Diverse forms of pulmonary hypertension remodel the arterial tree to a high shear phenotype.

Pulmonary hypertension (PH) is associated with progressive changes in arterial network complexity. An allometric model is derived that integrates diameter branching complexity between pulmonary arterioles of generation n and the main pulmonary artery (MPA) via a power-law exponent (X) in dn = dMPA2(-n/X) and the arterial area ratio ß = 2(1-2/X). Our hypothesis is that diverse forms of PH demonstrate early decrements in X independent of etiology and pathogenesis, which alters the arteriolar shear stress load from a low-shear stress (X > 2, ß > 1) to a high-shear stress phenotype (X < 2, ß < 1). Model assessment was accomplished by comparing theoretical predictions to retrospective morphometric and hemodynamic measurements made available from a total of 221 PH-free and PH subjects diagnosed with diverse forms (World Health Organization; WHO groups I-IV) of PH: mitral stenosis, congenital heart disease, chronic obstructive pulmonary lung disease, chronic thromboembolism, idiopathic pulmonary arterial hypertension (IPAH), familial (FPAH), collagen vascular disease, and methamphetamine exposure. X was calculated from pulmonary artery pressure (PPA), cardiac output (Q) and body weight (M), utilizing an allometric power-law prediction of X relative to a PH-free state. Comparisons of X between PAH-free and PAH subjects indicates a characteristic reduction in area that elevates arteriolar shear stress, which may contribute to mechanisms of endothelial dysfunction and injury before clinically defined thresholds of pulmonary vascular resistance and PH. We conclude that the evaluation of X may be of use in identifying reversible and irreversible phases of PH in the early course of the disease process.

Altered reactivity and nitric oxide signaling in the isolated thoracic duct from an ovine model of congenital heart disease with increased pulmonary blood flow.

We have previously shown decreased pulmonary lymph flow in our lamb model of chronically increased pulmonary blood flow, created by the in utero placement of an 8-mm aortopulmonary shunt. The purpose of this study was to test the hypothesis that abnormal lymphatic function in shunt lambs is due to impaired lymphatic endothelial nitric oxide (NO)-cGMP signaling resulting in increased lymphatic vascular constriction and/or impaired relaxation. Thoracic duct rings were isolated from 4-wk-old shunt (n = 7) and normal (n = 7) lambs to determine length-tension properties, vascular reactivity, and endothelial NO synthase protein. At baseline, shunt thoracic duct rings had 2.6-fold higher peak to peak tension and a 2-fold increase in the strength of contractions compared with normal rings (P < 0.05). In response to norepinephrine, shunt thoracic duct rings had a 2.4-fold increase in vascular tone compared with normal rings (P < 0.05) and impaired relaxation in response to the endothelium-dependent dilator acetylcholine (63% vs. 13%, P < 0.05). In vivo, inhaled NO (40 ppm) increased pulmonary lymph flow (normalized for resistance) ∼1.5-fold in both normal and shunt lambs (P < 0.05). Inhaled NO exposure increased bioavailable NO [nitrite/nitrate (NOx); ∼2.5-fold in normal lambs and ∼3.4-fold in shunt lambs] and cGMP (∼2.5-fold in both) in the pulmonary lymph effluent (P < 0.05). Chronic exposure to increased pulmonary blood flow is associated with pulmonary lymphatic endothelial injury that disrupts NO-cGMP signaling, leading to increased resting vasoconstriction, increased maximal strength of contraction, and impaired endothelium-dependent relaxation. Inhaled NO increases pulmonary lymph NOx and cGMP levels and pulmonary lymph flow in normal and shunt lambs. Therapies that augment NO-cGMP signaling within the lymphatic system may provide benefits, warranting further study.

Bifidobacterium bifidum in a rat model of necrotizing enterocolitis: antimicrobial peptide and protein responses.

