ACUTE RESPONSES OF THE CARDIOVASCULAR SYSTEM

Question 1

Cardiovascular responses

Answer 1

Numerous cardiovascular (heart, blood and blood vessels) responses occur when we start exercising. All are designed to facilitate the rapid and efficient delivery of increased amounts of oxygen to the working muscles in order to meet the body’s increased demand for energy.

Question 2

Acute responses of the cardiovascular system to exercise include:

Answer 2

• increased heart rate
• increased stroke volume
• increased cardiac output
• increased blood pressure
• redistribution of blood flow to working muscles
• increased arteriovenous oxygen difference.

Question 3

INCREASED HEART RATE

Answer 3

Heart rate (HR) refers to the number of times the heart contracts or beats per minute (bpm). Resting heart rate refers to the number of heart beats per minute while the body is at rest. For an untrained adult, this is usually somewhere between 60 and 80 beats per minute.

• Once an individual begins to exercise, their heart rate increases as a response to the extra energy required by the body.
• The increase in heart rate helps to increase oxygen delivery to the working muscles and aids in the removal of waste products from the muscles and body.

At the beginning of exercise the heart beats faster to deliver oxygen to the muscles and help remove waste products.

Your heart rate has a maximum and this can be APPROXIMATELY calculated by following equation
MAX HR = 220 - age
- Trained athletes will have a lower resting heart rate
- Heart rate increases in anticipation to exercise – Anticipatory rise

Question 4

what is steady state?

Answer 4

is when oxygen supply = oxygen demand

Question 5

INCREASED STROKE VOLUME (SV)

Answer 5

Stroke volume (SV) is defined as the amount of blood ejected from the left ventricle with each beat (contraction) of the heart. Stroke volume increases during exercise, plateauing at between 40 and 60 per cent MHR.
- Males will have generally higher stroke volumes due to their increased heart size.

Question 6

INCREASED CARDIAC OUTPUT (Q)

Answer 6

Cardiac output (Q̇) is the amount of blood ejected from the left ventricle of the heart per minute. It is the product of heart rate multiplied by stroke volume:

Cardiacoutput(Q˙)=strokevolume(SV)×heartrate(HR)
Cardiacoutput(Q˙)=SV×HR
Q˙=litres(L)
HR=beatsperminute(bpm)
SV=millilitres(mL)

Cardiac output predictably increases during exercise. During maximal exercise intensities, average cardiac output can be20–25 litres per minute, although among highly trained endurance athletes, cardiac output may be as high as35–40 litres per minute, giving these athletes a major physiological advantage.

Question 7

INCREASED BLOOD PRESSURE

Answer 7

—> Blood pressure is the pressure exerted by the blood against the arterial walls as it is forced through the circulatory system by the action of the heart.
- It has two components: systolic blood pressure and diastolic blood pressure.
Blood pressure is usually expressed as:
Blood pressure = systolic/diastolic mmHG

Question 8

systolic blood pressure

Answer 8

is the blood pressure recorded as blood is ejected during contraction phase of the heart cycle. Will be the higher of the 2 values

Question 9

diastolic blood pressure

Answer 9

is the blood pressure recorded during the relaxation phase of the heart cycle. Will always have a lower value.
„- A normal blood pressure is 120 over 80.

Question 10

REDISTRIBUTION OF BLOOD TOWARD WORKING MUSCLES

Answer 10

—> Under resting conditions, only about15–20 per centof total systemic blood flow is directed to the skeletal muscles. The rest is mainly distributed to the organs of the body (e.g. heart, liver, kidneys, intestines, brain).However, under exercise conditions, the majority of the blood (80–90 per cent) may be redirected to the working muscles.
- This is achieved by the capillaries and arterioles supplying the working muscles expanding in diameter (a process known as vasodilation). At the same time, blood flow to the organs of the body is reduced by the vasoconstriction (narrowing) of the capillaries and arterioles that supply blood to these organs.

Question 11

INCREASED ASTERIO-VENOUS DIFFERENCE

Answer 11

Thearteriovenous oxygen difference (a-VO2diff)is a measure of the difference in the concentration of oxygen in the arterial blood and the concentration of oxygen in the venous blood.
- This is measured in millilitres per100 millilitresof blood.

At rest, the arteries contain an oxygen concentration of approximately20 millilitres per 100 millilitresof blood (200 millilitresof oxygen per litre of blood), while the veins typically contain about15 millilitres per 100 millilitres. Thus, the a-VO2difference at rest is about5 millilitres per 100 millilitresof blood:

A-VO2 diff = 20ml/100ml – 15ml/100ml
a-VO2 diff = 5ml/100ml

During exercise, the body has a higher cardiac output to supply the muscles with more oxygen.

Question 12

↑ Venous return to heart

Answer 12

assisted by muscle pump, respiratory pump and venoconstriction (constriction of the veins)

Question 13

↓ Blood volume

Answer 13

plasma loss due to sweat in prolonged endurance activities