Impedance pneumography
First Claim
1. A method for monitoring respiratory condition by impedance pneumography, comprising the steps of applying a first pair of spaced electrodes to a human body, applying a second pair of spaced electrodes for detecting a resulting electrical signal at different points on the body, applying an electrical signal to the first pair of electrodes at a plurality of frequencies, monitoring the resulting electrical signal at the second pair of electrodes at said plurality of frequencies, obtaining from the resulting electrical signal a measure of the impedance of a part of the body at the plurality of frequencies, obtaining a difference signal representing the impedance change with frequency, and dividing the difference signal by a signal representative of the impedance measure itself at one or more frequencies, thereby suppressing the effect of those impedance signal components whose frequency dependent change is substantially proportional to the impedance signal value.
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Abstract
The invention concerns a method and apparatus for monitoring respiratory condition by impedance pneumography.
An electrical signal is applied at a plurality of frequencies to a human subject by way of a first pair of spaced electrodes applied to the trunk of the body, whilst the resulting electrical signal is monitored at the plurality of frequencies at different points on the body by way of a second pair of spaced electrodes. From the resulting electrical signal a measure of the impedance of a part of the body at the plurality of frequencies is obtained, and a difference signal representing the impedance change with frequency is calculated. The difference signal is normalized with respect to a signal representative of the impedance measure itself at one or more frequencies, thereby suppressing the effect of those impedance signal components--such as movement artifact--whose frequency dependent change is substantially proportional to the impedance signal value.
The invention improves the reliability of impedance pneumography, especially when employed in situations in which it is difficult to restrict subject movement, such as during sleep. It has particular application in neonatal and infant sleep apnea detection systems.
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Citations
17 Claims
- 1. A method for monitoring respiratory condition by impedance pneumography, comprising the steps of applying a first pair of spaced electrodes to a human body, applying a second pair of spaced electrodes for detecting a resulting electrical signal at different points on the body, applying an electrical signal to the first pair of electrodes at a plurality of frequencies, monitoring the resulting electrical signal at the second pair of electrodes at said plurality of frequencies, obtaining from the resulting electrical signal a measure of the impedance of a part of the body at the plurality of frequencies, obtaining a difference signal representing the impedance change with frequency, and dividing the difference signal by a signal representative of the impedance measure itself at one or more frequencies, thereby suppressing the effect of those impedance signal components whose frequency dependent change is substantially proportional to the impedance signal value.
- 11. An apparatus for monitoring respiratory condition by impedance pneumography, comprising a pair of spaced electrodes for applying an electrical signal to a human body and a pair of spaced electrodes for detecting a resulting electrical signal at different points on the body, a means for applying said signal to the first pair of electrodes at a plurality of frequencies, a means for monitoring the resulting electrical signal at the second pair of electrodes at said plurality of frequencies, a means for obtaining from the resulting electrical signal a measure of the impedance of a part of the body at the plurality of frequencies, a means for obtaining a difference signal representing the impedance change with frequency, and a means for dividing the difference signal by a signal representative of the impedance measure itself at one or more frequencies, such that the effect of those impedance signal components whose frequency change is substantially proportional to the impedance signal value can be suppressed.
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17. An apparatus for monitoring a respiratory condition by impedance pneumography, comprising:
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a pair of spaced electrodes for applying an electrical signal to a human body; a pair of spaced electrodes for detecting a resulting electrical signal at different points on the body; a signal generating device for applying said electrical signal to the first pair of electrodes at a plurality of frequencies; a monitoring device for monitoring the resulting electrical signal at the second pair of electrodes at said plurality of frequencies; a computing device for obtaining from the resulting electrical signal a measure of the impedence of a part of the body at the plurality of frequencies; a computing device for obtaining a difference signal representing the impedence change with frequency; a computing device for dividing the difference signal by a signal representative of the impedence measure itself at one or more frequencies, whereby the effect of those impedence signal components whose frequency is substantially proportional to the impedence signal value can be suppressed.
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Specification