Behaviour of Scrobicularia plana (Da Costa) in water of various salinities

Valve movements, heart and pumping rates have been recorded from Scrobicularia plana (Da Costa) when transferred stepwise from natural sea water to sea water of S = 30% (termed 100%) and then to 80, 60, 40, and 20% sea water, and after direct transfer from 100 to 20% Scrobicularia exhibits short periods of pumping alternating with short ventilatory pauses down to 40% sea water. These are termed activity cycles and contrast with periods of complete quiescence each ≈ 4–12 h long. The heart rate of animals in these salinities is fairly constant during activity cycles. When transferred to 20% sea water, either directly or gradually, short pumping phases alternate with long ventilatory pauses during the initial 72 h. At the same time the heart rate shows wide variation during activity cycles.On transference from 100 to 60% sea water, the valves opened and valve activity pattern returned to normal within 30 min and within 6 h of transfer from 60 into 40% SW. Transfer to 20%, whether stepwise or directly, resulted in valves remaining closed initially for ≈ 10 or 34 h, respectively before opening gradually to expose the mantle margin. The valve adductions were then of reduced frequency and extent.     

SOME BEHAVIOURAL AND ELECTRICAL RESPONSES OF SCROBICULARIA PLANA (BIVALVIA:TELLINACEA) TO SIPHONAL WOUNDING

Water pumping, valve movements and heart rate have been recordedfrom Scrobicularia for short periods of normal behaviour andthen after siphonal wounding. Scrobicularia exhibits regularand repetitive pumping periods interrupted for only 2–3s after siphonal wounding, without the regularity of these periodsbeing affected. Wounding does not prevent animals from usingtheir inhalant siphons for deposit feeding. A preliminary investigationof neural responses to stimulation has shown that wounding thesiphon causes minimal disturbance to the animal, a brief (2s)burst of nerve activity occurs, the siphon is retracted, butvalve adduction does not occur. In contrast to this tactilestimulation of the mantle edge always elicits a large burstof impulses in the posterior adductor nerve, valve closure results,usually for 14–15 s. ¹Present address: Dept of Zoology, University of Cape Town,Rondebosch 7700, South Africa. (Received 2 February 1981;     

Tube irrigation by Lembos websteri Bate and Corophium bonnelli Milne Edwards (Crustacea: Amphipoda)

The pumping activity of the tubicolous amphipods Lembos websteri Bate and Corophium bonnelli Milne Edwards was measured by an apparatus that incorporated a sensitive pressure measuring device. The pumping rate of C. bonnelli was many times that of L. websteri when the animals were pumping in clean glass tubes. There was no significant difference in the pumping activity when animals were allowed to establish a detritus lined tube within a glass tube, although there was an indication that the pumping rate was increased in the case of L. websteri. The presence of clay in suspension had no significant effect on the pumping activity of either species but, in the case of C. bonnelli, the proportion of time spent pumping was greater when animals were in moving water than when in still water. No differences in the pumping activity were found between brooding and non-brooding mature female C. bonnelli nor between male and brooding female L. websteri.     

The cardiac responses of the scallop Pecten maximus (L.) to respiratory stress

Heart activity of Pecten maximus (L.) has been recorded during various forms of experimentally induced respiratory stress. There was considerable variation in the responses of individual scallops but bradycardia generally occurred in response to all forms of respiratory stress, with the rate of fall in heart rate dependent upon the severity of hypoxia.When oxygen tension declined slowly in a closed respirometer there was regulation of both heart rate and oxygen consumption. The critical tension, P_c, for oxygen consumption lay between 70 and 80 mm Hg, and corresponded with a slight regulatory upswing of the heart rate, whereas the P_c for heart rate was much lower at 20–30 mm Hg. Sudden transfer to deoxygenated water for 3 h resulted in very rapid bradycardia and there was a rapid recovery and initial overshoot of the normal rate on return to well-oxygenated sea water. Aerial exposure for 3 h produced more gradual bradycardia followed by gradual recovery on return to sea water.The results of this work are compared in some detail with previous work on other species of bivalve from different geographical areas and habitats, and the mechanisms controlling cardiac and respiratory regulation are discussed. It is concluded that there are few clear-cut general differences between littoral and sublittoral species in their behavioural and physiological adaptations to hypoxia; the main distinguishing feature of littoral-adapted species is their ability to control air-gaping. Changes in heart activity generally indicate variations in metabolic rate, the speed at which the metabolic rate may be altered reflecting the degree of adaptation to the littoral environment.     

