KEY POINTS

1. Accuracy and precision are different. Accuracy is how close a value is to the true value. Precision is how repeatable the measurements are. An inaccurate, but precise monitor can be re-calibrated to be accurate, but an imprecise monitor cannot be improved.
2. Invasive pressure monitors are affected by damping and resonance. Damping leads to distortion, signal loss, and lowering of peak values. Resonance can lead to amplification and overestimation of the peak value.
3. Flow measurements are one of the most difficult to obtain and usually involve indirect measures. (For example, a temperature change or pressure drop is measured and a flow value is derived. A small error in the initial measurement leads to a much larger error in the derived flow value.)
4. Pulse oximetry combines analysis of optical plethysmography and absorption analysis with empirical data to produce an estimate of SaO₂ .
5. Wavelength and frequency are related to the speed of the wave by the following formula: speed = wavelength × frequency. Shorter wavelengths improve the resolution of both light and ultrasound measurements.
6. Filtering can improve the signal display, but it can also result in smoothing and loss of information.
7. A signal can be extracted from noise by repeated measurements because the noise is random over time but the signal is not.
8. Electrical signals can be converted from analog to digital. Conversion can introduce some artifacts but can allow for greater storage and analysis capabilities.