Harmonic analysis of nerve impedance in situ

A novel technique to assess electric activity of the whole nerve in situ is advanced based on harmonic analysis of impedance microvariations of femoral nerve in narcotized rats recorded with extracellular electrodes. The amplitude spectrum of nerve bioimpedance (Z-spectrum) made it possible to determine the level of neural asynchronous activity in the frequency band of 20–600 Hz with amplitude resolution of 1% and to reveal the rhythmic activity at Mayer (0.1 Hz) and respiration frequencies with amplitude resolution of 0.1%. Systemic administration of atropine used to shift the sympathovagal balance in favor of sympathetic system increased both rhythmic and unrhythmic (asynchronous) neural activity. The study demonstrated that harmonic analysis of nerve bioimpedance is a novel and potent tool to assess neural activity in the frequency domain.     

Regional lung perfusion estimated by electrical impedance tomography in a piglet model of lung collapse

The assessment of the regional match between alveolar ventilation and perfusion in critically ill patients requires simultaneous measurements of both parameters. Ideally, assessment of lung perfusion should be performed in real-time with an imaging technology that provides, through fast acquisition of sequential images, information about the regional dynamics or regional kinetics of an appropriate tracer. We present a novel electrical impedance tomography (EIT)-based method that quantitatively estimates regional lung perfusion based on first-pass kinetics of a bolus of hypertonic saline contrast. Pulmonary blood flow was measured in six piglets during control and unilateral or bilateral lung collapse conditions. The first-pass kinetics method showed good agreement with the estimates obtained by single-photon-emission computerized tomography (SPECT). The mean difference (SPECT minus EIT) between fractional blood flow to lung areas suffering atelectasis was -0.6%, with a SD of 2.9%. This method outperformed the estimates of lung perfusion based on impedance pulsatility. In conclusion, we describe a novel method based on EIT for estimating regional lung perfusion at the bedside. In both healthy and injured lung conditions, the distribution of pulmonary blood flow as assessed by EIT agreed well with the one obtained by SPECT. The method proposed in this study has the potential to contribute to a better understanding of the behavior of regional perfusion under different lung and therapeutic conditions.     

Effects of hypoxia on lung mechanics in the newborn cat

The present study was designed to investigate the effects of hypoxia on lung mechanics in the newborn cat and to determine if vagal efferent innervation to the airways is involved in the response. We studied 11 animals, aged 2-7 days, anesthetized with a mixture of chloralose-urethane administered intraperitoneally. A tracheal cannula was inserted just below the larynx and following paralysis (pancuronium bromide), mechanical ventilation was initiated. A pneumothorax was created by a midline thoracotomy and an end-expiratory load was applied to maintain functional residual capacity. Animals were placed in a flow plethysmograph from which measurements of transpulmonary pressure, flow, and volume, mean inspiratory resistance, and dynamic compliance of the lung were calculated. The experimental protocol consisted of a series of 8-min trials, each preceded by a controlled volume history. The hypoxia challenge was composed of 1 min of ventilation with 40% O2, followed by 5 min exposure to 10% O2 and 2 min of recovery. In the majority of animals (7 out of 11), hypoxia had no effect on lung mechanics compared with control trials. Four animals responded to hypoxia with an increase in resistance and a decrease in compliance. Resistance remained elevated throughout the hypoxia with an average maximal increase of 47.2 +/- 22.2% (SD). Dynamic compliance was significantly decreased at the 2nd, 3rd, and 4th min only of hypoxia. Bilateral vagotomy abolished the response in the four animals and hypoxia had no effect on mechanics postvagotomy. Our data suggest that in most cases changes in lung mechanics do not play a causal role in the biphasic ventilatory response to hypoxia seen in the newborn.     

Metabolism of prostaglandin endoperoxide by microsomes from cat lung

It has been reported that the prostaglandin (PG) precursor, arachidonic acid, produces divergent hemodynamic responses in the feline pulmonary vascular bed. However, the pattern of arachidonic acid products formed in the lung of this species is unknown. In order to determine the type and activity of terminal enzymes in the lung, prostaglandin biosynthesis by microsomes from cat lung was studied using the prostaglandin endoperoxide, PGH2, as a substrate. The major products of incubations of PGH2 with microsomes were thromboxane (TX) B2 (the major metabolite of TXA2), 6-keto-PGF1 alpha (the breakdown product of PGI2) and 12L-hydroxy-5,8,10-heptadecatrienoic acid (HHT). Formation of TXB2 was markedly reduced by imidazole. Tranylcypromine decreased the formation of TXB2 and HHT and inhibited the formation of 6-keto-PGF1 alpha. At low PGH2 concentrations, equal production of TXB2 and 6-keto-PGF1 alpha was observed. However, as PGH2 concentration increased, 6-keto-PGF1 alpha production approached early saturation while TXB2 production increased in a linear fashion. These results suggest that enzymatic formation of TXA2 and PGI2 is a function of substrate availability in the lung. These findings provide a possible explanation for the divergent hemodynamic responses to arachidonic acid infusions at high and low concentrations in the feline pulmonary vascular bed.     

