Pulmonary Monitoring System

• US 20090143663A1
• Filed: 06/30/2006
• Published: 06/04/2009
• Est. Priority Date: 07/01/2005
• Status: Active Grant

• Current Assignee: ImpediMed Limited
• Original Assignee: Impedance Cardiology Systems, Inc.
• Inventors: Chetham, Scott Matthew
• Granted Patent: US 8,781,551 B2
• Time in Patent Office: Days
• US Class Current: 600/372
• CPC Class Codes: A61B 2562/08 Sensors provided with means for identification, e.g. barcodes or memory chips
• CPC Class Codes: A61B 2562/226 comprising means for identifying the connector, e.g. to prevent incorrect connection to socket
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61B 5/0803 Recording apparatus specially adapted therefor
• CPC Class Codes: A61B 5/4878 Evaluating oedema

Abstract

A method of monitoring pulmonary oedema in a subject using a processing system. The method includes, determining a measured impedance value for at least two body segments, at least one of the body segments being a thoracic cavity segment. For each body segment, the measured impedance values are used to determine an index, which is in turn used to determine the presence, absence or degree of pulmonary oedema using the determined indices.

Claims

1-105. -105. (canceled)

106. A method of monitoring pulmonary oedema in a subject, the method including, in a processing system:

a) determining a measured impedance value for at least two body segments, at least one of the body segments being a thoracic cavity segment;

b) for each body segment, and using the measured impedance values, determining an index; and

c) determining the presence, absence or degree of pulmonary oedema using the determined indices.

107. A method according to claim 106, wherein the index is of a ratio of the extra-cellular to intra-cellular fluid.

108. A method according to claim 106, wherein the method includes, in the processing system:

a) comparing the indices of the body segments; and

b) determining the presence, absence or degree of pulmonary oedema using the results of the comparison.

109. A method according to claim 106, wherein the method includes, in the processing system:

a) determining an index ratio based on a ratio of the indices;

b) comparing the index ratio to at least one reference; and

c) determining the presence, absence or degree of pulmonary oedema using the results of the comparison.

110. A method according to claim 109, wherein the reference includes at least one of:

a) a predetermined threshold;

b) a tolerance determined from a normal population; and

c) a predetermined range.

111. A method according to claim 109, wherein the reference includes an index ratio previously determined for the subject.

112. A method according to any one of the claim 106, wherein the method includes, in the processing system:

a) determining a plurality of measured impedance values for each body segment, each measured impedance value being measured at a corresponding measurement frequency; and

b) determining the index ratio based on the plurality of measured impedance values.

113. A method according to claim 112, wherein the method includes, in the processing system, and for each body segment:

a) determining values for parameters R₀ and R_∞

from the measured impedance values; and

,

b) calculating the index (I) using the equation;

114. A method according to claim 113, wherein the method includes, in the processing system, determining the parameter values using the equation:

115. A method according to claim 114, wherein the method includes, in the processing system:

a) determining the impedance of each body segment at four discrete frequencies; and

b) determining values for the parameters by solving the equation using four simultaneous equations.

116. A method according to claim 114, wherein the method includes, in the processing system, determining the parameter values by:

a) determining an impedance locus using the measured impedance values; and

b) using the impedance locus to determine the parameter values.

117. A method according to claim 106, wherein the thoracic cavity segment corresponds to the entire thoracic cavity.

118. A method according to claim 106, wherein the other body segment is at least one other thoracic cavity segment.

119. A method according to claim 106, wherein the at least one other body segment is a limb.

120. A method according to claim 106, wherein the method includes, in the processing system, determining if the at least one other body segment suffers from oedema.

121. A method according to claim 106, wherein the method includes, in the processing system:

a) determining, using measured impedance values, the impedance of the entire subject and each limb; and

b) subtracting the limb impedance values from the entire subject impedance values to determine the impedance of the thoracic cavity.

122. A method according to claim 106, wherein the method includes, in the processing system:

a) causing one or more electrical signals to be applied to the subject using a first set of electrodes, the one or more electrical signals having a plurality of frequencies;

b) determining an indication of electrical signals measured across a second set of electrodes applied to the subject in response to the applied one or more signals;

c) determining from the indication and the one or more applied signals, an instantaneous impedance value at each of the plurality of frequencies; and

d) determining the index using the instantaneous impedance values.

