequencing techniques and both techniques identified FCS as lysozyme c (Lzm-S), consistent with that originating from the canine spleen. Confirmatory tests showed that purified Lzm-S produced myocardial depression in the RVT preparation at concentrations achieved during sepsis in the in vivo preparation. In addition, Lzm-S inhibited the adrenergic response induced by field stimulation and the beta- agonist isoproterenol in in vitro preparations, these results suggesting that Lzm-S may inhibit the sympathetic response in sepsis. The present findings indicate that Lzm-S originating from disintegrating leukocytes from organs such as the spleen contributes to myocardial dysfunction in this model. The mechanism may relate to its binding or hydrolysis of a cardiac membrane glycoprotein thereby interfering with myocardial excitation-contraction coupling in sepsis.
    Journal of Molecular and Cellular Cardiology 04/2003; 35(3):265-75. · 5.15 Impact Factor
  • Peter E Morris, R Bruce Light, Gary E Garber
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    ABSTRACT: Historically, clinical trials evaluating treatment of patients with severe sepsis have failed to show a reduction of mortality. However, retrospective analyses of some of these trials showed benefits in certain patient subgroups. Conversely, the recent Protein C Worldwide Evaluation in Severe Sepsis (PROWESS) trial, which evaluated the safety and efficacy of drotrecogin alfa (activated) (Xigris; Eli Lilly and Company, Indianapolis, IN), a recombinant form of human activated protein C, in adult patients with severe sepsis, is notable in that it is the first trial to show a reduction in 28-day all-cause mortality in the intent-to-treat population compared with the placebo group. When assessing a new intervention, patient exclusion criteria are important considerations in evaluating the evidence from a controlled clinical trial. Appropriate patient selection will be a key factor in the use of this newly approved therapeutic agent to treat severe sepsis. A review of the exclusion criteria used in the PROWESS trial should provide clinicians with a way of differentiating those patients in the critical care setting who will benefit most from treatment with drotrecogin alfa (activated) from those who should not be treated.
    The American Journal of Surgery 01/2003; 184(6A Suppl):S19-24. · 2.52 Impact Factor
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    ABSTRACT: Histamine H3 receptors and alpha2-adrenoceptors are presynaptic receptors that modulate norepinephrine (NE) release from sympathetic nerves innervating the cardiovascular system. We previously showed that cardiac H3 receptors are activated in sepsis, and that this activation leads to a decrease in the adrenergic response (AR) [J. Appl. Physiol. 85 (1998) 1693-1701] H3-receptors and alpha2-receptors appear to be coupled to GTP binding regulatory proteins (G) that modulate transmitter release by reducing calcium current into the nerve terminals through neuronal calcium channels. There may also be interaction between H3-receptors and alpha2-receptors on AR that may occur either at the receptor or a more downstream level. In the present study, we examined the effect of septic plasma on AR in a canine ventricular preparation in which field stimulation was used to produce AR. We determined whether there was interaction between H(3)-receptors and alpha2-adrenoceptors and tested whether H3 activation would attenuate the alpha2-agonist and alpha2-antagonist effects of clonidine and yohimbine, respectively. We also determined whether the mechanism by which septic plasma decreases the adrenergic response involves inactivation of an inhibitory G protein and used pertussis toxin (PTX) to assess this effect. We found that septic plasma attenuated AR produced by field stimulation, and that this decrease was mediated by a PTX sensitive inhibitory G protein. H3 activation also attenuated the alpha2-agonist and alpha2-antagonist effects on adrenergic activation as compared with nonseptic plasma. We conclude that presynaptic sympathetic dysfunction may contribute to cardiovascular collapse in sepsis.
