This expanded 6-level grading scale will not predict the size of the opening, rather the conductance or ability of the opening to transmit material from the venous circulation to the brain.  The conductance depends on both the size of the opening and the pressure gradient.  It is positive if any embolic track (ET) is detected by Power M-Mode or in the Doppler spectrogram.  All embolic tracks are counted separately on the PMD display for the two injections reporting both the resting conductance and the straining conductance according to the numbers of micro-bubble embolic tracks that are counted.

GRADE I 1 to 10 Embolic Tracks	GRADE II 11 to 30 Embolic Tracks
GRADE III 31 to 100 Embolic Tracks	GRADE IV 101 to 300 Embolic Tracks
GRADE V  5> 300 Embolic Tracks	GRADE V+ or Shower Effect Uncountable # of Embolic Tracks

For unilateral PMD monitoring, the scale is reduced to the following:  1-5, 6-15, 16-50, 51-150, and >150.  These conductance scales allow for quantification of the capability of the shunt to conduct embolic material directly from the venous to the cerebral circulations.

Pulmonary Shunts
Direct pulmonary artery injections of saline contrast during transcatherter closure of 13 PFO patients demonstrated only 1 to 2 embolic tracks in 7 patients.  These results indicate transpulmonary passage of bubbles through the pulmonary capillaries fall within GRADE I.  GRADE I does not represent a significant RLS.  If a patient with an intrapulmonary arteriovenous malformation is sent to closure on the basis of a positive bubble test, pulmonary injection and pulmonary angiography can be performed at this time without disservice to the patient.