Abstract:Objective To observe effects of the changes of respiratory frequency(RF) and tidal volume on rabbits' heart rate.Methods Mechanical ventilation model was constructed for rabbits and mechanical ventilation was performed under general anesthesia, with respiratory parameters regulated by breathing machine. Respiratory parameters regulation: (i) the tidal volume was constant at 10 mL/kg while respiratory frequency was set 40, 50, and 60 beats/min separately; (ii) The respiratory frequency was constant at 50 beats/min while tidal volume was set 8, 10, and 12 mL/kg separately. Experimental animal grouping: 72 healthy rabbits were divided into two major groups, medicine group(30 rabbits) and operation group(42 rabbits). The former was divided into three subgroups(no medicine, atropine, esmolol) further, each with 10 rabbits. The latter was divided into two subgroups(pneumogastric nerve and sympathetic nerve) further, each with 21 rabbits .Results (i) In medicine group, the heart rates of rabbits in all the three subgroups at a RF of 40 beats/min were significantly lower than those at a RF of 50 or 60 beats/min, and the differences were statistically significant(P<0.01). (ii) In operation group, when RF was 40 beats/min, the heart rates of rabbits in pneumogastric nerve subgroup and sympathetic nerve subgroup were significantly lower than those at a RF of 50 or 60 beats/min, no matter before or after separation of autonomic nerve, and the differences were statistically significant(P<0.01, P<0.05). (iii) In medicine group, when tidal volume was 8 mL/kg, the heart rates of rabbits in the three subgroups were all lower than those when tidal volume was 10 or 12 mL/kg, and the differences were statistically significant(P<0.01). (iv) In operation group, when tidal volume was 8 mL/kg, the heart rates of rabbits in pneumogastric nerve subgroup and sympathetic nerve subgroup were significantly lower than those when tidal volume was 10 or 12 mL/kg, no matter before or after separation of autonomic nerve, and the differences were statistically significant(P<0.01,P<0.05).Conclusion The slowdown of respiratory rate is in accordance with the slowdown of heart rate, which is in line with the HRV spectral composition theory. No matter when it is under normal condition or when automatic nervous system is blocked(both by medicine and by operation), the decrease of tidal volume is in correspondence with the slowdown of heart rate. However the reasons for that requires further investigation.
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