Continual recordings of cardiac sympathetic nerve activity in conscious sheep

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Abstract
Cardiac sympathetic nerve activity (CSNA) is of major importance in the etiology of heart disease but is impossible to measure directly in humans. Ovine and human cardiovascular systems are similar; therefore, we have developed a method for the daily recording of CSNA in conscious sheep. After thoracotomy, electrodes were glued into the left thoracic cardiac nerve and CSNA, blood pressure (BP), and heart rate were recorded daily. Satisfactory recordings ≥7 days of CSNA were obtained in 11 of 28 sheep (40%), mean recording time 10.6 days, range 7-47. During the first week, CSNA decreased gradually from 78 ± 8 at baseline to 60 ± 7 bursts/min on day 5(P = 0.02) or from 76 ± 9 to 57 ± 7 bursts/100 beats on day 7 (P = 0.04). Similarly, BP decreased from 103 ± 4 to 94 ± 4 mmHg (P = 0.03). Low-frequency heart rate variability decreased from 0.12 ± 0.02 to 0.06 ± 0.02 ms2on day 6 (P = 0.004) but was not correlated to CSNA. In conclusion, CSNA that can be continually recorded in conscious sheep decreases during the first week postsurgery and, thereafter, stabilizes. This model should provide valuable insights in future investigations of cardiac disease.