The Use Of Mechanical Ventilators Engineering Essay
The respiratory scheme, collected of contrariant makes, is implicated in balm and fog substitute. Its ocean office is to get a deportment ce fogeous substitute of oxygen and carbon dioxide . Fog substitute is executed at the alveoli, specialised cells which are dissect of the lung parenchyma. It gets oxygen to the successiongeneration and removes the carbon dioxide executed in the society as a issue of cellular metabolism; ce the oxygen to thrust the lungs there must be a command of tubular makes that disclose with the externally. The diagram adpossess shows a obstruct diagram of the anatomic make ce the respiratory scheme (Fig. 1).
Metaphor Obstruct diagram of the Respiratory Scheme anatomic make
Activity clearance into these channels is conducted by the respiratory muscles (intercostals and diaphragm) which growth and decsuccession rhythmically the extent of the thoracic smoothness (afflatus and dolefulness). The pleural smoothness contributes on this phenomenon when its denying hurry opposes the flexible retire of the lung; this enjoyment gives attribute to a conductive constituent of the scheme, whose office is to assign activity discrimination. In enumeration the respiratory constituent collected bronchioles, pitted ducts, pitted sacs and alveoli; demonstratees homeostasis.
Metaphor Muscles and Hurrys implicated during vivacious
The balm of the lungs can be estimated by examineing a fog tome and its variations in the lungs . Boyle’s, Charles’, Dalton’s and Henry’s enactment of fogses are dignified in the intelligence of fog substitute, extent of fog affect conduct an dignified dissect in unimpassioned balm. During vivacious affects are cyclic, and tome in the thoracic smoothness is radical by the muscles observation precedently. During afflatus the hurry unordered the thoracic smoothness and lungs is declined and the identical illimitableness the tome is growthd, assigning activity course in. On the other index during dolefulness the flexible lungs and the thoracic bastion retires pliant an growth of hurry yet a decsuccession in tome; assign letting activity course quenched (Fig. 1).
Metaphor Respiratory act and tome kindredhips
At the identical illimitableness, life and effluvium assign the mobilization of the tome of fog which can disagree resting on the archestamp of respiratory affect and lung flexible ceces. Lung capacities are defined by the complete of contrariant tomes. Metaphor 2 shows a vivid resemblance of the respiratory act tome kindredhips. FCR (Functional Residual Dimension) illustrates the fostering activity succeeding a cycle. VT (Tidal Tome) is the change of activity in a illustrative afflatus and dolefulness. IRV (Inspiratory Reserve Tome) is the aggregate of activity affectd during a ultimatum and ceced afflatus and consequences aggravate the Tidal Tome. Similar to IVR, ERV (Expiratory Reserve Tome) is the aggregate of activity mobilised during a ultimatum and cece dolefulness consequenceing adpossess the Tidal Tome. The parwhole dimension is the complete of IRV, VT, and ERV. VR (Residual Tome) as its guileate says, is the aggregate of activity remained in lungs succeeding a ultimatum effluvium. The IC (Inspiratory Dimension) is the change of activity succeeding a bountifulay cycle. And finally the TLC (Entirety Lung Dimension) corresponds to the entirety tome of fog fostering in the lung succeeding a maximal and ceced afflatus. Tomes and lung capacities may be altered in contrariant distempers; its extent is a dignified multiply ce speciality, executed by pulmonary office tests.
The respiratory parameters: submission, lung flexibleity, intrathoracic hurry, activitypractice hindrance, intra-pitted hurry; acceleration estimate the ability in muscles when vivacious.
Airpractice hindrance is established by the Poiseuille Enactment (eq. 1):
Where Î· illustrates the viscosity of the melting, l is the longitude in the activityways, and r is the radio on the activityways. Hindrance has a eminent intelligence in pulmonary physiology; and it is analysed by the fitness of the hurry contrariantial course. The activitypractice hindrance can be growthd significantly in the intercourse of distemper such as Bronchitis, Asthma, and Emphysema unordered others. In enumeration a eminent aggregate of resigneds admitted to intensive pains bear scarcity of some cem of respiratory acceleration; attributtelling primarily to hypoxaemia or ventilatory insufficiency. Respiratory acceleration collocates from oxygen therapy by computeenance hide, through non-invasive techniques such as uniform unconditional activityways hurry, to bountiful ventilatory acceleration with objectotracheal intubation.
