INTEGRATIVE SYSTEMATIC REVIEW OF CARBON MONOXIDE TOXICITY ON THE RESPIRATORY SYSTEM: MOLECULAR MECHANISMS, EXPOSURE ASSESSMENT, AND HEALTH IMPLICATIONS

Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [55] INTEGRATIVE SYSTEMATIC REVIEW OF CARBON MONOXIDE TOXICITY ON THE RESPIRATORY SYSTEM: MOLECULAR MECHANISMS, EXPOSURE ASSESSMENT, AND HEALTH IMPLICATIONS John Vincent S. Cagatin¹ Gabrella L. Cardinoza¹ Randall Ken M. Concepcion¹ Ma. Leidith M. Dela Torre¹ Gecelene Estorico¹’² Civil and Allied Department; Environmental Science and Chemical Technology Department ¹Technological University of the Philippines—Taguig, Taguig, Metro Manila 1630 Philippines ²De La Salle University – Dasmariñas, DBB-B, 4115 West Ave, Dasmariñas, ABSTRACT Carbon monoxide (CO) toxicity remains a major public health concern because it is widely produced by household combustion, traffic, and industrial sources, and it can impair oxygen delivery and damage lung tissues, placing millions at risk. This systematic review aimed to clarify how CO harms the respiratory system by identifying its key biological mechanisms, summarizing methods used to measure exposure, and determining both shortand long-term respiratory effects. Using PRISMA guidelines, studies published between 2010 and 2025 were screened across Google Scholar, PubMed/MEDLINE, ScienceDirect, Web of Science, and Scopus. Of 50 studies identified, 20 met inclusion criteria, involving human clinical data, laboratory models, and in vitro analysis specifically reporting molecular mechanisms, exposure measures, or respiratory outcomes. Evidence consistently showed that CO binds strongly to hemoglobin and cytochrome c oxidase, reducing oxygen transport and cellular energy production; this triggers oxidative stress, inflammatory responses involving cytokines such as IL-6 and TNF-α, and disruption of alveolar tight-junction proteins such as ZO-1 and claudin-3. Population studies found that even low-level ambient CO exposure (≈0.5–3 ppm) increased asthma, COPD, and pneumonia-related admissions, where each 1 mg/m³ rise was linked to roughly 1.2–22% higher respiratory consultations (p<0.05), with children, elderly populations, and women exposed to biomass fuels showing greatest vulnerability. Acute exposures often resulted in hypoxemia and acute respiratory distress, while long-term exposures contributed to reduced diffusion capacity (lower DLCO), emphysematous changes, and a 1.3–1.5-fold increased risk of COPD. Clinical and animal data further showed that hyperbaric oxygen therapy helped reduce mitochondrial injury and inflammation. Overall, CO exposure is confirmed to cause hypoxic stress, inflammation, and lasting impairment of lung structure and function, indicating the need for better monitoring, safer indoor fuel practices, and strengthened public-health policies. Keywords: Carbon Monoxide (CO), Respiratory Toxicity, Hypoxia, Inflammation, Oxidative Stress INTRODUCTION Carbon monoxide (CO) is a common environmental and workplace pollutant. It is colorless, odorless, and spreads easily, allowing it to enter enclosed or poorly ventilated areas. CO has a strong tendency to bind with hemoglobin, forming carboxyhemoglobin (COHb), which reduces the blood's ability to carry oxygen. This impairs oxygen delivery to tissues (Monroe et al., 2025; Afzal et al., 2025). The respiratory system is the main pathway for CO entry and is especially sensitive to its harmful effects. Evidence shows that both short-term and long-term exposure can cause various respiratory issues, ranging from mild low oxygen levels to severe lung injury and respiratory failure. While we have made significant strides in understanding CO's effects on the body, the exact molecular and cellular mechanisms behind CO-related respiratory toxicity are still not completely understood. Continued research is needed to improve diagnosis, treatment, and prevention strategies. Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [56] Exposure to CO occurs at different levels and for varying lengths of time. High-level exposure usually comes from accidents or work-related events, while low-level exposure often results from ongoing urban air pollution and indoor sources of combustion. Large epidemiological studies have revealed differences in CO-related incidence and deaths, often linked to socioeconomic factors, industrial activities, and fuel use patterns (Wang et al., 2024; Afzal et al., 2025). Recent developments in exposure assessment, particularly through blood COHb testing, lung function tests, and diffusion capacity measurements, have improved our understanding of the link between CO exposure and respiratory problems (Moss et al., 2025; Monroe et al., 2025). However, differences in study methods still make it hard to establish consistent exposure measures and risk estimates for affected populations. At the molecular level, CO mainly causes harm by binding to cytochrome c oxidase in the mitochondrial electron transport chain. This inhibits energy production and leads to low oxygen levels in cells (Wang et al., 2024; Monroe et al., 2025). This disruption produces reactive oxygen species (ROS) and activates inflammatory signals, causing damage to the lungs, blood vessel leaks, and problems with gas exchange. Interestingly, at low levels, CO may trigger protective responses by increasing heme oxygenase-1 (HO-1) and other anti-inflammatory substances (Annual Review of Medicine, 2024). These dual actions, where CO shows both harmful and regulatory effects, highlight the complexity of its interactions in the respiratory system and the need for a better understanding of the mechanisms involved. Clinically, CO poisoning can show up as slight drops in lung diffusion capacity (DLCO) or escalate to acute respiratory distress syndrome (ARDS), often accompanied by low oxygen levels throughout the body and neurological issues. New treatment methods, like hyperbaric oxygen therapy (HBOT), have proven effective in quickly removing CO from hemoglobin, boosting oxygen delivery, and reducing tissue damage (Chen et al., 2025; Annual Review of Medicine, 2024). Still, there are uncertainties regarding the best timing, duration, and longterm results of these treatments. Additionally, the long-term respiratory effects of CO exposure, such as ongoing lung problems and increased risk of infection, are not yet thoroughly covered in the available clinical literature. This systematic review aims to gather and assess recent findings on the molecular, environmental, and clinical aspects of CO-induced respiratory toxicity. By combining evidence from molecular toxicology, epidemiology, and clinical research, the review seeks to provide a complete understanding of CO's biological mechanisms, exposure patterns, and health effects. Ultimately, this work aims to guide future research, improve clinical management methods, and strengthen public health efforts to reduce the respiratory risks associated with carbon monoxide exposure. OBJECTIVES This systematic review has three primary objectives. First, it aims to synthesize current evidence on the molecular mechanisms by which carbon monoxide (CO) induces toxicity and dysfunction in the respiratory system, with emphasis on pathways involving oxidative stress, inflammation, and cellular injury. Second, it seeks to evaluate and compare the methods used to assess CO exposure in both clinical and environmental research settings, and to analyze how these assessment approaches correlate with the severity of respiratory outcomes. Finally, it aims to determine the spectrum of acute and chronic respiratory health effects associated with CO toxicity, including the incidence, progression, and long-term sequelae observed in affected populations. METHODOLOGY The present study employed a systematic review design to synthesize and critically analyze the current body of evidence regarding carbon monoxide (CO) toxicity on the respiratory system. The review was conducted in strict adherence to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines to ensure methodological rigor, transparency, and reproducibility in the identification, selection, and critical appraisal of relevant literature. Data Sources A comprehensive and systematic search was performed across several major academic databases to identify all pertinent published studies. The databases included Google Scholar, PubMed/MEDLINE, ScienceDirect, Web of Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [57] Science, and Scopus. This multi-database approach was adopted to maximize the coverage of literature from biomedical, environmental health, toxicological, and clinical disciplines, thereby minimizing the risk of publication bias. Literature Search To ensure a sensitive and effective search strategy, the electronic databases were queried using a combination of relevant keywords and Boolean operators (AND, OR). The search terms were strategically grouped into three core concepts related to the review's objectives: 1. Exposure: "Carbon Monoxide," "CO," "CO poisoning." 