123. A method according to claim 122, wherein a number of electrodes are provided on the subject'"'"'s thoracic cavity, and wherein the method includes, in the processing system:

a) causing one or more electrical signals to be applied to a pair of the electrodes;

b) determining an indication of electrical signals measured across each other pair of electrodes;

c) determining from the indication and the one or more applied signals, an instantaneous impedance value for at least one thoracic cavity segment; and

d) repeating steps a) to c) by applying electrical signals to each other pair of the electrodes to thereby determine impedance values for a number of thoracic cavity segments.

124. A method according to claim 106, wherein the method includes, in the processing system:

a) determining at least one impedance measurement to be performed;

b) determining at least one electrode arrangement associated with the determined impedance measurement;

c) displaying a representation indicative of the electrode arrangement; and

d) causing the impedance measurement to be performed once the electrodes have been provided in accordance with the displayed representation.

125. A method according to claim 106, wherein the method includes, in the computer system, displaying an indication of at least one of:

a) the parameter values;

b) the ratio of extra-cellular to intra-cellular fluid; and

c) an indication of the at least one of the presence, absence or degree of tissue oedema in the subject.

126. A method according to claim 106, wherein the method includes, in the processing system:

a) determining an electrode identifier associated with at least one electrode provided on the subject;

b) determining, using the electrode identifier, an electrode position indicative of the position of the at least one electrode on the subject; and

c) performing at least one impedance measurement using the electrode position.

127. A method according to claim 106, wherein the method includes, in the processing system:

a) determining a parameter associated with at least one electrode lead; and

b) causing at least one impedance measurement to be performed using the determined parameter.

128. A method according to claim 106, wherein the method includes, in the processing system:

a) receiving configuration data, the configuration data being indicative of at least one feature;

b) determining, using the configuration data, instructions representing the at least one feature; and

c) causing, using the instructions, at least one of;

i) at least one impedance measurement to be performed; and

ii) at least one impedance measurement to be analyzed.

129. A method according to claim 106, wherein the method includes, in the processing system:

a) causing a first signal to be applied to the subject;

b) determining at least one parameter relating to at least one second signal measured across the subject;

c) comparing the at least one parameter to at least one threshold; and

d) depending on the results of the comparison, selectively repeating steps (a) to (d) using a first signal having an increased magnitude.

130. Apparatus for monitoring pulmonary oedema in a subject, the apparatus including a processing system for:

a) determining a measured impedance value for at least two body segments, at least one of the body segments being a thoracic cavity segment;

b) for each body segment, and using the measured impedance values, determining an index; and

c) determining the presence, absence or degree of pulmonary oedema using the determined indices.

131. Apparatus according to claim 130, wherein the apparatus includes:

a) a current supply for generating an alternating current at each of a plurality of frequencies;

b) at least two supply electrodes for applying the generated alternating current to a subject;

c) at least two measurement electrodes for detecting a voltage across the subject; and

d) a sensor coupled to the measurement electrodes for determining the voltage, the sensor being coupled to the processing system to thereby allow the processing system to determine the measured impedances.

132. Apparatus according to claim 130, wherein the apparatus includes a number of electrodes arranged in a band for fitting to the subjects thoracic cavity.

133. Apparatus according to claim 132, wherein the apparatus includes a multiplexing system for selectively coupling the current supply and the sensor to the number of electrodes in a predetermined sequence.

134. A method of diagnosing a presence, absence or degree of pulmonary oedema in a subject, the method including, in a processing system:

a) determining a measured impedance value for at least two body segments, at least one of the body segments being a thoracic cavity segment;

b) for each body segment, and using the measured impedance values, determining an index; and

c) determining the presence, absence or degree of pulmonary oedema using the determined indices.

135. Apparatus for connecting measurement apparatus to an electrode, the apparatus including:

a) a housing having a connector for coupling the housing to an electrode; and

b) a circuit mounted in the housing, the circuit being electrically coupled to the electrode using the connector, and being coupled to a lead, the circuit being for at least one of;

i) generating predetermined electrical signals in accordance with control signals received from the measurement apparatus;

ii) providing an indication of electrical signals applied to the electrode; and

iii) providing an indication of electrical signals measured at the electrode.

136. Apparatus according to claim 135, wherein the circuit is provided on a circuit board having an electrical contact, and wherein in use the connector urges at least part of the electrode into abutment with the electrical contact.

137. Apparatus according to claim 136, wherein the connector includes a biased arm.

138. Apparatus according to claim 135, wherein the circuit includes a buffer circuit for:

a) sensing voltage signals at the electrode;

b) filtering and amplifying the voltage signals; and

c) transferring the filtered and amplified voltage signals to the measurement apparatus.

