Final answer:
To adjust the RC time constant in heart defibrillation with fixed capacitance, one must manipulate the resistance of the circuit; increasing resistance will increase the time constant, and decreasing it will reduce the time constant. Adjustments to the applied voltage may also be needed to ensure the correct current is delivered.
Step-by-step explanation:
The RC time constant is a measure of the time it takes for a capacitor to charge to about 63.2% of its maximum voltage or to discharge to about 36.8% of its initial voltage through a resistor. In heart defibrillation, the RC time constant is critical as it determines how long the current flows during the defibrillation process, which is crucial for the safety and effectiveness of the procedure.
If the capacitance (C) in the defibrillation unit is fixed, adjusting the resistance (R) is the way to modify the RC time constant. Increasing the resistance would result in a larger RC time constant, meaning it would take more time for the capacitor to charge or discharge. Conversely, decreasing resistance will result in a smaller RC time constant, allowing the capacitor to charge or discharge more quickly.
Regarding adjustments to the applied voltage, when the resistance changes, it might also be necessary to adjust the voltage to ensure that the correct amount of current is delivered for effective defibrillation, as the current delivered is determined by both the applied voltage and the total resistance of the circuit.