TY - JOUR
T1 - Threshold for adrenomedullary activation and increased cardiac work during mild core hypothermia
AU - Frank, Steven M.
AU - Cattaneo, Christine G.
AU - Wieneke-Brady, Mary Beth
AU - El-Rahmany, Hossam
AU - Gupta, Neeraj
AU - Lima, Joao A.C.
AU - Goldstein, David S.
PY - 2002
Y1 - 2002
N2 - Postoperative hypothermia increases the incidence of ischaemic cardiac events in patients at risk, but the underlying mechanism is unclear. One possibility is increased cardiac work related to the sympathoneural or adrenomedullary hormonal responses. In awake human volunteers, the present study assessed the effects of mild core hypothermia on these responses, and on the associated changes in indices of cardiac work. A total of II healthy men were studied on two separate days. On one day, core temperature (Tc) was decreased by the intravenous infusion of cold normal saline (4 °C; 60 ml/kg over 30 min) through a central venous catheter. On the other day (normothermic control), warm normal saline (37 °C; 60 ml/kg over 30 min) was given intravenously. Transthoracic echocardiograms, the sympathoneural response (noradrenaline) and the adrenomedullary response (adrenaline) were evaluated before, during and after the intravenous infusions. Echocardiography was used to measure left ventricular function and cardiac output. Compared with the normothermic control treatment, core cooling of 0.7 °C was associated with increased plasma noradrenaline (220% increase; P = 0.001), whereas adrenaline, cardiac output, heart rate and the rate-pressure product were unchanged. After core cooling of 1.0 °C, increases in noradrenaline (by 230%; P = 0.001), adrenaline (by 68%; P = 0.05), cardiac output (by 23%; P = 0.04), heart rate (by 16%; P = 0.04) and rate-pressure product (by 25%; P = 0.007) were all significant compared with the normothermic control treatment. In conclusion, there is a Tc threshold, below which an adrenomedullary (adrenaline) response is triggered in addition to the sympathoneural (noradrenaline) response. This Tc threshold (≅ I °C below the normothermic baseline) is also associated with an increase in haemodynamic indices of cardiac work. Mild core hypothermia therefore constitutes a catecholamine-mediated cardiovascular 'stress test'.
AB - Postoperative hypothermia increases the incidence of ischaemic cardiac events in patients at risk, but the underlying mechanism is unclear. One possibility is increased cardiac work related to the sympathoneural or adrenomedullary hormonal responses. In awake human volunteers, the present study assessed the effects of mild core hypothermia on these responses, and on the associated changes in indices of cardiac work. A total of II healthy men were studied on two separate days. On one day, core temperature (Tc) was decreased by the intravenous infusion of cold normal saline (4 °C; 60 ml/kg over 30 min) through a central venous catheter. On the other day (normothermic control), warm normal saline (37 °C; 60 ml/kg over 30 min) was given intravenously. Transthoracic echocardiograms, the sympathoneural response (noradrenaline) and the adrenomedullary response (adrenaline) were evaluated before, during and after the intravenous infusions. Echocardiography was used to measure left ventricular function and cardiac output. Compared with the normothermic control treatment, core cooling of 0.7 °C was associated with increased plasma noradrenaline (220% increase; P = 0.001), whereas adrenaline, cardiac output, heart rate and the rate-pressure product were unchanged. After core cooling of 1.0 °C, increases in noradrenaline (by 230%; P = 0.001), adrenaline (by 68%; P = 0.05), cardiac output (by 23%; P = 0.04), heart rate (by 16%; P = 0.04) and rate-pressure product (by 25%; P = 0.007) were all significant compared with the normothermic control treatment. In conclusion, there is a Tc threshold, below which an adrenomedullary (adrenaline) response is triggered in addition to the sympathoneural (noradrenaline) response. This Tc threshold (≅ I °C below the normothermic baseline) is also associated with an increase in haemodynamic indices of cardiac work. Mild core hypothermia therefore constitutes a catecholamine-mediated cardiovascular 'stress test'.
KW - Body temperature
KW - Catecholamines
KW - Echocardiography
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UR - http://www.scopus.com/inward/citedby.url?scp=0036183427&partnerID=8YFLogxK
U2 - 10.1042/CS20010073
DO - 10.1042/CS20010073
M3 - Article
C2 - 11749669
AN - SCOPUS:0036183427
SN - 0143-5221
VL - 102
SP - 119
EP - 125
JO - Clinical Science
JF - Clinical Science
IS - 1
ER -