1、Cataract Extraction Units, Phacoemulsification,Purpose,Phacoemulsification systems are used to break up and remove the cataractous lenses of eyes. A cataract is a fogging of the normally transparent lens that inhibits the transmission of light to the retina, causing a painless blurring of vision,Cat
2、aracts are caused by:,changes in the chemical composition of the lens associated with many factors: environment, drugs, Systemic diseases, age, traumatic eye injuries, Certain diseases of the eye, and genetic or birth defects If cataracts are not treated, progressive visual loss, leading to signific
3、antly impaired sight, can occur.,Phacoemulsification,widely used by ophthalmic surgeons because the entire procedure cataract extraction and implantation of an intraocular lens (IOL) can be done througha single small incisionthat may help control surgically induced astigmatism, quicken visual rehabi
4、litation, and decrease surgical complications.,Principles of operation,Phacoemulsification is one type of extracapsular cataract extraction, a procedure that removes the lens nucleus, surrounding cortex, and the enclosing anterior capsule; the zonules and posterior capsule are left intact to help su
5、pport an IOL implant During a phacoemulsification procedure, the surgeon performs several steps with the aid of an operating microscope,A 2.8 to 3.5 mm incision is made to gain access to the eyes anterior chamber. A viscoelastic material is then infused to deepen the anterior chamber and protect the
6、 corneal endothelium.,the surgeon inserts a phaco-emulsification probe, which consists of a hollow, cylindrical tip surrounded by an irrigation sleeve. When electrically activated, the probe tip oscillates rapidly,creating ultrasonic waves that cut tissue.The surgeon emulsifies the cataractous lens
7、using shaving or scooping motions of the probe tip. The lens fragments are then aspirated from the eye through the hollow tip of the phacoemulsifier. Remaining cortex is aspirated via the I/A attachment. Either a polymethyl methacrylate (PMMA) or a foldable silicone IOL is inserted through the incis
8、ion and into the bag of the capsule, which is then sutured; however, self-sealing, sutureless corneal incisions are becoming more widely used for phacoemulsification procedures.,Typical phacoemulsification systems integrate into a single handpiece the I/A and US capabilities needed to break up and r
9、emove a cataractous lens from the eye. The surgeon typically activates these capabilities by depressing a single footpedal.,A bottle of balanced salt solution is used as the irrigant; mounted on an adjustable intravenous (IV) pole, its pressure head can be controlled by adjusting its height.,Centrif
10、uges, Tabletop,PurposeCentrifuges apply centrifugal force to separate suspended particles from a liquid or to separate liquids of different densities. These liquids can be bodily fluids (e.g., blood, serum, urine), commercial eagents, or mixtures of the two with other additives.,In the clinical labo
11、ratory, centrifugation is one of several sample preparation steps commonly required before measuring analytes in a patient sample. By creating forces many times greater than gravity, centrifuges can greatly accelerate separations that occur naturally as a result of differences in density.,Centrifuge
12、s, Blood BankCentrifuges, Cell WashingCentrifuges, CytologicalCentrifuges, FloorCentrifuges, MicrohematocritMicrocentrifugesUltracentrifuges,Three general types,the low-speed centrifuge, the high-speed centrifuge,and the ultracentrifuge.,the low-speed centrifuge,general operating range of up to 10,0
13、00 rpm Available in nonrefrigerated or refrigerated versions, low-speed units are used primarily to centrifuge red blood cells or bulky precipitates; they cannot reach sufficient speed to adequately separate ultrasmall particles (e.g., viruses, DNA) or macromolecules or to perform density gradient c
14、entrifugation.,High-speed tabletop centrifuges,operate at 12,000 to 25,000 rpm, are used for most preparative applications, and some are refrigerated to cool the rotor chamber.,Ultracentrifuges,used for high-resolution separation of subcellular components, have a general operatingrange of 30,000 to
15、120,000 rpm, with centrifugal forces of up to 700,000 g, where g is the standard acceleration of gravity. Ultracentrifuges must be refrigerated because air friction created at high speeds generates heat that could decompose the proteins, viruses, or other components being centrifuged. Ultracentrifug
16、es are special-purpose floor units that are typically used in research laboratories.,Principles of operation,Centrifugation Centrifugation is based on the fact that an object moving in a circular path at a steady angular velocity is subjected to an outwardly directed force. The magnitude of this for
17、ce depends on both the rotor radius and the speed squared. This force is called the relative centrifugal force or relative centrifugal field (RCF).It is expressed as a multiple of g, the standard acceleration of gravity (e.g., 13,000 g).,Centrifuge components,The basic components of a tabletop centr
