Apparatus and method for non-invasively measuring cardiac output

• US 6,648,832 B2
• Filed: 02/06/2001
• Issued: 11/18/2003
• Est. Priority Date: 12/19/1996
• Status: Expired due to Term

• Current Assignee: RIC INVESTMENTS LLC (Respironics Incorporated)
• Original Assignee: NTC Technology, Inc. (Dixtal Medical, Inc.)
• Inventors: Orr, Joseph A., Westenskow, Dwayne, Kofoed, Scott A., Jaffe, Michael B.
• Primary Examiner(s): Nasser, Robert L.
• Application Number:
  US09/777,629
• Publication Number:
  US 20010029339A1
• Time in Patent Office: 1,015 Days
• Field of Search: 128/204.21, 128/204.23, 128/205.14, 600/529, 600/532
• US Class Current: 600/532
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence
• CPC Class Codes: A61B 5/0836 Measuring rate of CO2 production
• CPC Class Codes: A61M 16/0045 Means for re-breathing exhaled gases, e.g. for hyperventilation treatment
• CPC Class Codes: A61M 16/0833 T- or Y-type connectors, e.g. Y-piece
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase
• CPC Class Codes: A61M 2230/432 partial CO2 pressure (P-CO2)
• CPC Class Codes: G01N 33/004 for CO, CO2
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Abstract

Apparatus and methods for non-invasively determining the cardiac output or pulmonary capillary blood flow of a patient using partial re-breathing techniques. The apparatus includes a substantially instantaneously adjustable deadspace volume for accommodating differences in sizes or breathing capacities of various patients. The apparatus may be constructed of inexpensive elements, including one or more two-way valves, which render the apparatus very simple to use and inexpensive so that the unit may be employed as a disposable product. The method of the invention includes estimating the cardiac output or pulmonary capillary blood flow of a patient based on partial pressure of alveolar CO₂, rather than on the partial pressure of end tidal CO₂, as previously practiced. A computer program for calculating the cardiac output or pulmonary capillary blood flow of a patient is also disclosed.

Claims

1. A rebreathing method, comprising:

evaluating at least one of a lung capacity of a patient, a respiratory flow condition of the patient, and a respiratory carbon dioxide condition of the patient; and

selecting a deadspace volume to be used in rebreathing based on said evaluating, said selecting being effected without substantially changing airway pressure.

2. The rebreathing method of claim 1, wherein said selecting comprises defining a volume of a deadspace receptacle communicating with a breathing circuit in communication with an airway of the patient.

3. The rebreathing method of claim 1, wherein said selecting comprises selecting a concentration of exhaled gases to remain within at least one of a breathing circuit in communication with an airway of the patient and the airway.

4. The rebreathing method of claim 1, wherein said selecting comprises adjusting a deadspace within an airway of the patient.

5. A rebreathing method, comprising:

insufflating an airway of a patient;

monitoring at least one aspect of the patient'"'"'s breathing during said insufflating;

reducing a volume of said insufflating by adjusting a distance a tube in communication with a ventilation apparatus extends into an airway of the patient; and

monitoring said at least one aspect of the patient'"'"'s breathing with said volume of said insufflating reduced.

6. The method of claim 5, wherein said insufflating is effected with gas insufflation apparatus.

7. The method of claim 6, wherein said adjusting comprises adjusting a distance a catheter of said gas insufflation apparatus extends into the airway of the patient.