Cardiac perception and cardiac control

The evidence regarding specific cardiac perception and discrimination, and its relationship to voluntary cardiac control, is critically reviewed. Studies are considered in three sections, depending on the method used to assess cardiac perception: questionnaire assessment, discrimination procedures, and heartbeat tracking. The heartbeat tracking procedure would appear to suffer least from interpretative difficulties. Recommendations are made regarding the style of analysis used to assess heartbeat perception in such tracking tasks.     

Cardiac perception and cardiac control. A review.

The evidence regarding specific cardiac perception and discrimination, and its relationship to voluntary cardiac control, is critically reviewed. Studies are considered in three sections, depending on the method used to assess cardiac perception: questionnaire assessment, discrimination procedures, and heartbeat tracking. The heartbeat tracking procedure would appear to suffer least from interpretative difficulties. Recommendations are made regarding the style of analysis used to assess heartbeat perception in such tracking tasks.     

A simple genetic model with non-equilibrium dynamics

 It is implicit in earlier work that simple population genetic models with constant fertility selection at one locus with two alleles can have non-equilibrium dynamics. But the nature of these dynamics has never been investigated in detail. We show that locally stable 2-cycles occur in these models, which seems to be the simplest genetic models exhibiting such dynamics. Received: 5 December 1996 / Revised version: 14 November 1997     

Is Embryonic Limulus Heart Really Myogenic?

Although the neurogenic nature of the heartbeat in adult Limulushas been well studied and is undisputed, we contest the reportsthat the embryonic heartbeat is myogenic. This notion, basedon histological, calorimetric, and drug studies, is challengedby evidence from transmission electron microscopy and intracellularrecording. The first, infrequent heartbeats occur at the timeof the third embryonic molt when only the anterior portion ofthe heart tube is formed and functional. Contractions extendfurther caudad concomitant with lumen formation in the rearheart segments. All lumen-containing heart sections that wehave examined, from the earliest on, have revealed neural elementsin a bundle at the dorsal midline of the heart. Axons 1/m orless in diameter are prevalent: vesicle-filled terminal-likeareas adjacent to muscle cells are often present as well, evenin the youngest beating hearts. Myocardial cells show excitatorypostsynaptic potentials as soon as heartbeat has begun, butthey often fail to summate in the earlier stages so that contractionsare few. Resting potentials remain at –65 to –70mV from the onset of heartbeat until well after the larva hashatched, but heartbeat frequency, regularity, depolarizationheight (never overshooting) and duration all increase as embryosget older, probably as innervation of muscle fibers increasesand coordination between pacemaker and follower neurons improves.We have found no evidence that embryonic Limulus heart passesthrough a myogenic phase and believe that it is neurally drivenfrom the beginning.     

Nervous Versus Neurohormonal Control of Insect Heartbeat

Recording semi-isolated insect heartbeat at one time was anart only to be attempted by the most patient of research workers.Thanks to modern advances in biomedical instrumentation, insectheartbeat measurement by impedance conversion and contact thermographyallows not only heartbeat recordings, but recording of accessorypulsatile organs and diaphragm movements. The characteristicheartbeat patterns as recorded from adult insects vary enormouslyfrom very regular in orthopteroids to highly irregular in Diptera.Pupal stages in holometabolous insects are characterized bya heartbeat which appears to have little or no nervous influenceand is punctuated by cessation for periods up to several hoursin some insects. The controversy over nervous and/or hormonalcontrol of insect heartbeat has never been completely resolved.There is now a good deal of evidence for nervous control ofthe heartbeat of Dipteran adults, Lepidopteran adults, Orthopterannymphs and adults, Dictyopteran nymphs and adults, and Hymenopteranadults. The evidence of hormonal control of heartbeat remainsinferential, and is based mostly on the responses of semi-isolatedheart preparations. One of the most important events in recentyears in this field has been Brian Brown's elucidation of Proctolinin cooperation with Alvin Starratt in Canada. Proctolin is asuspected neurohormone or neurohumor of the proctodeum whichmay also be used to regulate heartbeat in insects.     