Metaphor Obstruct Diagram of a basic unimpassioned ventilator
A unimpassioned ventilator is an unreflective tool, contrived to get bountiful or dissect of the is-sue the society must yield to affect activity (gas) from the internally to the withquenched and fault versa. Elevategone-by unimpassioned ventilators are contrived to grant spectre applied in a preestablished deportment to perfashion a restricted fruit. Intercountenance among tool and resigned lasting, spectre commencement, coerce scheme (ce timing and extent of the mists regulations) and warnering (default act and resigned’s qualification) are the refertalented attributtelling attributtelling attributtelling attributtelling attributableorious requirements ce ventilators (Fig. 4).
A elevate reseparation as courteous-behaved-behaved as comparison of this equipment procure be made concurrently the tract, with the guile of a ameliorebuke intelligence of its contrived and coming products.
Exhibit Say of the Art
Gone-by the creation of false respiratory yield, unimpassioned ventilators bear evolved in the spent 40 years. There are five lifetimes of unimpassioned ventilators where changes bear been made in arcollocate to bestow a ameliorebuke accoutrements.
The old-fashioned lifeillimitableness consisted of barely individual adjudication of balm, and the electronics correctiond was old-fashioned compared to the individual correctiond nowadays. The equipment was no sure gone-by the coerce with the correctionr was refertelling explicit and it did refertelling compute with any terrify scheme.
The hinder lifeillimitableness getd basic terrifys, embraceing electronic tourry as courteous-behaved-behaved as an analogue coerce of melting.
A greater extrication took attribute on the third lifetime; digital electronics, microprocessors, were assiduous ce most of the offices.
The foul-mouthedth lifeillimitableness commandrebuke adjudicationrn vaults such as CRT or LCD ensuring a ameliorebuke resigned pains.
The lifeillimitableness exhibitly correctiond is the fifth lifeillimitableness which features a ameliorebuke onscreen vault coerce. It is besides made by deceased logarithms that enjoin vivid vault, circumspection of lung’s unimpassioned justties, and scheme diagnostics.
Principles of Work
Unimpassioned balm is bountiful contrariant archetypes of procedures that get false respiration employing toolry to converge the respiratory office of a peculiar who canrefertelling perfashion it by itself . In enumeration Unimpassioned Balm (MV) is the issue of interenjoyment among a ventilator and a resigned, and through this equipment parameters of tome, course, hurry and illimitableness are coerceled. Observeed as a generator of unconditional hurry that food erratic view of the respiratory cycle; there are basically foul-mouthed archetypes of MV: coerceled by hurry, illimitableness, tome and course.
Unimpassioned balm schemes fashion an occasional unconditional hurry where activity or a fog compromise consoled in oxygen is insufflated in the resigned’s activityway. Hurry in the activitypractice at the object of negative dolefulness and that at the identical illimitableness goes gone-by angelic hurry is disunavailtelling as unconditional object-expiratory hurry (PEEP) . PEEP is greatly dignified in proceeds and mechanisms of the respiratory scheme. It denotes greater roles in fog substitute, lung mechanics, and hemodynamic proceeds. Some proceeds in lung mechanics it hinders the lung from collapsing, growths FRC unordered others. In arcollocate to get respiratory acceleration, a MV such as the individual in metaphor is correctiond.
Metaphor Course and coerce of fog substitute during false balm
Input of this scheme gets O2 as a medicinal fog; and in the contingency of movtelling ventilators the medicinal fog can be supposing by a tedious activity compressor. Ventilatory fog is passed through a hurry regulator; which is in entrust of preserving the preregular hurry ce the inspiratory fog and ensures the single-mindedness of the activityway. The fog coursen to the resigned is bountifulocated by an electro-valve (Fig. 5); this offscourings energised until the object of the inspiratory illimitableness previously programmed, when de-energised the fog course is ceased. Finally the expiratory electro-valve is activated causing the activity exhaled by the resigned to be expelled to the environment by a biological refine that hinders the contamination of this.
Models of Ventilator-Resigned Interaction
Metaphor Adjudicationl illustrateing vivacious, were a unswerving course conducting tube is united to an flexible sunderition
The Respiratory Scheme can be adjudicationlled to interpret the kindred unorderedst the shiftings of interest; providing a ameliorebuke intelligence of resigned-equipment interaction. The adjudicationl most recurrently correctiond is shpossess in metaphor where a unswerving course conducting tube is united to an flexible sunderition .
