Impedance cardiography (ICG) is a popular bioimpedance application used for the non-invasive evaluation of the left ventricular stroke volume and contractility. It implies the correct determination of ejection start and end points and the amplitudes of certain peaks in a differentiated impedance cardiogram. An accurate identification of ejection onset by ICG is often problematic, especially in cardiologic patients, due to the peculiar character of the waveforms. A simple theoretical model was employed to test the consequences of the hypothesis that two major processes can contribute to the formation of an impedance systolic wave: (1) the pre-ejection changes in heart geometry and the surrounding vessels produced by ventricular contraction during the isovolumic phase, and (2) the expansion of aorta and adjacent arteries during the ejection per se. The former process initiates the pre-ejection wave while the latter triggers the ejection wave, both of which contribute to the impedance pulse waves associated with the heartbeats. A new two-bell model predicts a potential mechanism responsible for the abnormal shapes of ICG derivative dZ/dt due to the presence of the pre-ejection waves and explains the related errors in systolic time intervals and amplitude parameters derived from such ICG waveforms. It also advances an alternative viewpoint on the nature of the dZ/dt B-point notch. An appropriate decomposition method opens a promising way to avoid the masking effects of these waves and to correctly determine the onset of ejection as well as the corresponding peak amplitudes from the 'pathologically shaped' ICG signals.
To study the features of ionic conductance system in termination of sensory units the responses of feline cutaneous A-β mechano-sensitive and C-fiber mechano-heat-sensitive (CMH) units to mechanical and heat stimuli were recorded in intact skin and under the action of subcutaneously applied tetrodotoxin (TTX). Both mechanical and thermal sensitivity of CMH units were not inhibited by 30 µM and in some units by 300 µM TTX, while the responses of A-β units to mechanical stimulation was eliminated by 3 µM TTX. Taking into account the data on low-frequency use-dependent inhibition of CMH unit termination by amine local anesthetics, the availability of TTX-resistant sodium channels in the somatic membrane of C-neurons liable to low-frequency use-dependent inhibition and the slow inactivation of these channels which corresponds to the requirements of mathematical simulation of spike initiation in C-fibers, our results are thought to indicate the presence of TTX-resistant sodium channels in the regenerative region of cutaneous afferent C-fibers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.