We identified all the patients referred to ASV titration at our Sleep Medicine Center. Most of the patients had previously undergone an unsuccessful PAP trial.

The ASV titration was done by split-night PSG (SomnoStar® Sleep System). Sleep stage scoring was performed according to standard criteria of the American Association Sleep Medicine (2007). An apnea was defined as ≥90% airflow reduction for ≥10s, and a hypopnea was defined as ≥30% reduction in airflow for ≥10s accompanied by ≥3% desaturation from baseline. An arousal was defined as ≥3-s increase in EEG frequency following ≥10s of stable sleep, accompanied by an increase in submentalis EMG activity for ≥1s during REM sleep. The AHI was calculated as the number of apneas and hypopneas per hour of sleep. The arousal index was calculated as the number of arousals per hour of sleep. Obstructive sleep apnea syndrome was diagnosed if RDI was ≥5 events and the patient was symptomatic (daytime sleepiness, nocturnal gasping or choking, loud snoring with description of breathing interruptions) or if RDI was >15 even if patient was asymptomatic. CSA was diagnosed if the number of central apnea per hour was ≥5 and at least 50% of the total AHI was central in origin. Treatment-emergent SA was diagnosed if CPAP titration eliminated obstructive events but the residual central apnea index (CAI) was ≥5 or the CSR pattern became predominant.

After the baseline sleep study, patients diagnosed with treatment-emergent CSA, CSA or CSR were submitted to a second PSG (SomnoStar® Sleep System) for ASV titration. Titration was performed online by the neurophysiologist technician in sleep laboratory. Medical charts were reviewed and demographic, clinical and polygraphic/polysomnographic data were extracted.

After PSG with ASV titration, the eligible subjects were allocated into 2 groups: patients who received flow-triggered ASV (BiPAP Auto SV Phillips and VPAP Adapt SV Resmed) and those who received PAP (AutoCPAP/CPAP/BIPAP) (REMStar Auto Philips and Auto Spirit S8/S9). Both groups had a minimal follow-up of 6 months. The selection of the ventilator mode was exclusively based on differences in reimbursement.

In the CPAP group, airway pressure was manually modulated from 6cmH2O to the effective pressure, with a maximum of 14cmH2O. The appropriate fixed pressure was chosen as the pressure abolishing or significantly decreasing both obstructive events (including apnea, hypopnea, and snoring) and CSR without arousal.

After a minimum time of 6 months, residual IAH, compliance, Epworth sleepiness scale, left ventricular shortening fraction and cardiovascular events were recorded. Residual AHI was given by the ventilator support device data.

Statistical analysis was performed using SPSS version 17.0 for Windows. All values are shown as the means SD, and categorical variables are expressed as numbers and percentages. The baseline characteristics were compared using Student's t test for continuous variables, whereas the Chi-square test or Fisher's exact test was used for categorical variables. Within- and between-group comparisons of measurements were carried out using paired and unpaired Student's t tests for normally distributed data, and the Wilcoxon-signed rank test for non-normally distributed data.

Values <0.05 were considered statistically significant.

Thirty-three patients were included: 30 men and 3 women with an average age of 68±8 years.

Patient baseline characteristics before any positive pressure therapy are summarized in Table 1. Of the 33 patients submitted to ASV titration, 16 were allocated to ASV, 15 to the PAP and 2 patients were lost in follow-up. In PAP group, 12 patients were treated with AutoCPAP, 1 with BIPAP and 2 with CPAP.

Heart failure was present in 20.6% of cases, hypertension in 53% and dysrhythmia in 12%. Twenty-nine percent of the patients had history of diabetes mellitus.

In both groups (PAP vs. ASV) there were no statistical differences in terms of age (mean 71 years±6 vs. 66±10; P=0.11), sex (88% male vs. 93%), BMI (mean 30±4 vs. 31±5; P=0.39), Epworth sleepiness scale (mean 12±7 vs. 11±6; P=0.78) or diagnostic AHI (mean 44±18 vs. 52±25). There was also no significant difference in terms of cardiovascular comorbidities (Table 1).

As this study is retrospective, not all the patients had an initial echocardiogram available, prior to PSG with ASV titration; in fact, echocardiographic evaluation before and after ASV titration was only available in 16 patients (9 in ASV group vs. 7 in PAP group). The median of the initial left ventricular shortening fraction was 35±15 in ASV group and 35±4 in PAP group with no differences between them (P=0.96).

The diagnosis that led to an ASV study was treatment-emergent SA in 59.4% (44.4% in ASV group vs. 55.6% in PAP group), CSA and/or CSR in 40.6% (in 61.5% ASV group vs. 38.5% in PAP).

The indication for ASV titration was a suboptimal response to PAP. The summary of polysomnographic features of split-night of ASV titration is summarized in Table 2. During polysomnography ASV titration, the mean AHI was 7±10events/h after optimal pressure for ASV titration and the mean cumulative percentage time at a pulse oximetry oxygen saturation <90% was 11±27%.

After ASV titration, the mean follow-up was 25±14 months. Both groups (ASV vs. PAP) were considered compliant as they used their device for more than 4h per night and were similar: 77±23% in ASV group (P=0.191) and 88±14% in PAP group (P=0.482) (Fig. 1) (P=0.153). The average number of hours of daily use was 6h23±2h13 in ASV group and 6h59±1h08 in PAP group.

Figure 1.

Efficacy of adaptive servoventilation (ASV) on sleepiness.

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In terms of sleepiness, both groups improved the Epworth sleepiness scale score after the initial diagnosis with a statistically significant difference (P=0.016 in ASV group vs. P=0.031 in PAP group). However, comparing only the final Epworth, no significant statistical difference was found between them: 6±5 in ASV group and 7±5 in PAP group (P=5.06) (Fig. 2).

Figure 2.

Compliance (%) of ASV and PAP group.

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As shown in Fig. 3 there was a statistical difference in terms of residual AHI: mean AHI was 4±3 in ASV group and 9±3 in PAP group (P=0.005).

Figure 3.

Impact of adaptive servoventilation (ASV) treatment on apnea hipbones index (AHI) (events/h).

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We found no differences in terms of blood gases or left ventricular fractional shortening (ASV 33±10% vs. PAP 32±10%).

Table 3 includes a summary of cardiovascular events. There was no difference in terms of non-fatal cardiovascular events (3 events in each group) but in PAP group 2 patients died of sudden death. These 2 patients had treatment-emergent SA and the ventilator mode was CPAP in one patient and BIPAP in the other. Both of them had diabetes, hypertension and alcoholism. One suffered from heart failure.

The authors declare that the procedures followed were in accordance with the regulations of the relevant clinical research ethics committee and with those of the Code of Ethics of the World Medical Association (Declaration of Helsinki).

The authors declare that they have followed the protocols of their work center on the publication of patient data.

The authors have obtained the written informed consent of the patients or subjects mentioned in the article. The corresponding author is in possession of this document.