AirPAP

ASV — Adaptive Servo-Ventilation

Adaptive bilevel therapy that adjusts pressure support breath-by-breath to stabilise ventilation.

Adaptive Servo-Ventilation (ASV) is a bilevel therapy that continuously adjusts inspiratory pressure support breath-by-breath to hold ventilation close to a moving target, smoothing out irregular breathing patterns such as periodic breathing and Cheyne–Stokes respiration. Auto forms of ASV also raise EPAP in response to obstruction. By monitoring breathing in real time and providing a backup rate when needed, ASV reduces apneas and respiratory instability. It is designed for central sleep-disordered breathing — central and complex sleep apnea, mixed apnea and periodic breathing — which is often associated with cardiovascular disease, opioid use or PAP therapy.

How AirPAP’s ASV works

The AirPAP ASV algorithm continuously monitors the patient’s breathing to calculate a target ventilation that it applies when needed. Patterns recorded across a window of the last 100 breaths are combined with a moving average that is renewed with every breath, so the device continuously measures target minute ventilation, frequency and inspiration time. The initial default values are MV = 6000 mL/min, frequency = 15 bpm and inspiration time = 1.0 s.

When the patient’s spontaneous trigger is interrupted, the device compares the recorded target values with the instantaneous values to decide its response. The algorithm reacts to four events — obstructive apnea, central apnea, hypopnea and snoring — in that order of priority. For example, if snoring and hypopnea occur together, the device responds to the hypopnea, because hypopnea takes precedence.

Inside the algorithm — four events

Obstructive apnea

When the patient stops breathing the device no longer detects an effort, so spontaneous triggering does not occur and the device enters an apnea event. A 90% drop in airway flow for 10 seconds is treated as a possible obstructive apnea, and the timed backup cycle is activated (inspiration time 1 s, backup rate 15 bpm).

After 10 seconds the timed breaths are compared with the earlier spontaneous breaths. If the instantaneous minute volume has fallen below 80% of the target, this is classified as obstructive apnea. The device responds by raising EPAP in 0.5 mbar steps every five seconds — splinting the airway open — while pressure support is increased to maintain ventilation.

Central apnea

Central sleep apnea occurs when the brain does not send proper signals to the muscles that control breathing. As with an obstructive event, spontaneous triggering stops and the time-triggered breath cycle is activated.

The timed breaths are compared with the earlier spontaneous breaths. If the frequency has fallen below 80% with little or no drop in minute volume, this is classified as central apnea. The device responds by automatically adjusting the inspiratory pressure support (PS = IPAP − EPAP) together with the backup rate of 15 breaths per minute, within the set minimum and maximum PS limits — EPAP is not increased.

Snoring

Snoring is the vibration caused by partial obstruction of the airway and shows up as irregularities in the flow curve. The algorithm passes the respiratory signal through a high-pass filter to separate the rapid, high-frequency vibrations of snoring from the slower breathing signal and from noise.

After filtering, the signal is analysed for peaks: when three peaks are counted, snoring is detected and the device raises EPAP 0.5 mbar every five seconds.

Hypopnea

A change of ±10% in minute volume is not treated as an event. A 30% decrease in minute volume is recognised as hypopnea, and the device responds by raising EPAP 0.5 mbar every five seconds.

Clinical evidence

In a randomised comparison in patients with central sleep apnea, Cheyne–Stokes respiration, predominantly mixed apnea and complex sleep apnea syndrome (CompSAS), CPAP was inadequate (mean residual AHI 34.3/h). Non-invasive positive-pressure ventilation reduced AHI to 6.2/h, while ASV reduced it further to 0.8/h — and was notably more effective at reducing respiratory events and arousals, particularly in mixed apnea and CompSAS.

In opioid-induced central sleep apnea, ASV outperformed bilevel ST: it reduced AHI by 84.7%, central apnea index by 95.7% and arousal index by 77.1%, with respiratory parameters returning to normal in 83.3% of ASV-Auto patients versus 33.3% on bilevel ST.

ASV parameters 9

Maximum E Pressure

5 – 20 mbar — Highest pressure allowed during expiration.

Minimum E Pressure

3 – 20 mbar — Lowest pressure allowed during expiration.

Maximum Pressure Support

2 – 20 mbar — Highest pressure support that can be applied.

Minimum Pressure Support

2 – 20 mbar — Lowest pressure support that can be applied.

Inspiration Slope

1 – 8 — Sets how quickly pressure rises to the inspiratory pressure.

Expiration Slope

1 – 8 — Sets how quickly pressure transitions to the expiratory pressure.

Sigh

On / Off — Applies 1.5× the inspiratory pressure once every 20 breaths.

Inspiration Sensitivity

1 – 8 — Sensitivity required for the patient to trigger inspiration.

Expiration Sensitivity

1 – 8 — Sensitivity required to cycle from inspiration to expiration.

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