Maximal aerobic capacity at different levels of carboxyhemoglobin

Acetazolamide does not alter endurance exercise performance at 3,500-m altitude

Acetazolamide (AZ) is a medication commonly used to prevent acute mountain sickness (AMS) during rapid ascent to high altitude. However, it is unclear whether AZ use impairs exercise performance; previous literature regarding this topic is equivocal. The purpose of this study was to evaluate the impact of AZ on time-trial (TT) performance during a 30-h exposure to hypobaric hypoxia equivalent to 3,500-m altitude. Ten men [sea-level peak oxygen consumption (VO₂peak): 50.8 ± 6.5 mL·kg^-1·min^-1; body fat %: 20.6 ± 5.2%] completed 2 30-h exposures at 3,500 m. In a crossover study design, subjects were given 500 mg/day of either AZ or a placebo. Exercise testing was completed 2 h and 24 h after ascent and consisted of 15-min steady-state treadmill walking at 40%-45% sea-level VO₂peak, followed by a 2-mile self-paced treadmill TT. AMS was assessed after ~12 h and 22 h at 3,500 m. The incidence of AMS decreased from 40% with placebo to 0% with AZ. Oxygen saturation was higher (P < 0.05) in AZ versus placebo trials at the end of the TT after 2 h (85 ± 3% vs. 79 ± 3%) and 24 h (86 ± 3% vs. 81 ± 4%). There was no difference in time to complete 2 miles between AZ and PL after 2 h (20.7 ± 3.2 vs. 22.7 ± 5.0 min, P > 0.05) or 24 h (21.5 ± 3.4 vs. 21.1 ± 2.9 min, P > 0.05) of exposure to altitude. Our results suggest that AZ (500 mg/day) does not negatively impact endurance exercise performance at 3,500 m.NEW & NOTEWORTHY To our knowledge, this is the first study to examine the impact of acetazolamide (500 mg/day) versus placebo on self-paced, peak-effort exercise performance using a short-duration exercise test in a hypobaric hypoxic environment with a repeated-measures design. In the present study, acetazolamide did not impact exercise performance after 2-h or 24-h exposure to 3,500-m simulated altitude.

A review of the experimental evidence on the toxicokinetics of carbon monoxide: the potential role of pathophysiology among susceptible groups

BACKGROUND

Acute high level carbon monoxide (CO) exposure can cause immediate cardio-respiratory arrest in anyone, but the effects of lower level exposures in susceptible persons are less well known. The percentage of CO-bound hemoglobin in blood (carboxyhemoglobin; COHb) is a marker of exposure and potential health outcomes. Indoor air quality guidelines developed by the World Health Organization and Health Canada, among others, are set so that CO exposure does not lead to COHb levels above 2.0%, a target based on experimental evidence on toxicodynamic relationships between COHb and cardiac performance among persons with cardiovascular disease (CVD). The guidelines do not consider the role of pathophysiological influences on toxicokinetic relationships. Physiological deficits that contribute to increased CO uptake, decreased CO elimination, and increased COHb formation can alter relationships between CO exposures and resulting COHb levels, and consequently, the severity of outcomes. Following three fatalities attributed to CO in a long-term care facility (LTCF), we queried whether pathologies other than CVD could alter CO-COHb relationships. Our primary objective was to inform susceptibility-specific modeling that accounts for physiological deficits that may alter CO-COHb relationships, ultimately to better inform CO management in LTCFs.

METHODS

We reviewed experimental studies investigating relationships between CO, COHb, and outcomes related to health or physiological outcomes among healthy persons, persons with CVD, and six additional physiologically susceptible groups considered relevant to LTCF residents: persons with chronic obstructive pulmonary disease (COPD), anemia, cerebrovascular disease (CBD), heart failure, multiple co-morbidities, and persons of older age (≥ 60 years).

RESULTS

We identified 54 studies published since 1946. Six studies investigated toxicokinetics among healthy persons, and the remaining investigated toxicodynamics, mainly among healthy persons and persons with CVD. We identified one study each of CO dynamics in persons with COPD, anemia and persons of older age, and no studies of persons with CBD, heart failure, or multiple co-morbidities. Considerable heterogeneity existed for exposure scenarios and outcomes investigated.

CONCLUSIONS

Limited experimental human evidence on the effects of physiological deficits relevant to CO kinetics exists to support indoor air CO guidelines. Both experimentation and modeling are needed to assess how physiological deficits influence the CO-COHb relationship, particularly at sub-acute exposures relevant to indoor environments. Such evidence would better inform indoor air quality guidelines and CO management in indoor settings where susceptible groups are housed.

