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The AIM-8 Monitor and AIM_HOST System

For
Ambulatory Bioelectric Impedance Monitoring for Assessing Cardiac Performance
by
Bio-Impedance Technology,Inc.
88 VilCom Center, Suite 165
Chapel Hill, NC 27514

Basic AIM-8 Description and Characteristics:

In some medical and clinical research applications involving cardiovascular data measurement, it is important to obtain information regarding an individual's cardiac performance by using a reliable, noninvasive method or technique. It is even more useful if the noninvasive method can be employed on ambulatory research subjects and patients, since it can reflect the status of their cardiac performance in a more normal environment outside the research lab or clinic. The AIM-8 device has been developed to achieve this goal.

The AIM-8 Ambulatory Impedance Monitor

The AIM-8 (Ambulatory Impedance Monitor) is a microcomputer-based wearable bioelectric impedance monitor and signal processing system designed for the relatively long-term monitoring of cardiovascular parameters from ambulatory patients. These parameters include Heart Rate, Stroke Volume, Cardiac Output, Systolic Time Intervals (PEP, LVET, & TEP), Contractility, Basal Impedance (Zo), dZ/dt max, Patient Activity, etc. The device is wearable, since it is intended for ambulatory applications, and it is totally compatible with an existing "COP_WIN 5.0" laboratory Cardiac Output Program (COP) for Windows that is used for in-lab cardiovascular data acquisition and analysis.

The primary purpose of the AIM-8 device is for collecting cardiovascular data from ambulatory individuals, for up to 24 hours or more, as they go about their normal daily routines. The patients can then return to the clinic or laboratory facility, and the acquired cardiovascular data can be uploaded into a PC with a Windows-based Host Program System (AIM_HOST), and stored as Data Files that are totally compatible with the new COP_WIN 5.0 software system. The subject's (patient's) impedance cardiography data can then be viewed, reanalyzed, edited, printed, and graphed. The AIM-8 system was primarily developed to extend the in-house "COP" system's capabilities into the ambulatory data collection environment. This permits medical research investigators to acquire more valuable cardiac performance information than would be possible in only a laboratory or clinic environment.

Inside and Outside view of an old style AIM monitor compared with a Credit Card

The AIM-8 monitoring device consists of a small (3" X 4" X 1.5") plastic enclosure that contains a small (credit card size) bioelectric impedance cardiograph (labeled the "WHIC8" for Wearable Hutcheson Impedance Cardiograph), a small (credit card size) microcomputer/data logger with sleep-wake capability, a body-activity sensor, a 9 volt battery, and an electrode assembly consisting of five electrodes.

The AIM-8 device also contains the computer software (firmware) that implements the following functions:

  • Controls the various WHIC8 modes of operation, including calibration, operation on either a manual basis or an automatic fixed time-interval basis, and operation under a blood pressure monitor's control.
  • Controls the displays, visual indicators, and audible alarms of the device.
  • Detects user inputs and controls.
  • Acquires and processes all analog signals from the WHIC8 impedance cardiograph.
  • Handles all timing for the system including real time, the timing of physiological waveforms and events (e.g. electrocardiogram R to R intervals), and data transfers.
  • Performs all signal averaging and digital signal processing tasks.
  • Handles the data analysis of the ensemble averaged waveforms and measured cardiac parameters.
  • Performs the automatic computation of the various cardiac indices for each measurement.
  • Manages the storage of ensemble averaged waveforms (Zo, dZ/dt, and ECG), along with the "Data Scan" information regarding each cardiac cycle that makes up the ensemble averages.
  • Stores all of the important measured parameters and the computed cardiac indices.
  • Handles the serial data communication between the IBM-Type PC host computer and the AIM-8monitor.

