Cardiac output and venous return
description
Transcript of Cardiac output and venous return
![Page 1: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/1.jpg)
Cardiac output and venous return
![Page 2: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/2.jpg)
Cardiac output• The quantity of blood pumped into the
aorta– Amount of blood that flows through the
circulation– Most important factor in relation to the
circulation
![Page 3: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/3.jpg)
• Normal cardiac output– 5.6 L/min in young men when resting
• 10-20 % less in women– Factors
• Age• Level of body activity
![Page 4: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/4.jpg)
• Cardiac index– Cardiac output per sq. m of body surface area
• Body weight around 70 kg = 1.7 sq. m body surface
• Cardiac index = approximately 3 L/min/sq.m
• Effects of age– Rapid increase (4L/min/sq.m) at age 10
• Decline thereafter (2.4 L/min/sq.m at age 80)
![Page 5: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/5.jpg)
![Page 6: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/6.jpg)
Venous return
• Amount of blood flowing from the vein into the right atrium– Must be equal to cardiac output
• Exception– Few heartbeats at a time for storage/removal of
blood from heart and lungs
![Page 7: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/7.jpg)
Control of cardiac output
• Venous return– Primary controller
• Peripheral factors– Not heart
– Heart• Built-in mechanism to accommodate amount of
blood that flows into the right atrium– Frank-Starlings law of the heart (pumping of blood)– Bainbridge reflex (heart rate)
![Page 8: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/8.jpg)
• Venous return– sum of all blood flow from peripheral
system– Cardiac output
• sum of all local blood flow regulation• Controlled by factors that control local flow of
blood
![Page 9: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/9.jpg)
Cardiac output = sum of the various factors controlling local blood flow = sum of local blood flow = venous return
![Page 10: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/10.jpg)
• Effects of total peripheral resistance– Variation in cardiac
output under normal arterial pressure
• Reciprocal of peripheral resistance
• Increased peripheral resistance, decreased cardiac output
– Ohm’s law
![Page 11: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/11.jpg)
Plateau level in cardiac output• Amount of blood that a heart can pump out
– Limited• Plateau around 13L/min when normal
– 2.5 X above normal (5L/min)– Heart has a capacity to pump 2.5 X more blood than normal
venous return before becoming a limiting factor
– Abnormal condition• Hypereffective
– Greater output
• Hypoeffective– Lesser output
![Page 12: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/12.jpg)
![Page 13: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/13.jpg)
• Hypereffective heart– Nervous stimulation
• Sympathetic stimulation and parasympathetic inhibition
– Greatly increased heart rate (180-200 beats/min)– Increased contractility of heart muscle by 2 X
• Result– Raise in plateau level to 25L/min after sympathetic
stimulation
![Page 14: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/14.jpg)
• Hypereffective heart– Heart hypertrophy
• Increased workload– Increase in mass– Increase in contractile strength
• Net results– Increased plateau output to 30-40L/min in
marathon runners
![Page 15: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/15.jpg)
• Pathologically high cardiac output– Cause
• Chronically reduced total peripheral resistance– Not by excessive excitation of heart
– Excessive excitation of heart• Sudden increase in cardiac output
– Lasts only for a short time– Increased blood flow to tissue triggers vasoconstriction– Increased capillary filtration of fluid– Net result = decreased venous return
![Page 16: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/16.jpg)
![Page 17: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/17.jpg)
• Hypoeffective heart– Factors
• Nervous excitation inhibition• Abnormal rhythm/rate of heart beat• Valvular heart disease• Hypertension• Congenital heart disease• Myocarditis• Cardiac anoxia• Damage to myocardium
![Page 18: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/18.jpg)
![Page 19: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/19.jpg)
• Low cardiac output– Abnormalities that decrease pumping
effectiveness• Damage to cardiac muscles• Cause cardiac shock
– Abnormalities that decrease venous return• Decreased blood volume• Acute venous dilation• Vessel obstruction
– Cause circulatory shock• Reduced amount of nutrients being delivered
![Page 20: Cardiac output and venous return](https://reader036.fdocuments.net/reader036/viewer/2022081513/56815be6550346895dc9da59/html5/thumbnails/20.jpg)
Role of nervous system
• Maintenance of arterial blood pressure when cardiac output increases– Essential to achieve high cardiac output
• Increased local blood flow via dilation of blood vessel
– Increase arterial pressure during exercise• Increase cardiac output