Carbon monoxide exposure among police officers working in a traffic dense region of Southern India

Currently, in India, air pollution is widespread in urban areas where vehicles are major contributors. The aim of this study was to investigate the level of exposure in traffic police officers exposed to vehicle exhaust for less than 8 h/day. The specific objective of the study was to determine the levels of carboxyhaemoglobin (COHb) in these officers. The effect of exposure for 8 h/day is known, but shorter durations of chronic exposure need to be investigated, and there is a need to explore the policy options in this exposed population. This cross-sectional study, included non-smoking traffic police officers between 30 and 50 years of age working for more than 2 years in busy traffic junctions. The cases were sex matched with controls of same age group, working in offices at a teaching hospital. Venous blood was collected at the end of 3 h of duty for estimation of COHb among both the groups. The COHb levels were expressed as percentage values. Differences between the COHb levels among the traffic police officers and office workers were analysed using the Mann-Whitney U test and considered significant at p < 0.05. Traffic police officers had significantly elevated COHb levels compared with the controls; 76.5% of traffic police officers had COHb >2.5% compared with no office workers at this level and 41.2% of the police officers had COHb levels >4%. Overall, 53.8% of officers with COHb >2.5% reported headaches compared with 15.8% of officers with COHb <2.5%.

The health effects of exercising in air pollution

The health benefits of exercise are well known. Many of the most accessible forms of exercise, such as walking, cycling, and running often occur outdoors. This means that exercising outdoors may increase exposure to urban air pollution. Regular exercise plays a key role in improving some of the physiologic mechanisms and health outcomes that air pollution exposure may exacerbate. This problem presents an interesting challenge of balancing the beneficial effects of exercise along with the detrimental effects of air pollution upon health. This article summarizes the pulmonary, cardiovascular, cognitive, and systemic health effects of exposure to particulate matter, ozone, and carbon monoxide during exercise. It also summarizes how air pollution exposure affects maximal oxygen consumption and exercise performance. This article highlights ways in which exercisers could mitigate the adverse health effects of air pollution exposure during exercise and draws attention to the potential importance of land use planning in selecting exercise facilities.

Combined effects of inspired oxygen, carbon dioxide, and carbon monoxide on oxygen transport and aerobic capacity

We hypothesized that breathing hypoxic, hypercapnic, and CO-containing gases together reduces maximal aerobic capacity (V̇o2max) as the sum of each gas' individual effect on V̇o2max. To test this hypothesis, goats breathed combinations of inspired O2fraction (FiO2) of 0.06–0.21 and inspired CO2fraction of 0.00 or 0.05, with and without inspired CO that elevated carboxyhemoglobin fraction (FHbCO) to 0.02–0.45, while running on a treadmill at speeds eliciting V̇o2max. Individually, hypoxia and elevated FHbCOdecreased fractional V̇o2max(FV̇o2max, fraction of a goat's V̇o2maxbreathing air) in linear, dose-dependent manners; hypercapnia did not change V̇o2max. Concomitant hypoxia and elevated FHbCOdecreased V̇o2maxless than the individual gas effects summed, indicating their combined effects on V̇o2maxare attenuated, fitting the following regression: FV̇o2max= 4.24 FiO2+ 0.519 FHbCO− 8.22 (FiO2× FHbCO) + 0.117, ( R2= 0.965, P < 0.001). The FV̇o2maxcorrelated highly with total cardiopulmonary O2delivery, not peripheral diffusing capacity, and with arterial O2concentration (CaO2), not cardiac output. Hypoxia and elevated FHbCOdecreased CaO2by different mechanisms: hypoxia decreased arterial O2saturation (SaO2), whereas elevated FHbCOdecreased O2capacitance {concentration of hemoglobin (Hb) available to bind O2([Hbavail])}. When breathing hypoxic gas (FiO20.12), CaO2did not change with increasing FHbCOup to 0.30 because higher SaO2of Hbavailoffset decreased [Hbavail] due to the following: 1) hyperventilation with hypoxia and/or elevated FHbCO; 2) increased Hb affinity for O2due to both Bohr and direct carboxyhemoglobin effects; and 3) the sigmoid relationship between O2saturation and partial pressure elevating SaO2more with hypoxia than normoxia.

