Ch 16 Cardiac Output Measurement
Cardiac Output (CO) is the amount of blood the heart pumps into the circulatory system each minute. It is a key indicator of heart function and is calculated as the product of heart rate (HR) and stroke volume (SV): CO = HR × SV.
What is Cardiac Output ?
the amount of blood the heart pumps in a minute
Key Terms
What is Cardiac Output ?
the amount of blood the heart pumps in a minute
Calculation for Cardiac Output
HR X SV
What is Stroke Volume?
is the volume of blood ejected by a single ventricular contraction
What is the normal adult stroke volume?
60 - 130 mL/beat
What is the average cardiac output for men and women of all ages ?
5 L/min
What is the normal cardiac output range?
4 to 8 ml//min
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| Term | Definition |
|---|---|
What is Cardiac Output ? | the amount of blood the heart pumps in a minute |
Calculation for Cardiac Output | HR X SV |
What is Stroke Volume? | is the volume of blood ejected by a single ventricular contraction |
What is the normal adult stroke volume? | 60 - 130 mL/beat |
What is the average cardiac output for men and women of all ages ? | 5 L/min |
What is the normal cardiac output range? | 4 to 8 ml//min |
The normal individual Cardiac Output varies with what 5 things: | - age |
How much can the heart pump when stimulated by the SNS? | 20 - 25 mL/min |
What disease process occurs when the diseased or damaged heart can no longer pump all of the blood returned to it? | Congestive Heart Failure (CHF) |
How does Positive Pressure Ventilation affect Cardiac Output when the chest wall compliance is decreased and lung compliance is increased? | - decreases venous return |
Oxygen Transport equation (DO2) | CaO2 x CO x 10 |
What is the venous return? | the volume of blood returning to the right atrium |
What regulates capillary blood flow? | the concentrations of: |
What does the presence of LOW OXYGEN concentration and increased levels of HYDROGEN IONS and CO2 at the tissue level causes? | - vasodilation |
The pressure created by each stroke depends on 3 things: | 1. Efficacy of my heart as a pump |
Pulmonary artery wedge pressure (PAWP) is also known as | Pulmonary capillary wedge pressure (PCWP) |
_____________ ______________ is often used to describe flow output. | Cardiac Index |
How is cardiac index obtained? | CO/BSA (L/min/m2) |
What is the commonly cited RESTING Cardiac Index? | 2.5 - 4.0 L/min/m2 |
What is Cardiac Work? | is a measure of energy the ventricles use to eject blood against the aortic or pulmonary pressures (resistance). |
Why is the work performed by the left ventricle much greater than the right ventricle? | because it must eject against the mean aortic pressure (MAP), which is about 6x greater than the mean pulmonary artery pressure (MPAP) |
Mean Arterial Pressure (MAP) | (S + 2D)/3 |
What is the normal MAP? | 70 - 105 mm Hg |
What can occur if the MAP decreases lower than 60 mm Hg | - brain perfusion decreases |
End-Diastolic Volume (EDV) is defined as | the amount of blood in the ventricle at the end of filling (diastole) |
What can help estimate the ventricular size? | the end-diastolic pressure |
What does the Ejection Fraction (EF) represent? | the percentage of the EDV that is ejected with each heart beat |
EF calculation | SV/EDV |
What is the normal Ejection Fraction ? | 65%-70% |
SV is determined by the following 3 factors: | - preload |
Bradycardia does not drop cardiac output as long as the heart can compensate with increased ___________ _______________. | stroke volume |
What is Preload ? | is the stretch on the ventricular muscle fibers before contraction |
Starling's law of the heart | addresses the contractile properties of the heart: the more the muscle is stretched, the stronger it will react, until it is stretched to a point at which it will not react at all |
The filling of the right side of the heart is right atrial pressure, commonly measured as the ________________________________________________________________. | Central Venous Pressure (CVP) |
the filling pressure for the left side of the heart is left atrial pressure, commonly measured as _________________________________________________________________________________. | pulmonary artery wedge pressure (PAWP) |
Patients with CHF will have higher _____________. | PCWP |
