Given a passage, construct a question on the basis of the information present in the passage. Construct the question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) it answer uses text phrases from the passage. Avoid creating questions that (i) can't be answered correctly without actually understanding the passage and (ii) uses the same words or phrases given in the passage.

Large concentrations of meperidine inhibit N-methyl-D-aspartate-(NMDA) receptor channels by channel block mechanisms. Extracellular pH regulates the activity and drug sensitivity of NMDA-receptor channels. We examined the influence of extracellular pH on sensitivity to meperidine of epsilon/zeta heteromeric NMDA-receptor channels expressed in Xenopus oocytes. Inhibition of epsilon1/zeta1, epsilon2/zeta1, epsilon3/zeta1, and epsilon4/zeta1 channels by meperidine was dependent on pH, with more inhibition at acidic pH and less inhibition at alkaline pH. The degree of voltage-dependence of meperidine block was only slightly affected by changes in pH, whereas affinity for meperidine was greatly reduced at alkaline pH. Furthermore, interaction of meperidine with Mg(2+) block was reduced at alkaline pH. Because the percentage of the protonated form of meperidine is only slightly affected by pH, changes in properties of the meperidine binding site may be involved in mechanisms of alteration of meperidine potency by pH.
Is n-methyl-D-aspartate receptor channel block by meperidine dependent on extracellular pH?

Severe malaria (SM) is classically associated with Plasmodium falciparum infection. Little information is available on the contribution of P. vivax to severe disease. There are some epidemiological indications that P. vivax or mixed infections protect against complications and deaths. A large morbidity surveillance conducted in an area where the four species coexist allowed us to estimate rates of SM among patients infected with one or several species.', 'This was a prospective cohort study conducted within the framework of the Malaria Vaccine Epidemiology and Evaluation Project. All presumptive malaria cases presenting at two rural health facilities over an 8-y period were investigated with history taking, clinical examination, and laboratory assessment. Case definition of SM was based on the World Health Organization (WHO) criteria adapted for the setting (i.e., clinical diagnosis of malaria associated with asexual blood stage parasitaemia and recent history of fits, or coma, or respiratory distress, or anaemia [haemoglobin < 5 g/dl]). Out of 17,201 presumptive malaria cases, 9,537 (55%) had a confirmed Plasmodium parasitaemia. Among those, 6.2% (95% confidence interval [CI] 5.7%-6.8%) fulfilled the case definition of SM, most of them in children <5 y. In this age group, the proportion of SM was 11.7% (10.4%-13.2%) for P. falciparum, 8.8% (7.1%-10.7%) for P. vivax, and 17.3% (11.7%-24.2%) for mixed P. falciparum and P. vivax infections. P. vivax SM presented more often with respiratory distress than did P. falciparum (60% versus 41%, p = 0.002), but less often with anaemia (19% versus 41%, p = 0.0001).
Are plasmodium vivax and mixed infections associated with severe malaria in children : a prospective cohort study from Papua New Guinea?

There is a lot of evidence that angina during the 24-48 h before a reperfused myocardial infarction improves the evolution of the patients. However, there are studies that failed to demonstrate this protective effect of preinfarction angina in an interventional reperfusion setting.', 'To compare the effect of preinfarction angina (PIA) on inhospital evolution of thrombolysis vs. interventionally reperfused acute myocardial infarction (AMI).', 'There were prospectively studied 133 consecutive AMI patients, eligible for reperfusion (thrombolysis or interventional). History of PIA under 48 hours was obtained. Evolution of AMI was evaluated considering the following end-points: the ratio between the number of ECG leads with final pathologic Q wave and the number of leads with initial ST elevation, CK-MB values, separate and composite incidence of death, heart failure, shock and incidence of serious arrhythmia (sustained VT or ventricular fibrillation).', 'ECG ratio was lower in patients with PIA (0.511 +/- 0.281 vs. 0.646 +/- 0.274, p=0.02) in thrombolysed patients, but it was higher in interventionally reperfused patients (0.740 +/- 0.418 vs. 0.554 +/- 0.295 p=0.11). CK-MB values were lowered by PIA in thrombolysed AMI (122 +/- 74 vs. 190 +/- 89, p=0.0003), but they were not in the interventional group. Clinical end-points were slightly less frequent in patients with PIA, in both reperfusion groups, but not statistically significant. Major arrhythmia occurred less frequently in interventionally reperfused patients with PIA (9.5% vs. 31.6%, p=0.12).
Does prodromal angina reduce infarcted mass less in interventionally reperfused than in thrombolysed myocardial infarction?