Biological soil crusts across disturbance­recovery scenarios: effect of grazing regime on community dynamics.

Grazing represents one of the most common disturbances in drylands worldwide, affecting both ecosystem structure and functioning. Despite the efforts to understand the nature and magnitude of grazing effects on ecosystem components and processes, contrasting results continue to arise. This is particularly remarkable for the biological soil crust (BSC) communities (i.e., cyanobacteria, lichens, and bryophytes), which play an important role in soil dynamics. Here we evaluated simultaneously the effect of grazing impact on BSC communities (resistance) and recovery after livestock exclusion (resilience) in a semiarid grassland of Central Mexico. In particular, we examined BSC species distribution, species richness, taxonomical group cover (i.e., cyanobacteria, lichen, bryophyte), and composition along a disturbance gradient with different grazing regimes (low, medium, high impact) and along a recovery gradient with differently aged livestock exclosures (short-, medium-, long-term exclusion). Differences in grazing impact and time of recovery from grazing both resulted in slight changes in species richness; however, there were pronounced shifts in species composition and group cover. We found we could distinguish four highly diverse and dynamic BSC species groups: (1) species with high resistance and resilience to grazing, (2) species with high resistance but low resilience, (3) species with low resistance but high resilience, and (4) species with low resistance and resilience. While disturbance resulted in a novel diversity configuration, which may profoundly affect ecosystem functioning, we observed that 10 years of disturbance removal did not lead to the ecosystem structure found after 27 years of recovery. These findings are an important contribution to our understanding of BCS dynamics from a species and community perspective placed in a land use change context.

Effect of different treatments on the ability of α-lactalbumin to form nanoparticles.

Nanoparticles of bovine α-lactalbumin (α-LA) prepared by desolvation and glutaraldehyde crosslinking are promising carriers for bioactive compounds in foods. The objective of this work was to study the effect of changes in hydrophobic interactions by using different desolvating agents (acetone, ethanol, or isopropanol) and the use of a heat or high-pressure treatment step before the desolvation process on the size, structure, and properties of α-LA nanoparticles. In all cases, a high average particle yield of 99.63% was obtained. Smaller sizes (152.3 nm) can be obtained with the use of acetone as the desolvating agent and without any pretreatment. This is the first time that α-LA nanoparticles in the size range of 100 to 200 nm have been obtained. These nanoparticles, with an isoelectric point of 3.61, are very stable at pH values >4.8, based on their ζ-potential, although their antioxidant activity is weak. The use of the desolvating agent with the smallest polarity index (isopropanol) produced the largest particles (293.4 to 324.9 nm) in all cases. These results support the idea that controlling hydrophobic interactions is a means to control the size of α-LA nanoparticles. No effect of pretreatment on nanoparticle size could be detected. All types of nanoparticles were easily degraded by the proteolytic enzymes assayed.

[Biatrial re-synchronization in the treatment of paroxysmal atrial fibrillation. 3- and 4-chamber pacemaker]. / Resincronización biatrial en el tratamiento de la fibrilación atrial paroxística. Marcapaso tres y cuatro cámaras.

The reason for multisite pacing is to correct atrial and ventricular electrical and mechanical asynchrony found in paroxysmal atrial fibrillation (PAF) and dilated cardiomyopathy. We report the first two cases in Mexico treated with biatrial pacing for PAF. The first was treated with a three chamber pacemaker and the other with a four chamber pacemaker. The first patient was a young man with uncontrolled ventricular rate in whom the atrioventricular conduction was modified with radiofrequency energy to control ventricular rate during atrial fibrillation. The second patient was a woman with corrected transposition of the great arteries, left ventricular ejection fraction (LVEF) of 30% and complete heart block. The pacing modalities were DDD for the first patient and DDDR for the second, both with sleep rate and auto mode switching. The atria were paced in right appendage and the left through the coronary sinus. PAF episodes were, found only in the first patient but were decreased in number and duration. The LVEF and functional class improved in the patient with biatrial and ventricular resynchronization. We conclude that biatrial pacing is effective in PAF.

Refractory hiccough heralding transverse myelitis in the primary antiphospholipid syndrome.

The case of a 32-year-old female patient with a primary form of the antiphospholipid syndrome is presented. The initial symptom was a pathological form of hiccough, refractory to conventional therapy that was followed, weeks later, by a full-blown picture of transverse myelitis. Despite the fact that transverse myelitis has been described as associated with the presence of antiphospholipid antibodies, we could not find the description of refractory hiccough as the initial manifestation of the antiphospholipid syndrome. The administration of steroids, heparin and plasmapheresis resulted in resolution of the neurological symptoms.

[Usefulness of intracoronary ultrasound in percutaneous transluminal coronary angioplasty]. / Utilidad del ultrasonido intracoronario en la angioplastía coronaria transluminal percutánea.

UNLABELLED: From February 1995 to April 1996 we performed intracoronary ultrasound (ICUS) in 32 patients who had percutaneous transluminal coronary angioplasty (PTCA). Eccentric plaques were found in 53% (n = 17) and concentric in 47% (n = 15). We found that 59.3% (n = 19) were soft, hard 21.8% (n = 7) and calcified plaques in 19% (n = 6). More than 40% of the plaques had some degree of calcium and most of them had dissection post PTCA ICUS deferred the procedure in 25% (n = 8) of cases. Seven of them were patients with late control post PTCA and no significant obstruction and a patient was found not to be a good candidate for PTCA. In 24 lesions we found morphology changes post PTCA: 41.6% type A, 12.5% type B, 45.8% type C, 8.3% type D, 90.9% type E1 and 9.1% type E2. Dissection was present in 54.1% post PTCA, ICUS information indicated other interventions (prolonged insufflations or stents). Two cases with acute coronary syndromes had smooth and fibrous plaques with excellent response to PTCA. Residual percentage stenosis post PTCA for quantitative coronary angiography was 23.7% and with ICUS 52.4%. COMPLICATIONS: there were three cases with coronary spasm that responded well to nitroglycerin. In conclusion, ICUS provides information to evaluate results of PTCA. It also identifies complications and in some cases can improve results.

