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Within the conventional CPAP-therapy, which continues to be the gold-standard
therapy for treatment of obstructive sleep apnea, relevant compliance problems
caused by an increased expiration pressure frequently occur (Hill, 2000).
Against this background, Philips-Respironics (Murriville, USA) has developed a
pressure-relieving CPAP-therapy, which automatically reduces pressure during
expiration via controlling respiratory flow in three pressure-relief phases (C-Flex
1-3). The effect of a pressure-relieving CPAP-therapy with respect to inspiratory
flow limitations was examined, as previously studied by Canisius et al. (Canisius
et al., 2009), whose data was used for this post-hoc analysis. Here, no relevant
discrepancies were observed in the appearance of flow limitations between
CPAP and C-Flex. However a significant increase in the inspiration time
ratio/expiration time ratio (Ti7Te) and the inspiratory breath cycle (Ti/Ttot), as
well as a significantly increased respiratory rate in C-Flex2 and C-Flex 3 (REM
sleep) could be observed. Taking into account changes in the breathing
parameters, particularly the extension of the inspiratory time and the
simultaneous consecutive reduction of the expiration time, the question arose
as to what extent the breathing effort changes under the pressure relieving PAP
Scientific studies from Schneider et al. (Schneider et al., 2009) have led to the
presumption that the C-Flex therapy increases the respiratory effort due to the
increase of the inspiration time and the change of the inspiration/expiration time
ratio in favour of the inspiration to reach the tidal volume.
On the basis of the data from Canisius et al. (Canisius et al., 2009), an
alternative theory was put forward, i.e. that an extension of the inspiratory time
together with a consecutive reduction of the expiration time under C-Flex could
lead to the decrease of the exhalation effort.
A precise analysis of the respiratory effort under C-Flex has to date not been
possible due to technical limitations. This should now be clarified in the
presented post-hoc analysis.
The bases of the analysis were the waveforms of 24 patients from Canisius et
al. (Canisius et al., 2009). The majority of the patients were already treated
sufficiently with the CPAP-therapy, the rest were newly treated. 22 patients
passed through all ventilation modes (CPAP and C-Flex 1-3) during NREM- a
REM-sleep for 15 minutes each. In only two patients could the modi not be
measured in all sleep stages. With the help of computer assisted automated
respiratory effort analysis, the respiratory effort of a single breath could be
The result of this analysis could not demonstrate any increase of the respiratory
work under C-Flex in comparison to CPAP. Instead an average linear decrease
of the respiratory effort between CPAP and C-Flex of 1.22 joule was shown.
These differences occurred because of the large variation of values as well as
the insufficient numbers of patients and are therefore not statistically significant.
This applies for REM- as well as NREM-stages. A significant difference in the
respiratory effort could be detected by correlation between the respiratory effort
under C-Flex and BMI. A significant reduction of the respiratory effort under CFlex-
3 and a decreasing BMI could be shown.
To verify the existing hypothesis, further studies with higher case numbers are
necessary. Should a reduction of the breathing effort be traceable, the C-Flex
therapy could be applied to disorders, which are accompanied by an enhanced
respiratory effort such as amyotrophic lateral sclerosis or chronic obstructive