= Balloon catheter
A \b[balloon catheter] is a <catheter> carrying an inflatable balloon. A channel in the device permits controlled inflation or deflation, while other channels can serve functions such as drainage or access. The same broad mechanical design can have different biological purposes: a balloon can dilate a narrowed vessel or help retain a drainage catheter in position.
In <coronary angioplasty>, the primary historical apparatus used controlled expansion of a distensible balloon to enlarge a narrowed <coronary artery>.<Nonoperative dilatation of coronary-artery stenosis: percutaneous transluminal coronary angioplasty by A. R. Grüntzig and others>[Abstract, catheter system and balloon inflation]{ref} A <urinary catheter retention balloon> instead serves a positioning function. The EAUN equipment description distinguishes a channel for urine from a channel for the balloon that secures the catheter in the bladder.<Indwelling catheterisation in adults by EAUN (2024)>[Section 5.1.1, two-way balloon catheter; Figure 5]{ref} Balloon inflation is therefore not synonymous with vessel dilation.
Pressure, delivered liquid volume, balloon diameter and wall loading are related but distinct variables. A <balloon pressure-diameter curve> describes the response of a specified device under stated conditions. It depends on geometry, material behavior and external constraint; equal inflation pressure does not universally imply equal diameter or equal contact force on tissue.
An original thin-wall calculation illustrates one part of the mechanics. Model the central region as a uniform cylindrical membrane of radius $r$, wall thickness $h$ and length $L$, with internal-minus-external pressure $\Delta p$. Balancing forces on a longitudinal half-cylinder gives
$$
2rL\Delta p=2hL\sigma_\theta,\qquad
\sigma_\theta=\frac{\Delta p\,r}{h}.
$$
Here $\sigma_\theta$ is <hoop stress>. With chosen values $\Delta p=0.20\,\mathrm{MPa}$, $r=2.0\,\mathrm{mm}$ and $h=0.10\,\mathrm{mm}$, the model gives $4.0\,\mathrm{MPa}$. Internal pressure and tensile wall <stress> are not the same quantity. These values illustrate force balance, not a product rating.
The calculation neglects end shape, folding, thickness changes and nonlinear material behavior. It also does not determine how pressure is distributed against living tissue. A balloon's function must consequently be interpreted through its particular structure, its mechanical response and the anatomical task, rather than through the word balloon alone.
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