Environmental exposure to combustion-derived air pollution is associated with reduced functional capacity in apparently healthy individuals

Prior toxicological exposure reports demonstrated the decremental effect of several air pollutants on the metabolic equivalents achieved during exercise testing (METs). There are no prior large scale epidemiological reports about the effect of environmental air pollution exposure on those parameters. We analyzed a cohort of apparently healthy individuals attending a screening survey program held between 2003 and 2009. Participants were included if residing within an 11 km radius from the nearest air pollution monitoring station. Linear regression models were fitted for the metabolic equivalents and adjusted to short- and long-term air pollutant exposure (particulate matter under 10 micron, sulfur dioxide, nitrogen dioxide, carbon monoxide and ozone). The models were adjusted for possible confounders that affect air pollution and stress testing measurements. The study population comprised 6,612 individuals (4,201 males and 2,411 females). We found a statistically significant short- and long-term negative correlation between air pollutants, mainly CO and NO2 and between the metabolic equivalents achieved. A similar short-term effect was found for SO2. We conclude that exposure to combustion-derived air pollutants has a short- and long-term decremental effect on cardiorespiratory fitness as measured by exercise stress testing. Our epidemiological data support previous toxicological reports.

Carbon monoxide exposure during exercise performance: muscle and cerebral oxygenation

AIM

To investigate the effect of carbon monoxide (CO) in the inspired air as anticipated during peak hours of traffic in polluted megalopolises on cerebral, respiratory and leg muscle oxygenation during a constant-power test (CPT). In addition, since O(2) breathing is used to hasten elimination of CO from the blood, we examined the effect of breathing O(2) following exposure to CO on cerebral and muscle oxygenation during a subsequent exercise test under CO conditions.

METHODS

Nine men participated in three trials: (i) 3-h air exposure followed by a control CPT, (ii) 1-h air and 2-h CO (18.9 ppm) exposure succeeded by a CPT under CO conditions (CPT(COA)), and (iii) 2-h CO and 1-h 100% normobaric O(2) exposure followed by a CPT under CO conditions (CPT(COB)). All exercise tests were performed at 85% of peak power output to exhaustion. Oxygenated (Δ[O(2)Hb]), deoxygenated (Δ[HHb]) and total (Δ[tHb]) haemoglobin in cerebral, intercostal and vastus lateralis muscles were monitored with near-infrared spectroscopy throughout the CPTs.

RESULTS

Performance time did not vary between trials. However, the vastus lateralis and intercostal Δ[O(2)Hb] and Δ[tHb] were lower in CPT(COA) than in CPT. During the CPT(COB), the intercostal Δ[O(2) Hb] and Δ[tHb] were higher than in the CPT(COA). There were no differences in cerebral oxygenation between the trials.

CONCLUSION

Inspiration of 18.9 ppm CO decreases oxygenation in the vastus lateralis and serratus anterior muscles, but does not affect performance. Breathing normobaric O(2) moderates the CO-induced reductions in muscle oxygenation, mainly in the intercostals, but does not affect endurance.

How and why chemicals from tobacco smoke can induce a rise in blood pressure

The primary objective of this article is to analyze the role of tobacco smoke compounds able to damage the cardiovascular system and, in particular, to interfere with blood pressure. They are products of tobacco plant leaves, like nicotine, thiocyanate and aromatic amines, and a chemical derived from cigarette combustion, carbon monoxide. Of the other thousands of chemicals, there is no clear evidence of cardiovascular damage. Nicotine and its major metabolite, cotinine, usually increase blood pressure by a direct action and an action stimulating neuro-humoral metabolites of the body as well as sympathetic stimulation. An indirect mechanism of damage exerted by elevated carboxyhemoglobin concentrations is mediated by carbon monoxide, which, mainly induces arterial wall damage and, consequently, late rising in blood pressure by a toxic direct action on endothelial and blood cells. Thiocyanate, in turn, reinforces the hypoxic effects determined by carbon monoxide. Aromatic amines, depending on their chemical structure, may exert toxic effects on the cardiovascular system although they have little effect on blood pressure. A rise in blood pressure determined by smoking compounds is a consequence of both their direct toxicity and the characteristics of their chemical chains that are strongly reactive with a large number of molecules for their spatial shape. In addition, a rise in blood pressure has been documented in individuals smoking a cigarette, acutely and chronically, with irreversible artery wall alterations several years after beginning smoking. Since cigarette smoking has a worldwide diffusion, the evidence of this topic meets the interest of both the scientific community and those individuals aiming to control smoking.

Exposures to high levels of carbon monoxide from wood-fired temazcal (steam bath) use in highland Guatemala

The temazcal is a wood-fired steam bath used in the rural highlands of Guatemala for bathing and healing. We measured carbon monoxide (CO) among 288 participants in 72 temazcales. Participants were drawn from communities who participated in the RESPIRE (Randomized Exposure Study of Pollution Indoors and Respiratory Effects) chimney stove intervention trial. Temazcal CO exposures were extremely high, averaging 431 parts per million (time-weighted average). Compared to kitchen wood-smoke exposures, the temazcal contributes significantly to weekly exposures, despite the fact that the population spends less time in the temazcal than in the kitchen. This report 1) describes temazcal use patterns; 2) reports participants' signs and symptoms during temazcal use; 3) models the distribution of temazcal CO concentrations; 4) assesses reliability of exhaled breath CO as a biomarker of CO exposure; and 5) provides a proportional analysis of CO concentrations from temazcal use, as compared to kitchen concentrations.

