Systems and Methods Utilizing Plethysmographic Data

• US 20120271554A1
• Filed: 05/28/2010
• Published: 10/25/2012
• Est. Priority Date: 05/29/2009
• Status: Abandoned Application

• Current Assignee: Yale University
• Original Assignee: Yale University
• Inventors: Shelley, Kirk H., Silverman, David G.
• Application Number:
  US13/322,708
• Publication Number:
  US 20120271554A1
• Time in Patent Office: Days
• US Class Current: 702/19
• CPC Class Codes: A61B 5/02 Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
• CPC Class Codes: A61B 5/02042 Determining blood loss or bleeding, e.g. during a surgical procedure
• CPC Class Codes: A61B 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7257 using Fourier transforms

Abstract

Disclosed are apparatus, systems and methods utilizing attributes of the cardiac signal to calibrate/normalize components of the plethysmographic (PG) waveform indicating changes in venous and arterial blood volume. In the time-domain, amplitudes of respiratory-induced variations of the DC and AC components of the PG waveform may be calibrated/normalized based on an average amplitude of the PG waveform, e.g., over a respiratory cycle. Similarly, in the frequency domain, respiratory signal strength and side-band signal strength may be advantageously calibrated/normalized based on the strength of the cardiac signal or a harmonic thereof.

Claims

1. A method for facilitating detection of changes in blood volume, said method comprising steps of:

sampling a plethysmograph (PG) waveform;

calculating a spectrum for the PG waveform having a cardiac signal and at least one blood volume indicator;

detecting the cardiac signal or a harmonic thereof within normal cardiac frequencies of the PG waveform spectrum;

detecting the blood volume indicator;

determining a signal strength for each of the cardiac signal or the harmonic thereof and the blood volume indicator, wherein at least one of the determined signal strengths is calculated over a range of characteristic frequencies;

calculating a normalized value for the blood volume indicator by dividing the signal strength of the blood volume indicator by the signal strength of the cardiac signal or the harmonic thereof.

2. The method of claim 1, wherein the blood volume indicator is one of:

(i) a side-band detected on either side of the cardiac signal and (ii) a respiratory signal detected within normal respiratory frequencies of the PG waveform spectrum.

3. The method of claim 2, wherein the calculating a normalized value for the blood volume indicator includes either (i) calculating a scaled venous modulation value by dividing the signal strength of the respiratory signal by the signal strength of the cardiac signal or the harmonic thereof or (ii) calculating a scaled arterial modulation value by dividing the signal strength of the side-band by the signal strength of the cardiac signal or the harmonic thereof.

6. The method of claim 2, wherein the detecting the cardiac signal includes using a peak detection algorithm to detect the highest peak in the normal cardiac frequencies of the PG waveform spectrum, wherein the detecting the side-band includes using a peak detection algorithm to detect a peak on either side of the cardiac signal, wherein the spacing between the side-band and the cardiac signal is approximately equal to a respiratory frequency and wherein the detecting the respiratory signal includes using a peak detection algorithm to detect the highest peak in the normal respiratory frequencies of the PG waveform spectrum.

9. The method of claim 2, wherein the detecting the respiratory signal further includes an error checking process for checking whether a highest peak in the normal respiratory frequencies of the PG waveform spectrum is a harmonic of a true respiratory signal.

10. The method of claim 2, wherein an actual respiratory frequency is determined and the respiratory signal is detected based on said actual respiratory frequency.

11. The method of claim 1, wherein the range of characteristic frequencies are determined by points of inflection on either side of a peak defining the cardiac signal, the harmonic of the cardiac signal or the blood volume indicator.

12. The method of claim 1, wherein the at least one of the determined signal strengths is calculated as one of (i) an integral of the PG waveform spectrum over the range of characteristic frequencies and (ii) the root mean square of the PG waveform spectrum over the range of characteristic frequencies.

14. The method of claim 3, further comprising detecting changes in venous blood volume and arterial blood volume by monitoring changes in the scaled venous modulation value and scaled arterial modulation value over time.

16. The method of claim 3, further comprising comparing the scaled venous modulation value and scaled arterial modulation value to absolute points of reference, wherein the absolute points of reference are universally applicable threshold values indicative of initial blood loss affecting venous return and severe blood loss affecting cardiac output.

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29. A method for facilitating detection of changes in blood volume, said method comprising steps of:

sampling a plethysmograph (PG) waveform;

detecting an average amplitude of the PG waveform over a period of time;

detecting a blood volume indicator;

calculating a normalized value for the blood volume indicator by dividing the amplitude of the blood volume indicator by the average amplitude of the PG waveform.

30. The method of claim 29, wherein the blood volume indicator is one of:

(i) respiratory-induced variation of a DC component of the PG waveform and (ii) respiratory-induced variations of an AC component of the PG waveform.

31. The method of claim 29, wherein the period of time is a respiratory cycle.

32. A system for facilitating detecting changes in blood volume, said system comprising a plethysmorgraphic device coupled with a processing unit said processing unit further including:

means for sampling a plethysmograph (PG) waveform;

means for detecting an average amplitude of the PG waveform over a period of time;

means for detecting a blood volume indicator;

means for calculating a normalized value for the blood volume indicator by dividing the amplitude of the blood volume indicator by the average amplitude of the PG waveform.

18. The system according to claim 32, said processing unit further including:

means for calculating a spectrum for the PG waveform having a cardiac signal and at least one blood volume indicator;

means for detecting the cardiac signal or a harmonic thereof within normal cardiac frequencies of the PG waveform spectrum;

means for determining a signal strength for each of the cardiac signal or the harmonic thereof and the blood volume indicator, wherein at least one of the determined signal strengths is calculated over a range of characteristic frequencies, wherein the signal strength for the cardiac signal or the harmonic thereof represents the average amplitude of the PG waveform and wherein the signal strength for the blood volume indicator represents the amplitude of the blood volume indicator.

21. The system of claim 18, further comprising means for comparing the normalized value for the blood volume indicator to an absolute point of reference.

26. The system of claim 18, wherein the range of characteristic frequencies are determined by points of inflection on either side of a peak defining the cardiac signal, the harmonic of the cardiac signal or the blood volume indicator.

27. The system of claim 18, wherein the at least one of the determined signal strengths is calculated as one of (i) an integral of the PG waveform spectrum over the range of characteristic frequencies and (ii) the root mean square of the PG waveform spectrum over the range of characteristic frequencies.

33. The system of claim 32, wherein the blood volume indicator is one of:

(i) respiratory-induced variation of a DC component of the PG waveform and (ii) respiratory-induced variations of an AC component of the PG waveform.

34. The system of claim 32, wherein the period of time is a respiratory cycle.