Key factors that affect or limit Biomedical Measurements

Low measurement ranges – Biomedical instruments are used to measure various medical and physiological parameters. Most of the parameter measurement ranges are quite low compared with non-medical parameters. For example, most biomedical voltages are in the microvolt range and the pressures are also low about 1.93 psi. These general properties of medical parameters limit the practical choices that are available to designers for all the features of instrument design.

Inaccessibility of measurement variables – various crucial variables in living organisms are inaccessible because the proper measurand-sensor interface cannot be obtained without damaging the system. Unlike many sophisticated physical systems, a biological system is of such a nature that it is not possible to turn it off and remove parts of it during the measurement procedure. The physical size of many sensors prohibits the formation of a proper interface, even if interference from other physiological systems can be prevented. Either such inaccessible variables must be measured indirectly or corrections must be applied to data that are affected by the measurement process. A typical example of a biomedical measurement that is not accessible is the cardiac output.

Hardly deterministic measurements– unlike physical systems, variables measured from the biological systems are rarely deterministic. Most measured quantities vary with time, even when all controllable factors are fixed.  Many medical measurements vary widely among normal patients, even when conditions are similar. This inherent variability has been documented at the molecular and organ levels, and even for the whole body. The most common technique of coping with this variability is to assume empirical statistical and probabilistic distributions functions. Single measurements are then compared with these standards.

Difficulties in establishing safe levels of external energy to the living tissue from biomedical Instruments – almost all biomedical measurements depend either on some of energy being applied  to the living tissue or on some energy being applied as an incidental consequence of sensor operation. X-ray and ultrasonic imaging techniques, electromagnetic or Doppler ultrasonic blood flowmeters depend on externally applied energy interacting with the living tissue. It is difficult to establish safe levels of these various types of energy, because many mechanism of tissue damage are not well understood. Damage to tissue has been demonstrated in some cases at the molecular level at astonishingly low energy levels.

Related: Key Factors to Consider when Designing Biomedical Instruments

Instruments operational constraints – the operation of biomedical instruments in a medical environment imposes key restraints. The equipment must be reliable, easy to operate and capable of withstanding physical abuse and exposure to corrosive chemicals. The electronic equipment are designed to minimize electric-shock hazards. The safety of patients and medical personnel must be considered in all phases of the design and testing of instruments.

You can also read:

• The Introduction to Biomedical Instrumentation
• 3 Sources of Noise in Biomedical Measurement Systems
• Key Performance Requirements of Effective Biomedical Instrumentation Systems