Exercise Physiology and Cardiac Response

Concentric Contractions

• Shortening contractions increase peripheral vascular resistance
• Resistance increases in correlation with effort intensity and muscle mass utilized

Submaximal Upper Body Exercise

• Requires greater oxygen consumption compared to leg exercise at the same power output
• Lower mechanical efficiency due to recruitment stabilizing muscles
• Higher physiological strain compared to lower body exercise
• Higher heart rate, ventilation, blood pressure, and perceived exertion

Maximal Upper Body Exercise

• VO2 values are typically 20-30% less than lower body maximal exercise
• Lower maximum heart rate and pulmonary ventilation
• Smaller muscle mass activated

Cardiac Output & Total Peripheral Resistance (TPR)

• Example: SBP=210, DBP= 90, CO= 20 L/min
• TPR = DBP + [⅓ (SBP-DBP)]/ CO
• TPR = 6.5

Hypotensive Recovery Response

• Post-exercise blood pressure drops below pre-exercise levels for up to 12 hours in healthy and hypertensive individuals
• Blood pools in skeletal muscles during recovery

Exaggerated Blood Pressure Response Clinical Significance

• Increased risk of hypertension development
• Increased risk of cardiovascular mortality and events
• Cardiac hypertrophy

Heart's Blood Supply

• Coronary circulation provides 5% of the heart's blood supply, approximately 250ml
• Right and left coronary arteries originate from the aorta, behind the aortic valve
• Arteries branch into a dense capillary network, supplying the myocardium
• Coronary sinus and anterior cardiac veins collect blood and drain directly into the right atrium

Myocardial Oxygen Utilization

• At rest, the myocardium extracts 70-80% of oxygen from coronary blood flow
• During vigorous exercise, coronary blood flow increases 4-6 times resting levels
• Impaired coronary blood supply can lead to chest pain (angina pectoris) and myocardial infarction

Rate Pressure Product (RPP)

• Noninvasive estimate of myocardial workload (oxygen uptake)
• RPP = SBP x HR
• RPP has a linear relationship with exercise intensity

Cardiovascular Regulation and Integration

• Cardiac muscle naturally maintains its rhythm
• Intrinsic heart rate: 100 bpm
• Extrinsic control can adjust heart rate from 40 bpm to 220 bpm

Autorhythmic/Automaticity

• The heart can beat without external stimuli
• Signal originates in the SA node and propagates outward

Intrinsic Regulation of Heart Rate

• SA node initiates the depolarization process
• Signal travels from SA node to AV node, then to the Purkinje fibers and bundle of HIS
• AV node delays the electrical signal, allowing the atria to contract before ventricular filling

Concentric Contractions and Peripheral Vasculature

• Concentric contractions, which shorten muscle fibers, compress peripheral blood vessels, ultimately increasing resistance in the circulatory system
• The magnitude of this resistance increase is linked to the intensity of the exercise and the amount of muscle mass used.

Submaximal Upper Body Exercise

• Upper body exercise (UBE) demands a greater oxygen (O2) consumption than lower body exercise (LBE) at any given submaximal power output.
• This increased demand is due to:
  • Lower mechanical efficiency in UBE
  • Recruitment of stabilizing muscles in UBE
  • Greater physiological strain in UBE
  • Higher heart rate (HR), ventilation (Ve), blood pressure (BP) and Rating of Perceived Exertion (RPE) during UBE

Maximal Upper Body Exercise

• During maximal exercise, VO2 values are typically 20-30% lower in UBE compared to LBE.
• Lower maximal HR and pulmonary ventilation are also observed in UBE
• This reduced capacity is attributed to the smaller muscle mass activated during upper body activity.

Cardiac Output and Total Peripheral Resistance (TPR)

• An example calculation for TPR:
  • Systolic BP (SBP) = 210 mmHg
  • Diastolic BP (DBP) = 90 mmHg
  • Cardiac Output (CO) = 20 L/min
  • TPR = DBP + [⅓ (SBP-DBP)]/CO
  • TPR = 6.5
• This demonstrates the relationship between different cardiovascular parameters and TPR.

Hypotensive Recovery Response

• After sustained light to moderate exercise, a temporary decrease in SBP below pre-exercise levels occurs for up to 12 hours in both normal and hypertensive individuals.
• This is known as hypotensive recovery response.
• The mechanism behind this response is the pooling of blood in the skeletal muscle vascular beds during recovery.

Clinical Significance of Exaggerated Blood Pressure Response

• An exaggerated BP response to exercise could indicate future development of hypertension.
• It is associated with an increased risk of cardiovascular mortality and events.
• Additionally, it may be a sign of cardiac hypertrophy (an increase in heart muscle size).

Heart's Blood Supply

• The heart chambers themselves do not directly take up nutrients from the blood they contain.
• Coronary circulation, which accounts for 5% (250 ml) of the total cardiac output, provides oxygenated blood to the heart muscle.
• The right and left coronary arteries originate from the aorta, behind the aortic valve.
• These arteries branch into a dense network of capillaries that supply the myocardium.
• The coronary sinus and anterior cardiac veins collect deoxygenated blood, draining directly into the right atrium.

Myocardial Oxygen Utilization

• At rest, the myocardium extracts 70-80% of the oxygen from the blood flowing through the coronary vessels.
• Other tissues typically use only 25% of the oxygen.
• During vigorous exercise, coronary blood flow increases 4-6 times above resting levels.

Impaired Coronary Blood Supply

• The coronary muscle is purely aerobic.
• Interruption of blood flow results in chest pain known as angina pectoris.
• Exercise increases energy demands, making it a useful tool for diagnosing myocardial blood flow (ischemia) through stress tests.
• A blood clot in a coronary vessel can lead to myocardial infarction, causing varying degrees of damage to the heart muscle.
• Key terms:
  • Ischemia: restricted blood supply to tissues.
  • Hypoxia: a region of the body deprived of adequate oxygen supply.
  • Infarction: tissue death due to a local lack of oxygen.

Rate Pressure Product (RPP)

• RPP provides a non-invasive estimate of myocardial workload (myocardial oxygen uptake).
• RPP = SBP x HR
• RPP has a linear relationship with exercise intensity.
• Chronic exposure to higher myocardial workload can lead to cardiac hypertrophy.

Cardiovascular Regulation and Integration

• Cardiac muscle possesses the ability to maintain its own rhythm (heart rate).
• The intrinsic heart rate, without external stimuli, is approximately 100 BPM.
• Extrinsic control of the heart, through neurohumoral factors, can adjust heart rate from 40 BPM at rest to 220 BPM at peak exercise.

Autorhythmic/Automaticity

• The heart can beat spontaneously, without the need for external commands.
• It does not rely on a nerve to initiate contraction.

Intrinsic Regulation of Heart Rate

• The process begins with a change in membrane potential, shifting from negative to positive, and then initiating depolarization.
• This depolarization originates at the sinoatrial (SA) node and propagates outward.
• The signal travels from the SA node to the atrioventricular (AV) node, then to the Purkinje fibers, and finally to the bundle of HIS.
• As the signal reaches the bottom of the ventricle, it moves upwards along the ventricular walls.
• TheAV node introduces a delay of approximately 0.10 seconds to allow atrial contraction before ventricular filling.