Cardiovascular response to exercise The Heart

Outline General cardiac responses to exercise – Control of heart rate – Control of stroke volume – Blood pressure – Distribution of blood flow – Barroreceptors Adaptations to training Impact of the environment

Examples of work (METS) Rest 1 Cycling <10 mph 6 Cycling >20mph 16 Running (10 min/mile)10 Running (6 min/mile)16 METS=metabolic equivalent tasks 1 MET=resting energy expenditure= 3.5 mlO 2  kg -1  min -1 = 1 Kcal  kg -1  min -1

aO 2 content=20 ml O 2 /100 ml blood vO 2 content=15 ml O 2 /100 ml blood CO=5 L/min

Effects of Exercise on Blood Pressure MABP-RAP = CO  TPR

Pressure (mmHg) systolic diastolic mean

Impact of Dynamic and Isometric Exercise on Arterial Blood Pressure DynamicStatic (isometric)

Comparison of BP Response Between Arm and Leg Ergometry

Why is blood pressure going up? I thought we had sensors that control blood pressure.

Arterial Baroreceptors Cardiovascular Physiology. Berne and Levy 1972

Activation of Barroreceptor reflex Response to an increase in arterial pressure Withdrawal of sympathetic tone Activation of parasympathetic tone Results: – Decrease heart rate and contractility – Arterial vasodilation – Increase in venous compliance

Afferent nerve firing responds to absolute pressure and rate of change in pressure

Baroreceptors adapt

Afferent and efferent neural baroreflex responses Arterial Baroreflex Control of the Peripheral Vasculature in Humans: Rest and Exercise. FADEL, PAUL Medicine & Science in Sports & Exercise. 40(12): , December 2008

Afferent and efferent neural baroreflex responses to the application of neck pressure (NP) and neck suction (NS) Arterial Baroreflex Control of the Peripheral Vasculature in Humans: Rest and Exercise. FADEL, PAUL Medicine & Science in Sports & Exercise. 40(12): , December 2008

3 Heart rate control during exercise by baroreceptors and skeletal muscle afferents. OLEARY, DONAL Medicine & Science in Sports & Exercise. 28(2): , February Schematic illustration of the effect of exercise on arterial baroreflex control of heart rate. Exercise resets the relationship between arterial pressure and heart rate upward and to the right (OP = hypothetical arterial baroreflex operating point).

Oxygen Demand

aO 2 content=20 ml O 2 /100 ml blood vO 2 content=15 ml O 2 /100 ml blood CO=5 L/min

Meeting oxygen needs during exercise Fick equation VO 2 = Q  (Ca O 2 – Cv O 2 ) VO 2 = [HR  SV]  (Ca O 2 – Cv O 2 ) VO 2 = [BP  TPR]  (Ca O 2 – Cv O 2 )

Oxygen Extraction (E) Ca O 2 – Cv O 2 Ca O 2 Fick equation VO 2 = Q  (Ca O 2 – Cv O 2 ) VO 2 = Q  Ca O 2 x E E=

Arterial and venous oxygen during exercise O 2 Extraction =(19-12)/19 =0.33 O 2 Extraction =(19.5-2)/19.5 =0.90

Heart rate and stroke volume

Heart rate Estimate Maximal heart rate = x (age year) = x54=170 bpm

Autonomic Nervous System NervesNeurotran smitter DistributionEffect SNSCervical Thoracic Pregang: ACH Postgang: NE Heart, Arteries & Most veins  1 (  HR)  1  2 PNSVagus and lumbar Pregang: ACH Post gang ACH Heart Vessels of Genitalia & colon  HR

The heart is under net vagal tone

Epinephrine Source: Adrenal medulla Increase heart rate and contractility (  1 ), low concentrations vasodilation (  2 ) high concentrations vasoconstriction (  1 ), decrease venous compliance (  1 )

Norepinephrine Source: Adrenal medulla Increase heart rate and contractility (  1 ), Limited effect on  2 At all concentrations vasoconstriction (  1 ), decrease venous compliance (  1 )

Determinants of Cardiac Output Heart rate Stroke volume – Ventricular end-diastolic volume – Contractility – Afterload (aortic pressure)

Venus Blood Return to Heart muscle pump one-way venous valves breathing Return of blood to heart

Increase Preload

Increase Afterload

Increase Contractility

Stroke volume End diastolic volume – End-diastolic volume (Starling’s Law) End systolic volume – Afterload – Contractility

Time between beats

2 Heart rate control during exercise by baroreceptors and skeletal muscle afferents. OLEARY, DONAL Medicine & Science in Sports & Exercise. 28(2): , February Increase in heart rate decreases filling time Time between beats

What would happen if you could not increase adrenergic tone to the heart during exercise? Metaprolol=  1 antagonist

J Appl Physiol 106: , 2009 Ο average-trained  endurance trained

Training and the CV system VO 2 = Q  CaO 2 x E = SV x HR x CaO 2 x E

Training Benefits seen after 3x week for 6 weeks 70% of max heart rate > 30 min/bout Maintenance 2x week but maintain intensity

College StudentsWorld Class Athletes ControlBedrestTrained VO 2 max (L/min) Max Ventilation (L/min) Arterial O 2 (mlO 2/ 100 ml blood) Art-Ven O 2 (mlO 2/ 100 ml blood) Max. cardiac Output (L/min) Max Heart rate (bpm) Stroke Volume (ml)

Directly measured cardiac pressure–volume curves for athletes and non-athletic controls Note the marked improvement in both static and dynamic compliance in the endurance athletes Levine B D J Physiol 2008;586:25-34

Winder et al JAP 45:370,1978

Heart Adaptations to Training Endurance trained Sedentary Resistance trained

1995 Marathon Training Data (females)

Adaptations to Training Resting bradycardia Increased stroke volume Increased cardiac size and compliance Increased blood volume Lower vascular resistance at any work load Improved flow distribution Improved oxygen extraction Improved heat tolerance

Training Heart Rates Low range – Between 60-70% of maximal heart rate – ~50-60% of VO 2 max High range – 90% of max heart rate – 85-90% of VO 2 max

Thermal stress and exercise

Impact of duration of exercise

Rowell LR Ann Rev Physiol 54:75,1976

Rowell LR. Ann Rev Physiol 54:75,1976