Carbon monoxide (CO) is a colorless, odorless gas formed during the incomplete burning of carbon-containing materials. Cigarette smoke contains significant quantities of this gas, making it a particular concern for smokers. The presence of carbon monoxide in cigarette smoke directly threatens the body’s ability to transport oxygen effectively. This gas interferes with a fundamental biological process, leading to widespread effects.
From Smoke to Bloodstream
When a smoker inhales cigarette smoke, carbon monoxide rapidly enters the lungs. The gas then diffuses across the thin membranes of the alveoli, the tiny air sacs, directly into the surrounding capillaries. This process, known as gas exchange, allows CO to quickly enter the bloodstream. Once in the blood, carbon monoxide readily binds to hemoglobin, the protein in red blood cells responsible for carrying oxygen.
How Carbon Monoxide Hijacks Oxygen Transport
Carbon monoxide primarily affects a smoker’s blood by interacting with hemoglobin. Hemoglobin has a much stronger affinity for carbon monoxide than for oxygen, binding approximately 200 to 250 times more readily. When CO binds to hemoglobin, it forms carboxyhemoglobin (COHb). This formation occupies the sites on hemoglobin molecules that would normally carry oxygen, reducing the blood’s overall oxygen-carrying capacity.
The presence of carboxyhemoglobin also alters the shape of remaining hemoglobin molecules still bound to oxygen. This change makes it more difficult for oxygen to be released to the body’s tissues, even in low-oxygen areas. As a result, oxygen delivery to cells and organs is significantly impaired, leading to oxygen deprivation. Non-smokers typically maintain carboxyhemoglobin levels below 3%, while smokers can have levels ranging from 5% to 15%, with heavy smokers sometimes reaching 20% or more.
Systemic Effects of Reduced Oxygen
Impaired oxygen transport caused by carbon monoxide in a smoker’s blood leads to systemic consequences. Various organs and tissues receive insufficient oxygen. The heart, for instance, must work harder to compensate for reduced oxygen delivery, increasing its workload. This compensatory effort can elevate the risk of cardiovascular issues.
The brain is vulnerable to reduced oxygen levels. Cognitive impairment, headaches, and dizziness are common symptoms arising from this oxygen deprivation. Prolonged oxygen shortage to the brain causes confusion and memory problems. Muscles experience reduced endurance and increased fatigue due to insufficient oxygen supply, impacting physical performance.
Clearing Carbon Monoxide from the Blood
When a smoker ceases exposure to carbon monoxide, the body gradually clears carboxyhemoglobin from the bloodstream. Carbon monoxide slowly detaches from hemoglobin and is then exhaled through the lungs. The rate at which carboxyhemoglobin is eliminated is measured by its half-life: the time it takes for half of the compound to be removed.
In room air, the half-life of carboxyhemoglobin is approximately 300 to 320 minutes. Administering 100% oxygen significantly accelerates this process, reducing the half-life to about 74 to 90 minutes. For rapid removal, such as in severe poisoning, hyperbaric oxygen therapy further decreases the half-life to around 30 minutes. For smokers who quit, carbon monoxide levels in their blood return to normal within hours to days.