Polycythemia

Definition: Increased RBCs in the blood. Secondary polycythemia: Tissue hypoxia Failure of oxygen delivery to tissues. Large amount of RBCs are formed. RBC count increases to 6-7 million/mm3 Physiological polycythemia Altitudes of 14000 to 17000 feet. Atmospheric oxygen is low. Enables performance of activities.

Polycythemia vera/ erythremia: Pathological condition. 7-8 million/mm3. 60-70% hematocrit. Genetic variation in hemocytoblastic cells. Blast cells do not stop producing cells in presence of many cells. Excess production of WBCs and platelets also. Total blood volume also increases. Vascular system becomes intensely engorged. Viscocity increases to 10 times of water.

Effects on circulatory system: Blood flow is very sluggish. Usually decreased rate of venous return due to viscocity. In polycythemia vera, increased return of blood to heart due to increased volume. Cardiac output is almost normal. Arterial pressure is almost normal in most people but elevated in one third. Hypertension develops. Blood supply to skin is increased. Bluing of skin due to excessive deoxygenation. Ruddy complexion with bluish tint in the skin.

Erythrocyte sedimentation rate: Rate at which the erythrocytes settle down. Uniform suspension of cells in the blood is called suspension stability of RBCs.. Mixing blood with anticoagulants and allowing to stand on vertical tube would cause the RBCs to settle down due to gravity with supernatant layer of clear plasma. ESR is also called sedimentation rate, sed rate or Biernacki reaction.