[Intravascular ultrasound. Initial experience and review of the literature]. / Ultrasonido intravascular. Experiencia inicial y revisión de la literatura.

UNLABELLED: From February 1995 to February 1996, 52 patients underwent intravascular ultrasound (IVUS) imaging: three with aortic coarctation (AoCo), one with persistent ductus arteriosus (PDA), 5 with rheumatic heart disease (RHD) and normal coronary arteries by angiography, one with muscular bridge in anterior descending artery, 20 with percutaneous transluminal coronary angioplasty PTCA (Group I), one of them with eximer laser and 22 stents (Group II). In patients with AoCo was possible to observe obstruction mechanism and the effect of dilation. In patient with PDA we measured the diameter of ductus. In patients with RHD we found early atherosclerosis in four cases, no detected by angiography. In Group I, we found soft plaque in 8, fibrous/mixed in 7 and calcified plaque with the calcium located superficially near the lumen in 5, concentric in 6 and 14 eccentric plaques. In this group the objective was observational in most of the cases, except when the imaging was characteristic of mayor dissection or small final lumen. In 10 cases we observed fracture or dissection of the plaque, in some with small flaps into the lumen. In the last two cases, IVUS was used to optimize results after PTCA in one, in the other we postponed the procedure because the characteristics of the lesion (severe superficial calcification). The patient who underwent eximer laser, IVUS demonstrated irregular and small lumen and was followed by PTCA. In Group II, IVUS was used to optimize deployment of stents. We did not have any case with subacute thrombosis. COMPLICATIONS: Only four cases had angina with ischemic ECG changes during the procedure, but reverted after catheter pullback and intracoronary nitroglycerin. In summary, IVUS gives information about mechanism of obstruction, its complications and results of PTCA. Also detect early atherosclerotic disease not observed by angiography. Optimize deployment of stents and avoids cumarinic anticoagulation in most of the patients. Rational selection of device or deferral of the procedure is possible if we know the characteristics of the plaque before intervention. Utility in other cardiovascular diseases is limited at this time. It's a safe procedure, the morbidity is low and in our experience, without mortality. In the future this new technology will bring useful information in other types of coronary arteries diseases.

[Trichamber pacing in dilated myocardiopathy. TTDR pacing?]. / Estimulación tricameral en la miocardiopatía dilatada. Modo de estimulación TTDR?

This article describes the first case in Mexico city that received a three chamber pacing system. A 40 year-old man with dilated cardiomyopathy with variant cardiac rhythm and bradycardia. The three leads were introduced by right subclavian approaches. The right chamber leads were placed in atrial's appendage and in the right ventricular outflow tract and the last one was placed in the great cardiac vein. The two ventricular lead were connected a Y-connector to the ventricular channel of a standard bipolar DDDR pacemaker. The right ventricular lead was connected to the distal pole (anode) and the left ventricular lead to the proximal pole (cathode). Eight days later, the patient's clinical status improved, his functional class improved from IV to II and his left ventricular ejection fraction increased from 30% to 35% by conventional ventriculography. In this type of patients the improvement in cardiac output is this result an of increase in left ventricular filling, reduced mitral and tricuspid regurgitation a better synchronization of ventricular contraction. Multisite pacing has added a mayor complexity to contemporary pacing and a modification of the standard pacer-maker code should be considered to accommodate multisite pacing. The letter in the first and second position might be T (three) or F (four) according to number of pacing chamber and also the letter "t" may be suitable to designate trigger in the third position. We conclude that implant of three chamber pacing in patients with dilated cardiomyopathy is technically feasible. An improvement in the patient's condition may be obtained and a modification in standard pacemaker code is necessary.

[Stents: experience at the Cardiology Hospital of the 21st century National Medical Center]. / Stents: Experiencia en el Hospital de Cardiología del Centro Médico Nacional Siglo XXI.

UNLABELLED: From february 1995 to february 1997 we implanted 157 stents in 105 patients. Age ranged from 38 to 81 years (mean 58), there were 83 males and 22 females. In 62.8% cases we implanted one stent and in 39 (37.2%) cases 2 to 6. Eighty three were Palmaz/Schatz (P/S), 27 ACT-ONE, 18 Wiktor (W), 9 Gianturco Rubin (GR), 8 Wallstent, 6 XT-Bard and 6 microstent. Indication were de novo in 23.8%, 87.5% post failure PTCA and in 13.3% late PTCA restenosis. Implant was successful al 96.1% of the patients. The first 32 patients received oral anticoagulation, the last 72 received aspirin and ticlopidine only. COMPLICATIONS: 4.7% acute thrombosis, 0.9% sub-acute thrombosis, three of them (2.5%) developed myocardial infarction, 0.9% emergency surgical treatment, 2.8% vascular complications and death in 2.8%. During follow-up (1 to 18 months, mean 7.7) we repeated angiography and 35 patients two to 14 months (m = 5.6), 12 of them had restenosis, during dilation two cases had dissection of the main left coronary artery and were send to surgery, the others were dilated without complications. One case had restenosis of the stent with obstructive lesions in other vessels and was send to elective surgery. The reminded patients are symptom free and had negative stress test. We conclude that this technology is an excellent alternative to percutaneous myocardial revascularization. Larger trials with long term follow-up is necessary to determine the true incidence of restenosis with the different types of stents.