Assessment of upper airway dynamic properties using sternal phrenic nerve magnetic stimulation in awake subjects

To assess upper airway (UA) dynamic properties, magnetic stimulation of the phrenic nerves (MSPN) is usually performed at cervical level or anterior-laterally at the neck base. We hypothesized that UA dynamic properties could be effectively assessed by MSPN performed at the sternal level. Instantaneous flow, pharyngeal and mask pressures were recorded in 12 healthy awake subjects. End-expiratory MSPN were applied in random order with a non-focal coil placed behind the 7th cervical vertebrae (C7-MS) and at the sternal level (a-MS). The percentage of flow-limited twitches was greater with a-MS (a-MS: 33% and C7-MS: 2%; P<0.0001). For the non flow-limited twitches, maximal inspiratory flow was 36% greater (P<0.001) and isoflow UA resistance was lower with a-MS (0.6±0.1 and 0.9±0.1 cmH2Ol(-1)s; P=0.02). Maximal inspiratory flow of flow-limited twitches was 78% greater (P=0.05) and isoflow UA resistance tended to be lesser with a-MS (0.9±0.3 and 1.8±0.7 cmH2Ol(-1)s; P=0.09). a-MS could be a practical approach for assessing UA dynamic properties in awake subjects.