title: Effects of temperature on phrenic nerve and diaphragmatic function during cardiac surgery.
abstract: We have studied the effects of whole body cooling on phrenic nerve and diaphragmatic function in 26 patients using magnetic stimulation of the phrenic nerves with a pair of Magstim 200 HP stimulator coils during cardiopulmonary bypass. The diaphragmatic electromyogram in response to magnetic pulses was recorded with needle electrodes at two temperatures, approximately 31 degrees C (cold) and approximately 36 degrees C (warm) during the cooling or rewarming phase of hypothermic cardiopulmonary bypass. This 5 degrees C temperature change was associated with clear changes in the evoked electromyographical response of the diaphragm. Median latency between stimulus and electromyographic response was 10.1 (range 8.0-11.8) ms during cold and 8.3 (5.9-10.2) ms during warm stimulation (P < 0.001). Median duration of the muscle compound action potential was prolonged and its amplitude reduced in cold compared with warm stimulations (P < 0.01). These effects were enhanced by application of ice slush to the heart. We conclude that diaphragmatic function may be affected by mild hypothermia after cardiac surgery.
authors.affiliation: Department of Thoracic Medicine, King's College Hospital, London.
authors.forename: G H
authors.initials: GH
authors.lastname: Mills
authors.forename: Z P
authors.initials: ZP
authors.lastname: Khan
authors.forename: J
authors.initials: J
authors.lastname: Moxham
authors.forename: J
authors.initials: J
authors.lastname: Desai
authors.forename: A
authors.initials: A
authors.lastname: Forsyth
authors.forename: J
authors.initials: J
authors.lastname: Ponte
mesh_terms: D000328:Adult; D000368:Aged; D002315:Cardiopulmonary Bypass; D001026:Coronary Artery Bypass; D003964:Diaphragm / Q000503:physiopathology*; D004576:Electromyography; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D007036:Hypothermia, Induced / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D009431:Neural Conduction; D010791:Phrenic Nerve / Q000503:physiopathology*; D011312:Pressure; D011930:Reaction Time; D013270:Stomach / Q000503:physiopathology; D013696:Temperature