Ronald Brown

Airway Microbiota and Pathogen Abundance in Age- Stratified Cystic Fibrosis Patients

Bacterial communities in the airways of cystic fibrosis (CF) patients are, as in other ecological niches, influenced by autogenic and allogenic factors. However, our understanding of microbial colonization in younger versus older CF airways and the association with pulmonary function is rudimentary at best. Using a phylogenetic microarray, we examine the airway microbiota in age stratified CF patients ranging from neonates (9 months) to adults (72 years). From a cohort of clinically stable patients, we demonstrate that older CF patients who exhibit poorer pulmonary function possess more uneven, phylogenetically-clustered airway communities, compared to younger patients. Using longitudinal samples collected form a subset of these patients a pattern of initial bacterial community diversification was observed in younger patients compared with a progressive loss of diversity over time in older patients. We describe in detail the distinct bacterial community profiles associated with young and old CF patients with a particular focus on the differences between respective “early” and “late” colonizing organisms. Finally we assess the influence of Cystic Fibrosis Transmembrane Regulator (CFTR) mutation on bacterial abundance and identify genotype-specific communities involving members of the Pseudomonadaceae, Xanthomonadaceae, Moraxellaceae and Enterobacteriaceae amongst others. Data presented here provides insights into the CF airway microbiota, including initial diversification events in younger patients and establishment of specialized communities of pathogens associated with poor pulmonary function in older patient populations.

Long-term follow-up of borderline patients in a general hospital

Abstract One hundred borderline patients from a general hospital population were followed for a mean of 15 years. Seventy-five percent were no longer diagnosable as borderline. All scales of the Diagnostic Index for Borderlines (DIB) showed reduction of symptomatic behavior. The mean Health-Sickness Rating Scale (HSRS) was 63, with clear functional improvement. However, there was a high risk of completed suicide (8.5%).

A persistent and diverse airway microbiota present during chronic obstructive pulmonary disease exacerbations

Acute exacerbations of chronic obstructive pulmonary disease (COPD) are a major source of morbidity and contribute significantly to healthcare costs. Although bacterial infections are implicated in nearly 50% of exacerbations, only a handful of pathogens have been consistently identified in COPD airways, primarily by culture-based methods, and the bacterial microbiota in acute exacerbations remains largely uncharacterized. The aim of this study was to comprehensively profile airway bacterial communities using a culture-independent microarray, the 16S rRNA PhyloChip, of a cohort of COPD patients requiring ventilatory support and antibiotic therapy for exacerbation-related respiratory failure. PhyloChip analysis revealed the presence of over 1,200 bacterial taxa representing 140 distinct families, many previously undetected in airway diseases; bacterial community composition was strongly influenced by the duration of intubation. A core community of 75 taxa was detected in all patients, many of which are known pathogens. Bacterial community diversity in COPD airways is substantially greater than previously recognized and includes a number of potential pathogens detected in the setting of antibiotic exposure. Comprehensive assessment of the COPD airway microbiota using high-throughput, culture-independent methods may prove key to understanding the relationships between airway bacterial colonization, acute exacerbation, and clinical outcomes in this and other chronic inflammatory airway diseases.

Loss of Bacterial Diversity during Antibiotic Treatment of Intubated Patients Colonized with Pseudomonas aeruginosa

