Acute Responses to Exercise

Cardiopulmonary Aspects

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Responses to Exercise

Exercise places demands on the physiological systems in the human body resulting in multiple responses. These answers are based on[1]:

• Type or mode of exercise
• Intensity of exercise
• Duration of exercise
• Frequency of exercise
• Environmental conditions[2]
• Emotional influences[3]

Cardiovascular System

• Components[4]:
  • Circulatory system
  • Pulmonary system
• Function[4]:
  • Transfer and exchange of respiratory gases (oxygen and carbon dioxide) .
  • Transportation and exchange of nutrients and wastes
  • Hormone and chemical messengers
  • Thermoregulation of body temperature .
  • Regulation of fluid balance
  • Regulation of blood pressure
  • Maintenance of pH balance
  • Prevention of blood loss by hemostatic techniques
  • Prevention of infection by white blood cells and lymphoid tissue

Read more: Cardiovascular System

Heart Rate

• Increases linearly with workload and oxygen consumption (VO2) during dynamic exercise
• Heart rate (HR) response may be influenced by the following factors [5]:
  • age
  • body position
  • fitness
  • type of activity
  • medication
  • environmental conditions
  • blood volume

Maximal Heart Rate

• Maximum heart rate (HRmax) is achieved after exerting yourself to the point of mental fatigue. [6] It is the highest heart rate a person can achieve when they are exerting themselves to the point of exhaustion.
• HRmax is NOT trainable
• HRmax remains constant daily and decreases slightly each year
• HRmax can be estimated:
  • HRmax = 220 – age (this is the most common and widely used formula)
  • HRmax = 208 – (o.7 x age in years) – This is a more precise formula adjusted for people over 40
  • HRmax = 211 – (o.64 x age) – a more precise formula adjusted for the general active population
• A female’s maximum heart rate is approximately 5 – 10 beats per minute
• HRmax decreases with age through adrenergic receptor desensitization
• Assessment of HRmax:
  • Laboratory setting
    • Graded exercise test
  • Field test
    • Running and cycling protocols
• Used in performance prediction
• Health status

Steady-State Heart Rate

• Optimal heart rate to meet cycling demands at a given submaximal workload/intensity
• The lower the steady state heart rate for a given workload/intensity
  • Efficiency
    • Enhanced contractility
    • Increased stroke volume
• Functional capacity prediction based on steady-state heart rate

Maximal Oxygen Consumption (VO2 max)

• Gold standard assessment
• Product of maximal cardiac output (Q) and arteriovenous difference (a – vO2)
• The body’s maximum ability to use oxygen to produce energy
• Differences in maximal oxygen uptake in healthy people
  • Due to differences in maximum stroke volume (SVmax)
  • Some due to (a – vO2)max

VO2max = HRmax x SVmax x (a-vO2)max

Stroke Volume

• End-diastolic volume (EDV) depends on heart rate filling pressure and ventricular compliance
• End systolic volume (ESC) depends on afterload and contraction force
• Resting stroke volume (SV): 60 – 100 mL/beat
• Maximal stroke volume: 100 – 120ml/beat
• Maximize at about 50% of your best effort

SV = EDV – ESV

Regulation of Stroke Volume

• End-diastolic volume (EDV)
  • End-diastolic ventricular blood volume (preload)
• Average aortic blood pressure
  • The pressure with which the heart must pump to expel blood (afterload)
  • Increased afterload = decreased stroke volume (usually in sick people rather than in healthy exercisers)
• Strength of the ventricular contraction
  • “Contractility”

End Diastolic Volume

• Frank Starling mechanism
  • Greater preload results in ventricular stretch and more forceful contraction
• Affected by:
  • Vasoconstriction
  • Skeletal muscle pump
  • Respiratory pump

Cardiac Output

• Cardiac output(Q) = HR X SV
• Rest: 5 L/min
• Maximal: 20 L/min or more
• Up to about 50% of best effort HR and SV contribute to Q increase

Ejection Fraction

• SV/EDV X 100
• Normal 65% (55% – 70%)

Heart rate stroke volume and cardiac output – rest and activity

• Standing increases venous blood flow to the most dependent parts of the body
• This redistribution of blood results in less blood in the chest cavity returning to the heart. Through the Frank Starling mechanism, this results in a reduction in stroke volume (30% to 40% reduction)
• This rises again when returning to the supine position in response to increased venous return

Heart Rate Stroke Volume and Cardiac Output – Resting and Maximum (Peak)

ADD TABLE IF AVAILABLE

Blood Pressure

• Systolic blood pressure (SBP)
  • Linear increase, 8-12 mmHG/MET
• Diastolic blood pressure (DBP)
  • slight decrease or increase or no change

Arteriovenous Oxygen Difference (a-vO2)

• the amount of oxygen extracted from the blood as it flows through the body
• Calculated as the difference between arterial and venous oxygen levels
• Increases with movement speed as more oxygen is drawn from the blood
  • Rest (20ml O2/100ml – 15ml O2/100ml) = 5ml O2/100ml
  • Maximum exercise volume: 20 ml O2/100ml – 5 mlO2 ml/100ml = 15 ml O2/100 ml
  • Utilisation coefficient: 25 – 75%

Pulmonary Ventilation (Ve)

• Ve = RR x TV
• TV = volume of air inhaled in one breath
• Rest: 6L/min
• Maximal: 15 – 25 fold increase
• Mild to moderate exercise
  • Ve increases mainly due to increased TV
• Intense exercise
  • RR is important…proportional to exercise intensity

Blood Flow

• Rest: 15 – 25% of Q to skeletal muscle
• Exercise: 85 -90% of Q to skeletal muscle
• 5-fold increase in flow to the heart
• Decreased cutaneous renal hepatic and splanchnic blood flow during exercise
• Only minor changes in blood flow to the brain

Transition from rest to exercise and exercise to recovery

• Intensity-dependent adaptations to HR SV Q SBP RR Ve and VO2
• Plateaus during submaximal (below lactate threshold) exercise
• Recovery depends on:
  • Duration and intensity of exercise
  • Training state of the individual

Prolonged Exercise

• Cardiac output is maintained
  • Gradual decrease in stroke volume
  • Gradual increase in heart rate
• Cardiovascular drift
  • Due to dehydration and increased skin blood flow (increased body temperature) .
  • Due to decreased venous return

Acute Physiologic Exercise Responses

• Exercise Pressor Response
  • Invoked by muscle contraction
    • Nerve receptors are stimulated by nerve changes or metabolic byproducts – afferent signal transmission to the CNS
  • Sympathetic nervous system phenomena
    • Generalized vasoconstriction in nonfunctioning skeletal muscle
    • Increased myocardial contractility
    • Increased HR
    • Increased SBP
    • Increased and redistribution of Q
    • Response = exercise intensity
• One of the major challenges to exercise-induced homeostasis is the increased tissue oxygen demand
• During strenuous exercise, oxygen demand can increase 15 to 25 times
• Two major adjustments of blood flow are:
  • Increased cardiac output
  • Redistribution of blood flow
• Depends on:
  • Type, intensity and duration of exercise
  • Environmental conditions
  • Emotional influence

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