Week 4 Flashcards
(32 cards)
Structure & Function of the Autonomic Nervous System (ANS)?
- Two branches:
- Sympathetic Nervous System (SNS)– “Fight or flight”
- Parasympathetic Nervous System (PNS)– “Rest and digest”
- Controls involuntary functions such as heart rate, blood pressure, digestion.
- Regulates cardiovascular variables including:
- Heart rate (HR)
- Stroke volume (SV)
- Cardiac output (Q)
- Arterial blood pressure (BP)
- Neurotransmitters of ANS
- SNS:Releases norepinephrine(NE) → Increases HR & contractility
- PNS:Releases acetylcholine(ACh) → Decreases HR
- ACh = Cholinergic, NE = adrenergic
Nervous System Regulation of Heart Rate during exercise?
Low resting HR is primarily due to parasympathetic (PNS) tone.
HR increase at exercise onset:
- Initial rise (~up to 100bpm): Caused by withdrawal of PNS activity.
- Further increase: Due to increased sympathetic (SNS) activation.
Factors Affecting SV?
- End-Diastolic Volume (EDV) “Preload”
- More blood in ventricles = stronger contraction.
- Governed byFrank-Starling Mechanism(greater stretch = stronger contraction).
- Depends on venous return.
- Average Aortic Blood Pressure “Afterload”
- Pressure the heart must overcome to eject blood.
- Higher afterload = Lower SV.
- Mean arterial pressure (MAP) contributes.
- Strength of Ventricular Contraction (Contractility)
- Increased by:
- SNS stimulation (epinephrine & norepinephrine).
- Direct sympathetic activation of the heart.
- Increased by:
Factors Affecting Venous Return (Key for SV)?
- Venoconstriction (SNS-driven)
- Skeletal muscle pump(muscle contractions push blood back to the heart with help of one way valves).
- Respiratory pump(breathing mechanics and changes in thoracic pressure assist venous return pulling blood to heart).
Cardiac Output (Q)? Regulation? Influencing factors?
Cardiac Output (Q) = Amount of blood pumped by the heart per minute
Equation:
Q = Heart Rate (HR) × Stroke Volume (SV)
Regulation of Cardiac Output:
- Increased by higher HR and SV
- Higher in trained athletes
- Strong relationship with VO₂max (~6:1 ratio between Qmax and VO₂max)
Key Factors Influencing Q:
- Preload = End-Diastolic Volume (EDV)
- Afterload = Mean Arterial Pressure (MAP)
- Contractility = Strength of ventricular contraction
- Governed by Frank-Starling Law (greater EDV → stronger contraction)
Arterial Blood Pressure (BP)?
- Systolic BP (SBP):Pressure during ventricular contraction.
- Diastolic BP (DBP):Pressure during relaxation.
- Pulse pressure: Difference between systolic and diastolic
- Mean Arterial Pressure (MAP):MAP=DBP+0.33(SBP−DBP)
Factors Influencing BP?
- Cardiac output (Q)
- Total vascular resistance (TVR)
MAP=Q×TVR
Short-term regulation.
* Sympathetic nervous system.
* Baroreceptors in aorta and carotid arteries.
*Increase in BP = decreased SNS activity.
*Decrease in BP = increased SNS activity.
Long-term regulation.
*Kidneys (Via control of blood volume).
Mean Arterial Pressure equation?
Cardiac output x Total vascular resistance
Regulation of BP?
- Short-term:
- Controlled bybaroreceptorsin aorta & carotid arteries.
- ↑ BP→↓ SNS activity
- ↓ BP→↑ SNS activity
- Long-term:
- Kidneysregulate blood volume.
Cardiovascular Responses to Exercise?
- Increased metabolic demand → Adjustments in Q & blood flow.
- Mechanisms:
- Increased cardiac output (Q)
- Redistribution of blood flow to active muscles
Exercise & Stroke Volume (SV)? Body position effects?
In most people, SV plateaus at ~40–60% of VO₂max.
Elite endurance athletes: SV may not plateau, likely due to greater venous return and higher end-diastolic volume (EDV).
Body position affects SV:
- Supine (lying down) → Higher SV (better venous return).
- Upright (standing/exercising) → Lower SV (gravity reduces venous return).
What influences circulatory responses during exercise??
Changes in heart rate and blood pressure?
Type of exercise (e.g., resistance vs. endurance)
Intensity and duration of activity
Environmental conditions:
- Hot/humid → ↑ HR, ↑ blood flow to skin
- Cool → more stable responses
Emotional state:
- Anticipation or stress can activate the sympathetic nervous system (SNS), increasing HR before exercise begins
Responses ( HR, SV, Q, BP) to Different Exercise Types/Phases??
Rest to Exercise (Onset):
- HR, SV, Q: Rapid increase
- BP: Slight increase
Recovery (Post-Exercise):
- HR, SV, Q, BP: Gradual decrease
Incremental Exercise (e.g., graded test):
- HR & Q: Linear increase
- SV: Plateaus at ~50–60% VO₂max
- SBP: Increases
- DBP: Remains constant
Intermittent Exercise (e.g., intervals):
- HR & Q: Fluctuate
- SV: Recovers during rest intervals
- BP: May vary depending on temperature
Prolonged Steady-State Exercise:
- HR: Gradual upward drift
- SV: Gradual decline
- Q: Maintained
- BP: May decline (cardiovascular drift risk)
Transition from Rest to Exercise and
Exercise to Recovery
At the onset of exercise:
• Rapid ↑ in HR, SV, cardiac output.
• Plateau in submaximal (below lactate
threshold) exercise.
During recovery.
• ↓ in HR, SV, and cardiac output
toward resting levels.
