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Theory of frequency response of mechanically driven cardiomyocytes.

ABSTRACT: We theoretically predict and compare with experiments, transitions from spontaneous beating to dynamical entrainment of cardiomyocytes induced by an oscillating, external mechanical probe. In accord with recent experiments, we predict the dynamical behavior as a function of the probe amplitude and frequency. The theory is based on a phenomenological model for a non-linear oscillator, motivated by acto-myosin contractility. The generic behavior is independent of the detailed, molecular origins of the dynamics and, consistent with experiment, we find three regimes: spontaneous beating with the natural frequency of the cell, entrained beating with the frequency of the probe, and a "bursting" regime where the two frequencies alternate in time. We quantitatively predict the properties of the "bursting" regime as a function of the amplitude and frequency of the probe. Furthermore, we examine the pacing process in the presence of weak noise and explain how this might relate to cardiomyocyte physiology.

SUBMITTER: Cohen O

PROVIDER: S-EPMC5797104 | biostudies-other | 2018 Feb

REPOSITORIES: biostudies-other

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Theory of frequency response of mechanically driven cardiomyocytes.

Cohen Ohad O Safran Samuel A SA

Scientific reports 20180202 1

We theoretically predict and compare with experiments, transitions from spontaneous beating to dynamical entrainment of cardiomyocytes induced by an oscillating, external mechanical probe. In accord with recent experiments, we predict the dynamical behavior as a function of the probe amplitude and frequency. The theory is based on a phenomenological model for a non-linear oscillator, motivated by acto-myosin contractility. The generic behavior is independent of the detailed, molecular origins of ...[more]

PMID: 29396531

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Project description:BackgroundDespite a supportive evidence base and a push to implement, the uptake of early rehabilitation in critical care has been inconsistent. The objective of this study was to explore barriers and facilitators to early rehabilitation for critically ill patients receiving invasive mechanical ventilation.MethodsUsing the Theoretical Domains Framework (TDF) of behavior change, we conducted semi-structured interviews exploring barriers and facilitators to early rehabilitation among four purposively sampled ICU clinician groups (nurses, rehabilitation professionals, respiratory therapists, and physicians). The TDF is a comprehensive framework of 14 "construct domains," synthesized from 33 theories of behavior that was developed to study determinants of behavior and to design interventions to improve evidence-based healthcare practice. A topic guide was developed and piloted based on the TDF and expert knowledge. Interviews were audio-recorded and transcribed verbatim. Transcripts were content analyzed by coding items into domains and then synthesized into more specific, over-arching themes or "beliefs." An expert consensus group used structured decision rules to classify beliefs as high, moderate, or low in importance.ResultsWe interviewed 40 stakeholders from the four clinician groups and identified 135 separate beliefs. Of these, 19 were classified as high, 40 as moderate, and 76 of low importance as barriers or facilitators. All beliefs classified as highly important fell within one of seven TDF domains: skills, social/professional role and identity, beliefs about capabilities, beliefs about consequences, environmental context/resources, social influences, and behavioral regulation. Beliefs of lower importance fell under the following seven domains: knowledge; optimism; reinforcement; intention; goals; memory, attention, and decision processes; and emotion. Quantitative differences in stated beliefs about early rehabilitation between professional groups were not common.ConclusionsThis study identified important barriers and facilitators to early rehabilitation in critical care patients. Domains identified as important should be considered when designing interventions to increase uptake of early rehabilitation.

Project description:UnlabelledDividing cells of the coccoid Gram-positive bacterium Staphylococcus aureus undergo extremely rapid (millisecond) daughter cell separation (DCS) driven by mechanical crack propagation, a strategy that is very distinct from the gradual, enzymatically driven cell wall remodeling process that has been well described in several rod-shaped model bacteria. To determine if other bacteria, especially those in the same phylum (Firmicutes) or with similar coccoid shapes as S. aureus, might use a similar mechanically driven strategy for DCS, we used high-resolution video microscopy to examine cytokinesis in a phylogenetically wide range of species with various cell shapes and sizes. We found that fast mechanically driven DCS is rather rare in the Firmicutes (low G+C Gram positives), observed only in Staphylococcus and its closest coccoid relatives in the Macrococcus genus, and we did not observe this division strategy among the Gram-negative Proteobacteria In contrast, several members of the high-G+C Gram-positive phylum Actinobacteria (Micrococcus luteus, Brachybacterium faecium, Corynebacterium glutamicum, and Mycobacterium smegmatis) with diverse shapes ranging from coccoid to rod all undergo fast mechanical DCS during cell division. Most intriguingly, similar fast mechanical DCS was also observed during the sporulation of the actinobacterium Streptomyces venezuelaeImportanceMuch of our knowledge on bacterial cytokinesis comes from studying rod-shaped model organisms such as Escherichia coli and Bacillus subtilis Less is known about variations in this process among different bacterial species. While cell division in many bacteria has been characterized to some extent genetically or biochemically, few species have been examined using video microscopy to uncover the kinetics of cytokinesis and daughter cell separation (DCS). In this work, we found that fast (millisecond) DCS is exhibited by species in two independent clades of Gram-positive bacteria and is particularly prevalent among the Actinobacteria, a diverse group that includes significant pathogens as well as bacteria that generate medically important antibiotics.

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Theory of frequency response of mechanically driven cardiomyocytes.

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Theory of frequency response of mechanically driven cardiomyocytes.

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