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
- PFO** getting opened due to high mean RA pressure
- Pulmonary arterio venous channels.(Neogeneis or dormant channels activated )
- Altered QP/QS .This effectively means lung shunts some blood without oxygenation(A right to left to shunt within lungs )
- 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.