A nonlinear dynamical mechanism for bruit generation by an intracranial saccular aneurysm

 Intracranial saccular aneurysms have been clinically observed to emit a transient sound, a bruit, on each heartbeat. The mechanism causing the bruits has been a matter of contention. A qualitative analysis of the nonlinear dynamical properties of the Shah-Humphrey model for periodic pressure forcing of a thin-necked saccular aneurysm, using the Fung nonlinear constitutive model for the aneurysm material, shows that a small blood pressure jump on each beat, whether the pressure is weakly aperiodic or periodic, induces transients in the radial deformation response of the aneurysmal wall on each heartbeat. These transient vibrations, which have a component with frequency near the natural frequency of the system but are not resonant phenomena and which decay rapidly to a limit cycle during each distinct forcing pressure cycle, can generate the bruits. Received: 21 November 2000 / Revised version: 9 August 2001 / Published online: 23 August 2002 Mathematics Subject Classification (2000): 92B99, 70K40, 70K05 Key words or phrases: Intracranial saccular aneurysm – Bruit – Spectrum – Nonlinear dynamics – Transients – Vortex shedding – Fung model     

Episodes of low-dimensional self-organized dynamics from electroencephalographic α-signals

 Self-organized neuronal dynamics revealed by cortical α-rhythms occur as episodes, which are rarely observed without extraction of the α-band from the other spectral components. Three episodes of an unusually long duration of 10 s, two with no signal processing after data recording at the clinic, are described and show evidence of low-dimensional α-dynamics. The evidence is gained from an analysis of scaled structures appearing in families of slope curves of the correlation integrals and is checked against time reparametrization. The data for the two unprocessed 10-s episodes are used for a test of the methodology, as well as a re-examination of the adequacy of the model of an autonomous dynamic system in steady state and of the concept of an attractor in brain dynamics investigations. Striking evidence for the model’s inadequacy is provided by the episode of subject S₁. In this example five consecutive overlapping 6-s sections do show evidence for low-dimensional dynamics, whereas the 10-s section containing those sections does not. The episode of subject 1 provides an example of α-activity which may involve self-organized dynamics extending down to low frequencies. The system (the neuronal network) showing episodes of attractor-ruled dynamics, under conditions of blurred and smoothly fading out evidence that it stays on an attractor, is designated as being ruled by a ‘shadow-attractor’. This concept is compared with that of a ‘quasi-attractor’ introduced by H. Haken in studies of physiological systems. One possible mechanism for the observed episodes is proposed, based on a time-dependent number of enslaved sub-systems. Received: 28 June 1996 / Accepted in revised form: 27 May 1995     

Leucomyosuppressin modulates cardiac rhythm in the cockroach Blattella germanica

Several lines of evidence point to leucomyosuppressin (LMS) and myosuppressin-related peptides as inhibitory modulators of heartbeat frequency in arthropods. Previous studies in Blattella germanica demonstrated that heartbeat frequency decreases after ootheca formation, and remains low during the period of ootheca transport. Subsequent work in this cockroach resulted in the characterization of LMS and the cloning and sequencing of its precursor. The present paper describes the activity of LMS on modulation of heartbeat in B. germanica. Assays using semi-isolated heart preparations revealed that LMS reduces heartbeat frequency in a dose dependent manner, at physiological concentrations. Additional experiments showed that LMS inhibits heartbeat rates in vivo. Finally, injection of dsRNA for LMS elicited a decrease in LMS mRNA to virtually undetectable levels and heartbeat frequency increased significantly in females carrying oothecae. These data suggest that LMS contributes to the modulation of cardiac rhythm in B. germanica during the reproductive cycle.     