2. Organ System: "Respiratory System," "Lung," "Pulmonary," "Airways," "Alveoli." 3. Outcomes/Mechanisms: "Toxicity," "Molecular Mechanisms," "Oxidative Stress," "Inflammation," "Hypoxia," "Health Implications," "Exposure Assessment," "Biomarkers." The search was initially limited to peer-reviewed journal articles and scientific papers published in English between 2010 and 2025 to align the study with contemporary research. However, seminal papers and highly relevant literature published prior to 2010 were also considered for background context without strict year restrictions. The initial search results were exported to a reference management software (e.g., Zotero, Mendeley) for deduplication and organization. Inclusion Criteria: Studies were included if they: 1. Were original research articles (e.g., in vivo, in vitro, human cohort studies, case-control studies) or peerreviewed scientific reports. 2. Specifically, investigated the effects of carbon monoxide on the respiratory system. 3. Provided data on at least one of the following: molecular mechanisms (e.g., oxidative stress, inflammatory pathways, cellular apoptosis), exposure assessment methods (e.g., carboxyhemoglobin levels, ambient CO monitoring), or specific respiratory health implications (e.g., acute lung injury, exacerbation of asthma/COPD, long-term pulmonary function deficits). 4. Were published in English and available as full-text articles. Exclusion Criteria: Studies were excluded if they: 1. We're reviewing articles, editorials, conference abstracts, or opinion pieces without original data. 2. Focused solely on CO toxicity in non-respiratory systems (e.g., cardiovascular, neurological) without reporting pulmonary outcomes. 3. Lacked quantitative or qualitative data relevant to the review's objectives. 4. We're not available in English or as a full-text publication. 5. Examined combustion-related toxicity from multi-pollutant mixtures (e.g., smoke inhalation) without isolating or specifically analyzing the role of CO. Search Results The systematic search across the five academic databases (Google Scholar, PubMed/MEDLINE, ScienceDirect, Web of Science, and Scopus) initially identified a total of 50 records. To maintain the relevance and focus of this review, the search was confined to peer-reviewed research articles published in English between 2010 and 2024 that specifically addressed carbon monoxide toxicity, respiratory system effects, molecular mechanisms, and health implications. Following the initial identification, 15 duplicate records were removed using reference management software. The remaining 35 unique studies underwent a preliminary title and abstract screening based on the predefined inclusion and exclusion criteria. This screening phase led to the exclusion of 10 studies for reasons such as being outside the primary scope (e.g., focusing exclusively on neurological or cardiovascular effects without respiratory analysis) or being review articles. Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [58] The full text of the remaining 25 articles was then rigorously assessed for eligibility. Of these, 5 studies were excluded for the following reasons: insufficient quantitative data on respiratory outcomes (n=3), unavailability of the full text (n=1), and study design that did not isolate CO effects from other pollutants (n=1). Ultimately, 20 studies satisfied all inclusion criteria and were incorporated into the qualitative synthesis of this systematic review. The process of study identification, screening, eligibility assessment, and inclusion is summarized in the PRISMA flow diagram (Figure 1). Figure 1. Stages