INTRODUCTION: Necrotizing enterocolitis (NEC) is a devastating disease of premature infants. Probiotics decrease the risk of NEC in clinical and experimental studies. Antimicrobial peptides protect the gut against noxious microbes and shape the commensal microbiota, but their role in NEC remains unclear. METHODS: To investigate the expression of antimicrobial peptides in experimental NEC and the impact of probiotics on their expression, premature rats were divided into three groups: dam fed (DF), hand fed with formula (FF), or hand fed with formula containing Bifidobacterium bifidum (FF + BIF). All groups were exposed to asphyxia and cold stress. RESULTS: Like in human ontogeny, the rat pup has low expression of Paneth cell antimicrobials, which increases rapidly during normal development. The expression of lysozyme, secretory phospholipase A(2) (sPLA(2)), pancreatic-associated proteins 1 and 3 mRNA was elevated in the FF group with a high incidence of NEC, as compared with the DF and FF + BIF groups where the disease was attenuated. DISCUSSION: We conclude that induction of antimicrobial peptides occurs in experimental NEC similar to that reported in human disease and is attenuated when disease is averted by probiotic B. bifidum. The induction of antimicrobial peptides is likely an adaptive mucosal response that is often not sufficient to prevent disease in the premature gut.

A randomized placebo-controlled comparison of 2 prebiotic/probiotic combinations in preterm infants: impact on weight gain, intestinal microbiota, and fecal short-chain fatty acids.

OBJECTIVE: To compare the effect of 2 prebiotic/probiotic products on weight gain, stool microbiota, and stool short-chain fatty acid (SCFA) content of premature infants. PATIENTS AND METHODS: This randomized, blinded, placebo-controlled trial included 90 premature infants treated with either a dietary supplement containing 2 lactobacillus species plus fructooligosaccharides (CUL, Culturelle, ConAgra, Omaha, NE), a supplement containing several species of lactobacilli and bifidobacteria plus fructooligosaccharides (PBP, ProBioPlus DDS, UAS Laboratories, Eden Prairie, MN), or placebo (a dilute preparation of Pregestamil formula) twice daily for 28 days or until discharge if earlier. The primary outcome was weight gain. Secondary outcomes were stool bacterial analysis by culture and 16S rDNA quantitative polymerase chain reaction and stool SCFA content measured by high performance liquid chromatography. RESULTS: Both prebiotic/probiotic combinations contained more bacterial species than noted on the label. No significant effect on infant growth of either prebiotic/probiotic supplement was observed. By cultures, 64% of infants receiving PBP became colonized with bifidobacteria, compared with 18% of infants receiving CUL and 27% of infants receiving placebo (chi-square, P = 0.064). No differences were noted between groups in colonization rates for lactobacilli, Gram-negative enteric bacteria, or staphylococci. By 16S rDNA polymerase chain reaction analysis, the bifidobacteria content in the stools of the infants receiving PBP was higher than in the infants receiving CUL or placebo (Kruskal-Wallis, P = 0.011). No significant differences in stool SCFA content were detected between groups. No adverse reactions were noted. CONCLUSIONS: Infants receiving PBP were more likely to become colonized with bifidobacteria. No significant differences in weight gain or stool SCFA content were detected.

Burnout assessment in house officers: evaluation of an intervention to reduce stress.

BACKGROUND: Medical house officers are at increased risk for stress related symptoms leading to professional burnout. AIMS: Measure burnout in house officers and establish whether utilization of a psychotherapeutic tool individually by physicians reduces symptoms characteristic of burnout. METHOD: Two groups of pediatric house officers at the University of California Davis Health System completed a Maslach Burnout Survey (MBS) at the beginning and end of a three-month period in 2003. An Intervention group (7 of 15 enrolled) was trained in the use of a self-administered psychotherapeutic tool. Outcome Measures were MBS scores and a qualitative interview of intervention group members. RESULTS: There were no significant differences between the two groups, prior to the study or over time. Qualitative interviews revealed that subjects experience stressors in relation to their professional activities, but already utilize some elements of the tool and were too busy to implement the entire tool systematically. CONCLUSIONS: Pediatric trainees did not seem to manifest burnout symptoms based upon the MBS; interviews suggested that some do experience significant stress, although manifestations and responses were varied, some may be at risk. Methods identifying individuals at risk for burnout, and interventions to cope with stress may be valuable to their training.

