B. Bo Sramek, Ph.D.
(For explanation of terms new to you, go to Glossary of Terms)
A new generation of HSI-patented TEB technology, described below, is an accepted, main stream
technology for noninvasive, continuous measurement of global blood flow (Cardiac
Index, CI - the global blood flow per minute, and Stroke Index, SI - the global blood
flow per beat), respiratory and a host of cardiodynamic parameters.
HSI's proprietary TEB is utilized in the TEBCO® Module (Thoracic Electrical Bioimpedance Cardiac Output), which is integrated into the HOTMAN® System's hardware. TEBCO® measures Cardiac Index, CI, noninvasively, with the same clinical accuracy as the invasive thermodilution catheter, however, without its cost, risk, need for sterile environment and a skilled clinician. TEBCO® also measures other cardiodynamic parameters, such as Stroke Index, SI; Heart Rate, HR; Respiratory Rate, RR; Ventricular Ejection Time, VET; Pre-Ejection Period, PEP; Ejection Phase Contractility Index, EPCI; Inotropic State Index, ISI. TEBCO's TEB measurement current is 400-times lower than the measurement current of any competitive TEB/ICG product.
TEBCO® Module has the FDA 510(k) marketing clearance
TEBCO® is the blood flow measurement component of the HEMO SAPIENS' HOTMAN® System.
Thoracic Electrical Bioimpedance (TEB), with a symbol Z [Ω], is an electrical resistance of the thorax to a high-frequency, very-low magnitude TEB measurement current. TEB utilizes a patient's thorax as an impedance transducer. The patient is connected to TEBCO® via a patient cable attached to eight solid-gel, disposable electrodes (see Fig.1 below). The TEB measurement current is passed through the thorax in a direction parallel with the spine between a pair of electrodes placed on upper neck and a pair of electrodes placed on upper abdomen. On its way through the thorax, the TEB measurement current seeks the shortest and the most conductive pathway. As a result, the majority of the TEB measurement current flows through the thoracic aorta and vena cava superior and inferior - their black outlines are shown in Fig.1 below. The TEB measurement current produces a high-frequency voltage across the impedance of the thorax, directly proportional to the TEB. This induced high-frequency voltage is sensed by two other pairs of electrodes placed inside the current path, i.e., at the beginning of the thorax (the line of the root of the neck) and the end of the thorax (the level of diaphragm - the xiphoid process level). These four sensing electrodes also detect four different vectors of the ECG signal. The Heart Rate, HR, is derived from the R-R intervals of the ECG signal. Due to anatomical shape of the thorax, a preferential placement for all eight electrodes is along the frontal plane - the thoracic widest dimension.
The TEB level (the Base Impedance, Zo,
is indirectly proportional to total content of thoracic fluids, however,
the value of Zo cannot identify individual conductance contributions of the intravascular, intra-alveolar
and interstitial compartements. For clinical reasons, instead of Zo,
TEBCO® measures and displays its inverted value, i.e., the Thoracic
Fluid Conductivity, TFC = 1/ Zo,
which is then directly proportional to the thoracic fluids content.
The TEB variations and changes (ΔZ) are produced by:
slow changes of fluid levels in all thoracic compartments - a result of postural changes or, for instance, pulmonary edema,
tidal changes of venous and pulmonary blood volume caused by respiration (from these changes TEBCO® measures and displays the Respiratory Rate, RR),
volumetric (plethysmographic) and velocity (alignment of planes of erythrocytes as a function of blood velocity) changes of aortic blood produced by the heart's pumping (cardiodynamic) activity.
The rate of cardiovascular TEB changes over time (dZ/dt) [i.e., the first derivative of ΔZ] is an image of the aortic blood flow. Its maximum value, [(dZ/dt)max], is proportional to the aortic blood peak flow (please note the difference between TEB measured peak blood flow and peak velocity measured by Doppler technologies). The aortic blood peak flow is a mirror image of ejection phase myocardial contractility. This parameter's value is influenced both by the Frank-Starling mechanism (change in intravascular volume) and, pharmacologically, by inotropes. TEBCO® processes this parameter normalized by TFC and displays it as the Ejection Phase Contractility Index, EPCI:
The maximum rate of the second derivative of Z, [(d2Z/dt2)max], is, therefore, an image of the maximum acceleration of aortic blood flow - a true measure of inotropic state, essentially independent of preload and afterload (a detailed discussion and physiologic explanation of these phenomena can be found in the Chapter 7, Hemodynamics of the cardiovascular system, in the textbook Biomechanics of the Cardiovascular System and in the textbook Systemic Hemodynamics and Hemodynamic Management). TEBCO® measures the level of inotropic state through another normalized parameter - the Inotropic State Index, ISI:
The timing landmarks on ECG (specifically the Q-time of the QRS complex) and on
the dZ/dt signal enable measurement of the Systolic Time Intervals, namely
the Ventricular Ejection Time, VET, and the Pre-Ejection Period, PEP.
The TEBCO®-measured parameters, i.e., the TFC, VET, EPCI, in conjunction with the Volume of Electrically Participating Tissues, VEPT (a function of patient's gender, height and weight), are used to calculate the Stroke Volume, SV, according to Sramek's Equation:
Note 1: This equation reflects the physiologic basis of SV determination: (a) SV is directly proportional to the physical size of a patient (i.e., to VEPT - body habitus scaling constant), (b) SV is directly proportional to duration of delivery of blood into the aorta (i.e., to VET), and (c) SV is directly proportional to the peak aortic blood flow (i.e., to EPCI).
Note 2: This equation corrected most of the deficiencies associated with the original TEB Kubicek's equation, used in the '70s.
When SV is normalized by the Body Surface Area, BSA, the hemodynamically-significant blood flow parameter called the Stroke Index, SI, is calculated as
BSA [m2] is a complex function of a patient's height [cm] and weight [kg], calculated by TEBCO® from the DuBois & DuBois formula:
BSA = W0.425 x H0.725 x 0.007184
The perfusion significant blood flow - the Cardiac Index, CI, is then calculated as
Click here for the List of scientific papers related to new TEB utilizing the Sramek's equation.