Effect of Altitude on the Aeroform Tissue Expander

Background

The AeroForm Tissue Expander is filled with CO₂ and released in 10cc doses from an internal reservoir via remote control.  When external pressure is reduced (climbing at altitudes > 1000m or flying in a pressurized cabin), released CO₂ will expand. The degree of expansion can be estimated per the Ideal Gas Law: PV=nRT.  Because the inner chamber of the expander is non-distensible, at full volume, expansion will result in an increase in the relative pressure inside the expander. As CO₂ is a small molecule, there is an expected amount of permeation leading to a minor loss of volume. This amount has been measured between 0.8 and 1.4cc/day.

During clinical trials, subjects were restricted from flying until a predictable model of expected expansion and empirical data were available, which is described in this paper.

Methods

A computation model was developed estimating the expected increase in volume as a function of altitude.  Typically, the inner chamber has sufficient room to allow an increase in volume without an increase in the relative pressure.  This model has been verified by comparison of the predicted volume with the observed values, presented in Table 1.

Prior to flight, subjects were assessed to evaluate the expander fill volume, tissue perfusion, laxity, wound healing, and comfort.

Results

Eight subjects (6 in Australia, 2 in U.S.) have flown with expander in situ. All subjects were required to stop dosing up to two weeks prior and completed flight travel without discomfort.  As expected, subjects reported a sensation of pressure upon ascent which subsided on descent.  Pre-flight volumes ranged from 30% - 100%.  

Conclusions

If air travel is planned, dosing should be discontinued to allow permeation to occur and avoid over-pressurization of the expander. The physician should be consulted and assess the expander fill volume and tissue perfusion.  Based on the predictive model and empirical data, it is possible to travel safely to altitudes > 1000m with the AeroForm expander in situ.

 

 

 

Percent Full	0	10	20	30	40	50	60	70	80
Volume Increase (cc)
Small	0	12	23	35	47	58	70	82	93
Medium	0	19	37	56	74	93	112	130	149
Large	0	25	50	75	100	126	151	176	201

Table 1 - Volume Increase (cc) vs. Percent Full