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The Practice & Communication of Science 2015/2016 Mini-projects
Topics in Human Physiology (Monday, Tuesday)
Welcome to the Mini-Projects for the ‘physiology’ sessions in USSKAR-30-20, PaCoS. You will be working in
groups of three, and each group will be allocated an exercise by ‘lottery’. Your exercise will cover six twohour practical slots (though the last assessment one is three hours long) and will give you the opportunity
to get deeply involved in all the stages of scientific investigation, including background reading,
experimental design, development of methodology and its troubleshooting, data collection, data analysis
and communication of the results of your study via a scientific poster. The timetable for the exercise is as
follows...
Week 26 : Introduction, library work and method development
- Class split into groups; introduction to the Mini-Projects
- Exercises allocated by ‘lottery’
- Background reading and consideration of a risk assessment (laboratory work cannot start without this!)
- Development of methodology; we will be available for guidance, feedback, etc. You need to become
familiar with the subject matter of your particular experiment as this will assist greatly in the design and
execution of your experiments, thereby improving your data, your analysis, your interpretation and
conclusions, your poster, and your marks!
Weeks 28, 30 & 32 : Laboratory (experimental) work
- These three sessions should be devoted to practising the experimental methods and gathering lots of
good experimental data! You may wish to spend most or all of the first session to ‘ironing out the bugs’ in
your methodology before collecting data ‘for real’.
Week 34 : Data analysis & team poster preparation
- See the web-based module support for advice on poster preparation. PowerPoint or Publisher should be
used to produce your team’s poster (as for the Glassbeads experiment), and Word for the abstract
- We will be on hand to help with the data analysis; but ensure you bring your data in a spreadsheet!
Week 38 : Poster presentation and assessment
- The first 15 min will be available to arrange the posters/abstracts for display. Then, each team will be
asked to assess some of the posters. Assessed elements include - overall presentation, appearance, clarity
and content; amount of laboratory work completed and reported; quality of results, consistency,
replication and presentation; discussion and analysis, including statistical analysis and interpretation, and
further work; references cited and employed usefully in the presentation. Further details on the
assessment can be found on the support web-site.
Poster guidelines : Posters should be produced using PowerPoint or Publisher, and abstracts with Word.
One of the most important parts of the write-up is the Abstract which should provide a self-contained
précis of the introduction, methods, results, and conclusions (remember, you normally write the main
sections of the poster, and then précis it to produce the Abstract). In ‘real-life’ Abstracts are usually printed
in the Proceedings of the Meeting; they are usually word-limited (let us say up to 300 words, with one
Figure, if used, equalling 150 words). Posters should have a fairly 'dry' scientific style (no cartoons, etc!),
should be easy to read, and be reasonably self-explanatory. You may recall that the Intro and M&M we
provided for the Glassbeads were too long – try to make yours as concise as possible without interrupting
the ‘flow’ of the story. You will display your posters/abstracts during the first part of the final session; you
are likely to be asked questions about your poster during the last part of the session, on an individual basis
(as preparation for the assessment of your Final Year Project!).
The Practice & Communication of Science 2015/2016 Mini-projects
Physiology studies on offer (including the sort of equipment you may wish to use)...
How do the various ECG intervals change with heart rate?
ADI Powerlab/leads/electrodes
Real-time heart-rate meter
Exercise bike
Does the latency of the stretch reflex vary with body size?
ADI PowerLab/Leads/Electrodes/Reflex hammer
Relationship between breath-holding and blood oxygenation
Pulse oximeter
Stopwatch
Relationship between pulse pressure wave velocity and blood pressure when standing and lying down
ADI PowerLab (with ECG electrodes and finger plethysmograph)
Blood pressure recorder
Effect of exercise on blood pressure
Exercise bike
Blood pressure recorder
The Practice & Communication of Science 2015/2016 Mini-projects
How do the various ECG intervals change with heart rate?
Background
Heart rate is defined as the number of cardiac cycles per minute, so an increase in heart rate implies that
each cardiac cycle takes less time. Each cardiac cycle can be broken down into a number of mechanical
activities, the simplest being systole and diastole. Since the mechanical activity of the cardiac cycle is
controlled by electrical events, it follows that systole and diastole have electrical ‘equivalents’ - specifically,
the QT and TQ’ intervals on the ECG (another ECG interval is the PR interval). It might be expected,
therefore, that these ECG intervals would necessarily vary as heart rate changes - since more (or fewer)
cycles containing these intervals need to be fitted into the same amount of time.
