The amount of pressure required for effective CPAP therapy varies according to sleep stage, sleep position, and other factors. Insufficient pressure results in ineffective therapy while too much pressure can lead to discomfort, non-compliance, and pressure-related side effects.

ResMed’s AutoSet SpiritTM is an automatic titration system for the treatment of obstructive sleep apnea (OSA). AutoSet devices adjust pressure on a breath-by-breath basis to suit patient needs as they vary throughout the night. As a result, the patient receives the minimum pressure required for effective therapy. The lower pressures may improve patient comfort, reduce pressure-related side effects, and lead to increased patient compliance.

The AutoSet algorithm responds to three key respiratory parameters:

• Inspiratory flow limitation
• Snore
• Apnea

Additionally, AutoSet devices maintain pressure by compensating for mask leak.

AutoSet devices act preemptively by increasing pressure in response to inspiratory flow limitation, which typically precedes snore and obstruction. This early intervention prevents snoring and obstructive apneas, thereby reducing respiratory arousals.

Sudden Apnea Response

Apneas may occur suddenly, without being preceded by flow limitation or snore. These sudden apneas are generally associated with sleep onset, change in body position, or REM onset. Following a sudden apnea, AutoSet devices will increase pressure relative to the severity of the event. If no further events occur, AutoSet devices reduce the pressure back to a minimum level.

The AutoSet Algorithm

The efficacy of the AutoSet algorithm is due to its ability to increase pressure in response to the severity of the three parameters (flow limitation, snore, and apnea):

• The greater the flow limitation, the more pressure delivered
• The louder the snoring, the more pressure delivered
• The longer the apnea, the greater the increase in pressure

By responding to these three separate parameters, AutoSet devices effectively normalize sleep while delivering a mean pressure typically 37% lower than fixed pressure therapy.1

The most effective way to assess flow limitation is through analyzing the shape of the inspiratory flow-time curve, as shown in the diagrams below. A rounded inspiratory flow contour is the monitoring event that best predicts upper airway patency and a transition to deeper sleep stages without arousals. Studies recommend that this inspiratory flow contour characteristic be routinely used to achieve an optimal pressure level and is preferable to responding to apneas and hypopneas directly. 2,3

The rounded inspiratory flow curve in the left diagram indicates a normal breath. If the upper airway begins to narrow, causing flow limitation and upper airway resistance, the shape of the curve will flatten as shown in the right diagram. The AutoSet Spirit adjusts the pressure according to the extent of flattening, in order to maintain airflow and restore the curve to normal

Best Therapy at Lowest Pressures

AutoSet technology has been clinically validated in numerous peer-reviewed journals. Its combined measurement and response to flow limitation, snore, and apnea is unique within the field of sleep-disordered breathing therapy. The AutoSet advantage enables physicians to provide their patients with the best sleep therapy at the lowest possible pressures.

• Provides effective therapy at the lowest mean pressure, typically 37% lower than fixed pressure therapy
• Adapts to patients’ changing pressure needs on a short- and long-term basis
• Responds to flow limitation, snore, apneas, and mask leak
• Provides greater breathing comfort through smooth, quiet pressure delivery
• Provides visual display for quality of mask fit; optional alert tone in presence of significant leaks

References

1. Teschler, Berthon-Jones. Thorax 1998; Vol 53 (Suppl 3): S49-54
2. Berthon-Jones, et al. Sleep, 19(9):S131-S135, 1996
3. Montserrat, et al. Am J Respir Crit Care Med, Vol 152. pp1854-1859, 1995

> Please see also References relevant to AutoSet technology.