E

exam 4

CHAPTER 9: Cardiorespiratory Responses to Acute Exercise

Overview

  • Key Areas Discussed:

    • Cardiovascular responses to acute exercise

    • Respiratory responses to acute exercise

    • Recovery from acute exercise

Cardiovascular Responses to Acute Exercise

  • Overall Adjustments:

    • Increases blood flow to working muscles

    • Involves altered heart function and peripheral circulatory adaptations

Key Factors in Cardiovascular Responses

  • Heart Rate

  • Stroke Volume

  • Cardiac Output

  • Blood Pressure

  • Blood Flow

Cardiovascular Responses: Resting Heart Rate (RHR)

  • Normal Ranges:

    • Untrained individuals: 60 to 80 beats/min

    • Trained individuals: as low as 30 to 40 beats/min

  • Influencing Factors:

    • Neural tone

    • Temperature

    • Altitude

  • Anticipatory Response:

    • Heart Rate (HR) increases above RHR just before the start of exercise

    • Vagal tone decreases

    • Norepinephrine and epinephrine levels increase

Cardiovascular Responses: Heart Rate During Exercise

Heart Rate Variability

  • Definition: Measure of HR rhythmic fluctuation due to continuous changes in sympathetic and parasympathetic balance

  • Influences on HRV:

    • Body core temperature

    • Sympathetic nerve activity

    • Respiratory rate

Heart Rate Characteristics

  • Maximal HR:

    • Highest HR in an all-out effort to volitional fatigue

    • Highly reproducible with slight decline with age

    • Estimation Formula:

    • $HR_{max} = 220 - ext{age in years}$

    • For older adults, alternative estimates include:

    • $HR_{max} = 208 - (0.7 imes ext{age in years})$

    • $HR_{max} = 211 - (0.64 imes ext{age in years})$

  • Steady-state Heart Rate:

    • Point where HR plateaus to meet circulatory demands at a given submaximal intensity

    • Takes 2 to 3 minutes to adjust to a new intensity

Cardiovascular Responses: Stroke Volume (SV)

  • Importance: Major determinant of endurance capacity

  • Determinants of SV:

    • Volume of venous return to the heart

    • Ventricular distensibility (ability of the ventricles to stretch)

    • Ventricular contractility

    • Aortic or pulmonary artery pressure

  • Key Concepts:

    • Preload: End-diastolic ventricular stretch

    • Afterload: Resistance the ventricle must overcome to eject blood

  • SV Response to Intensity:

    • Increases from rest to 40%-60% V_{O2max}, plateau beyond this intensity

    • Maximally, exercise SV is approximately double that at rest

Stroke Volume Changes During Exercise

  • Influencing Factors:

    • Increase in venous return leads to increased preload

    • Muscle and respiratory pumps enhance venous return

    • HR increase can reduce filling time, potentially causing a slight decrease in EDV and SV

    • Increased contractility at higher intensities leads to increased SV

    • Decreased afterload due to vasodilation supports increased SV

Cardiovascular Responses: Cardiac Output (Q)

  • Formula:

    • Q = HR imes SV

  • Changes with Intensity:

    • Increases with intensity until it reaches a plateau near V_{O2max}

  • Normal Values:

    • Resting Q ~ 5 L/min

    • Untrained Qmax ~ 20 L/min

    • Trained Qmax ~ 40 L/min

Fick Principle

  • Definition:

    • Calculation of tissue O2 consumption depending on blood flow and O2 extraction

  • Formula:

    • V{O2} = Q imes (a-v)O{2} ext{ difference}

    • V{O2} = HR imes SV imes (a-v)O{2} ext{ difference}

Cardiovascular Responses: Blood Pressure

  • Overview:

    • Increase in mean arterial pressure (MAP) during endurance exercise

  • Characteristics:

    • Systolic BP increases proportionally with exercise intensity

    • Diastolic BP may decrease or slightly increase at maximum exercise

    • Key Relationships:

    • MAP = Q imes ext{TPR}

    • Cardiac output increases while total peripheral resistance decreases slightly due to muscle vasodilation

Blood Flow Redistribution

  • Mechanisms:

    • Cardiac output increases blood flow distributed toward exercising muscles

    • Blood is redirected away from less active regions

  • Sympathetic Vasoconstriction:

    • Occurs in splanchnic (liver, stomach, pancreas, GI) and renal circulation

  • Local Vasodilation:

    • Triggered to allow more blood flow to exercising muscle

  • Heat Response:

    • As body temperature rises, additional vasodilation occurs in skin to facilitate heat loss

Cardiovascular Responses: Hemoconcentration

  • Definition:

    • Reduction in plasma volume leading to an increase in the concentration of red blood cells (hematocrit)

  • Net Effects:

    • Increased red blood cell concentration

  • Increased hemoglobin concentration

  • Enhanced O2-carrying capacity

Cardiovascular Responses: Central Regulation

  • Key Stimulus for Rapid Changes:

    • Increases in HR, Q, and blood pressure during exercise precede metabolite buildup

    • HR begins to increase within 1 second of exercise onset

  • Mechanism:

    • Driven by "central command," involving higher brain centers and coactivation of motor and cardiovascular centers

Respiratory Responses: Ventilation During Exercise

Initial Changes

  • Anticipatory Response:

    • Immediate increase in ventilation before muscle contractions initiate

  • Second Phase Increase:

    • Gradual increase driven by chemical changes in arterial blood (increased CO2 and H+ detected by chemoreceptors)

Tidal Volume and Breathing Rate

  • Ventilation Proportional to Metabolic Demand:

    • At low intensity: only tidal volume increases

    • At high intensity: both rate and tidal volume increase

Recovery Phase

  • Delayed Recovery:

    • Recovery of ventilation takes several minutes and is affected by blood pH, PCO2, and temperature

Respiratory Responses: Breathing Irregularities

Common Irregularities

  • Exercise-induced Asthma:

    • Characterized by lower airway obstruction, coughing, wheezing, and dyspnea

  • Dyspnea:

    • Common with poor aerobic fitness, often associated with inability to cope with high blood PCO2 and H+

  • Hyperventilation:

    • May occur due to anticipation or anxiety, affecting blood PCO2 and subsequent drive to breathe

Valsalva Maneuver

  • Mechanism:

    • Involves closing the glottis, resulting in increased intra-abdominal and intrathoracic pressures, causing potential collapse of great veins leading to decreased venous return

Recovery From Acute Exercise: Cardiovascular Variables

  • Postexercise Hypotension (Aerobic and Resistance):

    • Driven by peripheral vasodilation and decreased cardiac output respectively, with lasting effects for several hours

Conclusions

  • Integration of Responses:

    • Cardiovascular and respiratory responses are complex, fast, and finely tuned to maintain blood pressure and blood flow with respect to metabolic demands during exercise.