The American lung fluke, Paragonimus kellicotti, in a cat model

Twenty-four specific-pathogen-free domestic cats were infected orally with from 2 to 30 Paragonimus kellicotti metacercariae and followed for 2-61 wk. Following infection by metacercarial cysts dissected from crayfish, the lungs of the cats undergo changes of intense eosinophilic pneumonia, granulomatous pneumonitis, squamous epithelial-lined cyst formation of bronchogenic origin, and finally (late in infection) partial resolution of the host response. Bronchograms and mechanical probing illustrate the patency of cyst communication with bronchi. The modulation of the host response and adaptive changes in the host lung tissue are seen late in infection and have previously been unreported or underemphasized. These adaptive responses may account for the number of asymptomatic cases accidentally found in veterinary patients and the difficulty in prompt and proper diagnosis in human cases.     

Electrical impedance analysis of single murine teratocarcinoma cells

Single murine teratocarcinoma cells were analysed by a new flow instrument that simultaneously measures the volume and high-frequency electrical impedance of individual cells at rates of several hundred cells per second. Differentiated cells were found to have larger high-frequency impedance than undifferentiated stem cells of the same size.     

Emergent behavior of regional heterogeneity in the lung and its effects on respiratory impedance

The ability to maintain adequate gas exchange depends on the relatively homogeneous distribution of inhaled gas throughout the lung. Structural alterations associated with many respiratory diseases may significantly depress this function during tidal breathing. These alterations frequently occur in a heterogeneous manner due to complex, emergent interactions among the many constitutive elements of the airways and parenchyma, resulting in unique signature changes in the mechanical impedance spectrum of the lungs and total respiratory system as measured by forced oscillations techniques (FOT). When such impedance spectra are characterized by appropriate inverse models, one may obtain functional insight into derangements in global respiratory mechanics. In this review, we provide an overview of the impact of structural heterogeneity with respect to dynamic lung function. Recent studies linking functional impedance measurements to the structural heterogeneity observed in acute lung injury, asthma, and chronic obstructive pulmonary disease are highlighted, as well as current approaches for the modeling and interpretation of impedance. Finally, we discuss the potential diagnostic role of FOT in the context of therapeutic interventions.     

Immunofluorescent analysis of meiotic recombination in the domestic cat

The paper presents the analysis of the frequency, density, and distribution of recombination sites in the male meiosis of the domestic cat (Felis silvestris catus). The study was carried out using immunofluorescent staining of synaptonemal complex (SC) proteins, centromeric proteins and mismatch repair protein MLH1, a reliable marker of crossingover sites. We mapped 2633 sites of crossing over in 1098 individual autosomes. Based on these data, we estimated the total length of the genetic map of the domestic cat to be 2176 centimorgans. Positive correlation between the length of SC and the number of recombination sites common for mammalians was also found in the domestic cat. It was shown that this species was characterized by the highest density of recombination and the lowest interference in mammals.     

Calcitonin and calcitonin gene-related peptide immunoreactivity and colocalization in newborn cat lung.

Calcitonin (CT) and calcitonin gene-related peptide (CGRP) are generated by alternate RNA processing from alpha and beta CT/CGRP genes. In this report, an immunocytochemical investigation was undertaken on the occurrence and distribution of immunoreactive CT as well as its colocalization with CGRP in newborn cat bronchopulmonary endocrine cells. A widespread distribution of solitary endocrine cells and neuroepithelial bodies immunostained for CT was recorded within the lung. In all animals studied, CT immunoreactivity represents a subpopulation of CGRP positive cells, while the intrapulmonary nerve fibers contain only CGRP. To the best of our knowledge, this is the first time that CT and its colocalization with CGRP have been demonstrated immunocytochemically in the cat lung. Our results indicate, that different molecular processing of both CT/CGRP genes may be represented by different patterns in the cellular immunoreactivity of the synthetized peptides.     

