Work of Breathing in Eucapnic and Hypercapnic Sleep Apnea Syndrome

Abstract

Background: Upper airways in patients with obstructive sleep apnea syndrome (OSAS) are more likely narrower than those of normal subjects, a factor in increasing the work of breathing (WOB) in these individuals. Objectives: To evaluate WOB while sitting and while supine, both awake and during stage 2 sleep, in patients with hypercapnic or eucapnic OSAS. Method: Twenty normal control subjects without OSAS, 20 patients with eucapnic moderate or severe OSAS and another 8 patients with hypercapnic severe OSAS were studied. WOB was measured by esophageal manometry with the subjects seated and then with the subjects supine, both while awake and during stage 2 sleep. Results: In both the control and the eucapnic group, WOB was normal in the sitting position. When the eucapnic subjects lay supine, their WOB increased, both while awake and asleep. In contrast, the hypercapnic subjects had an abnormally high WOB both sitting and supine, whether awake or asleep. Conclusion: WOB was increased in subjects with hypercapnic OSAS in both the sitting and supine positions. While eucapnic individuals with OSAS have increased WOB when supine, it is normal when they are sitting upright.

Anesthesia for the surgical procedures of the morbidly obese

“…[3,4] Supine position and obstructive sleep apnea intensify these symptoms. [5,6] Obesity causes small airway collapse as well aschronic inflammation, and Interleukin-6 and Cyclooxygenase-2 released from fatty tissue have also been implicated in the development of accompanying asthma in obesity. [7] As the need for oxygen increases, total blood volume and stroke volume also increase.…”

Nocturnal Noninvasive Ventilation in Obesity Hypoventilation Syndrome

“…Compared to eucapnic obese individuals, subjects with OHS have reduced chest wall compliance [38], increased respiratory resistance [39], lower lung volumes [40], and higher upper airway resistance [41]. As a consequence, the work of breathing is increased significantly in subjects with OHS compared to those able to maintain eucapnia [42,43]. Expiratory flow limitation and intrinsic positive end-expiratory pressure (PEEPi) develop during tidal breathing in eucapnic obesity [44,45], especially in the supine position.…”

“…Even sitting upright, patients with OHS have increased upper airway resistance compare to morbidly obese individuals who remain eucapnic [41]. This likely contributes to the abnormally high work of breathing irrespective of whether these individuals are awake or asleep [42].…”

Obesity Hypoventilation Syndrome

“…Patients with OHS have a significantly greater work of breathing when compared to individuals with normal weight or eucapnic obese patients with OSA while breathing spontaneously on room air [27,31]. Supine posture can further worsen the respiratory system compliance [23] and functional residual capacity (FRC) [29], while increasing upper airway inspiratory resistance to airflow [28].…”

“…Since majority of patients with OHS have OSA, CPAP therapy is recommended initially to improve nocturnal gas exchange by preventing obstructive apneas and hypopneas and reducing the work of breathing related to small airway closure and expiratory flow limitation [28,31]. PAP therapy improves FRC and the abrogates the effects of PEEPi [28] which in turn decreases the cost of breathing by reducing swings in intrathoracic pressures needed to maintain breathing.…”