title: Inspiration induced by phrenic nerve stimulation increases internal defibrillation energy requirements.
abstract: BACKGROUND
  The purpose of this study was to systematically evaluate the effects of active inspiration induced by phrenic nerve stimulation on the energy required for 50% successful defibrillation (E50).
  
  
  RESULTS
  Shocks (95-microF biphasic waveform) were delivered after 10 seconds of ventricular fibrillation between a right ventricular coil and left pectoral test can in ten anesthetized pigs (25 to 37 kg). Using a 1-J step size, the E50 was determined with an up/down, three-reversal method. Positive-pressure ventilation was halted just before fibrillation, and shocks were delivered during expiration or at the end of 2 seconds of bilateral phrenic stimulation (50 Hz, 0.3 msec, 5 to 6 V). Phrenic stimulation produced inspiratory volumes that were 15.3 +/- 1.7 mL/kg (mean +/- SD). The E50 was 9.8 +/- 1.9 J during expiration and increased to 13.0 +/- 1.7 during inspiration (P = 0.001). The leading-edge voltage at the E50 was 451 +/- 46 V during expiration and 519 +/- 33 V during inspiration (P = 0.001). The leading-edge current at the E50 was 9.7 +/- 1.0 A during expiration and increased to 11.3 +/- 1.4 A during inspiration (P = 0.002). The average impedance was 47.8 +/- 2.7 omega during expiration and 47.3 +/- 3.3 omega during inspiration (P = 0.12).
  
  
  CONCLUSIONS
  Inspiration induced by phrenic stimulation results in a 31% increase in the E50 compared with expiration. The decrease in shock efficacy occurs in the absence of a change in impedance. Active inspiration may alter the distribution of the electrical field leading to a decrease in shock efficacy.
authors.affiliation: Angeion Corporation, Minneapolis, Minnesota, USA. dave.euler@medtronic.com
authors.forename: D E
authors.initials: DE
authors.lastname: Euler
authors.forename: T A
authors.initials: TA
authors.lastname: Whitman
authors.forename: M J
authors.initials: MJ
authors.lastname: Kallok
mesh_terms: D000818:Animals; D004554:Electric Countershock; D004558:Electric Stimulation; D004562:Electrocardiography; D005260:Female; D008297:Male; D010791:Phrenic Nerve / Q000502:physiology*; D013552:Swine; D014693:Ventricular Fibrillation