Excitation region volume

As Balankin shown [4], the relative change of excitation region volume in deformed body can be presented in the form ... 

Fig. 13.19. Excitation region Tn the crossing volume of dye laser beam and atomic beam in the center of a confocal F.P.I. [13.33]...

Because the excitation intensity varies as the square of the distance from the focal plane, the probability of two-photon absorption outside the focal region falls off with the fourth power of the distance along the z optical axis. Excitation of fluorophores can occur only at the point of focus. Using an objective with a numerical aperture of 1.25 and an excitation beam at 780 nm, over 80% of total fluorescence intensity is confined to within 1 pm of the focal plane. The excitation volume is of the order of 0.1-1 femtoliter. Compared to conventional fluorometers, this represents a reduction by a factor of 1010 of the excitation volume. 

The decreased work capacity of the in-farcted myocardium leads to a reduction in stroke volume (SV) and hence cardiac output (CO). The fall in blood pressure (RR) triggers reflex activation of the sympathetic system. The resultant stimulation of cardiac 3-adreno-ceptors elicits an increase in both heart rate and force of systolic contraction, which, in conjunction with an a-adren-oceptor-mediated increase in peripheral resistance, leads to a compensatory rise in blood pressure. In ATP-depleted cells in the infarct border zone, resting membrane potential declines with a concomitant increase in excitability that may be further exacerbated by activation of p-adrenoceptors. Together, both processes promote the risk of fatal ventricular arrhythmias. As a consequence of local ischemia, extracellular concentrations of H+ and K+ rise in the affected region, leading to excitation of nociceptive nerve fibers. The resultant sensation of pain, typically experienced by the patient as annihilating, reinforces sympathetic activation. 

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