ABSTRACT
This study describes the application and evaluation of a novel didactic tool (thermodynamic device) developed for students in the area of biology who have conceptual deficiencies that render the learning of thermodynamic principles difficult. Systems of communicant vessels with equal and different compartments were constructed to correlate the equilibrium constant of the reactions and reagent/product ratios with the concept of standard and nonstandard Gibbs free energy changes (ΔG° and ΔG, respectively). The communicating vessels were filled respectively with equal and different volumes of a dye aqueous solution followed by the opening of a faucet that coupled the vessels. This procedure allows liquid flux leading to the movement of internal propellers. The movement of the propellers turns on an electronic circuit that processes the information to exhibit the energy released by the movement of the solution toward equilibrium. The thermodynamic device was evaluated regarding the efficiency of content comprehension and retention of the gain by challenging students to answer five subjective questions 1 week after a regular teaching module about thermodynamics. The overall mean score obtained by the students who accessed the thermodynamic device (7.0) was significantly higher (p < 0.01) than the mean score of the control group (3.4). The thermodynamic device increased twofold the percentage of students who gave more than 50% correct answers. The efficiency of the didactic tool was also evaluated and corroborated by objective questions. In conclusion, the use of the thermodynamic device was highly effective in improving the understanding of thermodynamic principles by undergraduate biology students.
ABSTRACT
OBJECTIVES: To compare carotid intima-media thickness (cIMT) of children and adolescents with and without HIV infection and to determine associations among independent socio-demographic, clinical or cardiovascular variables and cIMT in HIV-infected children and adolescents. PATIENTS AND METHODS: This is a matched case-control study comparing 83 HIV-infected and 83 healthy children and adolescents. Clinical and laboratorial parameters, cIMT and echocardiogram were measured. RESULTS: The cIMT was higher in HIV-infected individuals (median 480 microm; interquartile range 463-518 microm) compared with controls (426 microm; range 415-453 microm, P<0.001). In addition, the HIV-infected group showed higher levels of high-sensitive C-reactive protein (medians 1.0 mg/l vs. 0.4 mg/l, P<0.001), glycated hemoglobin (6.1+/-0.9 vs. 5.7+/-0.8%, P=0.028) and triglycerides (medians 0.9 vs. 0.8 mmol/l, P=0.031). Finally, this group showed lower levels of total and high-density lipoprotein-cholesterol. After multivariate analysis, increased cIMT was positively associated with stavudine use [odds ratio (OR): 18.9, P=0.005], left atrial/aorta index (OR: 15.6, P=0.019), suprailiac skinfold (OR: 7.9, P=0.019), tachypnea (OR: 5.9, P=0.031), CD8 lymphocyte count (OR: 5.7, P=0.033) and CD4 T-lymphocyte count (OR: 5.5, P=0.025). cIMT increment was negatively associated with total cholesterol (OR: 0.2, P=0.025) and with CD8 zenith (OR: 0.1, P=0.007). CONCLUSION: In this sample of children and adolescents, having HIV infection was associated with increased cIMT and elevated prevalence of cardiovascular risk factors. These findings suggest that this group should be included in cardiovascular prevention programs.