Chapter 15 Assessment of Cardiac Output

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What is the most important factor in assessment of the ability of the cardiovascular system to meet the body's metabolic demands?

Adequacy of perfusion

The amount of blood pumped out of the left ventricle in 1 minute is the definition of...

Cardiac output

The average cardiac output for adult men and women at rest is 5 L/min?

True. Normal range is 4 to 8 L/min

What can affect cardiac output?

The normal CO for an individual varies with age, sex (10% higher in men), body size, blood viscosity (hematocrit), and the tissue demand for oxygen

To enable the heart of a well-trained athlete to produce a cardiac output of up to 35 L/min, stimulation of the heart muscle is needed through what?

Sympathetic Nervous System

Blood flow is directed to organs that have the highest metabolic needs when at rest. Which organ would have the lowest metabolic needs when at rest?

Brain, heart, skin, and others (muscles, liver, and kidneys receive the greatest amount)

At rest, approximately what percentage of total blood volulme is stored in the venous system?

64%

Approximately how much blood can be lost before circulatory function and pressures are affected?

20% to 25% of total blood volume can be lost without altering circulatory function and pressures

Cardiac output is a product of which two variables?

Heart rate (HR) and Stroke volume (SV)

To standardize the measurement of cardiac output in individuals of different sizes, the value for cardiac output is divided by the persons body surface area. The result is known as?

Cardiac Index (CI): used to describe flow output

What is true about ejection fraction?

Represents the percentage of the end-diastolic volume that is ejected with each beat.
Normal EF is 65%-70%
EF is either measured directly or calculated (SV/EDV)
EF declines as cardiac function deteriorates
When the EF falls to the 30% range, a patients exercise tolerance is severely limited because of the heart's inability to maintain an adequate CO

The cardiac output of the right ventricle is the same as the cardiac out put of the left ventricle. Compared with the left ventricle, the cardiac work index of the right ventricle is?

Lower

Right Ventricle: has to eject blood against pulmonary pressure [resistance]

Left Ventricle: Must eject against the mean aortic pressure (MAP), which is 6x the mean pulmonary artery pressure (MPAP), Cardiac work is much higher for left ventricle.

In patients with pulmonary hypertension, the right ventricular stroke work index will be:

Increased

What does not have a direction effect on stroke volume?

SV is determined by three factors:
Preload
Afterload
Contractility

What best describes preload?

Is the stretch on the ventricular muscle fibers before contraction.

Is created by the EDV

Starling's law (the greater the stretch on the resting ventricle, the greater the contraction up to a critical limit)

The strength of contraction of the myocardial muscle fibers is related directly to the amount of stretch on the fiber before contraction is a definition of:

Starling's Law

When ventricular function curves are performed on a patient with a suspected failing right ventricle, how does cardiac output typically change as central venous pressure increases?

There is little and slow change in cardiac output for large changes in PCWP increases, but the curve then peaks (at approximately 5 L/min) and output begins to decline after PCWP reaches 20 mm Hg

The filling pressure of the right heart also is known as the _______ pressure.

RAP (right atrial pressure)
CVP (central venous pressure)

The filling pressure of the left heart also is known as the _________ pressure. The PCWP is used to measure the left ventricular filling pressure.

Left Atrial Pressure
Pulmonary Capillary Wedge Pressure (PCWP)

What may cause a decrease in ventricular compliance?

Myocardial ischemia and infarction
Hemorrhagic and septic shock
Pericardial effusions
Right ventricular dilation and overload
PEEP
CPAP
Inotropic drugs

What effect does an increase in intrathoracic pressure have on venous return?

Raised intrathoracic pressure decreases venous return

What effect does spontaneous deep inspiration have on venous return?

Increased venous return

The resistance to ventricular ejection also is known as?

Afterload

Intermittent positive-pressure breathing (IPPB) with positive end-expiratory pressure (PEEP) has what effect on afterload and preload?

Decreases afterload (resistance)
Decreases preload

The greatest determinant of peripheral resistance to blood flow is?

The radius of the vessels

What is used to determine the afterload of the right ventricle?

Pulmonary Vascular Resistance (PVR)

What can cause an increase in pulmonary vascular resistance?

PVR is increased by constriction, obstruction (e.g. emboli), or compression of the pulmonary vasculature or by backpressure from the left heart.

Hypoxemia, acidosis, and release of histamine from an allergic reaction also cause vasoconstriction with an increase in PVR.

A drug that increases the contractility of the heart is known as a positive?

Positive inotropic drugs >> increases the force and velocity of contraction and myocardial O2 consumption

To obtain the coronary perfusion pressure, what two values are needed?

CPP = Diastolic BP - PCWP

NI: 60 to 80 mm Hg

What method of measuring cardiac output is most popular in ICU's around the country?

Pulmonary artery catheter (PAC) thermodilution method

(TDCO >> thermodilution CO measurement)

When the Fick method is used to calculate cardiac output, if C(a-v)O2 is greater than expected and VO2 is normal, cardiac output probably will be?

Lower

Higher C(a-v)O2 valves indicate more O2 was removed, as when the following occurs:

Blood flow is slow (CO) or,
Tissue extraction of O2 is high (O2 consumption)

The periodic, noninvasive measurement of cardiac performance that requires only the use of sphygmomanometer is called?

Blood Pressure

>>A new method has been developed that estimates CO using pulse - waveform (PWA) from a brachial cuff sphygmomanometer.

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