Joint dynamic imaging of morphogenesis and function in the developing heart

In the developing heart, time-lapse imaging is particularly challenging. Changes in heart morphology due to tissue growth or long-term reorganization are difficult to follow because they are much subtler than the rapid shape changes induced by the heartbeat. Therefore, imaging heart development usually requires slowing or stopping the heart. This, however, leads to information loss about the unperturbed heart shape and the dynamics of heart function. To overcome this limitation, we have developed a non-invasive heart imaging technique to jointly document heart function (at fixed stages of development) as well as its morphogenesis (at any fixed phase in the heartbeat) that does not require stopping or slowing the heart. We review the challenges for imaging heart development and our methodology, which is based on computationally combining and analyzing multiple high-speed image sequences acquired throughout the course of development. We present results obtained in the developing zebrafish heart. Image analysis of the acquired data yielded blood flow velocity maps and made it possible to follow the relative movement of individual cells over several hours.Key words: cardiac imaging, zebrafish, fluorescence imaging, heart development, registration, fast imaging     

Molecular dynamics simulations of ion channels formed by bundles of amphipathic α-helical peptides

Ion channels may be formed by self-assembly of amphipathic α-helical peptides into parallel helix bundles. The transbilayer pores formed by such peptides contain extended columns of water molecules, the properties of which may differ from those of water in its bulk state. The de novo designed peptides of DeGrado et al., which contain only leucine and serine residues, are considered as a simple example of such channels. Molecular dynamics simulations of peptide helix bundles with water molecules within and at the mouths of their pores are used to refine such models and to investigate the properties of intra-pore water. The translational and rotational mobility of water molecules within the pores are reduced relative to bulk water. Furthermore, intra-pore waters orient themselves with their dipoles anti-parallel to the helix dipoles, as do the hydroxyl groups of serine residues. Comparison of approximate predictions of ionic conductances with experimental values provides support for the validity of these models. Received: 23 April 1996 / Accepted: 7 August 1996     

Effects of state contraceptive insurance mandates

Using U.S. Natality data for 1996 through 2009 and an event analysis specification, we investigate the dynamics of the effects of state insurance contraceptive mandates on births and measures of parental investment: prenatal visits, non-marital childbearing, and risky behaviors during pregnancy. We analyze outcomes separately by age, race, and ethnicity. Among young Hispanic women, we find a 4% decline in the birth rate. There is evidence of a decrease in births to single mothers, consistent with increased wantedness. We also find evidence of selection into motherhood, which could explain the lack of a significant effect on birth outcomes.     

Spatial dynamics of an invasive bird species assessed using robust design occupancy analysis: the case of the Eurasian collared dove (Streptopelia decaocto) in France

Aim The study of the spatial dynamics of invasive species is a key issue in invasion ecology. While mathematical models are useful for predicting the extent of population expansions, they are not suitable for measuring and characterizing spatial patterns of invasion unless the probability of detection is homogeneous across the distribution range. Here, we apply recently developed statistical approaches incorporating detection uncertainty to characterize the spatial dynamics of an invasive bird species, the Eurasian collared dove (Streptopelia decaocto). Location France. Methods Data on presence/absence of doves were recorded from 1996 to 2004 over 1045 grid cells (28 × 20 km) covering the entire country. Each grid cell included five point counts spaced along a route, which was visited twice a year, allowing for an estimation of detection probability. Each route was assigned to one of six geographical regions. We used robust design occupancy analysis to assess spatial and temporal variation in parameters related to the spatial dynamics of the species. These parameters included occupancy rate, colonization and local extinction probabilities. Our inference approach was based on the selection of the most parsimonious model among competitive models parametrized with conditional probabilities. Results The probability of detecting the presence of doves on a given route was high. However, we found evidence to incorporate detection uncertainty in inference processes about spatial dynamics, since detection probability was neither perfect (i.e. it was < 1), nor constant over space and time. Results showed a clear positive trend in occupancy rate over the study period, increasing from 55% in 1996 to 76% in 2004. In addition, occupancy rate differed among regions (range: 37–79%) and further analysis showed that colonization probability by region was positively related to occupancy rate. Finally, local extinction probability was lower than colonization probability and showed a tendency to decrease over the study period. Main conclusions Our results emphasize the importance of estimating detection probabilities in order to draw proper inferences about the spatial and temporal dynamics of the invasion pattern of the collared dove. In contrast to the perceived spatial dynamics from national atlas surveys, we provide evidence that the range of this species is currently increasing in France. Other results, such as regional specificity in colonization probabilities and time variation in local extinction are consistent with expectations from invasion and metapopulation theory.     