139. Apparatus according to claim 135, wherein the circuit includes a current source circuit for:

a) receiving one or more control signals;

b) filtering and amplifying the control signals to thereby generate one or more current signals;

c) applying the current signals to the electrode pad; and

d) transferring an indication of the applied signals to the measurement apparatus.

140. Apparatus according to claim 135, wherein the apparatus further comprises an electrode, the electrode including:

a) an electrode substrate; and

b) a conductive material for electrically coupling the electrode to the subject.

141. Apparatus according to claim 140, wherein the electrode substrate is electrically conductive, and wherein in use the connector couples the circuit to the electrode substrate.

142. Apparatus according to claim 135, wherein the housing includes curved edges.

143. Apparatus according to claim 135, wherein the housing is formed from a material that, at least one of:

a) has a low coefficient of friction; and

b) is resilient.

144. A method of performing impedance measurements on a subject, the method including, in a processing system:

a) determining an encoded value associated with at least one electrode lead; and

b) causing at least one impedance measurement to be performed using the encoded value.

145. A method according to claim 144, wherein the encoded value is used for calibration.

146. A method according to claim 144, wherein the encoded value is determined from a resistance value.

147. A method according to claim 144, wherein the encoded value is indicative of an identity of the lead.

148. A method according to claim 144, wherein the method includes, in the processing system, controlling the current applied to the subject using the determined encoded value.

149. A method according to claim 144, wherein the encoded value is a lead identifier, and wherein the method includes, in the processing system:

a) determining, using the lead identifier, an impedance measurement procedure; and

b) causing the determined impedance measurement procedure to be performed.

150. A method according to claim 149, wherein the method includes, in the processing system:

a) comparing the determined identity to one or more predetermined identities; and

b) determining the impedance of the subject in response to a successful comparison.

151. A method according to claim 149, wherein the method includes, in the processing system:

a) determining the lead identifier associated with the at least one electrode lead;

b) determining, using the lead identifier, a lead usage;

c) comparing the lead usage to a threshold; and

d) in accordance with the results of the comparison, at least one of;

i) generating an alert;

ii) terminating an impedance measurement procedure; and

iii) performing an impedance measurement procedure.

152. A method according to claim 144, wherein the method includes, in the processing system, at least one of:

a) processing electrical signals measured from the subject to thereby determine one or more impedance values; and

b) processing determined impedance values.

153. A method according to claim 144, wherein the encoded value is stored in a store.

154. Apparatus for performing impedance measurements on a subject, the apparatus including:

a) at least one lead for connecting to electrodes coupled to the subject, the at least one lead including an encoded value; and

b) a processing system coupled to the at least one lead for;

i) determining the encoded value; and

c) causing at least one impedance measurement to be performed using the encoded value.

155. A method of performing impedance measurements on a subject, the method including, in a processing system:

a) determining an electrode identifier associated with at least one electrode provided on the subject;

b) determining, using the electrode identifier, an electrode position indicative of the position of the at least one electrode on the subject; and

c) causing at least one impedance measurement to be performed using the electrode position.

156. A method according to claim 155, wherein the impedance measurement is performed using at least four electrodes, each having a respective identifier, and wherein the method includes, in the processing system:

a) determining an electrode identifier for each electrode;

b) determining, using each electrode identifier, an electrode position for each electrode; and

c) performing at least one impedance measurement using the electrode positions.

157. A method according to claim 156, wherein the method includes, in the processing system:

a) causing signals to be applied to at least two of the electrodes in accordance with the determined electrode positions; and

b) causing signals to be measured from at least two of the electrodes in accordance with the determined electrode positions.

158. A method according to claim 155, wherein the method includes, in the processing system, determining the electrode identifier for an electrode by selectively measuring the conductivity between one or more contacts provided on the electrode.

159. A method according to claim 155, wherein the processing system is coupled to a signal generator and a sensor, and wherein the method includes, in the processing system:

a) selectively interconnecting the signal generator and at least two electrode leads, to thereby allow signals to be applied to the subject; and

b) selectively interconnecting the sensor at least two electrode leads to thereby allow a signal to be measured from the subject.

160. A method according to claim 159, wherein the method includes, in the processing system controlling a multiplexer to thereby selectively interconnect the leads and at least one of the signal generator and the sensor.

161. A method according to claim 155, wherein the at least one electrode includes visual indicia indicative of the position of the at least one electrode on the subject.