Cardiac responses to first ever submergence in double-crested cormorant chicks (Phalacrocorax auritus)

Heart rates were recorded from double-crested cormorant chicks during their first ever and subsequent voluntary head submergences and dives, as well as during longer dives made after the chicks were accustomed to diving. Despite variation between chicks, the cardiac response to first ever and subsequent voluntary submergence (head submergences and dives) was similar to the response observed in adult cormorants. Upon submersion the heart rate fell rapidly when pre-submersion heart rate was high (325–350 beats min⁻¹). The heart rate established within the first second of voluntary submergence was between 230 and 285 beats min⁻¹, well above resting heart rate (143 beats min⁻¹). The same initial cardiac response occurred during longer dives performed after the chicks were accustomed to diving. In these dives the heart rate remained at the level established on submersion, unlike the response observed in shallow diving adult cormorants in which the heart rate declined throughout the dive. The heart rate was also monitored in a separate group of chicks in which the first exposure to water was during whole body forced submergence. Again, the observed response was similar to the adult response, although the cardiac response of chicks to forced submergence was more extreme than to voluntary submergence. Our results do not support the hypothesis that learning (by conditioning or habituation) is involved in the cardiac adjustments to voluntary submergence. It is suggested that the initial cardiac adjustments are reflex in nature and this reflex is fully developed by the first submergence event. Although the nature of this reflex pathway is obscure, cessation of breathing before submersion and the close linkage between breathing and heart rate might provide a plausible mechanism.     

Effects of altitude on exercise level and heart rate in patients with coronary artery disease and healthy controls

Background. To evaluate the safety and effects of high altitude on exercise level and heart rate in patients with coronary artery disease compared with healthy controls. Methods. Eight patients with a history of an acute myocardial infarction (ejection fraction >5%) with a low-risk score were compared with seven healthy subjects during the Dutch Heart Expedition at the Aconcagua in Argentina in March 2007. All subjects underwent a maximum exercise test with a cycle ergometer at sea level and base camp, after ten days of acclimatisation, at an altitude of 4200 m. Exercise capacity and maximum heart rate were compared between groups and within subjects. Results. There was a significant decrease in maximum heart rate at high altitude compared with sea level in both the patient and the control group (166 vs. 139 beats/min, p<0.001 and 181 vs. 150 beats/min, p<0.001). There was no significant difference in the decrease of the exercise level and maximum heart rate between patients and healthy controls (-31 vs. -30%, p=0.673). Conclusion. Both patients and healthy controls showed a similar decrease in exercise capacity and maximum heart rate at 4200 m compared with sea level, suggesting that patients with a history of coronary artery disease may tolerate stay and exercise at high altitude similarly to healthy controls. (Neth Heart J 2010;18:118-21.)     

Oxygen consumption and the respiratory responses to declining oxygen tension in the crab Ebalia tuberosa (Pennant) (Crustacea: Decapoda: Leucosiidae)

Oxygen consumption and its relationship to body weight and activity have been examined in Ebalia tuberosa (Pennant). Ebalia showed only very limited ability to regulate their oxygen consumption under conditions of declining P_O2. Respiratory independence was markedly affected by the level of activity of the animals. When inactive, respiratory independence was maintained down to a critical P_O2 of only about 130 mm Hg while when active, the crabs behaved as perfect conformers. Inactive Ebalia responded to a decrease in PO₂ by increasing the pumping activity of the scaphognathites and heart. This increased activity continued even at oxygen tensions lower than the P_c. The rate of reversals of the ventilatory currents did not change with decreasing P_O2. In the active crabs, the pumping activity of the scaphognathites and heart, and the rate of current reversals were higher than in the inactive animals, and a decrease in PO₂, did not bring about any further change in any of these responses. When exposed to hypoxic conditions for long periods initially inactive crabs survived longer than did active animals.     

