Method and apparatus for the non-invasive determination of the minute volume of the heart
First Claim
1. A method for the non-invasive determination of the minute volume Q of the heart of a subject, which method comprises the steps of (a) estimating the amount in which a sufficiently soluble gas is present in the blood of the subject, prior to and subsequent to the passage of the blood through the heart;
- (b) separating expired gas from inspired gas with each respiration cycle and measuring directly in the flow of respiration gas the magnitude of said respiration gas flow and the amount of said soluble gas contained therein; and
(c) using the determined values of said flow magnitude and said soluble-gas content to control metering of said soluble gas to the flow of inspiration gas from a source of such gas during the next following cycle, wherein the metering of said soluble gas is controlled in a manner to change the lung content of said gas in accordance with a given program;
the value Q for pairs of respiration cycles is determined as the ratio between the difference between (i) effective gas-flow/unit time V1 for each respiration cycle and V2 for the next respiration cycle and (ii) the difference between the gas-content in arterial blood Ca1 for each respiration cycle and Ca2 for the next respiration cycle;
Q for a plurality of pairs of respiration cycles is determined, each pair of said cycles being spaced by a given number of respiration cycles; and
the mean value of Q is calculated from the various values Q determined.
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Abstract
An arrangement for the non-invasive determination of the minute volume Q of the heart is arranged to determine the amount of a sufficiently soluble gas, e.g. carbon dioxide or nitrous oxide, present in the blood, prior to and subsequent to the passage of the blood through the heart. The expired and inspired gases are separated from one another with each breath taken. Transducers feed respective devices for determining the gas content of the respiration gas, and the magnitude of the expiration gas flow and the inspiration gas flow. These devices are controlled by a microprocessor, which is programmed to supply gas from a gas source, to meter the gas during a subsequent inspiration cycle, and to control an indicator for the Q-value. The gas is controlled in a manner such that the gas-content of the lungs is changed in accordance with a given program. The Q-value is calculated for pairs of respiration cycles in accordance with the formula: ##EQU1## in which V1 is the effective gas flow/unit time for a respiration cycle;
V2 is the effective gas flow/unit time for the next respiration cycle;
Ca1 is the gas content of arterial blood for the first respiration cycle;
Ca2 is the gas content of arterial blood for the next respiration cycle.
The microprocessor is arranged to calculate Q for a plurality of pairs of respiration cycles (e.g. 5-6 pairs) with a given number of respiration cycles therebetween (e.g. 4), and to send to the indicator a signal corresponding to the mean value of the Q-values obtained.
58 Citations
8 Claims
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1. A method for the non-invasive determination of the minute volume Q of the heart of a subject, which method comprises the steps of (a) estimating the amount in which a sufficiently soluble gas is present in the blood of the subject, prior to and subsequent to the passage of the blood through the heart;
- (b) separating expired gas from inspired gas with each respiration cycle and measuring directly in the flow of respiration gas the magnitude of said respiration gas flow and the amount of said soluble gas contained therein; and
(c) using the determined values of said flow magnitude and said soluble-gas content to control metering of said soluble gas to the flow of inspiration gas from a source of such gas during the next following cycle, wherein the metering of said soluble gas is controlled in a manner to change the lung content of said gas in accordance with a given program;
the value Q for pairs of respiration cycles is determined as the ratio between the difference between (i) effective gas-flow/unit time V1 for each respiration cycle and V2 for the next respiration cycle and (ii) the difference between the gas-content in arterial blood Ca1 for each respiration cycle and Ca2 for the next respiration cycle;
Q for a plurality of pairs of respiration cycles is determined, each pair of said cycles being spaced by a given number of respiration cycles; and
the mean value of Q is calculated from the various values Q determined. - View Dependent Claims (2, 3, 4, 5)
- (b) separating expired gas from inspired gas with each respiration cycle and measuring directly in the flow of respiration gas the magnitude of said respiration gas flow and the amount of said soluble gas contained therein; and
- 6. An apparatus for the non-invasive determination of the minute volume Q of the heart, said apparatus comprising means for separating expired gas from inspired gas at each respiration cycle, means for measuring the magnitude of the expired gas flow, means for determining the content of the soluble gas in the respiration flow, means controlled by said flow-measuring and content-determining means for metering said gas to the flow of inspiration gas from a gas source during the next following inspiration cycle, wherein a microprocessor is programmed to control the gas-metering process in a manner such that the lung content of said gas is changed in accordance with a given program and is arranged to determine Q for pairs of respiration cycles in accordance with the formula ##EQU4## in which V is the effective gas flow per unit of time, calculated breath for breath, Ca is the simultaneously calculated gas content per unit of arterial blood, the index 1 representing a first respiration cycle and the index 2 representing the next following respiration cycle, and wherein the microprocessor is arranged to calculate Q for a plurality of pairs of respiration cycles, said pairs being separated by a given number of respiration cycles, and to determine the mean value of the various values of Q obtained.
Specification