Pre amplifier isolation in ECG circuit is to

The correct answer is: A. Increase input impedance.

Preamplifier isolation in ECG circuit is to increase input impedance. This is because the ECG signal is very small and can be easily affected by noise. By increasing the input impedance, the preamplifier can reduce the effect of noise on the signal.

Option B is incorrect because decreasing the input impedance would make the preamplifier more susceptible to noise.

Option C is incorrect because increasing the output impedance would make the preamplifier less sensitive to the ECG signal.

Option D is incorrect because decreasing the output impedance would make the preamplifier more susceptible to noise.