Gerard Cybulski

Ambulatory monitoring device for central hemodynamic and ECG signal recording on PCMCI flash memory cards

The new ambulatory monitoring, universal 4-channel recorder enabling simultaneous collection of ECG and central haemodynamics signals was constructed. The system is based on 80C552 family controller with built-in analogue to digital converters and 20 MB PCMCIA (type II) FLASH MEMORY CARD is used as a data storage. The communication with the system is performed via specialised keys and the small, built-in LCD. We design and constructed the miniaturised, tetrapolar, current impedance cardiography device with built-in one channel of ECG, which was applied as a detector of the central haemodynamics signals. The device enables the full disclosure of the collected data, which could be used in off-line, beat-to-beat evaluation of cardiac output, stroke volume, ejection time, pre-ejection period and heart rate.

Ambulatory Impedance Cardiography

In this chapter the idea of the impedance cardiography will be presented followed by a description of a central hemodynamics ambulatory monitoring system, available for both research and clinical applications. Basing on the REOMONITOR system, developed in my home institution, the essential parts of the most of the ambulatory systems will be presented. Then will be described other systems used in the cardiology and physiological researches. All of the presented in this chapter systems were verified using the clinically accepted reference methods—non-invasive (ultrasound), invasive or at least, compared against the stationary impedance device Minnesota 304B.

Effects of a brief Valsalva manoeuvre on hemodynamic response to strength exercises

Strength training is a recommended measure against loss of strength and muscle mass because of age‐ or illness‐induced inactivity. Strength exercises may impose heavy cardiovascular load by increasing heart rate and blood pressure. To increase strength efficiently, a heavy load has to be applied; this, however, leads to a spontaneous Valsalva manoeuvre, which additionally raises blood pressure. Avoidance of this manoeuvre is recommended. If the additional rise in arterial blood pressure caused by Valsalva manoeuvre is smaller than intrathoracic or intracranial pressures during this manoeuvre, Valsalva manoeuvre may actually protect arteries located in the thorax and in the brain by diminishing transmural pressure acting across these vessels. Effect of controlled breathing or brief Valsalva manoeuvre on arterial pressure at rest and during knee extension against 15‐repetition maximum resistance was evaluated. In 12 healthy young men blood pressure was measured continuously and non‐invasively, knee angle, speed of respiratory air or mouth pressure (MP) were continuously registered. Each combination of respiratory and exercise manoeuvres was repeated six times, for every of last three repetitions peak and trough systolic and diastolic pressure were determined. Strength exercises elevated peak pressures more than trough pressures, systolic more than diastolic. Valsalva manoeuvre increased only peak systolic and peak diastolic pressure. This increase was in average lesser than MP, thus rendering an argument in favour of protective role of brief Valsalva manoeuvre because of decline in transmural pressure acting on thoracic and possibly cerebral arteries. However, there was strong individual variability, and in few instances, arterial pressure increased because of brief Valsalva manoeuvre more than MP; thus in some subjects, the manoeuvre might enhance transmural pressure acting on thorax arteries.

Application of impedance cardiography ambulatory monitoring system for analysis of central hemodynamics in healthy man and arrhythmia patients

The authors constructed the ambulatory monitoring, 4-channel recorder enabling simultaneous collection of ECG and ICG signals from a built-in miniaturised ICG device on 20 MB PCMCIA Flash Memory Card. The system allows for off-line, beat-to-beat automatic evaluation of cardiac output, stroke volume, ejection time, pre-ejection period and heart rate. The system was checked in more than 40 healthy subjects in ambulatory conditions and in 10 patients showing the hemodynamic effects of arrhythmia. The patients of ICG signal during atrial fibrillation, supraventricular and ventricular ectopy were recorded. The device could record signals with acceptable quality during sleep time, static and moderate dynamic exercise on cycloergometer, tilt test and Valsalva manoeuvre. The system has been continuously testing and improving.

Impedance pneumography: Is it possible?

The main purpose of this study was to describe the technique of impedance pneumography, the noninvasive method of quantitative, long lasting examination of respiratory system. In this paper there were presented physical foundations of the method, the measurement equipment and the different approaches to the measurement procedures. Also, various types and configurations of the electrodes were shown. The validation studies of impedance pneumography using clinically accepted reference the method were described, too. Finally, there were presented some proposals for future development of the technique.

