RESPONSE OF BREATHING PATTERN TO FLOW AND PRESSURE IN THE UPPER AIRWAY OF RATS

The effects of upper airway (UAW) flows and pressures on breathing pat tern and respiratory muscle activities were studied in anesthetized ra ts breathing through a tracheostomy. A steady flow (similar to 1000 ml /kg/min) of cold dry air, or cold wet air, or warm wet air was passed through the UAW, in the expiratory direction for approximately 20 sec (20-40 sec). In other trials positive or negative pressure was applied to the isolated UAW for a similar duration. There was a marked prolon gation of the expiratory duration and decreases in peak inspiratory fl ow, tidal volume, and peak diaphragm electromyogram (EMG) activity in response to cold dry airflow. The responses to cold wet air were reduc ed but still significant. Warm wet air had no effect on breathing. The se responses show that UAW cooling and drying depress breathing in the rat and that cooling itself could cause the inhibition of breathing. Negative pressure induced substantial increases in genioglossus and la ryngeal inspiratory activity while positive pressure caused a decrease in genioglossus activity. Positive pressure also increased expiratory time while negative pressure increased inspiratory time. These result s confirm the functional role of the UAW dilating muscles in preventin g UAW from collapse in rats. (C) 1998 Elsevier Science B.V. All rights reserved.