CO and NO pulmonary diffusing capacity during pregnancy: Safety and diagnostic potential

This paper reviews the scientific evidence for the safety of carbon monoxide (CO) and nitric oxide (NO) inhalation to measure pulmonary diffusing capacity (DL(CO) and DL(NO)) in pregnant women and their fetuses. In eight earlier studies, 650 pregnant women had DL(CO) measurements performed at various times during pregnancy, with a minimum of two to four tests per session. Both pregnant subjects that were healthy and those with medical complications were tested. No study reported adverse maternal, fetal, or neonatal outcomes from the CO inhalation in association with measuring DL(CO). Eleven pregnant women, chiefly with pulmonary hypertension, and 1105 pre-term neonates, mostly with respiratory failure, were administered various dosages of NO (5-80ppm for 4 weeks continuously in pregnant women, and 1-20ppm for 15min to 3 weeks for the neonates). NO treatment was found to be an effective therapy for pregnant women with pulmonary hypertension. In neonates with respiratory failure and pulmonary hypertension, NO therapy improved oxygenation and survival and has been associated with only minor, transient adverse effects. In conclusion, maternal carboxyhemoglobin ([Hb(CO)]) levels can safely increase to 5% per testing session when the dose-exposure limit is 0.3% CO inhalation for <or=3min, and for NO, 80ppm for <or=3min. The risk of late fetal or neonatal death from increased Hb(CO) from diffusion testing is considerably less than the risk of death from all causes reported by the Centers for Disease Control, and is therefore considered "minimal risk".

Carbon monoxide inhalation reduces skeletal muscle fatigue resistance

AIM

To determine whether inhalation of carbon monoxide (CO), resulting in carboxyhaemoglobin (COHb) levels observed in smokers, had an effect on muscle fatigue during electrically evoked and voluntary muscle contractions.

METHODS

Young non-smoking males inspired CO from a Douglas bag until their COHb level reached 6%. During the control condition the same participants inspired ambient air from a Douglas bag for 6 min. Fatigue was assessed as the decline in torque in isometric knee extensions, during 2 min of electrically evoked contractions (30 Hz, 1 s on, 1 s off) and during 2 min of maximal isometric voluntary contractions (1 s on, 1 s off). A fatigue index (FI) was calculated as the ratio of final torque : initial torque. Time to peak torque (TPT) and half relaxation time ((1/2)RT) were also determined for the electrically evoked contractions.

RESULTS

The FI during both the voluntary fatigue test (control: 0.80 +/- 0.09 vs. CO: 0.70 +/- 0.08; mean +/- SD) and that of the fatigue test with electrically evoked contractions (control: 0.61 +/- 0.09 vs. CO: 0.53 +/- 0.12) was significantly lower after CO inhalation than after inhalation of ambient air (P < 0.05). There was, however, no effect of CO on the changes in TPT or (1/2)RT during the fatigue test.

CONCLUSION

Carbon monoxide inhalation resulting in COHb levels found in smokers has an acute impact on the ability of the muscle to resist fatigue.

Arterial carboxyhemoglobin level and outcome in critically ill patients

OBJECTIVE

Arterial carboxyhemoglobin is elevated in patients with critical illness. It is an indicator of the endogenous production of carbon monoxide by the enzyme heme oxygenase, which modulates the response to oxidant stress. The objective was to explore the hypothesis that arterial carboxyhemoglobin level is associated with inflammation and survival in patients requiring cardiothoracic intensive care.

DESIGN

Prospective, observational study.

SETTING

A cardiothoracic intensive care unit.

PATIENTS

All patients admitted over a 15-month period.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Arterial carboxyhemoglobin, bilirubin, and standard biochemical, hematologic, and physiologic markers of inflammation were measured in 1,267 patients. Associations were sought between levels of arterial carboxyhemoglobin, markers of the inflammatory response, and clinical outcome. Intensive care unit mortality was associated with lower minimum and greater maximal carboxyhemoglobin levels (p < .0001 and p < .001, respectively). After adjustment for age, gender, illness severity, and other relevant variables, a lower minimum arterial carboxyhemoglobin was associated with an increased risk of death from all causes (odds risk of death, 0.391; 95% confidence interval, 0.190-0.807; p = .011). Arterial carboxyhemoglobin correlated with markers of the inflammatory response.

CONCLUSIONS

Both low minimum and high maximum levels of arterial carboxyhemoglobin were associated with increased intensive care mortality. Although the heme oxygenase system is protective, excessive induction may be deleterious. This suggests that there may be an optimal range for heme oxygenase-1 induction.

