Pulse generators complications

Most optical centers show luminescence decay times in the nanoseconds-milliseconds range. However, many other physical processes involved in optical spectroscopy are produced in the picoseconds-femtoseconds range, and mnch more complicated instrumentation becomes necessary. For instance, interband Inminescence in solids, which is of particular interest in semiconductors, can involve decay times in the range of picoseconds. Pulses generated from solid state lasers have already reached this femtosecond domain. 

Permanent pacemakers have also been implanted using the inferior vena cava via a retroperitoneal approach (Fig. 4.63) (117). This is usually in the setting of complex congenital anomahes and subsequent corrective procedures. Venous access to the right atrium and ventricle is complicated by loss of continuity between the right atrium and the superior vena cava. Bipolar active fixation screw-in electrodes are used for both the atrium and ventricle. The pulse generator is usually implanted in a subcutaneous pocket formed on the anterior abdominal wall. 

Pacemaker pocket erosion continues to be a problem (Fig. 4.104). This is best avoided by creating a pacemaker pocket that has maximum optimal tissue thickness. Occasionally, in extremely asthenic individuals, subpectorahs major muscle pulse generator placement should be considered to afford optimal tissue thickness. Patients can also present with preerosion secondary to pressure necrosis of the overlying tissue. Such situations represent a quasiemergency if one is to avoid complete erosion and wound infection. The patient should be reoperated, the old pocket abandoned, and new pacemaker pocket created away from the involved site. Sutton and Bourgeois incidence of pacemaker pocket complications are shown in Table 4.25 (17). 

Fig. 19.22 A patient was exercised in an effort to set-up the rate modulated features of his pacemaker as he was identified as having chronotropic incompetence complicating his marked sinus node dysfunction. Rather than using a formal exercise lab, he was taken for a walk in the Clinic corridor and then the Prediction Model of his Trilogy DR -I- pulse generator was accessed. The period between the two heavy vertical lines represents this exercise. The dotted lines represent the chaotic activity of his atrium during the walk. The sensor had been disengaged (passive) and the thin solid line shows the heart rate response that would have occurred if the sensor were controlling the paced rate at the displayed programmed parameters.

With broad-band pulses, pumping and probing processes become more complicated. With a broad-bandwidth pulse it is easy to drive fundamental and overtone transitions simultaneously, generating a complicated population distribution which depends on details of pulse stmcture [75], Broad-band probe pulses may be unable to distinguish between fundamental and overtone transitions. For example in IR-Raman experiments with broad-band probe pulses, excitation of the first overtone of a transition appears as a fundamental excitation with twice the intensity, and excitation of a combination band Q -t or appears as excitation of the two fundamentals 1761. 

The value of k so determined could then be compared with the theoretical value of 4ttN aD. However, when viscosity is considerable and/or for short lifetimes, the transient effect in diffusion is not negligible and -30% of the transfer may be attributable to the transient phase. In such a case, the luminescence decay is not simply exponential (Sveshnikov, 1935). For a brief pulse excitation, a complicated decay ensures on the other hand, for so prolonged an excitation as to generate a steady state, the resultant decay curve in many cases is indistinguishable from an exponential (Yguerabide et ah, 1964). 

The idea of using phase increment to achieve frequency-shifted excitation can be extended virtually to any sort of RF pulses, including the most complicated adiabatic inversion pulses where a non-linear phase increment has already been applied. Using the phase increment, double or multiple pulses can be constructed with only a single waveform generator in order to excite different regions of a NMR spectrum or to compensate the BSFS, BSPS, as well as BSOS. 

We have previously investigated ligand release in the 6-coordinate piperidine complexes of Ni octaethylporphyrin (10). For Ni(OEP), formation of the 6-coordinate complex is not complete, and so, the picture is complicated by the presence of both 4- and 6-coordinate species in the initial sample. However, upon excitation with the pulsed laser the relative proportions of the two Ni(OEP) species change as determined by changes in the relative intensities of the 4- and 6-coordinate sets of Raman marker lines. Thus, axial ligand release is observed in the excited state generated during the... 

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