Posted by jayaram in Normal blood volume
The total amount of blood present in the circulatory system, blood reservoirs, organs and tissues together constitute blood volume. In a normal young healthy person male weighing about 70 kg, the blood volume is about 5 liters. It is about 7% of total body weight. It ranges between 6 and 8% of body weight. In relation to the body surface area, the blood volume is 2.8 to 3.1 liters per square meter.
Variations in blood volume
Physiological variations
Age
Absolute blood volume is less at birth, and it increases steadily as the age advances. However, at birth, the blood volume is more when compared to body weight and less when compared to the body surface area. At birth and at 24 hours after birth, the blood volume is about 80ml/kg body weight. At the end of 6 months, it increases to about 86 ml/kg. At the end of one year, it is about 80 ml/kg. It remains at this level until 6 years of age. At 10 years, it is about 75ml/kg. At the age of 15 years, the blood volume is about 70-ml/kg body weights, which is almost the blood volume.
In males, the blood volume is more than in women’s because of the increase in erythropoietic activity, body weight and surface area of the body.
Surface area of the body
Blood volume is directly proportional to the surface area of the body.
Body weight
The blood volume is directly proportional to body weight.
Atmospheric temperature
Exposure to cold reduces the blood volume and exposure to warm environment increases the blood volume.
Pregnancy
During early stage of pregnancy, blood volume increases by 20 to 30 % due to the increased fetal mass and sodium retention. However, it reduces in later stages.
Exercises
Exercise increases the blood volume by increasing the release of erythropoietic and production of more red blood cells.
Posture
Erect posture reduces the blood volume by about 15%. This is because the pooling of blood in lower limbs while standing increases the hydrostatic pressure and passage of fluid from blood vessels into the tissue spaces.