Jawaharlal Nehru Technological University Hyderabad B.Tech IV FUNDAMENTALS OF BIOMEDICAL APPLICATIONS Previous Question Paper (July/August - 2022 - R18)

Measuring biological parameters presents unique challenges due to the nature of living systems and the sensitivity of the required instrumentation. Key problems include:

• Low Signal-to-Noise Ratio: Biological signals are typically very weak (microvolt to millivolt range) and are often masked by significant environmental noise, such as 50/60 Hz power line interference and motion artifacts.
• High Source Impedance: Electrodes used to pick up bio-potentials often have high and unstable impedance, which requires high input impedance amplifiers to prevent signal attenuation and loading effects.
• Motion Artifacts: Movement of the subject or the electrode-skin interface causes fluctuations in the half-cell potential, resulting in baseline drift and noise that can be larger than the physiological signal itself.
• Inaccessibility: Many physiological parameters are located deep within the body, requiring invasive probes or sophisticated non-invasive techniques that may alter the variable being measured.
• Safety and Isolation: Direct electrical connection to the body poses risks of electric shock. Strict electrical isolation (galvanic isolation) is mandatory to protect the patient from leakage currents.
• Variability: Biological parameters are non-stationary and exhibit high inter-subject and intra-subject variability, making it difficult to establish universal calibration standards.

The Nernst equation describes the equilibrium potential for a specific ion across a semi-permeable membrane. At equilibrium, the chemical driving force (due to the concentration gradient) is exactly balanced by the electrical driving force (due to the potential difference).

The chemical potential energy gradient for an ion is given by:

The electrical potential energy gradient is given by:

At equilibrium, ΔG_chem + ΔG_elec = 0. Therefore:

Rearranging for the membrane potential (E_m), we obtain the Nernst equation:

Where:

• R: Universal gas constant (8.314 J/mol·K)
• T: Absolute temperature in Kelvin
• z: Valence of the ion
• F: Faraday's constant (96485 C/mol)
• C_out / C_in: Ratio of extracellular to intracellular ion concentrations