Steven N. Mink

Hemofiltration Reverses Left Ventricular Dysfunction during Sepsis in Dogs

Depressed left ventricular (LV) contractility in sepsis has been ascribed to the presence of circulating cardiodepressant substance (filterable cardiodepressant factor in sepsis [FCS]); however, this finding is controversial. The authors hypothesized that if a decrease in LV contractility indeed occurred due to a circulating depressant substance, then removal of this substance by hemofiltration would reverse by dysfunction. In this study, LV mechanics were examined before and after hemofiltration in anesthetized dogs during continuous intravenous infusion of live Escherichia coli. Left ventricular anterior-posterior and apex-base dimensions were measured by subendocardial ultrasonic crystal transducers implanted 4 weeks before the experiments. Left ventricular contractility was determined from the end-systolic pressure-dimension relationship. The slope of this relationship (Emax) is an index of contractility. After 4 h of sepsis, Emax was reduced by one half. Hemofiltration resulted in a return of Emax to control values. The FCS activity in the plasma was also assessed by the percent reduction in isometric contraction of electrically stimulated, isolated right ventricular trabeculae obtained from nonseptic dogs. The FCS activity reached a peak 4 h after sepsis and was reduced after 2 h of hemofiltration. The results show that during experimental sepsis, a circulating substance of less than 30,000 d produces a decrease in LV contractility and that this LV dysfunction may be improved by hemofiltration.

Epinephrine fails to hasten hemodynamic recovery in fully developed canine anaphylactic shock.

Background: Epinephrine (Epi) is the treatment of choice for reversing cardiovascular collapse in anaphylactic shock (AS). However, there are few data supporting its use in this condition, and most treatment guidelines have been anecdotally derived. In the present study, the time course of hemodynamic recovery from maximal hypotension was investigated in a canine model of AS in which Epi was administered by the intravenous (IV), subcutaneous (SQ) and intramuscular (IM) routes on different occasions. The findings obtained with Epi treatment were compared to those in a nontreatment study. Methods: Ragweed-sensitized dogs were examined in respective studies approximately 5 weeks apart in which Epi was administered by one of the above routes in a randomized design. Either Epi (0.01 mg/kg) or placebo was administered at maximal hypotension, and hemodynamics were followed for 3 h after shock. The animals were studied while ventilated and anesthetized. Mean arterial pressure (MAP), cardiac output, stroke volume (SV), pulmonary wedge pressure (Pwp) and plasma Epi concentrations were obtained at each measurement interval. Results: In the IV study, Epi produced a transient immediate increase in MAP, SV and Pwp as compared to the nontreatment study (144 vs. 52 mm Hg; 32 vs. 12 ml; 9 vs. 5 mm Hg; p < 0.01), but no differences were observed 15 min after shock. Hemodynamics were not different between Epi and no treatment at any intervals when Epi was given by the SQ and IM routes. AS compared with the placebo study, plasma Epi concentrations were higher in the IV and IM studies, but not in the SQ study. Conclusions: Although higher Epi concentrations were observed in the IM and IV studies, a sustained benefit in hemodynamic recovery was not observed in this anesthetized, ventilated canine model. In AS, when administered during maximum shock after mediators have already been released, a single IM, IV or SQ dose of Epi may have limited utility in the treatment of cardiovascular collapse. Earlier administration of Epi, before maximal hypotension occurs, may produce a more beneficial effect.

Effect of Continuous Arteriovenous Hemofiltration Combined with Systemic Vasopressor Therapy on Depressed Left Ventricular Contractility and Tissue Oxygen Delivery in Canine Escherichia coli Sepsis

Background In a previous study, we showed that continuous arteriovenous hemofiltration (CAVH) reversed the depression in left ventricular (LV) contractility in canine Escherichia coli sepsis by the removal of a circulating substance the molecular weight of which is less than 30,000. Despite the normalization of LV contractility, however, we were unable to demonstrate an improvement in systemic arterial blood pressure (BP), presumably because the mechanisms underlying the depression in LV contractility and the decrease in BP are different in sepsis. In the current study, we examined the effect of combined treatment with CAVH and the alpha-adrenergic agonist phenylephrine on LV mechanics and tissue oxygen delivery in our canine E. coli model.

Lysozyme: a mediator of myocardial depression and adrenergic dysfunction in septic shock in dogs

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.

Altered left ventricular chamber stiffness and isovolumic relaxation in dogs with chronic pulmonary hypertension caused by emphysema.

BackgroundIn chronic obstructive lung disease, a right to left ventricular septal shift that occurs as a consequence of right ventricular pressure overload is the usual mechanism given to explain a decrease in left ventricular (LV) diastolic performance. The purpose of the present study was to examine the extent to which this mechanism could account for a decrease in LV diastolic function in a canine model in which pulmonary artery pressure was elevated to a level found in human disease. Methods and ResultsSevere emphysema was produced in dogs by repeated instillations of the enzyme papain into the lung. To assess LV diastolic function, we used sonomicrometry, in which three pairs of subendocardial crystal transducers were implanted along the three orthogonal axes of the LV. LV end-diastolic dimensions and pressure-strain relations along the three axes, as well as the time constant of LV isovolumic relaxation (T), were measured before (baseline) and after 1 year of emphysema (post-l-year study). The results showed that after 1 year of pulmonary hypertension, LV pressure-strain relations were decreased along the septal-lateral and anterior-posterior axes, but a right to left ventricular septal shift was not detected. The relation of average midwall circumferential stress to midwall circumferential strain was used to describe the intrinsic compliance of the LV. The results showed that myocardial stiffness increased in emphysema but that chamber volume was not reduced. At the post-i-year study, T was abnormally increased in the emphysema group in response to augmented preload and afterload compared with preemphysema measurements. ConclusionsWe conclude that mechanisms other than ventricular interdependence may be operative in leading to altered LV diastolic filling in chronic emphysema.

