Luis Araujo

Longitudinal evaluation and assessment of cardiovascular disease in patients with homozygous familial hypercholesterolemia.

Homozygous familial hypercholesterolemia (hoFH) is caused by mutations in the low-density lipoprotein receptor gene and is characterized by severe hypercholesterolemia from birth and onset of premature cardiovascular disease (CVD) during childhood. The onset and progression of CVD using currently available testing methods in children with hoFH have not been fully characterized. A large cohort of patients with hoFH referred to our subspecialty clinic was studied. Thirty-nine patients (22 aged < or =16 years) underwent extensive cardiovascular, lipid, and genetic evaluation. Sixteen children < or =16 years without known CVD when first evaluated were followed up longitudinally for up to 8 years. CVD was clinically evident in 88% of subjects aged >16 years and 9% of those < or =16 years. Markers of atherosclerosis correlated significantly with age at which lipid-lowering treatment was initiated (abnormal coronary angiogram, abnormal aortic valve using echocardiography, and high calcium score using electron beam computed tomography; all p <0.01; abnormal carotid Doppler result; p = 0.03). Twenty of 22 children had no clinical evidence of coronary artery disease, yet 7 of these children had angiographically confirmed mild coronary artery disease (<50%) and 8 had mild to moderate aortic regurgitation using echocardiography. Of noninvasive tests, only evaluation of aortic valve regurgitation using echocardiography predicted the presence of angiographic coronary stenosis (p <0.001). During follow-up, 7 children developed progression of coronary and/or aortic valvular disease during their teenage years and 4 required surgical interventions. In conclusion, in these patients aggressive lipid-lowering treatment initiated in early childhood is warranted. Careful coronary and valvular surveillance strategies and coronary revascularization when appropriate are also warranted in this high-risk population.

Trust-Based Trade

Weak enforcement of international contracts can substantially reduce international trade. We develop a model where agents build reputations to overcome the difficulties that this institutional failure causes in a context of incomplete information. The model describes the interplay between institutional quality, reputations and the dynamics of international trade. We find that the conditional probability that a firm will stop exporting decreases and its foreign sales increase as the firm acquires greater export experience. The reason is that the informational costs that an exporter faces fall as the exporter becomes more confident about the reliability of its distributor. An improvement in the institutional quality of a country affects its imports through several distinct channels, as it changes the incentives of both current and potential exporters. Trade liberalization induces current exporters to increase their sales. It could induce entry as well, but this will happen only when the initial tariff is high and/or the institutional quality of the country is low.

Noninvasive Assessment of Myocardial Viability in a Small Animal Model: Comparison of MRI, SPECT, and PET

Acute myocardial infarction (AMI) research relies increasingly on small animal models and noninvasive imaging methods such as MRI, single‐photon emission computed tomography (SPECT), and positron emission tomography (PET). However, a direct comparison among these techniques for characterization of perfusion, viability, and infarct size is lacking. Rats were studied within 18–24 hr post AMI by MRI (4.7 T) and subsequently (40–48 hr post AMI) by SPECT (99Tc‐MIBI) and micro‐PET (18FDG). A necrosis‐specific MRI contrast agent was used to detect AMI, and a fast low angle shot (FLASH) sequence was used to acquire late enhancement and functional images contemporaneously. Infarcted regions showed late enhancement, whereas corresponding radionuclide images had reduced tracer uptake. MRI most accurately depicted AMI, showing the closest correlation and agreement with triphenyl tetrazolium chloride (TTC), followed by SPECT and PET. In some animals a mismatch of reduced uptake in normal myocardium and relatively increased 18FDG uptake in the infarct border zone precluded conventional quantitative analysis. We performed the first quantitative comparison of MRI, PET, and SPECT for reperfused AMI imaging in a small animal model. MRI was superior to the other modalities, due to its greater spatial resolution and ability to detect necrotic myocardium directly. The observed 18FDG mismatch likely represents variable metabolic conditions between stunned myocardium in the infarct border zone and normal myocardium and supports the use of a standardized glucose load or glucose clamp technique for PET imaging of reperfused AMI in small animals. Magn Reson Med 59:252–259, 2008.

Collateral Development and Function in Man

The protective role of coronary collaterals in patients was questioned because collaterals were more frequently found in patients with myocardial infarction than in those without (1, 2). This apparent paradox is explained by the greater average frequency of coronary occlusion or very severe stenoses in patients with infarction than in those without (3).

