Junker M, Koller T, Monn C. An assessment of indoor air contaminants in buildings with recreational activity. https://www.atsdr.cdc.gov/mmg/mmg.asp?id=230&tid=42. Cognitive and affective outcomes of more severe compared to less severe carbon monoxide poisoning. hypoxic stress. No data are available to evaluate this conjecture, but quantitative physiological analyses to further delimit the range of effects would be possible. Accessed Feb. 17, 2018. A third questionnaire study (C) of 61 individuals sustaining chronic carbon monoxide poisoning was recently reported by Penney (121). They found a positive and statistically significant association between same-day carbon monoxide exposure and increased risk of hospitalization for multiple cardiovascular outcomes (ischemic heart disease, heart rhythm disturbances, heart failure, cerebrovascular disease and total cardiovascular disease). 0000001496 00000 n National Institute of Standards and Solubility parameter and thermodynamics of polymer-solvent mixing HSP is an extension to the original Hildebrand solubility parameter. Often, patients themselves were not aware of the presence of a hearing deficiency. In 2000,Greiner & Schwab (91) reviewed engineering aspects of carbon monoxide as it occurs in the living space. H\]k0+zQD(v/~c'/[:X@!9'!oPVJvjk^tgye:e"N^Js Therefore, it is of great significance to monitor CO in living samples. hY]T7+l;#J-}@Rlq2%-lQO["m- Y[r`kQ-h^*[IxT%}U-R{%nJQY1JI[-/59H3@R,Ko$Y,fHl@v`*\ 1 \!8$5@$k8Iz[5g. COHb is widely used as a biomarker for carbon monoxide exposure. in water at one atmosphere (101.325 kPa) and different temperatures are indicated in the diagrams below. Can cause flu-like symptoms that clear up after leaving home. An accumulating body of evidence indicates that direct carbon monoxide exposure (not COHb) can produce a number of brain cellular events that could potentially lead to serious functional consequences (see the section on health effects below). Seizures and unilateral cystic lesion of the basal ganglia: an unusual clinical and radiological manifestation of chronic non-fatal carbon monoxide (CO) poisoning. These two lines of data support a direct effect of carbon monoxide exposure on cardiovascular morbidity and are considered to have a high weight of evidence. [72], Carbon monoxide has been proposed for use as a fuel on Mars. Roughton FJW. Such effects of acute exposure can potentially lead to consequences ranging from minor injuries to serious injuries and death. For every 1.2-mg/m3 increase in carbon monoxide concentration, absence increased by 3.79% (95% CI 1.046.55). In: Ferri's Clinical Advisor 2018. The amount of such dissolved carbon monoxide and the diffusion into various tissues has not been described or modelled. Assessment A5. 0000011624 00000 n When too much carbon monoxide is in the air, your body replaces the oxygen in your red blood cells with carbon monoxide. Auto, truck, or bus exhaust from attached garages, nearby roads, or parking areas can also be a source. Here the subjects were also given maximal exercise tests, but the criterion for stopping was not exhaustion but the onset of angina. In 1942, End & Long treated carbon monoxide poisoning in experimental animals with hyperbaric oxygen. Another consideration in the angina data is the fact that COHb was not extended to higher levels as it was for normal subjects. To provide you with the most relevant and helpful information, and understand which Handbook of environmental data on organic chemicals. But the condition is a life-threatening medical emergency. Mayo Clinic does not endorse companies or products. They estimated 25% increases in the odds of increases in carbon monoxide, conditional on the previous day's asthma symptoms. The action of carbonic oxide on man. This has been known for some time, i.e. https://www.cdc.gov/co/faqs.htm. Nitrogen dioxide and ozone also appeared to play a role. Improperly ventilated appliances and engines, particularly in a tightly sealed or enclosed space, may allow carbon monoxide to accumulate to dangerous levels. American Journal of Respiratory and Critical Care Medicine. Some complained of shortness of breath, vomiting, muscle cramps, difficulty in concentrating, visual changes and confusion. Memory disturbances following chronic, low-level carbon monoxide exposure. At low concentrations, fatigue in healthy people and chest pain in people with heart disease. The general levels of carbon monoxide, however, vary so much between the locations and studies that patterns are easily discernible. 