The Association of Lung Distention, PEEP and Biventricular Failure

Although positive and expiratory pressure (PEEP) is known to depress the cardiac output, the mechanism remains debated. Two series of experiments were designed to explore this mechanism. In the first study, the application of 15 cm H(2)O of PEEP to nine anesthetized, ventilated dogs led to a reduction of cardiac index from (mean +/- one standard error of the mean) 2.71 L/min .m (2) +/- 0.35 to 2.19 L/min m(2) +/- 0.22 (p < .05) and a drop in mean arterial pressure (MAP) from 117 mm Hg +/- 8 to 91 mm Hg +/- 11 (p < .01). The mean net (vascular minus pleural pressure) pulmonary artery pressure (MPAP) rose from 15.3 mm Hg +/- 1.2 to 20.6 mm Hg +/- 1.8 (p < .02). The mean net central venous pressure (CVP) rose from 5.2 mm Hg +/- 0.9 to 8.4 mm Hg +/- 0.9 (p < .05) and the net pulmonary arterial wedge pressure (PAWP) rose from 6.7 mm Hg +/- 0.7 to 9.5 mm Hg +/- 0.9 (p < .01). There was a nonsignificant rise in the mean net left atrial pressure (LAP). As PEEP was raised in increments from 0 to 20 cm H(2)O, both LAP and PAWP increased. The rise in PAWP was always greater than the increase in LAP. The difference between PAWP and LAP was strongly correlated with the increase in MPAP (r = 0.98). This relationship was useful in correcting the PAWP during PEEP. The problem of cardiac depression was evaluated in a second series of eight dogs. These animals underwent complete chest wall excision to eliminate any possible direct effects of increased pleural pressure on the heart and great vessels. The absence of the chest wall permitted hyperexpansion of the lungs, particularly with positive end expiratory pressure. At 15 cm H(2)O of PEEP, the mean cardiac index fell in these animals from 2.36 L/min. m(2) +/- 0.26 to 1.47 L/min.m(2) +/- 0.18 (p < .01) and the MAP fell from 105 mm Hg +/- 16.2 to 68 mm Hg +/- 4.8 (p < .001). The CVP rose from a mean of 5.5 mm Hg +/- 0.4 to 8.3 mm Hg +/- 0.6 (p < .01) and the LAP rose from 6.3 mm Hg +/- 0.8 to 8.0 mm Hg +/- 1.1 (p < .05). The MPAP rose from 18.0 mm Hg +/- 0.6 to 23.3 mm Hg +/- 1.6 (p < .01). Comparison of Group I and II showed a significantly greater depression of the cardiac output and MAP in the open-chested animals. At the same time LAP was significantly higher. These data strongly suggest that PEEP and particularly pulmonary hyperinflation induce biventricular failure.     

Post-transplant lymphoproliferative disorder following pediatric heart transplantation

Immunosuppression after heart transplantation is implicated in development of post-transplant lymphoproliferative disorder (PTLD). Despite a higher prevalence of PTLD in children, there is scarce knowledge about incidence, pathophysiologic mechanisms and risk factors for PTLD in pediatric recipients of cardiac allografts. We examined retrospectively the medical records of all 143 pediatric patients (mean age 9.2 +/- 6.1 yr) who received donor allografts between 1984 and 2002 and survived over 30 days. Five children (3.5%) developed PTLD over a mean follow-up period of 41.1 +/- 46.0 months. Time from transplant to diagnosis of PTLD ranged from 3.9 to 112 months (mean 48.0 +/- 41.9 months). Excluding PTLD, no other malignancies were found in this population. Actuarial freedom from PTLD was 99.2%, 99.2% and 96.2% at 1, 2, and 5 yr, respectively. Children who developed PTLD were more likely (by univariate analysis) to have been Rh negative (p = 0.01), Rh mismatched (p = 0.003), Epstein-Barr virus (EBV) seronegative (p = 0.001) and transplanted for congenital heart disease (p < 0.02). PTLD was associated with significant morbidity and mortality with a mean survival following diagnosis of 21.2 months. PTLD is a serious complicating outcome of cardiac transplantation that occurs in approximately 3.5% of children. Aside of immunosuppression, risk factors in this series for developing PTLD include EBV seronegativity and Rh negative status and mismatch. Non-hematogenous malignancies are rare in light of short allograft half-life.     

