E. W. Taylor

Toward understanding respiratory sinus arrhythmia: relations to cardiac vagal tone, evolution and biobehavioral functions.

Respiratory sinus arrhythmia (RSA, or high-frequency heart-rate variability) is frequently employed as an index of cardiac vagal tone or even believed to be a direct measure of vagal tone. However, there are many significant caveats regarding vagal tone interpretation: 1. Respiratory parameters can confound relations between RSA and cardiac vagal tone.2. Although intraindividual relations between RSA and cardiac vagal control are often strong, interindividual associations may be modest.3. RSA measurement is profoundly influenced by concurrent levels of momentary physical activity, which can bias estimation of individual differences in vagal tone.4. RSA magnitude is affected by beta-adrenergic tone.5. RSA and cardiac vagal tone can dissociate under certain circumstances.6. The polyvagal theory contains evolution-based speculations that relate RSA, vagal tone and behavioral phenomena. We present evidence that the polyvagal theory does not accurately depict evolution of vagal control of heart-rate variability, and that it ignores the phenomenon of cardiac aliasing and disregards the evolution of a functional role for vagal control of the heart, from cardiorespiratory synchrony in fish to RSA in mammals. Unawareness of these issues can lead to misinterpretation of cardiovascular autonomic mechanisms. On the other hand, RSA has been shown to often provide a reasonable reflection of cardiac vagal tone when the above-mentioned complexities are considered. Finally, a recent hypothesis is expanded upon, in which RSA plays a primary role in regulation of energy exchange by means of synchronizing respiratory and cardiovascular processes during metabolic and behavioral change.

The respiratory and cardiovascular changes associated with the emersion response ofCarcinus maenas (L.) during environmental hypoxia, at three different temperatures

Summary1.When exposed to progressive hypoxia in shallow seawater,Carcinus maenas partially emerged into air and aerated its branchial chambers by reversing the direction of their irrigation. Emersion took place at a meanPI, O2 of 18 mm Hg at 6 °C, 21 mm Hg at 12 °C and 59 mm Hg at 17 °C.2.At low oxygen tensions submerged crabs underwent a progressive bradycardia. Heart rate first became significantly lower than the rate in normoxia below aPI O2 of 30 mm Hg at 6 °C, 40 mm Hg at 12 °C and below 60 mm Hg at 17 °C. The proportion of total time spent irrigating the gills in a reversed direction increased in hypoxic seawater (PI, O2< 50 mm Hg), but respiratory rate was unchanged.3.Emersion into air always occurred during a reversal of irrigation and was accompanied by prolonged reversals, with consequent aeration of the branchial chambers, and by an immediate and maintained tachycardia back towards the rate in normoxic seawater. Crabs emerging into a hypoxic atmosphere (

The effect of hypoxia on the levels of circulating catecholamines in the dogfishScyliorhinus canicula

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Response of the dogfish (Scyliorhinus canicula L.) to slowly induced and rapidly induced hypoxia

< 10mm Hg) showed neither a maintained reversal of irrigation nor a maintained tachycardia.4.The oxygen tension of the postbranchial blood (Pa,O2) was 94 mm Hg in crabs submerged in normoxic seawater (PI,O2 146 mm Hg) at 12 ° C. During progressive hypoxiaPa, O2 fell in direct proportion to the drop inPI,O2. Emersion caused no significant increase inPa, O2.5.The mean oxygen content of postbranchial blood (Ca, O2) was 0.96 vol. % at aPI,O2 of 145 mm Hg.Ca, O2 fell to 0.19 vol.-% in submerged crabs at a meanPI,O2 of 25 mm Hg but rose to 0.45 vol.-% following 10 min emersion into air at a meanPI, O2 of 22 mm Hg.6.The results provide evidence of a respiratory role for the emersion response and also of an adaptive role for the high affinity of the blood pigment inCarcinus.

Ventilation, heart rate and respiratory gas exchange in the crayfishAustropotamobius pallipes (Lereboullet) submerged in normoxic water and following 3 h exposure in air at 15°C

Summary1.Oxygen consumption

Protein synthesis and specific dynamic action in crustaceans: effects of temperature

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