0000016766 00000 n Armstrong CL, Cunningham J. Functional and developmental effects of carbon monoxide toxicity in children. Methylene chloride, a solvent commonly found in paint and varnish removers, can break down (metabolize) into carbon monoxide when inhaled. Out of 69 cases ophthalmologically examined, 66 gave positive results. The best understood health effects appear to be produced by hypoxia due to the binding of carbon monoxide to haemoglobin, which reduces the oxygen-carrying capacity of the blood as well as decreasing the dissociation of oxygen into extravascular tissue. The number of admissions for congestive heart failure was significantly associated with the environmental presence of carbon monoxide and several other pollutants. Journal of Industrial Hygiene and Toxicology. As a result, this probe has been proved to be able to monitor . Exposure to higher levels of ambient carbon monoxide (> 6.4 mg/m3, 3-month average) during the last trimester was associated with a significantly increased risk for low birth weight (odds ratio (OR) 1.22; 95% CI 1.031.44) after adjustment for potential confounders, including commuting habits in the monitoring area, sex of the child, level of prenatal care, and the age, ethnicity and level of education of the mother. (133) investigated an association between chronic carbon monoxide exposure and P-wave and QT interval characteristics of the electrocardiogram in 48 healthy male indoor barbecue workers and 51 age-matched healthy male controls. If you are an author contributing to an RSC publication, you do not need to request permission National Library of Medicine. Key: YEXPOXQUZXUXJW-UHFFFAOYSA-N SMILES O=[Pb] Properties Chemical formula PbO Molar mass 223.20 g/mol Appearance red or yellow powder Density 9.53 g/cm3 Melting point 888 C (1,630 F; 1,161 K) Boiling point 1,477 C (2,691 F; 1,750 K) Solubility in water 0.017 g/L[1] Solubility Myers AM, DeFazio A, Kelly M P. Chronic carbon monoxide exposure: a clinical syndrome detected by neuropsychological tests. [66] Above 800C, CO is the predominant product: Another source is "water gas", a mixture of hydrogen and carbon monoxide produced via the endothermic reaction of steam and carbon: Other similar "synthesis gases" can be obtained from natural gas and other fuels. All solubilities were measured with a constant pressure of 101.3 kPa (1 atm) of gas above the solutions. SOLUBILITY OF CARBON MONOXIDE AND HYDROGEN IN WATER AND SEA-WATER 69 Table 1. This review extends the discussion of those issues involving carbon monoxide exposure in humans summarized in the 1999 WHO and 2005 European Union reports (77,78). Infants living within 50 metres of a highway had an increased risk of 6%; those living in an area with higher exposure to wood smoke had an increase of 8% in their risk of bronchiolitis. closed) breathing spaces. Miller KA, et al. Another effect of COHb is to increase the binding strength of oxygen to haemoglobin, thus making release of oxygen into tissue more difficult (57). The logarithm of the daily high-hour ambient carbon monoxide concentration recorded on the day of admission displayed the strongest and most consistent association with hospital admission rates among the pollutants, after stratifying the time series by month of the year and simultaneously adjusting for temperature, dew point and the other ambient air pollutants. But if they're used in a closed or partially closed space cooking with a charcoal grill indoors, for example the carbon monoxide can build to dangerous levels. To these we must add the rate of oxygen utilization by the tissue. The information summarized above suggests that the damaging effects of carbon monoxide are not only due to its action in binding to haemoglobin and interfering with oxygen delivery, i.e. International Programme on Chemical Safety. Horvath SM, et al. The boiling point of CO is -191.5 . Lumio JS. It is only slightly soluble in water, blood serum and plasma; in the human body, it reacts with haemoglobin to form carboxyhaemoglobin (COHb). Since outdoor air inevitably becomes indoor air, some consideration of carbon monoxide levels in outdoor air and their effects on humans are required. 