Verification of the Respiratory Parameters Derived from Impedance Pneumography during Normal and Deep Breathing in Three Body Postures

We designed a small, battery-powered impedance pneumograph intended for holter monitoring of respiratory activity. Volume-related signal from impedance pneumo-graphy (IP) and airflow signal from reference method, pneumotachometry (PNT), were registered. First derivate of IP with PNT and IP with integral of PNT signals were compared in order to calculate slope values of linear regression. The effect of respiratory rate, depths of breathing, body posture, sex and body mass index (BMI) on slope values and coefficients of determination (R2) was determined. The measurements were conducted on a group of young volunteers without any respiratory diseases. An electrode configuration known for its good linearity between impedance and volume signals was chosen. Average R2 between IP signal and integral of PNT signal was 98.05%, and between first derivative of IP signal and PNT signal – 95.75%. It was demonstrated that the slope values were individually different and affected mostly by body posture.

Computer Program for Automatic Identification of Artifacts in Impedance Cardiography Signals Recorded during Ambulatory Hemodynamic Monitoring

The aim of this work was to design and verify a computer program which could detect artifacts in impedance cardiography (ICG) signals. It contains a procedure for creating a pattern of one typical cycle of the ICG trace and enabling the classification of each heart evolution as either a valid one or an artifact. It proposed an index characterizing the shape of the ICG signal pattern. The user can significantly influence the classification process by modifying the initial parameters of the patterns. The program automatically detects the characteristic points in the electrocardiographic (ECG) and ICG signals (dZ/dt) necessary for calculation of hemodynamic parameters and allows the user to browse previously recorded data. The program calculates basic cardiac hemodynamic parameters: heart rate (HR), pre-ejection period (PEP), left ventricular ejection time (ET), stroke volume (SV), cardiac output (CO) and other derivative ones, basing on previously classified data. We described the program structure and the operation of its main functions. The application is written in C++ using the Qt graphic library. It is flexible and can be modified or extended to suit the user’s needs. The analysis’ findings (based on on example data) are also presented.

Design and construction of the Artificial Patient module for testing bioimpedance measuring devices

The purpose of this study was to describe the design of the electronic module for testing bioimpedance measuring devices, for example impedance cardiographs or impedance pneumographs. Artificial Patient was conceived as an electronic equivalent of the impedance of skin-electrode interface and the impedance between electrodes - measured one. Different approaches in imitating a resistance of skin and an impedance of electrode-skin connection were presented. The module was adapted for frequently applied tetrapolar electrode configuration. Therefore the design do not enclose the elements simulating impedance between skin and receiver electrodes due to negligible effect of this impedance on the current flow through the receiver. The Artificial Patient enables testing either application generators, or receiver parts, particularly the level of noise and distortions of the signal. Use of digitally controlled potentiometer allows simulating different tissue resistances changes such as constant values, very-low-frequency and low-frequency changes corresponding to those caused by breathing or heart activity. Also it allows distorting signals in order to test algorithms of artifacts attenuation.

Identification of the Sources of Artefacts in the Holter-Type Impedance Cardiography Recordings

The evaluation of the rate of artefacts during ambulatory impedance cardiography monitoring is one of the fundamental question regarding the applicability of that method. It is also important to know which type of the patient movements create the noisiest recordings. With the aim to evaluate these uncertainties 14 healthy males (23-28 years) underwent examination (using ReoMonitor) in supine position, in moving during supine position, sitting, reading when sitting, walking and walking on stairs. Each of the part of the protocol lasted 3 minutes. The ratio of artefact free cycles to the total number of cycles was calculated for each evolution. It was averaged for each 60 seconds. For this ratio the parameters of descriptive statistics were calculated for the entire group of subjects. The maximum rate of artefacts free cycles was 1.0 and the minimal ratio was 0.25. The average ratio for all manoeuvres was 0.84±0.13. The data shown that the rate of artefacts is not very high and the system might be used to collect signals in a laboratory and in the field for monitoring changes in cardiovascular parameters.

Improvement of Body Posture Changes Detection During Ambulatory Respiratory Measurements Using Impedance Pneumography Signals

Impedance pneumography could be used for measuring respiratory parameters quantitatively in ambulatory conditions. It was noted that body posture affects the calibration coefficient connecting the measured impedance values and their first derivatives with volume and flow reference signals. Standard techniques for automatic detection of body posture and activity usually require additional motion sensors. However, in terms of the measurement comfort, less number of sensors is needed. Single sensor mounted on the chest provides good results, however its accuracy decreases during frequent changes of body posture. The aim of this study was to assess the possibility to detect body posture changes using the impedance signal itself, without any other devices or the active cooperation of the person being studied and prospectively improving the body posture change detection method using single motion sensor (e.g. 3D accelerometer). Fifteen healthy students (11 males) performed two body posture changes - get-ups and stand-ups. Six classification techniques were checked for prediction accuracy. It was found that artificial neural networks provided the best overall accuracy (90%).