Functional Capacity, Sleep Quality, and Cognitive Function in Obesity Hypoventilation Syndrome

Incremental Shuttle Walk Test (ISWT)

The ISWT is a field test consisting of 12 levels in which walking speed increases progressively. Participants are required to walk back and forth between two cones placed 10 meters apart, performing at their maximal capacity until symptom limitation. The test will be terminated if the patient is unable to maintain the required pace due to dyspnea, upon reaching maximal heart rate, or if the participant is more than 0.5 m behind the cone at the designated signal. The number of completed shuttles will be recorded, along with pre- and post-test measurements of blood pressure, heart rate, oxygen saturation, and dyspnea and leg fatigue scores using the Modified Borg Scale.

Montreal Cognitive Assessment (MoCA)

Cognitive functions including selective and sustained attention, information processing speed, short-term memory, and reaction time will be evaluated using standardized tests. To minimize environmental influences, all assessments will be conducted under identical conditions-in a quiet room with consistent physical settings-at the same time of day and by the same researchers for each participant. The MoCA will be used as a cognitive screening tool. It evaluates executive functions, attention and concentration, memory, language, abstract thinking, visuospatial skills, orientation, and calculation. The test takes approximately 10 minutes, and scores are calculated out of 30. A cutoff score of 26 is used; scores below this threshold indicate mild cognitive impairment.

Six-Minute Walk Test (6MWT)

Submaximal functional exercise capacity will be assessed with the 6MWT following ATS guidelines (86). Participants will be instructed to walk at their own pace along a 30-meter flat corridor for six minutes, covering as much distance as possible. Before the test, participants will rest in a seated position for 10 minutes, after which baseline SpO₂, heart rate, blood pressure, and Modified Borg Scale scores for dyspnea and fatigue will be obtained. The same measurements will be repeated after the test. The six-minute walking distance (6MWD) will be recorded in meters.

Visual Reaction Time

Reaction time will be assessed using the Simple Visual Reaction Time Task implemented via Inquisit version 6.0, a computer-based software platform that also includes cognitive tests and games. In this test, participants are instructed to press the space bar as quickly as possible when a red circle appears at random intervals (2000-8000 ms) on a white screen. Two sets of 20 trials will be performed, and the average will be calculated. The fastest, slowest, and mean reaction times will be recorded as outcomes.

Epworth Sleepiness Scale (ESS)

The ESS consists of 8 items assessing the likelihood of dozing off during daily activities. Each item is scored from 0 (never) to 3 (always). A total score ≥10 indicates excessive daytime sleepiness. The Turkish validity and reliability of the scale have been established, with high internal consistency across the eight items (Cronbach's α = 0.80).

Pittsburgh Sleep Quality Index (PSQI)

The PSQI is a 24-item self-reported questionnaire that evaluates sleep quality and disturbances over the past month (25). Its Turkish version has demonstrated validity and reliability (26). The index consists of seven components-subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleep medication, and daytime dysfunction-scored on a scale of 0-3. The sum of these component scores yields a global PSQI score ranging from 0 to 21, with scores \>5 indicating poor sleep quality.