Metabolic constraints on the body size scaling of extreme population densities

Pest outbreaks, harmful algal blooms and population collapses are extreme events with critical consequences for ecosystems. Therefore, understanding the ecological mechanisms underlying these extreme events is crucial. We evaluated theoretical predictions on the size scaling and variance of extreme population abundance by combining (i) the generalized extreme value (GEV) theory and (ii) the resource-limited metabolic restriction hypothesis for population abundance. Using the phytoplankton data from the L4 station in the English Channel, we showed a negative size scaling of the expected value of maximal density, whose confidence interval included the predicted metabolic scaling (α = -1) supporting theoretical predictions. The role of resources and temperature in the distribution of the size-abundance pattern and residuals was well characterized by the GEV distribution. This comprehensive modelling framework will allow to elucidate community structure and fluctuations and provide unbiased return times estimates, thereby improving the prediction accuracy of the timing of the population outbreaks.

Patients awaiting surgery for neurosurgical diseases during the first wave of the COVID-19 pandemic in Spain: a multicentre cohort study

OBJECTIVES

The large number of infected patients requiring mechanical ventilation has led to the postponement of scheduled neurosurgical procedures during the first wave of the COVID-19 pandemic. The aims of this study were to investigate the factors that influence the decision to postpone scheduled neurosurgical procedures and to evaluate the effect of the restriction in scheduled surgery adopted to deal with the first outbreak of the COVID-19 pandemic in Spain on the outcome of patients awaiting surgery.

DESIGN

This was an observational retrospective study.

SETTINGS

A tertiary-level multicentre study of neurosurgery activity between 1 March and 30 June 2020.

PARTICIPANTS

A total of 680 patients awaiting any scheduled neurosurgical procedure were enrolled. 470 patients (69.1%) were awaiting surgery because of spine degenerative disease, 86 patients (12.6%) due to functional disorders, 58 patients (8.5%) due to brain or spine tumours, 25 patients (3.7%) due to cerebrospinal fluid (CSF) disorders and 17 patients (2.5%) due to cerebrovascular disease.

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary outcome was mortality due to any reason and any deterioration of the specific neurosurgical condition. Second, we analysed the rate of confirmed SARS-CoV-2 infection.

RESULTS

More than one-quarter of patients experienced clinical or radiological deterioration. The rate of worsening was higher among patients with functional (39.5%) or CSF disorders (40%). Two patients died (0.4%) during the waiting period, both because of a concurrent disease. We performed a multivariate logistic regression analysis to determine independent covariates associated with maintaining the surgical indication. We found that community SARS-CoV-2 incidence (OR=1.011, p<0.001), degenerative spine (OR=0.296, p=0.027) and expedited indications (OR=6.095, p<0.001) were independent factors for being operated on during the pandemic.

CONCLUSIONS

Patients awaiting neurosurgery experienced significant collateral damage even when they were considered for scheduled procedures.

Impact of the first wave of the SARS-CoV-2 pandemic on the outcome of neurosurgical patients: a nationwide study in Spain

OBJECTIVE

To assess the effect of the first wave of the SARS-CoV-2 pandemic on the outcome of neurosurgical patients in Spain.

SETTINGS

The initial flood of COVID-19 patients overwhelmed an unprepared healthcare system. Different measures were taken to deal with this overburden. The effect of these measures on neurosurgical patients, as well as the effect of COVID-19 itself, has not been thoroughly studied.

PARTICIPANTS

This was a multicentre, nationwide, observational retrospective study of patients who underwent any neurosurgical operation from March to July 2020.

INTERVENTIONS

An exploratory factorial analysis was performed to select the most relevant variables of the sample.

PRIMARY AND SECONDARY OUTCOME MEASURES

Univariate and multivariate analyses were performed to identify independent predictors of mortality and postoperative SARS-CoV-2 infection.

