Cardiovascular Lecture Features of the Cardiovascular System PDF

Cardiovascular Lecture Features of the Cardiovascular System HN Mayrovitz PhD [email protected] drmayrovitz.com 1 of 20 Vascular Circuit with Pressures and Flows Defined ANS Lungs LAP Systolic (P ) RA LA S 120 mmHg ABP RV LV RAP O2 Flow = Q CO = HR x SV L/min) Veins Diastolic (PD) Arteries C DV CELL...

Cardiovascular Lecture Features of the Cardiovascular System HN Mayrovitz PhD [email protected] drmayrovitz.com 1 of 20 Vascular Circuit with Pressures and Flows Defined ANS Lungs LAP Systolic (P ) RA LA S 120 mmHg ABP RV LV RAP O2 Flow = Q CO = HR x SV L/min) Veins Diastolic (PD) Arteries C DV CELLS Ve n ul es CO2 O2 es l rio te Ar Capillaries Q 80 mmHg Aortic Blood Flow R DP LOCAL Pulse Pressure (PP)=PS-PD MAP = 2/3 PD + 1/3 PS = PD + 1/3 PP Aortic Blood Pressure CO = avg Q CO = SV x HR Dr HN Mayrovitz MAP = avg ABP 2 of 20 3 Cardiac Output & Stroke Volume: Absolute & Indices Q is symbol for blood flow (volume / time) Q ml/stroke=SV CO = SV x HR [liters/min] Series of Flow Pulses R. Heart Lungs L. Heart CO CI = CO/BSA SVI = SV/BSA BMI = 703W/H2 Kg/m2 BSA = 0.0179 x [H x W]1/2 m2 with H in inches and W in lbs Organ blood flow through multiple parallel pathways Summation and some take-homes SV → amount ejected / beat (ml) CO → flow output / time (ml/sec or l/min) Indices normalize among patients with BSA No need to memorize BMI or BSA formulas Dr HN Mayrovitz 3 of 22 Determining Cardiac Output (CO): Fick ~ 20 mlO2/dl = 1.34 x SAT x [Hb] Fick’s Equation = Oxygen Utilization Example 250 mlO2/min CO = (20 – 15) mlO2/100ml = 0.05 mlO2/ml blood CO = 5000 ml/min ~ 15 mlO2/dl CaO2 = Oxygen concentration in arterial blood = 1.34 x (Hb sat) x [Hb] ≈ 20 mlO2/dl CvO2 = Oxygen concentration in mixed venous blood returning to lung ≈ 15 mlO2/dl Dr HN Mayrovitz 4 of 22 Determining CO via Thermodilution Method Thermodilution Swan-Ganz catheter with thermistor placed into pulmonary artery via peripheral vein insertion Cold saline injected into right atrium at end of expiration Balloon When balloon inflated measure Pulmonary artery wedge pressure (PAWP) as estimate of LAP Pulmonary Vein Lungs Proximal Infusion Line (RA) LA Distal Infusion Line (PA) Balloon Inflation To CO Computer RA RA Port RV Pulmonary Artery Port Thermistor Port Temp Measured LV Temperature changes at thermistor sensed and recorded Blood flow (cardiac output, CO) is determined from temperature profile DV = volume injected K – calibration constant Dr HN Mayrovitz 5 of 22 Vascular Resistance Concept SVR = Systemic Vascular Resistance TPR = Total Peripheral Resistance DP/CO = (MAP – CVP)/CO ≈ 90 mmHg/(5 L/min) = 18 mmHg/L/min SVR = TPR = mmHg/(L/min) = Wood Unit If mmHg/ml/min = PRU = Wood Unit/1000 “Normal” values 15-20 Wood units → 0.015-0.020 PRU Organs or Vasculatures in SERIES Flow same in series-coupled parts Resistances sum directly Total R greater than individual R Pressure is lost sequentially Organs or Vasculatures in PARALLEL Perfusion Pressures are the same Resistances sum reciprocally Total R is LESS than any individual R Dr HN Mayrovitz 6 of 22 Cardiovascular Patterns and Arrangements Low Pressure Side 5 mmHg 95 mmHg Pumps High Pressure Side Arteries Veins Organs are in parallel with other organs So, flow to each organ depends on its vascular resistance since all have equal perfusion pressure Within Organs Arterioles are in parallel with arterioles Capillaries are in parallel with capillaries BUT Segments are in series with the other segments Since in series pressure is lost across each segment Dr HN Mayrovitz 7 of 20 Vasculature: Vessel Types-Structure-Components Note that: Smallest diameter is the capillary that has no vascular smooth muscle (VSM) What is called a “precapillary sphincter” refers to a terminal arteriole that immediately precedes the capillary network – largest relative amount of VSM The larger arteries have relatively more elastic material (elastin > fibrous collagen) Wall thickness to diameter is low in veins versus arteries → effects compliance Dr HN Mayrovitz 8 of 20 Circulation Pathways and Definitions VR CVP Right Atrium (RA) Left Atrium (LA) TV MV Right Ventricle (RV) Left Ventricle (LV) PVR = (MPAP-LAP)/CO LUNG MPAP CO TV = Tricuspid Valve PV = Pulmonic Valve