Cardiac and respiratory responses in the climbing perchAnabas testudineus

Summary The heart rate ofAnabas is about 40 beats/min when breathing water and air. Tachycardia occurs as the fish takes an air breath and the rate declines as the breath holding continues but water breathing stops. Bradycardia is observed during this later phase. By the time the next air breath is taken, the heart rate has dropped to 15–30 beats/min.The heart rate of a fish breathing normoxic water but prevented from surfacing is about 42/min. Bradycardia occurs in hypoxic water under similar conditions. Tachycardia is observed in active fish when breathing hypercarbic water and air.On exposure to air bradycardia is found in resting fish but tachycardia occurs during activity. In air,Anabas usually repeats a breath when the heart rate drops to 15–25 beats/min. Tachycardia occurs immediately following an air breath. Heart rate then returns over a period of 3–6 mins to the normal resting level of 30 beats/min.The gas composition of the suprabranchial chambers has been measured and its relationship with the occurrence of an air breath, tachycardia and bradycardia is described.The experimental results are discussed in relation to the anatomy of the blood supply to the respiratory organs. The possible role of respiratory gases and pH in the control of breathing and perfusion is also discussed.We wish to thank the Nuffield Foundation for their financial support. We are also grateful to the Smithsonian Institution, Washington, D.C., and especially Dr. Stan Weitzman of the Division of Fishes, whose co-operation made this work possible.     

Hypoxia tolerance associated with activity reduction is a key adaptation for Laternula elliptica seasonal energetics

Seasonal dormancy is a widespread mechanism for reducing energy expenditure during periods of low energy availability. Seasonal variation in activity and the cost of pumping water through the siphons were investigated to estimate the importance of activity regulation to the seasonal energy budget of the Antarctic clam, Laternula elliptica. In the laboratory, a metabolic rate of 26.35 μmol O₂ h⁻¹ was estimated for a 50-mm shell length L. elliptica pumping water at −0.4 °C. In the field, the proportion of time siphons were visible at the sediment surface varied seasonally (32% visible in June/July compared to 86% in December/January). L. elliptica were actively pumping for a minimum of 19% of each 24-h period during winter (August) compared to a summer maximum when animals were actively pumping for 73% of the time (February). This resulted in a 3.7-fold seasonal difference in the calculated energy consumption of a 50-mm L. elliptica (19.2 μmol O₂ h⁻¹ in February versus 5.0 μmol O₂ h⁻¹ in August), which closely matches the 3.0-fold seasonal variation in metabolic rate found previously. Seasonal variation in activity could therefore be responsible for much of the seasonal difference in energy consumption of L. elliptica. Inter-annual variation in timing of the seasonal activity maxima (January 2004 and March 1999) was correlated with variation in the timing of the summer plankton bloom in Ryder Bay. In the laboratory, periods of extended siphon closure (133 ± 114 min, mean ± SD) were accompanied by long periods of heart arrhythmia (167 ± 135 min), during which time blood oxygen levels dropped to values close to zero. Heart arrhythmia is most likely part of a hypo-metabolic adaptation to reduce energy costs during extended periods of siphon closure. Physiological and behavioural dormancy, with associated hypoxia tolerance, appear to be key mechanisms controlling the seasonal energy budget of L. elliptica.     

Periodic muscular activity and its possible functions in pupae of Tenebrio molitor

Abstract. During pupal development, Tenebrio molitor L. show regular periods of rhythmic muscular contractions and associated body movements. These periods of activity last 2.5-5.8 min and are more frequent in newly ecdysed pupae ( c. 3h^-1). They become less frequent ( c. 1.5 h^-1) when the basal metabolism reaches its lowest level. In the pharate adult stage the clear pattern of muscular activity disappears.
Muscular activity is temperature-dependent and is commonly absent below 20C. Muscular activity did not disturb the cyclic output of CO₂, which is characteristic of metamorphosis. The heart shows characteristic periods (1–3 min) of activity during pupal development. The frequency of these heart pulsation periods depends on metabolic rate. Heart pumping was correlated mostly with muscular contractions. Therefore we suggest that the main physiological function of muscular activity is to support circulation.     

