AUTONOMIC REGULATION OF NASAL VESSELS DURING CHANGES IN BODY POSITION

The effects of postural changes on nasal airflow and nasal capillary b lood flow were investigated in 15 healthy volunteers. Measurements wer e performed following nasal application of saline solution (control), the alpha-1 receptor antagonist prazosin, the alpha-2 receptor antagon ist yohimbine, and after application of both prazosin and yohimbine. N asal airflow in the control experiments did not significantly differ i n the upright (362 +/- 166 ml/s), dorsally recumbent (350 +/- 167 ml/s ) and 70-degrees head down position (311 +/- 167 ml/s). Following appl ication of prazosin, nasal airflow was reduced to 223 +/- 121 ml/s in the upright position. Prazosin treatment significantly reduced nasal a irflow to 177 +/- 111 ml/s when subjects were placed in dorsally recum bent positions and to 117 +/- 104 ml/s in 70-degrees head down positio ns (P < 0.001). Following application of yohimbine, nasal airflow rema ined stable when subjects were turned from upright (348 +/- 165 ml/s) to supine position (352 +/- 186 ml/s), whereas it was reduced to 199 /- 137 ml/s in the head-down position. Application of both prazosin an d yohimbine significantly increased nasal capillary blood flow in lase r Doppler flowmetry measurements (P < 0.05). Changes in body position with or without application of the active drugs did not alter nasal ca pillary blood flow. These findings suggest that nasal congestion due t o increased filling pressure in nasal capacitance vessels following po stural changes is mainly prevented by alpha-1 adrenergic mechanisms.