In our study of cervical CT in patients with OSA, we found that airway volume increased by 7.9 cm3 (17.5%) when a 44° upward inclination was compared with a neutral head position.(1) Our results are reliable and show statistically significant differences despite the small sample size.(1) The title states that the study involved cervical CT rather than CT with analysis of nasal airway volume. In the studies of imaging evalua-tion of airway volume cited in the Discussion section of our study, airway volume was measured from the hard palate to the base of the epiglottis for analysis of interventions involving a mandibular advancement splint, maxillomandibular advancement surgery, and continuous positive airway pressure.(1) The clinical foundation for our study was provided by a previous study of OSA patients undergoing polysomnography; in that study, which was cited in our article, the apnea-hypopnea index was measured at baseline (i.e., during standard polysomnography) and after elevation of the head of the bed, the latter having resulted in a reduction in the apnea-hypopnea index.(1) A possible functional explanation is that head elevation contributes to upper airway patency, prevents rostral fluid shift, and averts tongue collapse, reducing upper airway re-sistance, changing upper airway critical pressure, affecting gravitational effects, and altering neuromuscular activity.(1)

The late Professor Bruno Carlos Palombini (a notable Brazilian pulmonologist) coined the term "viaerologia" ("airwayology") to describe an integrated view of airway diseases in the fields of pulmonology, otorhinolaryngology, gastroenterology, and sleep medicine, advocating the importance of the anatomical and functional attributes of the airway.(2) Diseases such as OSA have multiple phenotypic characteristics, which were not fully addressed in our study.

In patients with OSA, the role of the nasal cavity is extremely important not only in clinical analysis but also in the apnea-hypopnea index. Nasal anatomic factors, appropriately pointed out by Rana & Kharbanda, can cause significant resistance and be a contributing factor to OSA. To our knowledge, there have been no studies involving nasal imaging with and without head elevation in patients with OSA. The anatomical re-gion of interest in our study is similar to that used in most studies involving imaging evaluation of upper airway volume and evaluating thera-peutic interventions. In addition, we sought to assess upper airway volume in a site in which collapsibility is increased; CT scans of patients sitting upright or lying supine have shown that the highest degree of variation with the postural change was in the oropharynx.(3) Anatomical changes with fixed nasal obstruction, such as septal deviation and polyps, are likely to vary little with postural changes. However, patients with intranasal edema might benefit from head elevation, a hypothesis that should be explored in future studies.

REFERENCES

1. Souza FJ, Evangelista AR, Silva JV, Périco GV, Madeira K. Cervical computed tomography in patients with obstructive sleep apnea: influence of head elevation on the assessment of upper airway volume. J Bras Pneumol. 2016;42(1):55-60. http://dx.doi.org/10.1590/S1806-37562016000000092
2. Palombini BC. Uma visão integradora. In: Palombini BC, Porto NS, Araújo E, Godoy DV, editors. Doenças das vias aéreas: uma visão clínica integradora (Viaerologia). 1st ed. Rio de Janeiro: Revinter; 2001. p. 3-8.
3. Sutthiprapaporn P, Tanimoto K, Ohtsuka M, Nagasaki T, Iida Y, Katsumata A. Positional changes of oropha-ryngeal structures due to gravity in the upright and supine positions. Dentomaxillofac Radiol. 2008;37(3):130-5. http://dx.doi.org/10.1259/dmfr/31005700