A method to detect obstructive and central apneas in the drug-free rat

Current studies on the control of breathing and sleep disorders in humans are necessarily limited to non-invasive procedures. Therefore, our long term objective is to develop an animal model to identify the underlying causes of breathing disorders. Respiratory parameters obtained with the traditionally used barometric method do not reveal obstructive apneas. Thus, our first goal was to develop a method that could be used over prolonged periods and would allow detection and distinction of central and obstructive apneas. An inspiratory effort in the absence of air movement is the hallmark of an obstructive apnea, whereas an absence of both an inspiratory effort and airflow characterizes a central apnea. Hence, we have recorded diaphragm or parasternal EMGs from chronically implanted wires as an index of respiratory drive, and airflow from a pair of thermocouples implanted in the tip of each nostril of the obligatory nose-breathing rat. To make the thermocouple, the wires were crimped into the cut end of a 27 gauge needle's shank. To implant the thermocouple, the needle was inserted from the inside through the tissue. This surgery entails minimal bleeding within the nasal cavity. After recovery from the anesthesia, chronic recordings can be made indefinitely. Recordings made during a tracheal occlusion, imposed to simulate an obstructive apnea, proved that this method provides the essential parameters for detection and distinction of obstructive and central apneas in the unrestrained rat.