Objective To investigate the effects of acute low-level exposure to carbon monoxide on higher cognitive functions in healthy humans. Design An empirical study of the effects of low-level exposure to carbon monoxide on higher cognitive functions in young healthy volunteers and a matched nonexposed control group. Setting A dormitory at the Hebrew University campus in Jerusalem, Israel. Participants Forty-five student volunteers who were exposed to carbon monoxide from residential kerosene stoves for 1.5 to 2.5 hours (air carbon monoxide concentrations of 17-100 ppm; mean ± SD, 61 ± 24 ppm) served as the experimental group and 47 nonexposed students served as the control group. Main Outcome Measures A battery of neuropsychological tests was administered to each participant including digit span, the revised Wechsler Memory Scale for verbal and figural memory, Trail-Making Test parts A and B, digit symbol, block design, and the Rey Auditory Verbal Learning Test. Results Venous blood carboxyhemoglobin (HbCO) levels in participants of the study group ranged from 0.01 to 0.11 (mean ± SD, 0.04 ± 0.03) and correlated with air carbon monoxide concentrations ( r =0.39; P =.01). The experimental group scored significantly lower than controls on the following tests: digit span forward ( P =.02), short-term ( P =.008) and long-term semantic memory ( P =.008), digit symbol ( P =.004), block design ( P =.009), recall of figural memory ( P =.02), and Trail-Making part A ( P =.04). No significant differences were found between the experimental and control groups in other tests. Conclusions The lower scores on neuropsychological tests indicate dysfunctions in memory, new learning ability, attention and concentration, tracking skills, visuomotor skills, abstract thinking, and visuospatial planing and processing. These dysfunctions correspond with previous reports of carbon monoxide neurotoxic effects in patients with moderate carbon monoxide poisoning. Low-level exposure to carbon monoxide results in impairment of higher cognitive functions. Neuropsychological testing appears to be sensitive in the detection of subtle neurologic dysfunctions resulting from carbon monoxide poisoning.

https://jamanetwork.com/journals/jamaneurology/articlepdf/773916/noc7114.pdf

Neuropsychological Impairment From Acute Low-Level Exposure to Carbon Monoxide

Exposure of 10 men with angina to heavy winter freeway driving increased their mean expired CO and mean COHb. These decreased at 2 hr after exposure. The mean CO in the car was 53 +- 6 ppM. Mean exercise performance was decreased by freeway driving (measured before and immediately after). Systolic pressure and heart rate at the time of angina were decreased. Increase in COHb was less than that expected from cigarette smoking. The effects were not from freeway stress as proven by the volunteers breathing filtered compressed air in similar tests. EKG changes in 3/10 patients were disturbing. The experiment was not double-blind but results were still consistent.

Effect of freeway travel on angina pectoris.

The National Aeronautics and Space Administration (NASA) is aware of the potential toxicological hazards to humans that might be associated with prolonged spacecraft missions. Despite major engineering advances in controlling the atmosphere within spacecraft, some contamination of the air appears inevitable. NASA has measured numerous airborne contaminants during space missions. As the missions increase in duration and complexity, ensuring the health and well-being of astronauts traveling and working in this unique environment becomes increasingly difficult. As part of its efforts to promote safe conditions aboard spacecraft, NASA requested the National Research Council (NRC) to develop guidelines for establishing spacecraft maximum allowable concentrations (SMACs) for contaminants, and to review SMACs for various space-craft contaminants to determine whether NASA's recommended exposure limits are consistent with the guidelines recommended by the subcommittee. In response to NASA's request, the NRC organized the Subcommittee on Guidelines for Developing Spacecraft Maximum Allowable Concentrations for Space Station Contaminants within the Committee On Toxicology (COT). In the first phase of its work, the subcommittee developed the criteria and methods for preparing SMACs for spacecraft contaminants. The subcommittee's report, entitled Guidelines for Developing Spacecraft Maximum Allowable Concentrations for Space Station Contaminants, was published in 1992. The executive summary of that report is reprinted as Appendix A of this volume. In the second phase of the study, the Subcommittee on Spacecraft Maximum Allowable Concentrations reviewed reports prepared by NASA scientists and contractors recommending SMACs for approximately 35 spacecraft contaminants. The subcommittee sought to determine whether the SMAC reports were consistent with the 1992 guidelines. Appendix B of this volume contains the SMAC reports for 12 chemical contaminants that have been reviewed for their application of the guidelines developed in the first phase of this activity and approved by the subcommittee. This report is the second volume in the series Spacecraft Maximum Allowable Concentrations for Space Station Contaminants. The first volume was published in 1994.

Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants

The carbon monoxide (CO) concentrations encountered by pedestrians and workers in the streets of a large metropolis were monitored by a reliable and sensitive portable detector (the Ecolyzer). Up to 1,000 observations per day were collected for several months during the summer and fall of 1973. The CO levels ranged from 10 to 50 ppm (varying with wind speed and direction, atmospheric stability, traffic density, and the height of nearby buildings). Much higher average concentrations were found in such adverse sites as poorly ventilated underpasses and underground garages. Street closures for a pedestrian mall reduced levels on the mall to around the general urban background without large increases in readings on adjoining streets. Many street-workers have little medical supervision, and for this reason the urban eight-hour CO ceilings may be a more appropriate air quality target than the usual industrial figure of 50 ppm. However, even the latter is sometimes exceeded on busy city streets.

Carbon monoxide in the urban atmosphere: hazards to the pedestrian and the street-worker.

Effects of passive inhalation of cigarette smoke at levels typically encountered in public buildings have been investigated. Twenty normal male and female nonsmokers (18 to 30 years) were each exposed for two hours on alternate days (in random order) to either room air or room air plus machine-produced cigarette smoke. Exposures were conducted in an unventilated chamber (14.6 m3). Subdivisions of lung volume, maximum expiratory flow-volume curves, single-breath nitrogen washout curves, blood carboxyhemoglobin levels, and heart rates were obtained before, during, and after exposure. A submaximal bicycle ergometer test and a symptom questionnaire were also administered after exposure. Statistical analysis revealed several significant differences between test and control days; the magnitude of the changes was small and of questionable biological significance, however, particularly when account was taken of the number of statistical comparisons made. Despite the relatively small physiological changes...

Physiological Effects of Acute Passive Exposure to Cigarette Smoke

Eighty milliliters of carbon monoxide (CO) or 80 ml of air was administered doubleblind to 50 adults (32 men, 18 women). Blood carboxyhemoglobin (COHb) levels increased by 3.4% in those receiving CO. Brake reaction time, night vision, glare vision, glare recovery, hand-steadiness, and depth perception all showed small and individually insignificant deterioration in the group receiving CO; grouping data in a nonparametric analysis, the performance difference became significant (P < .005). During operation of a driving simulator, the CO-exposed group showed a highly significant deficit in “careful driving” skills (P < .005), with a statistically insignificant facilitation of emergency-type movements. Since a 3.4% increase of COHb level is sufficient to prejudice safe driving, there is a need to revise the permitted eight-hour industrial CO exposure level of 50 ppm.

Philip Randell

Papers

Carbon monoxide and driving skills.