ABSTRACT Management of airway infections caused by Pseudomonas aeruginosa is a serious clinical challenge, but little is known about the microbial ecology of airway infections in intubated patients. We analyzed bacterial diversity in endotracheal aspirates obtained from intubated patients colonized by P. aeruginosa by using 16S rRNA clone libraries and microarrays (PhyloChip) to determine changes in bacterial community compositions during antibiotic treatment. Bacterial 16S rRNA genes were absent from aspirates obtained from patients briefly intubated for elective surgery but were detected by PCR in samples from all patients intubated for longer periods. Sequencing of 16S rRNA clone libraries demonstrated the presence of many orally, nasally, and gastrointestinally associated bacteria, including known pathogens, in the lungs of patients colonized with P. aeruginosa. PhyloChip analysis detected the same organisms and many additional bacterial groups present at low abundance that were not detected in clone libraries. For each patient, both culture-independent methods showed that bacterial diversity decreased following the administration of antibiotics, and communities became dominated by a pulmonary pathogen. P. aeruginosa became the dominant species in six of seven patients studied, despite treatment of five of these six with antibiotics to which it was sensitive in vitro. Our data demonstrate that the loss of bacterial diversity under antibiotic selection is highly associated with the development of pneumonia in ventilated patients colonized with P. aeruginosa. Interestingly, PhyloChip analysis demonstrated reciprocal changes in abundance between P. aeruginosa and the class Bacilli, suggesting that these groups may compete for a similar ecological niche and suggesting possible mechanisms through which the loss of microbial diversity may directly contribute to pathogen selection and persistence.

Systemically Administered α2-Agonist-induced Peripheral Vasoconstriction in Humans

Background &agr;2-Adrenoceptors mediate both sympatholytic and vasoconstrictive hemodynamic effects. The goal of this study was to profile the peripheral vasoconstrictive effects of a selective &agr;2-adrenoceptor agonist in isolation from the sympatholytic effects it also induces. Methods The authors administered increasing plasma target concentrations of dexmedetomidine (0.075, 0.15, 0.3, and 0.6 ng/mL) or saline placebo to healthy young volunteers in whom the sympatholytic effects of the drug were attenuated in one of two ways: general anesthesia (propofol–alfentanil–nitrous oxide) or axillary brachial plexus block. Measurements were made of finger blood volume (an indicator of vasoconstriction) by photoplethysmographic determination of light transmitted through a finger (LTF) and hemodynamic variables. Measurements made before and during the four steps of infusion were compared by repeated-measures ANOVA. Results In anesthetized volunteers, all concentrations of dexmedetomidine increased LTF (vasoconstriction) and systolic blood pressure (P < 0.001 for both), whereas placebo did not. In awake volunteers, all concentrations decreased systolic blood pressure (P < 0.001). Concentrations of 0.15, 0.3, and 0.6 ng/mL decreased LTF (vasodilation) in the neurally intact hand; in contrast, the same concentrations increased LTF (vasoconstriction) in the sympathectomized hand (P < 0.001 for both). Conclusions The results of this study are the first to characterize the lower end of the dose–response curve for vasoconstriction induced by dexmedetomidine. By denervating the vascular bed of interest or by decreasing sympathetic nervous system activity, the authors were able to observe vasoconstriction induced by a systemically administered &agr;2-agonist with minimal interference from the sympatholytic effects of the drug.

Hemoglobin desaturation after succinylcholine-induced apnea : A study of the recovery of Spontaneous ventilation in healthy volunteers

Background Because of the rapid recovery of neuromuscular function after succinylcholine administration, there is a belief that patients will start breathing sufficiently rapidly to prevent significant oxygen desaturation. The authors tested whether this belief was valid. Methods Twelve healthy volunteers aged 18–45 yr participated in the study. After preoxygenation to an end-tidal oxygen concentration greater than 90%, each subject received 5 mg/kg thiopental and 1 mg/kg succinylcholine. Oxygen saturation (Sao2) was measured at both a finger and an ear lobe (beat to beat). During the period of apnea and as they were recovering, the volunteers received continuous verbal reassurance by the investigators. If the Sao2 decreased below 80%, the volunteers received chin lift and, if necessary, assisted ventilation. The length of time the subject was apneic and level of desaturation were related by linear regression analysis. One hour after recovery and again 1 week later, subjects were asked a series of questions regarding their emotional experience. Results In six volunteers, Sao2 decreased below 95% during apnea; in four, Sao2 decreased below 80%, necessitating chin lift and assisted ventilation in three. Apnea time was significantly longer in volunteers who reached Sao2 less than 80% than in those who did not (7.0 ± 0.4 and 4.1 ± 0.3 min, respectively), and there was a significant correlation between the length of time the subject was apneic and the magnitude of desaturation. Conclusions Spontaneous recovery from succinylcholine-induced apnea may not occur sufficiently quickly to prevent hemoglobin desaturation in subjects whose ventilation is not assisted.

