Abdominal compression increases upper airway collapsibility during sleep in obese male obstructive sleep apnea patients

Abstract

Study objectives: Abdominal obesity, particularly common in centrally obese males, may have a negative impact on upper airway (UA) function during sleep. For example, cranial displacement of the diaphragm with raised intra-abdominal pressure may reduce axial tension exerted on the UA by intrathoracic structures and increase UA collapsibility during sleep.

Design: This study aimed to examine the effect of abdominal compression on UA function during sleep in obese male obstructive sleep apnea patients.

Setting: Participants slept in a sound-insulated room with physiologic measurements controlled from an adjacent room.

Participants: Fifteen obese (body mass index: 34.5 +/- 1.1 kg/m2) male obstructive sleep apnea patients (apnea-hypopnea index: 58.1 +/- 6.8 events/h) aged 50 +/- 2.6 years participated.

Interventions: Gastric (PGA) and transdiaphragmatic pressures (P(DI)), UA closing pressure (UACP), UA airflow resistance (R(UA)), and changes in end-expiratory lung volume (EELV) were determined during stable stage 2 sleep with and without abdominal compression, achieved via inflation of a pneumatic cuff placed around the abdomen. UACP was assessed during brief mask occlusions.

Measurements and results: Abdominal compression significantly decreased EELV by 0.53 +/- 0.24 L (P=0.045) and increased PGA (16.2 +/- 0.8 versus 10.8 +/- 0.7 cm H2O, P < 0.001), P(DI) (11.7 +/- 0.9 versus 7.6 +/- 1.2 cm H2O, P < 0.001) and UACP (1.4 +/- 0.8 versus 0.9 +/- 0.9 cm H2O, P = 0.039) but not R(UA)(6.5 +/- 1.4 versus 6.9 +/- 1.4 cm H2O x L/s, P=0.585).

Conclusions: Abdominal compression negatively impacts on UA collapsibility during sleep and this effect may help explain strong associations between central obesity and obstructive sleep apnea.

Figure 1

A schematic diagram of the breathing circuit used to deliver continuous positive airway pressure (CPAP) and the undertaking of external mask occlusions. CPAP was delivered to the patient via the inspiratory limb and air was expired via the plateau valve. During an external mask occlusion, a balloon located upstream of the mask was rapidly inflated near end-expiration. Occlusion termination was achieved by rapid balloon deflation.

Figure 2

A 30-sec trace showing the events during a brief external mask occlusion in an OSA patient. Note the parallel increase in mask (P_MASK), epiglottic (P_EPI) and esophageal (P_ES) pressures during the first inspiratory effort followed by a return back to baseline. During subsequent efforts, P_MASK again initially tracks P_EPI and P_ES until a point at which it deflects away from P_EPI and P_ES. This deflection point is indicative of UA collapse and is classified as the UACP.

Figure 3

The effect of external abdominal compression on (A) gastric pressure (P_GA) and transdiaphragmatic pressure (P_DI) and (B) upper airway closing pressure (UACP) Means ± SEM. (N = 14 for P_GA and P_DI and N = 15 for UACP).

Figure 4

Relationship between (A) upper airway closing pressure (UACP) with transdiaphragmatic pressure (P_DI) and (B) with gastric pressure (P_GA) without abdominal compression (N = 14).