of Study Selection and Results Presented in the PRISMA Flow Diagram RESULTS AND DISCUSSION This section provides the systematic review's consolidated evidence of Leptospira pathogenesis based on peerreviewed research conducted between 2015 and 2025. The discussion is organized into four thematic aspects reflective of the primary parameters of Leptospira research: (1) study characteristics and data search, (2) microbiological diversity and molecular identification, (3) molecular and cellular pathogenesis, and (4) host immune response and future research directions. Together, the findings of these results nt an overall picture of how microbiology, molecular genetics, and immunology advances have enhanced our understanding of Leptospira infection and its pathogenic processes. The individual sections integrate information from pertinent literature that explores Leptospira at diverse biological levels—ranging from genetic determinants and virulence markers to host–pathogen relationships and immunity. The aim is to determine decisive findings, examine newly emerging study trends, and recognize ongoing gaps that can influence future research in diagnostics, treatment, and disease prevention. The following subsections summarize the primary results and interpretations per thematic focus, with support from four summary Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [59] tables: Table 1, presenting included studies and their features; Table 2, reporting molecular identification and diagnostic markers; Table 3, reporting virulence and genomic features; and Table 4, reporting host immune responses and new avenues for research. Table 1. Summary of Reviewed Studies on Carbon Monoxide–Induced Respiratory Toxicity Country / Study Type Sample / Populati on CO Exposure / Source & Level Exposure Duration Respiratory Effects Observed Methods / Assessment Key Findings / Outcome Recommen dation Quality / Risk of Bias (brief) Author(s) & Year USA / Toxicolo gical profile General populatio n; occupati onal groups, pediatric and adult cohorts reviewed Household (heaters, generators) , occupation al enclosedspace exposures; variable concentrati ons (document ed low ppm to high acute levels) Acute (hours) and chronic (repeated or longterm exposures) Dyspnea, hypoxia, pulmonary edema, decreased ventilatory capacity, exacerbation of preexisting lung disease Clinical case reports; toxicological synthesis; biomonitorin g (COHb) referenced Comprehe nsive toxicologic al synthesis describing both acute pulmonary edema and longerterm reductions in ventilatory function; highlights vulnerable groups (children, workers in enclosed spaces). Implement targeted protection measures and awareness campaigns for identified high-risk groups (children, elderly, enclosedspace workers). High Wilbur et al., 2012 “Toxicolog ical Profile for Carbon Monoxide” USA / Review Review of clinical & experime ntal data (≈ 50,000 cases / year in U.S.) CO from incomplete combustio n (fires, exhaust, heaters); acute exposures > 10 ppm Acute (minuteshours) Hypoxia, oxidative stress, mitochondri al inhibition, neuroand cardiotoxicit y Review of clinical and pathophysiol ogical studies; biochemical evidence CO binds to hemoglobi n & cytochrom es → cellular hypoxia + inflammati on; hyperbaric O₂ beneficial but incomplete protection Promote the use of hyperbaric oxygen therapy (HBOT) for acute, severe poiso ning and invest in research to improve treatment efficacy. High Rose, J. J. et al., 2017 “Carbon Monoxide Poisoning: Pathogene sis, Manageme nt, and Future Directions of Therapy” Uganda / Cohort 300+ adults residing in rural househol ds Personal CO exposure from household biomass Chronic daily household exposure Cough, phlegm, wheeze, dyspnea; stronger in women and Personal CO monitors, respiratory symptom questionnair e, Increased CO exposure statistically associated with higher Promote cleaner cooking technologies and improved High North, C. M. et al., 2019 “Househol d air pollution Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [60] combustio n; median personal CO ~ 2–10 ppm, higher during cooking HIVpositive demographic survey frequency of respiratory symptoms; effects stronger among women and HIVpositive individuals