Consequences of brief exposure to high concentrations of carbon monoxide in conscious rats

Exposure to high-concentration carbon monoxide (CO) is of concern in military operations. Experimentally, the physiologic manifestations of a brief exposure to elevated levels of CO have not been fully described. This study investigated the development of acute CO poisoning in conscious male Sprague-Dawley rats (220-380 g). Animals were randomly grouped (n = 6) and exposed to either air or 1 of 6 CO concentrations (1000, 3000, 6000, 10,000, 12,000, or 24,000 ppm) in a continuous air/CO dynamic exposure chamber for 5 min. Respiration was recorded prior to and during exposures. Mixed blood carboxyhemoglobin (COHb) and pH were measured before and immediately after exposure. Before exposure the mean baselines of respiratory minute volumes (RMVs) were 312.6 +/- 43.9, 275.2 +/- 40.8, and 302.3 +/- 39.1 ml/min for the 10,000, 12,000 and 24,000 ppm groups, respectively. In the last minute of exposure RMVs were 118.9 +/- 23.7, 62.1 +/- 10.4, and 22.0 +/- 15.1% (p < .05) of their mean baselines in these 3 groups, respectively. Immediately after exposure, blood COHb saturations were elevated to 60.16, 63.42, and 69.37%, and blood pH levels were reduced to 7.43 +/- 0.09, 7.25 +/- 0.05, and 7.13 +/- 0.04 in the 3 groups, respectively. Mortality during exposure was 1/12 in the 12,000 ppm group and 4/12 in the 24,000 ppm group. Deaths occurred close to the end of 5 min exposure. In each animal that died by exposure, pH was <6.87 and COHb saturation was >82%. Blood pH was unaltered and no death occurred in rats exposed to CO at concentrations <6000 ppm, although COHb saturations were elevated to 14.52, 29.94, and 57.24% in the 1000, 3000, and 6000 ppm groups, respectively. These results suggest that brief exposure to CO at concentrations <10,000 ppm may produce some significant physiological changes. However, exposure to CO at concentrations >10,000 ppm for brief periods as short as 5 min may change RMV, resulting in acute respiratory failure, acidemia, and even death.

The optimised CO-rebreathing method: a new tool to determine total haemoglobin mass routinely

A routine method to determine total haemoglobin mass (tHb) in clinical practice and sports medicine is non-existent. Radioactive tracers or other dilution procedures like the common CO-rebreathing method (Proc(com)) are impractical, the latter in particular because of the relatively long time of respiration. According to the multicompartment model of Bruce and Bruce (J Appl Physiol 95:1235-1247, 2003) the respiration time can be considerably reduced by inhaling a CO-bolus instead of the commonly used gas mixture. The aim of this study was to evaluate this theoretical concept in practice. The kinetics of the HbCO formation were compared in arterialised blood sampled from an hyperaemic earlobe after inhaling a CO-bolus (Proc(new)) for 2 min and a CO-O(2) mixture (Proc(com)) for approximately 10 min. The reliability of Proc(new) was checked in three consecutive tests, and phlebotomy was used to determine the validity. VO(2max) was determined with and without previous application of Proc(new) and the half-time of HbCO was registered also in arterialised blood after resting quietly and after the VO(2max) test. Proc(new) yielded virtual identical tHb values compared to Proc(com) when HbCO determined 5 min after starting CO-rebreathing was used for calculation. The typical error of Proc(new) was 1.7%, corresponding to a limit of agreement (95%) of 3.3%. The loss of 95 g (19) haemoglobin was detected with an accuracy of 9 g (12). After application of Proc(new) VO(2max) was reduced by 3.0% (3.7) (P=0.022) and half-time was lowered from 132 min (77) to 89 min (23) after the VO(2max) test. Inhaling a CO-bolus markedly simplifies the CO-rebreathing method without reducing validity and reliability and can be used for routine determination of tHb for various indications.

Effects of habitual smoking on cardiorespiratory responses to sub-maximal exercise

The effects of habitual cigarette smoking on cardiorespiratory responses to sub-maximal and maximal work were evaluated in nine adult nonsmokers and nine smokers with a mean age of 33 yr. A maximal treadmill test was followed by three tests at 45, 60 and 75% of each subject's VO(2)max. Compared to nonsmokers, the habitual smokers had a non-significantly lower VO(2)max in L/min and per lean body mass (9 and 6%, respectively), but had higher %fat (p<0.01), resulting in a significantly lower VO(2)max per kg body wt (13%, p<0.03). Maximal exercise ventilation (V(E)) was 16% lower in smokers. During sub-maximal work at equivalent exercise stress levels in the two groups, the V(E)/VO(2) ratio was higher in smokers by an average of 11% because VO(2) was lower and the respiratory exchange ratio values were significantly elevated in smokers at 75% of VO(2)max. Blood lactate concentrations in smokers were higher as workloads increased and O(2) pulse (VO(2)/HR) was significantly lower throughout, indicating reduced O(2) extraction, probably due to carbon monoxide. The resting HR was significantly higher in smokers and the HR recovery following all three submaximal exercises was significantly slower in smokers. These results show that detrimental cardiorespiratory effects of chronic cigarette smoking in apparently healthy individuals are evident at moderate exercise levels as reduced gas exchange efficiency in lungs and muscles.