0000061715 00000 n Sari I, et al. Bass JL, et al. The endogenous formation of COHb has been described by Coburn, Forster & Kane (3). Hydrogen cyanide inhibits tissue respiration and thus adds to hypoxic effects, in addition to strongly stimulating increased pulmonary ventilation. White (86) reviewed carbon monoxide poisoning in children in 2000. These carbon monoxide associations generally remained robust in multiple pollutant models. Groups at highest risk from carbon monoxide exposure include the unborn and those adults, elderly or not, with coronary artery disease, congestive heart failure or potential stroke, those at risk of sudden death, etc. PubChem . Prediction of carboxyhemoglobin formation due to transient exposure to carbon monoxide. The final dose for carbon-monoxide-induced hypoxic effects is thus seen to be some measure of tissue oxygenation. Jensen LK, Klausen H, Elsnab C. Organic brain damage in garage workers after long-term exposure to diesel exhaust fumes. gabor.laurenczy@epfl.ch. The direct effect of carbon monoxide on tissue has not been demonstrated in vivo, although such effects have been inferred by the observation of tissue effects in exposures in vivo that are very similar to such effects found with in vitro preparations. The references in each of the relevant articles were searched to find any other articles that might have been missed by the automated searches. Bruinen de Bruin Y, et al. [85][74] In another example, carbon monoxide is a nutrient for methanogenic archaea which reduce it to methane using hydrogen. 1998; p. 179. Note: AM = arithmetic mean; GM = geometric mean; SD = standard deviation. The solubility of carbon monoxide in 37 ionic liquids and in some organic solvents has been determined using high-pressure 13C NMR spectroscopy; a method for predicting the CO solubility is demonstrated, and it was shown that the rate of the hydroformylation of 5-hexen-2-one does not correlate with the CO solubility, as expected from the determined relative solubility of CO compared to H2. Air quality guidelines for Europe, 2nd ed. @\g%_gX!(i.a"~ltfX9IfeI-gDWb`{L1bC`.f9mj#|kee OU*bW1c+5kpgM}[8VaVY,TL{WTrYXvcDw\6xQ 9qUmig-Nqs^Bfq[CE[qs~T.&S5:H$)[AQRJ6Umb Only emails and answers are saved in our archive. In some cases the disease seemed to progress, although the patients being examined were then in surroundings free from coal gas. Effectively, a so-called safe level is arbitrarily set at a point at which a level of health effects is deemed acceptable. and the carboxyl moiety acted as the water-soluble unit. The results of our detailed pH-dependent studies are explained consistently by a mechanism in which. The audiogram, however, showed changes in 78.3% of the patients with carbon monoxide poisoning. (144) analysed nearly 12 000 diagnoses of infant bronchiolitis between 1999 and 2002 in south-west British Columbia. The warning signs of carbon monoxide poisoning can be subtle. There are many hundreds of millions, indeed billions of people around the world who are currently chronically exposed to carbon monoxide indoors. The carbon monoxide effects were corrected by subtracting the effects of hypocapnia. In ancient history, Hannibal executed Roman prisoners with coal fumes during the Second Punic War. A critical analysis of the use of the CFK equation in predicting COHb formation. This is an area requiring additional study, since at the present stage of knowledge the question cannot be resolved. Because of inconsistencies in data reporting, exposure assessment and possible confounding of effects by co-pollutants the weight of this evidence is considered limited but suggestive of important health effects. Karr CJ, et al. Short term effects of carbon monoxide exposure on the exercise performance of subjects with coronary artery disease. Penney (85) reviewed the effects of carbon monoxide exposure on developing animals and humans in 1996. It is very flammable in air . Jetter et al. After adjustment for the effects of weather, day of the week, month, holidays and time trend, they found that carbon monoxide and oxygen were statistically significant predictors of daily absenteeism. It is a colourless, odourless and tasteless gas that is poorly soluble in water. Chen & Wang (83) reviewed the health effects of carbon monoxide in air pollution in major Chinese cities in 2000. Mechanisms of carbon monoxide toxicity. For more information, see - Carbon Monoxide's Impact on Indoor Air Quality, Carbon Monoxide's Impact on Indoor Air Quality. In the 1950s and 1960s, carbon monoxide levels in urban air often approached or even exceeded these reference values, but drastic reductions in emissions from space heating and traffic have substantially reduced anthropogenic emissions in spite of the growing size of cities and increasing traffic (9,29). As such, it is relatively undetectable. What is the average level of carbon monoxide in homes? Copyright Clearance Center request page. Moolgavkar SH. The human microbiome produces, consumes, and responds to carbon monoxide. with the development of data collections included in The writers have devised a method for the determination of carbon monoxide in serum and plasma. Thom SR, et al. (142) examined the relationship between asthma and air carbon monoxide levels in Seattle for data during the period 19871994. (153) conducted a study of nearly 400 000 emergency department visits to 14 hospitals in Canada between the early 1990s and the early 2000s. This gas is lighter in the air and released naturally as well as from forest fires, volcanic eruptions, and man mode processes. 