Vascular graft burst pressure

Vascular graft burst pressure is the internal-to-external pressure difference at which a vascular graft fails by rupture in a specified pressurization test. It is a destructive strength measurement. The vascular graft burst-test conditions, including mounting, surrounding pressure, pressure ramp and failure location, are needed to interpret the reported number. Leakage at a connector and rupture of the graft wall are different observed events.

An elementary thin-walled pressure vessel calculation explains the role of geometry. Cut a cylindrical tube of radius $r$, wall thickness $h$ and length $L$ along its axis. The resultant pressure force on a half-cylinder is $2rL\Delta p$, balanced by two cut walls carrying $2hL{\sigma }_{\theta }$. Thus the hoop stress isIf a stipulated wall failure stress is $1\mathrm{MPa}$, $h=0.20\mathrm{mm}$ and $r=2.0\mathrm{mm}$, this model predictsThis is an illustrative membrane-force balance, not a measured graft specification. It assumes a thin, uniform wall and ignores local defects, changing radius, nonlinear material response and attachment effects. The measured rupture pressure need not equal this estimate.

The primary engineered-bovine-artery study measured rupture strength as well as static and dynamic mechanical response within 24 hours of harvesting vessels. Those were distinct endpoints, rather than interchangeable definitions of graft quality.^[ref]

A graft that survives a particular pressure test has not thereby demonstrated a specified graft patency or repeated-loading lifetime. Conversely, a burst-pressure comparison alone does not measure vascular graft compliance mismatch. A useful report separates the observed failure event, its pressure difference and the test conditions from predictions about subsequent biological performance.

Vascular graft burst-test conditions specify the specimen state, loading and failure observation used to assign a vascular graft burst pressure. Relevant quantities include specimen dimensions, mounting and end constraints, test fluid and temperature, surrounding pressure, pressure-measurement location and loading history. A reported peak pressure is interpretable only together with the event classified as failure.

For example, a pressure trace can fall because the graft wall ruptures, a connection leaks or the specimen slips from its mounting. Those are different observations. A rupture comparison should identify the failure location and distinguish wall failure from apparatus failure, rather than silently combining them into one material-strength number.

The measured load is the internal-to-external pressure difference. If stipulated absolute lumen pressure at failure is $150\mathrm{kPa}$ and bath pressure is $100\mathrm{kPa}$, the difference is $50\mathrm{kPa}$. Reporting 150 as the wall load would confuse an absolute pressure with the distending pressure.

Constant fluid delivery also does not guarantee a constant pressure ramp. In a simple leak-free quasistatic model, define the compliance of a burst-test apparatus as $C_{\mathrm{sys}}=dV/dp$. ThenStipulated delivery $Q=0.10\mathrm{mL}{\mathrm{s}}^{-1}$ and total compliance $0.0020\mathrm{mL}\mathrm{kP}{\mathrm{a}}^{-1}$ give $dp/dt=50\mathrm{kPa}{\mathrm{s}}^{-1}$. Doubling that compliance halves the ramp, even at unchanged pump delivery. The total includes the specimen and any compliant tubing or trapped gas; the calculation is an instrument model, not a test prescription.

The primary engineered-bovine-artery study describes bench-top mechanical measurements after harvest and separately reports static, dynamic and rupture properties.^[ref] Specifying conditions makes such endpoints comparable; it does not turn destructive strength into a direct measurement of graft patency or long-term biological performance.