Alterations in upper airway cross-sectional area in response to lower body positive pressure in healthy subjects.
BACKGROUND
Fluid accumulation in the neck during recumbency might narrow the upper airway (UA) and thereby contribute to its collapse in patients with obstructive sleep apnoea (OSA). It is hypothesised that acute fluid shifts from the legs to the upper body in healthy subjects would increase neck circumference and reduce the cross-sectional area of the UA (UA-XSA).


METHODS
In 27 healthy non-obese subjects of mean (SE) age 39 (3) years and body mass index 23.2 (0.6) kg/m2 studied while supine, leg fluid volume was measured using bioelectrical impedance, neck circumference using a mercury strain gauge and mean UA-XSA between the velum and the glottis using acoustic pharyngometry at end expiration. Measurements were made at baseline after which subjects were randomly assigned to a 5 min time control period or to a 5 min application of lower body positive pressure (LBPP) at 40 mm Hg by anti-shock trousers, separated by a 15 min washout period. Subjects then crossed over to the opposite arm of the study.


RESULTS
Compared with control, application of LBPP significantly reduced leg fluid volume (p<0.001) and increased neck circumference (p<0.001), both at 1 min and 5 min, and reduced UA-XSA after both 1 min (-0.15 cm2; 95% CI -0.23 to -0.09, p<0.001) and 5 min (-0.20 cm2; 95% CI -0.33 to -0.09, p<0.001).


CONCLUSIONS
In healthy subjects, displacement of fluid from the legs by LBPP causes distension of the neck and narrowing of the UA lumen. Fluid displacement from the lower to the upper body while recumbent may contribute to pharyngeal narrowing and obstruction to airflow in patients with OSA. This may have particular pathological significance in oedematous states such as heart and renal failure.
Shiota
Satomi
S
Sleep Research Laboratory of the Toronto Rehabilitation Institute, Toronto, Ontario, Canada.
Ryan
Clodagh M
CM
Chiu
Kuo-Liang
KL
Ruttanaumpawan
Pimon
P
Haight
James
J
Arzt
Michael
M
Floras
John S
JS
Chan
Christopher
C
Bradley
T Douglas
TD
D000328:Adult; D000368:Aged; D001794:Blood Pressure / Q000502:physiology; D005260:Female; D018495:Fluid Shifts / Q000502:physiology*; D005676:Gravity Suits; D006801:Humans; D007866:Leg / Q000502:physiology; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D009333:Neck / Q000033:anatomy & histology; D010614:Pharynx / Q000033:anatomy & histology*; D011312:Pressure