“Apple Far from the Tree”: comparative effectiveness of fiberoptic single-operator cholangiopancreatoscopy (FSOCP) and digital SOCP (DSOCP)

Background

While the fiberoptic single-operator cholangiopancreatoscopy (FSOCP) system has demonstrated efficacy in the diagnosis and management of pancreaticobiliary diseases, the digital SOCP (DSOCP) appears to provide higher resolution digital imaging, however a comparison of these devices has not been established. The aim of this work was to compare the efficacy of FSOCP and DSOCP in biliary stone disease and indeterminate biliary strictures.

Acetylcholinesterase Complexes with the Natural Product Inhibitors Dihydrotanshinone I and Territrem B: Binding Site Assignment from Inhibitor Competition and Validation Through Crystal Structure Determination

Acetylcholinesterase (AChE) is a critical enzyme that regulates neurotransmission by degrading the neurotransmitter acetylcholine in synapses of the nervous system. It is an important target for both therapeutic drugs that treat Alzheimer’s disease and organophosphate (OP) chemical warfare agents that cripple the nervous system and cause death through paralysis. We are exploring a strategy to design compounds that bind tightly at or near a peripheral or P-site near the mouth of the AChE active site gorge and exclude OPs from the active site while interfering minimally with the passage of acetylcholine. However, to target the AChE P-site, much more information must be gathered about the structure-activity relationships of ligands that bind specifically to the P-site. Here, we review our recent reports on two uncharged, natural product inhibitors of AChE, dihydrotanshinone I and territrem B, that have relatively high affinities for the enzyme. We describe an inhibitor competition assay and comment on the structures of these inhibitors in complex with recombinant human acetylcholinesterase as determined by X-ray crystallography. Our results reveal that dihydrotanshinone I binding is specific to only the P-site, while territrem B binding spans the P-site and extends into the acylation or A-site at the base of the gorge.     

Chemical shift artifact on steady-state free precession cardiac magnetic resonance sequences as a result of lipomatous metaplasia: a novel finding in chronic myocardial infarctions

Background

Because balanced steady-state free precession (SSFP) sequences are opposed-phase gradient echo techniques, linear low signal due to chemical shift artefact is observed at fat-water interfaces. We observed that some patients with chronic myocardial infarctions had linear low signal along the inner myocardial wall in areas of infarction, which we postulated was due to chemical shift artefact, as a result of lipomatous metaplasia. The purpose of this retrospective review was to evaluate whether subendocardial low signal on SSFP, likely related to chemical shift artifact, could be used to identify chronic myocardial infarctions.

Methods

Of 128 patients who underwent cardiac magnetic resonance, 79 with myocardial infarctions were included in this retrospective study.

Results

Of the 79 patients, 35 (44%) demonstrated areas of linear subendocardial decreased signal. In 16 of those 35 (46%), the infarcts were confirmed as fatty by correlation with CT. In 29 of 35 (83%) of these patients, the infarcts were likely chronic based on fixed wall thinning to less than 4 mm. In 3 patients, chemical shift artifact due to lipomatous metaplasia was also confirmed with conventional in-phase and opposed-phase T1-weighted sequences. Subendocardial chemical shift artefacts were not seen in any of the 19 patients with known, acute infarcts included in this series. Aneurysms were more common when subendocardial chemical shift artefact was present (22 of 35), in comparison to patients who did not have this finding (10 of 44, P = 0.02).

Conclusions

Identification of linear subendocardial chemical shift artefacts on SSFP sequences is a sign of lipomatous metaplasia in chronic myocardial infarcts and is associated with an increased incidence of ventricular aneurysms.