ventilation in rural households, with a specific focus on protecting women and HIV-positive individuals. and respiratory symptoms in Uganda” China / Cohort 5,408,02 1 outpatien t visits from 8 hospitals in Yichang (2016– 2017) Ambient CO from traffic/indu stry (~1.07 mg/m³ mean daily level) Short-term (lag 0–6 days) Increased respiratory, cardiovascul ar, gastrointesti nal, and neuropsychi atric outpatient visits Generalized additive models (GAM); air pollutant monitoring; ICD-10 classification 1 mg/m³ CO increase → ~22% higher respiratory visits; stronger in warm season Public health advisories and emission control policies should target traffic and industrial sources, especially during warm seasons. High Wang, Y. et al., 2019 “Ambient carbon monoxide and increased risk of daily outpatient visits for respiratory diseases” South Korea / Cohort ~12,000 emergen cy room respirator y admissio ns (urban populatio n) Ambient urban CO (mean ~1.5–2.5 ppm in study regions) Short-term (lag 0–7 days) Increased ER visits for asthma and COPD exacerbation s; short-term respiratory events Air quality monitoring linked with hospital admissions; time-series regression models Short-term rises in ambient CO are associated with immediate increases in respiratory emergenci es, especially in individuals with preexisting lung disease. Air quality alerts should be used to warn individuals with preexisting asthma and COPD to limit outdoor exposure during high CO periods. High Lee et al., 2020 “A study on ambient CO and ER visits” Tanzania / Cohort 500 adult participa nts from rural and urban househol ds Household and biomassfuel CO exposure (≈ 20–35 ppm Chronic (daily exposure over years) Cough, dyspnea, chest tightness, reduced physical capacity SpCO (transcutane ous CO saturation), structured respiratory questionnair Higher CO exposure was associated with increased respiratory symptoms Strengthen ambient air quality standards for CO, as no safe threshold was identifie High Zoller T. et al., 2022 “Carbon monoxiderelated mortality in 337 cities Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [61] during cooking) e, pulse oximetry and functional limitations; women and children most affected d; focus on reducing trafficrelated pollution mix. across 18 countries” MultiCountry / Cohort 337 cities across 18 countries , data on 40,090,4 07 deaths Ambient (outdoor) air pollution. Daily 24hour average concentrati ons. Short-term (associatio ns with daily mortality) Increased daily total mortality Time-series analysis using generalized additive models and metaanalysis. Data from fixed-site air quality monitoring stations. A 1 mg/m³ increase in daily ambient CO was associated with a 0.91% increase in daily total mortality. The association was independe nt of O₃, but attenuated when adjusted for NO₂ and PM. Interventions to reduce household air pollution from biomass fuels are critical, with programs specifically designed for women and children. High Chen et al., 2021 “Househol d biomass fuel exposure” Systemat ic review & metaanalysis 42 populatio n-based studies; pooled cohorts (n > millions across studies) Ambient CO (various urban air concentrati ons; pooled means ~0.5–3 ppm) Short-term (daily to weekly exposure metrics) Elevated respiratory mortality and morbidity; asthma and COPD exacerbation s Metaanalysis of time-series and cohort studies; pooled effect estimates; exposureresponse assessment Short-term ambient CO exposure is positively associated with respiratory mortality and hospital admissions ; effects pronounce d in polluted urban settings. Public health policies should recognize and mitigate the shortterm impact of ambient CO on respiratory mortality and hospital admissions. High Guo et al., 2022 “Systemati c review & metaanalysis on ambient CO” Singapor e / Case Report A single 27-yearold male. Suicidal attempt via solid fuel combustio n in a Estimated 30 minutes of acute exposure. Delayed Presentation (2 weeks): Acute respiratory Clinical examination, chest radiograph, CT thorax, First reported case of delayed pneumoniti Clinicians should be aware of and monitor for delayed Moderate Tan Ching Yee et al., 2022 “A case of delayed Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [62] closed