Early but not delayed continuous arteriovenous hemofiltration improves cardiovascular function in sepsis in dogs

Objective: Continuous arteriovenous hemofiltration (CAVH) has been advocated as treatment to remove inflammatory mediators and thereby to improve hemodynamic parameters in sepsis. However, the results obtained with CAVH have been inconsistent. In a canine model of bacteremic Pseudomonas aeruginosa pneumonia, we tested the hypothesis that the time course of the institution of CAVH may be important in obtaining a beneficial treatment effect. Methods: Two protocols were performed in phenobarbital-anesthetized dogs. In the early hemofiltration study (EHS), CAVH for 3 h was initiated 2 h post-pneumonia before mean arterial pressure (MAP) fell. In the late hemofiltration study (LHS), CAVH for 3 h was initiated at 5 h post-pneomonia when a decrease in MAP had already occurred. Hemodynamic measurements included cardiac output (CO), stroke volume (SV), and stroke work (SW). Myocardial depressant activity [filterable cardiodepressant substance (FCS)] found in plasma was assessed by bioassay at each measurement interval. Results: In EHS, after 5 h of sepsis, SW, CO, and SV in the hemofiltered pneumonia group were higher as compared with the nonhemofiltered pneumonia group. In contrast, in LHS, no differences in hemodynamic parameters were found between the two pneumonia groups. In both EHS and LHS, plasma FCS activity was decreased to similar extents by CAVH. Conclusion: These results suggest the time course of institution of CAVH may be important in obtaining a beneficial treatment effect in sepsis.

N,n′,n′-triacetylglucosamine, an inhibitor of lysozyme, prevents myocardial depression in escherichia coli sepsis in dogs*

ObjectiveReversible 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. DesignRandomized experimental study. SettingUniversity laboratory. SubjectsAnesthetized, mechanically ventilated dogs. InterventionsWe produced sepsis by infusion of E. coli over an approximately 6-hr period. Measurements and Main ResultsWe 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. ConclusionsWe 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.

Effect of bolus epinephrine on systemic hemodynamics in canine anaphylactic shock

OBJECTIVE Epinephrine (Epi) is considered to be the drug of choice for anaphylactic shock (AS). However, the benefit of this drug on improving systemic hemodynamics in AS has never been shown. We used a canine ragweed model of AS to determine if an intravenous bolus of Epi hastened the recovery of hemodynamics and modified mediator release (Med) compared with no treatment (NT). METHODS In one protocol (n = 8), the effects on hemodynamics of two intravenous doses of Epi (0.01 and 0.025 mg/kg) were examined for 3 h postshock in respective studies approximately three weeks apart under pentobarbital anesthesia in the same animal. In five other dogs, left ventricular (LV) mechanics were additionally determined by sonomicrometric techniques to determine changes in contractility as defined by the preload recruitable stroke-work (SW) relationship. RESULTS Compared with NT values, Epi treatments produced only transient increases in mean arterial pressure (MAP) and cardiac output (CO) post-challenge. By 20 min postshock, CO in the Epi studies were generally lower (p < 0.05) and BP was not different from NT values. With Epi treatment, SW was reduced for a given LV end-diastolic volume compared with the control study. Epi treatments also caused relatively higher plasma thromboxane B2 concentrations postshock. CONCLUSION Our findings indicate that, when given immediately postshock, bolus-Epi did not hasten recovery and caused impairment in LV mechanics in canine AS.

Characterization of membrane N-glycan binding sites of lysozyme for cardiac depression in sepsis.

Purpose 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.Methods We measured isometric contraction in a right ventricular trabecular preparation.Results We found that lysozyme binds in a reversible manner to the Man β(1–4) GlcNAc β(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.Conclusions 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.

Role of autacoids in cardiovascular collapse in anaphylactic shock in anesthetized dogs

OBJECTIVE In anaphylactic shock (AS), the relative effects of the autacoids including histamine, prostaglandins (prost), and leukotrienes (leuk) on causing cardiovascular collapse and the extent to which receptor blocking agents and pathway inhibitors may prevent this collapse are not clear. METHODS In randomized design, we investigated whether blockade of histamine H1, H2, and H3 receptors or inhibition of the cyclooxygenase (cyclo) and lipoxygenase pathways (lipox) prevented AS in ragweed sensitized dogs. Seven dogs were studied under pentobarbital anesthesia in which the treatment studies were approximately 2 weeks apart. RESULTS During H1 receptor blockade, the decreases in blood pressure and cardiac output otherwise observed in AS were attenuated (P < 0.05) and the release of prost, thromboxanes, and leuk were reduced as compared with nontreatment studies. Cyclo inhibition also attenuated cardiovascular collapse and mediator release in AS, but the other treatments showed no effects. CONCLUSION H1 receptor blockade and cyclo may attenuate cardiovascular shock in AS. These agents inhibit autacoid release from mast cells in addition to any specific receptor blocking and pathway inhibition effects.