Effects of salinity on the respiration and heart rate of the common mussel, Mytilus edulis L., and the black chiton, Katherina tunicata (Wood)

The rate of oxygen consumption of stepwise acclimated Mytilus edulis L. increased linearly from 30 to 10‰ salinity (S) while that of Katherina tunicata (Wood) was not significantly different between 10 and 30‰ S. Heart rate was 21–22 and 17–18 beats m^?1 in Mytilus edulis and Katherina tunicata, respectively, and no difference was found in the heart rate of either species acclimated stepwise to 10, 20 or 30‰ S. The average oxygen consumption rate of Mytilus edulis exposed to 12 h, 30-10-30 and 10-30-10‰ S cycles of fluctuating salinity was significantly lower than the respective control rate: there was a similar response during the 30-10-30‰ S cycle in Katherina tunicata. The respiration rate of Mytilus edulis and Katherina tunicata declined as salinity deviated from the control salinity and increased as salinity returned to the control salinity. The rate of oxygen consumption by K. tunicata varied directly with the ambient salinity during the 10-30-10‰ S cycle. The average heart rate of Mytilus edulis was significantly lower during cyclic changes in salinity than at the respective control salinities; a similar relationship existed for Katherina tunicata during the 10-30-10‰ S cycle. Heart rate of Mytilus edulis varied in a parallel manner with oxygen consumption during both cycles. Katherina tunicata heart rate was relatively constant and could not be fitted to a regression line during the 10-30-10‰ S cycle. The normalized heart rate increased to 113% of control at 10‰ S of the 30-10-30‰ S cycle and returned to the control rate by 12 h. The oxygen consumption and heart rate of these two species are not directly coupled to regulation of water volume because different responses are observed with respect to salinity although there is poor water volume regulation in both species.     

Changes in nonlinear characteristics of heart rate variability under functional load on the cardiovascular system in healthy subjects and coronary heart disease patients

Some nonlinear characteristics of heart rate variability in the course of functional tests with physical exercise are described. Two groups of volunteers participated in the tests: a control group of 32 healthy subjects (group 1) and a group of 35 coronary heart disease (CHD) patients (group 2). Two series of experiments were performed for each group. An active orthostatic test (AOT) was used in the first series, and a gradually growing physical load on a bicycle ergometer (bicycle ergometer test, BET), in the second series. Along with statistical indices of heart rate (the mean RR interval and standard deviation), nonlinear indices of heart rate were estimated: the correlation dimensionality (D ₂) and approximate entropy (ApEn). Trends of the changes in nonlinear indices of heart rate have been found. The D ₂ and ApEn decreased in both groups of subjects during the AOT and BET under the maximum load. However, the groups of healthy subjects and CHD patients differed in the reactivity of indices, the amplitude of changes in nonlinear indices being narrower in the latter group than in group 1. Differently directed shifts in standard deviation (SDNN) and nonlinear indices have been found. Thus, the data obtained with the use of nonlinear heart rate characteristics show that heart rate under physical load is more multivariate and diverse in healthy subjects at rest and the amplitude of changes during the AOT and BET is greater than in CHD patients, which is a result of the specific autonomic control of heart activity in cardiovascular pathologies.     

