British Journal of Anaesthesia, Vol 79, Issue 1 35-40, Copyright © 1997 by The Board of Management and Trustees of the British Journal of Anaesthesia
D. C. Galletly and P. D. Larsen
In 20 spontaneously breathing patients undergoing minor surgical procedures
under general anaesthesia, we examined the timing relationship of heart
best and ventilation. Patients received propofol 2-2.5 mg kg-1 and fentanyl
1 microgram kg-1 and breathed a mixture of 1- 1.5% isoflurane and 66%
nitrous oxide in oxygen. We recorded ECG R wave times and the start of each
inspiration. We observed that: (1) all subjects showed evidence of phase
coupling in which heart beats occurred at constant phases of the
ventilatory cycle; (2) there was a significant preference for whole number
ratios of heart rate to ventilatory frequency; (3) phase coupling was
associated frequently with quantal changes in heart rate or ventilatory
frequency, or both; (4) six coupling patterns were described according to
the timing relationship between the ECG R wave and start of inspiration and
according to changes in the number of heart beats within each ventilatory
period; (5) phase coupling was achieved primarily by transient changes in
ventilatory period. Phase coupling, in concert with respiratory sinus
arrhythmia, may optimize the performance of the thoracic pump, matching
cardiac filling to venous return. Coupling may therefore have anaesthetic
relevance in conditions of impaired cardiac performance or hypovolaemia.
CLINICAL INVESTIGATIONS
Cardioventilatory coupling during anaesthesia
Section of Anaesthesia, Wellington School of Medicine, PO Box 7343, Wellington, New Zealand
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