Vibrational communication along plants by the stink bugs Nezara viridula and Murgantia histrionica

The velocity and spectral characteristics of vibrational signals of Nezara viridula (L.) and Murgantia histrionica (Hahn) (Heteroptera: Pentatomidae) were analyzed as the signals were transmitted through different plants. The velocity parameter of the body vibrations ranges from 0.1 to 1 mm/s. According to the mechanical properties of different substrates, the signal is attenuated or amplified during transmission from the insect's body to the substrate. Attenuation of up to 20 dB occurs during transmission of signals from leaves to stalks or stems. The velocity decrease with distance is below 0.5 dB/cm during transmission through less dense green stems, whereas it ranges between 0.6 and 1.6 dB/cm during transmission through more dense, woody stems. Signal velocity decreases non-linearly with increasing distance from the signal source. Regularly repeated velocity minima (nodes) and maxima (internodes) spaced 10-15 cm apart are characteristic of signal transmission through green plants but not woody stems. The signal velocity at some internodes exceeds the input value for N. viridula but not M. histrionica signals. The relative amplitude of the dominant frequency spectral peak varies with distance, along with overall signal velocity. Variable ratios of spectral peak amplitudes are characteristic for signals recorded at different distances from the source.     

Vibratory signals of the harlequin bug and their transmission through plants

Abstract. Males of the harlequin bug, Murgantia histrionica (Hahn), produce five different vibrational songs, whereas females produce one song. Songs differ from those of other stink bugs primarily in their species‐specific temporal characteristics. The broad band male courtship songs of M. histrionica are achieved by a combination of different frequency modulated and/or narrow band subunits, with several higher harmonic frequencies. Males rather than females initiate substrate‐borne vibrational communication, and the longer‐range calling songs found typically in other pentatomid species are lacking. Interindividual differences in song temporal and spectral characteristics are discussed. Transmission of vibrational songs through a cabbage head is more efficient along veins than along lamina. Attenuation of signals transmitted through veins is low and similar to that reported previously for plant stalks. On the leaf vein, distances between peak amplitude minima and maxima are different for the dominant and subdominant frequencies. At any distance from the vibration source, a different relationship between spectral peak amplitudes can be recorded. Resolution of these differences, together with velocity differences between signals recorded on the vein and lamina, may help small stink bugs to estimate distance and to locate each other on a plant.     

Spiders of the genus Cupiennius Simon 1891 (Araneae,Ctenidae)

Summary Cupiennius salei (Ctenidae) is a tropical wandering spider which lives in close association with a particular type of plant (see companion paper). These plants are the channels through which the spiders receive and emit various types of vibrations. We measured the vibrations the spiders are typically exposed to when they sit on their dwelling plants (banana plant, bromeliad) in their natural biotope in Central America. In addition a laboratory analysis was carried out to get an approximate idea of the complex vibration-propagating properties of the dwelling plants, taking a banana plant as an example. (1) Types of vibrations (Figs. 1–4). Despite variability in detail there are characteristic differences in spectral composition between the vibrations of various abiotic and biotic origins: (a) Vibrations due to wind are very low frequency phenomena. Their frequency spectra are conspicuously narrow with prominent peaks close to or, more often, below 10 Hz. Vibrations due to raindrops show maximal acceleration values at ca. 1000 Hz. Their frequency band at-20 dB extends up to ca. 250 Hz where-as that of the vibrations due to wind extends to only ca. 50 Hz. (b) The frequency spectra of prey vibrations such as those generated by a running cockroach are typically broad-banded and contain high frequencies; they have largest peaks mostly between ca. 400 and 900 Hz. Their-20 dB frequency bands usually extend from a few Hz to ca. 900 Hz. Some potential prey animals such as grass-hoppers seem to be vibrocryptic; they walk by the spider as if unnoticed. Their cautious gait leads to only weak vibrations at very low frequencies resembling the background noise due to wind. Courtship signals are composed maily of low frequencies, intermediate between background noise and prey vibrations (male: prominent peaks at ca. 75 Hz and ca. 115 Hz; female: dominant frequencies between ca. 20 Hz and ca. 50 Hz). The male signal is composed of syllables and differs from all other vibrations studied here by being temporally highly ordered. A comparison with previous electrophysiological studies suggests that the high pass characteristics of the vibration receptors enhance the signal-to-(abiotic)-noise ratio and that the vibration-sensitive interneurons so far examined and found to have band pass characteristics are tuned to the frequencies found in the vibrations of biotic origin. (2) Signal propagation (Fig. 5). In terms of frequency-dependent attenuation of vibrations the banana plant is well suited for transmitting the above signals. Average attenuation values are ca. 0.35 dB/cm. Together with known data on vibration receptor sensitivity this explains the range of courtship signals of more than 1 m observed in behavioral studies. Attenuation in the plant is neither a monotonic function of frequency nor of distance from the signal source.     

The effect of vibratory disturbance on sexual behaviour of the southern green stink bug Nezara viridula (Heteroptera, Pentatomidae)

The effect of vibratory disturbance on sexual behaviour and substrate-borne sound communication of the southern green stink bug, Nezara viridula L. was studied. Disturbance signals do not change the time N. viridula males need to locate the source of vibratory signals, but decrease the number of males responding with the calling and courtship song to calling females. Female N. viridula proceed calling during stimulation with disturbance signals but some of them change the song rhythm by skipping one or more signal intervals or emitting the repelling signals. The number of females which change the dominant frequency of the calling song decreases proportionally with increasing differences between the dominant frequency of the disturbance signals and the emitted female calling song. Variation of the song dominant frequency probably serves females to avoid interference by increasing the signal to noise ratio. Signal duration and repetition rate do not change significantly when the female is stimulated with the disturbance signals. This indicates that frequency shift by calling females is the main strategy for reducing interference by competitive signalers in N. viridula vibrational communication.     

FIELD RECORDINGS OF ECHOLOCATION AND SOCIAL SIGNALS FROM THE GLEANING BAT MYOTIS SEPTENTRIONALIS

ABSTRACT

We recorded echolocation and ultrasonic social signals of the bat Myotis septentrionalis. The bats foraged for insects resting on or fluttering about an outdoor screen to which they were attracted by a ‘backlight’. The bats used nearly linearly modulated echolocation signals of high frequency (117 to 49 kHz, see Tables) with a weak second harmonic. The orientational signals from patrolling bats were about 2.4 ms in duration and occurred at a repetition rate of about 18 Hz (see Figure 3). The signals used by bats as they approached the screen were of shorter duration (0.72 ms) and occurred at higher rates (33.8 Hz) (Table 2 and Figure 4). We registered one feeding ‘buzz’ (Figure 5). We recorded social signals when two bats patrolled the hunting area. The social signals were characterized by their longer durations (6 ms, see Table 1), lower frequencies (70 to 30 kHz), and curvilinear sweeps (Figures 7 and 8). We calculated the source levels of orientational and social signals using the differences in arrival times at three microphones in a linear array (Figures 1 and 2). The source levels were on average 102 dB peSPL at 10 cm (Table 1). We could not calculate source levels of the signals used by bats as they approached the screen at close range, but these signals were much weaker (about 65 dB peSPL at the microphone).     

Prey detection in antlions: propagation of vibrational signals deep into the sand

Trap‐building antlion larvae detect their prey according to the substrate vibrations produced during movement of the prey on the sand surface. Although most studies are devoted to surface vibrational waves, in the present study, we determine the role of vibrations travelling through deeper sand layers. A behavioural experiment confirms that vibrational stimuli from prey insects on the surface of the sand stimulate the antlions buried in deeper sand layers to move towards the surface. Sand depth and particle size both have a strong effect on signal transmission. The damping coefficient (α₁₀) varies from 0.49 dB to 3.30 dB cm^?1 and depends on frequency (in the range from 100 to 300 Hz), particle size (from finest to coarse sand) and distance from the source of the vibrations. The deeper the sand, the narrower the frequency range of the signal becomes. Sand is a filter for higher frequencies. The smaller the sand particles, the more intense the filtering becomes. Fine sand with a mean sand particle size of 360 μm is a more efficient filter than coarse sand; consequently, high frequencies (> 2.5 kHz) are eliminated at a depth of 3 cm. Mean frequency depends on both depth and particle size. However, low frequency signals still propagate at a certain distance, which is biologically important in prey detection. Although the most efficient signal propagation appears to occur in coarse sand, it contains overly large particles that are inconvenient for relatively small antlion larvae. Predators seek a compromise between fine and coarse sand choosing medium sand.     

Transmission of stridulatory signals of the burrower bugs, Scaptocoris castanea and Scaptocoris carvalhoi (Heteroptera: Cydnidae) through the soil and soybean

Abstract.  Males and females of the burrower bug species Scaptocoris castanea Perty and Scaptocoris carvalhoi Becker emit stridulatory signals when on the roots of soybean. The substrate-borne components of the signal can be recorded on the plant but not on the surrounding soil surface. The stridulatory apparatus is composed of the tergal plectrum (lima) and the stridulitrum (stridulatory vein) on the underside of the hind wings. The male plectrum has one ridge and the female lima has 13 ridges. Stridulitra of different species differ in the length and in the number of teeth. Rubbing of plectrum (lima) ridges over the stridulitrum in one or both directions produces pulse trains. The velocity of signals that are recorded less than 0.5 cm from the bug is below 0.013 mm s⁻¹ on the soil and below 0.066 mm s⁻¹ on the leaf surface. Broadband spectra have a dominant frequency of less than 1 kHz and subdominant peaks extending up to 7 kHz. The dominant frequency of the stridulatory signal transmitted through a plant decreases together with the proportion of its higher frequency spectral components. Signals are attenuated for 3–9 dB cm⁻¹ when transmitted through the soil or soybean leaf and for approximately 1 dB cm⁻¹ when transmitted through soybean stem.     

Communication ecology of webbing clothes moth: attractiveness and characterization of male-produced sonic aggregation signals

Abstract:  We tested the hypothesis that the webbing clothes moth, Tineola bisselliella (Hum.) (Lep., Tineidae), uses sonic signals in addition to pheromonal signals for communication. To record sound from individual or groups of moths of either or both sexes, we used a digital recording system, microphones sensitive to sonic and/or ultrasonic frequencies, and speakers capable of emitting sonic and ultrasonic sound. In a soundproof environment, male T. bisselliella produced sounds of 27 decibels (dB, sound pressure level; 0 dB corresponds to 20  μ Pa), with a base frequency of 40–50 Hz and a harmonic frequency of 80–100 Hz. Sound intensity and frequency increased to 55 dB and 65–75 Hz (with ≥3 harmonic frequencies), respectively, when calling males were near (<2 cm) conspecifics of either sex. There was no evidence that females produce sound and no evidence for ultrasonic sound production by either sex. In Y-tube bioassay experiments, virgin male and female T. bisselliella preferred played-back sonic signals from males to silent control stimuli, whereas mated females showed no preference for either stimulus. In arena bioassay experiments, males as well as virgin and mated females preferred played-back sonic signals from males over a white noise control. Use of pheromonal and sonic signals by T. bisselliella would be adaptive, because the capacity for sonic communication persists even if sensory adaptation or habituation to pheromonal signals occurred. This hypothesis is consistent with the fact that other inhabitants of enclosed microhabitats, such as the greater wax moth, Galleria mellonella L., and Indian meal moth, Plodia interpunctella (Hb.), have also evolved analogous multimodal communication systems.     

Variation in Plant Substrates and its Consequences for Insect Vibrational Communication

Many insects and other arthropods communicate using plant‐borne vibrational signals. Vibration transmission along plant stems imposes a frequency filter on signals, and may cause signal degradation from reflected waves. Furthermore, different plant species and plant parts can differ in their transmission properties. This variability in the communication channel may constrain the reliability of signals, with important consequences for the evolution of vibrational communication systems, as well as for researchers studying signal variation at an individual, population, or species level. In this study we estimate the magnitude of substrate‐related variation in the mate advertisement signals of a treehopper (Hemiptera: Membracidae: Umbonia crassicornis). We used laser vibrometry to record the signals produced by 25 adult males on two different plant species, one host and one non‐host. We recorded male signals on two plants per species; within each plant, signals were recorded simultaneously at two distances. We measured three spectral characteristics (dominant frequency, relative amplitude of the signals’ high and low frequency components, frequency at the end of the signal) and two temporal characteristics (signal duration and click repetition rate). Spectral characteristics were influenced by the distance at which the signal was recorded, and this influence varied among plant species and individuals. Temporal characteristics were less influenced, although signal length was influenced by distance, an effect that varied among individual plants. Overall, the magnitude of the effects was small. Furthermore, there was significant within‐individual repeatability of almost all signal traits across different plant substrates. Signal characteristics were thus reliably associated with individuals, even when they signaled on different plants.     

Social Correlates of Variation in Male Calling Behavior in Blanchard's Cricket Frog,Acris crepitans blanchardi

I studied variation in male calling behavior and its social correlates in Blanchard's cricket frog, Acris crepitans blanchardi. Calls were produced in distinct call groups, and they increased in duration and complexity from the beginning to end of a call group. Dominant frequency was the only character of 18 quantified consistently correlated with male snout-vent length. Calls from the beginning of a call group varied independently of calls from the middle and end of a call group, and only calls from the beginning of a call group exhibited significant variation among males, thus relative consistency within males. Other characters varied greatly within individual males. Unlike most other anurans, dominant frequency also exhibited tremendous within-male variation. The relative influence of caller density, local caller density, nearest neighbor distance, and nearest neighbor sound pressure level on variation in male calling behavior was examined. Nearest neighbor distance, mediated through the sound-pressure level of neighbor calls, appeared to have the greatest influence on variation in male calling behavior. The most profound changes in calling behavior occurred during aggressive encounters; males altered their calling behavior in a manner suggesting that they respond to competitors with graded aggressive signals. Furthermore, the structure of the communication system suggests that calls are graded not only in response to the level of social competition, but graded over a call group as well.     

The acoustic behaviour of the bushcricket Tettigonia cantans II. Transmission of airborne-sound and vibration signals in the biotope

The airborne-sound and the vibratory signals produced by stridulating $\text{Tettigonia cantans}$ males, and the transmission of these signals in the natural biotope were investigated.The song of $\text{T. cantans}$ is composed of repeated uniform syllables with a rate of ca. 30/sec. Intensity approaches 100 dB SPL, 10 cm away from the animal. The spectrum shows three dominant frequency ranges around 8, 16 and 32 kHz.Airborne transmission of the song in such vegetation layers as are found in the biotopes of $\text{T. cantans}$ shows an excess attenuation which increases with frequency. The relative intensities of the frequency components of the song vary as a result of the kind of vegetation, the positions of emitter and receiver, and the separation distance. These relative differences in intensity may be useful during the phonotactic approach to conspecific partners, providing a measure of the distance from the sound source.Stridulating males also produce vibratory signals in the plants they sit on. The spectrum of these signals includes frequencies up to 8 kHz, the first dominant frequency of the song: low frequency components are induced in the plants via the legs and abdomen of the animal. The vibratory signals are transmitted mainly in the form of bending waves. Near the animal, amplitude modulation corresponds to that of the song. At greater distances, reflections and frequency-dependent propagation velocities, cause distortions of this time pattern. Transmission depends greatly on the mechanical properties of the particular plant, attenuation values of 20–50 dB/m being found. Nevertheless, in most cases, vibratory signals may be perceived up to 1.5 – 2 metres away from a stridulating male.     

Digger wasp against crickets. II. An airborne signal produced by a running predator

Summary Females of the digger wasp Liris niger Fabr. hunt crickets to provide food for their offspring by running with high velocity on the ground (>20–50 cm/s). Crickets are able to detect the running wasps by the air particle movement generated by the predator. We measured signals produced by running wasps using a microphone sensitive to air particle velocity. The wasps generated single air puffs with peak air particle velocities of 1–2 cm/s measured close to the running wasp. We measured frequency spectra of the signals containing only components below 50 Hz, with increasing intensities towards lower frequencies, especially below 10 Hz.We measured the air particle movement generated by artificially moved wasps, crickets or a styrofoam dummy of similar size to investigate the effect of velocity and shape of the moving object upon the composition of the signal. The velocity of movement appeared to be important for the intensity and frequency composition of the air particle movement. The shape of the moved body had an influence on the intensity but only little effect on the frequency spectrum. Measurements with a thermistor anemometer showed that a moving object caused air currents lasting longer than 100 ms after passing or approaching the probe. The air particle movements generated by hunting wasps are entirely sufficient with respect to intensity and frequency range to be registered by the filiform hair sensilla upon the cerci of crickets.     

Auditory saccular sensitivity of the vocal Lusitanian toadfish: low frequency tuning allows acoustic communication throughout the year

A novel form of auditory plasticity for enhanced detection of social signals was described in a teleost fish, Porichthys notatus (Batrachoididae, Porichthyinae). The seasonal onset of male calling coincides with inshore migration from deep waters by both sexes and increased female sensitivity to dominant frequencies of male calls. The closely related Lusitanian toadfish, Halobatrachus didactylus, (Batrachoididae, Halophryninae) also breeds seasonally and relies on acoustic communication to find mates but, instead, both sexes stay in estuaries and show vocal activity throughout the year. We investigated whether the sensitivity of the inner ear saccule of H. didactylus is seasonally plastic and sexually dimorphic. We recorded evoked potentials from populations of saccular hair cells from non-reproductive and reproductive males and females in response to 15–945 Hz tones. Saccular hair cells were most sensitive at 15–205 Hz (thresholds between 111 and 118 dB re. 1 μPa). Both sexes showed identical hearing sensitivity and no differences were found across seasons. The saccule was well suited to detect conspecific vocalizations and low frequencies that overlapped with lateral line sensitivity. We showed that the saccule in H. didactylus has major importance in acoustic communication throughout the year and that significant sensory differences may exist between the two batrachoidid subfamilies.     

Stink bug interaction with host plants during communication

In solitary plant-dwelling stink bug species, success depends crucially on efficient mate location and recognition, mediated by signals transmitted through the plant. All stink bugs investigated so far communicate with species and sex-specific narrow-band calling and courtship song signals produced by abdomen vibration. Calling songs of lower specificity are characterized by readily repeated units emitted with regular repetition rate from the same place on a plant, while courtship songs take place at shorter distances in the process of species and sex recognition, together with signals of other modalities. Signal spectra with about 100Hz fundamental frequency and harmonics below 1000Hz are tuned to the resonant properties of their green host plants. The majority of the identified leg vibratory receptor cells and the underlying ventral cord interneurons respond best in the frequency range below 500Hz. Green plants with low pass filtering properties transmit optimally signals with a dominant frequency around 100Hz and strongly attenuate vibrations above 600Hz. Accurate tuning of signal spectral properties with the plant's mechanical characteristics enables communication over several meter distances, with dispersive bending waves running through the plant's rod-like structures under standing wave conditions.     

Sound is involved in multimodal communication of Loxosceles intermedia Mello-Leitão, 1934 (Araneae; Sicariidae)

Signals of different modalities are involved during courtship of the brown spider Loxosceles intermedia. A spine on the pedipalp is rubbed against the grooves on the retrolateral region of the chelicerae producing stridulatory signals, which have a dominant frequency of the airborne component range around 770 Hz for females and around 170 Hz for males. These values are significantly lower for the substrate-borne component. The sound pressure level of stridulatory signals lies below 50 dB and the velocity values below 1 mm/s. The copulation frequency does not depend on the presence of pedipalps in females; however, in males the removal of pedipalps decreases the courtship frequency. During courtship, females vibrate their abdomens after being touched by the courting male, producing tremulatory signals with the dominant frequency below 100 Hz, sound pressure level below 60 dB and velocity below 3 mm/s. This vibration may function as a sign of the akinesia state since it precedes the introduction of the embolus. Cuticular compounds probably determine the recognition of the male by the female. Data from the present study corroborate the generalist nature of L. intermedia in which signals of different modalities are used during courtship.     

Changes in the Frequency Structure of a Mating Call Decrease Its Attractiveness to Females in the Cricket Frog Acris crepitans blanchardi

In many species, females often prefer male signals that are more complex than in nature or beyond the range of calls naturally produced by conspecific males in spectral, temporal and amplitude features. In this study we examined both the ability of females to recognize signals outside the normal range of spectral frequency variation seen in male advertisement calls, and the influence of increasing call complexity by adding spectral components to enhance the attractiveness of a male advertisement call in the cricket frog Acris crepitans blanchardi, while keeping its amplitude constant. We used two different natural male call groups and created the following synthetic call groups: with a dominant frequency at 3500 Hz, i.e. at the normal dominant frequency with a frequency band within the sensitivity range of the inner ear basilar papilla; with a dominant frequency at 700 Hz, i.e. outside the normal range of variation and with a frequency band outside the sensitivity range of the basilar papilla but within the range of the amphibian papilla; with two dominant frequencies, one at 700 Hz and another at 3500 Hz, stimulating the basilar and amphibian papilla simultaneously. In double choice experiments we tested all combinations of the three call groups, and we tested the 3500 Hz call groups against the same natural call groups. Additionally, we tested the 700 Hz call groups against white noise to see whether these signals are meaningful in mate choice. Females preferred 3500 Hz call groups over all other call groups. The synthetic call group was as attractive to females as the same natural call group. The 700 Hz call group was not meaningful in mate choice. The combined (700 Hz + 3500 Hz) call group was significantly less attractive to females than the 3500 Hz call group. Thus, making a call more spectrally complex without increasing its overall amplitude decreases its attractiveness to cricket frog females.     

Sand as a medium for transmission of vibratory signals of prey in antlions Euroleon nostras (Neuroptera: Myrmeleontidae)

Abstract.  European pit-building antlions ( Euroleon nostras / Geoffroy in Fourcroy/) detect their prey by sensing the vibrations that prey generate during locomotory activity. The behavioural reactions and some of the physical properties of substrate vibrations in sand are measured to observe signal transmission through the substrate. The frequency range of the signals of four arthropod species ( Tenebrio molitor , Pyrrhocoris apterus , Formica sp. and Trachelipus rathkei ) is 0.1–4.5 kHz and acceleration values are in the range 400 μm s⁻² to 1.5 mm s⁻². Substrate particle size and the frequency of prey signals both influence the propagation properties of vibratory signals. The damping coefficient at a frequency 300 Hz varies from 0.26 to 2.61 dB cm⁻¹ and is inversely proportional to the size of the sand particle. The damping coefficient is positively correlated with the frequency of the pulses. Vibrations in finer sand are attenuated more strongly than in coarser sand and, consequently, an antlion detects its prey only at a short distance. The reaction distance is defined as the distance of the prey from the centre of the pit when the antlion begins tossing sand as a reaction to the presence of prey. The mean reaction distance is 3.3 cm in the finest sand (particle size ≤ 0.23 mm) and 12.3 cm in coarser sand (particle size 1–1.54 mm). The most convenient sands for prey detection are considered to be medium particle-sized sands.     