Microcirculation and oxidative stress

The microcirculation is a complex and integrated system, transporting oxygen and nutrients to the cells. The key component of this system is the endothelium, contributing to the local balance between pro and anti-inflammatory mediators, hemostatic balance, as well as vascular permeability and cell proliferation. A constant shear stress maintains vascular endothelium homeostasis while perturbed shear stress leads to changes in secretion of vasodilator and vasoconstrictor agents. Increased oxidative stress is a major pathogenetic mechanism of endothelial dysfunction by decreasing NO bioavailability, promoting inflammation and participating in activation of intracellular signals cascade, so influencing ion channels activation, signal transduction pathways, cytoskeleton remodelling, intercellular communication and ultimately gene expression. Targeting the microvascular inflammation and oxidative stress is a fascinating approach for novel therapies in order to decrease morbidity and mortality of chronic and acute diseases.     

Frequency-dependent membrane impedance inChara corallina estimated by Fourier analysis

Summary The white noise method of measuring membrane impedance has been applied to internodal cells ofChara corallina. Fourier analysis of a white noise transmembrane current signal and the voltage response has been used to obtain the frequency-dependent impedance of the in-series combination of the plasmalemma and tonoplast membranes. The results are similar to those of other workers who have measured membrane impedances by different techniques. At very low frequencies the equivalent capacitance of the membrane treated as an RC-circuit becomes negative, indicating a pseudoinductive effect.Membrane impedance has been measured over a range of pH values from pH 5.2 to pH 11; impedance magnitude reaches a maximum at pH 7. At interesting effect of fusicoccin at pH 11 has been observed, in which a decrease in membrane conductance occurs simultaneously with a small hyperpolarization of membrane PD.     

Serial changes in nasal potential difference and lung electrical impedance tomography at high altitude.

Recent work suggests that treatment with inhaled beta(2)-agonists reduces the incidence of high-altitude pulmonary edema in susceptible subjects by increasing respiratory epithelial sodium transport. We estimated respiratory epithelial ion transport by transepithelial nasal potential difference (NPD) measurements in 20 normal male subjects before, during, and after a stay at 3,800 m. NPD hyperpolarized on ascent to 3,800 m (P < 0.05), but the change in potential difference with superperfusion of amiloride or isoprenaline was unaffected. Vital capacity (VC) fell on ascent to 3,800 m (P < 0.05), as did the normalized change in electrical impedance (NCI) measured over the right lung parenchyma (P < 0.05) suggestive of an increase in extravascular lung water. Echo-Doppler-estimated pulmonary artery pressure increases were insufficient to cause clinical pulmonary edema. There was a positive correlation between VC and NCI (R(2) = 0.633) and between NPD and both VC and NCI (R(2) = 0.267 and 0.418). These changes suggest that altered respiratory epithelial ion transport might play a role in the development of subclinical pulmonary edema at high altitude in normal subjects.     

An analysis of the sources of musculoskeletal system impedance

When antagonistic muscles co-contract, the impedance of musculoskeletal systems to applied loads is known to increase. In this paper a physiologically-based, higher-order, nonlinear antagonistic muscle-joint model is utilized to clarify the sources of impedance modulation during a variety of tasks, ranging from resisting transient loads to holding steady loads to making fast movements in unpredictable surroundings. It is shown that impedance modulation occurs automatically as a function of the specific operating ranges utilized during a given task by each of four different muscle-joint mechanical relations. The relative contribution of each relation depends on the type of task, with impedance during quasi-static conditions sensitive to muscle tension-length and sometimes joint parallel elastic properties and during dynamic tasks dominated by the series element and muscle force-velocity properties. Elimination of any of these causes a decrease in built-in biomechanical capabilities. These findings raise questions concerning past theories on stiffness-impedance modulation which appear to underestimate the role of inherent biomechanical properties.     

Statistical analysis of unit activity in the cat motor cortex

Activity of 366 neurons in the motor area of the biceps brachii muscle was studied in chronic experiments on cats during an instrumental placing response. Of these cells, 59 received afferentation from the skin, joints, or deep structures of the limb participating in movement. Of 160 neurons which changed their discharge during the placing response, 52 (32.5%) had a peripheral input. Three types of motor cortical neurons are described: I) changing their discharge frequency before movement began, II) after movement began, and III) before and during movement. Positive correlation (r=0.3926) was found between the presence of a peripheral input for the neurons studied and changes in discharge frequency during the placing response. Correlation between the presence of a concrete input in the neurons and the type to which they belonged was studied.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 11, No. 3, pp. 201–207, May–June, 1979.