When using the URP module, the attribute settings are acceptance and rejection criteria. It’s important to note that the analysis relies on one attribute (Minimum Flow) to control the identification of respiration cycles. The remaining attributes are either used to eliminate invalid cycles (Baseline Shift, Max Variation, and Volume Match) or in the calculation and reporting of derived parameters. Start by disabling these rejection attributes, by defining their values to negate any rejection and only allow the acceptance of breaths. Then, go through and fine tune the attributes to reject certain breaths, if desired.
The attributes are grouped under various “tabs.” “Std Attrib” contains commonly used Attributes, “Adv Attrib1” contains filter parameters, "Attrib2" is used to define channels or static values for adjusted volume calculations (not displayed), “Marks” controls the display of the available fiducial marks.
The Standard Attributes tab contains the attributes that are most commonly adjusted to ensure that the analysis triggers correctly.
This edit field allows the user to set the minimum flow that must be achieved before the algorithm will detect and validate a respiration cycle. The Minimum Flow is useful in preventing the algorithm from triggering on small variations in the signal that do not correspond to a breath.
In the figure above, the boxes superimposed on the waveform represent the attribute selected by the radio button, in this case, Minimum Flow. The attribute is used to identify both positive and negative peaks. In the case of the double peaked waveform towards the right in the figure, the Minimum Flow is greater than the variation in the signal thus the analysis will move past both the peaks before attempting to interpret the signal. If the Minimum Flow attribute were set to a smaller value, less than the height of the double peak, the analysis would have attempted to interpret the variation as two individual peaks, the peaks may or may not be marked depending on the rejection criteria.
Baseline Shift is used as a rejection criterion.
This attribute gives the user control over how sensitive the algorithm is to changes in the baseline from one cycle to the next. During the analysis, a new baseline is established for each cycle. The baseline level is at the end of inspiration point for each cycle. The baseline levels for successive cycles are compared. If the baseline shift attribute is larger than the difference between successive cycles, the cycles will be accepted. If not, the analysis will reset itself and no marks will be seen for a few cycles till the analysis determines that valid data is available.
NOTE: If rejection of cycles is not desired, regardless of shifts in baseline, set the baseline shift attribute to a value several times larger than the respiration signal, it will be effectively disabled.
Max Variation is used as a rejection criterion.
This attribute is used to eliminate breaths that exhibit fluctuations during inspiration or expiration. Such fluctuations may be due to extraneous disturbances and the user may wish to exclude the affected cycles from the analysis. The amplitude of these fluctuations is used to determine whether the associated cycle is eliminated or not. In each cycle, the inspiration and expiration are analyzed separately. The Max Variation attribute is specified as a percentage of the peak inspiration and peak expiration, i.e. the maximum permitted variation in an inspiration or expiration is the specified percentage of the distance between the inspiration peak and the baseline or the expiration peak and the baseline.
In the figure above, some cycles are not validated due to the Max Variation setting. The Minimum Flow attribute is set such that the analysis interprets the double peaked cycle as one large cycle with a notched peaks. The current Max Variation setting (55%) instructs the analysis to reject any peak that exhibits greater than 55% variation i.e. variation greater than the height of the shaded box . The boxes are displayed on the expiration peak however they are applied to both the inspiration and expiration portions of a cycle. The variation in the double peaked inspiration does exceed 55% of the inspiration peak and hence it is rejected. The effect of increasing the Max Variation attribute is shown below.
NOTE: If rejection of cycles is not desired, regardless of variation, set the Max Variation attribute to 100% it will be effectively disabled.
Volume Match is a rejection criterion.
This attribute is used to ensure that the ratio of inspiration and expiration volumes in validated cycles are within specified limits. Once the analysis identifies a cycle, based on Minimum Flow, Baseline Shift and Max Variation, it calculates and compares the inspiration and expiration volumes. If the relative volumes are not within the specified percentage of each other, the analysis will discard the cycle and wait for a valid cycle before validating the waveforms.
In the figure above, the relative volumes in inspiration and expiration must be within 80% of each other (only 20% difference permitted) for the cycles to be validated.
NOTE: If rejection of cycles is not desired, regardless of differences in volume, set the Volume Match attribute to 50%, this will permit a 50% difference between inspiration and expiration volumes.
This attribute determines the point in time used to obtain timing information for the calculation of “Pause” and “PEnh”. The point used is marked by the Percent Recovery Mark and is the point at which the area under the expiration signal equals the specified percentage of the area under the entire expiration.
This attribute determines the format used to report the Tidal Volume.
Invert Flow Signal
Select this attribute to invert the flow signal.