R
R'
T
P
Q S
T'
P'
Q' S'
PR
QT
TQ'
Aim
It is the aim of this exercise to define graphically (and perhaps mathematically via ‘lines of best fit’) the
relationships between the various ECG intervals (y-axis) and heart rate (x-axis).
Specific problems you will face in the experimental design and analysis
Range of heart rates
You want to use as wide a range of heart rates as possible. Use some form of exercise to increase subjects’
heart rates (eg exercise bike), and record ECG as the subjects’ heart rates return to normal. You should
then aim to take measurements from the recording in each of the ‘decade ranges’ of heart rate for each
subject (eg 60-70 bpm, 70-80 bpm, etc). Subjects may recover quickly from exercise, so be prepared to
make recordings as soon as possible after the end of exercise.
Safety You must get informed consent from your subjects. Do not use subjects with a history of heart
problems. Do not let their heart rate go above 220 minus their age. Use a heart rate meter to monitor
continuously subjects’ heart rate (or have the ADI software do this for you). If using an exercise bike,
ensure that the ECG leads can’t get caught in the pedals.
Measuring the intervals You must use the ECG Lead pair (I, II, or III) that gives the clearest signal. Measure
the PR, QT and TQ’ intervals and also the RR interval (to calculate the heart rate at that point), and be
consistent in the way you measure (maybe give the job to one person).
Analysis You will need to collect as much data as possible from as many subjects as possible. Some of the
relationships may not be linear, in which case you will need to look at ways of transforming the data in
order to allow linear regression in Minitab (or use curve-fitting techniques in, say, Excel).
Equipment
ADI Powerlab/leads/electrodes
Real-time heart-rate meter
Exercise bike
The Practice & Communication of Science 2015/2016 Mini-projects
Does the latency of the stretch reflex vary with body size?
Background
The stretch reflex is a ubiquitous and classic monosynaptic reflex pathway. Muscle stretch causes
activation of muscle spindle 1-a afferents within the muscle; these axons synapse directly onto the alphamotoneurones in the spinal cord which control the main force-producing (extrafusal) muscle cells of the
stretched muscle; stimulation of those alpha-motoneurones causes a reflex twitch. The 1-a afferents are
among the fastest conducting fibres found in the body.
Each component of the reflex pathway introduces a delay and, in the case of the conduction time along the
nerves, this delay might well be related to path length (ie distance between muscle and cns). We may be
able to take advantage of the natural variation in path length that arises from differences in height to gain
some insight into the delays introduced by the various parts of the reflex pathway. Could it be that taller
people have faster-conducting nerve fibres so that their overall stretch reflex delay is the same? Or do we
all have the same type of nerve fibre so that taller people have longer stretch reflex delays?
Aim
To use the natural variation within the student population to investigate the components of the stretch
reflex.
Specific problems you will face in the experimental design and analysis
The need for a large number of differing subjects
This is not an experiment in which you can directly investigate the elements under study. You must rely on
natural variation within the general population in order to draw conclusions (in the same way that an
investigation into the relationship between height and weight would not seek to force-feed or starve
subjects; instead, the natural variation in height of a large number of subjects would be used to derive the
relationship between height and weight). This requires you to study ‘normal’ subjects as well as those
showing wide variation from ‘normal’ - ie short and tall. Hopefully, the class is varied enough to permit
this!
Measuring stretch reflex latency
The stretch reflex is initiated by hitting the Achilles tendon with a hammer containing a sensor. The
moment of impact is captured by monitoring this sensor using the ADI PowerLab. The reflex twitch that
arises sometime later is captured by simultaneously recording the electrical activity of the calf muscle
(EMG) using adhesive electrodes. The time delay can be measured, as can various aspects of the subject
that reflect the ‘path length’ the reflex operated over such as height, leg length etc.
Analysis
Presumably, some sort of regression analysis of ‘measure of path length’ (x-axis) versus reflex delay (y-axis)
would be appropriate.
Equipment
ADI PowerLab/Leads/Electrodes/Reflex hammer
The Practice & Communication of Science 2015/2016 Mini-projects
Relationship between breath-holding and blood oxygenation
Background
The spirometry experiment in EDA has shown the importance of the respiratory gases in driving
ventilation. Sensory systems exist within the body to monitor the respiratory gases and that information is
used by the respiratory centre to adjust ventilation so that homeostasis of blood gases is achieved.
