STRUCTURE OF THE THESIS The main thesis has 134 pages, including: Introduction: 2 pages Chapter 1 - Overview: 34 pages Chapter 2 - Subjects and methods: 22 pages Chapter 3 - Results: 38 pages Chapter 4 - Discussion: 35 pages Conclusion and recommendations: 3 pages The thesis has 160 references, 71 references in Vietnameses and 89 references in English.