Alcohol and the response of upper airway resistance to a changing respiratory drive in normal man.

We studied the effects of alcohol ingestion on the response of upper airway resistance (UAR) to changing respiratory motor output in 9 normal subjects. Nasal and pharyngeal pressures were measured with two low bias flow catheters placed at the tip of the epiglottis and in the posterior nasopharynx. Respiratory flow was measured with a Fleisch no. 3 pneumotachograph connected to a tightly fitting mask. Breath-by-breath inspiratory upper airway resistances were calculated at isoflow during 1) a CO2 rebreathing (increase in drive), 2) 2 min following five slow vital capacities of 100% O2 (decrease in drive) (Post-O2 period), and 3) 1 min before each procedure (baseline measurements). The respiratory motor output was estimated by the pressure developed 0.1 sec after the onset of inspiration (P0.1) during rebreathing and by the mean inspiratory flow (VT/TI) during the post-O2 period. Measurements were performed before and after the ingestion of 1.5 ml/kg of 40% alcohol. Blood alcohol level rose from 0 to 14.9 +/- 1.8 mmol.L-1 (Mean +/- SD) and total supralaryngeal resistance increased from 2.8 +/- 1.8 cm H2O.L-1.sec to 4.2 +/- 1.8 cm H2O.L-1.sec (P less than 0.001, Student's paired t-test). During CO2 rebreathing UAR decreased exponentially as P0.1 increased both before and after alcohol intake. The slope of the plot Log (pharyngeal resistance) against P0.1 decreased from -17.0 x 10(-3) +/- 9.3 x 10(-3) before alcohol to -11.0 x 10(-3) +/- 6.6 x 10(-3) after alcohol intake (P = 0.03). The slope of the decrease in nasal resistance remained unchanged. A decrease in VT/TI occurred during the Post-O2 period and was accompanied by an exponential increase in UAR at each experiment. The slope of Log (pharyngeal resistance) over VT/TI was significantly higher after (-27.0 x 10(-3) +/- 7.1 x 10(-3)) than before alcohol (-12.0 x 10(-3) +/- 4.2 x 10(-3), P less than 0.001). The slope of the increase in nasal resistance with decreasing VT/TI rose from -8.4 x 10(-3) +/- 6.5 x 10(-3) to -13.0 x 10(-3) +/- 7.4 x 10(-3) after alcohol ingestion (P = 0.06). We conclude that alcohol ingestion depresses the pharyngeal responses to changing central drive in normal subjects.