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Effects of CO Level on Pain, Sensory Function, and Subjective Health

Evaluation of the Effects of Carbon Monoxide (CO) Levels on Pain Threshold, Sensory Function, Anxiety, Depression, and Subjective Health Complaints

Status
Not yet recruiting
Phases
Unknown
Study type
Observational
Source
ClinicalTrials.gov
Registry ID
NCT07571941
Enrollment
70
Registered
2026-05-07
Start date
2026-06-01
Completion date
2026-09-01
Last updated
2026-05-07

For informational purposes only — not medical advice. Sourced from public registries and may not reflect the latest updates. Terms

Conditions

Carbon Monoxide, Pain Perception, Sensory Thresholds, Anxiety, Depression, Tobacco Smoking

Keywords

CO exposure, exhaled carbon monoxide, pain threshold, sensory function, smoking and CO, healthy adults

Brief summary

Carbon monoxide (CO) is a colorless and odorless gas that can enter the human body through environmental exposure and especially tobacco use. CO binds to hemoglobin with a much higher affinity than oxygen, thereby reducing oxygen transport to tissues. This condition may lead to various physiological and psychological effects, particularly on the nervous system. In the literature, CO exposure has mainly been investigated in the context of acute poisoning cases and smoking-related effects. However, studies evaluating the effects of low-level and chronic CO exposure-more commonly encountered in the general population-on pain perception, sensory functions, and psychological status are limited. Tobacco smoke is an important source of CO, and exhaled CO levels have been shown to be significantly higher in smokers and associated with various neurocognitive changes. Evidence suggests that CO exposure may influence anxiety, depression, attention, and cognitive functions. In addition, some studies indicate that CO may affect brain regions involved in pain perception and emotional regulation. However, there is insufficient research examining the relationship between low-level carbon monoxide exposure and pain threshold, sensory functions, anxiety, depression, and subjective health complaints within the same study framework. This study aims to evaluate the relationship between exhaled carbon monoxide (CO) levels and pain threshold, sensory functions, anxiety, depression, and subjective health complaints in healthy adults. By examining the multidimensional effects of low-level CO exposure, the study seeks to fill an important gap in the literature and provide a more comprehensive understanding of this issue.

Detailed description

Carbon monoxide (CO) is a colorless, odorless, and toxic gas that can adversely affect human health through both environmental and behavioral exposure pathways. In the literature, most studies on CO exposure have focused on acute poisoning cases and smoking cessation processes. In contrast, research addressing the physiological and psychological effects of chronic low-level CO exposure, which is more commonly encountered in the general population, remains limited. According to the World Health Organization (WHO), tobacco use causes approximately 8 million deaths annually and represents a major public health concern. CO, one of the main components of tobacco smoke, binds to hemoglobin with a much higher affinity than oxygen, impairing oxygen transport to tissues and leading to systemic hypoxia. This condition has particularly pronounced effects on the central nervous system. Studies on the neurological and psychiatric outcomes of CO exposure have reported that cognitive impairments, anxiety, and depressive symptoms are frequently observed following acute poisoning. Significant associations have also been demonstrated between the severity of poisoning and the level of depressive and anxious symptoms. In addition, voxel-based morphometry studies have reported that CO exposure may lead to reductions in gray matter volume in brain regions associated with pain perception and emotional regulation, such as the frontal lobe, cerebellum, and periaqueductal gray matter. In studies involving smokers, exhaled CO levels have been shown to be significantly higher compared to non-smokers and positively correlated with daily cigarette consumption. Even at low carboxyhemoglobin levels, neurological effects such as visual perception impairments, attention deficits, learning difficulties, and reduced motor performance have been reported. At the molecular level, CO is thought to induce oxidative stress and neuroinflammatory processes, potentially leading to neuronal damage. These mechanisms may influence pain perception, sensory functions, and emotional status. However, studies simultaneously evaluating the relationship between chronic low-level CO exposure and pain threshold, sensory function, anxiety, depression, and subjective health complaints are still insufficient. In this context, the planned study aims to systematically and comprehensively evaluate the relationships between exhaled carbon monoxide (CO) levels and pain threshold, sensory functions, anxiety, depression, and subjective health complaints in healthy adults. The study is expected to fill an important gap in the literature by shedding light on the multidimensional effects of chronic low-level CO exposure and contributing novel insights to the scientific knowledge base.