car. COHb level was 36% 3 hours postexposure. distress, hypoxemia, inhalational pneumonitis, pneumomedi astinum, subcutaneou s emphysema. blood tests (COHb, cultures, eosinophil count). s and pneumome diastinum following CO poisoning. Symptoms resolved rapidly with corticoster oid treatment. respiratory complication s, such as pneumonitis, for several weeks postCO exposure. inhalation al pneumoniti s and pneumome diastinum following carbon monoxide poisoning China / Cohort 72,430 hospitali zations for respirator y diseases Ambient CO; mean: 1.2 mg/m³ (range: 0.6–2.9 mg/m³) Daily exposure over 5 years Hospitalizati ons for total respiratory diseases, asthma, COPD, LRTI, influenzapneumonia Generalized additive model (GAM) with quasiPoisson regression; ICD-10 codes for diagnoses Each 1 mg/m³ increase in CO (lag02) associated with increased hospitaliza tions: total respiratory diseases: 13.56%; asthma: 17.74%; COPD: 12.45%; LRTI: 41.25%; influenzapneumonia : 13.50%. Healthcare systems should antici pate increase d respiratory admissions linked to CO levels, particularly for children, the elderly, and during warm seasons. ModerateHigh Song et al., 2023 “Associati ons between ambient carbon monoxide and hospitaliza tions for respiratory diseases” Clinical Case Reports / Case Report Individua l patients with househol d CO poisonin g (closedspace exposure ; ppm not quantifie d) Acute exposure with delayed pulmonary complicati ons (daysweeks) Delayed respiratory failure; prolonged hypoxia, possible fibrosis in follow-up imaging Clinical follow-up, imaging (CT), arterial blood gases, clinical history Illustrates that severe or even moderate poisoning may lead to delayed pulmonary deterioration ; recommends extended clinical follow-up postexposure. Moderate — singlecase evidence; valuable for clinical signal but limited generaliza bility. Implement extended clinical follow-up protocols for CO poisoning patients to monitor for and manage delayed pulmonary deterioration . High Case Report, 2023 Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [63] India / Narrative Review Narrative review of multiple COPD clinical studies CO used as tracer gas in DLCO tests for gas exchange assessment Varied (chronic monitoring ) Reduced DLCO indicating alveolarcapillary membrane damage and poor gas exchange Review of pulmonary function tests (DLCO, FEV₁, FVC) and comparative data DLCO is a sensitive indicator of respiratory toxicity and disease severity linked to CO diffusion deficits Incorporate DLCO testing as a standard tool for monitori ng respirator y disease progression and gas exchange impairment in at-risk patients. High Deyalla L., et al., 2024 “A review on DLCO testing” Republic of Korea / Cohort 13,336 COpoisoned patient’s vs 53,344 controls from national database Document ed acute CO poisoning from fires, vehicles, and indoor sources Up to 10 years follow-up Higher incidence of COPD, asthma, and pneumonia postexposure National health claims data, CO registry, ICD-10 diagnoses Previous CO poisoning raised risk of chronic lung disease by ~1.3–1.5× vs controls → longterm respiratory impact Establish long-term respiratory health monitoring for survivors of acute CO poisoning due to their significantly elevated risk of chronic lung disease. High Lee S. J., Lee S., Kim Y. H., & Cha Y. S., 2024 “Longterm risk of respiratory diseases in patients with carbon monoxide poisoning” USA / Review Preclinic al and clinical studies reviewed Endogenou s CO; smokers: 3–8% COHb; clinical trials: up to 6.4% COHb (inhaled CO) Variable (acute to chronic) Therapeutic potential (antiinflammator y, organ protection); toxicity at high doses Literature review; clinical trials; molecular and biochemical assays CO has a wide safety margin comparabl e to common drugs; noninhalation routes (e.g., COreleasing molecules) are safer; COHb alone is not a reliable toxicity marker. For therapeutic applications, prioritize the development of noninhalation CO delivery systems (e.g., COreleasing molecules) for safer dosing. High Bansal et al., 2024 “Therapeut ic application s and toxicity of carbon monoxide” Internal Medicine Review / Review Synthesis of experime ntal, clinical, Controlled experiment al