Instrumentation and Waveform Analysis
Core concepts
Understand the recording chain: electrodes (surface vs needle), amplifier, filters (low-frequency/high-frequency), sensitivity, sweep speed, and averaging. Filters shape the waveform: a high low-frequency filter removes slow components; a low high-frequency filter smooths sharp peaks and can distort onset latency. Sensitivity (gain) affects displayed amplitude, not the underlying signal. Averaging improves signal-to-noise ratio for small SNAPs.
Know how to identify waveform landmarks: onset latency (first deflection from baseline), peak latency, amplitude (baseline to peak or peak to peak), and area. Recognize artifacts: stimulus artifact, 60 Hz interference, movement, and EKG artifact. Understand impedance and electrode placement.
Traps
Questions test whether you know that changing sensitivity does not change true amplitude, and that filter settings can shift measured latency. A common error is reading peak latency when onset is required, or confusing stimulus artifact with a physiologic response.
Worked example / rule of thumb
If a SNAP is buried in noise, increase the number of averages rather than excessive gain; averaging reduces random noise by roughly the square root of the number of sweeps. Rule of thumb: onset latency for conduction velocity, peak latency for amplitude comparisons-state which you are measuring.