Classification of coupling patterns among spontaneous rhythms and ventilation in the sympathetic discharge of decerebrate cats

 The spontaneous low- and high-frequency rhythms in the sympathetic discharge of decerebrate artificially ventilated cats are affected by external ventilation. Two graphical methods (i.e. the space-time separation plot and the frequency tracking locus) are used to classify the non-linear interactions. The observed behaviours in the sympathetic discharge consist of phase-locked periodic dynamics (at various frequency ratios with ventilation), quasiperiodic and aperiodic patterns. They depend on the experimental condition. In control condition the sympathetic discharge appears more frequently locked to each ventilatory cycle (1 : 1 dynamics). However, some cases of quasiperiodic dynamics are found. A sympathetic activation stimulus, such as inferior vena cava occlusion, is able to synchronise slow rhythms in the sympathetic discharge to a subharmonic of ventilation. During a sympathetic inhibition stimulus, such as aortic constriction, 1 : 1 dynamics is detected but the amplitude of the sympathetic responses can be modulated by unlocked slow rhythms. Moreover, some cases of aperiodic dynamics are observed. Vagotomy reduces the 1 : 1 coupling between sympathetic outflow and ventilation. Vagotomy plus spinalisation disrupts periodic dynamics in the sympathetic discharge so that irregular and complex patterns are found. Received: 19 July 1995/Accepted in revised form: 20 May 1996     

Spontaneous embryonic death on Days 20 to 40 in heifers

Transrectal ultrasound examinations were used in nulliparous Holstein heifers to study the association between time of spontaneous embryonic death (cessation of heartbeat) and luteal regression, and to determine the fate of the conceptus after embryonic death. There was no significant difference between nonbred heifers (n = 135) and bred, nonpregnant heifers (embryonic heartbeat never detected, n = 40) for day of onset of luteal regression (means, 17.6 and 17.9, respectively) or for length of interovulatory interval (means, 20.6 and 20.9 days, respectively). Pregnancy was confirmed by detection of an embryonic heartbeat on Day 24 (ovulation = Day 0) or later, or on two consecutive days prior to Day 24; on average, an embryonic heartbeat was detected on Day 22.0 (n = 104). Pregnancy rate on Day 24 was higher (P<0.02) in heifers bred on Day -1 (116/149, 77.8%) than in heifers bred on Day -2 (51/79, 64.6%), and was higher (P<0.05) in heifers with an embryo transferred ipsilateral to the corpus luteum than in heifers with an embryo transferred contralateral to the corpus luteum (3/4 vs 0/5). Embryonic death (lack of embryonic heartbeat following confirmation of pregnancy) and presumptive embryonic death (embryonic heartbeat detected on one day only, prior to Day 24) were detected prior to Day 25 in one and two bred heifers, respectively, and in one and two heifers with an embryo transferred contralateral to the corpus luteum, respectively. In these six heifers, luteal regression preceded, and apparently caused, embryonic death. In seven of eight heifers in which embryonic death was detected between Days 25 and 40, the onset of luteal regression was detected at least 3 d (range, 3 to 42 d) after detection of embryonic death. The incidence of embryonic death on Days 29 to 32 was lower (P<0.02) in heifers bred on Day -1 than in heifers bred on Day -2 (0 of 96 vs 3 of 40, respectively). In heifers in which luteal regression preceded embryonic death, the conceptus was lost rapidly, with minimal evidence of degeneration. In heifers in which embryonic death preceded luteal regression, there was ultrasonic evidence of conceptus degeneration, but conceptus fluid and tissue appeared to be maintained. In all heifers with embryonic death, the conceptus and its breakdown products apparently were eliminated by expulsion through the cervix rather than by resorption.     