RESULTS

Sixteen hospitals registered 1677 operated patients. The overall mortality was 6.4%, and 2.9% (44 patients) suffered a perioperative SARS-CoV-2 infection. Of those infections, 24 were diagnosed postoperatively. Age (OR 1.05), perioperative SARS-CoV-2 infection (OR 4.7), community COVID-19 incidence (cases/10⁵ people/week) (OR 1.006), postoperative neurological worsening (OR 5.9), postoperative need for airway support (OR 5.38), ASA grade ≥3 (OR 2.5) and preoperative GCS 3-8 (OR 2.82) were independently associated with mortality. For SARS-CoV-2 postoperative infection, screening swab test <72 hours preoperatively (OR 0.76), community COVID-19 incidence (cases/10⁵ people/week) (OR 1.011), preoperative cognitive impairment (OR 2.784), postoperative sepsis (OR 3.807) and an absence of postoperative complications (OR 0.188) were independently associated.

CONCLUSIONS

Perioperative SARS-CoV-2 infection in neurosurgical patients was associated with an increase in mortality by almost fivefold. Community COVID-19 incidence (cases/10⁵ people/week) was a statistically independent predictor of mortality.

TRIAL REGISTRATION NUMBER

CEIM 20/217.

Community fluctuations and local extinction in a planktonic food web

Determining statistical patterns irrespective of interacting agents (i.e. macroecology) is useful to explore the mechanisms driving population fluctuations and extinctions in natural food webs. Here, we tested four predictions of a neutral model on the distribution of community fluctuations (CF) and the distributions of persistence times (APT). Novel predictions for the food web were generated by combining (1) body size-density scaling, (2) Taylor's law and (3) low efficiency of trophic transference. Predictions were evaluated on an exceptional data set of plankton with 15 years of weekly samples encompassing c. 250 planktonic species from three trophic levels, sampled in the western English Channel. Highly symmetric non-Gaussian distributions of CF support zero-sum dynamics. Variability in CF decreased while a change from an exponential to a power law distribution of APT from basal to upper trophic positions was detected. Results suggest a predictable but profound effect of trophic position on fluctuations and extinction in natural communities.

The invariance of production per unit of food consumed in fish populations

The amount of biomass production per unit of food consumed (P/Q) represents an important quantity in ecosystem functioning, because it indicates how efficient a population transforms ingested food into biomass. Several investigations have noticed that P/Q remains relatively constant (or invariant) across fish population that feed at the same food-type level (carnivorous/herbivorous). Nevertheless, theoretical explanation for this invariant is still lacking. In this paper, we demonstrate that P/Q remains invariant across fish populations with stable-age distribution. Three key assumptions underpin the P/Q invariant: (1) the ratio between natural mortality M and von Bertalanffy growth parameter k (M/k ratio) should remain invariant across fish populations; (2) a parameter defining the fraction of ingested food available for growth needs to remain constant across fish that feed at the same trophic level; (3) third, the ratio between length at age 0 ([Formula: see text]) and asymptotic length ([Formula: see text]) should be constant across fish populations. The influence of these assumptions on the P/Q estimates were numerically assessed considering fish populations of different lifespan. Numerical evaluations show that the most critical condition highly relates to the first assumption, M/k. Results are discussed in the context of the reliability of the required assumption to consider the P/Q invariant in stable-age distributed fish populations.

Fatal cardiac and renal allograft rejection with lenalidomide therapy for light-chain amyloidosis

We describe a patient who underwent a successful heart and kidney transplant for light-chain amyloidosis. She had an excellent hematologic response to bortezomib/dexamethasone therapy. Follow-up therapy with lenalidomide was started, and the patient quickly had a fatal allograft rejection of the heart and kidney. We present evidence to support the theory that lenalidomide, a known immunomodulator, may have stimulated the immune system and precipitated the fatal rejection episode.

