Final answer:
Long-term smokers develop secondary polycythemia due to carbon monoxide binding with hemoglobin, reducing oxygen transportation and leading to an overproduction of red blood cells to compensate, which increases blood viscosity and can cause cardiovascular complications.
Step-by-step explanation:
Long-term smokers experience secondary polycythemia because the harmful substances in cigarette smoke, such as carbon monoxide, bind with hemoglobin in red blood cells (RBCs). This reduces the blood's ability to carry oxygen, which triggers the body to produce more RBCs to compensate for the lowered oxygen capacity. As a result, smokers have an overproduction of RBCs, leading to polycythemia. This condition increases the viscosity of the blood, making it more difficult for the heart to pump it, which can lead to various cardiovascular issues as well as COPD, which further reduces the lungs' capacity to exchange gases.