Biogenic amines evoke heartbeat reversal in larvae of the sweet potato hornworm,Agrius convolvuli

The sweet potato hornworm, Agrius convolvuli, possesses a pair of anterior cardiac nerves innervating the dorsal vessel. The anterior cardiac nerves branch off the visceral nerve that arises posteriorly from the frontal ganglion. Heartbeat reversal from anterograde heartbeat to posterograde heartbeat is triggered by the anterior cardiac nerves. Application of octopamine (OA) during the anterograde heartbeat phase reverses the anterograde heartbeat to the posterograde heartbeat, while application of OA during the phase of posterograde heartbeat accelerates heartbeat. The heartbeat reversal from anterograde heartbeat to posterograde heartbeat evoked by stimuli applied to the visceral nerve is blocked by application of the octopaminergic antagonists, phentolamine and chlorpromazine. The results suggest that OA may be a neurotransmitter for the anterior cardiac nerve. The alary muscle of the second segment receives excitatory innervation from the posterior cardiac nerve and from the nerve which extends from the second abdominal ganglion. Activation of the alary muscle results in acceleration of posterograde heartbeat. Other neurotransmitters, besides OA, may take part in the resultant acceleration.     

Estimation of the involvement of subconsciousness in heartbeat perception in healthy volunteers

The results of analysis of heartbeat parameters and characteristics of its self-monitoring by 25 healthy volunteers have been used as the basis for original estimation of the involvement of subconsciousness in heartbeat perception. The first objective index for such estimation is proposed. It is calculated as the individual fragmentation coefficient of heartbeat perception. The discreteness of heartbeat perception is related to changes in the degree (weight) of involvement of subconsciousness in the perception of cardiac signals. A conclusion is drawn on the relationship between the efficiency of perception of one’s own heartbeat and the degree of involvement of subconsciousness in this process. The practical implication of the study is the possibility of using a similar approach to estimating the weight of unconscious processes in perception of stimuli of different types, including those used in psychodiagnostic studies.     

A morphology alignment method for resampled heartbeat signals

A morphology alignment method for digital heartbeat signals of a person is proposed. In this method, a heartbeat is delineated into stable and flexible segments which are resampled at two different rates and then concatenated again. A resampling rate is decided based on the analysis of spatial error introduced by the interpolation method. Baseline shift of the resampled heartbeat is removed by amplitude normalization. The alignment of resampled heartbeat by this piecewise-uniform resampling method is then compared with those by uniform and non-uniform resampling methods. Four different morphological features are extracted from resampled heartbeats by each of three methods. Improvement of alignment is evaluated by to two metrics known as morphology alignment score and correlation coefficient. The method is tested on ECG signals obtained from two publicly available databases having different sampling frequencies. Statistical analyses suggest that the piecewise-uniform resampling method improves the alignment of morphology significantly. Computational time for the alignment is linear to the number of samples in a heartbeat and hence the method should be efficient enough for different practical applications using morphological features for automatic classification and decision making.     

