METHODS AND APPARATUS FOR DETERMINING CARDIAC OUTPUT

• US 20110034813A1
• Filed: 10/13/2010
• Published: 02/10/2011
• Est. Priority Date: 02/10/2003
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology, The Board of Trustees of Michigan State University (Michigan State University)
• Original Assignee: Massachusetts Institute of Technology, The Board of Trustees of Michigan State University (Michigan State University)
• Inventors: Cohen, Richard J., Mukkamala, Ramakrishna, Sherman, Derin A.
• Granted Patent: US 9,289,133 B2
• Time in Patent Office: Days
• US Class Current: 600/485
• CPC Class Codes: A61B 5/02007 Evaluating blood vessel condition, e.g. elasticity, compliance
• CPC Class Codes: A61B 5/02255 the pressure being controlled by plethysmographic signals, e.g. derived from optical sensors
• 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 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• CPC Class Codes: A61B 5/726 using Wavelet transforms

Abstract

The present invention provides methods and apparatus for determining a dynamical property of the systemic or pulmonary arterial tree using long time scale information, i.e., information obtained from measurements over time scales greater than a single cardiac cycle. In one aspect, the invention provides a method and apparatus for monitoring cardiac output (CO) from a single blood pressure signal measurement obtained at any site in the systemic or pulmonary arterial tree or from any related measurement including, for example, fingertip photoplethysmography.

According to the method the time constant of the arterial tree, defined to be the product of the total peripheral resistance (TPR) and the nearly constant arterial compliance, is determined by analyzing the long time scale variations (greater than a single cardiac cycle) in any of these blood pressure signals. Then, according to Ohm'"'"'s law, a value proportional to CO may be determined from the ratio of the blood pressure signal to the estimated time constant. The proportional CO values derived from this method may be calibrated to absolute CO, if desired, with a single, absolute measure of CO (e.g., thermodilution). The present invention may be applied to invasive radial arterial blood pressure or pulmonary arterial blood pressure signals which are routinely measured in intensive care units and surgical suites or to noninvasively measured peripheral arterial blood pressure signals or related noninvasively measured signals in order to facilitate the clinical monitoring of CO as well as TPR.

Claims

1-88. -88. (canceled)

89. A method for determining cardiac output to within a constant scale factor, comprising:

receiving an input representing a measurement of a physiological signal indicative of cardiovascular system activity over a plurality of cardiac cycles;

analyzing the input to capture long time scale information which reflects the variability of the signal between cardiac beats; and

determining cardiac output to within a constant scale factor using the long time scale information.

90. The method of claim 89 further comprises measuring the physiological signal invasively or non-invasively at any site in the systemic or pulmonary arterial tree.

91. The method of claim 89 wherein the physiological signal is arterial blood pressure.

92. The method of claim 89 wherein the physiological signal is pulmonary arterial blood pressure.

93. The method of claim 89 wherein the physiological signal is a signal related to arterial blood pressure.

94. The method of claim 89 wherein analyzing the input further comprises estimating a function that represents the response of the physiological signal to a single cardiac contraction over a time period greater than a single cardiac cycle.

95. The method of claim 94 further comprises determining a characteristic time of the function and determining cardiac output to within a constant scale factor by dividing the magnitude of the physiological signal by the characteristic time.

96. The method of claim 89 further comprises determining vascular resistance to within a constant scale factor using the long time scale information.

97. The method of claim 89 wherein analyzing the input further comprises

constructing a cardiac contractions timing signal from the physiological signal by forming an impulse train in which each impulse is located at the onset of upstroke of each pulse;

determining an impulse response, which when convolved with the cardiac contractions timing signal, fits the physiological signal;

determining a time constant by fitting an exponential function to a tail end of the impulse response; and

determining cardiac output to within a constant scale factor using the time constant.

98. A method for determining a dynamical property of the systemic or pulmonary arterial tree, comprising:

measuring a physiological signal indicative of cardiovascular system activity over a plurality of cardiac cycles;

determining the timing of cardiac contractions from the physiological signal;

determining a relationship between the timing of a cardiac contractions and the physiological signal that indicates the evolution of the signal over a time period greater than a single cardiac cycle;

determining a dynamical property of the systemic or pulmonary arterial tree using the relationship.

99. The method of claim 98 wherein the physiological signal is arterial blood pressure.

100. The method of claim 98 wherein the relationship is an impulse response function characterizing the systemic or pulmonary arterial tree.

101. The method of claim 98 wherein the dynamical property is a characteristic time of the systemic or pulmonary arterial tree.

102. The method of claim 98 further comprises determining at least one of cardiac output and vascular resistance to within a constant scale factor from the dynamical property.

103. A method for determining a dynamical property of the systemic or pulmonary arterial tree, comprising:

measuring a physiological signal indicative of cardiovascular system activity over a plurality of cardiac cycles;

determining the timing of cardiac contractions from one of the physiological signal and a second physiological signal that is not indicative of blood pressure or blood flow;

capturing long time scale information by obtaining a relationship between the timing of cardiac contractions and the physiological signal; and

determining a dynamical property of the systemic or pulmonary arterial tree using the relationship.

104. The method of claim 103 wherein the physiological signal is arterial blood pressure.

105. The method of claim 103 wherein the physiological signal is a signal related to arterial blood pressure.

106. The method of claim 103 further comprises determining the timing of cardiac contractions by measuring and analyzing a surface electrocardiogram (ECG).

107. The method of claim 103 further comprises determining at least one of cardiac output and vascular resistance to within a constant scale factor from the dynamical property.

108. The method of claim 103 further comprises fitting an exponential-like function to a portion of the relationship, estimating a time constant of the function and determining cardiac output to within a constant scale factor by dividing arterial blood pressure by the time constant.