Upper Airway Resistance in Normal Man During Mouth Breathing

Abstract

Upper airway resistance was measured as the relationship between pressure drop across, and flow through, the upper airway in 10 men and 8 women. The pressure drop was measured by a direct method after puncture of the cricothyroid membrane. The relationship between pressure difference and flow was curvilinear during both inspiration and expiration and for both resting ventilation and hyperventilation; this indicates the presence of turbulent flow. All curves could be represented by second degree polynomials. Resting ventilation resistance tended to be higher than hyperventilation resistance this was especially apparent during expiration and for women. The mean upper airway resistance at a flow rate of 0.5 1/sec was 1.0 cm H2O/1/sec at rest. During hyperventilation it was 0.8 and 1.2 cm H2O/1/sec for flow rates of 0.5 and 1.0 1/sec, respectively. The upper airway resistance was approximately one-half of the total airway resistance. The mechanical work performed in moving air through the upper airway was determined as the product of the ventilated volume and pressure drop across this segment of the tract. During resting ventilation it was 0.008 and 0.006 kpm* /1 of VE for men and women, respectively.