JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV FUNDAMENTALS OF BIOMEDICAL APPLICATIONS Previous Question Paper (February/March - 2022 - R18)

Static characteristics refer to the performance parameters of a medical instrument when the input signal is constant or varies very slowly over time. The key characteristics are:

• Accuracy: The closeness of the instrument reading to the true or accepted value of the measured quantity.
• Precision: The ability of an instrument to reproduce the same reading consistently for multiple measurements of the same input.
• Sensitivity: The ratio of the change in output signal to the change in input signal.
• Resolution: The smallest change in the input variable that produces a detectable change in the instrument output.
• Linearity: The closeness of the actual calibration curve to a specified straight line.
• Hysteresis: The difference in output readings for the same input when approached from increasing versus decreasing directions.
• Drift: The gradual variation in the output of an instrument over time while the input remains constant.
• Threshold: The minimum value of the input required to produce a detectable output.

The Nernst equation describes the equilibrium potential of an ion across a semi-permeable membrane, where the electrical gradient exactly balances the chemical concentration gradient.

For an ion with valence z, the electrochemical potential energy difference is given by the sum of chemical and electrical work. At equilibrium, the net flux is zero:

Where R is the gas constant, T is absolute temperature, F is Faraday's constant, and E is the membrane potential. Rearranging for E:

Or, by inverting the ratio:

At body temperature (37°C), converting to base-10 logarithm, the equation simplifies to:

This equation defines the resting potential by calculating the potential at which the diffusion of ions (primarily K⁺) through the membrane is balanced by the electrical attraction of the negative intracellular charge.