Monophasic waveform

Figure 6.11 Unipolar potentials from a current dipole moving along the horizontal x-axis. Dipole length is L c) the unit of the x-axis is L c- The recording electrode is at distance SL c and lOLcc (a) horizontal dipole orientation, biphasic waveforms, and high spatial resolution (b) vertical dipole orientation, monophasic waveforms, and largest signal amplitude of...

The waveform pattern obtain by duplex scanning can also be used for diagnosing proximal or distal disease (/6,77). A triphasic waveform in the common femoral artery indicates that the ipsUateral proximal vessels are normal. A biphasic waveform would indicate stenosis that is not significant, and a monophasic waveform would signify the presence of significant stenosis or occlusion (Fig. 3). A low-end diastolic velocity indicates a tight stenosis or occlusion distal to the measurement (Fig. 4). 

Fig. 3. continued from page 31) stenosis. (C) Monophasic waveform denotes the presence of significant stenosis or occlusion. (D) Angiography and duplex scanning in a patient with intermittent claudication in the left lower extremity. In the right lower extremity the waveform is triphasic and the ipsilateral iliac artery in the angiogram is normal. In the contralateral limb the waveform is monophasic and a significant stenosis is present in the ipsilateral iliac artery (solid arrow). 

Fig. 4. Low amplitude waveform with absence of end diastolic velocity is common in patients with oecluded arterial segments above and below the segment under investigation. (A) Low amplitude and absence of end diastolic velocity in the superficial femoral artery in the mid-thigh in a patient with common iliac significant stenosis and distal superficial femoral artery occlusion. (B) Very low velocities and a monophasic waveform in the posterior tibial artery of a patient with multiple stenoses and occlusions proximal and distal to the site of measurement.

The degree of deviation from the symmetry of a normal or Gaussian distribution is measured by skewness. This third central moment of the amplitude histogram has a value of zero when the distribution is completely symmetrical and assumes some nonzero value when the EEG waveforms are asymmetrical with respect to the baseline (as is the case in some characteristic sleep patterns, murhythms, morphine spindles, barbiturate spiking, etc.). In general, a nonzero value of the skewness index reflects the presence of monophasic events in the waveform. The following methods can be used to obtain the measure of skewness ... 

Improved defibrillator waveforms have been developed and been advocated during the years from [1] multiple pulse sine waveform to [2] simple capacitor discharge waveform to [3] damped sine (RLC) waveform, to [4] monophasic truncated exponential decay waveform, to [5] a pair of truncated exponential waveforms, to [6] paired, biphasic truncated exponential decay waveforms. It is evident that the... 

The most used current waveform is rectangular monophasic or biphasic. With defined electrode/tissue geometry, there is a relationship between the pulse duration and the current level necessary for nerve excitation. Figure 5.17 shows an example as the pulse duration increases, the necessary current approaches asymptotically a baseline current called the rheobase. The chronaxie is the pulse duration with the double rheobase current. 

There is a certain range of accepted current duration. Figure 10.18 shows some current discharge current waveforms. Note that some models use hiphasic waveforms, some use truly monophasic. 

Defibrillators are also made as implanted types, using intracardial catheter electrodes. To reduce energy consumption, new waveforms have been taken into use the exponential truncated waveform. It may be monophasic or biphasic. The idea of the hiphasic waveform is that the second pulse shall cancel the net charge caused by the first pulse and thereby reduce the chance of refibrillation. 

Fig. 5.12a-f. Normal waveform changes in the cavernosal arteries during the onset of erection, a Phase 0. Monophasic flow with minimal or no diastolic flow occurring in the flaccid state, b Phase 1. Increased systolic and diastolic flow, c Phase 2. Dicrotic notch appearance at end systole and progressive decrease of the diastolic flow, d Phase 3. End diastolic flow disappearance, e Phase 4. Diastolic flow reversal, f Phase 5. Reduction of the systolic peak during rigid erection... 

Initially, light pressure is used so as not to collapse the vein (Fig. 4.33a). With the probe straddling both artery and vein, further pressure is subsequently applied. If the vein is patent, the walls collapse and appose each other completely (Fig. 4.33b). When the pressure is released, the lumen of the vein returns to normal. If the vein contains clots, it will not collapse but remains distended when applying probe pressure (Fig. 4.33a,b). In lower limb veins, Doppler imaging and spectral analysis reveal monophasic venous flow rather than triphasic waveforms. In contrast, upper limb veins demonstrate more pulsatile flow because of their closer proximity to the heart (Chin et al. 2005). The use of low velocity (3-6 cm/s)... 

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