References 1.Paredi P, Caramori G, Cramer D, et al. From the authors:We would like to thank J.B. McCafferty and J.A. Innes for their interest and constructive criticism relating to our paper which reported low exhaled breath temperature gradients in chronic obstructive pulmonary disease patients compared to normal subjects [1].J.B. McCafferty and J.A. Innes suggest that it is controversial that bronchial blood flow has a role in airway heat exchange. We disagree and would like to draw their attention to numerous papers that demonstrated the opposite effect. First, it has been shown that changes in airway blood volume are reflected in fluctuations in intra-thoracic heat exchange, whereas even large increases in blood flow through the pulmonary circulation do not influence airstream temperature [2]. This proves that bronchial and not pulmonary blood flow plays a major role in airway heat exchange. Secondly, changes in bronchial blood flow can alter airway responsiveness and temperature [3], confirming that the bronchial circulation may control airstream temperature and contribute to airway narrowing. Thirdly, temperature changes induce bronchoconstriction, which can be prevented by reducing mucosal blood supply using inhaled vasoconstrictors [3], indicating that airway temperature and bronchial blood flow are correlated. Furthermore, preliminary data presented as an oral presentation at the American Thoracic Society meeting in Atlanta last year by our group showed a correlation between bronchial blood flow, measured noninvasively by an inhaled soluble gas technique, and exhaled breath temperature gradients [4]. Therefore, there is substantial evidence that airway blood flow is the major determinant of airway heat exchange.In their letter, J.B. McCafferty and J.A. Innes also state that heat transfer occurs in the upper airways (above the glottis) when breathing normally at room temperature. They quote a manuscript published in 1953 by COLE [5], but they have not interpreted the manuscript correctly and have ignored more recent publications by the same author. Even though we agree that inspired air is mostly conditioned in the upper airways, in our study we concentrated on exhaled air. The work of COLE [6] has demonstrated that "during expiration heat and water are returned to the exhaled air along the whole of the respiratory tract", including the bronchial tree. We would also like to stress that the patients included in our study, as described in the method session, were not "respiring at low flow rates" as indicated by J.B. McCafferty and J.A. Innes. Rather, they were breathing normally at tidal volume before being asked to exhale at a constant exhalation flow rate (10 L?min -1 ) after a deep inhalation to total lung capacity.Regarding the methodology for the measurement of exhaled breath temperature gradients, J.B. McCafferty and J.A. Innes point out that we did not report the method of flow targeting. However, after describing the exhalation manoeuvre as flow and pressure controlled, we refer the reader to a ...

to the readers of the European Respiratory Journal. Michael Goldman passed away on March 18, 2010 at the age of 74 yrs, following a myocardial infarction. He will be an immense loss to lung physiology.