Some of the AIM-8 Features:

The AIM-8monitoring device is wearable for long periods of time (up to 24 hours, or more if necessary) in scientific research applications involving the assessment of cardiac performance from ambulatory human subjects. The device contains an Impedance Cardiograph that has been reduced to the size of a credit card. The internal computer, used for system control as well as data acquisition and analysis, is also a low-power, credit card size module. The entire AIM-8 device is powered from a standard (snap-connector type) 9-volt alkaline battery. It is important to note that the AIM-8 is capable of both data acquisition as well as the analysis of the acquired data. Other attempts at developing a wearable cardiac output monitoring device based upon impedance cardiography techniques has resulted in prototype systems that only acquire the data (at best), and require additional data processing and analysis by another computer system in order to determine he cardiac performance results. The AIM-8 determines this information as the data is collected. The device can acquire up to 200 Ensemble Averages including both Computed Indices as well as the Ensemble Averaged Waveforms. Since the device has a low-power sleep mode, consuming only 200 microamperes from the battery, it can acquire the cardiac data over appreciably long time-intervals as indicated above.The AIM-8 can also be used for in-lab scientific and clinical studies involving the acquisition of cardiovascular information in addition to the ambulatory applications. When used in conjunction with a Personal-Computer (PC) running the AIM_HOST 3.0 software (described below), the AIM-8 device provides a real-time Oscilloscope Display of the physiological signals produced by the subject. This capability lets the user know whether the electrodes are applied to the patient correctly, and whether the quality of the signals is acceptable for good data analysis. The AIM-8 contains both visible and audible indicators for indicating the operational status of the device to both the user and the subject (patient). The AIM-8 has the capability for automatic calibration for all signal parameters. When the device is connected to the AIM_HOST Computer, the user simply chooses the Calibrate Command Button, and the device instantly calibrates itself. In addition to monitoring the various cardiac indices associated with cardiac performance, the AIM-8 has the capability to monitor and acquire gross body activity, along with the time and data that each measurement is made.

HIC System

The AIM-8 device is also designed to operate in with any blood pressure (BP) monitor and BP cuff. This feature allows the AIM-8's measurements to be synchronized with the BP monitor so that the blood pressure values and cardiac performance parameters can be acquired in the same time frame, which in turn, can yield a measure of Total Peripheral Vascular Resistance. Other wearable impedance cardiography devices do not employ this synchronized blood pressure monitoring technique. The AIM-8 device also employs a five-electrode arrangement, consisting of a roving ECG + electrode in addition to the four Bioelectric Impedance electrodes. This arrangement permits greater ECG electrode placement flexibility, and enables the user (research investigator) to establish an electrode placement, independent of the impedance electrodes, that produces the "best" electrocardiogram signal for impedance cardiography applications.

The AIM-8 Ambulatory Impedance Monitor with the Five-Electrode Assembly

Additionally, the AIM-8 device is designed to analyze and process the acquired cardiac data in a format totally compatible with the COP_WIN 5.0 system for in-lab or in-clinic cardiac performance evaluation currently used by medical investigators working in the impedance cardiography field. This feature is important because it allows the ambulatory cardiac data to be collected and analyzed in exactly the same manner as the in-lab (in-clinic) cardiac data, resulting in a consistent and uniform analysis for both applications. It also allows the research investigator use the more sophisticated in-lab system (COP_WIN or COPWORKS) to view, edit, and analyze the ambulatory cardiac data collected by the wearable AIM-8 device.

The AIM-8 system either measures or derives the following cardiac indices:

  • Heart RateHR
  • Stroke VolumeSV
  • Cardiac OutputCO
  • Basal ImpedanceZo
  • Pre-Ejection PeriodPEP
  • Left Ventricular Ejection PeriodLVET
  • Cardiac ContractilityPEP/LVET
  • Heather IndexHI
  • Maximum Negative dZ/dtdZ/dt max
  • Gross Body ActivityAct
  • Date & Time of each measurement
  • Total Peripheral ResistanceTPR (when used with the AccuTracker II)

Potential Applications for the AIM-8 and AIM_HOST System:

