Читать книгу Body Sensor Networking, Design and Algorithms - Saeid Sanei - Страница 18

Human physiology is a very complicated and vast area of science. It covers a large number of conditions and abnormalities in humans as well as animals. Wakefulness is taken to be a prime physiological state during which a person is conscious and aware of their environment. Sleep or coma are other states during which the person is not aware of their environment. Wakefulness may also be slightly different from being alert or vigilant as each state has its own characteristics and applications.

There are, however, states which describe abnormalities in the human body. Being deaf, dumb, lam, or blind are often considered abnormalities. Automatic techniques in instrumentation and data processing are able to distinguish most of these abnormalities from the human normal state. For example, a limp is a type of asymmetric abnormality of the gait and can be assessed or monitored using gait analysis techniques. There are many other state types of abnormalities or disabilities which require scrutinised medical examinations for their diagnosis and monitoring. Diverse examples include acathexia, an inability to retain bodily secretion; anhidrosis, the failure of the sweat glands; anaesthesia, the loss of bodily sensation with or without loss of consciousness; and elastosis, loss of elasticity in the skin of elderly people that results from degeneration of connective tissue.

There are some mechanical states of the body such as those related to joint flexion and extension. Gait analysis fully describes such states. Nevertheless, in a number of research works particularly related to brain–computer interfacing (BCI) applications for imaginary movement or related to amputated organs, electromyography (EMG) or EEG signals have been exploited.

Hypercarbia and hypocapnia (acapnia) represent abnormally high or low levels of carbon dioxide in the blood, respectively. It is not so difficult to measure and evaluate the carbon dioxide level in the blood using noninvasive sensors called oximeters, a relatively cheap monitoring modality widely available in hospitals and intensive care units (ICUs). The oximeters can also be used equivalently for measuring the blood oxygen level as well as the oxygen–carbon dioxide exchange during breathing caused by chocking, drowning, electric shock, or inhaling chemical gas.

Hyperthermia refers to high body temperature. The temperature can be measured using thermometers or nonintrusively using thermal imaging systems. Those who suffer from hyperthermia may have abnormalities in their heart rate, breathing, muscle activity, or brain rhythms, and the patterns of these signals can confirm the diagnosis.

Upon some mental or physical diseases such as Parkinson's or stroke, the patients may gradually lose their ability to walk, move their hands, or speak. In many such cases their muscles become weaker and they develop so-called myasthenia. In addition to measurement (using accelerometers) and characterisation of gait, surface or invasive EMG is one of the recording modalities often used to measure the muscle activity and its response to various stimuli.

Many heart diseases and abnormalities can be diagnosed by analysing the electrocardiogram (ECG) measuring heart muscle electrical activities, or stethoscope, which is used for auscultation and recording the heart sound.

Heart diseases refer to conditions that involve the heart, its vessels, muscles, valves, or internal electric pathways responsible for muscular contraction. Common heart diseases are coronary artery disease, heart failure, cardiomyopathy, heart valve disease, and arrhythmias.

In the case of heart attack, a coronary artery is blocked (usually by a blood clot), meaning an area of heart tissue loses its blood supply. This reduction of blood can quickly damage or kill the heart tissue, so quick treatments in an emergency department or catheterization suite are necessary to reduce the loss of heart tissue [10]. However, over 70 000 people die from heart disease in the UK each year, which accounts for approximately 25% of the total number of deaths.

Coronary artery disease occurs when a plaque, a sticky substance such as lipid or calcium compound, narrows or partially obstructs coronary arteries and can cause reduced blood flow. This consequently leads to chest pain (angina), a warning sign of potential heart problems such as a heart attack. The plaque may also trap small blood clots, causing full blockage of a coronary artery and resulting in a heart attack [11]. Figure 2.1 shows a schematic of the blocking of heart arteries with different severities.

Figure 2.1 Schematic of some possible blocking of heart arteries with different severities. (See color plate section for color representation of this figure)

A heart attack can cause other problems which may lead to more complication than the original problem of blocked arteries. For example, sudden cardiac death may occur when the ECGs become erratic. When the heart tissue that is responsible for regular electrical stimulus of heart muscle contractions is damaged, the heart stops effectively pumping the blood. Cardiomyopathy is a condition indicated by abnormal heart muscle. Abnormal muscles make it harder for the heart to pump blood to the rest of the body.

With cardiomyopathy, the abnormal muscles make it harder for the heart to pump blood to the rest of the body. There are three main types of cardiomyopathy: dilated, owing to stretched and thinned muscles, which lessens the heart's ability to pump blood; hypertrophic, meaning thickened heart muscle; or restrictive, which is a rare problem where the heart muscle does not stretch normally so the chambers do not sufficiently fill with blood.

Heart failure, or congestive heart failure, is when the heart's pumping action cannot meet the body's demand for blood. Heart failure has the same symptoms and signs as those seen with cardiomyopathy.

There are also many types of congenital heart defects. A congenital heart defect is a defect in the development of the heart that is usually first noticed at birth, though some abnormal cases are not diagnosed until adulthood. Some people with such defects don't need any treatment, but others may need medication or surgical repair.

In almost all heart diseases and abnormalities the ECG or heart sound patterns captured using a stethoscope deviate from the normal waveforms, and therefore researches have been undertaken to recognise or classify these patterns by applying signal processing and machine learning algorithms.

