NSE 13A/B Lecture Notes - Lecture 3: Ductus Arteriosus, Left Axis Deviation, Bundle Branch Block
31 Jan 2016
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Document Summary
Heart begins to beat the end of 3 weeks" gestation. The ductus arteriosus closes usually within 10-15 hours of birth. The left ventricle reaches the adult size proportion at the age of one. The heart"s position is more horizontal in the infant than in the adult: the ratio of left ventricle to right ventricle is 2:1, it reaches adult position at the age of 7. Blood volume increases by 30%-40% during pregnancy. Expansion is more rapid in the second trimester: this causes an increase in stroke volume and cardiac output and increase in pulse rate by 10-15 beats per minute. Arterial blood pressure decreases as a result of peripheral vasodilation. Blood pressure drops to its lowest during the second trimester and then rises: blood pressure depends on the person"s position. This is shown by a decrease in maximum heart rate with exercise and diminishing of sympathetic response: arrhythmias: presence of supraventricular and ventricular arrhythmias increases with age.