[Recovery from exercise in trained smokers]

AIM

Assess the influence of tobacco on recovery after exercise in sportsmen.

METHODS

Sixty-three smokers aged 18-33 years, practising soccer, participated in this study. These subjects belonged to second division congolese league clubs. Heart rate (HR) was studied during recovery of moderate exercise (Ruffer's test), but also recovery index and arterial pressure. Kinetics of the HR was studied for 7 min for recovery. A control group consisted of 50 non smokers, practising soccer at similar level.

RESULTS

Smokers showed heart rate values significantly higher (P < 0.001). Non smokers presented a low recovery index. The recovery has generally two components: the first is slow in smokers, while the second is a fast one. However, recovery rate for the smokers was more rapid during the alactic phase. There exists also differences with regards to smoking tobacco dependence: when compared to great smokers, lower smokers exhibited a faster first phase and a slower second phase. These differences were significant.

DISCUSSION AND CONCLUSION

The smokers and non smokers differences are discussed with reference to the effects of nicotinemia and carbon monoxide on sympathetic-parasympathetic balance. Cardiovascular changes during exercise have a twofold control: decrease a vagal tone and increase of sympathetic activity. The comparison of smokers and non smokers concerning recovery led to suppose that there exists a difference in regards of the catecholaminergic sensitivity. The problem of thermoregulation must not be neglected during recovery. As smokers are considered, cutaneous thermolysis is perhaps important when these subjects perform exercise in ambient hot air. Here against, it is known that thermolysis mechanisms are not similar in smokers and non smokers. In conclusion, this study showed that smoking tobacco induce a lower physical condition in sportmen. Recovery rate after exercise may function as a predictor of fitness in smokers.

The combined effect of heat and carbon monoxide on the performance of motorsport athletes

Two of the major stressors endured by a motorsport athlete (MSA) during a racing event are the effects of heat and carbon monoxide. To date, there has been little research into their combined effect on driving performance. Using an interactive racecar simulator located within an environmental chamber, subjects drove a simulated race (60 min) in environmental conditions similar to those that develop during a NASCAR Winston Cup oval track race (50 degrees C ambient temperature and 10-12% carboxyhaemoglobin levels). Subjects also completed cool (20 degrees C) and heat only (50 degrees C) race simulations. During the simulations, oxygen consumption, heart rate, core and skin temperatures and psychomotor performance were measured. The results demonstrated that exposure to a racecar micro-environment combining both heat and CO produced significantly greater (P<0.05) sweat loss and core temperature change (1.53 kg; 1.06 degrees C) when compared to the heat only (1.14 kg; 0.73 degrees C) and cool conditions (0.35 kg; 0.09 degrees C). Furthermore, a significant decrease (P<0.05) in psychomotor performance was also shown between the heat/CO condition (contact points=38), and both the heat only (25 points) and cool conditions (22 points). It follows that lengthy exposure to these two stressors could produce a substantial decrement in driving performance, thereby endangering the MSA and other race competitors.

Exercise-induced arterial hypoxemia

Exercise-induced arterial hypoxemia (EIAH) at or near sea level is now recognized to occur in a significant number of fit, healthy subjects of both genders and of varying ages. Our review aims to define EIAH and to critically analyze what we currently understand, and do not understand, about its underlying mechanisms and its consequences to exercise performance. Based on the effects on maximal O(2) uptake of preventing EIAH, we suggest that mild EIAH be defined as an arterial O(2) saturation of 93-95% (or 3-4% <rest), moderate EIAH as 88-93%, and severe EIAH as <88%. Both an excessive alveolar-to-arterial PO(2) difference (A-a DO(2)) (>25-30 Torr) and inadequate compensatory hyperventilation (arterial PCO(2) >35 Torr) commonly contribute to EIAH, as do acid- and temperature-induced shifts in O(2) dissociation at any given arterial PO(2). In turn, expiratory flow limitation presents a significant mechanical constraint to exercise hyperpnea, whereas ventilation-perfusion ratio maldistribution and diffusion limitation contribute about equally to the excessive A-a DO(2). Exactly how diffusion limitation is incurred or how ventilation-perfusion ratio becomes maldistributed with heavy exercise remains unknown and controversial. Hypotheses linked to extravascular lung water accumulation or inflammatory changes in the "silent" zone of the lung's peripheral airways are in the early stages of exploration. Indirect evidence suggests that an inadequate hyperventilatory response is attributable to feedback inhibition triggered by mechanical constraints and/or reduced sensitivity to existing stimuli; but these mechanisms cannot be verified without a sensitive measure of central neural respiratory motor output. Finally, EIAH has detrimental effects on maximal O(2) uptake, but we have not yet determined the cause or even precisely identified which organ system, involved directly or indirectly with O(2) transport to muscle, is responsible for this limitation.

