Method and apparatus for continuous cardiac output monitoring

A method for continuously monitoring the volume flow rate of a fluid flowing through a vessel based on the relationship, Q=V×A, where Q is the volume flow rate, V is the velocity of the fluid flowing through the vessel, and A is the cross sectional area of the vessel proximate a location in the vessel where the flow velocity is measured, said method comprising:

• ascertaining the electrical impedance of the vessel and deriving the cross-sectional area of the vessel based on the electrical impedance within the vessel, wherein the derived cross-sectional area is directly proportional to the resistivity, ρ, of the fluid flowing in the vessel and inversely proportional to the resistance, R, of the vessel;
• measuring the velocity of the fluid flowing in the vessel;
• and
• measuring the temperature of the fluid flowing in the vessel and compensating in the cross-sectional area derivation for variations in the resistivity ρ with temperature based upon the measured temperature.

A velocity sensor for remote fluid flow measurements, said sensor comprising:

• a flexible tube having an optical opening formed in a sidewall thereof;
• an optical fiber disposed within said tube, said optical fiber having a longitudinal fiber axis, a terminal end disposed proximate said optical opening, and an end face at said terminal end, said end face having a plurality of concentric Fresnel rings formed thereon to focus light passing through said Fresnel rings in front of said end face;
• and
• a reflective surface disposed within said tube adjacent said terminal end of said optical fiber,
• said reflective surface being oriented such that the focused light emitted from said terminal end of said optical fiber is reflected by said reflective surface in a direction having a component normal to the fiber axis through said optical opening into a measurement volume of the flow located outside and alongside said sensor.

A velocity sensor for remote fluid flow measurements, said sensor comprising:

• a flexible tube having an optical opening formed in a sidewall thereof;
• an optical fiber disposed within said tube, said optical fiber having a longitudinal fiber axis and a terminal end disposed proximate said optical opening, said terminal end being formed in a generally conical shape to focus light passing through said optical fiber in front of said terminal end;
• and
• a reflective surface disposed within said tube adjacent said terminal end of said optical fiber,
• said reflective surface being oriented such that the focused light emitted from said terminal end of said optical fiber is reflected by said reflective surface in a direction having a component normal to the fiber axis through said optical opening into a measurement volume of the flow located outside and alongside said sensor.

An instrument for ascertaining the impedance of a vessel in which said instrument is disposed, the cross-sectional area of the vessel being derivable from the ascertained impedance, said instrument comprising:

• a pair of signal-emitting electrodes for injecting a known electrical signal into the vessel in which said instrument is disposed;
• a first pair of measurement electrodes across which a voltage can be measured;
• and
• a second pair of measurement electrodes across which a voltage can be measured,
• wherein said signal-emitting electrodes inject the known signal into the vessel, a first voltage is measured across said first pair of measurement electrodes, and a second voltage is measured across said second pair of measurement electrodes, and the impedance of the vessel, from which the cross-sectional area can be derived, is determined from the known signal and the difference between the first and second voltages.