0000002050 00000 n PDF Chapter 5.5 Carbon monoxide - World Health Organization Ischiropoulos et al. These are really questions of physiological mechanisms. The operation of these pathways and their products explain the effects of carbon monoxide at very low aircarbon monoxide and COHb levels, and what occurs during extended exposure, and finally the seeming lack of a doseresponse relationship between aircarbon monoxide concentration, COHb, immediate symptoms and the long-term health effects. Its molecular weight is 28.01 g/mol, melting point 205.1 C, boiling point (at 760 mmHg) 191.5 C (312.7 F), density 1.250 kg/m3 at 0 C and 1 atm and 1.145 kg/m3 at 25 C and 1 atm, and relative density (air = 1) 0.967 (1,2). 0000014446 00000 n Penney DG, Dunham E, Benjamin M. Chronic carbon monoxide exposure. 2126 July 1996; pp. Exposure to carbon monoxide may be particularly dangerous for: Depending on the degree and length of exposure, carbon monoxide poisoning can cause: Simple precautions can help prevent carbon monoxide poisoning: Keep your fuel-burning appliances and engines properly vented. 68 August 2014 CO compoundshave shown efcacy animalmodels disease,including postoperative ileus, chronic colitis, necrotizing . Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro .Add the Engineering ToolBox extension to your SketchUp from the SketchUp Pro Sketchup Extension Warehouse! The release of nitric oxide from platelets and endothelial cells inside blood vessels, forming the free radical peroxynitrite, further inactivates mitochondrial enzymes and damages the vascular endothelium of the brain. Furthermore, smoking at increased elevation dramatically increases the extent of the polycythaemia. [89][90][91], Carbon monoxide poisoning is the most common type of fatal air poisoning in many countries. It was concluded that there is an association between change in short-term air pollution levels and the occurrence of asthma symptoms among children in Seattle. Kim D, et al. Thus, a separate guideline is needed to address minimal exposure over 24 hours, rather than the 8-hour period used in the acute guidelines. Stern et al. In: Penney DG, editor. It readily combines with hemoglobin to produce carboxyhemoglobin which potentially affects gas exchange; therefore exposure can be highly toxic. Prochop (132) reports on the case of four people chronically exposed to carbon monoxide in an apartment building in Florida as the result of a faulty gas heater. Preliminary evaluation, using passive tubes of carbon monoxide concentrations in outdoor and indoor air at street level shops in Genoa Italy. However, the relationship in reality between blood carbon monoxide levels and symptomatology is extremely poor. Tobacco smoke can be a major source of indoor exposure, as can exhaust from motor vehicles operating in attached garages (6). Carbon monoxide level was particularly found to have a stronger association with mortality than level of particulate matter. At 760 mmHg and 20 C, 1ppm = 1.165 mg/m3 and 1 mg/m3 = 0.858 ppm; at 25 C, 1 ppm = 1.145 mg/m3 and 1 mg/m3 = 0.873 ppm. We don't collect information from our users. For acute exposures, as COHb increases, arterial blood flow to the brain increases proportionally. A study of the effect of protracted occupational exposure to carbon monoxide: with special reference to the occurrence of so-called chronic carbon monoxide poisoning. If you want to promote your products or services in the Engineering ToolBox - please use Google Adwords. Carbon monoxide has over a 200-fold greater affinity for hemoglobin than has oxygen (5.15, 5.16). 