title: Role of airway resistance in the control of ventilation during exercise.
abstract: To analyze the interdependence of respiratory drive, ventilation and airway resistance during exercise, mouth occlusion pressure (P0.1), minute ventilation (V) and mean inspiratory flow (VT/TI) were studied in eight normal subjects performing cycle-ergometer exercise at loads ranging from 0 W to 200 W under two different ambient conditions: 1) during oxygen breathing at 1.3 ATA, and 2) during air breathing at 6 ATA (PO2 = 1.3 ATA). Comparison of measurements at 6 ATA with those at 1.3 ATA indicated that a 4.2-fold increase in respired gas density (D) had little or no influence on the V and VT/TI responses whereas P0.1 at any given VT/TI was increased by a factor of 1.9. In both conditions, P0.1 increased at a faster rate than VT/TI as the work load increased. At loads higher than 40 W, the relationship between P0.1, D and VT/TI was found to approximate the equation P0.1 = K X D0.5(VT/TI)1.4, where K is a constant that varies among subjects. The results indicate that the ratio P0.1/(VT/TI), an estimate of respiratory impedance, increased with both D and VT/TI. Evidence is presented that the respiratory drive was reflexly enhanced in response to loading as airway resistance increased with D and/or VT/TI. We conclude that neural mechanisms compensating for internal flow-resistive loading play an important role in the control of ventilation during exercise, both at normal and at raised air pressures.
mesh_terms: D000328:Adult; D000403:Airway Resistance; D006801:Humans; D006931:Hyperbaric Oxygenation; D008297:Male; D009055:Mouth / Q000502:physiology; D010101:Oxygen Consumption; D010313:Partial Pressure; D005082:Physical Exertion; D011312:Pressure; D012119:Respiration; D012129:Respiratory Function Tests; D012143:Respiratory Physiological Phenomena