CTB5: Assessing performance of the cardiopulmonary system Flashcards
What specialised cells produce the hearts’ rhythm?
sinoatrial node
How does the heart contract?
These cells spontaneously depolarise which triggers a wave of excitation through the heart’s conduction system, which resulted in coordinated contraction of the atria and, after a short delay, the ventricles.
How does the parasympathetic nervous system affect the heart
via the vagus nerve it slows down the heart rate to about 72 bpm
At rest, what is breathing controlled by?
By the phrenic nerves which send impulses from the medulla to the diaphragm to contract
Most of the breaths we take are triggered from where?
Centrally, in the respiratory centres of the medulla oblongata
What afferent (sensory) signal is most significant in affecting respiratory rhythm?
Principal driver is arterial carbon dioxide concentration (inferred via proton concentration in the cerebrospinal fluid)
What chemoreceptors are highly sensitive and tightly regulate other inputs including the higher centres (e.g. motor control mentioned above) and peripheral sensory neurons (chemosensitive and mechanosensitive)?
proton concentration in the cerebrospinal fluid chemoreceptors
Activation of inspiratory muscles has what effect on the vagus nerve? (PNS)
inhibitory action
Since activation of the inspiratory muscles has an inhibitory effect on the PNS, what happens to the interbeat interval?
The interbeat interval is often shorter while breathing in, compared with breathing out
Define physical activity
any biomechanical movement produced by the musculoskeletal system that requires metabolic energy
Define exercise
Sub-set of physical activity and can be defined as any ‘purposeful increase in energy expenditure’. This can then be further subclassified into aerobic and anaerobic exercise
How can anaerobic exercise be classified
High intensity and short duration. This includes activities and sports that take a matter of seconds to do and rely on the energy stored within the muscle ready to be used at a moments notice
How can aerobic exercise be classified?
Low intensity and long duration. It includes activities that typically last several minutes to several hours or sometimes days. It relies on a steady supply of oxygen and nutrients to the working muscle that can meet local demand.
What is the immediate increase in ventilation is mediated by what?
neurogenic afferents from active skeletal muscle
When are neurogenic afferent nerves (attached to mechanoreceptors) activated?
When the muscles shorten and lengthen
What is ventilation in plateau phase fine-tuned by?
Peripheral chemoreceptors
What is this plateau is also referred to as? why?
‘steady state’ because the supply and demand are (just about) perfectly balanced
Once exercise stops, what happens to the volume expired (Ve)?
There is an immediate sharp decrease in volume expired
What does repaying oxygen debt do to the volume expired over time curve?
Causes steady decrease of Ve
What is the respiratory rate during light and moderate intensity exercise?
Respiratory rate takes a small increase to 20 breaths/min (from 12-15 breaths per minute), where it stays stable
At moderate-high intensity exercise what becomes inefficient? Why?
To further increase the depth of breathing.
Because getting the lungs really full or really empty takes a considerable amount of energy. Instaed Respiratory rate incraeses slightly to achieve an exponential rise in ventilation
What is biomechanically more efficient to do during moderate to high exercise?
To increase the rate of ventilation (exponential)
What is cardiac volume usually?
70ml
How much can cardiac output increase during exercise in adults?
four-fold
What happens to the blood from the four-fold increase in cardiac output during exercise in adults?
Redistribution of blood flow secondary to the sympathetic nervous system. Specifically, arterioles supplying non-essential organs (e.g. the kidneys, liver, stomach and intestines) constrict, reducing local blood flow, and vessels supplying skeletal muscle dilate, considerably increasing blood flow.
What can the cardiac output of elite endurance athletes be?
35 L/min
What is the equation for cardiac output?
cardiac output = HR x SV
What is arrhythmia?
Abnormal heart rhythm
What is ventricular tachycardia?
very high heart rate (e.g. 280 bpm) it requires rapid intervention or it could be fatal
If the heart is beating too fast, why is this a health problem?
The atria are the first to contract which pushes blood into the ventricles. If the heart is beating too fast, the ventricles contract before they’re full. This has a big impact on stroke volume and results in a reduction in overall cardiac output.
How do you calculate the age-predicted max heart rate?
220 - age
How do you calculate max stroke volume?