  • The AIM-8 device can be used for assessing cardiac performance in ambulatory patient applications for clinical diagnosis purposes.
  • The AIM-8 system will be extremely useful for medical research studies involving the measurement of cardiac performance during both laboratory-based and ambulatory patient situations.
  • The AIM-8 device is also useful in cardiovascular research studies involving the measurement of systolic time intervals over a number of cardiac cycles.
  • When used in conjunction with a blood pressure monitor, the AIM-8 device is useful for the assessment of Total Peripheral Resistance (TPR).
  • The AIM-8 is useful for both clinical and laboratory applications involving real-time estimates of changes in a patient's cardiac output.
  • The AIM-8 is also useful for long-term assessment of cardiac performance changes in ambulatory patients.
  • The AIM-8 device can be used for both research and clinical applications involving the study of cardiac performance relative to gross body activity.
  • The AIM-8 would be useful in many blood pressure assessment applications by giving a more complete picture of the cardiovascular system's status relative to the blood pressure measures.
  • The AIM-8 device can also be used in Cardiovascular Biofeedback Applications when used in conjunction with (left connected to) the AIM_HOST 3.0 PC system.

The AIM_HOST 3.0 Host Software Package:

The AIM_HOST 3.0 Software System is a "Host Program" designed to permit easy and efficient communication with the Bio-Impedance Technology's Wearable Ambulatory Impedance Monitor (AIM) for assessing cardiac performance information during ambulatory conditions. The AIM-HOST system also allows the user to control nearly all of the AIM's operational functions. AIM-HOST is a Windows-based program that will operate properly on any of the Intel 486 or Pentium-based Personal Computers (PC's) running Windows 95, 98,ME or 2000. No additional hardware is required except a special Serial RS-232 communication cable which is provided with the AIM device, and which connects between the Host Computer's serial communication (COMM) port and the AIM device.

The AIM-HOST system is intended for medical research applications involving the use of AIM-8 devices to monitor cardiac function, using Impedance Cardiography techniques, by qualified and knowledgeable professional medical personnel. Thus, it is of vital importance that AIM-8 and AIM-HOST users familiarize themselves with the scientific literature on impedance cardiography, so they will be in a better position to understand the impedance cardiography methodology and the various measurement operational parameters involved with the techniques employed. This will also help the user to interpret the information generated by the AIM-8 device in a manner consistent with the strengths and limitations of bioelectric impedance cardiography. While the AIM-HOST system does not actually perform the impedance data measurements or generate the derived cardiac indices (the AIM-8 does this), it is necessary for the user to have a knowledge of how these measurements are made, and what operational parameters are necessary for correct data acquisition.

The primary purpose of the AIM-HOST system is to provide bi-directional communication with the AIM monitoring device for operational control, information display, data display, and troubleshooting purposes. Nearly all of the control operations are made with the host computer's mouse, thereby making all operations by the user very quick, easy, and efficient. Very little typing by the user is required. The Main (primary) Control Window of the AIM-HOST system contains a number of command and control buttons that are available to the user for sending operational commands to the AIM device. Some of these command buttons also invoke other special purpose Windows within the AIM-HOST program in addition to sending appropriate digital control signals to the AIM unit. The AIM-HOST system also receives operational and data control and status information from the AIM unit, and then responds accordingly. The AIM-HOST Main Control Window also contains a large interactive Display Window that useful user information transmitted by the AIM device. This information includes status information, data results, user prompts for certain operations, error information and conditions, operational procedures to follow, plus other useful information. Another purpose of AIM-HOST is to allow the user to easily setup the operational conditions of the AIM monitor before it is sent out with a subject or patient. The AIM-HOST also enables the user to quickly calibrate the AIM unit if and when this needs to be done. However, the AIM device is exceptionally good about maintaining its calibration over long periods of time, even for as much as a year. The AIM-HOST program also has yet another very important purpose. It serves as an oscilloscope to the AIM unit, allowing the user to view the real-time bioelectric impedance signals generated at the electrodes. This feature allows the user to quickly evaluate electrode connections and AIM operation and signal detection. It also helps to easily troubleshoot any AIM instrumentation problems. And finally, recovery of the AIM's accumulated data is a very important purpose of the AIM-HOST system. It checks the AIM unit to determine if there is any accumulated data, allows the user to transfer the data to the AIM-HOST system, and permits the storage of all of the accumulated AIM data into a compressed file on the HOST system's user-specified disk drive.

