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Frecuencia cardiaca - Tensión arterial - Tamaño de las cavidades del corazón - Incremento del volumen sistólico - Vasos sanguíneos - El volumen plasmático - El consumo máximo de oxígeno (VO2 máx.)

When the system is oscillatory or excitable, more complex behaviour can arise. By excitable we mean that the system has a stable steady state that when perturbed by a small amount quickly returns to its initial concentrations, but perturbations that exceed a threshold .rst grow before the system relaxes back to the original state. Such excitable media occur not only in chemical systems but also in biological contexts, such as nerve cells and heart muscle. Instead of a simple front, one observes either a single pulse or a series of pulses, in which the concentrations are at one level before and after the pulse and at a di.erent level within the pulse, which has fronts both ahead of and behind it (“wave front” and “wave back”).

A continuació podeu consultar també l'explicació sobre la recerca que està realitzant el professor Sagués, coautor de l'assaig:
"En l'equip de recerca que encapçalo tenim una llarga tradició en
l'estudi de reaccions oscil.lants i en altres fenomens relacionats
propis de reaccions quimiques no lineals. Darrerament ens hem
interessat en la propagació d'ones en medis quimics excitables. Es conegut que
existeix efectivament una relació d'aquest tipus d'estudis, formulats
diguem en un context quimic, amb problemes de cardiologia. La relacio
es clara des del moment en que podem considerar el teixit cardiac com un
medi excitable i la contracció de les seves fibres com el resultat de
la propagació al llarg del teixit d'una senyal electrica anomenada
potencial d'acció. Aixo ens ha portat molt recentment a estudiar
aspectes de propagació irregular d'aquestes "ones de potencial", en
situacions que d'alguna manera estarien relacionades amb episodes de
fibril.lacio ventricular."

Just because cells don't have a heart doesn't mean that they can't have a 'heartbeat'. Biologists Howard Petty and colleagues from Wayne State University in Detroit, USA, now report that single cells undergo pulsations akin to those of a beating heart.
The researchers have made videos of the changes in concentration of certain chemical compounds, 'NADPH' and 'NADH' (collectively NAD(P)H), within individual blood cells called neutrophils, as they explain in Physical Review Letters1. These substances are fluorescent, and so the researchers could monitor their distribution in the cells by shining light onto them, and then photographing the emitted light through a microscope.
They saw a 'wave' of NAD(P)H travelling from one end of each sausage-shaped cell to the other and back again. The oscillations happened at a rate of about three per second. Petty's group also found evidence that the cells' acidity -- the concentration of hydrogen ions -- oscillated too. They saw a wave of high acidity pass back and forth along a cell when they added an acid-sensitive fluorescent dye.

We have investigated periodic and turbulent waves in excitable media and, in particular, in the Belousov-Zhabotinsky (BZ) reaction. We found that turbulence can be induced by high light intesity or low catalyst concentrations (in the Ru-catalyzed reaction) by oxygen, or by methanol.

A recent television program told of a surgical procedure developed to repair an aneurism in the brain of a patient. In order to perform this delicate repair it was necessary to remove a large fraction of the blood from the patient to deflate the aneurism. However, the body needs oxygenated blood to keep cells, and particularly brain cells, alive. How is this to be done? Furthermore, the cells use energy through biochemical processes and these need to be slowed down. The program described the process by which the body temperature was lowered from 98.6F (37C) to 65F (18.3C) and made a big thing about the fact that the patient's heart beat stopped. It is this we wish to consider from the point of view of rhythms and chemistry.(...)

En aquesta pàgina web pots torbar informació referent als passos a seguir per portar a terme un experiment de laboratori per estudiar les reaccions d'oscil.lació.
"The next step in our kinetics part of the show is to move from single-step and multistep (clock) reactions to oscillating reactions. Here, after reaction is completed, the system returns to its “initial” state and the reaction starts over again. The particular example we use (the Briggs-Rauscher (BR) reaction) is perhaps the most impressive of the chemical oscillations. Three colourless solutions are mixed in a beaker and the stirred batch goes through 15 or more cycles of colourless, to amber, to blue-black, before ending as a blue-black mixture with the odour of iodine. The reaction was developed by Thomas S. Briggs and Warren C. Rauscher of Galileo High School in San Francisco [1]. This reaction is a hybrid of two other oscillating chemical reactions, the Bray-Liebhafski reaction and the Belousov-Zhabotinsky reaction [2]. The simplified (but still rather lengthy) explanation of the chemistry involved is given in the end of this section.(...)"

The oscillating reactions are more than a laboratory curiosity. If in the industrial processes they appear in few cases, in biochemical systems there are numerous examples of oscillating reactions. For instance, the oscillating reactions maintain the rhythm. All live processes are based on one or more oscillating reactions.