exposures and Acute lung injury, oxidative stress, chronic Review of molecular mechanisms (cytochrome c oxidase CO impairs mitochondri al respiration and induces pulmonary High — authoritati ve peerreviewed review Treatment strategies for CO poisoning should target High Annual Review of Medicine, 2024 Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [70] This systematic review gives an extensive overview of the present research regarding the molecular, environmental, and clinical aspects of carbon monoxide (CO) toxicity in the lungs. The studies that were analyzed all agreed that acute and chronic CO exposures would impair the respiratory system, and the argued mechanisms were hypoxia, oxidative stress, apoptosis of the cells, and inflammation. CO’s binding to hemoglobin and cytochrome c oxidase causes an interruption of oxygen transport and mitochondrial respiration, resulting in cellular energy failure and tissue death. Active metabolic imbalances present as medical conditions, such as acute hypoxemia, pulmonary edema, and eventually, chronic bronchitis or COPD progressing as long-term effects. Environmental and occupational exposure assessments discovered that people living in very polluted urban areas with heavy traffic, near industries, and domestic use of wood for fuel are most likely to suffer from respiratory problems due to CO. At-risk populations, especially infants, old people, and patients with existing lung or immune disorders, must bear the largest share of the health costs that come with the prolonged or repeated exposure. Moreover, the research indicates that low-level ambient CO concentrations, which were previously regarded as safe, can still be a factor in influencing lung diffusion capacity (DLCO) to the extent of being noticeable and leading to more hospital admissions for asthma and COPD.Moreover, the combination of molecular toxicology and epidemiology points out the double role of CO: it is effective in controlled doses in experimental models but at the same time it is a strong environmental hazard if inhaled accidentally. The review paper calls for standardized exposure monitoring, better biomarkers for early detection, and long-term cohort studies to clarify chronic effects. The other area where public health interventions—tighter air quality regulations, occupational safety measures, and educational campaigns—all play a role is the exposure risk reduction and respiratory morbidity and mortality linked to CO poisoning that must be mitigated. In short, carbon monoxide is still a smoking gun and a highly underestimated respiratory toxin. Its effects are felt from molecular level disruptions right up to the health challenges of whole populations. It will be the interdisciplinary collaboration between toxicologists, clinicians, and environmental scientists that will eventually lead to accurate diagnostics, new treatment strategies, and preventive frameworks that will together reduce the global burden of CO-induced respiratory disease. REFERENCES [1] Al-Batool, W., Al-Batool, H., Hassan, A., Zarecka, I., Hassan, S., Bienia, S., Kossakowska, A., Leicht, J., & Konieczna, K. (2025). Carbon monoxide poisoning: Pathophysiology, diagnosis, symptoms and advances in acute and chronic management. Medical Science, 29, e9ms3482. https://doi.org/10.54905/disssi.v29i155.e9ms3482 [2] Author(s). (2023). Unusual delayed pulmonary presentation of carbon monoxide poisoning: A case report. Clinical Case Reports. https://clinicalcasereportsjournal.com/article/1000152/unusual-delayedpulmonary-presentation-of-carbon-monoxide-poisoning-a-case-report [3] Author(s). (2024). Carbon monoxide poisoning: Molecular and clinical perspectives. Annual Review of Medicine. https://www.annualreviews.org/doi/10.1146/annurev-med-052422-020045 [4] Barn, P., Giles, L., Héroux, M., & Kosatsky, T. (2018). A review of the experimental evidence on the toxicokinetics of carbon monoxide: The potential role of pathophysiology among susceptible groups. Environmental Health, 17(1). [5] Bartington, S., Bakolis, I., Devakumar, D., Kurmi, O., Gulliver, J., Chaube, G., Manandhar, D., Saville, N., Costello, A., Osrin, D., Hansell, A., & Ayres, J. (2016). Patterns of domestic exposure to carbon monoxide