MICRO
CARDIOVASCULAR SYSTEMppt.pptx

During inspiration the pressure in the thoracic

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DURING INSPIRATION THE PRESSURE IN THE THORACIC CAVITY DECLINES. DUE TO NEGATIVE PRESSURE IN THE THORACIC CAVITY THE VENOUS RETURN TO THE HEART INCREASES. 15
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THIS RESULTS IN AUGMENTED SYSTEMIC VENOUS RETURN TO RIGHT SIDED CHAMBERS AND MARKED INCREASE IN RIGHT VENTRICULAR VOLUME. WHEN THIS LARGE AMOUNT OF BLOOD REACHES THE PULMONARY CIRCULATION, IT GETS TRAPPED IN THE PULMONARY CIRCULATION BECAUSE THE PULMONARY VASCULAR BED IS A VAST AND COMPLIANT CIRCUIT DUE TO DECREASED INTRATHORACIC PRESSURE. 16
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THEREFORE BLOOD PREFERENTIALLY ACCUMULATES IN THE PULMONARY CIRCULATION AT THE EXPENSE OF IV FILLING. THIS RESULTS IN REDUCED CARDIAC OUTPUT WHICH DECREASES SYSTOLIC PRESSURE. IN CARDIAC TAMPONADE , THERE IS ACCUMULATION OF FLUID IN THE PERICARDIUM. THE ACCUMULATED FLUID IN THE PERICARDIUM FORMS A NONCOMPLIANT CHAMBER, THUS IF ONE VENTRICLE INCREASES IN SIZE, IT CAN DO SO ONLY AT THE EXPENSE OF OTHER VENTRICLE AS THE PERICARDIUM IS NONCOMPLIANT. 17
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SO, WHEN THE RIGHT VENTRICULAR VOLUME INCREASES DURING INSPIRATION AS A RESULT OF INCREASED VENOUS RETURN IT CAUSES THE INTERVENTRICULAR SEPTUM TO BULGE TOWARDS THE LEFT VENTRICLE, LEADING TO SEVERE IMPAIRMENT IN THE FILLING OF THE LEFT VENRICLE. THE DECREASE IN PRELOAD WILL LEAD TO DECREASE IN CARDIAC OUTPUT AND WILL ULTIMATELY CAUSE FALL IN BLOOD PRESSURE. 18
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19 Ans. 'a' i.e., Emphysema; 'b' Pulmonary embolism; 'c' Hypovolemic shock
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20 Ans. is 'c' i.e., Seen in constrictive pericarditis [Ref Harrison 18th/e p. 1824, 1825; 17/e p. 1384] Pulse volume and stroke volume are decreased during pulsus paradoxus.
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21 A
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22
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USUALLY PALPATION OF PERIPHERAL ARTERIAL PULSES SUCH AS RADIAL ARTERY GIVES LESS INFORMATION THAN EXAMINATION OF A MORE CENTRAL PULSE (CAROTID PULSE) REGARDING ALTERATIONS IN LEFT VENTRICULAR EJECTION OR AORTIC VALVE FUNCTION. PALPATION OF THE CAROTID ARTERY IS PREFERRED FOR ASSESSING CARDIAC PERFORMANCE, SINCE THE CAROTID PULSE CORRESPONDS MORE CLOSELY TO THE CENTRAL AORTIC PRESSURE. HOWEVER CERTAIN FINDINGS SUCH AS BISFERIENS PULSE OF AORTIC REGURGITATION OR PULSUS ALTERNANS ARE MORE EVIDENT IN PERIPHERAL ARTERIES . 23
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48 24
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25
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BISFERIANS PULSE IT IS CHARACTERIZED BY TWO SYSTOLIC PEAKS'. THE PULSE WAVE UPSTROKE RISES RAPIDLY AND FORCEFULLY PRODUCING THE FIRST SYSTOLIC PEAK. (PERCUSSION WAVE). A BRIEF DECLINE IN PRESSURE IS FOLLOWED BY A SMALLER AND SOMEWHAT SLOWER RISING POSITIVE PULSE WAVE. IN BISFERIANS PULSE THE SECOND RISE IN SYSTOLE IS ENHANCED BY REFLECTION FROM PERIPHERAL ARTERIES THEREFORE IT IS MORE PROMINENT IN PERIPHERAL PULSE. 26
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CAUSES OF BISIFERIANS PULSE PURE AORTIC REGURGITATION. COMBINED AORTIC STENOSIS AND SEVERE AORTIC REGURGITAION. HYPERTROPHIC CARDIOMYOPATHY. CAN ALSO OCCUR IN CONDITIONS ASSOCIATED WITH THE RAPID EJECTION OF AN INCREASED STROKE VOLUME FROM THE LEFT VENTRICLE.
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  • Winter '16
  • jean grey
  • Cardiology, Ans., Constrictive pericarditis

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