Clinical Hemodynamics

Flow of Blood

Right ventricle Þ pulmonary arteries Þ alveolar capillaries Þ pulmonary veins Þ left ventricle Þ aorta Þ arteries (extensive elastic tissue and smooth muscle, high pressure) Þ arterioles (site of highest resistance, largest drop in pressure) Þ capillaries (largest total cross-sectional and surface area) Þ venules Þ veins (under low pressure)Þ back to right ventricle

Blood volume in body:

heart 18%
arteries 13%
arterioles and capillaries 7%
veins and venules 50% (acts as a capacitance)

Determinants of Cardiac Output

CO = SV * HR

Heart rate

Stroke volume – amount of blood ejected by ventricle during systole

influenced by three inputs: preload, afterload, and contractility. (End diastolic volume - end-systolic volume) = SV.

Preload – ventricular wall tension at end of diastole. In clinical terms, it is the stretch on the ventricular fibers just prior to contraction, often approximated by the end-diastolic volume or end-diastolic pressure.

The end diastolic volume is related to the mean right and left atrial pressure.
Right atrial pressure and left atrial pressure can be used to measure preload; end-diastolic ventricular pressure is best estimate of preload.
Preload is dictated by volume, stiff ventricles can increase end diastolic pressure with same volume.

Afterload – ventricular wall tension during contraction; resistance that must be overcome in order for the ventricle to eject its contents. It is often approximated by the systolic ventricular (or arterial) pressure.

Left-sided afterload is determined by the systemic vascular resistance, aortic arch, and arteriolar cross-sectional changes. It is equivalent to the aortic pressure. It has to deal with the big capacitance of the systemic circulation.

Right-sided afterload is determined by pulmonary vascular resistance or pulmonic arch pressure, which is considerably less (1/10) than the left side, and is equivalent to the pulmonary artery pressure.

Contractility (Ionotropic State)

Property of heart muscle that accounts for changes in the strength of contraction, independent of the preload or afterload. Often reflects chemical or hormonal influences (e.g., catecholamines) on the force of contraction.

Ejection Fraction

Definition – the fraction of end-diastolic volume ejected from the ventricle of interest during each systole contraction.

Normal range is 55%-75% for left ventricle

EF = SV/EDV

Right ventricle has a lower EF than the left but CO’s are the same and SV’s are same therefore EDV varies

Important with respect to prognosis: 40% or less Þ Ý mortality

Uncomplicated, normal – inferior wall does not move, EF=52% (50 – 75%)

Heart failure, anterior infarct – inferior wall moves, no anterior movement, EF=23%

Anterior-Inferior infarct – shock, EF=13%

Does not necessarily equate with functionality of the heart

Systemic arterial pressure (by way of the Swan-Ganz catheter)

P_a(systemic arterial pressure) = HR * SV * SVR = CO * SVR

SV = stroke volume

SVR = systemic vascular resistance (measured using balloon of Swann-Ganz catheter to plug a pulmonary artery)

Pulmonary wedge pressure – try to estimate left sided heart pressures; balloon wedges into one of the pulmonary arteries; can measure left atrial

ressure. Since no blood flowÞ can measure the left-sided waveforms with the balloon.

CO = cardiac output (Inject bolus of cold fluid Þ measure CO by thermistor in a Swann-Ganz catheter)

Procedure: Swann-Ganz catheter is inserted into the right side of the heart (via internal jugular vein) Þ balloon is inflated and carried into the right atria Þ right ventricle (through the tricuspid valve) Þ pulmonary artery (through pulmonary valve) signified by the appearance of a dichrotic notch in the wave form Þ pulmonary arteriole

Can measure: right preload, blood flow, right atrial pressure, right ventricular pressure, and pulmonary wedge pressure with a Swann-Gantz catheter.

Resistance = V/I (Ohm’s law); where R= resistance being measured, I = cardiac output, V = difference in pressures from beginning to end.

