Wasted Effort: Quantification of Flow Limitation In Obstructive Sleep Apnoea
Authors List
Bastien Lechat1* PhD, Amal Osman1 PhD, Duc Phuc Nguyen1 PhD, Ganesh Naik1 PhD, Danny J Eckert1 PhD, Peter G. Catcheside1 PhD
1 Adelaide Institute for Sleep Health and FHMRI Sleep Health, College of Medicine and Public Health, Flinders University, Adelaide, Australia
Introduction
Limitations with traditional manually scored metrics of obstructive sleep apnea (OSA) severity and heterogeneity in clinical outcomes observed in treatment trials have motivated recent efforts toward better markers of OSA severity. This study proposes a new approach to quantify the severity of obstructed breathing using the respiratory equation of motion.
Methods
This study included data from 41 participants with OSA who underwent detailed physiology studies to quantify OSA endotypes with a nasal mask, pneumotachograph and epiglottic pressure sensor. Participants spent half of the night on continuous airway positive pressure (CPAP). Attempted flow during sleep was estimated via the respiratory equation of motion, with resistance and compliance estimated using wakefulness breaths. Minute ventilation was calculated for attempted and measured flow breath-by-breath. Wasted effort was derived from the difference between attempted vs. measured minute ventilation, expressed as a percentage of attempted ventilation. Wasted effort on and off CPAP was compared using linear regression.
Results
Participants were middle-aged (Mean±SD; 52±14 y), mostly men (76%), obese (BMI; 31±6 kg∙m-2) and on average had severe sleep apnea (apnea-hypopnea-index: 34±23 events/h). Approximately 90% (95%CI: [85 to 96]) of breathing effort was wasted during apnea events, compared to 73% [67 to 78] for hypopneas and 45% [41 to 49] for other breaths during sleep (all pairwise comparison p-values < 0.001). Wasted effort was greater in deep versus lighter sleep (e.g., N3 vs. N1 sleep; 20% [12 to 29] greater wasted effort, p-value < 0.001). Even with breaths not meeting conventional apnoea or hypopnea criteria, there was substantial wasted effort. The proportion of non-apnoea or hypopnoea breaths with wasted effort at or above the median wasted effort during hypopnea breaths was similar to the proportion of breaths within scored hypopnoea or apnoeas (19.8±11.6% vs. 18.9±14.2%).
Median wasted effort markedly reduced on CPAP (65% [60 to 70] vs. 9% [4 to 14], p < 0.001; 87% reduction). Even after excluding breaths during scored respiratory events, CPAP reduced wasted effort from 54% to 9% (p <0.001).
Conclusion
Wasted breathing effort is common in people with OSA and improves with CPAP therapy. Conventional hypopnoea and apnoea scoring fails to characterise a substantial degree of obstructed breathing during sleep in OSA.
Bastien Lechat1* PhD, Amal Osman1 PhD, Duc Phuc Nguyen1 PhD, Ganesh Naik1 PhD, Danny J Eckert1 PhD, Peter G. Catcheside1 PhD
1 Adelaide Institute for Sleep Health and FHMRI Sleep Health, College of Medicine and Public Health, Flinders University, Adelaide, Australia
Introduction
Limitations with traditional manually scored metrics of obstructive sleep apnea (OSA) severity and heterogeneity in clinical outcomes observed in treatment trials have motivated recent efforts toward better markers of OSA severity. This study proposes a new approach to quantify the severity of obstructed breathing using the respiratory equation of motion.
Methods
This study included data from 41 participants with OSA who underwent detailed physiology studies to quantify OSA endotypes with a nasal mask, pneumotachograph and epiglottic pressure sensor. Participants spent half of the night on continuous airway positive pressure (CPAP). Attempted flow during sleep was estimated via the respiratory equation of motion, with resistance and compliance estimated using wakefulness breaths. Minute ventilation was calculated for attempted and measured flow breath-by-breath. Wasted effort was derived from the difference between attempted vs. measured minute ventilation, expressed as a percentage of attempted ventilation. Wasted effort on and off CPAP was compared using linear regression.
Results
Participants were middle-aged (Mean±SD; 52±14 y), mostly men (76%), obese (BMI; 31±6 kg∙m-2) and on average had severe sleep apnea (apnea-hypopnea-index: 34±23 events/h). Approximately 90% (95%CI: [85 to 96]) of breathing effort was wasted during apnea events, compared to 73% [67 to 78] for hypopneas and 45% [41 to 49] for other breaths during sleep (all pairwise comparison p-values < 0.001). Wasted effort was greater in deep versus lighter sleep (e.g., N3 vs. N1 sleep; 20% [12 to 29] greater wasted effort, p-value < 0.001). Even with breaths not meeting conventional apnoea or hypopnea criteria, there was substantial wasted effort. The proportion of non-apnoea or hypopnoea breaths with wasted effort at or above the median wasted effort during hypopnea breaths was similar to the proportion of breaths within scored hypopnoea or apnoeas (19.8±11.6% vs. 18.9±14.2%).
Median wasted effort markedly reduced on CPAP (65% [60 to 70] vs. 9% [4 to 14], p < 0.001; 87% reduction). Even after excluding breaths during scored respiratory events, CPAP reduced wasted effort from 54% to 9% (p <0.001).
Conclusion
Wasted breathing effort is common in people with OSA and improves with CPAP therapy. Conventional hypopnoea and apnoea scoring fails to characterise a substantial degree of obstructed breathing during sleep in OSA.
