Pharmaceutical & medical
Originally, vital sign monitoring took place in hospitals and clinics under strict medical supervision. Advances in microelectronics have led to cost reduction in monitoring systems, making these technologies more accessible and common in areas such as telemedicine, sports, fitness and wellness, and workplace safety, as well as the automotive market, which is becoming increasingly focused on autonomous driving. Despite this expansion and given the health- related nature of these applications, quality standards remain high.
V
VitAl SignS Monitoring vital signs involves measuring a series of physiological parameters that can give an indication of the health of an individual. Heart rate is one of the most common parameters, and it can be detected via an electrocardiogram, which measures the frequency of the heartbeat and, above all, its variations. Changes in heart rate tend to be based on activity. During sleep or when resting, the rhythm is slower, but tends to increase following physical activity, an emotional response, stress, or anxiety. A heart rate that falls outside the normal range
may indicate the presence of a disorder such as bradycardia (when the heart rate is too low) or tachycardia (when it is too high). Breathing is another key vital sign. The oxygenation level of the blood can be measured using a technique called
photoplethysmography (SpO2). Poor oxygenation can be related to the onset of diseases or disorders affecting the respiratory system. Other vital sign measurements that can provide indications as to a person’s physical condition are blood pressure, body temperature, and skin conductance response. Skin conductance response, also known as electrodermal response, is closely linked to the sympathetic nervous system, which in turn is directly involved in the regulation of emotional behaviors. Measuring skin conductance provides indications as to the stress, fatigue, mental state, and emotional response of a patient. Additionally, measuring body composition,
Figure 1. Signal chain for optical measurements.
ital sign monitoring has extended beyond the boundaries of medical practice and into many areas of our everyday lives.
vital Sign technologieS
Here, Cosimo Carriero, field applications engineer at Analog Devices, considers technology for condition-based monitoring of the human body.
the percentages of lean mass and fat mass, and the degree of hydration and nutrition provides clear indications as to a person’s clinical status. Lastly, measuring motion and posture can provide useful information on the activity of the subject.
teCHnologieS for MeASuring VitAl SignS In order to monitor vital signs such as heart rate, breathing, blood pressure and temperature, skin conductance, and body composition, various
sensors are required and solutions must be compact, energy efficient, and reliable. Vital sign monitoring includes:
Optical measurements
Biopotential measurements Impedance measurements
Measurements using MEMS sensors
optiCAl MeASureMentS Optical measurements go beyond standard semiconductor technology. In order to take this type of measurement, an optical measurement toolbox is required. Figure 1 shows a typical signal chain for optical measurements. Light sources (generally LEDs) are needed to generate a light signal, which may consist of different wavelengths. The combination of several wavelengths allows for greater measuring precision. A series of silicon or germanium sensors (photodiodes) are also required to transform the optical signal into an electrical signal, also known as the photocurrent. Photodiodes must respond to the wavelength of the light source with enough sensitivity and linearity. The photocurrent must then be amplified and converted, hence the need for a high performance, energy efficient, multichannel analogue front end that
32 June 2021 Instrumentation Monthly
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