A new method for hemodynamic and echocardiographic assessment of conscious dogs: comparison with thiopental-morphine anaesthesia.
A method allowing assessment of cardiac structure and function in the conscious dog using readily available instrumentation is desirable and should provide physiologic advantages when compared to anaesthesia. Accordingly, we studied 19 dogs (22 +/- 2.5 kg), using two-dimensional echocardiographic and Swan-Ganz and femoral artery catheterization; ten were conditioned to permit conscious studies and nine received anaesthesia. Dogs receiving anaesthesia were induced with intravenous thiopental (16 +/- 4 mg/kg), followed by a maintenance dose (7 +/- 1 mg/kg/h) plus morphine sulphate (213 +/- 5 micrograms/kg/h). Cardiac index, mean blood pressure, and systemic vascular resistance were similar between groups. However, anaesthesia as compared to conscious studies resulted in a marked tachycardia (147 +/- 30 bpm, vs 98 +/- 19 bpm, p less than 0.0005), significantly lower right atrial pressure (5 +/- 2 mmHg vs 8 +/- 2 mmHg, p less than 0.05), and a trend towards a lower pulmonary capillary wedge pressure (6 +/- 5 mmHg vs 9 +/- 3 mmHg). Simultaneous echocardiography showed left ventricular diastolic cross sectional area to be smaller in the anaesthesia group (8.5 +/- 1.7 cm2 vs 10.4 +/- 1.5 cm2, p less than 0.05); however, ejection fraction in the two groups was similar. Velocity of circumferential fiber shortening (Vcf), normalized for heart rate and preload, was significantly lower in the anaesthetised dogs (0.63 +/- 0.22 circ/sec vs 0.89 +/- 0.26 circ/sec, p less than 0.05); this decline in Vcf, in association with a lower systolic wall stress (85 +/- 29 10(3) dynes/cm2 vs 119 +/- 23 10(3) dynes/cm2, p less than 0.05) indicates that thiopental-morphine anaesthesia depresses contractility.(ABSTRACT TRUNCATED AT 250 WORDS)
Howard, RJ; Stopps, TP; Moe, GW; Armstrong, PW
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