Heart rate patterns under stress in three species of macaques

Cardiac responses during one hour exposures to three stressful experimental conditions were compared among juvenile females of three species of the genus Macaca (M. mulatta, M. radiata, and M. fascicularis). M. fascicularis showed the highest overall heart rate, and M. mulatta the lowest, in all three conditions. The principal difference between species was in the pattern of change in heart rate over the test sessions. Heart rate declined during the hour for all three species in the first two conditions (home cage novel environment), and the change was most rapid in M. mulatta and slowest in M. fascicularis. In the third and most stressful condition (physical restraint), each species showed a distinct temporal pattern. Heart rate increased over the hour in M. fascicularis, declined in M. radiata, and increased rapidly then declined gradually in M. mulatta. Individual differences in heart rate tended to be consistent within and across conditions. Correlations between behavioral measures of somatic activity and heart rate were generally modest. The results are in accord with other behavioral and physiological differences obtained for the same subjects, and suggest that responses to environmental stimuli reflect fundamental aspects of temperament that may vary substantially even among closely related species. © 1994 Wiley-Liss, Inc.     

Heart rate variation patterns in some representatives of Bivalvia

The pattern of heart rate variation was studied in bivalves sublittoral (aquaculture) and littoral mussels Mytilus edulis L. and Hiatella arctica L. in a long-term experiment at constant salinity (25‰) and temperature (10°C). Periodic changes in heart rate were observed in both littoral and sublittoral mussels. Heart activity could regularly decrease up to temporary cardiac arrest. Changes in H. arctica heart rate were much less pronounced compared to mussels and no cardiac arrest was observed.     

Ecophysiological aspects of cardiac activity in the subtropical mussel Perna viridis (L.) (Bivalvia: Mytilidae)

Cardiac activity in the subtropical mytilid mussel Perna viridis was monitored to assess the influence of various endogenous and exogenous parameters. Temperature had a positive, significant, effect on heart rate; the Q₁₀ ranged from 2.5 to 2.6. Salinity, over a wide range (15-35‰), had no significant influence on heart rate reflecting the species' euryhalinity. Reduced oxygen tensions, either induced by emersion or seawater hypoxia, elicited rapid, significant, bradycardia. Positive inotropisms (indicative of greater heart output) were evident during seawater hypoxia and may represent an energetically advantageous mechanism of reducing heart rate while increasing stroke volume to maintain haemolymph circulation to organs associated with digestion and basal metabolism. Malnourishment for 14 days did not affect heart rate. The heart rate of larger mussels was slower than those of smaller individuals. Gender-based differences in P. viridis' heart rate were not present. No diurnal (24 h) variation in cardiac activity was evident while mussels were exposed to relatively stable, immersed conditions. Heart rate plasticity often reflected the ambient environmental conditions and such a flexible physiological response may partly explain the species' dominance in transitional, polluted harbours.     

Circulatory Responses to Asphyxia Differ if the Asphyxia Occurs In Utero or Ex Utero in Near-Term Lambs

Background

A cornerstone of neonatal resuscitation teaching suggests that a rapid vagal-mediated bradycardia is one of the first signs of perinatal compromise. As this understanding is based primarily on fetal studies, we investigated whether the heart rate and blood pressure response to total asphyxia is influenced by whether the animal is in utero or ex utero.

Methods

Fetal sheep were instrumented at ∼139 days of gestation and then asphyxiated by umbilical cord occlusion until mean arterial blood pressure decreased to ∼20 mmHg. Lambs were either completely submerged in amniotic fluid (in utero; n = 8) throughout the asphyxia or were delivered and then remained ex utero (ex utero; n = 8) throughout the asphyxia. Heart rate and arterial blood pressure were continuously recorded.

Results

Heart rate was higher in ex utero lambs than in utero lambs. Heart rates in in utero lambs rapidly decreased, while heart rates in ex utero lambs initially increased following cord occlusion (for ∼1.5 min) before they started to decrease. Mean arterial pressure initially increased then decreased in both groups.

Conclusions

Heart rate response to asphyxia was markedly different depending upon whether the lamb was in utero or ex utero. This indicates that the cardiovascular responses to perinatal asphyxia are significantly influenced by the newborn''s local environment. As such, based solely on heart rate, the stage and severity of a perinatal asphyxic event may not be as accurate as previously assumed.     

