Body Sensor Networking, Design and Algorithms. Saeid Sanei

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alt="Photos depict the new patch type ECG systems including electrodes and wireless connection."/>

      3.3.2 Other Sensors

      In principle, oximeters can operate in either transmissive or reflective mode. Those using an earlobe or finger measure the absorbed transmitted light through the tissue and others such as those used on the wrist work based on the reflective light by the tissue layers including the blood.

Photo depicts an electronic stethoscope of Littmann 3200 model. Schematic illustration of the concepts of transmissive and reflective oximetry. Photos depict two different models of oximeters. (a) digital pulse oximeter used on the finger and (b) wireless wrist pulse oximeter.

      The impedance pneumograph is a bioimpedance recorder for indirect measurement of respiration. Using superficial thoracic electrodes, the system measures respiratory volume and rate through the relationship between respiratory depth and thoracic impedance change [41].

      In the et-CO2 system, a device called a capnometer uses a small plastic tube inserted in the patient's mouth. The capnometer tube accumulates the expelled CO2 in each breath. An infrared light is then emitted to the CO2 from a moving source. Following absorption of infrared radiation overtime, a variation with breathing rate will be induced. The et-CO2-based systems are used in hospitals mainly for patients in critical conditions often within ICUs as well as ambulances for emergency checking of patient states. The capnographs, which look approximately like square waveform in normal conditions, significantly change during intubation, after cardiac arrest, ventilation problem, shock, emphysema, or leaking alveoli in pneumothorax, hypoxia due to asthma or mechanical obstruction, poor lung compliance, obese, and pregnancy [42].

      Body plethysmography is another common lung function test. It measures how much air is actually in the lungs when one inhales deeply. It also checks how much air remains in the lungs after they breathe out as much as they can. A plethysmograph has the same applications as a spirometer.

      The need for biological sensors was perhaps initially raised by the Department of Defense in the United States. In 2004 they announced an urgent need for the development of sensors for early-warning systems and the protection of military forces against potential chemical and biological attacks [43]. Traditionally, these sensors are particular types of chemical sensors and benefit from the high selectivity and sensitivity of biologically active materials.

      Such sensors produce an electrical signal proportional to the concentration of a specific chemical or set of chemicals in the human body. Therefore, they should be biocompatible with and have no toxic effect on humans. However, current biosensors are more than a chemical sensor and are often used in biomedical applications.

      The biosensors generally consist of a transducer, biological-recognition membrane in intimate contact with the transducer, and biologically active material, which is sensitive to the analyte molecule through a shape-specific recognition. Biosensors are generally divided into two categories: affinity-based and metabolic.

      3.4.1 The Structures of Biological Sensors – The Principles

      A biosensor consists of a biological sensing element and a transducer. The sensing elements can be organisms, tissues, cells, organelles, membranes, enzymes, receptors, antibodies, or nucleic acids. On the other hand, transducer types can be electrochemical, optical, calorimetric (thermal), or acoustic.

      Bio-affinity transducers rely on very strong binding through which the transducer detects the bound receptor-analyte pair. The most common bio-affinity recognition processes are receptor-ligand binding and antibody-antigen binding.

      Metabolic biosensors, on the other hand, sense the instances where the analytes are bound or the co-reactants are chemically altered, which in turn product molecules are formed, and the transducer detects the changes in concentration of the product molecules or co-reactants and consequently heat is released by the reaction. The common biometabolic processes are enzyme-substrate reactions and metabolism of specific molecules by organelles, tissues, and cells.

      Various kinds of biosensors are mainly based on:

       chemically sensitive semiconductor devices;

       thermistors;

       chemically

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