Using multiscale spatial models to assess potential surrogate habitat for an imperiled reptile.

UNLABELLED: In evaluating conservation and management options for species, practitioners might consider surrogate habitats at multiple scales when estimating available habitat or modeling species' potential distributions based on suitable habitats, especially when native environments are rare. Species' dependence on surrogates likely increases as optimal habitat is degraded and lost due to anthropogenic landscape change, and thus surrogate habitats may be vital for an imperiled species' survival in highly modified landscapes. We used spatial habitat models to examine a potential surrogate habitat for an imperiled ambush predator (eastern diamondback rattlesnake, Crotalus adamanteus; EDB) at two scales. The EDB is an apex predator indigenous to imperiled longleaf pine ecosystems (Pinus palustris) of the southeastern United States. Loss of native open-canopy pine savannas and woodlands has been suggested as the principal cause of the species' extensive decline. We examined EDB habitat selection in the Coastal Plain tidewater region to evaluate the role of marsh as a potential surrogate habitat and to further quantify the species' habitat requirements at two scales: home range (HR) and within the home range (WHR). We studied EDBs using radiotelemetry and employed an information-theoretic approach and logistic regression to model habitat selection as use vs. AVAILABILITY: We failed to detect a positive association with marsh as a surrogate habitat at the HR scale; rather, EDBs exhibited significantly negative associations with all landscape patches except pine savanna. Within home range selection was characterized by a negative association with forest and a positive association with ground cover, which suggests that EDBs may use surrogate habitats of similar structure, including marsh, within their home ranges. While our HR analysis did not support tidal marsh as a surrogate habitat, marsh may still provide resources for EDBs at smaller scales.

Shear stress paradigm for perinatal fractal arterial network remodeling in lambs with pulmonary hypertension and increased pulmonary blood flow.

Congenital heart disease with increased blood flow commonly leads to the development of increased pulmonary vascular reactivity and pulmonary arterial hypertension by mechanisms that remain unclear. We hypothesized a shear stress paradigm of hemodynamic reactivity and network remodeling via the persistence and/or exacerbation of a fetal diameter bifurcation phenotype [parent diameter d(0) and daughters d(1) >or= d(2) with alpha < 2 in (d(1)/d(0))(alpha) + (d(2)/d(0))(alpha) and area ratio beta < 1 in beta = (d(1)(2)+ d(2)(2))/ d(0)(2)] that mechanically acts as a high resistance magnifier/shear stress amplifier to blood flow. Evidence of a hemodynamic influence on network remodeling was assessed with a lamb model of high-flow-induced secondary pulmonary hypertension in which an aortopulmonary graft was surgically placed in one twin in utero (Shunt twin) but not in the other (Control twin). Eight weeks after birth arterial casts were made of the left pulmonary arterial circulation. Bifurcation diameter measurements down to 0.010 mm in the Shunt and Control twins were then compared with those of an unoperated fetal cast. Network organization, cumulative resistance, and pressure/shear stress distributions were evaluated via a fractal model whose dimension D(0) approximately alpha delineates hemodynamic reactivity. Fetus and Control twin D(0) differed: fetus D(0)=1.72, a high-resistance/shear stress amplifying condition; control twin D(0) = 2.02, an area-preserving transport configuration. The Shunt twin (D(0)=1.72) maintained a fetal design but paradoxically remodeled diameter geometry to decrease cumulative resistance relative to the Control twin. Our results indicate that fetal/neonatal pulmonary hemodynamic reactivity remodels in response to shear stress, but the response to elevated blood flow and pulmonary hypertension involves the persistence and exacerbation of a fetal diameter bifurcation phenotype that facilitates endothelial dysfunction/injury.

