Subject specific effects of hyperpnea but not hypocapnia on airway conductance

• Published in: Respiratory physiology & neurobiology Vol. 177; no. 2; pp. 127 - 132
• Main Authors: Steinback, Craig D., Whitelaw, William A., Poulin, Marc J.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 31.07.2011; Elsevier
• Subjects: Adult; Biological and medical sciences; Female; Fundamental and applied biological sciences. Psychology; Humans; Hypercapnia - physiopathology; Hyperpnea; Hyperventilation; Hypocapnia; Hypocapnia - physiopathology; Male; Medical Education; Pulmonary conductance; Pulmonary resistance; Pulmonary Ventilation - physiology; Pulmonary/Respiratory; Respiratory Function Tests; Respiratory Mechanics - physiology; Vertebrates: respiratory system; Pulmonary resistance; Hyperpnea; Hyperventilation; Hypocapnia; Pulmonary conductance; Human; Respiratory tract; Vertebrata; Mammalia; Lung; Carbon dioxide; Respiratory system
• ISSN: 1569-9048; 1878-1519; 1878-1519
• DOI: 10.1016/j.resp.2011.03.022

We investigated the effects of hypocapnia in normal subjects on airway tone while controlling airway cooling and drying. We hypothesized that airway tone is positively related to the degree of hypocapnia. Participants (8; 2 women) underwent 3 protocols consisting of 20min of hyperpnea (breathing frequency=20 breathsmin−1; tidal volume=2.5L) and 10min recovery. End-tidal PCO2 was maintained at +1Torr above rest (ISO; 37.9±1.2Torr), 8Torr below resting values (H-8; 29.2±1.7Torr) or 15Torr below resting values (H-15; 23.2±2.9Torr). Breath-by-breath lung conductance (GL) was calculated from flow, volume, and esophageal pressure. GL responses to hyperpnea varied widely across subjects. However, individual responses during ISO correlated highly with responses during H-8 (r=0.976, p<0.001) and H-15 (r=0.952, p<0.001), with the magnitude of change inversely related to basal GL (r=−0.555, p=0.006). Thus, inter-subject variation in GL was due to hyperpnea, with no detectable effect of hypocapnia.