Читать книгу Manual of Equine Anesthesia and Analgesia - Группа авторов - Страница 91

 HR is primarily regulated by autonomic input.Parasympathetic (decreases) and sympathetic (increases) HR.Horses have inherently high vagal tone which contributes to the slow HR and normally occurring intermittent second‐degree AV block.

 HR is also affected by factors such as ambient temperature, body temperature, exercise, pain, fever and anemia, and reflexively controlled by BP through baroreceptor responses.

 Various other activities affect HR.For instance, the Bainbridge reflex is an increase in HR secondary to increased right atrial volume and stretching of the SA node.

 Anesthetic drugs can affect HR either directly or indirectly.Anticholinergics (e.g. atropine) decrease parasympathetic tone and increase HR.Alpha2 agonists (e.g. xylazine) decrease HR via direct effects on the SA node and indirect effects via the baroreceptor response.Alpha2 agonists cause vasoconstriction and hypertension.Acepromazine and inhalant anesthetic gases may cause hypotension, which can, in turn, cause a baroreceptor‐mediated increase in HR.