0000000016 00000 n * )0Q.jX+0WuabX!YL"& a diAQq jX4QR6JA'/QJGL90a-9ZS16eWs,. Roles for platelet-activating factor and NO-derived oxidants causing neutrophil adherence after CO poisoning. Hay AWM. >tlvz* Y/RQP6#SUea=Gpigl}an*Qv;qXx:=$IPJ@@ ()PJA;Pvh:JtLLLLLLLLEEvb=SL%E z:`Z3B=<3x*R==^u1%c'~ 6= Interestingly, the prevalence of depression was higher in patients with the less compared with the more severe poisoning at six months. ozone, nitrogen oxides, chlorine and its oxides, carbon dioxide, hydrogen sulfide, hydrogen selenide and sulfur dioxide, are re-corded as bulk solubilities; i.e., all chemical species of the gas and its reaction products with water are included. In 2000, Hazucha (92) reviewed the effects of carbon monoxide on work and exercise capacity in humans. Compatible figures were obtained. In: Penney DG, editor. Electrocardiographic changes in healthy men during continuous low-level carbon monoxide exposure. Journal of Exposure Analysis and Environmental Epidemiology. Chapter 5.5, carbon monoxide. To estimate environmental guidelines that provide reasonable protection against adverse health effects, information is required about what tissue dose produces what health effects. McCartney ML. Ely EW, Moorehead B, Haponik EF. There has been no major attempt to recapitulate the review of most studies before roughly 1999. [87], The technology was first given "generally recognized as safe" (GRAS) status by the U.S. Food and Drug Administration (FDA) in 2002 for use as a secondary packaging system, and does not require labeling. For hydroformylation processes, synthesis-gas solubilities at pressures of up to 17 MPa and at temperatures between 323 K and 383 K are of particular interest. In 1996, Hiramatsu et al. The same phenomena were demonstrated in patients with stable angina, but only at a lower range of COHb. Bell et al. Even though the carbon monoxide in these environments might be insufficient to produce effects in controlled laboratory experiments, the real world is much more complicated and the possibility of such complex multiple effects cannot be dismissed. Toxic substances portal Methylene chloride. Heart and Circulatory Physiology. Hexter AC, Goldsmith JR. Exposure to high, potentially lethal levels are not considered here at any length and delayed effects are not examined because neither would be seen in indoor carbon monoxide exposure situations under normal circumstances. Chronic carbon monoxide exposure is different from acute exposure in several important respects, as noted above. This pattern of hearing deficiency was noted in 67.7% of patients who had suffered chronic carbon monoxide poisoning, but in only 14% of patients not so affected. Clark M, et al. Review/update the Epidemiological studies involving large population groups, where exposures are generally at relatively low carbon monoxide levels, have demonstrated increased incidences of low birth weight, congenital defects, infant and adult mortality, cardiovascular admissions, congestive heart failure, stroke, asthma, tuberculosis, pneumonia, etc. (94) reviewed the impairment of learning and memory and neuronal dysfunction resulting from carbon monoxide exposure. Health Effects Associated with Carbon Monoxide. [82][83][84] The scope of the biological roles for carbon monoxide sensing is still unknown. Haldane J. Aviation, Space, and Environmental Medicine. Because animal studies cannot at present provide much useful data about many aspects of the carbon monoxide poisoning syndrome (76), they have been considered only in order to understand basic mechanisms by which carbon monoxide may impair human health. Was the victim exposed to sources of carbon monoxide such as uncontrolled fires, motor vehicles, fuel-burning heaters or other internal combustion engines in a poorly ventilated enclosed space? In: Penney DG, editor. Effects of ambient air pollution on symptoms of asthma in Seattle-area children enrolled in the CAMP study. Lee K, Park E. Residential air quality in wood burning houses in Costa Rica; Proceedings of Indoor Air 2002, The 9th International Conference on Indoor Air Quality and Climate; Monterey, CA. provided correct acknowledgement is given. In a clinical review, Weaver (134) states that lower level CO exposures can cause headache, malaise, and fatigue and can result in cognitive difficulties and personality changes. x+u{N?t1+0a>nz-U Raw GJ, et al. Morris RD. Lead(II) oxide - Wikipedia Annals of the New York Academy of Sciences. Quantitative PET scan findings in carbon monoxide poisoning. These studies were, however, not replicable in any case where such replication was attempted. A metal-free coumarin-based fluorescent probe for the turn-on Maisonet et al. Evidence exists that non-hypoxic events are responsible for impairments that sometimes develop several days after reduction of COHb due to high-level acute carbon monoxide exposure. CO 2 is soluble in water, forming carbonic acid, although high amounts of impurities are known to reduce water solubility. At pressures exceeding 5 GPa, carbon monoxide converts to polycarbonyl, a solid polymer that is metastable at atmospheric pressure but is explosive.