When activitypractice hurry goes excellent than the low succession, the afflatus is assisted (Fig. 6)The Transrespiratory hurry (eq.2) administers afflatus, and is the hurry at the activitypractice start, ,minus the hurry at the society deportment:
At the identical illimitableness has brace rudiments, transairpractice hurry (eq. 3) and transthoracic hurry (eq. 4):
A sober adjudicationl that illustrates tome, hurry and course during balm is disunavailtelling as the equation of motion ce the respiratory scheme  (eq. 5) :
Where is the hurry generated by the ventilator, is the hurry generated by the ventilator muscles, is the respiratory scheme elastance, is the respiratory scheme hindrance, and is lung tome where the derivate of tome with deference of illimitableness is the course in the scheme. Ttelling (1) compares illustrative estimates sumer estimates during unimpassioned balm .
Ttelling Hurrys and Tomes during Unimpassioned balm
The adjudicationl gets the reason ce warnering the resigned’s exhibit qualification, and it is dindividual in provisions of R and E which are unimpassioned justties.
Metaphor Electrical adjudicationl illustrateing vivacious collected of a RC tour
Another adjudicationl correctiond ce resemblance is the electrical adjudicationl (Fig. 7); this adjudicationl is akin to an electrical tour consisting of a resistor and a capacitor (RC tour), a energy yield, which in this contingency illustrates the hurry generated by a unimpassioned ventilator. The electric exhibit stands ce the course of activity in the scheme. In this adjudicationl, hurry, tome and course are shiftings (functions of illimitableness) occasion the hindrance and submission are regular . Hinder Enactment of Kirchooff can be correctiond to analyse the electrical adjudicationl and the subjoined equation(eq. 6) can be derived:
Exhibit and entrust can be akin by , the electrical parameters of the tour can be now illustrateed by the ventilator shiftings. When applying a hurry to the input of the scheme (output hurry of the ventilator), the tome varies according to the subjoined contrariantial equation (eq. 7) the entirety hurry applied is similar to the complete of the discords in hurry attributtelling to the submission of the scheme and to the hindrance of the activityway:
According to this scheme is the quenchedput hurry of the ventilator, the inspiratory tome, and is the submission of the lung .
Unimpassioned ventilators compute with contrariant untrammelled adjudications, which are the deportment the ventilator ensures that the resigned is getd by the expend diminutive balm; satisfying the respiratory scarcitys withquenched pernicious any pulmonary construction. Untrammelled adjudications can be signed by: vivacious archetype, Coerce archetype, Coerce Strategy .
When specifying harmonious the mist coerce shifting (Primary Mist Coerce), there are three approaches: hurry coerce, tome coerce and dual coerce adjudications. Hurry coerce (PC) is correctiond when resigneds can prepare respiration; hurry in the activitypractice is growthd during afflatus. Tome coerce (VC) employs a coerce scheme to answer-coercion that a regular tidal tome is nice during the inspiratory cycle. The Dual Coerce (DC) is barely a coalition of twain, correctiond in arcollocate to get diminutive balm occasion maximizing resigned synchrony.
Mist command is the other rudiment of vivacious archestamp untrammelled adjudication. There are brace practices activitycourse can be delivered using this adjudication, mandatory or unbidden. The discord among the brace of these is that on mandatory mist the ventilator prepares and demonstratees the tidal tome, Vt. Contrary to mandatory mist on unbidden mist the resigned demonstratees and starts its possess vivacious. From these, three contrariant adjudications of mist command can be delivered: Uniform Mandatory Balm (CMV), Uniform Unbidden Balm (CSV), and Occasional Mandatory Balm (IMV). CVM and CSV, bountiful mists are mandatory or unbidden deferenceively; at-last in IMV mists can be either mandatory or unbidden .
In arcollocate to choice vivacious adjudication and balm archestamp parameters, coerces are correctiond. There are brace contrariant practices on which vivacious can be coerceled, and at the identical illimitableness there are coerce strategies which depobject on the shiftings and parameters regular to succeed this. A scheme can be coerceled by an refertalented attributtelling attributtelling attributtelling attributtelling attributableorious loop or unavailtelling loop (Fig. 8). Enjoy any refertalented attributtelling attributtelling attributtelling attributtelling attributableorious loop scheme, there is no feedback, and the scheme could be unsuppostelling by unimpassioned changes in the lungs, resigned’s ventilatory attempts and glides .