162. Apparatus for performing impedance measurements on a subject, the apparatus including a processing system for:

a) determining an electrode identifier associated with at least one electrode provided on the subject;

b) determining, using the electrode identifier, an electrode position indicative of the position of the at least one electrode on the subject; and

c) causing at least one impedance measurement to be performed using the electrode position.

163. A method of performing impedance measurements on a subject, wherein the method includes, in a processing system:

a) causing a first signal to be applied to the subject;

b) determining at least one parameter relating to at least one second signal measured across the subject;

c) comparing the at least one parameter to at least one threshold; and

d) depending on the results of the comparison, selectively repeating steps (a) to (d) using a first signal having an increased magnitude.

164. A method according to claim 163, wherein the method includes, in the processing system:

a) determining an animal type of the subject; and

b) selecting the threshold in accordance with the animal type.

165. A method according to claim 163, wherein the threshold is indicative of at least one of:

a) a minimum second signal magnitude; and

b) a minimum signal to noise ratio for the second signal.

166. A method according to claim 163, wherein the method includes, in the processing system:

a) determining at least one parameter relating to the at least one first signal;

b) comparing the at least one parameter to at least one threshold; and

c) selectively terminating impedance measurements depending on the results of the comparison.

167. A method according to claim 166, wherein the threshold is indicative of a maximum first signal magnitude.

168. Apparatus for performing impedance measurements on a subject, wherein the apparatus includes a processing system for:

a) causing a first signal to be applied to the subject;

b) determining at least one parameter relating to at least one second signal measured across the subject;

c) comparing the at least one parameter to at least one threshold; and

d) depending on the results of the comparison, selectively repeating steps (a) to (d) using a first signal having an increased magnitude.

169. Apparatus according to claim 168, wherein the apparatus further includes a variable magnitude current supply.

170. A method of providing an electrode for use in impedance measurement procedures, the method including:

a) providing on a substrate;

i) a number of electrically conductive contact pads; and

ii) a corresponding number of electrically conductive tracks, each track extending from an edge of the substrate to a respective contact pad;

b) applying an insulating layer to the substrate, the insulating layer including a number of apertures, and being positioned to thereby overlay the tracks with at least a portion of each pad contact aligned with a respective aperture; and

c) providing an electrically conductive medium in the apertures.

171. A method according to claim 170, wherein the electrically conductive medium is formed from a conductive gel.

172. A method according to claim 171, wherein the conductive gel is silver/silver chloride gel.

173. A method according to claim 170, wherein the method includes, providing a covering layer on the insulating layer to thereby cover the electrically conductive medium.

174. A method according to claim 173, wherein the insulating layer has an adhesive surface that releasably engages the covering layer.

175. A method according to claim 170, wherein the substrate is an elongate substrate, and wherein the method includes aligning the pad contacts along the length of the substrate.

176. A method according to claim 170, wherein the method includes providing the tracks and contact pads using at least one of:

a) screen printing;

b) inkjet printing; and

c) vapour deposition.

177. A method according to claim 170, wherein the tracks and contact pads are formed from silver.

178. A method according to claim 170, wherein the method includes forming the substrate by:

a) overlaying a plastic polymer with a shielding material; and

b) covering the shielding material with an insulating material.

179. An electrode for use in impedance measurement procedures, the electrode including:

a) a substrate having provided thereon;

i) a number of electrically conductive contact pads; and

ii) a corresponding number of electrically conductive tracks, each track extending from an edge of the substrate to a respective contact pad;

b) an insulating layer provided on the substrate, the insulating layer including a number of apertures, and being positioned to thereby overlay the tracks with at least a portion of each pad contact aligned with a respective aperture; and

c) an electrically conductive medium provided in the apertures.

180. A method for use in diagnosing conditions in a subject, the method including, in a processing system:

a) determining an encoded value associated with at least one electrode lead; and

b) causing at least one impedance measurement to be performed using the encoded value.

181. A method for use in diagnosing conditions in a subject, the method including, in a processing system:

a) determining an electrode identifier associated with at least one electrode provided on the subject;

b) determining, using the electrode identifier, an electrode position indicative of the position of the at least one electrode on the subject; and

c) causing at least one impedance measurement to be performed using the electrode position.

182. A method for use in diagnosing conditions in a subject, the method including, in a processing system:

a) receiving configuration data, the configuration data being indicative of at least one feature;

b) determining, using the configuration data, instructions representing the at least one feature; and

c) causing the measuring device to perform, using the instructions, at least one of;

i) impedance measurements; and

ii) analysis of impedance measurements.

