| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
,
* From the Department of Anesthesia, University of Manitoba, Winnipeg, Canada; the
Department of Surgery, School of Medicine, Washington University in St. Louis, St. Louis, Missouri, USA; the
Department of Physics, Duke University, Durham, North Carolina, USA; the
Mathematics Division, Army Research Office, Research Triangle Park, North Carolina, USA; and the
|| James Hogg iCapture Centre, University of British Columbia, Vancouver, Canada.
Address correspondence to: Dr. W.A.C. Mutch, Department of Anesthesia, University of Manitoba, Winnipeg, Manitoba, Canada. Phone: 204-789-3449; Fax: 204-789-3945; E-mail: amutch{at}cc.umanitoba.ca
Purpose: Variable ventilation is superior to control mode ventilation in a number of circumstances. The nature of the breathing file used to deliver the variable rate and tidal volume has not been formally examined.
Methods: We compared two different noise files in a randomized prospective trial of variable ventilation. Pigs were anesthetized, intubated, and mechanically ventilated. Oleic acid was infused to introduce lung injury. The animals were ventilated at a tidal volume of 7 mL·kg–1, in variable mode, with either physiologically-derived noise (variability file – 1,587 breath intervals–obtained from a spontaneously breathing volunteer; n = 10) or a variability file of identical length derived from computer- generated white noise (n = 10).
Results: The physiologically-derived noise had a power law 
-exponent of –0.27 and a Hölder exponent of –0.38, indicative of auto-correlated noise. The computer-generated noise had an -exponent of –0.52 and a Hölder exponent of –0.49, indicative of white noise. Both files showed multifractal characteristics. There were no differences between groups, at any time period, for PaO2, PaCO2, and static or dynamic respiratory system compliance. No differences were observed between groups for wet:dry lung weight ratios or for interleukin-8 in bronchoalveolar lavage fluid.
Conclusion: This study demonstrates that the nature of the variability files, chosen to drive the variable ventilator, had no effect on indices of gas exchange or respiratory mechanics in this model. A considerable overlap of the multifractal files existed. The potential to drive a variable ventilator using algorithm-derived files with multifractal characteristics, thereby eliminating the requirement to use physiologically-derived signals, is discussed.
1 West BJ, Shlesinger M. The noise in natural phenomena. Am Sci 1990; 78: 40–5.
2 Goldberger AL, West BJ. Fractals in physiology and medicine. Yale J Biol Med 1987; 60: 421–35.[Medline]
3 Goldberger AL, Rigney DR, West BJ. Chaos and fractals in human physiology. Sci Am 1990; 262: 42–9.[Medline]
4 Goldberger AL, Amaral LA, Hausdorff JM, Ivanov pC, peng CK, Stanley HE. Fractal dynamics in physiology: alterations with disease and aging. Proc Natl Acad Sci USA 2002; 99(Suppl 1): 2466–72.
5 Ivanov pC, Amaral LA, Goldberger AL, et al. Multifractality in human heartbeat dynamics. Nature 1999; 399: 461–5.[Medline]
6 West BJ, Scafetta N, Cooke WH, Balocchi R. Influence of progressive central hypovolemia on Hölder exponent distributions of cardiac interbeat intervals. Ann Biomed Eng 2004; 32: 1077–87.[Medline]
7 Norris pR, Ozdas A, Cao H, et al. Cardiac uncoupling and heart rate variability stratify ICU patients by mortality: a study of 2088 trauma patients. Ann Surg 2006; 243: 804–12.[Medline]
8 papaioannou VE, Maglaveras N, Houvarda I, Antoniadou E, Vretzakis G. Investigation of altered heart rate variability, nonlinear properties of heart rate signals, and organ dysfunction longitudinally over time in intensive care unit patients. J Crit Care 2006; 21: 95–103.[Medline]
9 Norris pR, Morris JA Jr, Ozdas A, Grogan EL, Williams AE. Heart rate variability predicts trauma patient outcome as early as 12 h: implications for military and civilian triage. J Surg Res 2005; 129: 122–8.[Medline]
10 Mutch WA, Lefevre GR. Health, ‘small-worlds’, fractals and complex networks: an emerging field. Med Sci Monit 2003; 9: MT19–23.[Medline]
11 Boker A, Graham MR, Walley KR, et al. Improved arterial oxygenation with biologically variable or fractal ventilation using low tidal volumes in a porcine model of acute respiratory distress syndrome. Am J Respir Crit Care Med 2002; 165: 456–62.
12 Boker A, Haberman CJ, Girling L, et al. Variable ventilation improves perioperative lung function in patients undergoing abdominal aortic aneurysmectomy. Anesthesiology 2004; 100: 608–16.[Medline]
13 Brewster JF, Graham MR, Mutch WA. Convexity, Jensen’s inequality and benefits of noisy mechanical ventilation. J R Soc Interface 2005; 2: 393–6.[Medline]
14 Graham MR, Haberman CJ, Brewster JF, Girling LG, McManus BM, Mutch WA. Mathematical modelling to centre low tidal volumes following acute lung injury: a study with biologically variable ventilation. Respir Res 2005; 6: 64.[Medline]
15 Glenny RW, Robertson HT, Yamashiro S, Bassingthwaighte JB. Applications of fractal analysis to physiology. J Appl Physiol 1991; 70: 2351–67.
16 Mols G, priebe HJ, Guttmann J. Alveolar recruitment in acute lung injury. Br J Anaesth 2006; 96: 156–66.[Medline]
17 Kolobow T. Volutrauma, barotrauma, and ventilator-induced lung injury: lessons learned from the animal research laboratory. Crit Care Med 2004; 32: 1961–2.[Medline]
18 Funk DJ, Graham MR, Girling LG, et al. A comparison of biologically variable ventilation to recruitment manoeuvres in a porcine model of acute lung injury. Respir Res 2004; 5: 22.[Medline]
19 Mutch WA, Harms S, Graham MR, Kowalski SE, Girling LG, Lefevre GR. Biologically variable or naturally noisy mechanical ventilation recruits atelectatic lung. Am J Respir Crit Care Med 2000; 162: 319–23.
20 McMullen MC, Girling LG, Graham MR, Mutch WA. Biologically variable ventilation improves oxygenation and respiratory mechanics during one-lung ventilation. Anesthesiology 2006; 105: 91–7.[Medline]
21 Mutch WA, Eschun GM, Kowalski SE, Graham MR, Girling LG, Lefevre GR. Biologically variable ventilation prevents deterioration of gas exchange during prolonged anaesthesia. Br J Anaesth 2000; 84: 197–203.
22 Yum MK, Kim JT, Kim HS. Increased non-stationarity of heart rate during general anaesthesia with sevoflurane or desflurane in children. Br J Anaesth 2008; PMID 18403379.
23 Fadel pJ, Barman SM, phillips SW, Gebber GL. Fractal fluctuations in human respiration. J Appl Physiol 2004; 97: 2056–64.
24 Noujaim SF, Berenfeld O, Kalifa J, et al. Universal scaling law of electrical turbulence in the mammalian heart. Proc Natl Acad Sci USA 2007; 104: 20985–9.
Related articles in CJA:
This article has been cited by other articles:
 |
|
 |
|
  G. L. Gebber and S. M. Barman Variable rate ventilation strategies for the injured lung/Strategies de ventilation a debit variable pour le poumon blesse Can J Anesth, September 1, 2008; 55(9): 572 - 576. [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