Paneth cells and antibacterial host defense in neonatal small intestine.

Paneth cells are specialized epithelia in the small bowel that secrete antimicrobial proteins. Paneth cells are vital to the innate immunity of the small bowel in adult mammals, but their role during neonatal infection of the small bowel is not well established. Dithizone selectively damages Paneth cells, and when dithizone-treated newborn rats are infected enterally with Escherichia coli, the numbers of E. coli cells in their jejunal and ileal lavage fluid are significantly increased compared to controls. The data support that Paneth cells are necessary for neonatal antibacterial defense.

Evaluation of stroke volume via arterial pulse pressure waveforms in neonatal lambs.

Arterial pulse waveforms contain information about stroke volume (SV) as an integral of pulsatile flow. SV estimation is accurate in adults with proper pulse pressure measurement technique. It is unclear whether the same methods are suitable in critically ill infants in the neonatal clinical setting where the fidelity of pulse pressure measurements are uncertain. We compared three pulse waveform SV methods with three systolic area SV methods in neonatal lambs in order to identify the most accurate and precise approach. Six newborn lambs were studied. Each lamb had a ligated ductus arteriosus and was instrumented to record high-fidelity pulsatile waveforms of arterial blood pressure using a transducer-tipped catheter and pulsatile flow via calibrated ultrasonic flow probe, respectively. Three steady-state hemodynamic conditions were induced experimentally: control, hypertension via infusion of angiotensin II, and hypotension by phlebotomy. Recordings of a range of SVs were made during a steady state that was interrupted by a transient period of decreasing SV, induced by momentarily increasing preload by pulmonary artery occlusion. Modification of pulse wave pressure measurement conditions, simulating an overdamped fluid-filled catheter system, were achieved by low-pass digital filtering of the original high-fidelity waveforms (high) to an 8-Hz cut-off (medium) and to a 2-Hz cut-off (low). The six SV estimates were then calibrated against flowmeter-derived SV and their accuracy and precision evaluated. Based on 6,479 waveforms, a systolic area method with pulse contour integration was the most accurate and precise. We conclude that neonatal pulse arterial waveforms embed SV information under a wide variety of hemodynamic and pressure waveform measurement conditions, and thus may be of potential clinical value in the assessment of newborn cardiovascular status.

Neonatal small bowel epithelia: enhancing anti-bacterial defense with lactoferrin and Lactobacillus GG.

BACKGROUND AND AIMS: Extremely preterm human infants have increased susceptibility to small bowel infection. We hypothesized that early colonization of the immature small intestine with Lactobacillus GG (LGG), and use of a recombinant lactoferrin (rhLF) to promote growth of LGG, would enhance gut defenses against enteroinvasive Escherichia coli. METHODS: Newborn rat pups were treated with nothing, intra-gastric LGG, or rhLF + LGG on days 3 and 4 of life. Gut colonization by LGG was quantified in lavaged jejunal and ileal fluid and gut wall homogenates on day 5 of life. Separate studies used similarly treated litters of newborn rats that were infected late on day 4 of life with E. coli [10(12) CFU/kg]. Sixteen hours later, the numbers of E. coli were measured in small bowel fluid and gut wall homogenates. RESULTS: Control pups initially had lactic acid bacteria colonize the bowel, but these bacteria were not LGG. Pups treated with LGG or rhLF + LGG had significantly higher numbers of LGG in the ileum versus jejunum. Contrary to our hypothesis, rhLF did not augment LGG colonization. After E. coli-related gut infection, planktonic [lavage fluid] and epithelia-adherent growth [gut wall homogenates] of E. coli in the small bowel were most effectively reduced by pre-treatment with rhLF and LGG (P < .05). CONCLUSION: Prophylactic therapy with recombinant human lactoferrin and the probiotic, Lactobacillus GG, act to enhance defenses against invasive E. coli in the nascent small intestine. We suggest that rhLF and LGG are therapeutic agents that may reduce necrotizing enterocolitis and gut-related sepsis in preterm human infants.