Competition drives clumpy species coexistence in estuarine phytoplankton

Understanding the mechanisms that maintain biodiversity is a fundamental problem in ecology. Competition is thought to reduce diversity, but hundreds of microbial aquatic primary producers species coexist and compete for a few essential resources (e.g., nutrients and light). Here, we show that resource competition is a plausible mechanism for explaining clumpy distribution on individual species volume (a proxy for the niche) of estuarine phytoplankton communities ranging from North America to South America and Europe, supporting the Emergent Neutrality hypothesis. Furthermore, such a clumpy distribution was also observed throughout the Holocene in diatoms from a sediment core. A Lotka-Volterra competition model predicted position in the niche axis and functional affiliation of dominant species within and among clumps. Results support the coexistence of functionally equivalent species in ecosystems and indicate that resource competition may be a key process to shape the size structure of estuarine phytoplankton, which in turn drives ecosystem functioning.

Partial left ventriculectomy: which patients can be expected to benefit?

BACKGROUND

Although some patients with end-stage heart disease will benefit from a partial left ventriculectomy, no criteria have been found for identifying this group preoperatively. Our experience with partial left ventriculectomy at two institutions-the Texas Heart Institute in Houston, TX, USA, and Dedinje Cardiovascular Institute in Belgrade, Yugoslavia-showed a higher survival rate and better postoperative myocardial function in the Yugoslavian patients.

METHODS

We reviewed data from 42 patients (21 at each center) who had idiopathic cardiomyopathy, a left ventricular end-diastolic dimension of more than 70 mm, wall thickness of 1 cm or greater, and New York Heart Association class III or IV symptoms. The only significant difference in preoperative status between the two groups was duration of symptoms. Histologic specimens, blinded as to origin, were graded with regard to myocyte hypertrophy, cytoplasmic vacuolation, and fibrosis. Computer-assisted myocyte and nuclear morphometry was also performed.

RESULTS

Immediately postoperatively, there were no significant intergroup differences in the reduction in cardiac dimension or in corrections of mitral regurgitation. During 6-month follow-up, however, the Texas Heart Institute patients had a lower cardiac index (1.8 versus 3.0 L x min(-1) x m(-2); p = 0.001) and left ventricular ejection fraction (24% versus 34%; p = 0.006) than the Dedinje Cardiovascular Institute patients. The Texas Heart Institute patients differed from the Dedinje Cardiovascular Institute patients in the degree of severe or moderate changes in myocyte hypertrophy (90% versus 29%; p = 0.0003) and fibrosis (71% versus 29%; p = 0.006), as well as in the measurements of median myocyte diameter (35 +/- 7 microm versus 27 +/- 4 microm; p = 0.0002) and median nuclear size (15 +/- 4 microm versus 12 +/- 2 microm; p = 0.0029).

CONCLUSIONS

In the Texas Heart Institute patients, the significant intergroup difference in clinical outcome may have been related to increased myocyte hypertrophy and fibrosis. Further studies should be performed to determine the usefulness of these criteria in selecting patients for partial left ventriculectomy.

Intensity of infection in AIDS-related intestinal microsporidiosis

To quantify intensity of infection in AIDS-related microsporidiosis, 20 patients with known microsporidiosis submitted stools for quantitative spore counts after staining with a calcofluor white stain. Nine patients collected stools for 24 h, for assessment of daily spore excretion, stool-to-stool variation in spore excretion, and patient-to-patient variation in intensity of infection. The number of organisms seen in small bowel biopsy specimens from 7 patients was compared with quantitative fecal spore excretion. Fecal spore concentration in 20 patients ranged from 4.5x105 to 4.4x108 spores/mL of stool. There was a strong correlation between fecal spore excretion and duodenal biopsy spore counts (r=.82; P<.024). Microsporidium infections in AIDS patients can be quantified by counting spores in stool and by small bowel biopsy. Variations in intensity of infection from patient to patient are great and are similar to those in AIDS-related Cryptosporidium infection.

Immunohistochemistry of matrix metalloproteinases and their inhibitors in thoracic aortic aneurysms and aortic valves of patients with Marfan's syndrome

BACKGROUND

Thoracic aortic aneurysms (TAAs) and valvular insufficiency, the main cardiovascular lesions in Marfan's syndrome, are associated with destruction of connective tissue; however, their pathogenesis remains unclear.

