![]() ![]() The conventional cardiovascular physiology terms for the hemodynamic modulators are preload, contractility and afterload. However, a patient who is hypovolemic can exhibit the same normal level of EPC if given positive inotropes, and a patient who is volume overloaded (hypervolemic) can also have normal level of EPC if given negative inotropes A patient, who is normovolemic and normoinotropic, exhibits normal level of Ejection Phase Contractility (EPC). SI variability and MAP variability are accomplished through activity of hemodynamic modulators.įig.5: The Frank-Starling Law and Inotropy: Three Frank-Starling curves shown for normoinotropy, hyperinotropy and hypoinotropy. Digestive disorders, male impotence, tiredness, sleepwalking, environmental temperature intolerance, are classic examples of a low-flow-state, resulting in reduced blood flow. In a hemodynamically compromised person, when the system is unable to satisfy increased oxygen demand, the blood flow to organs lower on the oxygen delivery priority list is reduced and these organs may, eventually, fail. In a healthy person, the cardiovascular system always increases blood flow in response to increased oxygen demand. The task of the healthy cardiovascular system is to provide adequate perfusion to all organs and to maintain a dynamic equilibrium between oxygen demand and oxygen delivery. The primary function of the cardiovascular system is transport of oxygen: blood is the vehicle, oxygen is the cargo. There is clear relationship between these blood flow parameters:ĬO = (SV × HR )/1000 Systemic (global) blood flow parameters are (a) the blood flow per heartbeat, the Stroke Volume, SV, and (b) the blood flow per minute, the Cardiac Output, CO. Their instantaneous values may be used in research in clinical practice, their mean values, MAP and SV, are adequate. The relationship between the instantaneous values of aortic blood pressure and blood flow through the aortic valve over one heartbeat interval and their mean values are depicted in Fig.1. ICG uses the baseline and changes in impedance to measure and calculate hemodynamic parametersįig.1: Aortic blood pressure and aortic blood flow over one heartbeat interval: S = Systolic blood pressure D = Diastolic blood pressure MAP = Mean Arterial Pressure SV = Stroke Volume DN = dicrotic notch (aortic valve closure).ICG attributes the changes in impedance to (a) the volumetric expansion of the aorta (this is the main difference between ICG and electrical cardiometry) and (b) to the blood velocity-caused alignment of erythrocytes as a function of blood velocity.ICG measures the corresponding change in impedance and its timing.With each heartbeat, blood volume and velocity in the aorta change.ICG measures the baseline impedance (resistance) to this current.The inside pairs, placed at the anatomic landmarks delineating thorax, sense the impedance signals and the ECG signal.Current seeks path of least resistance: the blood filled aorta (the systolic phase signal) and both vena cava superior and inferior (the diastolic phase signal, mostly related to respiration).High frequency, low magnitude current is transmitted through the chest in a direction parallel with the spine from the set of outside pairs.Four pairs of electrodes are placed at the neck and the diaphragm level, delineating the thorax.With ICG, the placement of four dual disposable sensors on the neck and chest are used to transmit and detect electrical and impedance changes in the thorax, which are used to measure and calculate cardiodynamic parameters. ![]() A comprehensive list of references is available at ICG Publications. Subsequently, the recommendations of Miller and Horvath were confirmed by a standards group in 1990. The use of impedance cardiography in psychophysiological research was pioneered by the publication of an article by Miller and Horvath in 1978. NASA helped develop the technology in the 1960s. Impedance cardiography (ICG), also referred to as electrical impedance plethysmography (EIP) or Thoracic Electrical Bioimpedance (TEB) has been researched since the 1940s. The sensing electrodes also detect the ECG signal, which is used as a timing clock of the system. Impedance cardiography (ICG) is a non-invasive technology measuring total electrical conductivity of the thorax and its changes in time to process continuously a number of cardiodynamic parameters, such as stroke volume (SV), heart rate (HR), cardiac output (CO), ventricular ejection time (VET), pre-ejection period and used to detect the impedance changes caused by a high-frequency, low magnitude current flowing through the thorax between additional two pairs of electrodes located outside of the measured segment. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |