Alterations in Sympathetic Nervous System Activity with Intraoperative Hypothermia during Coronary Artery Bypass Surgery: AssaysAssays
Serum T3 (normal: 85 to 200 ng/dl) and T4 (normal: 5.1 to 10 (Ag/dl) concentrations were measured by sensitive and specific radioimmunoassays. The FT, (normal: 230 to 480 pg/dl) and FT, (normal: 1.3 to 3.8 ng/dl) values were determined by equilibrium dialysis. The dialyzable fraction of the total hormone concentration as well as the calculated free hormone concentration are reported. The serum ACE activity was measured by a sensitive radiometric assay as described previously (normal: 16.8 ±5 units/ml). The plasma EPI and NE concentrations were measured by a sensitive radioenzyme technique in which a partially purified enzyme, catechol-o-methyl-transferase, catalyzes the transfer of a 3H-methyl group from commerically available 3H-S-adenosyl methionine to the metahydroxyl group of endogenous NE and EPI, forming 3H-normetanephrine and 3H-metanephrine, respectively. The measurements are accurate to values of 30 to 40 pg of EPI or NE per milliliter of plasma. sildenafil citrate pink

Statistics
The data are expressed as mean ± SEM. Data were analyzed by paired Students t-test with post-hoc testing including a Bonferroni test and Duncans multiple range test so as to avoid errors of repetitive measures testing. The data are expressed as concentrations corrected for hemodilution followed by the absolute concentration in parentheses.
Results
The patients studied during hypothermia (n = 10) were similar to the patients studied during rewarming (n = 11) with regard to age, body weight, preoperative use of medications, degree of angina, cardiac function, number of coronary arteries bypassed, and intraoperative administration of anesthetics (Table 1).
Findings in Patients During Induction of Hypothermia.
The mean time required for reduction of core temperature to 24°C from preinduction was 90 ±15 minutes.
Table 1—Comparison of Preoperative and Operative Variables of Patients Studied During Induction of Hypothermia and Those Studied During Rewarming

Patients Studied During Hypothermia Patients Studied During Rewarming
Number 10 11
Age, yrs 57 ±2 58±3
Body weight, kg 83.4 ±4.6 77.1 ±3.8
Preoperative use of medications, %
Beta blockers 90 100
Calcium channel blockers 50 55
Nitrates 100 100
New York Heart Assoc class (mean + SD) 3.2 ±1 3.4 ±1
Left ventricular ejection fraction, % 75 ±2 68±5
Number of arteries bypassed, mean + SD 2.9±4 3.2 ±5
Anesthesia used, %
Halothane 50 82
Opiate 90 82