Methods for in vivo evaluation of pulmonary physiology and/or function using NMR signals of polarized Xe
In certain embodiments, methods of the present invention obtain dynamic data sets of an NMR spectroscopy signal of polarized 129 Xe in a selected structure, environment, or system. The signal data can be used to evaluate: (a) the physiology of a membrane or tissue; (b) the operational condition or function of a body system or portion thereof (when at rest or under stimulation); and/or (c) the efficacy of a therapeutic treatment used to treat a diagnosed disorder, disease, or condition. Thus, the present invention provides methods for screening and/or diagnosing a respiratory, cardiopulmonary disorder or disease such as chronic heart failure, and/or methods for monitoring the efficacy of therapeutics administered to subject to treat the disorder or disease.
1. An in vivo method for evaluating the physiological response of a subject to a therapeutic agent, comprising:
delivering polarized 129 Xe gas in vivo to a subject;
obtaining a first NMR spectroscopic signal of the polarized gas in the subject at at least one chemical shift frequency to generate a first dynamic data set of the NMR spectroscopic signal values over time, with the polarization of the 129 Xe being repetitively destroyed at predetermined delays in a compartment or compartments of interest, the dynamic data set being representative of the polarized gas in a physiologic structure, environment, or system of interest;
administering a physiological active therapeutic agent to the subject;
obtaining a second NMR spectroscopic signal of the polarized gas in the subject at the at least one chemical shift frequency to generate a second dynamic data set of the NMR spectroscopic signal values over time, with the polarization of the 129 Xe being repetitively destroyed at predetermined delays in a compartment or compartments of interest; and
comparing the first and second dynamic data sets to evaluate the physiological response of the subject to the therapeutic agent.
2. A method according to claim 1 , wherein the compartment of interest comprises the alveolar-capillary membrane.
3. A method according to claim 1 , further comprising the step of calculating the time constant associated with the time it takes the polarized 129 Xe to diffuse across the alveolar-capillary membrane based on the data provided by the obtaining steps.
4. A method according to claim 1 , further comprising the steps of generating a plurality of 129 Xe uptake curves of signal strength versus time based on said first and second dynamic data sets and determining the thickness of the alveolar-capillary membrane based on data provided by said calculating and generating steps.
5. A method according to claim 1 , wherein the evaluating step considers the response in the function of the cardiopulmonary system based on the comparing steps.
6. A method according to claim 1 , wherein the evaluating step considers the response in the function or structure of the alveolar-capillary membrane.
7. A method according to claim 6 , wherein the evaluating step comprises calculating and comparing the time constants associated with each data set to assess the function of the alveolar-capillary membrane.
8. A method according to claim 7 , further comprising determining the thickness of the alveolar-capillary membrane before and after administration of the therapeutic agent based on the obtaining steps.
9. A method according to claim 1 , wherein the step of administering 129 Xe is carried out by the subject inhaling a quantity of the polarized 129 Xe the 129 Xe diffusing across the alveolar-capillary membrane into pulmonary blood, and wherein the first and second obtaining steps are carried out to include two frequencies, one associated with the 129 Xe in tissue and one associated with 129 Xe in the blood, and wherein the step of comparing considers both the first and second tissue and blood signal data sets.
10. A method according to claim 1 , wherein the compartment of interest is one of the glomerular capillary membrane, bowel membrane, placental membrane, and blood brain barrier.
11. A method according to claim 1 , wherein the compartment of interest is a membrane in the body of the subject.
12. A method according to claim 1 , wherein the compartment of interest is the bowel wall.
13. A method according to claim 1 , wherein the compartment of interest is the blood brain barrier.
14. A method according to claim 1 , further comprising the step of evaluating organ perfusion based on said obtaining steps;
up portion and a dynamic equilibrium portion in a time period of interest, the signal having an associated asymptote slope and intercept after the initial exponential build-up portion, wherein the uptake curve has an uptake diffusing time constant associated with the initial build-up portion of the NMR signal, and wherein total diffusing thickness “L” is calculated directly from the uptake time constant τ 1 , using the equation:
L
≈
π
2
D
τ
1
where D is the diffusion coefficient of xenon.