On the Essentiality of Banks

We compare allocations sustained by credit with allocations sustained by bank notes (inside money) in a search model with decentralized trade and limited monitoring. We demonstrate that there exists a credit arrangement that is superior to inside money. However, in contrast with inside money, this arrangement is not robust to an expansion of trade that is not accompanied by an adequate increase in the degree of monitoring. Therefore, banks are essential when trade is intense and monitoring is limited. As a historical application, we argue that our model helps explain the origins of banking in Medieval and Early Modern Europe.

Endogenous supply of fiat money

We consider whether reputation concerns can discipline the behavior of a long-lived self-interested agent who has a monopoly over the provision of fiat money. We obtain that when this agent can commit to a choice of money supply, there is a monetary equilibrium where it never overissues. We show, however, that monetary equilibria with no overissue do not exist when there is no commitment. This happens because the incentives this agent has to maintain a reputation for providing valuable currency disappear once its reputation is high enough. More generally, we prove that in the absence of commitment overissue happens infinitely often in any monetary equilibrium. We conclude by showing that imperfect memory can restore the positive result obtained with commitment.

Intertemporal coordination with delay options

This paper studies equilibrium selection in intertemporal coordination problems with delay options. The risk-dominant action of the underlying one-shot game is selected when frictions are arbitrarily small. Larger frictions introduce real option effects in the model and inhibit coordination.

Effects of oxyfedrine on regional myocardial blood flow in patients with coronary artery disease

SummaryMedical treatment of angina pectoris is largely based on the use of beta-blocking agents, calcium antagonists, and nitrates. Oxyfedrine, an amino ketone derivative and partial agonist at beta receptors, has been shown to have potent antianginal properties and to increase coronary blood flow in normal and ischemic myocardial regions in experimental studies. We assessed the effects of intravenous oxyfedrine on regional myocardial blood flow, using positron emission tomography (15-oxygen water), in six patients with chronic stable angina, positive exercise tests, and documented coronary artery disease. Myocardial blood flow was measured in all patients before (baseline) and 10 minutes after the intravenous administration of a single bolus (0.11–0.13 mg/kg) of oxyfedrine. Compared to baseline, heart rate and systolic blood pressure remained almost unchanged after the administration of oxyfedrine. Mean baseline myocardial blood flow was 0.90±0.15 ml/g/min in areas supplied by arteries with significant coronary stenosis and 1.08±0.19 ml/g/min in areas supplied by nonstenotic coronary vessels (p<0.05). After the adminsitration of oxyfedrine, myocardial blood flow increased significantly in both the regions supplied by stenotic vessels (by 25%; from 0.90±0.15 to 1.20±0.31 ml/g/min; p=0.002) and in areas supplied by angiographically normal coronary vessels (by 22%; from 1.08±0.19 to 1.38±0.49 ml/g/min; p<0.05). The results of this study indicate that in patients with coronary artery disease, intravenous oxyfedrine significantly increases regional myocardial blood flow, both in areas supplied by critically obstructed vessels and in areas supplied by normal or less severely narrowed coronary arteries.

Optimal monetary interventions in credit markets

In an environment based on Lagos and Wright (2005) but with two rounds of pairwise meetings, we introduce imperfect monitoring that resembles operations of unsecured loans. We characterize the set of implementable allocations satisfying individual rationality and pairwise core in bilateral meetings. We introduce a class of expansionary monetary policies that use the seignorage revenue to purchase privately issued debts. We show that under the optimal trading mechanism, both money and debt circulate in the economy and the optimal in‡ation rate is positive, except for very high discount factors under which money alone achieves the …rstbest. Our model captures the view that unconventional monetary policy encourages lending while it may create in‡ation.

Informality in an economy with active labour courts

ABSTRACT Job regulations and the justice branch interfere on several aspects of labour contracts. We build a model which explores the role of labour courts on the wage distribution in both formal and informal sectors. We obtain that the presence of active labour courts produces a negative relation between the wage gap and the productivity of the worker, a regularity documented in the empirical literature. Active labour courts also reduce informality of unskilled workers but do not have an impact on informality of skilled workers. Some elements and implications of our model are tested using Brazilian data.