Mechanical aspects of heartbeat reversal in pupae of Manduca sexta

Pulsations of the dorsal vessel were investigated with new optocardiographic techniques based on the transmission and reflection of pulse-light through optic fibers. This noninvasive technique enabled simultaneous, in vivo multisensor recordings of the heartbeat without touching the pupal integument. There was a very regular heartbeat reversal with 3 distinctive phases: (a) a backward-oriented (retrograde) cardiac pulsation; (b) a forward-oriented (anterograde) pulsation with faster frequency; and (c) shorter or longer periods of temporary cardiac standstill that usually occurred after the termination of the anterograde phase. Occasionally, there were localized series of systolic cardiac contractions during the retrograde phase. Simultaneous recordings from the base and the tail of the abdomen revealed a reciprocal, "mirror image-like", quantitative relationship. The most intensive anterograde hemolymph flow occurred at the base while the most intensive retrograde flow occurred at the tail of the abdomen. The bi-directional switchovers of heartbeat (reversal) were occasionally associated with modifications during each of the unidirectional cardiac phases. Anterograde peristalsis showed a 2-fold higher frequency of pulsation in the thoracic aorta in comparison with the posterior parts of the heart. Thus, in addition to the "odd" peristaltic waves originating at the tail, there were intercallated "even" peristaltic waves originating in the middle of the abdomen. Both of them propagated hemolymph through the thoracic aorta into the head; the first waves took the hemolymph in from the distal end, while the second sucked it from the middle of the abdomen. The use of multiple optocardiographic sensors also enabled detection of cardiac pulsations on the opposite, ventral side of the body, within the ventral perineural sinus. The ventral side of the head showed only the presence of an anterograde pulse, whereas the ventral side of the tail exhibited a strong reciprocal retrograde phase and a very weak anterograde phase. These results explain why the existence of a periodic heartbeat reversal should be essential for circulatory functions at both extremities of the cylindrical insect body. In diapausing pupae, regular cycles of heartbeat reversal were substituted by prolonged periods of anterograde pulsation during the entire duration of bursts of CO2 release (average duration of the burst was 18-20 min, periodicity 5 to 18 h). The physiological nature of such feed-back correlation between heartbeat and metabolic CO2 production is not yet clear, because the anterograde heartbeat could be also induced by a number of nonspecific factors unrelated to CO2 (mechanical irritation, injury, injections, elevated temperature). During the postdiapause, developing pharate-adult stage, the correlation between CO2 and anterograde heartbeat completely disappeared. It has been concluded that regulation of insect heartbeat represents a highly coordinated, myogenic stereotype with inherent rhythmicity, which can be modified by a number of external and internal factors.     

Climate-driven changes on phytoplankton–zooplankton coupling and nutrient availability in high mountain lakes of Southern Europe

1. The effect of climate variability on phytoplankton and zooplankton dynamics and nutrient availability was studied in two high mountain fishless lakes (La Caldera and Río Seco) of contrasting morphology, hydrology and dissolved inorganic nitrogen : soluble reactive phosphate (DIN : SRP) ratios during 1986 and after a 10‐year‐long drought in 1996 and 1997. 2. Thaw was delayed and water temperatures were lower in both lakes in 1996 than in 1986 and 1997. However, the lake‐specific DIN : SRP ratio was maintained in the 3 years studied, reflecting its local control. 3. On other hand, the presumptive limiting nutrient in each lake, P in La Caldera and N in Río Seco, showed higher concentrations in 1996 versus 1986 and 1997. Significant positive correlations between temperature and chlorophyll a were found in both lakes in 1996 but these relationships were negative or not significant in 1986 and 1997. Zooplankton biomass showed lower values in 1996 than in 1986 or 1997. 4. These findings can be explained by a decoupling of the phytoplankton–zooplankton interaction because of a constraint on zooplankton growth by low temperatures in the coldest year studied. This observation furnishes evidence that regional climatic control on the phytoplankton–zooplankton link can modulate the overall demand for nutrients.     

Estimation of Instantaneous Complex Dynamics through Lyapunov Exponents: A Study on Heartbeat Dynamics

Measures of nonlinearity and complexity, and in particular the study of Lyapunov exponents, have been increasingly used to characterize dynamical properties of a wide range of biological nonlinear systems, including cardiovascular control. In this work, we present a novel methodology able to effectively estimate the Lyapunov spectrum of a series of stochastic events in an instantaneous fashion. The paradigm relies on a novel point-process high-order nonlinear model of the event series dynamics. The long-term information is taken into account by expanding the linear, quadratic, and cubic Wiener-Volterra kernels with the orthonormal Laguerre basis functions. Applications to synthetic data such as the Hénon map and Rössler attractor, as well as two experimental heartbeat interval datasets (i.e., healthy subjects undergoing postural changes and patients with severe cardiac heart failure), focus on estimation and tracking of the Instantaneous Dominant Lyapunov Exponent (IDLE). The novel cardiovascular assessment demonstrates that our method is able to effectively and instantaneously track the nonlinear autonomic control dynamics, allowing for complexity variability estimations.