Intracranial pressure monitoring system

A catheter assembly adapted for measurement of a fluid pressure within a body cavity of a patient, comprising:

• a light source having a temperature providing an optical signal having thermal drift characteristics which vary in response to a change in the temperature of the light source;
• optical sensor means adapted to receive the optical signal from the light source to provide a measurement signal indicative of the fluid pressure in the cavity, the measurement signal having undesirable characteristics related to the thermal drift characteristics of the light source;
• detection means coupled to the optical sensor means for detecting the measurement signal to provide an output signal indicative of the fluid pressure in the cavity;
• a filter included in the detection means and having optical characteristics which substantially offset the undesirable characteristics of the measurement signal;
• whereby
• the output signal is substantially independent of the temperature of the light source.

A catheter assembly adapted for measurement of a fluid pressure within a body cavity of a patient, comprising:

• an electrical power source;
• optical conversion means responsive to the electrical power source for providing an optical signal;
• a light emitting diode included in the optical conversion means and having a spectrum, the diode having thermal drift characteristics which vary in response to a change in temperature such that the spectrum of the diode shifts to longer wavelengths in response to an increase in temperature;
• optical sensor means adapted to receive the optical signal from the optical conversion means and to provide a measurement signal indicative of the fluid pressure in the cavity, the measurement signal having undesirable characteristics related to the thermal drift characteristics of the diode;
• detection means coupled to the optical sensor means for detecting the measurement signal to provide an output signal indicative of the fluid pressure in the cavity;
• a filter included in the detection means and having a spectrum, the filter having optical characteristics such that the spectrum of the filer shifts to longer wavelengths in response to an increase in temperature;
• the output signal is dependent upon the area of the spectral envelope which is defined on one side by the spectrum of the diode and which is defined on the other side by the spectrum of the filter;
• whereby
• the area beneath the envelope is substantially unchanged in response to an increase in temperature.

A catheter assembly for measuring a fluid pressure within a body cavity of a patient, comprising:

• a catheter having a distal end adapted for disposition in the body cavity of the patient;
• optical pressure sensor means coupled to the catheter, the sensor means having a temperature and properties for providing an optical measurement signal indicative of the fluid pressure in the body cavity;
• detection means responsive to the optical measurement signal for providing an electrical signal indicative of fluid pressure in the body cavity;
• the optical measurement signal including undesirable optical components which vary with the temperature of the sensor means and provide the optical measurement signal with a signal-to-noise ratio;
• and
• filter means included in the detection means for inhibiting the undesirable optical components of the optical signal which vary with the temperature of the sensor means in order to increase the signal-to-noise ratio of the optical measurement signal.

A catheter assembly for measuring a fluid pressure within a body cavity of a patient, comprising:

• a catheter having a distal end adapted for disposition in the body cavity of the patient;
• a light source disposed in a particular environment that establishes the temperature of the light source, the light source providing an optical signal having characteristics which vary in response to a change in the temperature of the light source;
• an optical pressure sensor disposed generally at the distal end of the catheter and responsive to the optical signal of the light source to provide an optical measurement signal indicative of the fluid pressure in the body cavity;
• detection means responsive to the optical measurement signal for providing an electrical signal indicative of fluid pressure in the body cavity;
• the optical measurement signal including undesirable optical components which vary with the temperature of the light source and provide the optical measurement signal with a signal-to-noise ratio;
• and
• filter means includes in the detection means and disposed in the particular environment that establishes the temperature of the filter means, the filter means having properties for inhibiting the undesirable optical components of the optical signal which vary with the temperature of the light source in order to increase the signal-o-noise ratio of the optical measurement signal.

A catheter assembly for measuring a fluid pressure within a body cavity of a patient, comprising;

• a catheter having a distal end adapted for disposition in the body cavity of a patient;
• optical pressure sensor coupled to the catheter, the sensor means having a temperature and properties for providing an optical measurement signal indicative of the fluid pressure in the body cavity;
• detection means responsive to the optical measurement signal for providing an electrical signal indicative of fluid pressure in the body cavity;
• the optical measurement signal including undesirable components which vary with the temperature of the sensor means;
• means included in the detection means for compensating for the undesirable components of the optical signal which vary with the temperature;
• first amplifier means included in the detection means and responsive to the optical measurement signal for providing the electrical signal with first components representative of the optical measurement signal including the undesirable components;
• means included in the compensation means for filtering the optical signal to provide a corrected signal adjusted in accordance with the undesirable components of the optical signal;
• second amplifier means included in the detection means and responsive to the corrected means for providing the electrical signal with second components representative of the optical measurement signal excluding the undesirable components;
• conversion means coupled to the detection means for providing a digital signal indicative of the fluid pressure in the body cavity;
• and
• output means responsive to the digital signal for displaying the fluid pressure in the body cavity.

A catheter assembly for measuring a fluid pressure within a body cavity of a patient, comprising:

• a catheter having a distal end adapted for disposition in the body cavity of a patient;
• a light source disposed in a particular environment that establishes the temperature of the light source, the light source providing an optical signal having characteristics which vary in response to a change in the temperature of the light source;
• an optical pressure sensor disposed generally at the distal end of the catheter and responsive to the optical signal of the light source to provide an optical measurement signal indicative of the fluid pressure in the body cavity;
• detection means responsive to the optical measurement signal for providing an electrical signal indicative of fluid pressure in the body cavity;
• the optical measurement signal including undesirable components which vary with the temperature of the light source;
• compensating means included in the detection means and disposed in the particular environment that establishes the temperature of the compensating means, the compensating means having properties for compensating for the undesirable components of the optical signal which vary with the temperature of the light source;
• first amplifier means included in the detection means and responsive to the optical measurement signal for providing the optical measurement signal including the undesirable components;
• means included in the compensating means for filtering the optical signal to provide a corrected signal adjusted in accordance with the undesirable components of the optical signal;
• second amplifier means included in the detection means and responsive to the corrected signal for providing the electrical signal with second components representative of the optical measurement signal excluding the undesirable components;
• conversion means coupled to the detection means for providing a distal signal indicative of the fluid pressure in the body cavity;
• and
• output means responsive to the digital signal for displaying the fluid pressure in the body cavity.

A method for reducing the effect of a change in temperature on an optical system including a sensor having properties dependent upon a change in pressure, the method comprising the steps of:

• directing an incident light signal onto the sensor, the incident light signal having undesirable properties dependent upon the change in temperature;
• sensing the change in pressure;
• receiving a reflective light signal from the sensor, the reflective light signal having first characteristics dependent upon the change in pressure sensed by the sensor, and second characteristics dependent upon the change in temperature;
• directing the reflective light signal through an optical filter to inhibit the second characteristics in the reflective light signal;
• and
• detecting the first characteristics in the reflective light signal to provide an indication of the pressure sensed by the sensor.