Equipment

Capnographic measurement of bronchospasm requires linking the patient to a capnograph via a sampling catheter fixed to the upper lip and introduced into the nostril for a few millimeters. The analog output of the apparatus is connected to an analog-digital conversion card slotted into a PC computer. Specific software converts PeCO2 data into capnographic waveform, measures shape indices and draws their trend curves.

Patient

The patient, 4 to 99 years old, should be relaxed and resting, either awake or asleep .

Catheter

The catheter (1mm x 1.5m) is fixed to the upper lip using adhesive tape. It enters the nostril for a few millimeters.

 A significant recording requires good nasal permeability which can be improved using a nasal decongestant.
 

Capnograph

An infra-red aspirating CO2 monitor continuously draws a sample from expelled gas, measures PeCO2, draws its time-related waveform and sends the data to the analog output of the apparatus.

Analog-digital conversion card : analog output of the CO2 monitor is connected to a specific conversion card (Digimétrie R) slotted into a PC computer. This card converts the analog signal into numeric data. 

PC computer : The conversion card is slotted into an 8 bit ISA connector of a PC computer (DOS or Windows).

Software : Specific DOS-Windows software (Capno ^R) processes numeric data and measures capnographic indices.

It combines 4 simultaneous functions performed in real-time:

• 20 hz reading of PeCO2 values and tracing the capnogram in a 60 second auto refresh window,
• measuring shape indices S1, S2 and SD of each expiratory capnogram such as some usual spirometric parameters (I/E, PetCO2, respiratory rate etc...),
• calculating and displaying mean value of each indice, every 60 seconds,
• drawing and displaying their trend curves (1 point/minute).

Length of recording is unlimited (12-24 hours). Display allows use of a controllable zoom (1h-12h/screen).

In addition, software has semi-automatic validity functions which clear invalid trends related to deteriorated cycles.

Screen capture: Upper window : capnographic waveform (one minute scrolling / screen) . Middle band : mean values (and SD) of the capnographic measurements for the minute elapsing. Lower window : Capnographic indice trends using a controllable zoom. At the top : rolling menu for accessing software functions. At the bottom : quick access to main functions.

 

Finaly, computerized capnography provides bronchospasm assessment which is:

• easy to use,
• non-invasive,
• subject cooperation independent.

Automation of the method allows monitoring of asthma in various conditions.