The following steps are usually followed in running a CPX test:
- Calibrate Flow, Volume and Gas Analyzers
- Complete the “Patient Biographical” screen.
- Prepare the patient in the following way: a) If used, fit the Polar Chest Band for heart rate. (b) If used, fit the pulse oximeter. (c) If used fit the 12 lead EKG and launch the EKG program.
- Adjust the ergometer to suit the patient.
- Fit the pateint with a face mask and pneumotach.
- Perform a Flow Volume Loop at rest.
- Go to the [CPX] tab and start the exercise test.
- Select the exercise protocol you wish to follow.
- Observe the pre-test screen and confirm that the signals for flow, SpO2, HR, CO2 and O2 appear normal.
- Begin the exercise test.
CPX Verification Screen
The CPX verification screen allows the operator to check that various patient interfaces have been selected correctly, that the correct test protocol is in place and that sensors are providing data in acceptable ranges. The operator may choose to collect breath from a mouthpiece or from various face masks. Different styles of pneumotach may be selected for measuring breath flow and volume, and heart rate can be derived from an oximeter, EKG or heart rate monitor.
With the face mask in place and the patient breathing normally at rest, the display shows breath by breath levels of CO2 and O2 in a graphical waveform and numerically in tables. Heart rate, breathing rate, SpO2 and breath volume are alos shown. if the measurements are within normal ranges they are shown against a green background. If measurements appear erroneous they are shown against ared background, prompting the operator to check the system.
Environmental parameters, such as temperature, pressure and ambient relative humidity may be viewed by clicking the Environmental button.
CPX Run Screen
The CPX run screen can be configured to display whatever parameters the operator wishes to view during the test. Up to four graphs may be displayed at the same time, as chosen from a menu, or by clicking on axes and selecting from options. The display may be changed at will during the test.
Data are constantly evaluated to ensure that meaningful values are being measured. If a parameter appears to be outside of expected clinical range an “Alert” is shown in red.
Note: These alerts are based upon script settings and the ranges can be changed by the user if desired.
A CPX test may be paused at any time by clicking the PAUSE button. button. Time continues to be recorded, but data acquisition is halted temporarily the test is resumed.
The TAKE MANUAL CONTROL button allows the operator to over-ride the test protocols and to change work load etc. without pausing the test.
Clicking the STOP TEST button concludes the test and takes the operator to the post test screens.
At any time during an exercise study, the user can mark an “event”. The EVENT button displays a pull-down list of choices tpre-configured by the user. Events could include PFT tests, manual blood pressure readings or even just making a note. All “events” are logged at the time of selection and data can be entered at the conclusion of the test.
Maximum Voluntary Ventilation (MVV)
MVV is the volume of gas that can be breathed during a 15 second period when a person breathes as deeply and quickly as possible. In older journals and publications, MVV is also called maximum breathing capacity. The result is extrapolated from 15 seconds to show what could be achieved over a one minute period. As a general guide, the value should correlate closely to the FEV1 x 35.
This test is usually performed whenever spirometry is done. It identifies weakness in the muscles used for breathing. In exercise testing, the MVV is used in the calculation of Breathing Reserve.
The run-time screen displays target lines at 6, 12 and 15 seconds. The patient MUST reach the 6-second mark and it is preferable to encourage them to the full 15 seconds. If the patient reaches 15 seconds, the test will automatically end. If the [Spacebar] is pressed at any time after six seconds test duration, the result are calculated and stored, but will not, of course, pass the ATS recommended criteria.
The values shown for FEV1 x 35 and FEV1 x 40 are very good guides of what to expect from a good patient effort. They will only be displayed if you have completed a flow volume loop prior to doing the MVV test. A genuine effort should get very close to the FEV1 x 35 or exceed it.
M V V Adjust Screen
The MVV result is automatically processed to obtain the greatest value across the panting effort. At the same time, each test effort is evaluated and given a “confidence” rating. By clicking Adjust MVV it is possible to review which segment of the effort was evaluated to calculate the result and view a detailed evaluation. By clicking on either the starting or ending markers these can be dragged to include or exclude different segments of the test.
Once released, the MVV is recalculated. Since the evaluation utilizes the Tidal Volume (TV), Breathing Frequency (F) and Tidal Volume/Vital Capacity ratio (TV/VC), each of these values are recalculated any time an adjustment is made.
To return to the original computer assessment of the MVV, the Revert MVV button is clicked.
As for flow volume loops, the operator may manually override the automatic selection of reported MVV results. Both the data and the graphic can be selected using the right-click options on the mini-results screen.
Meaurements FVC and IC During Exercise
For users wanting to evaluate ventilatory responses to exercise, the ability to perform either a maximal Forced Vital Capacity (FVC) or just an Inspiratory Capacity (IC) is provided. The baseline flow volume loop taken from the separate FVC test is shown including the position and size of the tidal volume.
During any stage of the exercise test, subsequent FVC or IC efforts along with the tidal volumes can be recorded by clicking the Perform FVC button.
TLC is recognized as the most reproducible measures of lung volume; it is a natural feeling for subjects to “breathe right-in” and fill their lungs. For this reason performing an IC during exercise provides a reliable ‘anchor point’ to record the true position of tidal volume. At the conclusion of the test the user can select which efforts and views to record and send to the final report.