Hemodynamics

Hemodynamics

1. Revision

   • Regulation of Blood Flow
     • Depends on: HR-Strength of Contraction-Blood Vessel Diameter-Degree of turbulence-pressure (He said body don't pinch)
     • Flow
       • The amount of fluid moved over time. Flow=PressureDifference/Resistance
     • Pressure
       • Force exerted on fluid.
     • Resistance
       • Opposition to the flow. Depends on: Viscosity, Radius, Length.  (VRL)
   • Cardiac Output
     • The amount ejected from the heart and measured in liters per min. Normal is 4 to 8 L/min CO=HR*SV
     • Directly proportional to preload and contractility.  1. Increased Stretch of the myocardial fiber during diastole results in increased contraction during systole leading to increased CO. (F-S Law) 2. Increased contractility --> Increased SV--> Increased COIndirectly proportional to afterload. Increased afterload --> Decreased SV --> Decreased CO
     • HR
       • The number of times the heart beats per min.
     • SV
       • The amount of blood ejected per heart beat.
   • Preload
     • The degree of ventricular stretch at the end of the diastole. Volume/Stretch
     • High Preload: Hypervolemia or Ventricular Failure Low Preload: Hypovolemia
   • Afterload
     • The amount of resistance the ventricles need to overcome to deliver a SV.
     • LV afterload is affected by: Vasoconstriction-Vasodilation-Blood Viscosity-Valve Competency-Flow Pattern (Four Vs) 
     • RV afterload is affected by: Hypoxia-PEEP-Pulmonary Embolism-Pulmonary edema-ARDS-COPD-Fibrosis (FAPCH)
   • Contractility
     • The pushing force or the strength of the myocardium during systole. The Squeeze.
     • SNS-PNS EF: 60-75% - CO/CI - LOC, urine output, skin color, temperature, moistness.  Na,K,Ca --> actin-myosin
     • Affected by:  MI-Cardiomyopathy

2. Intra-arterial Pressure Monitoring

3. Right Atrial Pressure Central Venous Pressure