Читать книгу Manual of Equine Anesthesia and Analgesia - Группа авторов - Страница 95

 Defined as the ability of cardiac muscle fibers to shorten or develop tension.Cardiac muscle contraction is initiated by an action potential which triggers the release of intracellular calcium and the flux of extracellular calcium into the cell, ultimately resulting in cross bridging of actin and myosin and a shortening of the sarcomere.

 Ejection fraction is a simple measurement of contractility.Ejection fraction is the ratio of the SV to the end‐diastolic volume.Normal ejection fraction is 60–70%.

 Other indices used to evaluate contractility include the rate of change of ventricular pressure with respect to time (dP/dt), ventricular function curves, and pressure‐volume loops.

 Increased contractility causes an increase in myocardial oxygen consumption.

 Factors that affect contractility include:Autonomic tone.Acidosis, hypoxia.Thyroid disorders.Electrolyte imbalance.Anesthetic drugs.

 Anesthetic agents that affect contractility include:Barbiturates, propofol and inhalant anesthetic gases cause a decrease in myocardial contractility.Ketamine causes an indirect increase in myocardial contractility via stimulation of the sympathetic nervous system (the direct effect of ketamine is decreased contractility).