An esthesiometer (British spelling aesthesiometer) is a device for measuring the tactile sensitivity of the skin (or mouth, or eye, etc.). The measure of the degree of tactile sensitivity is called aesthesiometry. The device was invented by Edward Henry Sieveking. There are different types of aesthesiometers depending on their particular function.
The simplest is a manual tool with adjustable points similar to a caliper. It can determine how short a distance between two impressions on the skin can be distinguished. To differentiate between two points and one point of equal area (the sum of the areas of the two points equals the area of the third point), Dr. Sidney Weinstein created the three-point esthesiometer. A scale on the instrument gives readings in millimeter gradients.
Another type of manual aesthesiometer is used to test lower thresholds of touch or pain. The tool uses nylon monofilaments with varying calibrated diameters. The force needed to cause the monofilament to buckle determines the tactile reading. The filaments are calibrated by force applied, rather than by gram/mm2 pressure ratings, because sensation follows force (when the stimulated area is small).
A von Frey hair is a type of aesthesiometer designed in 1896 by Maximilian von Frey. Von Frey filaments rely on the principle that an elastic column, in compression, will buckle elastically at a specific force, dependent on the length, diameter and modulus of the material. Once buckled, the force imparted by the column is fairly constant, irrespective of the degree of buckling. The filaments may therefore be used to provide a range of forces to the skin of a test subject, in order to find the force at which the subject reacts because the sensation is painful. This type of test is called a mechanical nociceptive threshold test.
The buckling force is inversely proportional to the length of the column (so the shorter the column, the higher the force required to buckle it) and proportional to the cube of the diameter, so that increasing the diameter of a filament by a small amount increases the buckling force considerably. Sets of filaments [1] are normally made of nylon hairs, all the same length, but of various diameters so as to provide a range of forces, typically from 0.008 grams force up to 300 grams force. Von Frey filaments are a diagnostic, research, and screening tool, used both in human and animal medicine. They are readily used to study skin areas with normal responsiveness, as well as hyper- or hyposensitive areas.
The determination of a mechanical threshold using von Frey filaments requires a number of discrete tests using filaments with different bucking forces. There are two commonly used algorithms, the up-down method and the percent response method. The up-down method is most commonly used, [2] usually requiring a minimum of four tests after the first response is detected. The first measurement should be made with a filament with a buckling force close to the expected mean of the population. Errors may result if testing is commenced a long way above or below the mean. These errors have been evaluated by a combination of experimentation and mathematical simulation. [3]
The Semmes-Weinstein Aesthesiometer, and its variant the Weinstein Enhanced Sensory Test (WEST, e.g., WEST-hand), present nylon monofilaments of approximately the same length (38 mm) and of varying diameters. The diameter and length are used to control the force applied. Whereas Dr. Weinstein used 3-digit numbers to reflect the force of the Semmes-Weinsein Aesthesiometer (3 digit number equals the common log of the force measured in tenths of a milligram), the WEST esthesiometers (also created by Weinstein and group) use grams (e.g., 0.70 g) to describe the force.
For small-area stimulating instruments like WEST, force, rather than area, is the appropriate measure. This is because an approximately equal area of skin is indented for the heavy and light forces (see Weinstein et al., Evaluation of sensory methods in neuropathy, in Tendon and Nerve Surgery in the Hand—a Third Decade, by Hunter et al.).
The area of stimulation of the Semmes-Weinstein Aestheiometer is not correctly described by the area of the stimulating nylon (the nylon twists on the skin, pushing a sharp edge into the skin). Therefore, the unit gram/mm2 is descriptive of the geometry but not the function. The WEST esthesiometer has a bulb for a contacting tip, so when the tip bends it presents the same contacting face.
A non-intrusive device called a corneal aesthesiometer is used to test cornea nerve sensitivity by using a controlled pulse of air as stimulation. The device gives readouts in millibars. Also, a thermal aesthesiometer is used to determine sensitivity of thermal stimuli.
Weinstein and group created an air-based corneal esthesiometer using gram-force (tens of micrograms force). They also created an air-based oral esthesiometer. For example, smokers' upper throats are much less sensitive than nonsmokers.
Yarn is a long continuous length of interlocked fibres, used in sewing, crocheting, knitting, weaving, embroidery, ropemaking, and the production of textiles. Thread is a type of yarn intended for sewing by hand or machine. Modern manufactured sewing threads may be finished with wax or other lubricants to withstand the stresses involved in sewing. Embroidery threads are yarns specifically designed for needlework. Yarn can be made of a number of natural or synthetic materials, and comes in a variety of colors and thicknesses. Although yarn may be dyed different colours, most yarns are solid coloured with a uniform hue.
A speargun is a ranged underwater fishing device designed to launch a tethered spear or harpoon to impale fish or other marine animals and targets. Spearguns are used in sport fishing and underwater target shooting. The two basic types are pneumatic and elastic. Spear types come in a number of varieties including threaded, break-away and lined. Floats and buoys are common accessories when targeting larger fish.
Stimulus modality, also called sensory modality, is one aspect of a stimulus or what is perceived after a stimulus. For example, the temperature modality is registered after heat or cold stimulate a receptor. Some sensory modalities include: light, sound, temperature, taste, pressure, and smell. The type and location of the sensory receptor activated by the stimulus plays the primary role in coding the sensation. All sensory modalities work together to heighten stimuli sensation when necessary.
A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, are sent to the central nervous system.