18、ifuge include: an electric motor, a shaft and rotor heads (often interchangeable) on which the centrifuge head turns,and a motor drive assembly. If the centrifuge is refrigerated, a compressor and associated components are included. The entire system is housed within a chamber.,Incubators, Infant,Pu
19、rpose An infant incubator provides a closed, controlled environment that warms an infant by circulating heated air over the skin. The heat is then absorbed into the body by tissue conduction and blood convection,At birth, an infants core and skin temperatures tend to drop significantly because of he
20、at loss from conduction (heat loss to cooler surfaces in direct contact with the infant), convection (heat loss to air moving past the infant), radiation (heat loss to cooler objects not in direct contact with the infant), and water evaporation (heat loss from the infants lungs and skin surface).,Wh
21、ereas term neonates naturally regulate their body temperature to some extent, premature infants have thinner skin, which allows surface blood vessels to more readily lose heat to the environment; a large ratio of surface area to volume, resulting in greater heat losses from radiation and convection;
22、and almost no subcutaneous fat to either metabolize into heat or act as an insulator.,Prolonged cold stress in neonates can cause oxygen deprivation, hypoglycemia, metabolic acidosis, and rapid depletion of glycogen stores. Therefore, energy conservation provided by thermal support is critical.,Prin
23、ciples of operation,The neonate lies on a mattress in the infant compartment, which is enclosed by a clear plastic hood. Most incubators warm the infant by a forced or natural flow of heated air Heating and humidification systems are located beneath the infant compartment. A fan or natural flow circ
24、ulates air past the heater and the temperature measuring device, over a water reservoir used to humidify the air (if desired), and up into the infant compartment,Oximeters, Pulse,Purpose Pulse oximeters noninvasively monitor the oxygen saturation (expressed as a percentage or decimal) of arterial he
25、moglobin by measuring light absorbance changes resulting from arterial blood flow pulsations.,Principles of operation,Pulse oximeters provide a spectrophotometric assessment of hemoglobin oxygenation (SpO2) by measuring light transmitted through a capillary bed, synchronized with the pulse. The dete
26、ction system consists of single-wavelength light-emitting diodes (LEDs) and microprocessors.,The pulse oximeter probe is applied to an area of the body such as a finger, a toe, or an ear. Two wavelengths of light (e.g., 660 nm red and 930 nm infrared) are transmitted by the probe through the skin an
27、d are differentially absorbed by oxyhemoglobin, which is red and absorbs infrared light, and deoxyhemoglobin, which is blue and absorbs red light. The ratio of red to infrared light is used to derive oxygen saturation. The photo-detector on the other side of the tissue converts the transmitted light
28、 into electrical signals proportional to the absorbance,Nebulizers, Heated; Ultrasonic,Purpose Nebulizers provide aerosol treatment and/or medicine to patients with certain respiratory disorders Nebulizer therapy is particularly effective in treating conditions such as cystic fibrosis, emphysema, cr
29、oup, bronchitis, and severe asthma,Most nebulizers are either pneumatic (driven by compressed air) or ultrasonic. Both types provide an effective aerosol mist for depositing medication into the lungs.,Heated nebulizers provide warmed aerosol mist to spontaneously breathing patients being treated wit
30、h oxygen or compressed air, which, delivered cold, can cause severe bronchospasm in patients with hyperac-tive airways (asthma patients).,Principles of operation,Heated nebulizers A heated nebulizer generally consists ofa reservoir, a heating element, a compressor, and a nebulizer jet.,Ultrasonic ne
31、bulizers,An ultrasonic nebulizer consists of several compo-nents: an electronic oscillator, an ultrasound transducer (piezoelectric crystal),a coupling basin,a nebulizer chamber (also called a cup), and a fan,To begin nebulization, a high-frequency (typically 1 to 2 MHz) electrical voltage is applie
32、d to a piezoelectric crystal within the oscillator circuit, which changes the applied electrical signal into mechanical vibrations.,These vibrations, in turn, produce 1 to 2 MHz sound waves in the coupling basin. The coupler (water or saline) transmits the sound waves to the solution in the nebulize
33、r chamber. The ultrasonic waves induce cavitation (formation of partial vacuums in a liquid), which causes bubbles to form when the low-pressure phase of the wave is lower than the liquids vapor pressure. When the sound waves reach the liquid/air interface, the liquid forms a geyser and disperses in
34、to an aerosol mist,During drug therapy, medication cups hold small quantities of medication such as albuterol; the water in the chamber serves only as a medium to transmit the ultrasonic energy,The size of the mist particles is determined primarily by the vibrating frequency; the higher the frequency, the smaller the particles. Ultrasonic nebulizers produce particles in the range of 0.5 to 35 mm;,