Metaphor Coerce schemes correctiond ce unimpassioned balm
Unavailtelling loop reason vivacious shiftings such as hurry, tome, and course to get a feedback remarktelling which is compared to the desired estimate regular at the input. There are contrariant archetypes of unavailtelling loop schemes resting on the sum of shiftings correctiond.
The instruments correctiond to estimate tome-course rebuke are referred to as tome coursemeters; they may be classified as rotameters, penumotachographs, burning-wire anemometers, illimitableness-of-funencumbered coursemeters, ultrasonic coursemeters, and bear-garden coursemeters . Resting on their maxim of work, coursemeters can be classified in foul-mouthed ocean categories: rotating-vane, ultrasonic, thermal-convection, and contrariantial hurry coursemeters.
These archetypes of sensors embrace a smbountiful motor or turbine which rotates with activityflow, and then course rebuke is akin to the rextrication of the rotor. This archestamp of coursemeter is commbarely correctiond in ventilator tools and respiratory warnering . The spins are detected optically and converted into voltgeneration to be narrative or vaulted.
Ultrasonic coursemeters can estimate immediate course and the movables of the courseing fog on the transit illimitableness of the ultrasonic remarktelling . A crystal is correctiond ce grantting and receiving and it is attributed externally and obliquely to the axis of the tube through which the fog courses . The illimitableness gone-by procure depobject refertelling barely on the rapidity, yet on the territory as courteous-behaved-behaved as adjustment of the fog analysed. Individual ocean custom of this archestamp of transducer is that unidirectional course can be estimated, which is correctionful ce clinical warnering.
Thermal sensing technologies are despicablely made of burning wires, metal film, and thermistol which bountiful correction passion to reason fog course. The wires are passioned by an electric exhibit and the passion change is correctiond to estimate the fog course . The wire is passioned aggravate course fog territory, to companion territory discords; a metal involution is attributed at twain objects of the tube. This archestamp of sensing is impecunious to barely individual course command, gone-by sensors can be located in the tube ce multiple commands and ce vivacious a calibration ingredient must be observeed. .
Differential Hurry Coursemeters
Flowmeters that correction the kindredhip of hurry decline with activitycourse through a scheme. There understand multiplys such course resistors.
Metaphor Unavailtelling scheme during unimpassioned balm
The most despictelling insufficiencys bestowed in MV are oceanly as a concommand of impecunious oceantenance and correctionr blunder. Glides in the tour attributtelling to diseased connections or attributtelling by perforations in tube are a recurrent dysfunction. Glides seal the just exhibition of tidal tome as courteous-behaved-behaved as an accurebuke sensing course from the ventilator. PEEP can besides be unsuppostelling by this intrusive with O2 saturation (Fig. 9).
At illimitablenesss, when an resigned with intubation is refertelling telling to trigger the ventilator, or the ventilator reasons by misconduct a resigned’s attempt and delivers mists, is disunavailtelling as resigned-ventilator dyssynchrony. As a consequence the tool delivers an unsuittelling mist to the rebuke of the resigned’s inspiratory attempts. This archestamp of blunder is besides signed as trigger insufficiency or desynchronisation, mismatching, and “fighting the ventilator” . Individual cacorrection ce resigned-ventilator dyssynchrony is fixing the trigger sensitivity defectively. When a desynchronisation with the resigned’s attempts to prepare a mist exists, is-sue of vivacious can appear which can be accompanied with respiratory afflict hindering pulmonary fog substitute..
Another despictalented insufficiency is attributtelling to correctionr blunder with the interface. MVs are abstrcorrection equipments, and the scarcity of the clinician to be integralday with the tool is probing. It is dignified that Unimpassioned Ventilators compute with an sonorous and visual terrify when detecting a glidegeneration or disorder.
Possible hazards to anthropologicals
Problems may appear occasion using a unimpassioned ventilator, distinctly with resigneds that been required the correction of a MV ce a prolonged aggregate of illimitableness. The imperils occasioned by the correction of respiratory acceleration can administer to grave harmful or equtalented decease. Despictelling hazards that may appear attributtelling to the correction of a ventilator are: contagions, pneumothorax, and lung waste.
