On the other hand, independent capillary hyperaemia cannot always be regarded as of the active type as it ay sometimes represent a state of want of tone. We shall now consider thesedifferent forms of hyperaemia.
Arterial hyperaemia. This, as has been said, is produced by a dilatation of the arterioles, and ther is thus an increased supply of blood to the particular area.
Thedilatation lead to diminution in the frictional resistance to the blood flow, and thus there is a rise of pressure in the terminal arterioles, which extends to the capillaries.
The latter become widenedand the rate of flow through them is increased, whilst they appear to become more numerous, as some which were formerly empty become dilated.
At the same time, there is a slight increase of lymphformation owing to their dilatation and the increased intra-capillary pressure. The pulse wave extends farther down and may appear in the capillaries or even in the minute veins.
Arterial hyperaemia is aphysiological process and is to be regarded as the normal response when there is a call for an increased supply of blood.
It may be produced by paralysis of the vasoconstrictor nerves or bystimulation of vaso-dilators, directly or reflexly; and in condition of disease we find arterial hyperaemia corresponding to the modes of production.
Active hyperaemia result also from the action of chemicalsubstances, or slight irritants, e.g. mustard, turpentine, and the like; also from heat in mild degree.
And another important point is that temporary anaemia of a part is followed by activehyperaemia when the circulation is restored.
This is of importance in connection with bloodless operations, as the full degree of hyperaemia is not established till some time after the circulation has been...