A Brief Description of the AIM_HOST Program:

The AIM-HOST program is comprised of three primary windows designed to either perform important control tasks, or to display important information. The control tasks include operational setup, data acquisition control, data manipulation, system operation, and mode control of the AIM device. The display of important information includes user instruction prompts, error messages, operational status conditions, calibration information, device setup parameters, and data results.

The Main Interactive Communication & Control Window:

The Main Interactive Communication Window is the primary AIM-HOST control and display window, which allows functional control of the AIM device, as well as the display of data and information transmitted by the AIM. This window contains numerous user-command buttons for the majority of the control functions required by the AIM unit. It also contains the communication port option buttons that permit easy selection of the communication port for use with the AIM unit. An interactive AIM-8 Display Screen is also contained in this window for the purpose of displaying information coming from the AIM device. This display screen also allows the user to type certain commands and instructions to the AIM device from the keyboard when necessary.

The AIM_HOST Main Communication & Control Screen.

The AIM Setup Window allows the user to specify all of the operational parameters and setup information for the AIM device. It also permits the user to download all of the specified setup information to the AIM at one time. The setup information includes such things as data acquisition timing information, ensemble average time duration, real time and date, and subject electrode distances. This window also allows the user to save the specified information as the default for the AIM-HOST system.

The AIM-HOST Setup Window for Specifying AIM Operational Parameters

The AIM-HOST Oscilloscope Window is used to display the real-time, analog Impedance and ECG signals that appear at the AIM-8's electrodes. This window essentially functions as a dual channel oscilloscope, displaying the ECG and Impedance signals in an oscilloscope format. The oscilloscope has several important uses. It allows the user to quickly determine if both the AIM-HOST system and the AIM-8 device are working properly. It also enables the user to determine if the AIM's electrodes are applied to the subject correctly, and if the bioelectric signal quality is adequate for proper operation. It can also be used for troubleshooting both the AIM unit and the AIM-HOST system if problems arise while using the AIM-HOST system.

Additional Software for AIM-8 Data Editing and Analysis:

In order to view, edit, and analyze the AIM-8 data, and to create printed reports and ASCII files of the data, one of two additional software packages is also required. COPWORKS 5.0 is a off-line Cardiac Output Program Workstation package for Windows that is designed to allow easy off-line editing, analysis, observation, and report generation of cardiac performance data (in "COP 5.0" format) acquired with the COP_WIN 5.0 laboratory-based acquisition system. Since the AIM device is designed to be totally compatible with the COP_WIN system, COPWORKS 5.0 for Windows also has the capability of handling the AIM data as well. Therefore, either COP_WIN 5.0 or COPWORKS 5.0 will work with the AIM-8 data files created by the AIM-HOST system. COPWORKS 5.0 is the standard analysis package that is shipped with the Complete Standard AIM-8 System. If the customer already has either the COP_WIN 5.0 or COPWORKS 5.0 software package, then the AIM8 System can be obtained without the COPWORKS 5.0 package at a reduced cost.

Minimum Computer System for the AIM-HOST System:

  • 486DX-based Personal Computer with a clock speed equal to or greater than 100 MHzWindows 95
  • 3.5" Floppy Drive
  • At least 16 MB RAM
  • At least 500 MB Hard Drive
  • At least a 1 MB Video Card
  • At least a 14" .28dp SVGA Video Monitor

Recommended Computer System for the AIM-HOST System:

  • At least a 200 MHz Pentium II Personal Computer
  • At least 32 MB System Memory
  • At least 1.2 GB Hard Drive
  • Windows 95 or 98
  • At least 2 MB Video Card
  • At least a 15" .28dp SVGA Video Monitor
  • 3.5" Floppy Drive

Pricing Information for the AIM-8 System

To Order Contact sales@microtronics-bit.com or telephone MicroTronics - BIT (919) 960-7799


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