183. A method for use in diagnosing conditions in a subject, the method including, in a processing system:

a) determining configuration data required for a measuring device, the configuration data being indicative of at least one feature; and

b) causing the configuration data to be received by a processing system in the measuring device, the processing system being responsive to the configuration data to configure the measuring device to allow the at least one feature to be used.

184. A method for use in diagnosing conditions in a subject, the method including, in a processing system:

a) causing a first signal to be applied to the subject;

b) determining at least one parameter relating to at least one second signal measured across the subject;

c) comparing the at least one parameter to at least one threshold; and

d) depending on the results of the comparison, selectively repeating steps (a) to (d) using a first signal having an increased magnitude.

185. A method for configuring a processing system for use in impedance analysis of a subject, the method including, in a processing system:

a) receiving configuration data, the configuration data being indicative of at least one feature;

b) determining, using the configuration data, instructions representing the at least one feature; and

c) causing, at least in part using the instructions, at least one of;

i) impedance measurements to be performed; and

ii) analysis of impedance measurements.

186. A method according to claim 185, wherein the configuration data includes the instructions.

187. A method according to claim 185, wherein the method includes, in the processing system:

a) determining an indication of the at least one feature using the configuration data; and

b) determining the instructions using the indication of the at least one feature.

188. A method according to claim 185, wherein the method includes, in the processing system, decrypting the received configuration data.

189. A method according to claim 188, wherein the method includes, in the processing system:

a) determining a device identifier associated with the processing system;

b) determining, using the device identifier, a key; and

c) decrypting the received configuration data using the key.

190. A method according to claim 185, wherein the processing system includes first and second processing systems, and wherein the method includes:

a) in the first processing system, selecting the instructions using the configuration data; and

b) in the second processing system, generating the control signals using selected instructions.

191. A method according to claim 190, wherein the method includes, in the processing first system, at least one of:

a) transferring the instructions to the second processing system; and

b) causing the second processing system to access the instructions from a store.

192. A method according to claim 191, wherein the method includes, in the processing system, receiving the configuration data from at least one of a computer system and a communications network.

193. A method according to claim 185, wherein the method includes, in the processing system:

a) determining if a feature selected by a user is available;

b) if the feature is not available, determining if the user wishes to enable the feature; and

c) if the user wishes to enable the feature, causing configuration data to be received.

194. A method according to claim 193, wherein the method includes, in the processing system:

a) causing the user to provide a payment to a device provider; and

b) receiving the configuration data in response to payment.

195. Apparatus for configuring a processing system for use in impedance analysis of a subject, the apparatus including a processing system for:

a) receiving configuration data, the configuration data being indicative of at least one feature;

b) determining, using the configuration data, instructions representing the at least one feature; and

c) causing, at least in part using the instructions, at least one of;

i) impedance measurements to be performed; and

ii) analysis of impedance measurements.

196. Apparatus according to claim 195, wherein the processing system forms at least part of at least one of:

a) an end station; and

b) a measuring device.

197. A method for configuring a processing system for use in impedance analysis of a subject, the method including, in a computer system:

a) determining configuration data required for the processing system, the configuration data being indicative of at least one feature; and

b) causing the configuration data to be received by the processing system being responsive to the configuration data to cause, at least one of;

i) impedance measurements to be performed; and

ii) analysis of impedance measurements.

198. A method according to claim 197, wherein the method includes, in the computer system:

a) determining a device identifier, the device identifier being associated with the processing system to be configured; and

b) using the device identifier to at least one of;

i) transfer the configuration data to the processing system; and

ii) encrypt the configuration data.

199. A method according to claim 197, wherein the method includes, in the computer system, determining the configuration data is required in response to at least one of:

a) payment made by a user of the processing system; and

b) approval of the feature.

200. A method according to claim 199, wherein the method includes, in the computer system:

a) determining regulatory approval of the at least one feature in at least one region;

b) determining at least one processing system in the at least one region; and

c) configuring the at least one processing system.

201. Apparatus for configuring a processing system for use impedance analysis of a subject, the method including, in a computer system:

a) determining configuration data required for a processing system, the configuration data being indicative of at least one feature; and

b) causing the configuration data to be received by the processing system being responsive to the configuration data to cause, at least one of;

i) impedance measurements to be performed; and

ii) analysis of impedance measurements.