The respiratory responses of Carcinus maenas (L.) to changes in environmental salinity

Exposure of Carcinus to a reduction in salinity is accompanied by an increase in oxygen consumption. The highest rates of oxygen consumption are found during the first 2–3 h after a reduction in salinity, after which oxygen consumption then declines, but to a higher than ‘normal’ level which is maintained throughout the period of exposure to low salinity. This augmented rate of oxygen consumption persists even after 3–4 days in water of reduced salinity and indicates that the respiratory rate of Carcinus does not acclimate rapidly to reduced salinity. The increased oxygen consumption is associated with an increase in ventilation volume resulting from an increase in the rate of beating of the scaphognathites, while oxygen utilization remains at a low level. Since the oxygen-transporting properties of the blood of Carcinus show little change under conditions of reduced salinity, the increased oxygen demand of the tissues is met by a rise in cardiac output resulting mainly from an increase in heart rate.     

Light Effects on the Synthesis of Ribulose-1,5-Bisphosphate Carboxylase in Lemna gibba L. G-3

Placing light-grown Lemna gibba L. G-3 into the dark results in a changed pattern of protein synthesis. Although the amount of protein in the tissue and the over-all rate of incorporation of [³⁵S]methionine into protein does not significantly decline during four days of darkness, the rate of synthesis of three polypeptides declines dramatically. One of these polypeptides is the chlorophyll a/b-binding protein and the two others are the large and small subunits of ribulose-1,5-bisphosphate carboxylase. The changed rates of synthesis of the two subunits were examined after transitions of plants from light to dark and dark to light. The in vivo synthesis of both subunits, while declining to a low level during four days of darkness, increases rapidly upon returning the plants to white light. In addition, the level of poly(A) mRNA coding for the precursor polypeptide of the small subunit of the enzyme falls to a low level in the dark and increases rapidly in response to white light. The increase in translatable mRNA for the small subunit is rapid enough to account for a major part of the increased synthesis of this subunit.     

The respiratory responses of the dog cockle Glycymerisglycymeris (L.) to declining environmental oxygen tension

The subtidal bivalve Glycymeris glycymeris (L.) exhibits a high degree of respiratory independence in conditions of declining environmental oxygen tension. In contrast to other bivalves previously studied, the index of respiratory independence, $\text{K}{}_1\text{K}{}_2$ decreases with increasing weight specific oxygen consumption indicating that small Glycymeris are better regulators of oxygen consumption than large Glycymeris.The respiratory responses of Glycymeris to hypoxia include a small initial increase in ventilation, brought about by increasing the percentage of time spent pumping and a large increase in oxygen utilization. Heart activity is elevated, principally through a large increase in the amplitude of heart beat, which suggests increased perfusion of the respiratory surfaces. The ventilation : relative perfusion ratio, therefore, declines over the range of oxygen tension that respiratory independence is maintained.The respiratory mechanism of Glycymeris is compared with that previously described for other bivalves and it is concluded that there are no clearcut differences between the respiratory responses to hypoxia of intertidal and subtidal species.     

Lizard heart rate and motor activity relationships in the circadian and ultradian ranges

• 1.1. The heart rate and motor activity of lizards (Gallotia galloti) maintained in a light-dark cycle (12:12 hr) and with changing cyclic temperature were recorded. Both variables showed a circadian pattern, motor activity variations leading heart rate by approximately 110 min.
• 2.2. Results from cross spectral analysis showed that heart rate was highly correlated with temperature and both variables were changing practically in phase. However, motor activity and temperature were less correlated and in this case motor activity led temperature by approximately 100 min.
• 3.3. In the ultradian range, two periodicities could be distinguished in the power spectra of motor activity and heart rate variations during the day: one between 0.019 and 3.9 × 10⁻³ cycles/min (central peak around 85 min period) and another, of lower power, between 0.05 and 0.02 cycles/min (central peak around 34 min period). During the night, only the heart rate showed both periodicities but with a lower amplitude.
• 4.4. The presence of ultradian oscillations in heart rate during the night suggested that they do not depend on motor activity which was almost absent during that daily period.
• 5.5. Motor activity and heart rate were also highly correlated in the ultradian range, motor activity leading heart rate by around 5 min at the 85 min main peak.