If the right ventricle fails the __________ will be higher. | CVP |
What is persistent pulmonary artery hypotension treated with? | nitric oxide |
What is ventricular compliance ? | the ability of the ventricle to expand as blood enters from the atrium |
List the 3 factors that decrease ventricular compliance and therefore cause the pressure to increase out of proportion to the volume include the following: | - right ventricle dilation and overload (cause the septum to shift to the left and impinge on the left ventricle) |
If the CVP is higher than normal, the problem being caused by the RV because it is not pumping out enough. Therefore what happens? | - Blood backs up to the RA |
What is the normal Central Venous Pressure? | 2-6 mmHg |
What is the normal pulmonary artery wedge pressure? | 6-12 mmHg |
When the PAWP is less than _____ there is an issue in the LV. | 18 |
List the 3 main factors affecting the amount of blood returned to the heart: | 1. changes in the circulating blood volume |
The presence of which conditions increases intrathoracic pressure and thereby decreases venous return: | - tension pneumothorax |
________________ (+/-) pressures around the heart push on the heart, making it harder for blood to enter the heart, but easier for blood to be ejected | Positive |
_______________ (+/-) pressures around the heart pull blood toward the heart but make it more difficult for blood to leave the heart. | Negative |
What is afterload? | - the hemodynamic factor that represents all resistance to blood flow. |
What are the two components of afterload? | - ventricular wall stress |
The resistance in the lungs is __________________ ____________________ ________________ and the resistance is much less. | pulmonary vascular resistance (PVR) |
the resistance in the left ventricle is the _______________ __________________ ____________________ and the resistance is much greater. | systemic vascular resistance (SVR) |
Elevated SVR is associated with clinical conditions that cause: | - vasoconstriction (such as cold) |
What drugs elevate the SVR? | - norepinephrine (levophed) |
PVR is increased by conditions that decrease blood flow through the pulmonary artery, such as: | - contraction |
What can help decrease the SVR? | - warming a patient to normal temperatures |
PVR is increased by conditions that decrease blood flow through the pulmonary artery, such as: | - contraction |
4 things that cause the pulmonary artery to constrict | - decrease in PO2 |
Overtime, increased PVR results in: | - pulmonary hypertension |
myocardial contractility is affected by the following factors: | - sympathetic nerve innervation |
Sympathetic nerve stimulation with release of ___________________ and other circulating ________________ increases the strength and rae of cardiac contraction. | norepinephrine, |
A drug with a ___________________ (+/-) inotropic effect increases the strength of contraction of the myocardial fibers, most often by increasing intracellular calcium levels. | positive |
List positive inotropic drugs: | - calcium |
Drugs with a ______________ (+/-) inotropic effect decrease the strength of contraction but may also decrease the myocardial oxygen demand. | negative |
List negative inotropic agents: | - beta blockers |
physiologic depressants of cardiac contractility include: | - hypoxia |
Ficks cardiac output equation | The CO is calculated as the quotient of oxygen uptake and the difference of the arterial and mixed venous oxygen content |
Calculate the expected oxygen consumption (VO2). The normal range of (VO2) is 120 to 160 mL/min/m2, with an average of 125 mL/min/m2. for a patient with a body surface area of 2 m2 would be calculated as follows: | |
Calculate the arterial and mixed venous oxygen contents and C(a-v)O2. For example, given a hemoglobin of 14 g/dL, an arterial oxygen saturation (SaO2) of 90%, and a mixed venous oxygen saturation (SvO2) of 60%, the C(a-v)O2 is computed as follows: | 120 to 160 ml/mon |
What is the normal range of the C(a-v)O2? | 3.0 to 5.5 mL/dL |
Why has the use of the PA catheter decreased? | costs and hazards |
How does the TDCO, thermodilution cardiac output, work? | Sterile dextrose in water or normal saline solution at least 2°C colder than blood temperature is injected into the proximal port (right atrium) of the PA catheter. The resultant cooling is detected by a thermistor bead located just behind the balloon of the catheter, which is positioned in the pulmonary artery |