Increased mortality of ventilated patients with endotracheal Pseudomonas aeruginosa without clinical signs of infection.

Objective:To investigate the frequency and outcomes of ventilated patients with newly acquired large burdens of Pseudomonas aeruginosa and to test the hypothesis that large quantities of bacteria are associated with adverse patient outcomes. Design:A prospective, single-center, observational, cohort study. Setting:Medical-surgical intensive care units in a tertiary care university hospital. Patients:All adult patients requiring ≥48 hrs of mechanical ventilation and identified as having newly acquired P. aeruginosa in their lower respiratory tracts between October 2002 and April 2006. Interventions:None. Measurements and Main Results:Daily surveillance cultures of endotracheal aspirates were performed on patients intubated ≥48 hrs; 69 patients with newly acquired P. aeruginosa were enrolled. Daily P. aeruginosa quantification of endotracheal aspirates was performed; clinical signs of infection were noted. Of 45 patients with high P. aeruginosa burdens (≥1,000,000 colony-forming units/mL in endotracheal aspirates; ≥10,000 colony-forming units/mL in bronchoalveolar-lavage), 17 (37.8%) patients did not meet clinical criteria for ventilator-associated pneumonia and had a statistically significant higher risk of death (adjusted hazard ratio, 37.53; 95% confidence interval, 3.79–371.96; p = 0.002) when compared with the patients who had P. aeruginosa ventilator-associated pneumonia. When excluding the ten patients who had ventilator-associated pneumonia attributed to bacteria other than P. aeruginosa or attributed to multiple bacteria including P. aeruginosa, the risk of death remained statistically significant (adjusted hazard ratio, 23.98; 95% confidence interval: 2.49–230.53; p = 0.006). Furthermore, more patients with high P. aeruginosa burdens secreted the type III secretion facilitator protein, PcrV (p = 0.01). Conclusions:A group of patients with large burdens of P. aeruginosa who did not meet clinical criteria for ventilator-associated pneumonia had an increased risk of death when compared with patients who had high P. aeruginosa burdens and met ventilator-associated pneumonia criteria. Patients with high P. aeruginosa burden seemed to possess more virulent strains.

Pharmacodynamic modeling of vecuronium-induced twitch depression : Rapid plasma-effect site equilibration explains faster onset at resistant laryngeal muscles than at the adductor pollicis

Background After bolus doses of nondepolarizing muscle relaxants, the adductor pollicis recovers from paralysis more slowly than the diaphragm and the laryngeal adductors, suggesting that the adductor pollicis is more sensitive than the respiratory muscles to effects of those drugs. In contrast, during onset, the respiratory muscles are paralyzed more rapidly than the adductor pollicis, suggesting that the respiratory muscles are more sensitive than the adductor pollicis. To reconcile these apparently conflicting findings, we determined vecuroniums pharmacokinetics and its pharmacodynamics at both the adductor pollicis and the laryngeal adductors. Methods Six volunteers were studied on two occasions during anesthesia with propofol. Mechanical responses to train‐of‐four stimulation were measured at the adductor pollicis and at the laryngeal adductors. Vecuronium (15–60 micro gram/kg) was given and arterial plasma samples were obtained from 0.5–60 min. Vecuronium doses differed by twofold on the two occasions. A pharmacokinetic model accounting for the presence and potency of vecuroniums 3‐desacetyl metabolite and a sigmoid e‐max pharmacodynamic model were fit to the resulting plasma concentration and effect (adductor pollicis and laryngeal adductors) data to determine relative sensitivities and rates of equilibration between plasma and effect site concentrations. Results The steady‐state plasma concentration depressing laryngeal adductor twitch tension by 50% was approximately 1.5 times larger than that for the adductor pollicis. The equilibration rate constant between plasma and laryngeal adductor concentrations was about 1.5 faster than that between plasma and adductor pollicis concentrations. The Hill factor (gamma) that describes the steepness of the laryngeal adductor concentration‐effect relation was approximately 0.6 times that of the adductor pollicis. Conclusions More rapid equilibration between plasma and laryngeal adductor vecuronium concentrations explains why onset is more rapid at the laryngeal adductors than at the adductor pollicis. During recovery, both rapid equilibration and lesser sensitivity of the laryngeal adductors contribute to earlier recovery.

