Uterine contraction sensing device and method for manufacture and use thereof

A sensing device for repeatably measuring changes in pressure comprising:

• A. a sensor comprising:
• i. a variable resistor formed of a pressure sensitive ink;
• ii. a first electrically conductive member interfacing said variable resistor;
• and
• iii. a second electrically conductive member interfacing with said variable resistor and spaced from said first electrically conductive member, said sensor of the type that experiences signal drift due to having direct current passing therethrough;
• B. a first member secured to said variable resistor and a second member secured to said first electrically conductive member, wherein said variable resistor contacts said first electrically conductive member and said second electrically conductive member forming a sensing area portion and said sensing area portion is symmetrical about an axis;
• and
• C. means for passing an alternating current through a sensor, wherein the direct current component of the alternating current is approximately zero, whereby said sensor experiences no drift over a prolonged period of time when said variable resistor electrically contacts said first electrically conductive member and said second electrically conductive member while alternating current having the direct current component being approximately zero passes through the sensor.

A method for measuring changes in pressure for a sensor having:

• i. a variable resistor formed of a pressure sensitive ink;
• ii. a first electrically conductive member interfacing with said ink;
• and
• iii. a second electrically conductive member interfacing with said ink and spaced from the first electrically conductive member, said sensor of the type that experiences signal drift due to having direct current passing therethrough, wherein said variable resistor contacts said first electrically conductive member and said second electrically conductive member forming a sensing area portion and said sensing area portion is symmetrical about an axis, said method comprising the steps of:
• A. applying an alternating current across said sensor;
• B. applying a force to said sensor;
• C. causing the direct current component of said current flowing through the sensor to equal approximately zero, thereby eliminating the signal drift of the sensor due to the direct current;
• and
• D. measuring the electrical resistance of said sensor.

An extra-uterine sensing device for directly measuring changes in pressure brought about by uterine contractions of a wearer comprising:

• A. a rigid outer member adapted for fixed attachment to the abdomen in an area of the wearer's uterus to establish a mechanical pre-load;
• B. a sensing unit attached to said outer member and adapted to be positioned between said outer member and the abdomen and including:
• i. a variable resistor formed of a pressure sensitive ink;
• ii. a first electrically conductive member interfacing with said ink;
• and
• iii. a second electrically conductive member interfacing with said ink and spaced from the first electrically conductive member, wherein a perimeter of said sensing unit is contained within a perimeter of said outer member so that said outer member and said sensing unit for substantially rigid sensor that is incompressible while measuring uterine contraction;
• C. means attached to said first and said second electrically conductive members to monitor changes in electrical resistance;
• and
• D. a belt that receives said outer member, said belt capable of establishing mechanical pre-load.

An extra-uterine method of sensing uterine contractions of a wearer having a fundus comprising the steps of:

• A. attaching a sensing device to the abdomen in the area of the wearer's uterus, said sensing device including:
• i. a variable resistor formed of a pressure sensitive ink;
• ii. a first electrically conductive member interfacing with said ink;
• and
• iii. a second electrically conductive member interfacing with said ink and spaced from the first electrically conductive member;
• B. creating a mechanical pre-load on the sensing device sufficient to establish a reference level for instantaneously detecting changes in pressure caused by contractions;
• C. non-mechanically and directly converting a change in pressure to a change in electrical resistance;
• D. converting said change in resistance to a non-decaying electrical signal;
• and
• E. monitoring said electrical signal.

An extra-uterine sensing device for sensing contractions of a wearer comprising:

• A. means for attaching a substantially rigid sensing device to the abdomen in the area of the wearer's fundus where said sensing device includes a variable resistor formed of a pressure sensitive ink, a first electrically conductive member interfacing with said ink, a second electrically conductive member interfacing with said ink and spaced from said first electrically conductive member;
• B. means for creating a mechanical pre-load on the sensing device sufficient to establish a reference level value for instantaneously detecting changes in pressure caused by contractions;
• C. means for non-mechanically and directly converting a change in pressure to a change in electrical resistance;
• D. means for converting said change in resistance to a non-decaying electrical signal;
• and
• E. means for monitoring said electrical signal.

An extra-uterine method of sensing uterine contractions of a wearer having a uterus comprising the steps of:

• A. attaching a sensing device to the abdomen in the area of the wearer's uterus, said sensing device including:
• i. a variable resistor formed of a pressure sensitive ink;
• ii. a first electrically conductive member interfacing with said ink;
• iii. a second electrically conductive member interfacing with said ink and spaced from the first electrically conductive member;
• B. creating a mechanical pre-load on the sensor sufficient to establish a reference level for instantaneously detecting changes in pressure caused by contractions;
• C. applying an alternating electrical current across said sensor;
• D. causing the direct current component of the current flowing through the sensor to equal approximately zero;
• E. non-mechanically and directly converting a change in pressure to a change in electrical resistance;
• F. converting said change in resistance to a non-decaying electrical signal;
• and
• G. monitoring said electrical signal.

An extra-uterine sensing device for directly measuring changes in pressure brought about by uterine contractions of a wearer comprising:

• A. a rigid outer member adapted for fixed attachment to the abdomen in an area of the wearer's uterus to establish a mechanical pre-load;
• B. a sensing unit attached to said outer member and adapted to be positioned between said outer member and the abdomen and including:
• i. a variable resistor formed of a pressure sensitive ink;
• ii. a first electrically conductive member interfacing with said ink;
• and
• iii. a second electrically conductive member interfacing with said ink and spaced from the first electrically conductive member, wherein a perimeter of said sensing unit is contained within a perimeter of said outer member so that said outer member and said sensing unit for substantially rigid sensor that is incompressible while measuring uterine contraction;
• C. means attached to said first and said second electrically conductive members to monitor changes in electrical resistance;
• and
• D. a belt that coacts with said outer member, said belt capable of establishing mechanical pre-load.