Divide 22 L/min maximum cardiac output by 200 to calculate your maximum stroke volume, which is 110 mL
By what percentage does heart rate and stroke volume increase in normal individuals during exercise?
stroke volume: 60% increase
heart rate: 300% increase
What happens to the heart muscle after much training?
Becomes stronger and bigger
What consequence does a stronger and bigger heart have?
The volume of blood pumped out per beat increases:
- maximum cardiac output can be increased as the heart can push more blood out per beat: overall a higher cardiac output can be achieved.
- a stronger heart pushing more blood out each beat needs to beat less often, so resting heart rate decreases
Trained individuals have greater recoil and thus greater force, helping to push more blood out per beat: what does this mean for venous return and left-ventricular end-diastolic volume
Increase in both
venous return (blood returning back to the heart per beat)
left ventricular end-diastolic volume (the amount of blood in the ventricles prior to their contraction)
List the 5 benefits of sustained exercise
1) ventricular remodelling
2) increased vascularisation of aveoli
3) increased vascularisation of myocardium
4) increased oxidation enzyme density
5) no meaningful change to lung volumes
Explain ventricular remodelling
Characterised by a slight thickening of the heart muscle in the ventricles. A thicker muscle is able to contract more forcefully to eject a larger volume of blood at a faster rate than normal. This is can be achieved in two ways: hypertrophy (which is enlargement of the muscle cells) and hyperplasia (which is increased number of muscle cells)
Explain increased vascularisation of avleoli
exercise requires a significant supply of oxygen to ensure that no harmful by-products (such as lactic acid) are produced. This can be achieved by increasing the density of capillaries at the gas exchange surface, to make better use of the ventilated air. Think back to Fick’s Law – this is basically increasing the surface area of the lung
Explain increased vascularisation of myocardium
s mentioned above, the heart muscle needs a plentiful supply of oxygen to keep it healthy, especially during exercise. As such, the density of small blood vessels that penetrate the myocardium from the surface (where the coronary arteries lie) increases
Explain increased vascularisation of myocardium
the myocardium and respiratory muscles are always active, from when you’re a tiny baby to the day you die, and they have to withstand periods of increased activity (i.e. exercise) without getting too fatigued. Exercise training helps to improve the concentration of enzymes that allow oxygen-dependent aerobic energy production to happen
Explain no meaningful change to lung volumes
the existing lung volumes don’t really change with exercise training, these are usually fixed based on your genetics. There is however a small body of evidence to suggest that training in elite swimmers can make small improvements
What are the two main ways to assess the function of the heart in a clinical environment?
1) electrocardiography (ECG)
2) echocardiography
What does ECG measure?
The electrical activity of the heart
What is the electrical activity of the heart that ECGs measure?
The frequency of the beats (the rate) the timing between beats (the rhythm) and the way the signal is propagated through the specialised conduction pathway and the myocardium
What does the P wave show on an ECG?
wave of depolarisation (excitation) passes through the atria from the sino-atrial node, causing them to contract
When does the QRS complex, which is the biggest deflection, happen?
When the wave of excitation moves really fast through the large amount of muscle at the apex (bottom) of the heart causing ventricular systole
What is the T wave?
Repolarisation of the ventricles and happens during diastole
What is Echocardiology?
a method of ultrasound imaging which allows someone to look at different cross sections of the heart
When is echocardiology particularly useful?
For evaluating the heart valves, but can also be used to estimate the volume of blood in the heart before and after contraction
What two variables are measured in spirometry?
Forced vital capacity (FVC) and Forced expiratory volume in 1 second (FEV1)
What ratio is used in diagnosis of obstructive and restrictive lung diseases?
The ratio of FEV1 to FVC
What is the Wright peak flow meter designed to do?
PEF (peak expiratory flow)
Mechanically measure the maximum flow rate during maximum expiration from total lung capacity (TLC). Highest value is used
How can PEF be used to discriminate between COPD and asthma?
COPD would have stable PEF and asthma would have variable PEF
What is a modern version of spirometry?
flow-volume loops
What are the labels of the axis for flow-volume loops
volume (L; x-axis) and flow velocity (L·s-1; y-axis)
The left side of the loop always represents TLC, but the x-axis can either ascend (from 0 at TLC) or descend from TLC if FRC is known
What is the flow loop drawn from?
changes in air flow (inspiration/expiration). Further (upwards or downwards) from the x-axis reflects higher flow rates, and steep lines represent rapid changes in flow rate.
