Cardiovascular and endocrine responses to haemorrhage in the pig

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Abstract
Heart rate (HR), mean arterial pressure (MAP), indices of sympathetic and parasympathetic activity (plasma concentrations of adrenaline, noradrenaline and pancreatic polypeptide, PP), vasopressin (VP) and aldosterone (ALDO) were measured in six pigs during continuous bleeding resulting in hypovolaemic shock, from which five survived. Three stages of haemorrhage could be defined. Stage I. Resting MAP was 85 .+-. 6 mm Hg and increased to 96 .+-. 5 mm Hg with a blood loss of 275 (range 250-300) (10(9-12)% of the estimated blood volume) concomitant with an increase in HR from 105 .+-. 5 to 113 .+-. 6 beats min-1 (P < 0.05). Stage II. After a blood loss of 375 (300-500) ml (15(13-16)%) MAP fell to 62 .+-. 9 mm Hg and HR to 95 .+-. 5 beats min-1 (P < 0.05). Stage III. A blood loss of 1113 (825-1450)ml (44(30-52)%) resulted in a MAP of 50 .+-. 4 mm Hg and an increase in HR to 206 .+-. 3 beats min-1 (P < 0.05). Adrenaline increased from 0.3 .+-. 0.1 to 0.8 .+-. 0.3 (stage II) and 3.6 .+-. 1.1 nmol l-1 (stage III) (P < 0.05); noradrenaline from 0.4 .+-. 0.1 to 1.5 .+-. 0.4 (stage II) and 5.9 .+-. 1.7 nmol l-1 (stage III) (P < 0.05); PP from 6.2 .+-. 1.6 to 13.3 .+-. 2.3 (stage II) and 20.9 .+-. 7.8 pmol l-1 (stage III) (P < 0.05). VP changed only marginally, but ALDO increased from 496 .+-. 54 to 623 .+-. 76 pmol l-1 (stage III) (P < 0.05). The results suggest that a high HR and intense sympathetic activity is seen during severe haemorrhage in the pig while vagal slowing of the heart and moderate hypotension are prominent when bleeding amounts to approximately 15% of the estimated blood volume.