Interventions

None listed

Sponsors

Izmir Democracy University
Lead SponsorOTHER

Study design

Observational model
COHORT
Time perspective
PROSPECTIVE

Eligibility

Sex/Gender
ALL
Age
18 Years to 65 Years
Healthy volunteers
Yes

Inclusion criteria

* Being between the ages of 18 and 65 Having a regular smoking history for the past 6 months No history of respiratory, cardiovascular, or neurological/psychiatric diseases No recent surgery or trauma that could affect respiratory muscles Not having an acute infection (especially upper or lower respiratory tract infection)

Exclusion criteria

\- Having chronic respiratory diseases such as COPD or asthma Having a history of cardiovascular disease Having a diagnosed neurological or psychiatric disorder Having a history of surgery or trauma affecting respiratory muscles within the last 3 months Being pregnant or having a suspicion of pregnancy

Design outcomes

Primary

MeasureTime frameDescription
Exhaled Carbon Monoxide (CO) LevelJune 2026- July 2026Exhaled carbon monoxide levels will be measured using a Bedfont Smokerlyzer-piCO+ device. Participants will be instructed to take a deep breath, hold their breath for 15 seconds, and then exhale slowly and completely into the device mouthpiece. The measured CO values will be classified as follows: 0-6 ppm: non-smoker 7-10 ppm: light exposure 11-15 ppm: regular smoker 16-25 ppm: heavy smoker 25 ppm: very heavy smoker

Secondary

MeasureTime frameDescription
Pain Threshold MeasurementJune 2026- July 2026Pressure pain thresholds will be assessed using an algometer, which is a validated and reliable tool for measuring muscle and soft tissue sensitivity. The device consists of a 1 cm diameter rubber-tipped metal probe attached to a pressure gauge measuring force in kilograms and pounds. Pressure pain thresholds will be measured bilaterally at the upper, middle, and lower portions of the trapezius muscle
Beck Anxiety Inventory (BAI)June 2026- July 2026Anxiety levels will be assessed using the Beck Anxiety Inventory, a 21-item self-report questionnaire. Each item will be scored between 0 and 3, with total scores ranging from 0 to 63. Higher scores will indicate greater anxiety severity.
Beck Depression Inventory (BDI)June 2026- July 2026Depressive symptoms will be evaluated using the Beck Depression Inventory, a 21-item self-report scale assessing cognitive, emotional, motivational, and somatic symptoms of depression. Each item will be scored from 0 to 3, with total scores ranging from 0 to 63. Higher scores will indicate more severe depressive symptoms.
Semmes-Weinstein Monofilament TestJune 2026- July 2026Sensory function will be assessed using the Semmes-Weinstein monofilament test, a widely used method for evaluating light touch and pressure perception. Monofilaments ranging from 0.086 gm to 448 gm will be applied in ascending order. Testing will be performed from distal to proximal regions, including the anterior and posterior surfaces of all fingers. The smallest detectable monofilament will be recorded. When the filament bends, the applied force will be considered constant, and participants' perception will be recorded accordingly
Subjective Health Complaints InventoryJune 2026-July 2026Physical and psychological health complaints will be assessed using the Subjective Health Complaints Inventory, a self-report questionnaire developed in Norway and widely used internationally. The scale consists of 29 items rated from 0 (none) to 3 (severe), covering symptoms experienced during the last 30 days. Total scores will range from 0 to 87, with higher scores indicating more complaints. The scale includes five subdomains: musculoskeletal, pseudoneurological, gastrointestinal, allergy, and flu-like symptoms.
Fagerström Test for Nicotine DependenceJune 2026- July 2026Nicotine dependence will be assessed using the Fagerström Test for Nicotine Dependence, a 6-item self-report questionnaire. Total scores will range from 0 to 10. Based on the score, participants will be classified as very low, low, moderate, high, or very high dependence.

Contacts

CONTACTBetül Taşpınar, Professor
+90 506 680 44 26

Outcome results

None listed

Source: ClinicalTrials.gov · Data processed: May 8, 2026