LAP AV PV 2 pumps in series CO ORGANS MV = Mitral Valve AV = Aortic Valve Dr HN Mayrovitz MAP Venous Return TPR = (MAP-CVP)/CO 9 of 22 Determining Pulmonary Artery Wedge Pressure PVR = (MPAP - LAP)/CO PVR = (MPAP - PAWP)/CO RA Swan-Ganz Catheter Inserted Inflated Balloon Pulmonary Artery PV IVC TV LV Pressure Sensor Measures Pulmonary Artery Wedge Pressure (PAWP) Estimate of LAP RV MPAP = Mean Pulmonary Artery Pressure PVR = Pulmonary Vascular Resistance Dr HN Mayrovitz 10 of 20 Right Sided Pressures mmHg 30 20 10 0 Right Atrium Right Ventricle Pulmonary Artery PA Wedge Pressure 11 of 20 Cardiovascular Pressure Variations mmHg Systolic Large pressure loss across arterioles is due to their high vascular resistance Diastolic Mean Small mean pressure loss in large arteries aorta arteries Central Venous Pressure (CVP ~ RAP) Diaphragm Dp ~ 50 mmHg arterioles caps vnls Dr HN Mayrovitz veins RA RV PULM LA LV 12 of 20 Arterial Pressure Pulse r C0 Pulses at any point in the artery are the algebraic sum of forward transmitted pulses and reflected backward pulses each moving at a speed of C0 m/sec r = blood density C = arterial compliance Dr HN Mayrovitz 13 of 20 Resting Cardiac Output Distribution Percentages are approximate; vary by person Absolute cardiac output (CO, L/min) varies by age, gender, weight and other Cardiac Index (CO/BSA, L/min/m2) helps minimize variance also (SVI = SV/BSA) For a fixed perfusion pressure, flow (Q) distribution to organs depends on its vascular resistance; Q = DP/R The diagram below shows pressures in mmHg and illustrates normal average values at the different locations The above figure shows approximate percentages of cardiac output distribution. If CO were 6 L/min then absolute flow to the kidneys would be 1.2 L/min. Dr HN Mayrovitz Perfusion pressure = DP = 95-5 = 90 mmHg If cardiac output were 6 L/min then TPR = 90/6 = 15 Wood units and PVR = 10/6 = 1.67 Wood units 14 of 20 Vascular Pathways: Volume-Pressure-Velocity A B Volume Mean Pressure Area C Mean Velocity D (A) Blood volume: Arterial 15% Venous 60% Pulmonary 25% (B) Mean arterial pressure: 1. little change in large arteries; 2. large change across arterioles 3. low value in capillaries & veins (C) Cross-sectional area: Largest in capillary network despite their small diameter due to their large numbers (D) Mean Blood Velocity: 1. Same total flow passes through each series vascular network 2. Network with largest cross-sectional area has the least blood velocity. 3. Least in systemic/pulmonary capillaries Dr HN Mayrovitz 15 of 22 Systemic vs. Pulmonary Hemodynamic Features SYSTEMIC High Pressure High Resistance Systemic (93) DP=90 RV Pressure Pulse RA 120/80 120/0 (3) 120 LV 25 0 RV 0 Flow Pulse 24/9 25/0 LA (6) PV (14)→→→→→→ DP=8 Pulmonary Blood Volume ~ 10-12% Dr HN Mayrovitz LV Pressure Pulse Flow Pulse Pressures (mmHg) Mean Values ( ) PULMONARY Low Pressure Low Resistance 16 of 20 Interactive Question 5. Which of the following features is numerically similar in the systemic and pulmonary circulations? A. Systolic blood pressure B. Diastolic blood pressure C. Mean blood pressure D. Total blood flow E. Ventricular maximum pressure Dr HN Mayrovitz 17 of 20 Interactive Question Bill has the following hemodynamic data ABP = 150/60 mmHg CVP = 3 mmHg SV = 100 ml HR = 50 What is his TPR in Wood units? One minute! Dr HN Mayrovitz 18 of 20 Interactive Question 6. Which of the following best describes conditions within a vascular bed of an organ? A. All capillaries of the same type are effectively in parallel with each other B. All arterioles of the same type are effectively in parallel with capillaries they supply C. The greatest pressure loss is attributable to the small lumen of the capillaries D. All arterioles of the same type are effectively in series with each other E. A decrease in the number of arterioles leads to a decrease in organ resistance Dr HN Mayrovitz 19 of 22 Interactive Question 4. If all arterioles of an organ vasoconstrict then: A. Blood flow to the organ increases B. Blood pressure in the organ’s capillaries decreases C. Total resistance of the organ decreases D. Blood flow within arterioles increases E. Total peripheral resistance decreases Dr HN Mayrovitz 20 of 20 End CV Physiology Lecture 2 Dr HN Mayrovitz