Wk 4 - The ANS, assessing autonomic balance and CV system overview Flashcards
Describe ANS structure and function:
-Key role during homeostasis
-Para and sympathetic nervous system is important for fight or flight
-When we exercise, parasympathetic decreases and sympathetic system increases
-Sympathetic nervous system travels down the spine
-Some people can control the systems through biofeedback
-SNS have ganglion chains down the spinal cord and they exist outside of the CNS.
What are the neurotransmitters of the ANS:
-Parasympathetic fibres release Ach and is called polyergic
-Synapse point in PNS, the preganglionic nerve is much longer and closer to the receptor site, whereas the synapse point in the sympathetic preganglionic fibre is much shorter.
Describe nervous system regulation of HR and ANS control of exercise HR:
-Nervous system regulation of HR -> AP leave the SA node.
-ANS control of exercise HR -> Low resting HR due to parasympathetic tone. Increase in HR at onset of exercise: Initial increase due to parasympathetic withdrawal (up to ~100 beats per min). Later increase due to increased SNS outflow, in order to increase HR to maximal outputs. Vagus nerve gives us our lowered HR.
How is stroke volume regulated and what is EDV?
- End-diastolic volume (EDV) -> Volume of blood in the ventricles at the end of diastole (‘preload’)
- Average aortic blood pressure -> Pressure the heart must pump against to eject blood ‘afterload’. Mean arterial pressure. Increase in cardiac afterload results in a decreased SV during resting conditions where the influences on cardiac contractility (sympathetic stimulation and Frank-Starling law) are not at play
- Strength of the ventricular contraction (contractility) -> Enhanced by: Circulating epinephrine and norepinephrine. Direct sympathetic stimulation of the heart
-End-diastolic volume (EDV) -> Frank-Starline mechanism -> Greater EDV results in a more forceful contraction – due to stretch of ventricles. It is dependent on the rate of venous return.
Name some factors involved in regulation of venous return:
- Venoconstriction – via SNS
- Skeletal muscle pump – Rhythmic skeletal muscle contractions force blood in the extremities towards the heart. One-way valves in veins prevent backflow of blood
- Respiratory pump – Changes in thoracic pressure pull blood towards the heart
What is cardiac output and what are the factors that regulate Q?
-Cardiac output -> The amount of blood pumped by the heart each minute. Q (l/min) = HR(beats/ min) x SV (ml/ beat). Increased delivery to skeletal muscle during exercise is through increased cardiac output during exercise. SV is much greater at a trained male than an untrained male (100 v 60).
-Factors that regulate Q -> Mean arterial pressure and End-diastolic volume and Contraction strength (of the ventricles)
Why are maximal cardiac output and VO2 max tightly coupled?
-> There is a strong positive correlation between both variables – at sedentary and endurance athletes. There is a ratio of 6:1 (Q max: VO2 max)
Describe arterial blood pressures (systolic, diastolic, pulse pressure and MAP)
- Systolic pressure -> pressure genertaed duriong ventricular contraction
- Diastolic pressure -> pressure in the arteries during cardiac relaxation
- Pulse pressure -> difference between systolic and diastolic
- Mean arterial pressure (MAP) -> average pressire in the arteries
+High BP risk factor for LV hypertrophy, atherosclerosis and heart attack, kidney damage and stroke
What are the factors that influence arterial blood pressure?
- Determininants of mean arterial pressure -> Cardiac outpur ( = stroke volume x heart rate) and Total vascular resistance (sum of resistance to blood flow)
-MAP = cardiac output x total vascular resistance - Short-term regulation -> Sympathetic nervous system. Baroreceptors in aorta and cartoid arteries. Increase in BP = decreased SNS activity. Decrease in BP = increased SNS activity.
- Long-term regulation -> Kidneys (via control of blood volume)
What is double product (rate-pressure product)?
-> Index of myocardial. Double product = HR x systolic BP. The double product is a dimensionless term that reflects the relative changes in the workload.
Describe changes in cardiovascular variables during exercise:
-> Increased metabolic need for oxygen, blood flow delivery to exercising skeletal muscle is increased via 2 mechanisms:
1. Increased cardiac output
2. A redistribution of blood flow from inactive organs to the working skeletal muscle
-Cardiac output increases during exercise is directly proportional to the metabolic rate required to perform the exercise.
-Stroke volume responses to exercise in elite athletes -> Some suggestion that SV does not plateau in elite runners (during treadmill exercise). There is not a plateau but an increase.
-Body position and SV -> When lying down, the SV increases as more blood is able to get to the heart. If we’re exercising in water, there is hydrostatic pressure which increases the SV.
What are circulatory responses to exercise?
-> Changes in heart rate and blood pressure. Depends on :
* Type, intensity and duration of exercise
* Environmental conditions
* Emotional influence pre-exercise and during submaximal exercise – due to increases in SNS activity
Describe changing cardiovascular variables in exercise in a transition from rest to exercise and exercise to recovery:
- At the onset of exercise -> Rapid increase in HR, SV and cardiac output. Plateau in submaximal (below lactate threshold) exercise
- During recovery -> Decrease in HR, SV and cardiac output towards resting levels. Depends on: duration and intensity of exercise and training state of subject
Describe changing cardiovascular variables in incremental exercise:
- Heart rate and cardiac output -> Increase linearly with increasing work rate. Reaches plateau at 100% VO2 max
- Blood pressure -> Mean arterial pressure increases linearly. Systolic BP increases and diastolic BP remains fairly constant
Describe changing cardiovascular variables in intermittent exercise:
-> Heavy-intensity intermittent exercise – Near maximal HR values are possible. Recovery of heart rate and blood pressure between bouts depend on: fitness level, temperature and humidity and duration and intensity of exercise.
Describe changing cardiovascular variables in prolonged exercise at a constant work rate:
-> Cardiac output is maintained – gradual decrease in stroke volume and due to dehydration and reduced plasma volume. Gradual increase in heart rate during prolonged exercise (particularly in heat) – cardiovascular drift.
What is reliability and validity with wearable devices?
-> Trade-off between feasibility and accuracy (cost/ practicality). Realistically there will always be some measurement error. Important to compare new, inexpensive or more practical methods with criterion methods
What are the criterion measures of energy expenditure? (4 points)
- Direct calorimetry -> Measures heat exchange between the human body and the environment
- Indirect calorimetry -> Measures the type and rate of substrate utilization, whereby energy metabolism is estimated from respiratory gas exchange measurements
- Doubly labelled water -> Measures total carbon dioxide production by observing the differential rates of elimination of a bolus dose of the stable isotope racers (hydrogen (H2) and oxygen (O18)).
- Cost, complexity and practicality -> Issues limit the use of criterion methods to measure free-living TDEE in this population