Absorbents differ enormously in their capacity to produce compound A and carbon monoxide.

Concern persists regarding the production of carbon monoxide (CO) and Compound A from the action of carbon dioxide (CO2) absorbents on desflurane and sevoflurane, respectively. We tested the capacity of eight different absorbents with various base compositions to produce CO and Compound A. We delivered desflurane through desiccated absorbents, and sevoflurane through desiccated and moist absorbents, then measured the resulting concentrations of CO from the former and Compound A from the latter. We also tested the CO2 absorbing capacity of each absorbent by using a model anesthetic system. We found that the presence of potassium hydroxide (KOH) and sodium hydroxide (NaOH) increased the production of CO from calcium hydroxide (Ca[OH]2) but did not consistently affect production of Compound A. However, the effect of KOH versus NaOH was not consistent in its impact on CO production. Furthermore, the effect of KOH versus NaOH versus Ca(OH)2 was inconsistent in its impact on Compound A production. Two absorbents (Amsorb® [Armstrong Medica, Ltd, Coleraine, Northern Ireland], composed of Ca(OH)2 plus 0.7% polyvinylpyrrolidine, calcium chloride, and calcium sulfate; and lithium hydroxide) produced dramatically lower concentrations of both CO and Compound A. Both produced minimal to no CO and only small concentrations of Compound A. The presence of polyvinylpyrrolidine, calcium chloride, and calcium sulfate in Amsorb® appears to have suppressed the production of toxic products. All absorbents had an adequate CO2 absorbing capacity greatest with lithium hydroxide. Implications Production of the toxic substances, carbon monoxide and Compound A, from anesthetic degradation by carbon dioxide absorbents, might be minimized by the use of one of two specific absorbents, Amsorb® (Armstrong Medica, Ltd., Coleraine, Northern Ireland) (calcium hydroxide which also includes 0.7% polyvinylpyrrolidine, calcium chloride, and calcium sulfate) or lithium hydroxide.

A pharmacodynamic explanation for the rapid onset/offset of rapacuronium bromide.

BACKGROUND Nondepolarizing muscle relaxants differ in their time course at the laryngeal adductors and the adductor pollicis, a result of differences in equilibration delays between plasma and effect sites, the sensitivity of each muscle to the relaxant, and the steepness of the concentration-effect relation at each muscle (the Hill factor). To determine whether similar differences exist for rapacuronium, a muscle relaxant with rapid onset and offset, the authors determined its pharmacodynamic characteristics. METHODS The twitch tensions of the adductor pollicis and the laryngeal adductors (via a tracheal tube cuff positioned at the vocal cords) were measured in 10 volunteers who were anesthetized with propofoL Rapacuronium, 1.5 mg/kg, was given and blood samples were collected. A semiparametric effect compartment pharmacodynamic model was fit to values for rapacuronium plasma concentrations and twitch tension of the adductor pollicis and laryngeal adductors. RESULTS Equilibration between the rapacuronium plasma concentration and both effect sites was rapid (typical values for the rate constant for equilibration between plasma and the effect site are 0.405 per min for the adductor pollicis and 0.630 per min for the laryngeal adductors) and was more rapid at the laryngeal adductors than at the adductor pollicis (ratio, 1.59+/-0.16; mean +/- SD). The steady state rapacuronium plasma concentration that depressed twitch tension by 50% and the Hill factor were similar for the two muscles. CONCLUSIONS The rapid onset and offset of rapacuronium can be explained by the rapid equilibration between concentrations in plasma and at the effect site. Unlike the finding for other nondepolarizing muscle relaxants, the laryngeal muscles are not resistant to rapacuronium.