Regeneration of a keystone semiarid shrub over its range in Spain: habitat degradation overrides the positive effects of plant-animal mutualisms.

Global change drivers are currently affecting semiarid ecosystems. Because these ecosystems differ from others in biotic and abiotic filters, cues for plant regeneration and management derived from elsewhere may not be applicable to semiarid ecosystems. We sought to determine the extent to which regional variation in regeneration prospects of a long-lived semiarid keystone shrub depends on anthropogenic habitat degradation, plant-animal interactions and climate determinants. We investigated the regeneration ability (via population size structure, juvenile density and juvenile/adult ratio), fruit set and seed dispersal of Ziziphus lotus in 25 localities spanning the range of its threatened habitats in Spain. We dissected the relative contribution of different regeneration determinants using multiple regression and structural equation modelling. Population regeneration was extremely poor, and size structures were biased towards large classes and low juvenile densities and juvenile/adult ratios. Poor regeneration was often coincident with seed dispersal collapse. However, the positive effect of seed dispersal on population regeneration disappeared after considering its relationship with habitat degradation. Protected areas did have juveniles. Together, these data suggest that habitat degradation directly impacts juvenile establishment. Our results provide insights into habitat and species management at the regional level. Z. lotus populations are currently driven by persistence-based dynamics through the longevity of the species. Nonetheless, collapsed seed dispersal, poor regeneration and the removal of adults from their habitats forecast extinction of Z. lotus in many remnants. The extreme longevity of Z. lotus provides opportunities for recovery of its populations and habitats through effective enforcement of regulations.

Is imaging at intermediate doses necessary during dobutamine stress magnetic resonance imaging?

To determine if visualization of left ventricular contraction throughout the course of a pharmacologic stress test performed with magnetic resonance imaging (MRI) (rather than solely at baseline and peak stress) is necessary, we retrospectively reviewed dobutamine MRI results in 469 consecutively referred patients for diagnosis of inducible ischemia. At each stage of pharmacologic stress, six image planes of the heart were viewed and left ventricular wall motion was scored as normal, hypokinetic, akinetic, or dyskinetic. Inducible ischemia was identified in 102 patients; in 39 patients (38%), evidence of ischemia occurred before receiving high doses of dobutamine. During testing, 103 patients developed chest discomfort consistent with angina, but only 26 of the 103 patients (25%) developed new wall motion abnormalities indicative of ischemia. Continuous image acquisition and review during dobutamine MRI pharmacologic stress testing provides a mechanism to detect ischemia and avoid premature test termination during the early stages of the procedure. Compared with protocols that image only at baseline and at peak stress, continuous acquisition and review may enhance the safety and improve the diagnostic accuracy of pharmacologic stress testing during dobutamine MRI.

Utility of fast cine magnetic resonance imaging and display for the detection of myocardial ischemia in patients not well suited for second harmonic stress echocardiography.

BACKGROUND: Some patients referred for pharmacological stress testing with transthoracic echocardiography (TTE) are unable to undergo testing owing to poor acoustic windows. Fast cine MRI can be used to assess left ventricular contraction, but its utility for detection of myocardial ischemia in patients poorly suited for echocardiography is unknown. METHODS AND RESULTS: One hundred fifty-three patients (86 men and 67 women aged 30 to 88 years) with poor acoustic windows that prevented adequate second harmonic TTE imaging were consecutively referred for MRI to diagnose inducible myocardial ischemia during intravenous dobutamine and atropine. Diagnostic studies were completed in an average of 53 minutes. No patients experienced myocardial infarction, ventricular fibrillation, exacerbation of congestive heart failure, or death. In patients who underwent computer-assisted quantitative coronary angiography, the sensitivity and specificity for detecting a >50% luminal diameter narrowing were 83% and 83%, respectively. In the 103 patients with a negative MRI examination, the cardiovascular occurrence-free survival rate was 97%. CONCLUSIONS: Fast cine cardiac MRI provides a mechanism to assess left ventricular contraction and diagnose inducible myocardial ischemia in patients not well suited for stress echocardiography.