# Node & Cavity

The `Node`

serves as a pivotal component in circulatory models, playing a central role in the system. The pressure within a node is determined by the interplay of flow (\(q\)) and wave impedance (\(Z\)).

When the node is characterized as a `Cavity`

, an additional factor comes into play – the transmural pressure (\(p_{trans}\)).
In such cases, the total pressure (\(p\)) is a composite of the transmural pressure and the flow-to-impedance ratio.
The transmural pressure \(p_{trans}\) is a result of the stress in the wall around the cavity volume \(V\).
This can be handled by the `Cavity`

itself, e.g. in the Tube0D or Chamber, but can also be set by an external component, e.g. the TriSeg.

The mathematical representation is expressed by the equation:

The `Cavity`

is derived from the `Node`

and has no other derived modules.
The following objects are derived from the `Cavity`

: