The synchronization of chaotic systems

Summary The occurrence of hiccoughs (hiccups) is very widespread and yet their neuronal origin and physiological significance are still unresolved. Several hypotheses have been proposed. Here we consider a phylogenetic perspective,startingfromtheconceptthattheventilatory central pattern generator of lower vertebrates provides the base upon which central pattern generators of higher vertebrates develop. Hiccoughs are characterized by glottal closure during inspiration and by early development in relation to lung ventilation. They are inhibited when the concentration of inhaled CO2 is increased and they can be abolished by the drug baclofen (an agonist of the GABAB receptor). These properties are shared by ventilatorymotorpatternsoflowervertebrates,leadingto

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A phylogenetic hypothesis for the origin of hiccough

Many articles in this section of Comprehensive Physiology are concerned with the development and function of a central pattern generator (CPG) for the control of breathing in vertebrate animals. The action of the respiratory CPG is extensively modified by cortical and other descending influences as well as by feedback from peripheral sensory systems. The central nervous system also incorporates other CPGs, which orchestrate a wide variety of discrete and repetitive, voluntary and involuntary movements. The coordination of breathing with these other activities requires interaction and coordination between the respiratory CPG and those governing the nonrespiratory activities. Most of these interactions are complex and poorly understood. They seem to involve both conventional synaptic crosstalk between groups of neurons and fluid identity of neurons as belonging to one CPG or another: neurons that normally participate in breathing may be temporarily borrowed or hijacked by a competing or interrupting activity. This review explores the control of breathing as it is influenced by many activities that are generally considered to be nonrespiratory. The mechanistic detail varies greatly among topics, reflecting the wide variety of pertinent experiments.

Coordination of breathing with nonrespiratory activities.

Fetal hiccups emerge as early as nine weeks post-conception, being the predominant diaphragmatic movement before 26 weeks of gestation. They are considered as a programmed isometric inspiratory muscle exercise of the fetus in preparation for the post-natal respiratory function, or a manifestation of a reflex circuitry underlying the development of suckling and gasping patterns. The present paper provides the first evidence of non-invasive biomagnetic measurements of the diaphragm spasmodic contractions associated with fetal hiccups. The magnetic field patterns generated by fetal hiccups exhibit well-defined morphological features, consisting of an initial high frequency transient waveform followed by a more prolonged low frequency component. This pattern is consistent across recordings obtained from two fetal subjects, and it is confirmed by signals recorded in a neonatal subject. These results demonstrate that fetal biomagnetometry can provide insights into the electrophysiological mechanisms of diaphragm motor function in the fetus. Additionally, we study the correlation between hiccup events and fetal cardiac rhythm and provide evidence that hiccups may modulate the fetal heart rate during the last trimester of pregnancy.

https://iopscience.iop.org/article/10.1088/0967-3334/28/6/005/pdf

Magnetographic assessment of fetal hiccups and their effect on fetal heart rhythm

Fetal biomagnetometry offers an unprecedented opportunity to study the longitudinal development of the human fetus in a noninvasive manner. Magnetic fields emanating from the electrical currents of the fetal body pass through the maternal body with little distortion, making it possible to distinguish electrophysiologic activity of the heart, diaphragmatic movements associated with hiccup and breathing movements, and oromotor activity associated with nonnutritive suck and swallow. Our research interest is focused on developmental origins and in that regard, we have found fetal biomagnetometry to be superior when measuring the effects of interventions on the development of fetal neurobehaviors and cardiac autonomic control. In this chapter, we first describe our experience characterizing specific fetal neurobehaviors and their associated magnetic field properties along with the effect on cardiac autonomic control. Next, we describe our findings in two separate research studies. The first was designed to determine the impact of maternal physical activity during pregnancy on fetal and infant cardiac autonomic control. The second describes the results of a clinical trial that was designed to determine the effect of docosahexaenoic acid (DHA), supplemented to pregnant women during the last two trimesters of pregnancy, on fetal autonomic development. Finally, we discuss the need for a comprehensive analytical approach that takes into account the complex integration of physiologic systems in the developing fetus. We hope that this work serves as a foundation for future studies that will determine how the fetus adapts as an individual to the in utero environment.

Fetal Assessment Using Biomagnetometry: Neurobehaviors, Cardiac Autonomic Control, and Research Applications

We explored a possible link between the cardiac cycle and the timing of recurrent hiccups in 10 patients with chronic, intractable hiccups. Recordings made during daytime naps in a sleep laboratory included sleep state; electrocardiogram; and respiration by means of a thermistor to detect airflow, bands around the rib cage and abdomen to assess expansion, and a bipolar surface electrode electromyogram over parasternal intercostal muscles. Hiccups could be detected on the abdominal bands and the parasternal electromyogram. The time of occurrence of each hiccup and each R wave in a continuous tracing of 100 or more hiccups were recorded and analyzed together with semiquantitive estimates of the phase of hiccup respiration. Whereas the hiccup rate ranged from approximately one-third to one-eighth of heart rate and was more variable than heart rate, hiccups showed a tendency, stronger in some subjects than others, to occur in midsystole. Variation in R-wave-R-wave (R-R) interval in association with hiccups was found in five patients. In three of these patients, hiccups were synchronized with respiration so that the cyclic change in R-R interval posthiccup could be explained as sinus arrhythmia, but, in two patients, the hiccups were not synchronized with respiration, so that hiccups are most likely responsible for the variation in heart rate. Also, the variation of R-R interval with hiccups suggests that there is some phasic autonomic efferent activity associated with hiccups.

https://www.physiology.org/doi/pdf/10.1152/jappl.2000.88.6.2159

K. Vasilakos

Papers

Linkage of hiccup with heartbeat