Effect of head flexion on airway resistance measured in a body plethysmograph

We measured the effects of partial (21 degrees) and full (43 degrees) flexion of the head on airway resistance (Raw) and specific conductance (SGaw) in eight normal subjects and two patients with mild obstructive lung disease. With partial head flexion, mean Raw increased by 32% and SGaw decreased by 26% compared to control. With full head flexion Raw increase 75% and SGaw decreased 42%. All values are significantly different from control (p less than 0.005). We suggest that subjects in a body plethysmograph be instructed to sit as erect as mouthpiece positioning will allow.