METHODS AND RESULTS

To test the hypothesis that changes in the activity of the matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) are responsible for the damage to connective tissue in these lesions, histochemical studies of the immunoreactivity (IR) for MMPs and their tissue TIMPs (MMP-1, MMP-2, MMP-3, MMP-9, TIMP-1, and TIMP-2) were made in TAAs (n = 7) and aortic valves (n = 5) from 7 patients with Marfan's syndrome. All TAAs showed cystic medial necrosis (CMN), with loss of elastic fibers and smooth muscle cells. Extensive areas of myxoid change were found in all aortic valves. Areas of CMN showed no IR for any MMPs or TIMPs. The IR of smooth muscle cells at the borders of areas of CMN was stronger for all MMPs, especially MMP-2 and MMP-9, than in other regions. The surfaces of disrupted elastic fibers showed IR for MMP-2 and MMP-9. Areas of myxoid change showed similar but less pronounced alterations.

CONCLUSIONS

We hypothesize that the defect in fibrillin-1 in Marfan's syndrome leads to (1) formation of elastin that is abnormally aggregated and more easily degraded by MMPs than is normal elastin, (2) upregulation of the synthesis of MMPs, (3) progressive destruction of connective tissue by these enzymes, and (4) development of TAAs and valvular lesions.

Histologic assessment of Helicobacter pylori status after therapy: comparison of Giemsa, Diff-Quik, and Genta stains

To compare the Giemsa, Diff-Quik, and Genta stains for detection of Helicobacter pylori in gastric biopsy specimens, we stained, coded, and randomized slides, which were then independently reviewed by two pathologists and one trainee. H. pylori was graded from 0 (absent) to 5 (maximal intensity). Negative cases were from recently cured patients to ensure that a background of chronic inflammation was present. The time required to complete the evaluation was tabulated. The pathologists interpreted 72 H. pylori-negative slides, of which 1 (1.3%), 2 (3%), and 3 (4%) were scored positive (each with the score of 1) with Diff-Quik, Genta, and Giemsa stains, respectively (P = ns). Of the 128 H. pylori-positive slides, 5 (4%) had false-negative results with Diff-Quik, 8 with Genta (6%), and 14 with Giemsa stains( 11%). No Grade 2 slides were missed by Genta or Diff-Quik stains, but 3 of 20 were missed by Giemsa stain. The combination of hematoxylin and eosin and Diff-Quik provides accuracy similar to that of the Genta stain but requires more processing time. No stain was excellent after therapy for detecting one or two bacteria per slide; this finding emphasizes the need for obtaining multiple biopsy specimen to exclude failure of H. pylori therapy.

Mast cell involvement in gastritis with or without Helicobacter pylori infection

BACKGROUND & AIMS

Mast cells are initiators and regulators of inflammation, but their role in the human stomach remains unclear. Therefore, the extent and distribution of mast cell involvement in gastritis with or without Helicobacter pylori infection was investigated.

METHODS

Mapped biopsy specimens from 17 H. pylori-positive and 20 H. pylori-negative subjects were examined. Sections were assessed for infection and inflammation and stained with anti-human mast cell tryptase to count mucosal and epithelial mast cells. Density of mast cells in different gastric compartments, their response to infection treatment, and their relationship with other inflammatory cells were evaluated. Mast cell degranulation was evaluated by electron microscopy.

RESULTS

Mast cell density was significantly greater in the mucosa with gastritis, with or without H. pylori infection, than in the mucosa of noninfected normal subjects. In the antrum, density was much greater in H. pylori-infected peptic ulcer subjects than in the other gastritis groups. It also correlated significantly with the intensity of inflammation. Mast cell degranulation was demonstrated by electron microscopy in H. pylori-infected mucosa. Mast cell density in ulcer patients decreased significantly after cure of H. pylori infection.

CONCLUSIONS

Mast cells may be important effector cells in the pathogenesis of gastritis, especially in H. pylori-associated peptic ulcer.