• Depends on:
• Duration and intensity of
exercise.
• Training state of subject
Rate pressure product?
Aka as Double product = HR x Systolic BP
Criterion Methods for Measuring Energy Expenditure? Limitations?
Direct Calorimetry:
Measures heat exchange between the body and the environment to estimate energy expenditure.
Indirect Calorimetry:
Estimates energy metabolism by measuring respiratory gas exchange, reflecting the type and rate of substrate utilisation.
Doubly Labelled Water (DLW):
Assesses total CO₂ production using the differential elimination rates of stable isotope tracers:
- Hydrogen (²H)
- Oxygen (¹⁸O)
Limitations:
These criterion methods are limited in free-living populations due to high cost, complexity, and practical constraints
ANS – structure and function?
The ANS plays a key role in maintaining homeostasis, both at rest and during physiological stress (e.g., exercise, emotional stress, illness).
Homeostasis is regulated through dynamic adjustments in the activity of two branches:
- Sympathetic Nervous System (SNS): Prepares the body for “fight or flight” (↑ HR, ↑ BP, ↑ blood flow to muscles).
- Parasympathetic Nervous System (PNS): Promotes “rest and digest” functions (↓ HR, ↑ digestion, energy conservation).
The balance/change between SNS and PNS activity ensures the body can adapt to internal and external changes efficiently.
Accurate Measurement of Heart Rate (HR) and Heart Rate Variability (HRV)??
Electrocardiogram (ECG):
- Criterion (gold standard) method.
- Measures electrical activity during heart depolarization and repolarization, detectable on the skin.
Photoplethysmography (PPG):
- Reliable and valid alternative.
- Uses a light emitter and photosensor on the skin (usually wrist or finger) to detect changes in light absorption caused by blood flow with each heartbeat
Heart rate variability? Interpretations? Significance? Measurement?
Definition: Beat-to-beat variation in the length of cardiac cycles (R-R intervals(= exact times between each heartbeat on ECG)).
Interpretation:
- Higher HRV indicates greater vagal (parasympathetic) modulation of heart rate.
- Wide HRV variation is considered healthy meaning your body can adapt well to stress, rest, and exercise.
- Low HRV predicts cardiovascular morbidity and mortality, especially in patients with existing heart disease.
Significance:
- This is significant as it is a good non-invasive measure of sympathovagal balance (interaction between sympathetic and parasympathetic nervous systems).
Measurement: SDNN (Standard Deviation of Normal-to-Normal Intervals):
- A common statistical measure used in HRV analysis which looks at how much the R-R intervals vary over a period of time
- SDNN = standard deviation of normal sinus beats; ectopic beats(irregular beats) excluded to avoid skewing of results.
- SDNN is the gold standard for medical risk stratification
- Higher SDNN = more variability = better adaptability.
Application of HRV? Stressors?
- HRV shows strong diurnal variation (changes across the day).
- HRV decreases with age.
- Increased daily physical activity is linked to improved HRV in a dose-dependent way (more activity = better HRV).
- Population-specific normative values have been established to help interpret individual HRV scores.
- By monitoring resting HR and HRV, we can assess how stressors (e.g. training, lifestyle) affect physiology and adjust behaviours to support health and performance.
Types of Stressors Affecting HRV:
- Acute stressors: Short-term effects (minutes to ~48 hours)
→ e.g. hard workout, intercontinental travel, alcohol, caffeine. - Chronic stressors: Long-term or repeated stress
→ e.g. ongoing work/study pressure, illness, infections.
HRV measurement considerations?
Environmental Conditions:
- Temperature-controlled room (21–24°C)
- Quiet and free of distractions
Participant Preparation:
- Avoid alcohol, caffeine, intense exercise, and nicotine for ≥12 hours before testing
- No food or drink for ≥3 hours before testing
- Schedule testing at the same time of day after normal sleep
- Ensure participant is awake and has emptied bladder
- Record relevant medical history and current medications
Purpose:
- Standardising conditions improves accuracy and reliability of Heart Rate Variability (HRV) data.
Testing the integrity of the ANS?
- Activity
Measures normal/resting autonomic function (e.g. heart rate, blood pressure at rest).
- Sensitivity
Assesses how the system responds to stimulation.
Common tests: Valsalva manoeuvre, head-up tilt, lower body negative pressure.
- Reactivity
Evaluates the autonomic response to stress.
Tests include: isometric handgrip, mental stress, cold pressor test.
✅ Reliable testing requires a controlled research environment to ensure accurate autonomic measurements.
The Circulatory integrated System?Roles? Components? Exercise adaptations??
Integrated System:
- Works alongside the pulmonary system → forms the cardiorespiratory or cardiopulmonary system.
Main Purposes:
- Deliver oxygen and nutrients to tissues.
- Remove carbon dioxide and metabolic waste.
- Regulate body temperature.
Exercise Adaptations:
- Increased cardiac output to meet oxygen demand.
- Redistribution of blood flow from inactive areas to working muscles.
Components:
- Heart: Generates pressure to circulate blood.
- Arteries & Arterioles: Transport blood away from the heart.
- Capillaries: Site of gas and nutrient exchange.
- Veins & Venules: Return blood to the heart.
The Structure of Blood Vessels?
Arteries
- Function: Distribution of blood, resistance regulation
- Thick, muscular walls to handle high pressure
Capillaries
- Function: Exchange of gases, nutrients, and waste
- Thin walls for efficient diffusion
Veins
- Function: Capacitance (blood storage and return)
- Contain valves to prevent backflow
Wall Components:
- Smooth Muscle – regulates vessel diameter
- Collagen – provides strength
- Elastin – allows stretch and recoil
- Endothelium – inner lining, controls exchange and vascular tone