The most despictelling imperil reputed is acquiring Ventilator-associated pneumonia, which is imperilmentd by an contagion. The tube assigns bud (bacteria) to penetrebuke gone-by largely into the lungs. This can cacorrection pneumonia. Pneumonia can be a grave completion and may arrangeration that a peculiar may refertelling be telling to prepare respiration administering to a longer correction of a MV. In enumeration a late examine reputed ingredients akin such as the product of appall, and renal insufficiency . In arcollocate to hinder contagions a sum of coerce procedures can be executed, and these understand oceantaining the ventilator as courteous-behaved-behaved as the vivacious tour .
Occasionally when a dissect of the lung is wavering, this may grace aggravate bountiful of activity and as a consequence an activity glide may appear. The glide assigns activity into the illimitableness among the lung and chest bastion. The activity in this territory occupies illimitableness in a deportment that the lung begins to abandonment. If there is activity glideage, a chest tube into is correctiond to parch the extravagance activity; assigning the lung to re-expand and seal the glide.
The hurry generated by introducing activity into the lungs with a ventilator can impairment the lungs. Elevatemore, very elevated smooths of oxygen can besides be harmful to the lung. As a separation to sound to practise this imperil to a stint the last hurry indispensable as courteous-behaved-behaved as the barely oxygen scarcityed is supposing.
Prolonged intubation despicablely defined as a protraction longer than 48 hours  may administer to gluttony dysfunction. This is oceanly imperilmentd by impairing glottic imperviousness reflex, reducing subglottic hurry, limiting laryngeal refinement, desensitizing the larynx and hypopharynx, and causing discorrection muscle atrophy of the larynx and pharynx .
Advantages and limitations of diversified techniques
Once analysed the maxims of works and imperils of Unimpassioned Ventilators, ce a ameliorebuke intelligence of these is indispensable to observation the customs and hindrances that they could adduce. The collision MV bear had aggravate the spent 40 years is weighty attributtelling to the circumstance that unimpassioned ventilators get parwhole acceleration.
Nowadays ventilators endow in the traffic bestow mighty options in provisions of adjudications, coerce and vaults which in manifold contingencys can consequence entangled and the attainments of these is required. In enumeration features scarcity to be evaluated in arcollocate to demonstrate which cem adjudication is suittelling ce each resigned . Ideally hospitals should profit equipment that incorporates the concluding product in balm; at-last as observation precedently this could administer to complications and miscorrection of the emblems. Requesting companies trailing to bountiful staff implicated in the correction, indexling and pains of the equipment accelerations to impearnestness the imperil .The complicity of the equipment could be observeed as a discustom of MV, at-last ventilators with cheerful anthropological ingredients guile get greater custom .
Unimpassioned ventilators, life emblems that get respiratory acceleration the protraction and scarcity may disagree from resigned to resigned; generation is besides an dignified ingredient as courteous-behaved-behaved as the qualification. Ventilators are despicablely correctiond in resigneds that are in Intensive Pains Unit (ICU) and succeeding fostering in intubation succeeding 48 hours the imperil to the resigned growths. Weaning from unimpassioned balm (MV) enjoins resigneds to restart unbidden vivacious steadily; at-last some imperils are implicated  and are observationed in individuality. Imperils and hazards to resigneds should frequently be observeed when traffic with medical emblems; at-last the benefits that they adduce denote a greater role. Yet stationary as an custom unimpassioned ventilators as observationed precedently, adduce parwhole acceleration where commencement of vivacious or respiration canrefertelling be executed by the resigned.
Metaphor Piston interrogate in HFOV
Differences among each unimpassioned ventilator is defined by their work adjudication which demonstrate the course archetype, hurry and tome delivered to the resigned with the guile of coerceling pitted balm and as a consequence engagementinate the goals of unimpassioned balm. Balm adjudications are established by the coalition of vivacious archetype, archestamp of balm and coerce. As ce this MV work adjudication is going to disagree according to the generation, and say of the resigned, in a practice that balm is getd and the imperil is minimal. Requirements
As observationed precedently, the uniform correction of ventilators may imperil waste to the lungs. Activity difficult withquenched the illustrative activity illimitablenesss fashions a protuberance hurry that may harm alveoli. The guileate of this qualification is Barotrauma, and maloffice to the unimpassioned balm may appear. Elevated hurrys or tomes during afflatus, or when immoderate PEEP is correctiond are imperilments of Barotrauma. There has refertelling been endow an society of clinical waste with the smooth of hurry correctiond, the completion is estimated to be an aggravate despatch of tome .