    Cardiovascular Research 12/2002; 56(2):225-34. · 5.81 Impact Factor
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    ABSTRACT: Lactic acidosis is an important complication of septic shock. Alkali treatment such as sodium bicarbonate is often used to treat the low pH level that develops in sepsis. The effect of this treatment on lactate (Lac) clearance is not clear. In the present study, the objective was to examine whether blood pH level alters Lac metabolism in sepsis. Measurements were determined in a canine model of Escherichia coli sepsis after bolus infusion (5 mmol/kg) of either lactic acid (LA) or sodium lactate (NaL). In one preparation, Lac uptake by the splanchnic organs (SP), liver, lung, kidneys (Kid), and soft tissues of the lower extremity (SOL) was primarily determined, whereas in another preparation, Lac uptake by the head and neck region and lung was obtained. The dogs were studied while anesthetized and ventilated. After 4 hours of sepsis, either LA or NaL was given through a catheter positioned in the abdominal aorta in respective sepsis (SepLA, SepNaL) and nonsepsis groups (ConLA, ConNaL) (n approximately equal to 6 in each preparation). Catheters and flow probes were used to measure organ Lac uptake. Measurements were obtained at end infusion and at 15-minute intervals after infusion until 75 minutes after infusion. Arterial clearance of Lac in the sepsis groups was slower as compared with the nonsepsis groups. In the liver, sepsis inhibited the uptake of LA as compared with the nonseptic group. In SP, both sepsis and pH affected Lac uptake in which an increase in uptake was found only after NaL infusion in the nonseptic group. In the head and neck region, Lac uptake was pH-level dependent and was found after LA infusion in the sepsis and nonsepsis groups. In the lung, Lac was produced after either LA or NaL infusion in all groups. Neither Kid nor SOL contributed to Lac uptake in any of the groups. Lactate clearance was reduced in sepsis. Both effects of pH level and sepsis modulated the organ uptake of Lac in septic shock. Only a small amount of the total Lac infused could be accounted for by the organs measured in the present study. This suggests that additional organs may account for lactate removal in sepsis.
    Journal of Critical Care 10/2002; 17(3):188-202. · 2.50 Impact Factor
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    ABSTRACT: Blastomyces dermatitidis is a dimorphic fungus endemic to Canada and the United States. Few reports regarding blastomycosis in Canada have been published. We retrospectively reviewed the medical charts of 143 patients with confirmed cases of blastomycosis diagnosed in hospitals in Manitoba, Canada, from 1988 through 1999. The annual incidence rate of blastomycosis in Manitoba was 0.62 cases per 100,000 population, compared with 7.11 cases per 100,000 population in the Kenora, Ontario district. The average age of patients was 38.0 years, and males accounted for 65.0% of cases. An increased incidence of blastomycosis was observed in the Aboriginal subpopulation. Organ systems involved were as follows: respiratory system (93.0% of cases), skin (21.0%), bone (13.3%), genitourinary tract (1.4%), and the central nervous system (1.4%); 6.3% of patients died, and death was associated with a short clinical course. This study provides a summary of the current status of blastomycosis in this area of endemicity in Canada.
    Clinical Infectious Diseases 06/2002; 34(10):1310-6. · 9.37 Impact Factor
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    ABSTRACT: In the heart, histamine H3 receptors may function as inhibitory presynaptic receptors that decrease adrenergic neural norepinephrine release in conditions of enhanced sympathetic tone. In a previous study, we found that H3 receptor blockade improved cardiac contractility and systemic hemodynamics in experimental bacteremia in dogs. Because histamine H3 receptors have been found in the splanchnic circulation in other animal models, it was not clear the extent to which H3 receptor blockade may have altered splanchnic hemodynamics, and variables of venous return, that in turn contributed to the overall improvement in systemic hemodynamics observed in the previous experiment. In the present study, we examined splanchnic hemodynamics in the presence of H3 receptor blockade in a canine model of Escherichia coli bacteremia. Bacteremia was produced by intravenous infusion of live E. coli administered throughout the experiment. Variables of venous return included mean systemic pressure, resistance to venous return, and mean right atrial pressure. Splanchnic measurements included hepatic and portal pressures and flows. Measurements were obtained before and after H3 receptor blockade with thioperamide maleate. The animals were studied while ventilated and anesthetized. H3 receptor blockade caused a decrease in mean right atrial pressure from 5.9 mm Hg pretreatment to 3.5 mm Hg posttreatment (p < .05), although it did not affect mean systemic pressure or resistance to venous return. There were no changes in portal or hepatic flows after H3 receptor blockade. The cardiac function curve after H3 receptor blockade was shifted upward and to the left compared with the pretreatment curve. The results showed that the primary effect of H3 receptor blockade in experimental bacteremia was attributable to an increase in inotropy. There was no evidence to indicate that H3 receptor activation contributed to altered splanchnic hemodynamics in this model.