Smoking-induced elevations in blood carboxyhaemoglobin levels. Effect on maximal oxygen uptake

Many people engage in physical activity to reduce their cardiovascular risk associated with smoking. These people should be made aware of the metabolic and cardiorespiratory changes induced by chronic and acute smoking and, in particular, the exercise ramifications of increased levels of blood carbon monoxide (CO). Smoking-induced elevations in the CO content of the blood can reduce exercise tolerance and maximal aerobic capacity. Smoking also increases the reliance upon glycolytic metabolism during exercise. Together, these factors contribute to earlier fatigue in smokers compared with nonsmokers who exercise. Similar effects upon exercise tolerance are noted in those who inhale environmental tobacco smoke.

Carbon monoxide and water vapor contamination of compressed breathing air for firefighters and divers

Compressed breathing air, used in self-contained breathing apparatus (SCBA) by firefighters and other categories of workers as well as by recreational and commercial divers, is prepared with the aid of high-pressure compressors operating in the range of 5000 psig. There have been reports of unexplained deaths of SCUBA divers and anecdotal accounts of decreased time to exhaustion in firefighters using SCBAs. Compressed breathing air has been found to contain elevated levels of carbon monoxide (CO) and water vapor that are consistent with carboxyhemoglobin (COHb) poisoning and freezing of the user's regulator on the breathing apparatus. The Coburn-Forster-Kane equation (CFK equation) was used to estimate COHb levels at rest and at maximum exercise when exposed to different levels of CO in contaminated breathing air. The results demonstrated that, at maximum exercise, the COHb ranged from 6.0 to 17% with the use of 1 to 4 SCBA cylinders contaminated by 250 ppm CO. Standard operating procedures have been developed at the Montreal Fire Department to minimize the risk of compressed breathing air contamination. Results of the quality analysis/quality control program indicate that implementation of these procedures has improved the quality of the compressed breathing air. Recommendations are made for improvement of the air testing procedures mandated by the Canadian CAN3 180.1-M85 Standard on Compressed Breathing Air and Systems.

Arterial hypoxemia and performance during intense exercise

In order to determine the level of hypoxemia which is sufficient to impair maximal performance, seven well-trained male cyclists [maximum oxygen consumption (VO2max) > or = 5 l.min-1 or 60 ml.kg-1.min-1] performed a 5-min performance cycle test to exhaustion at maximal intensity as controlled by the subject, under three experimental conditions: normoxemia [percentage of arterial oxyhemoglobin saturation (%SaO2) > 94%], and artificially induced mild (%SaO2 = 90 +/- 1%) and moderate (% SaO2 = 87 +/- 1%) hypoxemia. Performance, evaluated as the total work output (Worktot) performed in the 5-min cycle test, progressively decreased with decreasing % SaO2 [mean (SE) Worktot = 107.40 (4.5) kJ, 104.07 (5.6) kJ, and 102.52 (4.7) kJ, under normoxemia, mild, and moderate hypoxemia, respectively]. However, only performance in the moderate hypoxemia condition was significantly different than in normoxemia (P = 0.02). Mean oxygen consumption and heart rate were similar in the three conditions (P = 0.18 and P = 0.95, respectively). End-tidal partial pressure of CO2 was significantly lower (P = 0.005) during moderate hypoxemia compared with normoxemia, and ventilatory equivalent of CO2 was significantly higher (P = 0.005) in both hypoxemic conditions when compared with normoxemia. It is concluded that maximal performance capacity is significantly impaired in highly trained cyclists working under an % SaO2 level of 87% but not under a milder desaturation level of 90%.

