Central sleep apnea (CSA) differs from obstructive sleep apnea in that, instead of an obstruction causing breathing to become shallow or stop periodically throughout the night, the brain fails to send signals to the respiratory system to instruct it to continue breathing during sleep.
Whereas obstructive sleep apnea (OSA) is a physiological problem in which the upper respiratory system becomes blocked by muscles and tissues in the throat and mouth, central sleep apnea is a neurological problem that can have many different causes including other underlying medical conditions, diseases, and even from taking certain medications.
To help patients with central sleep apnea continue breathing freely and easily through the night, a different kind of positive airway pressure device is needed for CSA's unique symptoms: the adaptive servo-ventilation machine (ASV).
How do Adaptive Servo-Ventilation Machines work?
All of the various PAP machines, including the ASV, deliver pressurized air from a motor that draws in air from the room, pressurizes it to specific settings for the patient, and delivers the air to the patient via a hose and a mask to keep the patient breathing steadily throughout the night.
CPAP machines blow a steady, single fixed pressure of air that keeps obstructions from causing apnea events.
APAP are set to have a range of pressures with a minimal pressure and maximum pressure that it fluctuates between to deliver the perfect pressure for each individual breath.
BiPAP machines are for patients with high pressure needs and offer two pressure settings: a pressure for inhalation, and a pressure for exhalation. This allows the pressure delivered from the machine to blow air at a lesser pressure during exhalation so the patient doesn't feel as if they're fighting to exhale against the incoming pressure. BiPAPs also have a feature that can tell how many breaths per minute the patient should be taking, and if the time between breaths exceeds the set limit, the machine can force the person to breath by temporarily increasing the air pressure.
How are ASV machines different?
ASV machines are a little different than other PAP machines. To begin with, most other PAP machines are used primarily in treating obstructive sleep apnea. ASV machines on the other hand are meant to treat central sleep apnea (CSA), mixed sleep apnea, and also Cheynes-Stokes respiration ( an abnormal pattern of breathing characterized by progressively deeper and sometimes faster breathing, followed by a gradual decrease that results in an apnea event).
Patients who either have central sleep apnea, or begin to develop mixed sleep apnea after treatment for OSA gives rise to CSA events, patients will sometimes end up on ASV machines once BiPAP with back-up respiratory rate has first been tried and failed. ASV is often the last line of defense in treating CSA and mixed sleep apnea.
The key difference in ASV therapy is that it provides support to regular breathing. It uses an algorithm which detects significant reductions or pauses in breathing and intervenes with just enough support to maintain the patient's breathing at 90% of what had been normal prior to decreased breathing.
The algorithm is based off a set rate of breaths per minute that the patient should be taking. When the patient's breathing dips below these rates, the ASV delivers just enough air pressure to keep the patient breathing regularly.
"The ASV machines differ from other PAP machines in that the pressure being delivered to the patient is not as important as the amount of air that the patient is receiving," says Cori Murphy, RPSGT for Alaska Sleep Clinic.
Even when the patient's breathing is stable the ASV machine acts as a back-up support to help keep the airway open just enough to prevent obstructions, which provides a 50% reduction in the physical work of breathing.
Who benefits from ASV machines?
Patients with central sleep apnea after BiPAP has failed to reduce rates of apnea/hypopnea events.
Patients who begin to develop mixed sleep apnea after starting CPAP, APAP, or BiPAP therapy for OSA.
- Patients with both OSA and CSA in which 50% of the sleep study shows central apnea events.
Who may not benefit from ASV?
For this particular group there is a 33.5% increased risk of cardiovascular death, compared to control patients who are not on ASV therapy, compared to control patients who are not on ASV therapy (absolute annual risk 10% in ASV patients vs. 7.5% in control group).
Before beginning ASV therapy make sure that your physician is aware that you may fit into this group. Alternative therapy will best be determined by the physician.
Do Patients still need a Titration study for ASV?
Even though the machine has an algorithm that detects breathing patterns in patients, the machine still needs to be calibrated to the patient's individual breathing needs. This includes finding the patient's minimum and maximum pressure support settings that the algorithm will fluctuate between to find the perfect amount of oxygen support.
If you live in Alaska and are suffering from a sleep related breathing disorder including obstructive, central, or mixed sleep apnea the Alaska Sleep Clinic can help. Contact us for a free 10-minute phone consultation and have one of our trusted sleep experts help determine if a sleep study is needed to diagnose your sleep troubles.
Or if you have a prescription for a PAP machine and would like to order a device through Alaska Sleep Clinic, click the link below.