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Distribution of blood flow and ventilation in the lung: gravity is not the only factor. Br J Anaesth
- Mahesh Nirmalan, I Galvin, Drummond GB (15 May 2007)
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Distribution of blood flow and ventilation in the lung
- Krishnan Melarkode (11 April 2007)
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Mahesh Nirmalan Manchester Royal Infirmary, I Galvin, Drummond GB
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Editor, Thank you very much for giving us the opportunity to respond to the question raised by Dr Krishnan Melarkode on our article entitled “Distribution of blood flow and ventilation in the lung: gravity is not the only factor” 1. The traditional gravitational model would imply that in the lateral position both ventilation and perfusion will be greater in the dependant lung. However the work by Chang et al. has demonstrated that this is not necessarily true. In fact, their work showed that in the left lateral position, both blood flow and ventilation were less in the dependant lung than in the non dependant lung (Table 3)2. Furthermore, the gravity- dependant vertical gradient in blood flow was greater in the right lateral than in the left lateral position. This observation was attributed to impaired blood flow in the dependant left lung in the left lateral position. These findings would strongly support the view that there are some underlying structural features (probably the weight of the heart and mediastinum) that impede blood flow and ventilation to the left lung in the left lateral position. The reduction in ventilation to some of the areas in the dependant left lung was sufficient to trigger hypoxic pulmonary vasoconstriction. Since hypoxic pulmonary vasoconstriction is a generalised phenomenon it affects blood flow to the entire lung. This independent reduction in blood flow would lead to an increase in the ventilation/perfusion ratio (as perfusion is reduced due to hypoxic pulmonary vasoconstriction) as shown clearly by Chang et al2. We believe that this message is clear enough in our Review. References: 1. Galvin I, Drummond GB, Nirmalan M. Distribution of blood flow and ventilation in the lung: gravity is not the only factor. Br J Anaesth 2007;98:420-8 2. Chang H, Lai-Fook SJ, Domino KB et al. Spatial distribution of ventilation and perfusion in anaesthetised dogs in lateral postures. J Appl Physiol 2002;92:745-62 Conflict of Interest:We are the authors of the original manuscript |
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Krishnan Melarkode, Specialist Registrar - Anaesthesia Cambridge, UK
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Editor - I read with interest the review article by Galvin I, Drummond GB and Nirmalan M ¹ on the distribution of blood flow and ventilation in the lung.The authors need to be congratulated for their extensive review on this important aspect in respiratory physiology. However, I would like to highlight one important statement which I feel needs to be clarified. The authors state that in the left lateral position, the total blood flow, total ventilation and V/Q ratio can be less in the dependent lung than in the non-dependent lung (which is against the traditional gravitational model). This concept has been explained well by the authors. This point has been highlighted again in the penultimate paragraph on the implications in left lateral position. However, in the same paragraph, the authors make a contradictory statement and conclude that the V/Q ratio for the whole lung was greater in the left as opposed to the right lateral position. Could the authors kindly clarify this point? References: 1.Galvin I, Drummond GB, Nirmalan M. Distribution of blood flow and ventilation in the lung: gravity is not the only factor. Br J Anaesth 2007; 98: 420-28. Conflict of Interest:None declared |
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