I. Galvin, G.B. Drummond, M. Nirmalan British Journal of Anaesthesia

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Distribution of blood flow and ventilation in the lung: gravity is not the only factor I. Galvin, G.B. Drummond, M. Nirmalan British Journal of Anaesthesia Volume 98, Issue 4, Pages 420-428 (April 2007) DOI: 10.1093/bja/aem036 Copyright © 2007 British Journal of Anaesthesia Terms and Conditions

Fig 1 Change in distribution of ventilation (upper to lower ratio) caused by changes in inspiratory flow rate. The filled square shows the quasi-static value. Data from Bake and colleagues.3 Adapted with permission from the American Physiological Society. British Journal of Anaesthesia 2007 98, 420-428DOI: (10.1093/bja/aem036) Copyright © 2007 British Journal of Anaesthesia Terms and Conditions

Fig 2 Relative blood flow in the saggital and transverse planes of an upright baboon, measured using microsphere injection. The relative blood flow is shown in equal proportional steps, in relation to the mean, from 0.2 to 3 times. In the saggital plane, the flow is shown by increasing diameter, and in the transverse section, by increasing height. Data from Glenny and colleagues.12 Adapted with permission from the American Physiological Society. British Journal of Anaesthesia 2007 98, 420-428DOI: (10.1093/bja/aem036) Copyright © 2007 British Journal of Anaesthesia Terms and Conditions

Fig 3 The vertical gradient of blood flow in baboons anaesthetized with ketamine and mechanically ventilated in four different postures. Measurements were made using microsphere injections. Data are from Table 2 of Glenny and colleagues.12 Adapted with permission from the American Physiological Society. In the upper panels, the linear regression of blood flow (expressed as a fraction of the overall flow) in relation to the vertical height is shown. This depiction resembles conventional diagrams, but it is important to note that height is the independent variable. The lower diagram indicates the orientation of the lung in relation to gravity. The influence of gravity on blood flow is greatest in the head up position and least in the prone position. However, it should be noted that the confidence limits of these relationships (not shown) are very large. British Journal of Anaesthesia 2007 98, 420-428DOI: (10.1093/bja/aem036) Copyright © 2007 British Journal of Anaesthesia Terms and Conditions

Fig 4 A bronchial cast showing the asymmetric branching structure typical of both airway and vascular branching in the lung. British Journal of Anaesthesia 2007 98, 420-428DOI: (10.1093/bja/aem036) Copyright © 2007 British Journal of Anaesthesia Terms and Conditions

Fig 5 A method of quantifying asymmetry of branching. Both the branch angle and the relative diameters of the parent to the daughter branches can vary. The relative flow depends on these features, tube length, the nature of the flow, and considerations such as minimizing energy loss. British Journal of Anaesthesia 2007 98, 420-428DOI: (10.1093/bja/aem036) Copyright © 2007 British Journal of Anaesthesia Terms and Conditions

Fig 6 The consequence of asymmetry in branching. The total flow divides into two fractions in each of the branches. The greater fraction is γ and hence the remaining fraction is 1−γ. When this asymmetrical pattern is continued for many generations of branches, this results in a distribution where different lung segments receive a wide range of flows (upper distribution histogram) and ventilations (lower distribution). The resultant blood flow and ventilation values in lung segments (samples) have a skewed normal distribution. British Journal of Anaesthesia 2007 98, 420-428DOI: (10.1093/bja/aem036) Copyright © 2007 British Journal of Anaesthesia Terms and Conditions

Fig 7 Two hypothetical models of correlation between ventilation and blood flow, using both the same number of lung samples and the same distribution of blood flow and ventilation [(a) and (b), distributions shown parallel to the axes] in each case. (a) The correlation between blood flow and ventilation in each lung sample is close, and the resultant scatter of V/Q values in the samples in small (c). Gas exchange is efficient. (b) Despite the same overall distribution of ventilation and blood flow values, the correlation is less close and the resultant distribution of V/Q values is broader (d) and gas exchange less good. British Journal of Anaesthesia 2007 98, 420-428DOI: (10.1093/bja/aem036) Copyright © 2007 British Journal of Anaesthesia Terms and Conditions