and particulate matter in households using biomass fuel in Janakpur, Nepal. Environmental Pollution, 220, 38–45. https://doi.org/10.1016/j.envpol.2016.08.074 [6] Devalla, L., Ghewade, B., Jadhav, U., & Annareddy, S. (2024). Resolving the complexity: A comprehensive review on carbon monoxide diffusion capacity in chronic obstructive pulmonary disease patients. Cureus. https://doi.org/10.7759/cureus.53492 [7] Ergözen, S., Demir, A., & Acar, E. (2019). A carbon monoxide poisoning case due to lung diffusion test. American Journal of Emergency Medicine. https://doi.org/10.1016/j.ajem.2019.12.056 [8] Goldin, J., & Cascella, M. (2024, October 6). Diffusing capacity of the lungs for carbon monoxide. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK556149 [9] Guo, X., et al. (2022). Short-term exposure to carbon monoxide and respiratory mortality: A systematic review and meta-analysis. Environmental Research. https://pubmed.ncbi.nlm.nih.gov/35257337 [10] Jadoon, S., Nawazish, S., Mahmood, Q., Rafique, A., Sohail, S., & Zaidi, A. (2022). Exploring health impacts of occupational exposure to carbon monoxide in the labour community of Hattar Industrial Estate. Atmosphere, 13(3), 406. https://doi.org/10.3390/atmos13030406 Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [71] [11] Lee, H., et al. (2020). Short-term CO exposure and respiratory events. Environmental Research. https://www.sciencedirect.com/science/article/pii/S0160412020318560 [12] Lee, S. J., Lee, S., Kim, Y. H., & Cha, Y. S. (2024). Risk of lung diseases in patients with previous carbon monoxide poisoning: A nationwide population-based cohort study in the Republic of Korea. Clinical Toxicology, 62(7), 425–431. https://doi.org/10.1080/15563650.2024.2371020 [13] Liu, H., Tian, Y., Xiang, X., Li, M., Wu, Y., Cao, Y., Juan, J., Song, J., Wu, T., & Hu, Y. (2018). Association of short-term exposure to ambient carbon monoxide with hospital admissions in China: A multicity case-crossover study in 26 largest cities. Scientific Reports, 8, 13336. https://doi.org/10.1038/s41598-018-31434-1 [14] Nair, A., Nandini, M., Adappa, S., & Mahabala, C. (2016). Carbon monoxide exposure among police officers working in a traffic-dense region of Southern India. Toxicology and Industrial Health, 33(1), 46–52. https://doi.org/10.1177/0748233716654071 [15] North, C. M., MacNaughton, P., Lai, P. S., Vallarino, J., Okello, S., Kakuhikire, B., Tsai, A. C., Castro, M. C., Siedner, M. J., Allen, J. G., & Christiani, D. C. (2019). Personal carbon monoxide exposure, respiratory symptoms, and the potentially modifying roles of sex and HIV infection in rural Uganda: A cohort study. Environmental Health, 18(1). https://doi.org/10.1186/s12940-019-0517-z [16] Roderique, J. D. (2015). Modern literature review of carbon monoxide poisoning. Toxicology Letters. https://www.sciencedirect.com/science/article/abs/pii/S0300483X1500092X [17] Rose, J. J., Wang, L., Xu, Q., McTiernan, C. F., Shiva, S., Tejero, J., & Gladwin, M. T. (2017). Carbon monoxide poisoning: Pathogenesis, management, and future directions of therapy. American Journal of Respiratory and Critical Care Medicine, 195(5), 596–606. https://doi.org/10.1164/rccm.201606-1275CI [18] Song, Y., et al. (2023). Association of ambient carbon monoxide exposure with respiratory hospitalization. Frontiers in Public Health, 11, Article 1106336. https://www.frontiersin.org/articles/10.3389/fpubh.2023.1106336/full [19] Wang, Y., Yao, C., Xu, C., Zeng, X., Zhou, M., Lin, Y., Zhang, P., & Yin, P. (2019). Carbon monoxide and risk of outpatient visits due to cause-specific diseases: A time-series study in Yichang, China. Environmental Health, 18(36). https://doi.org/10.1186/s12940-019-0477-3 [20] Wilbur, S. K., et al. (2012). Toxicological profile for carbon monoxide. U.S. Department of Health and Human Services. https://www.ncbi.nlm.nih.gov/books/NBK153687/ [21] Zoller, T., Mfinanga, E. H., Zumba, T. B., Asilia, P. J., Mutabazi, E. M., Wimmersberger, D., Mhimbira, F., Haraka, F., & Reither, K. (2022). Symptoms and functional limitations related to respiratory health and carbon monoxide poisoning in Tanzania: A cross-sectional study. Environmental Health, 21(1). https://doi.org/10.1186/s12940-022-00847-x