Determination of source distance in the surface-feeding fish Pantodon buchholzi Pantodontidae

The African butterfly fish Pantodon buchholzi localizes its prey by means of surface waves of the water. Pantodon also responds and orientates well to artificial, short lasting prey-like signals (clicks), produced by a single air-puff or by dipping a small rod once into the water. When stimulated with clicks, which contain many frequencies, Pantodon determines the source distance (test range 5–20 cm) very precisely, regardless of stimulus amplitude, amplitude modulation and frequency band width. However, when the signal is a sine wave at a single frequency (sf) or with upward frequency modulation (ufm), the distance determination is generally impaired, i.e. the distance covered by the fish is too small to reach the wave source. However, the fish can also be tricked into moving too far by presenting it with a sine wave signal which, at a source distance of only 7 cm has a frequency modulation equivalent to a click at 15 cm. In contrast to distance determination, the ability to estimate the target angle is independent of the kind of wave signal presented. The results are discussed with respect to possible mechanisms used for prey localization.     

Predatory bug <Emphasis Type="Italic">Picromerus bidens</Emphasis> communicates at different frequency levels

The Asopinae (Heteroptera: Pentatomidae) are a subfamily of stinkbugs with predaceous feeding habits and poorly understood communication systems. In this study we recorded vibratory signals emitted by Picromerus bidens L. on a non-resonant substrate and investigated their frequency characteristics. Males and females produced signals by vibration of the abdomen and tremulation. The female and male songs produced by abdominal vibrations showed gender-specific time structure. There were no differences in the temporal patterns of male or female tremulatory signals. The signals produced by abdominal vibrations were emitted below 600 Hz whereas tremulatory signals had frequency ranges extending up to 4 kHz. Spectra of male vibratory signals produced by abdominal vibrations contained different peaks, each of which may be dominant within the same song sequence. Males alternated with each other during production of rivalry signals, using different dominant frequency levels. We show that the vibratory song repertoire of P. bidens is broader than those of other predatory stinkbugs that have been investigated. The emission of vibrational signals with different dominant frequencies but the same production mechanism has not yet been described in heteropteran insects, and may facilitate location of individual sources of vibration within a group.     

Frequency modulation within electrocardiograms during ventricular fibrillation

Periods of reentrant activation and effective refractory periods are correlated with dominant frequency or reciprocal of cycle periods during ventricular fibrillation (VF). In the present study, we used an analysis technique based on Wigner transforms to quantify time-varying dominant frequencies in electrocardiograms (ECGs) during VF. We estimated dominant frequencies within orthogonal ECGs recorded in 10 dogs during trials of 10 s of VF and in 9 dogs during trials of 30 s of VF. In four additional dogs, we compared dominant frequencies during 10 s of VF before and after administration of amiodarone. Our results showed the following. 1) There was substantial frequency variation or modulation within the ECGs during 10 and 30 s of VF, the average variation being +/-15% from the mean frequency. Amiodarone decreased mean frequencies (P < 0.05) as expected; however, amiodarone also decreased the variation in frequencies (P < 0.05). 2) During 30 s of VF, the dominant frequencies increased continuously from 7.3 to 8.1 Hz (P < 0.05). The increase in frequency was almost linear with a rate of 0.022 Hz/s (r(2) = 0.93, P < 0.0005). 3) Modulation of frequencies during the first and the last one-half of 30 s of VF was not different. Average (in time) mean frequencies and modulation of frequencies were similar in all three ECGs. 4) Although the averages were similar, during any VF episode, dominant frequencies in ECGs recorded from different locations on the body surface were similar to each other at some times and markedly different from each other at other times. We conclude that during VF, 1) frequencies in ECGs vary considerably and continuously, and amiodarone decreases this variation; 2) mean frequencies increase linearly during first 30 s; 3) the variability in frequency does not change during 30 s; and 4) at any given time, the frequencies within spatially different body surface ECGs can be either similar or markedly different.