[61][62]. Journal of Exposure Science and Environmental Epidemiology. Carboxymyoglobin is more stable than the oxygenated form of myoglobin, oxymyoglobin, which can become oxidized to the brown pigment metmyoglobin. endstream endobj 39 0 obj[58 0 R] endobj 40 0 obj<>stream For the acute health effects, the literature search was conducted in the PubMed and Web of Science databases, searching the keywords carbon monoxide and health. June 30July 5, 2002; pp. Past reviews of air quality mainly discuss acute studies of carbon monoxide exposure at lower concentrations. 630-08-0) Prevalence and Use With the single exception of CO 2 . Carbon monoxide and the nervous system. The highest reported non-accidental carbon monoxide levels are observed in public or residential garages and in primitive kitchens when cooking with open fires (Guatemala). Cerebrovascular effects of carbon monoxide. Here, a 4.5% increase in COHb level reduced the maximum exercise from a total expenditure of about 112 kcal to some 90 kcal. [43], Carbon monoxide is colorless, odorless, and tasteless. The effect of carbon monoxide on the oxyhemoglobin dissociation curve. Thus it is seen that the magnitude of effect produced by an increase in COHb of 4.5% in not dramatically greater than for normal subjects. The solvents include water, aqueous and non-aqueous salt solutions, a variety of hydrocarbons, a variety of oxygen-containing, halogen-containing, sulfur-containing, and nitrogen-containing organic compounds, and also some biological fluids with which carbon monoxide has an important interaction. 0000004004 00000 n Many of these models have been combined into whole-body models, which hold much promise for estimating physiological function (http://physiology.umc.edu/themodelingworkshop/). The experimental values of the solubility of H 2 and. Maximal aerobic capacity at different levels of carboxyhemoglobin. As shown above, tissue oxygenation is determined by (a) the blood oxygen content (inversely proportional to COHb level), (b) the ease of dissociation from blood to tissue (the oxyhaemoglobin dissociation curve), (c) the volume of blood delivered to tissue and (d) the ability of tissue to utilize the oxygen (tissue respiration). Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. 79 0 obj<>stream Carbon monoxide in the pregnant mother and fetus and its exchange across the placenta. Carbon monoxide poisoning and pregnancy: Critical nursing interventions. Bruce EN, Bruce MC. Jones MD, Traystman RJ. Hauck H, Neuberger M. Carbon monoxide uptake and the resulting carboxyhemoglobin in man. ", "Heme: emergent roles of heme in signal transduction, functional regulation and as catalytic centres", "Gaseous O2, NO, and CO in Signal Transduction: Structure and Function Relationships of Heme-Based Gas Sensors and Heme-Redox Sensors", "Biochemistry of methanogenesis: a tribute to Marjory Stephenson. Typical levels of carbon monoxide used in the facilities that use this process are between 0.4% and 0.5%. CO is the leading cause of poisoning deaths in the United States and occurs when there is incomplete combustion of carbon-containing material such as coal, wood, natural gas . Endogenous carbon monoxide (CO) is an essential cell signaling molecule, which is closely related to numerous physiological and pathological processes. The end result is lipid peroxidation of the brain, which starts during recovery from carbon monoxide poisoning. K and T = 303. Pope CA III, et al. Proceedings of the 7th International Conference on Indoor Air Quality and Climate; Nagoya, Japan. Carbon Monoxide: Properties, Preparation, Hazards & Uses This site complies with the HONcode standard for trustworthy health information: verify here. Langston P, et al. DOI: 10.1039/B401537A. It is naturally produced by many enzymatic and non-enzymatic pathways,[74] the best understood of which is the catabolic action of heme oxygenase on the heme derived from hemoproteins such as hemoglobin. Commun., 2004, 1070 Of the less severely poisoned patients, 39% had cognitive deficits at six weeks. 0000031491 00000 n Georgoulis LB, et al. 461466. Hydroformylation is coupled to the Shell higher olefin process to give precursors to detergents. Anthropogenic emissions are responsible for about two thirds of the carbon monoxide in the atmosphere and natural emissions account for the remaining one third. Age, anaemia, increased elevation, cardiopulmonary disease and prior exposure to carbon monoxide can increase susceptibility to carbon monoxide toxicity. Comparison of cerebrovascular response to hypoxic and carbon monoxide hypoxia in newborn and adult sheep.