Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB075

Poster Communications

Determinants of apnoea -hypopnoea-index (AHI) levels in newly diagnosed obstructive sleep apnoea patients

J. owen1, C. Earing2, C. Griffith-Mcgeever1, J. Moore1, D. McKeon2, H. Kubis1

1. School of Sport, Health and Exercise Sciences, Bangor University, Bangor, Conwy, United Kingdom. 2. Pulmonary Department, Ysbyty Gwynedd Hospital, Bangor, United Kingdom.

Obstructive sleep apnoea (OSA) is a sleep-related breathing disorder with repeated partial or complete closure of upper airway during sleep, despite ongoing efforts to breathe. OSA is associated with a high prevalence for cardiovascular disease, hypertension, and stroke. Patients face cyclical deoxygenation/re-oxygenation resulting in episodic hypercapnia and hypoxia. Events are graded by the apnoea-hypopnea index (AHI; the sum of apnoea and hypopnoea events per hour during sleep). The severity of OSA has been linked to various factors, including: body characteristics, upper respiratory tract muscle activity, chemosensitivity, as well as to cytokines. The contribution of chemosensitivity to the severity of OSA and its subsequent association to body characteristics is not clear. Consequently, we investigated newly diagnosed, untreated OSA patients (n=48) and assessed ventilatory responses to breathing normoxic carbon dioxide (6%) gas mixture, oxygen (13%), and combined carbon dioxide (6%) with oxygen (13%) mixture (Earing et al. 2016) to assess chemosensitivity. Moreover, body characteristics, lung function, and blood parameters, including adiponectin, CRP, leptin, and endocannabinoids (AEA and 2AG) were measured. In addition, a group of healthy people (n=49) were assessed on all parameters, except blood factors, for comparison with OSA patients. In OSA patients, AHI was significantly correlated with ventilatory response to carbon dioxide (6%), r=-0.511, p=0.001; there was no significant association with response to hypoxic gas breathing. Additionally, there were significant correlations of AHI with body characteristics, in particular with neck circumference (r=0.509, p=0.001). Blood parameters showed no significant correlations with AHI. Healthy participants, revealed significant differences in all measured parameters. To investigate whether body characteristics were likely to be a contributing factor to reduced chemosensitivity to CO2, we performed multiple regression analysis for prediction of CO2 sensitivity variance in the whole participant group. From this analysis, neck circumference was the best predictor, explaining about 30% (r2=0.286, p<0.0001, n=87) of CO2 response variance. Conclusion: AHI is strongly associated with CO2 sensitivity and body characteristics in OSA patients; however, only a smaller proportion of the altered CO2 sensitivity can be attributed to selected body characteristics. It is likely that factors other than those related to body characteristics influence the observed alteration in chemosensitivity in OSA.

Where applicable, experiments conform with Society ethical requirements