Cure of Helicobacter pylori infection improves gastric acid secretion in patients with corpus gastritis

BACKGROUND

For more than 30 years it has been known that gastric acid secretion is inversely related to the extent and severity of corpal gastritis. We therefore evaluated the effect of cure of Helicobacter pylori infection on basal and pentagastrin-stimulated acid secretion.

METHODS

Basal acid output (BAO) and maximal acid output (MAO) were assessed in 11 H. pylori-infected dyspeptic patients (8 women and 3 men; mean age, 28 years) before and after successful anti-H. pylori therapy.

RESULTS

The gastritis index was significantly lower after therapy and was associated with an increase in both BAO and MAO after cure of the H. pylori infection (BAO from 0.3 mmol/h and MAO from 4.8 mmol/h to 19 mmol/ h). Basal and stimulated acid concentrations also increased (29.1 +/- 36.6 to 54 +/- 31 mmol/l and 72.5 +/- 46 to 120.1 +/- 30 mmol/l, respectively, for basal and stimulated acid concentrations; P < 0.05 for peak and MAO, P = 0.07 for BAO).

CONCLUSION

Gastric acid secretion increased into the normal range after successful treatment of H. pylori infection, suggesting that gastric function can recover to normal or almost normal after cure of H. pylori infection.

Furazolidone, amoxycillin, bismuth triple therapy for Helicobacter pylori infection

BACKGROUND

Metronidazole-resistant Helicobacter pylori are generally the rule in developing countries such as Colombia. Developing countries need an effective, simple and inexpensive non-metronidazole therapy for H. pylori infection.

AIM

To evaluate the combination of bismuth, furazolidone and amoxycillin for the treatment of H. pylori infection in Colombia.

METHODS

Thirty patients with histologically documented H. pylori infection received the combination of bismuth subcitrate 240 mg b.d., furzolidone 100 mg q.d.s. and amoxycillin 500 mg q.d.s. for 14 days. Four or more weeks after ending therapy patients were re-endoscoped and gastric biopsies were obtained and examined using the Genta stain. Each slide was scored for presence, absence and density of H. pylori, active and chronic inflammation, intestinal metaplasia, erosions and atrophy. Cure was defined as the absence of H. pylori.

RESULTS

All patients completed the course of therapy. Twenty-five patients were cured (86%, 95% CI: 65-94%). Mild, well-tolerated side-effects were reported by six patients (20%).

CONCLUSIONS

This combination of bismuth, furazolidone and amoxycillin fulfills the criteria for successful H. pylori therapy and appears particularly well suited for developing countries since it is simple, inexpensive and effective. Furazolidone-containing therapies may become especially useful in the face of a world-wide increase in H. pylori resistance to metronidazole and macrolides.

Adherence of Helicobacter pylori to areas of incomplete intestinal metaplasia in the gastric mucosa

BACKGROUND & AIMS

Helicobacter pylori is not usually found in areas of intestinal metaplasia. Thus, the development of intestinal metaplasia has been viewed as a mechanism by which the stomach eliminates H. pylori. The aim of this study was to evaluate the frequency of H. pylori adherence to intestinal metaplasia in different populations.

METHODS

Mapped gastric biopsy specimens from 378 H. pylori-positive subjects from various geographical regions were examined. Intestinal metaplasia was typed by staining with periodic acid-Schiff/alcian blue and high-iron diamine/alcian blue.

RESULTS

In 32 patients, H. pylori was found in intimate contact with intestinal metaplasia. This was documented by electron microscopy. All areas of intestinal metaplasia showing adherence contained sulfomucins and had no brush border. Posttreatment biopsy specimens from 4 patients whose infection was not cured showed persistence of H. pylori in intestinal metaplasia.

CONCLUSIONS

These patients may have a strain of H. pylori with unusual adhesion characteristics, or their type of intestinal metaplasia may have biochemical properties that make it hospitable for H. pylori. The exclusive association of H. pylori adherence with incomplete intestinal metaplasia (a putative precursor of carcinoma) and its greater frequency in Koreans (a population at risk for gastric cancer) suggest that this phenomenon may play a role in the hypothetical sequence metaplasia > dysplasia > carcinoma.