Among patients with sleep apnea, risk for impaired driving is highest among those with both severe excessive daytime sleepiness and historic evidence of an unintended motor vehicle crash or, by history, an equivalent level of concern. The level of apneic activity by itself is not a factor that increases risk. The high-risk individual can be recognized by pulmonary physicians who, in turn, are in a position to inform and notify the patient of increased driving risk and to explore immediate measures to reduce risk. Effective therapy needs to be instituted promptly and the effectiveness of therapy and compliance with therapy should be monitored on a routine basis. Historic information on sleepiness and driving impairment are at present the best information for medical follow-up. Among this group of high-risk patients, what is best for the patient's effective treatment is also best for society. In the opinion of the Committee, there is as yet no compelling evidence to restrict the driving privileges in apnea patients where there has not been a motor vehicle crash or an equivalent level of concern for increased driving risk. However, it is very appropriate for the physician to warn of potential dangers of driving while sleepy and inform the patient of this potential personal and social risk. Whether and under what circumstances patients with sleep apnea should be reported to the licensing authority will depend on the laws of the state in which the physician practices. in those jurisdictions in which conditions such as excessive daytime sleepiness caused by sleep apnea may be construed as reportable events, we recommend reporting to licensing bureaus if: (a) the patient has excessive daytime sleepiness and steep apnea and a history of a motor vehicle accident or equivalent level of clinical concern; and (b) one of the following circumstances exists: (i) the patient's condition is untreatable or is not amenable to expeditious treatment (within two months of diagnosis); or (ii) the patient is not willing to accept treatment or is unwilling to restrict driving until effective treatment has been instituted. Because of the imprecision of current markers of cognitive or biologic performance to prospectively identify patients at foreseeable driving risk, there can be no recommendations at this time for objective testing in patients diagnosed with or treated for sleep apnea or even for those patients presenting with either moderate or mild sleepiness. Licensing agencies are challenged to develop guidelines and mechanisms to assist in the recognition and treatment of excessive sleepiness, of which untreated sleep apnea is but one cause. The public should be advised of the dangers of driving while sleepy or extremely fatigued and educational materials developed appropriate for all operators of motor vehicles. Finally pulmonary specialists along with other medical experts familiar with sleep apnea should help formulate public policy and support reasonable regulations and behavior that will identify and treat sleepy drivers.

Ventilatory responses to CO2 and hypoxia were measured in four normal volunteers breathing 30-50 per cent N2O with and without added inspiratory resistance. CO2 response was measured by a steady-state technique, hypoxic response by a non-steady-state progressive technique. Added inspiratory resistance depressed ventilatory responses to both CO2 and hypoxia. N2O had no effect on CO2 response either with or without resistance. N2O depressed the ventilatory response to hypoxia without added resistance and further depressed the response measured with added resistance. It is thought that this was probably the result of selective depression of peripheral chemoceptor function by N2O.