Page 156 - Biomedical Engineering and Design Handbook Volume 2, Applications

DESIGN OF RESPIRATORY DEVICES 135

Solving this for V i yields

V i = V e F EN 2 (4.24)
F IN 2
are known, so long as inspired concentrations of oxygen and carbon dioxide are
Both F EN 2 and F IN 2
known and no other gases (besides water vapor) are present, as follows:
=− − (4.25)
1
F IN 2 F IO 2 F ICO 2
=− − (4.26)
1
F EN 2 F EO 2 F ECO 2

Thus, combining these equations, V O 2 may be calculated as follows:
⎡1 − F EO − F ECO ⎤
2
2
V O 2 = V e ⎢ ⎥ F IO − VF (4.27)
eEO 2
2
⎣ 1 − F IO − F ICO ⎦
2
2

Measurements of V O 2 and V CO 2 , while possible with balloons (“Douglas bags”) or large spirometers,
are more commonly performed with a flow sensor and continuous O and CO sampling.
2 2
4.6 OTHER DEVICES
It is not possible in this space to describe all respiratory measurements and devices. However, those
that have been described do represent some of those most commonly encountered in routine clinical
and research applications. Commercially available systems, complete with software and printers,
make easy work of performing these common measurements in the usual manner, and are con-
structed with components as described above. Often, however, these systems are ill-suited to mak-
ing measurements that differ, even only slightly, from common practice. Thus, an understanding of
their function may benefit both the researcher and the clinician.

4.7 DESIGN OF RESPIRATORY DEVICES

The designer of respiratory devices is, in many ways, faced with the same challenges as with other
medical devices. There are many different aspects to consider, with device function being but one of
these. In addition to device performance, there are safety, user interface, legal, biocompatibility, mar-
keting, cost, and adaptability issues to face.

4.7.1 Concurrent Engineering
Modern engineering design methods often employ concurrent engineering, wherein designs are the
result of teams of people representing various specialties working together toward a common goal.
Especially for larger projects, teams may be formed from design engineers, marketing specialists,
manufacturing engineers, packaging specialists, legal and regulatory specialists, servicing special-
ists, and others. Their common goal is to design an acceptable product in the shortest possible time
for the smallest cost.
Before the adoption of concurrent engineering practices, each of these functions occurred in
sequence: the marketing specialist surveyed past and potential users to determine what people liked