When spectral analysis of the heart rate (HR) signal is performed, it is quite common to attribute the HF indexes of heart rate variability (HRV) to cardiac vagal control. The paradigm underlying this attribution states that changes in cardiac vagal outflow correspond to a proportional change in respiratory sinus arrhythmia (RSA). However, recent studies have demonstrated that variations in these indexes do not necessarily reflect proportional changes in vagal tone. The current study provides a theoretical evaluation of the relationship between mean HR, RSA, and cardiac vagal tone. This evaluation is based on a theoretical model, which quantifies the differential effects of vagal blockade by a competitive muscarinic antagonist on the HF indexes of HRV. The model relies on several assumptions that reflect the basic physiology of the sinoatrial (SA) node, as well as pharmacological relations that describe agonist/antagonist equilibrium at the SA receptors. The mathematical framework of this model is the integral-pulse-frequency-modulation (IPFM) process, and its derivations lead to a specific expressions for the dependence of HF and mean HR on the level of vagal blockade. These expressions provide a new insight into the relationship between mean HR, RSA, and vagal tone, and explain conflicting experimental results previously published.

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The derivations of the model lead to a closed set of equations, from which the dependence of the HF indices on the level of vagal blockade is deduced. It is shown that several aspects of the physiological condition may have a substantial effect on this relationship: the level of baseline vagal activity, the relationship between vagal tone and the fluctuations in its traffic, the level of sympathetic activity, etc em leader Hence, changes in the HF indices of HRV provide a plausible assessment of the changes in cardiac vagal tone only under a specific range of physiological conditions.

The Future Scientists' and Inventors' Program at Tel Aviv University was initiated by the Israeli president, Mr. Shimon Peres, in response to the decline in the number of students applying to scientific and technological studies. The program is tailored for the proficient nourishment of gifted teenagers. Our vision is to create a scientific community whose members are committed, skillful and happy to collaborate and share. Our courses go beyond mere enrichment for leisure or acquisition of academic merits. We offer a worthwhile purpose for the so-far unchallenged youth. The program demands academic standards, hard work, and is designed to take young teenagers through a journey of revelation, following the historical process of scientific thought. Instead of formal lectures, our lessons assume the form of discussion, during which the students are encouraged to take part in the development of scientific discoveries. The students search for questions, experience the excitement of discovery as well as its difficulties and limitations, and deeply understand the basics of the material.After four years of running the program, we achieved great results: our young students have passed difficult undergraduate exams with exceptionally high grades, and our senior students have already started partaking in actual academic research. Our program demonstrates a method for maximizing gifted children's potential, and arousing their passion for scientific work. In addition, a young community of scientists is formed within the program, and its members develop the skills to work together, consult peers and are positively committed to high quality scientific research.