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Heart rate decreases unexpectedly during late hemorrhage in unanesthetized sheep
Author(s) -
Gunther Robert A,
Talken Linda,
Davis Jessica
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.6.a1279-b
Subject(s) - bradycardia , medicine , heart rate , anesthesia , blood pressure , mean arterial pressure , cardiac output , hemodynamics , blood volume , cardiology
The literature contains reports of unexpected decreases in heart rate (HR) in hypotensive patients (paradoxical bradycardia). This observation has not been fully explained due to the lack of an appropriate animal model. The purpose of this study was to review data recorded from sheep experiencing hemorrhage to determine if there is a reproducible decrease in HR as the hemorrhage progresses. Changes in arterial pressure (MAP) and cardiac output (CO) were observed in relation to HR. Methods: 15 sheep were studied. Vessel catheterization was completed under general anesthesia several days prior to an experiment. Conscious sheep were bled over 60 min to an MAP of 55 mmHg. Vascular pressures, cardiac output, and heart rate were recorded. Results: Data are mean ± SEM. Baseline HR was 100 ± 3 bpm, and during hemorrhage HR was 132 ± 9 bpm at 20 min, 140 ± 12 bpm at 40 min, and 99 ± 5 bpm at 60 min. CO decreased from baseline of 7.2 ± 0.25 L/min to 5.6 ± 0.35 L/min at 20 min, 4.2 ± 0.30 L/min at 40 min, and 3.1 ± 0.1 L/min at 60 min. Conclusion: Decreasing blood volume with decreasing MAP and CO was associated with a significant increase in HR at 20 and 40 min of hemorrhage but at 60 min HR was similar to baseline in spite of a significant reduction in MAP and CO. This data suggest that the sheep could serve as a useful model for further investigation of the mechanisms responsible for the decline in HR observed in the conscious sheep during late hemorrhage.