Sleep Breath DOI 10.1007/s11325-015-1180-4

ORIGINAL ARTICLE

Effect of oxygen desaturation threshold on determination of OSA severity during weight loss Katja Myllymaa 1 & Sami Myllymaa 1,2,3 & Timo Leppänen 1,2 & Antti Kulkas 4 & Salla Kupari 1,5 & Pekka Tiihonen 1 & Esa Mervaala 1,5 & Juha Seppä 5,6 & Henri Tuomilehto 7,8 & Juha Töyräs 1,2

Received: 22 January 2015 / Revised: 27 March 2015 / Accepted: 7 April 2015 # Springer-Verlag Berlin Heidelberg 2015

Abstract Purpose Weight loss leads to improvement of obstructive sleep apnea (OSA), based on frequency of respiratory events (apnea-hypopnea index, AHI). However, AHI does not incorporate the severity of individual obstruction events. The American Academy of Sleep Medicine suggests two alternative oxygen desaturation thresholds (ODT) for scoring of hypopneas. We hypothesize that lowering the ODT level increases the determined impact of weight loss on OSA severity. We investigate this during weight change with AHI and adjusted AHI. Adjusted AHI is a novel parameter incorporating both severity and number of the events. Methods Ambulatory polygraphic data of 54 OSA patients (F 15/M 39, 51.7±8.4 years), divided into weight loss (>5 %, n= Katja Myllymaa and Sami Myllymaa contributed equally to this work. * Sami Myllymaa [email protected] 1

Department of Clinical Neurophysiology, Kuopio University Hospital, PO Box 100, 70029 Kuopio, Finland

2

Department of Applied Physics, University of Eastern Finland, Kuopio, Finland

3

Institute of Dentistry, University of Eastern Finland, Kuopio, Finland

4

Department of Clinical Neurophysiology, Seinäjoki Central Hospital, Seinäjoki, Finland

5

Institute of Clinical Medicine, University of Eastern Finland, Kuopio, Finland

6

Department of Otorhinolaryngology, Kuopio University Hospital, Kuopio, Finland

7

Oivauni Sleep Clinic, Kuopio, Finland

8

Institute of Public Health and Clinical Nutrition, University of Eastern Finland, Kuopio, Finland

20), control (weight change 0–5 %, n=26), and weight gain (>5 %, n=8) groups, were evaluated at baseline and after 5year follow-up. Effect of ODT (ODT2%–ODT6%) on AHI and adjusted AHI was investigated. Results The greatest changes in AHI (decrease in weight loss group and increase in weight gain group) were observed with ODT2%. Changes in AHI diminished with increasing ODT. In weight loss group, adjusted AHI showed a similar but nonsignificant trend. In contrast, the higher ODT was used in weight gain group, the greater increase in adjusted AHI resulted. Using adjusted AHI instead of AHI, led to a smaller number of patients (20 vs. 55 %, ODT3%) whose OSA severity category improved along weight loss. Conclusions Weight loss significantly reduced AHI. This reduction was highly dependent on selected ODT. The change in adjusted AHI did not occur in the same extent. This was expected as the more severe events which tend to remain during the weight loss have greater importance in adjusted AHI, while the event severity is neglected in AHI. Keywords Hypopnea . Apnea-hypopnea index (AHI) . Adjusted AHI . Obstructive sleep apnea (OSA) . Oxygen desaturation . Hypoxia . Weight loss

Introduction Obstructive sleep apnea (OSA) is characterized by repetitive episodes of cessation of respiratory airflow caused by an upper airway collapse during sleep. The most important risk factor for OSA is obesity [1–3]. Excess fat tissue impairs breathing during sleep via multiple mechanisms, including alterations in upper airway structure and function and disturbance of the relation between respiratory drive and load compensation [4]. A significant association between OSA and

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overweight has been demonstrated in numerous studies [1, 5–7]. Body mass index (BMI) greater than 29 kg·m−2 has been reported to increase the risk for OSA to 10-fold [8]. The prevalence of OSA among obese individuals exceeds 30 % [8], and at least 70 % of OSA patients are obese [2]. Detection and classification of OSA are currently based on apnea-hypopnea index (AHI) [9]. This parameter indicates the average number of total breathing cessation (apnea) and partial breathing cessation (hypopnea) events occurring per hour of sleeping time. In recent years, multiple recommended rules for scoring hypopneas have been given [10–12]. The variation in hypopnea scoring rules is related to the degree of airflow reduction and/or the required level of associated oxygen desaturation. It has been demonstrated that AHI is highly dependent on the selection of oxygen desaturation threshold (ODT) used for scoring of hypopneas, subsequently affecting the diagnosis and classification of OSA patients [13–17]. According to the latest recommendations of the American Academy of Sleep Medicine (AASM) in 2012, hypopnea event is scored when the airflow decreases by ≥30 % for ≥10 s and is associated with ≥3 % oxygen desaturation or an arousal [11]. AHI relies only on the frequency of apnea and hypopnea events but contains no information on the severity of the individual events [18, 19]. Thus, AHI might not fully reflect the overall severity of the disease and under certain circumstances, this index may misestimate the severity of the disease and physiological stress it causes [20–22]. In previous studies, a significant association between weight change and change in OSA severity has been demonstrated [1, 6, 23–27]. However, that association has been investigated using frequency-based outcome variables, i.e., AHI and oxygen desaturation index (ODI). Instead, according to our best knowledge, the effect of weight change on the characteristics of individual events, i.e., the length of individual obstruction events, and depth of related desaturations have been investigated only scarcely [28, 29]. In order to account for the severity of individual events, Muraja-Murro et al. [30] recently introduced a parameter called adjusted AHI. This parameter comprises information on the number and severity of individual breathing cessation events but still allows the use of the current AASM criteria for classifying patients to different OSA severity categories (i.e., normal, AHI

Effect of oxygen desaturation threshold on determination of OSA severity during weight loss.

Weight loss leads to improvement of obstructive sleep apnea (OSA), based on frequency of respiratory events (apnea-hypopnea index, AHI). However, AHI ...
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