Assessment of upper airway dynamics by anterior magnetic phrenic stimulation in conscious sleep apnea patients.

Phrenic nerve magnetic stimulation (PNMS) performed anterolaterally at the base of the neck (BAMPS) and cervical magnetic stimulation are common techniques for assessing upper airway (UA) mechanical properties in conscious humans. We considered that if NMS performed at the sternal level (a-MS) could induce a similar percentage of flow-limited twitches as BAMPS in conscious subjects, gauging UA dynamic properties by PNMS would be simplified. Instantaneous flow, pharyngeal and esophageal pressures, as well as thoraco-abdominal motion were recorded in 10 conscious sleep apnea patients. BAMPS and a-MS were applied at end expiration. The percentage of flow-limited twitches, maximal tolerated intensity, and minimal stimulator output associated with flow-limited twitches were similar between BAMPS and a-MS. Examining the effects of stimulation site, stimulation intensity and site*intensity interaction on the characteristics of flow-limited twitches, the former was responsible for more negative peak esophageal pressure (BAMPS: -11.5 ± 0.9 cmH(2)O; a-MS: -6.5 ± 1.1 cmH(2)O; P = 0.002) and UA closing pressure (BAMPS: -7.7 ± 0.5 cmH(2)O; a-MS: -5.8 ± 0.6 cmH(2)O; P = 0.02) as well as for lower mean linear upper airway resistance (UAR) (BAMPS 3.5 ± 0.4 cmH(2)O·l(-1)·s(-1); a-MS 2.2 ± 0.4 cmH(2)O·l(-1)·s(-1); P = 0.02). a-MS systematically evoked outward/inward thoracic displacement, although this movement pattern was observed in only 50% of patients when they were subjected to BAMPS. Linear UAR of BAMPS-induced flow-limited twitches was lower in the presence of initial outward thoracic movement (2 ± 0.05 cmH(2)O·l(-1)·s(-1)) than with inward motion (4.3 ± 1.5 cmH(2)O·l(-1)·s(-1); P = 0.03). We conclude that a-MS represents a practical and functional technique to evaluate UA mechanical properties in conscious sleep apnea patients.