On the other hand, in auscultation of heart sound, for example to detect heart murmur, often the lung sound due to breathing is also heard. Examining the lung sound can assist clinicians in the detection of wheezing, lung infection, asthma, and many other pulmonary diseases.

In addition to the ECG (or EKG) and stethoscope, there are other anatomical or functional screening modalities to test and diagnose a heart disease. For example, a continual multichannel ECG system may be used to check the level of stress. This test measures the ability of a person's heart to respond to the body's demand for more blood during stress (exercise or work). Combination of ECG, heart rate, and blood pressure information may be examined as a person's exercise is gradually increased on a treadmill. The information helps to show how well the heart responds to the body's demands and may provide information to help diagnose and treat the defects. It can also be used to monitor the effects of heart treatment.

Many people have intermittent symptoms such as intermittent chest pain or occasional feelings of their heart beating faster or irregularly. In such cases, ECG changes may not be sufficiently useful for monitoring the heart over a long period or outside clinics. Instead, a device called a Holter monitor can be used and worn for a longer time. This device acts similarly to a normal ECG.

As another heart screening modality, an echocardiogram is a real-time moving picture of a functioning heart made by using ultrasound waves and generating meaningful images. It can show how well the heart chambers and heart valves operate (for example, effective or poor pumping action as the blood flows through the valves), before and after treatments, as well as other features.

Calcium build-up (plaque), blood clot, or lipid in coronary arteries, which are indeed life-threatening, can also be detected from three-dimensional (3D) computerised tomography (CT) scan of the heart.

Body muscles, on the other hand, translate thoughts to actions and therefore are considered as the most important movement related component of human body. EMG recordings check the health of both the muscles and the nerves controlling the muscles. The EMG signals can be used to detect the problems with muscles during rest or activity. Disorders or conditions that cause abnormal EMG patterns can be neurological, pathological, or biological. These disorders include [12]:

 alcoholic neuropathy: damage to nerves from drinking too much alcohol;

 amyotrophic lateral sclerosis (ALS): disease of the nerve cells in the brain and spinal cord that control muscle movement;

 axillary nerve dysfunction: damage of the nerve that controls shoulder movement and sensation;

 Becker muscular dystrophy: weakness of the legs and pelvis muscles;

 brachial plexopathy: problem affecting the set of nerves that leave the neck and enter the arm;

 carpal tunnel syndrome: problem affecting the median nerve in the wrist and hand;

 cubital tunnel syndrome: problem affecting the ulnar nerve in the elbow;

 cervical spondylosis: neck pain from wear on the disks and bones of the neck;

 common peroneal nerve dysfunction: damage of the peroneal nerve leading to loss of movement or sensation in the foot and leg;

 denervation: reduced nerve stimulation of a muscle;

 dermatomyositis: muscle disease that involves inflammation and a skin rash;

 distal median nerve dysfunction: problem affecting the median nerve in the arm;

 Duchenne muscular dystrophy: inherited disease that involves muscle weakness;

 facioscapulohumeral muscular dystrophy (Landouzy–Dejerine): disease of muscle weakness and loss of muscle tissue;

 familial periodic paralysis: disorder that causes muscle weakness and sometimes a lower than normal level of potassium in the blood;

 femoral nerve dysfunction: loss of movement or sensation in parts of the legs due to damage to the femoral nerve;

 Friedreich ataxia: inherited disease that affects areas in the brain and spinal cord that control coordination, muscle movement, and other functions;

 Guillain-Barré syndrome: autoimmune disorder of the nerves that leads to muscle weakness or paralysis;

 Lambert–Eaton myasthenic syndrome: autoimmune disorder of the nerves that causes muscle weakness;

 multiple mononeuropathy: a nervous system disorder that involves damage to at least two separate nerve areas;

 mononeuropathy: damage to a single nerve that results in loss of movement, sensation, or other function of that nerve;

 myopathy: muscle degeneration caused by a number of disorders, including muscular dystrophy;

 myasthenia gravis: autoimmune disorder of the nerves that causes weakness of the voluntary muscles;

 peripheral neuropathy: damage of nerves away from the brain and spinal cord;

 polymyositis: muscle weakness, swelling, tenderness, and tissue damage of the skeletal muscles;

 radial nerve dysfunction: damage of the radial nerve causing loss of movement or sensation in the back of the arm or hand;

 sciatic nerve dysfunction: injury to or pressure on the sciatic nerve that causes weakness, numbness, or tingling in the leg;

 sensorimotor polyneuropathy: condition that causes a decreased ability to move or feel because of nerve damage;

 Shy–Drager syndrome: nervous system disease that causes body-wide symptoms;

 thyrotoxic periodic paralysis: muscle weakness from high levels of thyroid hormone;

 tibial nerve dysfunction: damage of the tibial nerve causing loss of movement or sensation in the foot.

Surface EMGs are very noisy and often include the effects of heart pulsation, movement, and system noise. Therefore, computerised systems and algorithms for recognition of the abnormalities should be robust against noise. In some cases, however, EMG is taken invasively by inserting a needle electrode into the muscle.

A physical or physiological condition caused by a disease is often called the pathological state. Such a state is also evaluated by examining biochemistry and chemical metabolism of the human body often through sampling and laboratory analysis of human blood, exhale, tissue, urine, or faeces.