Hi @Yabadabadoo. Here is a little explanation of the basic mechanics of CPAP, aside from the fact that the purpose is to help hold the airway open and prevent sleep apnea. A CPAP machine is basically an adjustable blower motor housed inside the unit that is calibrated so that it can be adjusted to various levels of pressure. The machine pulls in room air (much like a fan) and passes it through the blower motor. If a humidifier is part of the machine, the cool room air is then passed out of the blower motor, through the humidifier and over the water so that humidification is added to the air, and then passed out of the humidifier and through the CPAP tubing and the mask. The humidification helps prevent cold, dry air from entering the mouth and nose. The humidifier setting is usually preset, but it can be adjusted by the patient.
Regarding the CPAP prescription, CPAP pressure is measured in centimeters of water. If your pressure is 11, then your prescription was for CPAP at 11 cm of water. The pressure does not fluctuate unless other features, like C-Flex or those that are specific to various manufacturers, are active. If you are on CPAP at a fixed pressure and have a ramp feature, the ramp settings are usually also part of the prescription. The most common I have seen is a ramp setting of 20 minutes starting at usually 4 or 5 cm of water. When the machine is turned on, the machine starts at whatever ramp pressure was prescribed and builds to the final pressure, 11 cm in your case, over the 20 minute period. The starting ramp pressure and the ramp time period are usually adjustable by the equipment provider and are part of the prescription. Some machines allow minor adjustments of ramp pressure and time by the patient. You mentioned that your physician had your pressure increased from 8 cm to 11 cm, and you did not understand why she could not change the pressure herself. The reason is similar to why a physician cannot just change your medication dose and give you a new medication right in the doctor's office. A prescription is usually required and is sent to the provider of the equipment, and they change the setting and continue to monitor your treatment and provide necessary information to your physician and to your insurance company. Some physicians will adjust pressures in the office if they know how to do so, and they can communicate the changes to the home care company and make prescription updates electronically if they have that access. This is less common. C-Flex and similar manufacturer features can be activated to enhance treatment comfort. C-Flex is a feature that causes the pressure to lower, usually within a range of a couple of centimeters, to make exhalation easier. The machine detects your cycle of inhalation and exhalation and lowers the pressure briefly when you begin to exhale and quickly increases the pressure back to the prescribed level to prevent the obstructions that occur with sleep apnea. For patients who are on APAP or other auto-adjusting types of treatment, their pressures can vary and fluctuate within a wider range of settings. These types of machines detect breathing patterns and adjust pressures within the range of prescribed settings to treat obstructions and other types of respiratory events.
When you have a sleep study and are placed on treatment with CPAP, there is usually a pressure (or range of pressures) that work best and are patient-specific. The machine is adjusted to meet your requirements. The reason that patients are not provided information on how to adjust the machines is because the devices are regulated by the FDA and require a prescription for settings and adjustments from a physician. The machines are usually adjusted by a Respiratory Therapist to match the physician's prescription, much like a pharmacist will fill prescriptions for medications in the proper form (tablet, liquid, etc.) and dosage. There is a lot of debate about whether patients should adjust their own settings. The important thing to remember is that improper treatment (too little pressure or too much pressure) can cause continued breathing problems, so it is important to monitor your treatment and make sure you discuss any issues or changes with your physician.
Regarding mask fit and dry mouth, mask fit is a very important component of CPAP therapy. Poor mask fit that causes leak and discomfort is a primary reason that patients become frustrated with treatment. Proper mask fit usually involves working with your equipment provider to try on various masks, checking the fit and the leak levels, and finding one that is most comfortable for you. It is not uncommon for patients to change mask types or styles early in treatment because of discomfort or fit problems. Pressure changes, such as your increase from 8 cm to 11 cm, can also change how well a mask performs. If leak has increased and you are not able to make adjustments to correct that while maintaining comfort and control your AHI (apnea numbers), I encourage you to work with your equipment provider to either get the mask fitted appropriate or to obtain a mask that works with you newly prescribed pressures. For dry mouth, you may need to consider increasing the setting on your humidifier. This will increase the amount of heat so that the water is more warm and moist. The chin strap you mention may also help.
I hope this information is helpful, and best wishes! Please keep us posted on your progress, and we welcome your questions and feedback.