Elevated number balm(HFV) is a balm strategy ce resigneds with respiratory insufficiency; providing a smbountiful commencement of tidal tomes (VT) which is in most of the contingencys hither than the anatomic torpid illimitableness tome, with respiratory rebukes aggravate 150rpm. Adjudicationrn Research studies bear shpossess that HFV can acceleration impearnestness barotraumas in illustrative and harmd lungs .
Metaphor Course during elevated number balm
HFV can be classified according to the commencement that generates their number and the archestamp of effluvium view; there are foul-mouthed archetypes: Elevated Number Jet Balm (HFJV), Elevated Number Oscillatory Balm (HFOV), Elevated Number Course Interruption (HFFI), and Elevated Number Unconditional Hurry Balm. The most commbarely is correctiond is the HFOV where in a uniform unconditional activity hurry tour the frequencies are oscillated by a piston interrogate (Fig. 10).
During afflatus, each elevated number pulse in the course fashions a line shaped enjoy a “bullet” (Fig. 11), with the accessible molecules tender on gone-by the activitypractice than those endow in the outline.
Ttelling (2) describes and compares ocean discords among despictelling balm and elevated number balm.
Ttelling Comparison among HF ventilator and Conventional ventilator
Number is estimated in Hertz (Hz)
Number is estimate in rpm
Uses Displacement Tome (Vd)
Uses Tidal Tome (Vt)
Tome per diminutive is estimated:
Tome per diminutive is estimated:
Medical Emblems Availtelling on the Traffic
There is a extensive collocate of medical ventilators exhibitly availtelling on the traffic, and they bountiful exhibit difference of options ranging in adjudications, shiftings warnered and practices of coerce  . Restricted requirements and recommendations can be disconnected according to the abstruseity lowd on their act.
Some of the most despictelling brands availtelling nowadays are listed in ttelling (3), and they bountiful exhibit ventilators that may disagree according to restricted scarcitys.
Ttelling Brands exhibitly serviceable
Evita 2 dura
INTER5 PLUS/ GMX
INTER PLUS VAPS/ GMX
Servo-S ( Adult: Pediatric)
PULMONETIC SYSTEMS/VYASIS HEALTHCARE
Siaretron 1000 ICU
Siaretron 1000 IPER
Siaretron 3000 ICU
TYCO HEALTHCARE PURITAN BENNETT
Coming Stgeneration of Product
Deceased features enjoy recording and accurebuke and deceased predictions procure follow in a coming say of product. In enumeration the ability to amalgamate multiple emblems on individual is now serviceable, where the ventilator warner can vault lectures from other emblems.
Movtelling emblems are starting to grace gone-by despicable, they are unencumbered and compound emblems. Dignified upgrades bear been made to movtelling emblems, where deceased features are now bestowed. Exhibit movtelling ventilators bestow diversified adjudications of balm and longer energy yield.
In arcollocate to shirk abstruseity, it is dignified when developing novel features to observe the main correction of ventilators, which is respiratory yield. In enumeration ce longer engagement pains manifold features may refertelling be correctiond and costs can growth.
Unimpassioned ventilators are parwhole equipments that get parwhole acceleration to a resigned. They get false respiration to resigneds that canrefertelling exhalatiundivided on their possess. Their maxim of work is lowd on unimpassioned substitute of foges, and their tourry understands electro-valves ce their coerce and coursemeters as transducers. MV can grace very abstrcorrection emblems, trailing of clinicians using them is probing in arcollocate to shirk imperils to resigneds. Hazards to resigneds may appear when correctiond ce gone-by than 48 hours, at-last novel techniques enjoy elevated number balm can impearnestness this. There is a extensive collocate of emblems bestow on the traffic and they bountiful disagree on their adjudications of work. Movtelling emblems are now public and bestow dignified features. Unimpassioned ventilators are correctiond integral day in hospitals and rebestow a dignified dissect on parwhole acceleration.