SVR= 80(mean systemic arterial pressure – right atrial pressure)/CO (blood flow in system)

PVR = 80(mean pulmonary artery pressure – left atrial pressure (PWP))/ CO

Miscellaneous

Clarification of terms: venoconstrict – venous constriction; vasoconstrict – arteriolar constriction

Arterioles have smooth muscle around them, adjusts resistance in the body, when measuring resistance Þ get one number which is a representation of all arterioles.

Wave forms on the venous pulse curve (M-shaped):

A-wave – Active phase of atrial filling; atrial contraction; just after the P wave; followed by the X descent.

C-wave – When the ventricles begin to contract; it is caused partly by slight backflow of blood into the atria at the onset of ventricular contraction but probably mainly by bulging of the A-V valves backward toward the atria due to increasing pressure in the ventricles.

V-wave – Passive-filling phase of atria; occurs toward the end of ventricular contraction; it results from slow flow of blood into the atria from the veins while the A-V valves are closed during ventricular contraction. Then, when ventricular contraction is over, the A-V valves open, allowing this blood to flow rapidly into the ventricles causing the V-wave to disappear. Followed by the Y descent.

Cardiac-thoracic ratio = ratio of width of heart to width of thorax on x-ray; usually less than 0.5. Increased ratio in CHF.

Abbreviations	Parameter	Normal Values
SP DP MAP	systemic arterial systolic pressure systemic arterial diastolic pressure mean systemic arterial pressure	90-140 mmHg 60-90 mmHg 70-105 mmHg
PCW aPCW vPCW	mean pulmonary capillary wedge pressure "a" wave "v" wave	1-10 mmHg 3-15 mmHg 3-15 mmHg
PAS PAD MPA	pulmonary artery systolic pressure pulmonary artery diastolic pressure mean pulmonary artery pressure	15-30 mmHg 4-12 mmHg 9-16 mmHg
RVSP RVEDP	right ventricular systolic pressure right ventricular end diastolic pressure	15-30 mmHg 0-8 mmHg
MRA aRA vRA	mean right atrial pressure "a" wave "v" wave	0-8 mmHg 2-10 mmHg 2-10 mmHg
CO	cardiac output	4-8 L/min
HR	heart rate	60-120 beats/min
SVR PVR	systemic vascular resistance pulmonary vascular resistance	770-1500 dynes-sec-cm^-5 20-120 dynes-sec-cm^-5
SVRI PVRI	systemic vascular resistance index pulmonary vascular resistance index	1700-2600 dynes-sec-cm^-5 70-200 dynes-sec-cm^-5
CI SV SVI	cardiac index stroke volume stroke volume index	2.8-4.2 L/min/M² 70-130 cc/beat 30-60 cc/beat
BSA	body surface area	M²
LCW LCWI LVSW LVSWI	left cardiac work left cardiac work index left ventricular stroke work left ventricular stroke work index	Kg^.min 3.2-4.2 Kg^.min/M² 60-80 gm 30-100 g/M
RCW RCWI RVSW RVSWI	right cardiac work right cardiac work index right ventricular stroke work right ventricular stroke work index	Kg^.min 0.5-0.7 Kg^.min/M² 10-15 gm 6-11 g/M

Hemodynamic Equations

SV = CO/HR; SI = SV/BSA

CI = CO/BSA

SVR = (MAP-MRA)/CO x 79.92

SVRI = svr X bsa

PVR = (MPA-PCW)/CO X 79.92

PVRI = RVR x BSA

LCW = CO x (MAP-PWP) x 0.0136

LCWI = LCW/BSA

LVSW = SV x (MAP-PWP) x 0.0136

LVSWI = LVSW/BSA

RCW = CO x (MPA-CVP) x 0.0136

RCWI = RCW/BSA

RVSW = SV x (MPA-CVP x 0.0136

RVSWI = RVSW/BSA