Microbial anabolic and catabolic utilization of hydrocarbons in deep subseafloor sediments of Guaymas Basin.

Guaymas Basin, located off the Gulf of California, is a hydrothermally active marginal basin. Due to steep geothermal gradients and localized heating by sill intrusions, microbial substrates like short-chain fatty acids and hydrocarbons are abiotically produced from sedimentary organic matter at comparatively shallow depths. We analyzed the effect of hydrocarbons on uptake of hydrocarbons by microorganisms via nanoscale secondary ion mass spectrometry (NanoSIMS) and microbial sulfate reduction rates (SRR), using samples from two drill sites sampled by IODP Exp. 385 (U1545C and U1546D). These sites are in close proximity of each other (ca. 1 km) and have very similar sedimentology. Site U1546D experienced the intrusion of a sill that has since then thermally equilibrated with the surrounding sediment. Both sites currently have an identical geothermal gradient, despite their different thermal history. The localized heating by the sill led to thermal cracking of sedimentary organic matter and formation of potentially bioavailable organic substrates. There were low levels of hydrocarbon and nitrogen uptake in some samples from both sites, mostly in surficial samples. Hydrocarbon and methane additions stimulated SRR in near-seafloor samples from Site U1545C, while samples from Site U1546D reacted positively only on methane. Our data indicate the potential of microorganisms to metabolize hydrocarbons even in the deep subsurface of Guaymas Basin.

Biological Sulfate Reduction in Deep Subseafloor Sediment of Guaymas Basin.

Sulfate reduction is the quantitatively most important process to degrade organic matter in anoxic marine sediment and has been studied intensively in a variety of settings. Guaymas Basin, a young marginal ocean basin, offers the unique opportunity to study sulfate reduction in an environment characterized by organic-rich sediment, high sedimentation rates, and high geothermal gradients (100-958°C km-1). We measured sulfate reduction rates (SRR) in samples taken during the International Ocean Discovery Program (IODP) Expedition 385 using incubation experiments with radiolabeled 35SO4 2- carried out at in situ pressure and temperature. The highest SRR (387 nmol cm-3 d-1) was recorded in near-surface sediments from Site U1548C, which had the steepest geothermal gradient (958°C km-1). At this site, SRR were generally over an order of magnitude higher than at similar depths at other sites (e.g., 387-157 nmol cm-3 d-1 at 1.9 mbsf from Site U1548C vs. 46-1.0 nmol cm-3 d-1 at 2.1 mbsf from Site U1552B). Site U1546D is characterized by a sill intrusion, but it had already reached thermal equilibrium and SRR were in the same range as nearby Site U1545C, which is minimally affected by sills. The wide temperature range observed at each drill site suggests major shifts in microbial community composition with very different temperature optima but awaits confirmation by molecular biological analyses. At the transition between the mesophilic and thermophilic range around 40°C-60°C, sulfate-reducing activity appears to be decreased, particularly in more oligotrophic settings, but shows a slight recovery at higher temperatures.

The mitral L wave: a marker of advanced diastolic dysfunction in patients with atrial fibrillation.

BACKGROUND: The prominent mid-diastolic filling wave (mitral L wave) indicates advanced diastolic dysfunction in patients in sinus rhythm. The aim of the present study was to determine the clinical implications of the mitral L wave in patients with atrial fibrillation (AF). METHODS AND RESULTS: Ninety-nine consecutive non-valvular chronic persistent AF patients were enrolled. The mitral L wave was defined as a distinct mid-diastolic flow velocity following the E wave with a peak velocity>20 cm/s. The prevalence of the L wave in AF patients (34/99, 34%) was significantly higher than that observed in patients in sinus rhythm during the same study period (23/946, 2.4%, p<0.001). Patients with AF and L wave were older, more frequently female and had a slower heart rate, shorter isovolumic relaxation times, larger E wave velocities and lower early diastolic mitral annulus velocity (E') resulting in the higher E/E' compared to those without L waves. The left atrial volume index was significantly larger in patients with an L wave. The Valsalva maneuver decreased, and leg elevation increased, the amplitude of the L wave in the subset of patients who received these procedures. CONCLUSIONS: The appearance of the mitral L wave in AF is relatively common, and its presence indicates advanced diastolic dysfunction, including elevated filling pressures and distended noncompliant LA.

Hypertrophic cardiomyopathy is associated with more severe left ventricular dyssynchrony than is hypertensive left ventricular hypertrophy.

OBJECTIVE: To evaluate left ventricular (LV) dyssynchrony in patients with left ventricular hypertrophy (LVH), and to compare abnormalities associated with hypertrophic cardiomyopathy (HCM) and hypertensive heart disease (HHD) using 2D speckle tracking imaging. METHODS: Basal, middle, and apical 2D LV short-axis images were acquired in 43 patients with LVH including 20 with HCM and 23 with HHD, and in 15 age-matched controls. Radial strain, circumferential strain, time interval from the R-wave to peak radial strain (Trs), and time to peak circumferential strain (Tcs) were measured in six equidistant segments at each level of the 3 LV short-axis views using 2D speckle tracking analysis. To assess LV dyssynchrony, Trs(cs)-18SD, the standard deviation (SD) of Trs(cs) in all 18 segments, was calculated. RESULTS: Regional radial strain in the middle and apical short-axis segments was significantly less in patients with HCM than in those with HHD. Regional circumferential strain in the apical short-axis segments was also less in HCM. Trs-18SD and Tcs-18SD were significantly longer in patients with HCM than in age-matched controls and patients with HHD (Trs-18SD: HCM: 88 +/- 32 ms, HHD: 51 +/- 20 ms, control: 45 +/- 12 ms P < 0.001, Tcs-18SD: HCM: 71 +/- 27 ms, HHD: 46 +/- 14 ms, control: 45 +/- 14 ms P < 0.001). CONCLUSIONS: The presence of LVH is thus not always associated with LV dyssynchrony. However, the greater reduction of regional strain and severe LV dyssynchrony in HCM may contribute to the adverse cardiovascular outcomes associated with this disease.

Reduced and delayed untwisting of the left ventricle in patients with hypertension and left ventricular hypertrophy: a study using two-dimensional speckle tracking imaging.

AIMS: Newly developed two-dimensional ultrasound speckle tracking imaging allows measurements of left ventricular (LV) rotation and twist. Because LV untwisting predominantly occurs during the isovolumic relaxation period, its assessment reflects the process of LV relaxation. The aim of this study was to examine whether LV hypertrophy (LVH) adversely affects LV untwisting and abnormalities in LV untwisting could become a novel marker in assessing LV relaxation abnormalities. METHODS AND RESULTS: We acquired basal and apical LV short-axis images in 49 hypertensive patients. Using two-dimensional strain software, a time-domain speckle tracking was performed, and the mean value of LV rotation was obtained at each plane. LV twist was defined as apical rotation relative to the base. In order to adjust for inter-subject differences in heart rate, the time sequence was normalized to the percentage of systolic and diastolic duration. The degree of LV untwisting was calculated as the percentage of systolic twist : untwisting = (TwistES-Twistt/TwistES) x 100, where Twistt is twist at time t and TwistES is twist at end-systole. Although peak systolic twist was not different, early diastolic LV untwisting and untwisting rate during isovolumic relaxation period was significantly delayed and reduced in parallel to the severity of LVH, as assessed by LV mass index. CONCLUSION: The observed delayed and reduced diastolic untwisting during the isovolumic relaxation period noted in hypertensive patients with LVH may contribute towards the LV relaxation abnormality. Two-dimensional speckle tracking imaging is a novel tool which can be used for the non-invasive assessment of LV relaxation.