Cardiovascular Physiology Flashcards
Heart size
Size matters - the larger the heart, the more blood it can pump (and oxygen) throughout the body
Generally 0.8-1.0% of BW
Structure of Heart
Left side - moves oxygenated blood from the pulmonary vein into the atria (through mitral valve) and into the ventricle, leaving to the body through the aorta (aortic valve)
Right side - takes in deoxygenated blood from the vena cava into the atria (through tricuspid valve) and into the ventricle, leaving to the lungs through the pulmonary artery (pulmonary valve)
Cardiac Output
The measure of the amount of blood pumped throughout the body in one minute
- higher output = more blood pumped= more oxygen circulated
Cardiac Output Equation
Q = SV x HR
- SV - stroke volume - the amount of blood pushed in one pump of the heart
- HR - heart rate - max 220 BPM, average 32-36 BPM
Effects on Heart Size
Sex - males tend to have larger hearts, tied to “X” chromosome (males XY, females XX)
Body size - larger horses have larger hearts
Breed - horses bred for aerobic/stamina exercises then to have larger hearts than horses bred for anaerobic/ power exercise (TB vs. draft)
Predicting Heart Size
Heart ratio = heart size : body weight
- higher ratio = larger heart
Calculate heart score using ECG machine
Heart Score
Measured between the QRS peak, in milliseconds
- longer the distance, the larger the heart is and the more blood it pumps per beat
Blood Flow Distribution
At rest, the blood flow is divided relatively evenly between all body systems
During work, 80% of blood is directed to the muscles
The heart has constant 5% of blood flow
Blood is 1% of BW
Response to Exercise
Spleen contractions and dumps 30% more RBC into circulation to increase oxygen carrying capacity
- PCV increases from 30% to 70%
- removal of the spleen can cause up to 30% decrease in exercise capabilities
- High RBC turnover rate
Heart rate increases
- stroke volume increases about 70%
Blood pressure increases
Arterial Pressure
Thicker arteries around the heart can cope with increased pressure due to exercise; the thinner arteries around the rest of the body are put under more stress and adapt by:
- Recruitment - capillaries not previously in use are filled
- Distention - capillaries in use grow larger
The added stress makes diffusion of oxygen easier from capillaries to muscles
Control of Capillary Adaptation
Nitric oxide signals for vasodilation of blood vessels
Arginine (and Citrulline) can increase the number of capillaries, which in turn increases blood flow and oxygen delivered to muscles
