Charge-duration curves

Charge-Duration Curve Short Duration Pulses Are More Efficient... 

Charge duration curve. The threshold charge injected Qth = /th x W is plotted in Figure 28.11b and increases as the pulse width increases. 

Stimulation Waveform effect on threshold, 28-15-28-18 charge duration curve,... 

Fig. 13 Strength-Duration and Charge-Duration Curves for Initiation of an Action Potential Rheobase current /rh is the current required when using an infinitely long pulse width. Chronaxie time is the pulse width corresponding to two times the rheobase current...

FIGURE 14.1 Strength-duration curves for current, energy, and charge. Adequate current shocks are above and to the right of the current curve. (Modified from Tacker WA, Geddes LA. 1980. Electrical Defibrillation, Boca Raton, FL, CRC Press. With permission.)... 

FIGURE 28.11 Effect of pulse width on excitation threshold, (a) Strength-duration curve. The amplitude of the current required to reach threshold decreases with the width of the pulse. This effect can be derived theoretically by assuming that the charge on the cable at threshold is constant, (b) The threshold charge (amplitude x pulsewidth) injected into the tissue increases with the pulse width. Narrow pulse are recommended to minimize charge injection. 

Dmg distribution into tissue reservoirs depends on the physicochemical properties of the dmg. Tissue reservoirs include fat, bone, and the principal body organs. Access of dmgs to these reservoirs depends on partition coefficient, charge or degree of ionization at physiological pH, and extent of protein binding. Thus, lipophilic molecules accumulate in fat reservoirs and this accumulation can alter considerably both the duration and the concentration—response curves of dmg action. Some dmgs may accumulate selectively in defined tissues, for example, the tetracycline antibiotics in bone (see Antibiotics,tetracyclines). 

The form of the signal is similar to the second derivative of the NPV curve and when the time duration of the second and third potential pulses fulfills T3 = 2r>/3, the DDTPV response coincides with that obtained in ADDPV for reversible charge transfer processes [88]. 

Details of the neutralization process following radiation-induced primary charge separation may be examined via the medium of ultrafast techniques now employed in studies of luminescence decay processes. As an example, the form of luminescence decay curves of dilute organic scintillator in aliphatic hydrocarbon solution excited by x-ray pulses of about 0.5-1.0 nsec, duration is attributed (in previous papers) to neutralization processes involving ions. The relation, t cc r3, for the time required for neutralization of an ion pair of initial separation r, when applied to such curves, leads to a distribution function of ion-pair separations. A more appropriate and desirable approach involves solution of a diffusion equation (which includes a Coulomb interaction term) for various initial conditions. Such solutions are obtained by computer techniques employed in analogy to corresponding electrical networks. The results indicate that the tocr3 law affords a fair description of the decay if the initial distribution can be assumed to be broad. 

---