HEXAAXIAL SYSTEM
I.
II.III.
aVF
aVR
aVL
I
II III
aVF
aVR aVL
R
L
F
RESPIRATORY (SINUS) ARRHYTHMIA
1847, Ludwig, ECG and breathing of dog – respiratory sinus arrhythmia
Detectable already during prenatal life.
Present in numerous species in animal kingdom – in all vertebrates.
Physiological meaning ???? STABILISATION OF MEAN BP (protection against mechanical
effect of intrathoracic pressure on arterial BP)
Key effect of parasympathetic NS(decrease of its tonus), sympathetic NS modulates.
MECHANISMS:
1) CENTRAL
2) REFLEXES FROM LUNGS
3) REFLEXES FROM BARORECEPTORS
4) REFLEXES FROM RECEPTORS IN THE RIGHT ATRIUM
5) LOCAL EFFECTS ON SA NODE
6) EFFECT OF OSCILLATIONS OF pH, paO2, paCO2
Central mechanisms
• Central generator of RSA
• Respiratory neurons in medulla oblongata hyperpolarise preganglionic
vagal neurons
• Vagal tonus decreases during inspiration – HR increases
Reflexes from lungs – inflation reflexes
• Stimulation of vagal stretch-receptors during inspiration supresses
inspiratory centre and also cardio-inhibitory centre in medulla
oblongata
Reflexes from baroreceptors
• Diverse opinions about the effect of arterial baroreceptors on RSA
• Fluctuation of sensitivity of baroreceptors during respiratory cycle
Reflexes from receptors in the right atrium
• Bainbridge, 1915
• Reflex increase of HR during atria stretching
• Applicable in explanted (denerved) heart
Local effects on SA node
• Stretching of SA node causes faster spontaneous depolarisation
• Effect of mechanosensitive chloride channels
• Changes of SA node perfusion (a. centralis) and possible compression of SA
node by expanding lungs
Effect of oscillations of pH, paO2 a paCO2
• Oscillatory activity of peripheral chemoreceptors contributes to
formation of RSA and increases its amplitude