Intraairway thermal profiles during exercise and hyperventilation in normal man.

Abstract

When large volumes of air are inhaled at rapid rates of ventilation, substantial segments of the tracheobronchial tree become involved in the conditioning process and the inspirate does not reach body conditions of temperature and humidity until it passes well into the peripheral bronchi. To determine if the manner in which ventilation is elevated is an important factor in producing this response, we measured the temperature of the airstream at six points in the tracheobronchial tree from the pharynx to the subsegmental bronchi during 5 min of exercise and voluntary hyperventilation in seven normal subjects while they inhaled frigid air. Minute ventilation and respiratory frequency were recorded at minute intervals and intrathoracic temperatures were measured continuously. With both forms of hyperpnea, airway temperature fell dramatically, and there were no significant differences between exercise and hyperventilation. These results demonstrate that the thermal events that occur within the lung during short, moderately intense degrees of exercise can be readily simulated by voluntary hyperventilation when ventilation and inspired air conditions are matched. Our data also indicate that this form of exercise does not result in an increase in airstream temperature and raise the possibility that the bronchial blood supply may be determined by the local thermal needs of the airways to recover heat and water independent of, at least moderate, increases in cardiac output.

Selective response of human airway epithelia to luminal but not serosal solution hypertonicity. Possible role for proximal airway epithelia as an osmolality transducer.

“…Evaporative water loss in excess of replenishment in the proximal airways cools airway surfaces and raises the osmolality of airway surface liquids (8,9). Recent attention has focused on these effects in man because of observations that exercise-induced asthma appears to be triggered by the inspiration of cool, dry air (8).…”

Postexertional airway rewarming and thermally induced asthma. New insights into pathophysiology and possible pathogenesis.

“…It is now appreciated that reductions in airstream and tracheal wall temperatures are normal occurrences during periods of hyperpnea, and it is well established that when these intrapulmonary thermal changes become sufficiently severe, bronchial obstruction develops in asthmatic as well as in normal individuals (1)(2)(3)(4)(5)(6)(7). The mechanism by which airflow limnitation develops is unknown, however, and although several theories have been proposed, hione of them accounts for all of the observations in the literature (8)(9)(10).…”

Airway cooling and rewarming. The second reaction sequence in exercise-induced asthma.

“…We have used similar experimental designs successfully in the past (9,10,15). We have also documented previously that the effects of repetitive bouts of hyperpnea on pulmonary mechanics (10,14,18) and airstream temperature ( 10,17,19) are identical when inspired air conditions and VE are held constant.…”

“…As in our previous studies, the distances from the tip ofthe nose to the major anatomic landmarks were recorded, and a flexible thermal probe containing multiple small thermistors was inserted into the tracheobronchial tree (9,10,15). The technical features ofthe probe have been reported previously ( 16,17). Once the tip ofthe probe was placed beyond the end of the bronchoscope, the latter was removed.…”