Intro to Hemodynamics

Question 1

What is hemodynamics

Answer 1

Refers to dynamics (flow, pressure, resistance) of the cardiovascular system
- Involves blood pressures (BP or MAP, PA or MPAP, PCWP)
- Blood flow = Cardiac output
- Vascular resistance (SVR or PVR)
Pressure = flow X resistance

Question 2

Two types of blood pressures

Answer 2

Systolic blood pressure - pressure created as the LV contracts and propels blood into the aorta
Diastolic blood pressure - relaxation or filling pressure of the LV

Question 3

What are the normal, hypertension, hypotension ranges of systolic and diastolic blood pressures?

Answer 3

Measured in mmHg
Normal: systolic = 100-140, diastolic = 60-90
Hypertension: systolic = > 160, diastolic = > 95
Hypotension: systolic =

Question 4

What is MAP, the normal range, and how it is calculated

Answer 4

MAP is mean arterial pressure. It determines blood flow and is the average driving pressure between the LV and RA.
Normal values is 80-100 (93) mmHg
MAP = systolic + 2 (diastolic) / 3

Question 5

How does the body try to maintain MAP

Answer 5

Pump: How much blood is being pumped by the heart
Pipes: If heart starts pumping less the body tries to keep MAP at a normal range by constricting or dilating to change the resistance
Flow: How often the heart beats and how much is pumped out. If the heart is not pumping enough blood out it will start pumping faster to try and make up that volume. (cardiac output = L/min)

Question 6

Calculating cardiac output and cardiac index

Answer 6

Cardiac output = SV and HR
It is the amount of blood pumped into the aorta by the LV
Normal values are 4-8 L/min
Increased cardiac output can be caused by disease or exercise

Cardiac Index = CO/BSA (body surface area)
Normal values are 2.5-5.0 L/min/meters squared

Question 7

What is stroke volume and what is it affected by

Answer 7

Stroke volume is volume of blood ejected by each ventricular contraction
Normal range = 60-130mL/beat (average 70mL)
Stroke volume is affected by:
- Volume preload (blood volume in the heart at end-diastole)
- Myocardial contractility (force of contraction = inotropism)
- Ventricular afterload (resistance heart has to pump against) - SVR

Question 8

What is HR affected by?

Answer 8

Heart rate is influenced by parasympathetic and sympathetic innervation as well as hormonal influences such as epinephrine
Normal values: 60-100 beats/min

Question 9

What affect does Sympathetic/ parasympathetic innervation stimulation have on the heart?

Answer 9

Sympathetic stimulation results in:

• Increased HR
• Increased inotropic effect (affect on muscle contraction of the heart)
• Increased blood flow

Parasympathetic stimulation results in:

• Decreased HR
• Decreased rate of conduction through AV node
• decreased blood flow through coronary artery

Question 10

Contractibility of the heart is is affected by?

Answer 10

Preload, calcium, and afterload

Afterload is affected by viscosity, diameter and length

Question 11

What does SVR pertain to?

Answer 11

Systemic vascular resistance - pressure needed to deliver a flow of blood of 1L/min
Normal range = 900-1400 dynes x sec x cm-5
SVR is the average resistance the left ventricle needs to work against to eject the SV = afterload
SVR = MAP - RAP / CO

Question 12

What factors affect pulmonary circulation?

Answer 12

• Gravity
• Interstitial fluid pressure
• Regional pulmonary blood flow
• Pulmonary artery pressure
• Lung volume
• Vasomotor tone
• PAO2 and PACO2

Question 13

What affects do vascular tone have on PaO2 and PaCO2

Answer 13

Increase PaO2 = pulmonary vasodilation and systemic vasoconstriction
decrease PaO2 = pulmonary vasoconstriction and systemic vasodilation
Increase PaCO2 = pulmonary vasoconstriction and systemic vasodilation
Decrease PaCO2 = pulmonary vasodilation and system vasoconstriction

Question 14

How is CO measured

Answer 14

1. Continuous CO measurement technique
   - Uses a esophageal Droppler transducer to measure blood flow velocity in the descending aorta
   - Doppler transducer uses very high frequency ultrasonic waves
2. Thermodilution technique (10% error)
   - Known quantity of cold fluid injected into the right atrium via proximal port of PAC
   - Thermister at distal end of catheter senses temperature drop
   - Records a temperature time curve: area under the curve reflects CO

The faster the temperature returns to normal the larger the CO

Question 15

What are the normal values for the follow:

• RAP
• PAP
• MPAP
• PCWP
• BP
• MAP
• CO
• CI
• SV
• HR
• SVR
• PVR

Answer 15

• RAP = 2-6 mmHg
• PAP = 25/10 mmHg
• MPAP = 15 mmHg
• PCWP = 4-12 mmHg
• BP = 120/80 mmHg
• MAP = 93 mmHg
• CO = 4-8 L/min
• CI = 2.5-5.0 L/min/m2
• SV = 70 mL
• HR = 60-100 beats/min
• SVR = 900-1400 dynes x sec x cm-5
• PVR = 150-250 dynes x sec x cm-5

Question 16

What is shock

Answer 16

Hypotension which results in inadequate perfusion of tissue
Metabolic needs of tissue is not being met, since delivery of oxygen is decreased, and if it prolongs, it will result in death

Question 17

Three types of shock and affect on HR, BP, CO, SVR, and PCWP

Answer 17

• Cardiogenic: Initial problem is CO. Compensative method is to increase HR and try to increase vascular resistance. Results in congestive heart failure
  Increased HR, SVR, and PCWP.
  Decreased BP and CO
• Distributive (septic): Caused by decreased systemic vascular resistance. Compensative method is to increase HR and CO to get a higher blood volume.
  Increased HR and CO
  Decreased BP and SVR
  No effect on PCWP
• Hypovolemic: Overall blood volume is low. Caused by major bleeding. Less blood is returning to the heart so CO drops. Compensative methods are to increase HR and SVR.
  Increased HR and SVR
  Decreased BP, CO, and PCWP