Direct recordings of the temperatures in the tracheobronchial tree in normal man.

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Abstract
In an effect to determine how far inspired air could penetrate into the respiratory tract before being brought to body conditions, we measured the temperature in the airways of the anterior basilar segment of the right lower lobe in five normal subjects while they breathed air at subfreezing and ambient conditions. During quiet breathing, most of the heating of the incoming gas took place in the upper airways as expected. However, as the thermal burden was increased by rapid inspirations, frigid air, and hyperventilation, the temperature of the distal airways progressively fell and the point at which the incoming air reached body conditions moved deep into the periphery of the lung. These findings demonstrate that heat and water transfer is not localized to one region, but rather is a continuous process that begins the moment the air enters the body and involves as much of the respiratory tract as necessary to complete the task.