Fractal ventilation enhances respiratory sinus arrhythmia.
BACKGROUND
Programming a mechanical ventilator with a biologically variable or fractal breathing pattern (an example of 1/f noise) improves gas exchange and respiratory mechanics. Here we show that fractal ventilation increases respiratory sinus arrhythmia (RSA) -- a mechanism known to improve ventilation/perfusion matching.


METHODS
Pigs were anaesthetised with propofol/ketamine, paralysed with doxacurium, and ventilated in either control mode (CV) or in fractal mode (FV) at baseline and then following infusion of oleic acid to result in lung injury.


RESULTS
Mean RSA and mean positive RSA were nearly double with FV, both at baseline and following oleic acid. At baseline, mean RSA = 18.6 msec with CV and 36.8 msec with FV (n = 10; p = 0.043); post oleic acid, mean RSA = 11.1 msec with CV and 21.8 msec with FV (n = 9, p = 0.028); at baseline, mean positive RSA = 20.8 msec with CV and 38.1 msec with FV (p = 0.047); post oleic acid, mean positive RSA = 13.2 msec with CV and 24.4 msec with FV (p = 0.026). Heart rate variability was also greater with FV. At baseline the coefficient of variation for heart rate was 2.2% during CV and 4.0% during FV. Following oleic acid the variation was 2.1 vs. 5.6% respectively.


CONCLUSIONS
These findings suggest FV enhances physiological entrainment between respiratory, brain stem and cardiac nonlinear oscillators, further supporting the concept that RSA itself reflects cardiorespiratory interaction. In addition, these results provide another mechanism whereby FV may be superior to conventional CV.
Mutch
W Alan C
WA
Department of Anesthesia, Faculty of Medicine, Anesthesia Research Laboratory, University of Manitoba, Winnipeg MB, Canada. amutch@ms.umanitoba.ca
Graham
M Ruth
MR
Girling
Linda G
LG
Brewster
John F
JF
D000818:Animals; D001146:Arrhythmia, Sinus / Q000209:etiology / Q000503:physiopathology* / Q000517:prevention & control*; D017709:Fractals; D006339:Heart Rate; D012121:Respiration, Artificial / Q000379:methods*; D012131:Respiratory Insufficiency / Q000150:complications / Q000503:physiopathology* / Q000628:therapy*; D015656:Respiratory Mechanics; D013552:Swine; D013813:Therapy, Computer-Assisted / Q000379:methods*; D016896:Treatment Outcome