Cardiovascular System6

CVS changes during Exercise

• The Cardiovascular system changes to match supply and demand.Components of the CV system during exercise

heart rate strove volume cardiac output blood flowblood pressure

Heart rate

• Measure at the radial or carotid site.• Reflects the amount of work that it is

performing to meet the demands of the body with increasing work.

• Resting HR: 60 to 80 bts/min. – Anticipatory response-prior to starting

exercise just knowing that you are going to have to start exercise.

– 220-age= predicted Max HR.

Heart Rate

100

120

140

160

180

200

40 90 140 190 240 290 340

Treadmill Speed (m/min)

HR

(b

pm

)

trained

sedentary

Change in HR during ExerciseChange in HR during Exercise

As exercise begins, Para-SNS withdraws influence.

SNS stimulates heart. Adrenal gland secretes catecholamines. Increase in body temperature ,as in intense

exercise.

Stroke VolumeStroke Volume

May increase with increasing rates of work up to intensities of 40% to 60% of maximum exercise.

May continue to increase up through maximal exercise intensity, generally in highly trained athletes

Depends on position of body during exercise•upright-SV is less, supine is greater (easier to heart)upright-SV is less, supine is greater (easier to heart)

STROKE STROKE VOLUMEVOLUME

Cardiac Output• Resting is 5.0 L/min-

• 20 to 40 L/min during exercise.

• The need for an increase is to meet the muscle’s demands during exercise.

• An increase in HR and SV increases Q, (separate or together)

• After 40 to 60% of max, SV plateaus, Q increases due to increase in HR .

CARDIAC OUTPUTCARDIAC OUTPUT

Cardiac Output

0

5

10

15

20

25

30

40 90 140 190 240 290 340 390

Treadmill Speed (m/min)

Ca

rdia

c O

utp

ut

(L/m

in)

trained

detrained

Redistribution of Blood Flow

• Blood flow to tissues is controlled in relation to tissue needs– Tissue needs may 20-30 fold, but cannot Q

that much: 5 L/min 100 -150 L/min ! ? So flow is redistributed between tissues

• Muscle blood flow to working skeletal muscle• Splanchnic blood flow to less active organs

– Liver, kidneys, GI tract, & also to non-working muscle

Redistribution of Blood Flow During Exercise

Redistribution of Blood Flow

Local SystemicVasodilation Vasoconstriction

PO2 PCO2 [H+] adenosine [K+] Nitric oxide

Metabolites Epinephrine

Adrenal medulla

SympatheticNervousSystem

overrides

Blood pressure during Blood pressure during endurance activitiesendurance activities

• SBP increases in proportion to exercise intensity.

• DBP changes very little during endurance exercise.

• There is modest increase in mean arterial pressure .

Effects of Incremental Exercise on BPEffects of Incremental Exercise on BP

0

25

50

75

100

125

150

175

200

225

250

0 50 100 150 200 250 300Workload (W)

Blo

od

Pre

ss

ure

(m

m H

g)

Systolic BP

Diastolic BP

Cardiovascular Adjustments to Exercise

Cardiac Output Components in Trained & Untrained Subjects

Untrained

Rest 70 72 5.0

Max Exercise 195 113 22.0

Endurance Trained

Rest 50 100 5.0

Max Exercise 195 179 35.0

Heart rate Stroke volume Cardiac outputSubject/Activity (beats/min) (ml/beat) (L/min)