Air flow to pressure differential transducer for pneumotachography

• US 3,960,142 A
• Filed: 12/02/1974
• Issued: 06/01/1976
• Est. Priority Date: 12/02/1974
• Status: Expired due to Term

• Current Assignee: Medical Research Institute (Jarrow Formulas Incorporated)
• Original Assignee: Institutes of Medical Sciences
• Inventors: Shore, Jack H., Elliott, Stanley E.
• Primary Examiner(s): Michell, Robert W.
• Assistant Examiner(s): Cohen, Lee S.
• Application Number:
  US05/528,600
• Time in Patent Office: 547 Days
• Field of Search: 128/2.08, 128/2.07, 128/2 C, 128/DIG. 29, 272/57 F, 73/205 R, 73/205 D, 73/205 L, 73/206
• US Class Current: 600/538
• CPC Class Codes: A61B 5/087 Measuring breath flow
• CPC Class Codes: Y10S 128/912 Connections and closures for tubes delivering fluids to or from the body

Abstract

A pneumotachograph having an improved air flow to pressure differential transducer is disclosed for producing a pressure differential during inspiration and expiration of respirative air to and from a hospital patient. Typically, the air flow to pressure differential transducer is attached to endotracheal tubing between the patient'"'"'s trachea and the respirator valve. Specifically, the transducer provides the endotracheal tube with an enlarged and typically cylindrical volume having offset air passages communicating to the endotracheal tube. The unit area of the measuring chamber is greater than the unit area of the communicated endotracheal tubing and is typically cylindrical with respect to such tubing. Likewise, the area of the communicated endotracheal tube is preferably less than one quarter the cross-sectional area of the chamber. The endotracheal tubings are preferably offset so that their respective air flows are not in line and the generated air flow interior of the volume is turbulent but not circuitous. Both the communicated endotracheal tubings are provided with manometer taps substantially normal to the path of fluid flow therein so that pressure differential and not velocity head of the fluid flow is measured. The manometer taps are communicated to a differential pressure transducer. The output of this transducer passes to a linearization circuit to produce a measure of intake and outflow during the patient'"'"'s respective inspiration and expiration to provide a quantitative measure of patient respiration.

Claims

1. An improved air flow to pressure differential transducer adapted to be used by a patient comprising a chamber having at least one sidewall closed by two end walls and enclosing therein a predetermined volume, the distance between said end walls being such that the airflow to or from a patient is normal, said chamber defining an unobstructed volume therewithin;

first and second air passages each transpiercing one of said end walls for the flow of air into and out of said chamber across said unobstructed volume, said air passages having axes of flow offset by an amount equal to or greater than their cross-section at said chamber and each having a unit area equal to or less than one quarter the cross-sectional area of said chamber; and

, first and second manometer taps for measuring the pressure differential of fluid flow between said passages across said chamber, said first manometer tap connected to said first passage and said second manometer tap connected to said second passage.

2. The invention of claim 1 and wherein said air passages are offset with respect to said unobstructed chamber so that flow through each passage impinges upon an end wall of said chamber.

3. The invention of claim 1 and wherein said volume interior of said chamber defines a fluid collection area.

4. The invention of claim 1 and wherein said chamber is cylindrical.

5. The invention of claim 1 and wherein said first and second air passages communicate to said chamber along parallel, non-intersecting flow paths.

6. An improved pneumotachograph including the combination of a respirator;

an air passage connected to said respirator and adapted to communicate air from said respirator to a patient;

an air flow to pressure differential transducer connected to the passage and adapted to be across the air flow from said respirator to said patient; and

, linearization, integrating and flow readout circuits operatively connected to said pressure differential transducer providing electrical signals indicative of the respiration of said patient, the improvement in said air flow to pressure differential transducer comprising;

a chamber having at least one sidewall closed by two end walls and enclosing therein a predetermined volume, the distance between said end walls being such that the airflow to or from a patient is normal, said chamber defining an unobstructed volume therewithin;

first and second air passages each transpiercing one of said end walls for the flow of air into and out of said chamber across said unobstructed volume, said air passages at said end walls having axes of flow offset by an amount equal to at least their cross-section at said chamber and each having a unit area equal to or less than one quarter the cross-sectional area of said chamber; and

, first and second manometer taps for measuring the pressure differential of fluid flow between said passages across said chamber, said first manometer tap connected to said first passage, and said second manometer tap connected to said second air passage, said taps being operatively connected to said circuits.

7. An improved air flow to pressure differential transducer adapted to be used by a patient comprising:

a chamber enclosing therein a predetermined unobstructed volume;

first and second air passages transpiercing the walls of said chamber for the flow of air into and out of said chamber across said unobstructed volume, the distance between the walls at the points where the passages transpierce them being such that the airflow to or from a patient is normal, said first and second air passages aligned with respect to the volume of said chamber for impact of air inflow through one passage upon a wall of said chamber rather than upon the opening for the remaining air passage, said passages having a unit area equal to or less than one quarter the cross-sectional area of said chamber; and

, first and second manometer taps for measuring the pressure differential of fluid flow across said chamber with said first manometer tap connected to said first passage and said second manometer tap connected to said second passage, and, where flow rate through said chamber is proportional to the product of a constant and the pressure differential raised to the 0.57 ±

0.1 power.

8. An improved air flow to pressure differential transducer comprising:

a cylindrical chamber having a diameter greater than one half inch;

two circular end walls closing said cylindrical chamber at either end, the distance between said end walls being between one quarter inch and three quarters of an inch, said chamber defining an unobstructed volume therewithin;

first and second passages each transpiercing one of said end walls to permit airflow into and out of said chamber across said unobstructed volume, said air passages each aligned with respect to the unobstructed volume of said chamber for impact of air inflow through one passage upon a wall of said chamber rather than upon the opening for the remaining air passage, said passages having a unit area equal to or less than one quarter the cross-sectional area of said chamber; and

, first and second manometer taps at said passages each having an interior diameter equal to or greater than one eighth inch for measuring the pressure differential of fluid flow across said chamber, said first manometer tap connected to said first passage and said second manometer tap connected to said second passage.