A new method for hemodynamic and echocardiographic assessment of conscious dogs: comparison with thiopental-morphine anaesthesia
Howard, R.J.; Stopps, T.P.; Moe, G.W.; Armstrong, P.W.
Clinical and Investigative Medicine 13(1): 6-10
1990
ISSN/ISBN: 0147-958X PMID: 2311313 Document Number: 365457
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 .mu.g/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 < 0.0005), significantly lower right atrial pressure (5 .+-. 2 mmHg vs 8 .+-. 2 mmHg, p < 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 < 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 < 0.05); this decline in Vcf, in association with a lower systolic wall stress (85 .+-. 29 103 dynes/cm2 119 .+-. 23 103 dynes/cm2, p < 0.05) indicates that thiopental-morphine anaesthesia depresses contractility. We conclude that acute hemodynamic and echocardiographic assessments done in the conscious state are feasible using readily available instrumentation. Additionally, conscious animal experiments are preferable in order to ensure physiologically valid measurements.