Determinants of respiratory sinus arrhythmia in the vagotomized rabbit.
After cardiac denervation, a small-amplitude respiratory sinus arrhythmia (RSA) has been described in animals and humans. Its mechanical and chemical determinants were investigated in 19 urethan-anesthetized, vagotomized, and mechanically ventilated rabbits. We measured the influence on RSA of arterial blood gases, beta-adrenergic blockade, and phasic and steady changes in right atrial pressure (RAP) induced by changes in tidal volume (VT, 20, 40, 60 ml), respiratory frequency (RF, 10, 20, 30 cycles/min), and dextran-induced RAP increases. Phasic changes in RAP during each recording were quantified as standard deviation of the first derivative of the RAP signal (dRAP) as a measure of magnitude of variations of the rate of change due to respiration. RSA was assessed by combined autoregressive power spectral analysis of R-R interval and respiration on sequences of 256 heart-beats. Despite vagotomy, RSA was present in all recordings in all animals. During room air breathing, RSA changes were dependent on RF and VT (P < 0.025 and P < 0.001, respectively) and correlated with dRAP (P < 0.001) and arterial PO2 (P < 0.001). beta-Adrenergic blockade did not change the amplitude of this residual RSA or its dependence on ventilatory mechanics. Dextran-induced increase in mean RAP from 2.9 to 11.9 mmHg did not modify RSA or dRAP. During 100% O2 inhalation, RSA changes were no longer significantly linked to RF and VT, and also the correlation of RSA with dRAP was reduced (P < 0.05). Changing the arterial PCO2 from 28 to 79 mmHg (induced by increasing dead space at fixed ventilation) did not modify RSA.(ABSTRACT TRUNCATED AT 250 WORDS)
Perlini
S
S
Department of Internal Medicine, University of Pavia, Italy.
Soldá
P L
PL
Piepoli
M
M
Sala-Gallini
G
G
Calciati
A
A
Finardi
G
G
Bernardi
L
L
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000758:Anesthesia; D000818:Animals; D001146:Arrhythmia, Sinus / Q000503:physiopathology*; D016280:Atrial Function, Right; D001696:Biomechanical Phenomena; D002245:Carbon Dioxide; D003714:Denervation; D006339:Heart Rate; D010100:Oxygen; D010275:Parasympathetic Nervous System / Q000503:physiopathology; D010313:Partial Pressure; D011312:Pressure; D011817:Rabbits; D012119:Respiration; D012121:Respiration, Artificial; D013908:Thoracotomy; D014628:Vagotomy
D000319:Adrenergic beta-Antagonists; D002245:Carbon Dioxide; D010100:Oxygen