Method and apparatus for ultrasonic detection of air bubbles

A method for detecting the presence of inclusions in a liquid flowing in a conduit while compensating for changes in the detection environment comprising:

• transmitting a signal through the liquid at a transmitted signal level;
• receiving the signal at a received signal level;
• interpreting the signal to detect the presence or absence of an inclusion, a sudden change in the received signal level being indicative of the presence of an inclusion;
• and
• adjusting the transmitted signal level to maintain the received signal level at a relatively constant level.

An extracorporeal blood processing apparatus comprising:

• a conduit for conveying blood;
• transmitting means for transmitting an ultrasonic signal through the blood conveyed in the conduit at a transmitted signal level;
• receiving means for receiving and interpreting the ultrasonic signal transmitted by the transmitting means, a relatively sudden change in a received signal level being indicative of the presence of at least one bubble of at least one of air or gas in the blood;
• and
• signal adjusting means for adjusting the transmitted signal level to maintain an average value of the received signal level at a relatively constant value.

A tubing holder for retaining flexible tubing in contact with at least one ultrasonic transducer comprising:

• a first mounting block;
• a first generally planar tubing engagement face having an axis and a first leading edge generally parallel to the axis;
• a first tubing retaining groove recessed into the first tubing engagement face, the first tubing engagement groove being generally parallel to the axis and spaced a predetermined distance from the leading edge and having a generally arcuate cross sectional configuration;
• a first ultrasonic transducer mounted in the first mounting block below and in proximity with the first tubing retaining groove;
• a second mounting block;
• a second generally planar tubing engagement face having an axis and a second leading edge generally parallel to the axis;
• a second tubing retaining groove recessed into the second tubing engagement face, the second tubing engagement groove being generally parallel to the axis and spaced a predetermined distance from the leading edge and having a generally arcuate cross sectional configuration;
• and
• a housing securing and supporting the first and second mounting blocks in a relationship wherein:
• the first tubing engagement face faces the second tubing engagement face, is generally parallel to the second tubing engagement face and is spaced a predetermined distance from the second tubing engagement face;
• the first leading edge is generally parallel to and opposite the second leading edge;
• the first tubing retaining groove is generally parallel to and opposite the second tubing retaining groove;
• and
• the predetermined distance is selected to permit the tubing to be inserted between the first tubing engagement face and the second tubing engagement face at the location of the first and second leading edges when the tubing is relatively greatly compressed, and retained in the first and second tubing retaining grooves when the tubing is relatively less compressed.

A method for measuring the amount of air in the form of microbubbles in a liquid flowing in a tube comprising:

• transmitting a signal through the liquid at a transmitted signal level;
• receiving the signal at a received signal level;
• interpreting the signal to detect the presence or absence of a microbubble, a change in the received signal level being indicative of the presence of a microbubble;
• generating at least one logic signal pulse for each microbubble detected:
• counting the number of logic pulses generated over a predetermined time period;
• establishing the number of logic signal pulses that represent one microbubble and
• ascertaining the number of microbubbles in the tube during the predetermined time period;
• wherein:
• the logic pulses are generated at a predetermined frequency during a detection time period when a microbubble is detected;
• and
• the establishing step comprises:
• determining a value of a constant that is directly proportional to the frequency at which the logic pulses are generated and directly proportional to an expected microbubble size;
• and
• dividing the constant by a flow rate of the liquid in the tube.