Dr.S.Venkatesan MD

How  central cyanosis occurs  in primary pulmonary hypertension ?

While , peripheal cyanosis*  is easily explained in PPH ,the mechanism of central cyanosis is not straight forward.

The following explanations are offered

1. PFO**  getting  opened due to high mean RA pressure
2. Pulmonary arterio venous channels.(Neogeneis or dormant channels activated )
3. Altered QP/QS .This effectively means lung shunts some blood without oxygenation(A right to left to shunt within lungs )
4. Associated lung pathology -like pneumonia resulting in pathological right to left shunt across the alveolar circulation.

* Peripheral cyanosis can occur in PPH with cardiac failure

**PFOs are often anatomically patent in 20 % of normal population , which gets functionally patent  when exposed to high RA pressure

Cyanosis -A brief  description .

Cyanosis occurs when the arterial saturation goes below 85 % . Cyanosis  manifests in two ways . Central and peripheral.The term peripheral  does not  denote  peripheral parts of the body  rather it is  peripheral  circulation.(Capillary) The mechanism of peripheral cyanosis is somewhat  different from central cyanosis . It is generally due to sluggish circulation ,  more  oxygen extraction and resultant bluish discoloration .

Peripheral cyanosis is seen in finger tips, lips etc . Peripheral cyanosis can not occur in warm areas of the body for the  simple reason warmth  causes vasodilatation , better tissue perfusion  which prevents stagnation of  deoxygenated blood.

Central oxygenation defect alone can not result in  classical central cyanosis .

For central cyanosis  to occur ,  there need to be mixing of  deoxygented and oxygenated blood somewhere in the  circulation.(Right to left shunt in the heart or lungs )

Since it is a defect in central  oxygenation it  manifests  in both warm mucous membranes as well as cold extremities.