Dissociation of temperature-gradient and evaporative heat loss during cold gas hyperventilation in cold-induced asthma.
We examined temperature-gradient and evaporative energy losses during cold gas inhalation challenges in patients with exercise-induced asthma by using gases with similar water-carrying capacities but significantly different volume heat capacities. Seven subjects were asked to hyperventilate mixtures of 80% helium/20% oxygen (HeO2) or 80% sulfur hexafluoride/20% oxygen (SF6O2) for 5 min at a fixed target minute ventilation of 20 x FEV1 and an inspired gas temperature of 0 degrees C. Each subject equilibrated his or her lungs with the appropriate gas mixture prior to testing: PETCO2 and FIO2 were monitored and maintained at constant values (CO2 = 0.05; O2 = 0.20) by CO2 scrubbing and addition of compressed gas to the system. Gas composition, inspired and expired flow rates, and gas temperatures at the airway opening were recorded in real time using a computer-based data collection system that calculated respiratory heat loss on a per breath basis. Bronchoconstriction was quantitated using specific airway conductance measured before and serially after each challenge. The degree of bronchoconstriction correlated closely with evaporative respiratory heat loss (r = 0.658 p less than 0.05), but poorly with both temperature-gradient (r = 0.114, p greater than 0.20) and total (r = 0.268, p greater than 0.15) heat loss. These findings suggest that total respiratory heat loss is not the primary stimulus in exercise-induced asthma, and further suggest that total water loss, or focal heat/water loss, may be important in inducing bronchospasm in this subset of asthmatics.
Ingenito
E
E
Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115.
Solway
J
J
Lafleur
J
J
Lombardo
A
A
Drazen
J M
JM
Pichurko
B
B
D000328:Adult; D001249:Asthma / Q000209:etiology / Q000503:physiopathology*; D001250:Asthma, Exercise-Induced / Q000209:etiology / Q000503:physiopathology; D055592:Biophysical Phenomena; D001703:Biophysics; D001833:Body Temperature Regulation; D001980:Bronchi / Q000503:physiopathology; D003080:Cold Temperature / Q000009:adverse effects*; D003251:Constriction, Pathologic / Q000209:etiology / Q000503:physiopathology; D005260:Female; D006371:Helium; D006801:Humans; D006985:Hyperventilation / Q000209:etiology / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010100:Oxygen; D012129:Respiratory Function Tests / Q000379:methods; D013459:Sulfur Hexafluoride; D013696:Temperature
D006371:Helium; D010100:Oxygen; D013459:Sulfur Hexafluoride