Effects of short-term exposure to carbon monoxide in subjects with coronary artery disease

Twenty-four male subjects with stable angina pectoris performed graded exercise tests after being exposed to either carbon monoxide (CO) or clean air in a randomized crossover double-blind experiment in which each subject acted as his own control. Subject's blood carboxyhemoglobin levels were increased from a baseline level of approximately 1.5% to 3% of saturation, post-CO exposure. Cardiographic and respiratory gas exchange data were obtained during the tests in which the subjects exercised to the point of onset of anginal pain. The goal of the study was to determine if low-level CO exposure compromised the ability of these individuals to perform work. Data were evaluated statistically using a two-factor analysis of variance with repeated measures; the factors were exposure ATMOSPHERE (clean air vs. CO) and ORDER of exposure (clean air first, CO second vs. CO first, clean air second). One-tailed tests were used, and differences were considered significant at the p less than .05 level. The time to onset of angina was reduced 6% (p = .046) after CO exposure relative to clean air. Oxygen uptake (VO2) at angina was reduced by approximately 3% (p = .04). A subgroup of individuals who exhibited depression in the ST segment of their electrocardiograph tracings showed a 12% reduction in time to onset of angina and a 20% reduction in the time to onset of 0.1 mV ST segment depression; both of these findings were also statistically significant.

Ergometer within a whole-body plethysmograph to evaluate performance of guinea pigs under toxic atmospheres

A guinea pig ergometer was constructed within an enclosure, with inlet and outlet ports for continuous ventilation, designed so that the enclosure would work as a whole-body plethysmograph as well as an inhalation exposure chamber. This system provided continuous measurement of tidal volume, respiratory frequency, oxygen uptake, and carbon dioxide output which enabled an evaluation of performance in terms of distance traveled over time with the animals running at a known speed and constant oxygen uptake. The effects of CO or HCl in running versus sedentary animals were investigated using this apparatus. For CO, exercise increased the rapidity of the onset of incapacitation as would be predicted by the increase in metabolic rate. HCl produced a more severe incapacitating effect in exercising animals that was out of proportion with the increase in minute volume induced by exercise.

Lack of effect of low levels of carboxyhemoglobin on cardiovascular function in patients with ischemic heart disease

We studied 30 patients 38-75 yr of age who had ischemic heart disease to assess the effect of acute elevation of carboxyhemoglobin (COHb) concentration. Patients were nonsmokers with ischemia defined by exercise-induced ST depression (ST decreases)--25/30, angina--23/30, or abnormal ejection fraction (EF) response--18/30. After an initial familiarization and exercise session patients were exposed to air (carboxyhemoglobin [COHb] = 1.5 +/- 0.05%) and to carbon monoxide (CO) (100 ppm-COHb-average = 3.8 +/- 0.1%) on successive days in a double blind, randomized fashion. There was no significant difference in time to onset of angina (air = 312 sec, CO = 306 sec), maximal exercise time (air = 711 sec, CO = 702 sec), maximal ST decreases (1.5 mm for both), or time to significant ST decreases (air = 474 sec, CO = 475 sec). Double product at ST decreases and maximal double products were similar for both conditions. Resting ejection fraction was slightly but nonsignificantly higher after CO exposure (air = 53.9%, CO = 55.2%). Maximal ejection fraction was similar for both conditions (air = 57.4%, CO = 57.1%). Change in ejection fraction was slightly lower for CO exposure (air = 3.5%, CO = 2%), p = .049. In conclusion, there is no clinically significant effect of 3.8% COHb (representing a 2.2% increase from resting values) on the cardiovascular system in this study.

Air Pollution: Adverse Effects on Athletic Performance

Airborne pollutants can have significant objective and subjective effects on athletes and can cause substantial decrements in their performance.

Association of the frequency of acute cardiorespiratory complaints with ambient levels of carbon monoxide

Intial cardiorespiratory complaints in an emergency room were studied to determine their relationship to ambient levels of carbon monoxide recorded at a nearby permanent station. All 8,556 encounters with patients (daily mean, 93) were studied during Denver's peak season for carbon monoxide pollution (three-month winter period). The one-hour mean maximum level of carbon monoxide was above 17.8 ppm, averaging 27.2 +/- 4.3 ppm (vs 12.1 +/- 1.8 ppm on "low carbon monoxide days," P less than 0.0001); and when significantly higher frequencies of cardiorespiratory complaints occurred (7.9 +/- 0.7 percent vs 6.4 +/- 0.3 percent [+/- 1 SE]; P less than 0.04), the mean 24-hour level of carbon monoxide averaged 9.3 +/- 1.4 ppm (vs 5.9 +/- 0.8 ppm on "low carbon monoxide rays;" P less than 0.001). The frequency of cardiorespiratory complaints also was correlated with each measurement of the ambient level of carbon monoxide (one-hour mean maximum level, 24-hour mean level, and two-day moving averages of each) in six of eight comparisons. These observations strongly suggest that the frequency of thoracic complaints in an emergency room can be affected by the ambient level of carbon monoxide.