Diaphragmatic Responses to Body Position Changes in Obese Patients with Obstructive Sleep Apnea^1–3

Abstract

Patients with severe obesity and obstructive sleep apnea (OSA) have been shown to have abnormalities in respiratory muscle function and respiratory control. The present study was done to evaluate diaphragmatic function and the diaphragm fiber-length-compensating reflex in morbidly obese patients with OSA (1). Twelve normal subjects and 13 morbidly obese patients with OSA were studied in recumbent and upright positions. In the normal subjects, the diaphragm fiber-length-compensating reflex operated normally causing the diaphragm's inspiratory EMG to increase when the diaphragm's fibers shortened with assumption of the upright position. However, 8 of the 13 obese patients with OSA showed a decrease rather than an increase in the inspiratory diaphragmatic EMG on assuming the upright posture. Further data indicate greater diaphragmatic efficiency in the upright than in the supine position in a majority of the obese patients, a reversal of the normal response. Two possible explanations of these observations are: an abnormality of central respiratory control in obese patients with OSA and overstretching of the diaphragm in the recumbent obese patient. The observation of reduced maximal transdiaphragmatic pressures in the recumbent position in some of the obese patients with OSA supports the second explanation. Diaphragmatic overstretching may be an important mechanism in the development of hypoventilation in the morbidly obese.

Screening for sleep-disordered breathing in neuromuscular disease using a questionnaire for symptoms associated with diaphragm paralysis

“…Whilst the majority of patients have obstructive sleep apnoea (OSA) [4,5], other causes of SDB may similarly cause health problems [6][7][8][9][10][11][12]. In the present study, we considered the group of patients with neuromuscular disease (NMD) who are affected by SDB because of weakness of the respiratory muscles [9,[13][14][15][16][17][18] influenced by posture and sleep stage [9,19] and who do not necessarily present with symptoms, such as daytime fatigue, that are measured by the Epworth Sleepiness scale (ESS) [20].…”

Correlation of body mass index with flow rates and maximum voluntary ventilation: A comparative study

“…It has been suggested that the additional load causes a length-tension disadvantage for the diaphragm due to fiber overstretching, which is particularly worse while the individual is supine. [11] There is a significant negative correlation of BMI with FEF 75-85% (−0.173) and MVV(−0.196). FEF 25-75%: The mean (±SD) FEF 25-75% at rest in overweight group was 3.76 ± 0.88 L/s, in obese group was 3.75 ± 1.08 L/s, and in controls was 1.66 ± 0.85 L/s.…”

“…This is the reason why obese people are at increased risk of respiratory symptoms, such as breathlessness, particularly during exercise, even if they have no obvious respiratory illness. [10,11] …”

Obesity Hypoventilation Syndrome

“…Respiratory muscle function is impaired and worse in the supine position in OHS when compared to eucapnic morbidly obese individuals [39][40][41]. Several theories have been postulated to explain this observation.…”

“…Several theories have been postulated to explain this observation. Diaphragmatic impairment by mechanical overstretching by abdominal fat [41], chronic hypoxia and hypercapnic state [42], low insulin growth factor (IGF-I) levels, reduced ventilatory drive are all potential mechanisms [43].…”