components flow generator (pap machine) provides the airflow hose connects the flow generator (sometimes via an in-line humidifier) to the interface interface (nasal or full face mask, nasal pillows, or less commonly a lip-seal mouthpiece) provides the connection to the user's airway optional features humidifier adds moisture to low humidity air heated: heated water chamber that can increase patient comfort by eliminating the dryness of the compressed air. the temperature can usually be adjusted or turned off to act as a passive humidifier if desired. in general, a heated humidifier is either integrated into the unit or has a separate power source (i.e. plug). passive: air is blown through an unheated water chamber and is dependent on ambient air temperature. it is not as effective as the heated humidifier described above, but still can increase patient comfort by eliminating the dryness of the compressed air. in general, a passive humidifier is a separate unit and does not have a power source. mask liners: cloth-based mask liners may be used to prevent excess air leakage and to reduce skin irritation and dermatitis. ramp may be used to temporarily lower the pressure if the user does not immediately sleep. the pressure gradually rises to the prescribed level over a period of time that can be adjusted by the patient and/or the dme provider. exhalation pressure relief: gives a short drop in pressure during exhalation to reduce the effort required. this feature is known by the trade name c-flex or a-flex in some cpaps made by respironics and epr in resmed machines. flexible chin straps may be used to help the patient not breathe through the mouth (full-face masks avoid this problem), thereby keeping a closed pressure system. the straps are elastic enough that the patient can easily open his mouth if he feels that he needs to. modern straps use a quick-clip instant fit. velcro-type adjustments allow quick sizing, before or after the machine is turned on. data logging records basic compliance info or detailed event logging, allowing the sleep physician (or patient) to download and analyse data recorded by the machine to verify treatment effectiveness. automatic altitude adjustment versus manual altitude adjustment. dc power source versus ac power source. such features generally increase the likelihood of pap tolerance and compliance. care and maintenance as with all durable medical equipment, proper maintenance is essential for proper functioning, long unit life and patient comfort. the care and maintenance required for pap machines varies with the type and conditions of use, and are typically spelled out in a detailed instruction manual specific to the make and model. most manufacturers recommend that the end user perform daily and weekly maintenance. units must be checked regularly for wear and tear and kept clean. poorly connected, worn or frayed electrical connections may present a shock or fire hazard; worn hoses and masks may reduce the effectiveness of the unit. most units employ some type of filtration, and the filters must be cleaned or replaced on a regular schedule. sometimes hepa filters may be purchased or modified for asthma or other allergy clients. hoses and masks accumulate exfoliated skin, particulate matter, and can even develop mold. humidification units must be kept free of mold and algae. because units use substantial electrical power, housings must be cleaned without immersion. for humidification units, cleaning of the water container is imperative for several reasons. first, the container may build up minerals from the local water supply which eventually may become part of the air breathed. second, the container may eventually show signs of "sludge" coming from dust and other particles which make their way through the air filter which must also be changed as it accumulates dirt. to help clean the unit, some patients have used a very small amount of hydrogen peroxide mixed with the water in the container. they would then let it stand for a few minutes before emptying and rinsing. if this procedure is used, it is imperative to rinse the unit with soap and water before reinstalling onto the machine and breathing. anti-bacterial soap is not recommended by sellers. to reduce the risk of contamination, distilled water is a good alternative to tap water. if traveling in areas where the mineral content or purity of the water is unknown or suspect, an alternative is to use a water from a "purifier" such as brita. in cold climates, humidified air may require insulated and/or heated air hoses. these may be bought ready-made, or built from commonly available materials. automated activated oxygen (ozone) cleaners are becoming more popular as a preferred maintenance method. however, the biological effects of using ozone as a pap cleaning method has not scientifically been proven to provide a benefit to pap users. portability since continuous compliance is an important factor in the success of treatment, it is of importance that patients who travel have access to portable equipment. progressively, pap units are becoming lighter and more compact, and often come with carrying cases. dual-voltage power supplies permit many units to be used internationally - these units only need a travel adapter for the different outlet. long-distance travel or camping presents special considerations. most airport security inspectors have seen the portable machines, so screening rarely presents a special problem. increasingly, machines are capable of being powered by the 400-hz power supply used on most commercial aircraft and include manual or automatic altitude adjustment. machines may easily fit on a ventilator tray on the bottom or back of a power wheelchair with an external battery. some machines allow power-inverter or car-battery powering. a limited study in amsterdam in january 2016 using an induced sleep patient and when awake whilst on cpap stretched the pectoralis major frontal chest muscles to bring back the shoulders and expand the chest and noted an increase in blood oxygen levels of over 6% during the manual therapy and 5% thereafter. the conclusion by palmer was that the manual stretching of the pectoralis major combined at the time of the maximum inflation of cpap allowed the permanent increase in blood oxygen levels and reinflation of collapsed alveoli. further studies are required. some patients on pap therapy also use supplementary oxygen. when provided in the form of bottled gas, this can present an increased risk of fire and is subject to restrictions. (commercial airlines generally forbid passengers to bring their own oxygen.) as of november 2006, most airlines permit the use of oxygen concentrators. availability in many countries, pap machines are only available by prescription. a sleep study at an accredited sleep lab is usually necessary before treatment can start. this is because the pressure settings on the pap machine must be tailored to a patient's treatment needs. a sleep medicine doctor, who may also be trained in respiratory medicine, psychiatry, neurology, paediatrics, family practice or otolaryngology (ear, nose and throat), will interpret the results from the initial sleep study and recommend a pressure test. this may be done in one night (a split study with the diagnostic testing done in the first part of the night, and cpap testing done in the later part of the night) or with a follow up second sleep study during which the cpap titration may be done over the entire night. with cpap titration (split night or entire night), the patient wears the cpap mask and pressure is adjusted up and down from the prescribed setting to find the optimal setting. studies have shown that split-night protocol is an effective protocol for diagnosing osa and titrating cpap. cpap compliance rate showed no difference between the split-night and the two-night protocols. in the united states, pap machines are often available at large discounts online, but a patient purchasing a pap personally must handle the responsibility of securing reimbursement from his or her insurance or medicare. many of the internet providers that deal with insurance such as medicare will provide upgraded equipment to a patient even if he or she only qualifies for a basic pap. in some locations a government program, separate from medicare, can be used to claim a reimbursement for all or part of the cost of the pap device. in the united kingdom, pap machines are available on national health service prescription after a diagnosis of sleep apnea or privately from the internet provided a prescription is supplied. in australia, pap machines can be bought from the internet or physical stores. there is no requirement for a doctor's prescription, however many suppliers will require a referral. low-income earners who hold a commonwealth health care card should enquire with their state's health department about programmes that provide free or low-cost pap machines. those who have private health insurance may be eligible for a partial rebate on the cost of a cpap machine and the mask. superannuation may be released for the purchase of essential medical equipment such as pap machines, on the provision of letters from two doctors, one of whom must be a specialist, and an application to the australian prudential regulation authority (apra). in canada, cpap units are widely available in all provinces. funding for the therapy varies from province to province. in the province of ontario, the ministry of health and long-term care's assistive devices program will fund a portion of the cost of a cpap unit based on a sleep study in an approved sleep lab showing obstructive sleep apnea syndrome and the signature of an approved physician on the application form. this funding is available to all residents of ontario with a valid health card.