Carbon monoxide poisoning occurs from a buildup of CO gas in the bloodstream, measured by the amount of hemoglobin that is saturated with carbon monoxide molecules. The binding of hemoglobin and carbon monoxide creates what is known as carboxyhemoglobin. High levels of carboxyhemoglobin lead to tissue damage in the brain and heart from a combination of blocking oxygen and of causing inflammation.
Building up carboxyhemoglobin can happen slowly (chronic exposure) or quickly (acute exposure). Chronic exposure is often caused by a faulty or poorly ventilated appliance in the home that leads to the presence of low concentrations of carbon monoxide in the air. Think of this as a slowly leaking roof that eventually fills up a bucket placed below it.
Acute exposure typically comes from an accidental change in environment that leads to a high concentration of carbon monoxide in the air. In that case, the levels of carboxyhemoglobin rise quickly and symptoms are more pronounced. Acute exposure is more easily recognized and more often reported.
Symptoms of chronic exposure often go unrecognized for long periods and carbon monoxide poisoning might not be reported.