Exercise Physiology and Cardiac Output Flashcards
Cardiac Output (CO)
The volume of blood the heart pumps through the circulatory system in a minute. It is detrmibed by stroke volume and heart rate
Stroke Volume (SV)
The amount of blood expelled by the left ventricle of the heart in one contraction.
Mean Arterial Pressure (MAP)
An average arterial pressure which is influenced by the CO and the total peripheral vascular resistance.
Starling’s Law
The more the ventricles fill with blood, the more force the heart can generate for contraction. This expels more blood from the LV, so volume of blood entered the ventricle basicallly equal to blood that exits.
Cardiac Output (CO) Formula
CO = Stroke Volume (SV) x Heart Rate (HR).
Normal Cardiac Output at Rest
Approximately 5 litres of blood per minute.
Cardiac Output Calculation Example
Left ventricle: End Diaastolic V - End Systolic V = SV
75 bpm x 70 mL = 5250 mL/min.
(HR x SV)
What CO tells us?
A measure of heart performance. This info is needed because Cardiac Output changes
Sympathetic Nervous System
Increases ventricular contractility by adrenaline, pushing against srterial pressue (afterload)
Parasympathetic Nervous System
Decreases heart rate by acetylcholine.
Preload
The amount of blood in the ventricles before contraction. Increases dur to increased heart rate as a result of adrelanines action on the SAN.
How and why is the volume of the blood that can enter the ventricles limited?
By a transpaent memrane surrounding the heart that reduces friction of the hearts movement and prevents it enlarging and stretching too much.
If preload icreases, CO increases. Why?
If more blood enters ventricles, they contract more (starlings law), so more blood leaves the ventricles, increasing CO.
Afterload
The pressure the ventricles must overcome to eject blood.
Blood Flow Distribution at Rest
Digestive tract and liver receive ~27% of cardiac output, muscles 21%, and kidneys ~20%.
Blood Flow During Exercise
Muscles can receive as much as 85% of cardiac output.
Vasoconstriction
The tightening of smooth muscle cells around arterioles to restrict blood flow to certain organs during exercise. As a result they recieve near the same volume of blood as at rest, since SV and CO are increased during exercise.
Vasodilation
The widening of arterioles supplying blood to the skeletal muscle system so they receive greater blood volume than at rest.
How does vasoconstirction occur?
Arteriole walls change diameter as they are made of smooth muscle. Alo pre capilliary sphincters (at junction of capilliaries) can close, so oxyenated blood is directed into larger arterioles and not capilliaries (causing cold fingers).
Normal Heart Rate at Rest
Between 60 and 100 bpm.
Increased Heart Rate and Cardiac Output During Exercise
Can go up to 130-150 bpm because the body needs more oxygen. Stroke volume (volume of blood pumped out) also increases.
Average Blood Pressure
The mean arterial pressure (MAP) changes depending on activity.
MAP, Mean Arterial Pressure
Average pressure in arteries. Tells us how much blood the heart is pumping and how it may be changing.
Gives us the average blood pressure in the circulator system.
How to meaure MAP
Pressure gauge and stethoscope together
Microcirculation
The flow of blood through the smallest blood vessels.
Pulmonary Circuit
The circuit that carries blood from the heart to the lungs.
Systemic Circuit
The circuit that carries blood from the heart to the rest of the body.
Cardiac Output at Rest
CO (at rest): ~5,000 ml.
Blood Pressure Measurement
When the cuff is inflated to stop arterial blood flow, no sound is heard through a stethoscope.
Cuff pressure
Pressure applied by inflatable cuff during measurement.
How to use pressure gauge to measure MAP
Korotkoff sounds
Sounds indicating blood flow through compressed artery.
Systolic pressure
First Korotkoff sound detected by stethoscope.
Diastolic pressure
No sound heard in stethoscope when artery pressure equals cuff pressure.
MAP formula
MAP = diastolic P + 1/3(systolic P - diastolic P).
Sympathetic system
Promotes activation, increases heart rate and contraction. Connected to SAN, left atrium and left ventricle.
Parasympathetic system
Inhibits heart activity, reduces heart rate.
How many sympathetic and parasympathetics paths from the brain to the heart?
1 Parasympathetic (vagus nerve in medulla) and 3 Sympathetic (nerves in the spinal cord)
Vagus nerve
Parasympathetic nerve affecting heart rate regulation.
Adrenaline
Neurotransmitter released by sympathetic system - increases HR anf force of contration of left ventricular wall.
Acetylcholine
Neurotransmitter released by parasympathetic system, near the left atrium. Helps reduce HR
PO2
Partial pressure of oxygen in blood.
How much PO2 required for saturated binding of O2 to Hb?
Around 100mmHg gives 98% saturation. All 4 binding sites (haem groups) are occupied by molecular oxygen on Hb.
At 0 mmHg, what is the oxygen saturation of Hb?
0%. Dull/pale red colour to RBS
At 40 mmHg, what is the oxygen saturation of Hb?
75%. 3 of 4 binding sites on Hb are occupied by olecular oxygen
Hb-oxygen dissociation curve
Graph showing oxygen binding affinity to hemoglobin. Once saturated, there is a plateau as little additional oxygen binds since Hb is occupied.
3 factors affecting O2 affinity to Hb
Acidity (pH)
Temperature
PCO2 (partial pressure)
Normal blood pH
Typical range is 7.38 to 7.42.
Explain how Hb-oxygen dissociation curve changes at pH 7.3, 7.4 and 7.6
Cellular activity creates more acidic environment (lactic acid build up) which reduces oxygen’s affinity to Hb. Active cells hold on to oxygen more than non active cells due to their acidity so oxygen demand is able to be met.
Explain how oxygen affinity to Hb changes at temperatures 20, 37 and 43 degrees celcius
At low temperatures oxygen affinity to Hb is high (cold fingers plus vasoconstriction). O2 affinity decreases at higher temperatures so oxygen is given to active (warmer) cells that require it.
Explain how O2 affinity to Hb changes at PCO2 of 20mmHg, 40mmHg and 80mmHg.
Active cells generate more CO2 as a product of respiration so are in a more acidic envirionment. So oxygen affinity to Hb decreases and O2 is delivered to active cells.
Why is a pulse-oximeter provided to those at risk?
The human body has relatively limited sensitivity to low oxygen levels in our blood
What are the sugnals that tell our body to breathe more air?
PCO2 and pH, not just O2
Carbonic anhydrase (CA)
Enzyme converting CO2 and H2O to carbonic acid which then dissociates into bicrbonate (HCO3-) which is the most common molecule produced in the reaction.
Carotid bodies
Chemosensors (just above aorta) detecting blood CO2 and pH changes in the CVS.
Respiration
Process of gas exchange in lungs and tissues.
O2 saturation
Percentage of hemoglobin bound to oxygen.
Active tissues
Generate heat and CO2, lowering pH.
Intercalated disc
Structure connecting cardiomyocytes for electrical signaling.
Connexin 43 (Cx43)
Primary connexin in ventricular myocardium.
Blood flow silence
Occurs when artery is no longer compressed.
Elevated CO2
Detected by chemoreceptors, signals increased breathing.
Sympathetic nerve activation
Increases heart rate and breathing during low O2.