A nociceptor is a sensory neuron that responds to damaging or potentially damaging stimuli by sending "possible threat" signals to the spinal cord and the brain. The brain creates the sensation of pain to direct attention to the body part, so the threat can be mitigated; this process is called nociception.
Hyperalgesia is an abnormally increased sensitivity to pain, which may be caused by damage to nociceptors or peripheral nerves and can cause hypersensitivity to stimulus. Prostaglandins E and F are largely responsible for sensitizing the nociceptors. Temporary increased sensitivity to pain also occurs as part of sickness behavior, the evolved response to infection.
Monofilament fishing line is fishing line made from a single fiber of plastic material, as opposed to multifilament or braided fishing lines constructed from multiple strands of fibers. Most fishing lines are now nylon monofilament because they are cheap to produce and can be produced in a range of diameters which have different tensile strengths. Monofilament line is also manufactured in different colors, such as clear, white, green, blue, red, and fluorescent.
Neuralgia is pain in the distribution of one or more nerves, as in intercostal neuralgia, trigeminal neuralgia, and glossopharyngeal neuralgia.
In neuroscience and psychophysics, an absolute threshold was originally defined as the lowest level of a stimulus – light, sound, touch, etc. – that an organism could detect. Under the influence of signal detection theory, absolute threshold has been redefined as the level at which a stimulus will be detected a specified percentage of the time. The absolute threshold can be influenced by several different factors, such as the subject's motivations and expectations, cognitive processes, and whether the subject is adapted to the stimulus.
The absolute threshold can be compared to the difference threshold, which is the measure of how different two stimuli must be for the subject to notice that they are not the same.
Sensory substitution is a change of the characteristics of one sensory modality into stimuli of another sensory modality.
A dolorimeter is an instrument used to measure pain threshold and pain tolerance. Dolorimetry has been defined as "the measurement of pain sensitivity or pain intensity". Dolorimeters apply steady pressure, heat, or electrical stimulation to some area, or move a joint or other body part and determine what level of heat or pressure or electric current or amount of movement produces a sensation of pain. Sometimes the pressure is applied using a blunt object.
Microneurography is a neurophysiological method employed to visualize and record the traffic of nerve impulses that are conducted in peripheral nerves of waking human subjects. It can also be used in animal recordings. The method has been successfully employed to reveal functional properties of a number of neural systems, e.g. sensory systems related to touch, pain, and muscle sense as well as sympathetic activity controlling the constriction state of blood vessels. To study nerve impulses of an identified nerve, a fine tungsten needle microelectrode is inserted into the nerve and connected to a high input impedance differential amplifier. The exact position of the electrode tip within the nerve is then adjusted in minute steps until the electrode discriminates nerve impulses of interest. A unique feature and a significant strength of the microneurography method is that subjects are fully awake and able to cooperate in tests requiring mental attention, while impulses in a representative nerve fibre or set of nerve fibres are recorded, e.g. when cutaneous sense organs are stimulated or subjects perform voluntary precision movements.
Maximilian (Max) Ruppert Franz von Frey was an Austrian-German physiologist who was born in Salzburg.
A surgical suture, also known as a stitch or stitches, is a medical device used to hold body tissues together and approximate wound edges after an injury or surgery. Application generally involves using a needle with an attached length of thread. There are numerous types of suture which differ by needle shape and size as well as thread material and characteristics. Selection of surgical suture should be determined by the characteristics and location of the wound or the specific body tissues being approximated.
Targeted reinnervation enables amputees to control motorized prosthetic devices and to regain sensory feedback. The method was developed by Dr. Todd Kuiken at Northwestern University and Rehabilitation Institute of Chicago and Dr. Gregory Dumanian at Northwestern University Division of Plastic Surgery.
A tactile sensor is a device that measures information arising from physical interaction with its environment. Tactile sensors are generally modeled after the biological sense of cutaneous touch which is capable of detecting stimuli resulting from mechanical stimulation, temperature, and pain. Tactile sensors are used in robotics, computer hardware and security systems. A common application of tactile sensors is in touchscreen devices on mobile phones and computing.
The tail flick test is a test of the pain response in animals, similar to the hot plate test. It is used in basic pain research and to measure the effectiveness of analgesics, by observing the reaction to heat. It was first described by D'Amour and Smith in 1941.
A nociception assay evaluates the ability of an animal, usually a rodent, to detect a noxious stimulus such as the feeling of pain, caused by stimulation of nociceptors. These assays measure the existence of pain through behaviors such as withdrawal, licking, immobility, and vocalization. The sensation of pain is not a unitary concept; therefore, a researcher must be conscious as to which nociception assay to use.
As long as humans have experienced pain, they have given explanations for its existence and sought soothing agents to dull or cease the painful sensation. Archaeologists have uncovered clay tablets dating back as far as 5,000 BC which reference the cultivation and use of the opium poppy to bring joy and cease pain. In 800 BC, the Greek writer Homer wrote in his epic, The Odyssey, of Telemachus, a man who used opium to soothe his pain and forget his worries. While some cultures researched analgesics and allowed or encouraged their use, others perceived pain to be a necessary, integral sensation. Physicians of the 19th century used pain as a diagnostic tool, theorizing that a greater amount of personally perceived pain was correlated to a greater internal vitality, and as a treatment in and of itself, inflicting pain on their patients to rid the patient of evil and unbalanced humors. This article focuses both on the history of how pain has been perceived across time and culture, but also how malleable an individual's perception of pain can be due to factors like situation, their visual perception of the pain, and previous history with pain.
Tactile induced analgesia is the phenomenon where concurrent touch and pain on the skin reduces the intensity of pain that is felt.