    Critical Care Medicine 03/2002; 30(3):628-36. · 6.12 Impact Factor
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    ABSTRACT: In septic shock, myocardial dysfunction develops over the course of illness, but the mechanism of this depression is not clear. In this study, mechanisms of myocardial dysfunction were examined in a porcine model of Escherichia coli sepsis. Animals were subjected to 4 hours of bacteria infusion (n = 5) (septic group) or saline infusion (n = 5) (nonseptic group), after which trabeculae were removed from the right ventricle and placed into a recirculating water bath. Measurements of steady-state contraction (SSC) were obtained at 0.5, 1, and 2 Hz. Indirect indices were used to assess abnormalities in myocardial calcium metabolism in sepsis. Extrasystoles (ES) were used to assess transsarcolemmal (TSL) calcium flux and were measured at 300 milliseconds, 400 milliseconds, and 500 milliseconds after the preceding stimulus. Postrest contraction (PRC) is an indicator of SR recirculation from the uptake to the release site and was obtained after interposing intervals of rest between steady-state beats at 0.5 Hz. Rapid-cooling contracture (RCC) is an indicator of sarcoplasmic reticulum (SR) content and was obtained at 0.5, 1, and 2 Hz and after interposing intervals of rest at 0.5 Hz. SSC was not different between groups at 0.5 Hz, but compared with the nonseptic group, SSC decreased at 1 and 2 Hz in the septic group (P < .05). PRC and TSL were not different between groups. During rest intervals, calcium leaks out of SR through the ryanodine channel (ie, SR calcium release channel). In the septic group, as assessed by RCC, SR calcium leak was less than that found in the nonseptic group. These results indicate that myocardial dysfunction in sepsis is frequency dependent, and that the mechanism is most likely caused by inhibition of SR calcium release owing to blockade of the ryanodine channel.
    Journal of Critical Care 06/2000; 15(2):64-72. · 2.50 Impact Factor
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    ABSTRACT: In septic shock, the extent to which lactic acidosis (LA) is a consequence of splanchnic lactate overproduction (SLP) or impaired hepatic lactate extraction (HLE) is not clear. We examined SLP and HLE in E. coli sepsis in dogs. We further determined the effects of vasopressor treatments, which included phenylephrine, dopamine, norepinephrine, and a combination of dobutamine and norepinephrine treatment, on SLP and HLE in respective groups. The animals were studied while anesthetized and ventilated. During sepsis, SLP increased as compared with presepsis (-0.017 versus 0.07 mmol/min, p < 0.05), but this increase could not be explained by reduced splanchnic oxygen delivery (SOD). During sepsis, HLE increased as compared with baseline (0.8 versus 8%, p < 0.05), but was significantly lower than that found during lactic acid loading in nonseptic dogs. None of the vasopressor treatments had a detrimental effect on SLP. These results indicate that LA in sepsis occurs secondary to an increase in splanchnic lactate production that is not related to reduced splanchnic oxygen delivery, as well as to a decrease in hepatic lactate extraction. Effects of different vasoactive agents did not alter either splanchnic lactate production or hepatic lactate extraction in this sepsis model.
    American Journal of Respiratory and Critical Care Medicine 02/2000; 161(2 Pt 1):517-26. · 11.04 Impact Factor

Publication Stats

427 Citations
111.51 Total Impact Points

Institutions

  • 2009
    • Hôpital St-Boniface Hospital
      Winnipeg, Manitoba, Canada
  • 1995–2009
    • University of Manitoba
      • • Faculty of Medicine
      • • Department of Pharmacology and Therapeutics
      Winnipeg, Manitoba, Canada
  • 2008
    • Health Sciences Centre Winnipeg
      Winnipeg, Manitoba, Canada
  • 1998
    • The University of Winnipeg
      Winnipeg, Manitoba, Canada