Given a stroke volume of 62 mL and an HR of 88 beats/min, what is the CO? a. 5.5 L/min b. 6.2 L/min c. 7.0 L/min d. 11.0 L/min | a. 5.5 L/min |
What is the normal range for CO in an adult? a. 2 to 4 L/min b. 4 to 8 L/min c. 6 to 10 L/min d. 10 to 13 L/min | b. 4 to 8 L/min |
A 75-year-old man is admitted to the ICU after aortic valve surgery. A pulmonary artery catheter yields the following data: central venous pressure (CVP): 5 mm Hg; cardiac output (CO): 4.0 L/min; mean arterial pressure (MAP): 80 mm Hg; mean pulmonary artery pressure (MPAP): 26 mm Hg; pulmonary artery wedge pressure (PAWP): 10 mm Hg; and heart rate (HR): 80 beats/min. Calculate the patient’s pulmonary vascular resistance (PVR): a. 40 dynes-s/cm5 b. 320 dynes-s/cm5 c. 160 dynes-s/cm5 d. 220 dynes-s/cm5 | b. 320 dynes-s/cm5 |
What happens to CO in the presence of sympathetic nervous stimulation? a. Increases significantly b. Decreases significantly c. Remains unchanged d. Decreases by only 20% | a. Increases significantly |
Which of the following statements are true regarding the distribution of blood flow and venous return? 1. 60% to 70% of the total blood volume is in the venous system 2. Blood is shunted to vital organs during cardiac failure 3. Circulatory function and pressures can be maintained with a loss of 20% of the blood volume 4. 50% of the total blood volume is in the venous system a. 1, 2, and 3 b. 2 and 3 c. 1 and 2 d. 2, 3, and 4 | 1. 60% to 70% of the total blood volume is in the venous system |
What is the normal range for CI? a. 0.2 to 1.3 L/min/m2 b. 1.5 to 2.6 L/min/m2 c. 2.5 to 4.0 L/min/m2 d. 4 to 8 L/min/m2 | c. 2.5 to 4.0 L/min/m2 |
Which of the following correlates best with the oxygen requirements of the heart? a. SV b. EF c. EDV d. Cardiac work | d. Cardiac work |
What is the normal range for ejection fraction? a. 25% to 40% b. 40% to 55% c. 65% to 75% d. 75% to 85% | c. 65% to 75% |
The amount of precontraction stretch applied to the ventricles is called: a. Preload b. Afterload c. Contractility d. EF | a. Preload |
Preload of the left ventricle is assessed by which of the following parameters? a. Arterial diastolic blood pressure b. MAP c. CVP d. PAWP | d. PAWP |
Which of the following conditions would cause a reduction in ventricular preload? a. Decreased ventricular compliance b. Increased venous return c. Cardiac tamponade d. Hypovolemia | d. Hypovolemia |
Which of the following are possible hemodynamic effects of using mechanical ventilation? 1. Reduced preload 2. Reduced CO 3. Increased PVR 4. Increased preload a. 1, 2, and 3 b. 2, 3, and 4 c. 1 and 2 d. 3 and 4 | 3. Increased PVR |
Which of the following conditions would increase left ventricular afterload? a. Pulmonic valve stenosis b. Decreased blood viscosity c. Positive end-expiratory pressure d. Systemic hypertension | d. Systemic hypertension |
Which of the following is most closely related to systemic vascular resistance? a. Right ventricular afterload b. Left ventricular afterload c. CO d. Left ventricular preload | b. Left ventricular afterload |
Which of the following abnormalities would increase PVR? 1. Hypoxemia 2. Acidosis 3. Pulmonary emboli 4. Hypervolemia a. 1, 3, and 4 b. 1, 2, and 3 c. 2 and 4 d. 1, 2, 3, and 4 | 1. Hypoxemia |
Which of the following is TRUE regarding cardiac contractility? a. It cannot be measured directly b. It is increased by β-blocking drugs c. It is increased by hypercapnia d. It is increased by parasympathetic neural stimulation | a. It cannot be measured directly |
Which of the following invasive CO techniques requires the measurement of inhaled and exhaled gas concentrations? a. Thermodilution b. Fick c. Pulse contour d. Transtracheal Doppler | b. Fick |
Which of the following techniques can provide beat-by-beat measurement of stroke volume and cardiac output? a. Thermodilution b. Fick c. Pulse contour d. NM3 | c. Pulse contour |
Which of the following are noninvasive techniques for determining cardiac performance? 1. Echocardiography 2. Transthoracic electrical bioimpedance 3. Partial CO2 rebreathing 4. Thermodilution a. 1, 2, and 3 b. 1, 2, and 4 c. 2, 3, and 4 d. 2 and 4 | 1. Echocardiography |