However, if we deliberately suppress exhalation, we might expect the concentration of carbon dioxide to
increase and for oxygen to decrease. These changes would not go on indefinitely as eventually the
respiratory centre would over-ride our conscious suppression of breathing and force us to breath (you
cannot commit suicide by holding your breath!). Although we can’t measure the levels of carbon dioxide in
the blood directly, we can determine the degree of blood oxygenation using a pulse oximeter. From the
EDA ‘spirometry’ experiment, it was determined that carbon dioxide was the most important ‘driver’ for
ventilation, one reason being that the presence of haemoglobin in the blood means that oxygen is very
well ‘buffered’ (ie held fairly constant) so its lack of variation means it is a poor ‘signal’ to control
ventilation. Nevertheless, it would be interesting to see by how much oxygenation varies during breathholding.
Aim
To investigate the degree to which blood oxygenation drops during sustained breath-holding.
Specific problems you will face in the experimental design and analysis
Pulse oximetry
These devices are fairly accurate, but the changes we are likely to see are likely to be small. Therefore,
careful and accurate placement and measurement of the device is likely to be needed.
What are you investigating?
You have to decide what exactly you will be investigating. You could look at simple ‘before and after’
readings from the oximeter (including pulse rate?) after a fixed period of breath-holding, or you could
monitor readings every, say, 15 sec, until the person was forced to ‘break’ their breath-hold (you could
record that break-time and see if it correlated to, say, the drop in oxygen levels). Or you could record the
time that the oximeter changed its reading (it decrements by single percentages) until the person ‘breaks’.
Analysis
Presumably, some sort of regression analysis for the changes in oxygen with time, or correlation of time of
breath-hold and change in oxygen, or a paired test of before vs after breath-hold could be used.
Equipment
Pulse oximeter
Stopwatch
The Practice & Communication of Science 2015/2016 Mini-projects
Relationship between pulse pressure wave velocity and blood pressure when standing
and lying down.
Background
When the heart contracts and ejects blood from the left ventricle, a wave of pressure (not to be confused
with normal blood flow) propagates out through the arterial ‘tree’, stretching the arteries as it goes; this
can be felt as the pulse at certain points – eg the wrist. The speed at which the pulse pressure wave travels
depends on the ‘stretchiness’ of the arteries; the more compliant they are, the slower the wave travels.
The velocity of propagation can be measured by timing the delay between the wave being generated at the
heart (the R-wave ‘spike’ of the ECG) and its arrival at a peripheral site such as the finger (the finger swells
slightly when the pulse wave arrives, and can be picked up using a sensitive pressure transducer referred
to as a pulse plethysmograph). It is thought that the velocity of the pulse wave is related to blood pressure
and can also be influenced by things that may change the level of smooth muscle contraction in the arterial
wall such as the haemodynamic changes that result from changes in posture.
Aim
To measure the pulse pressure wave velocity and see if it changes with posture and also if it correlates with
blood pressure.
Specific problems you will face in the experimental design and analysis
Pulse plethysmograph
Accurate results require a good clean ‘signal’ to be recorded; this is fairly straightforward for the ECG, but
the pulse plethysmograph is extremely sensitive to movement artifacts and the strap being too tight or
loose.
Analysis
Presumably, some sort of regression analysis for the correlation between blood pressure and pulse
pressure wave velocity, and a paired test to see if pulse pressure wave velocity is affected by posture
(standing up vs lying down).
Equipment
ADI PowerLab/ECG lead/electrodes/pulse plethysmograph
Blood pressure recorder
Mat
The Practice & Communication of Science 2015/2016 Mini-projects
Effect of exercise on blood pressure.
Background
Blood pressure varies with each cardiac cycle between systolic (the peak pressure generated by ventricular
contraction) and diastolic (the lowest pressure in the major arteries just before the ventricles contract
again); mean arterial pressure reflects the ‘average’ pressure during the cardiac cycle. In general, systolic
pressure is a function of the pumping activity, and diastolic pressure is a function of the resistance offered
by the circulation (the higher the resistance, the less rapidly pressure drops while the heart is relaxed and
the higher the diastolic pressure).
Exercise produces major changes in cardiovascular function; the heart works harder and the resistance of
the skeletal muscle beds reduces. So, changes in blood pressure measurements might be expected.
Aim
To quantify the changes in systolic, diastolic and mean blood pressures to increasing levels of exercise.
Specific problems you will face in the experimental design and analysis
Blood pressure measurements
The automatic blood pressure recorders work by monitoring small oscillations in pressure as the cuff
deflates and the artery in the arm starts to open for longer and longer periods. This means that
measurements can only be taken accurately when the subject is still. It is, therefore, important that the
subject exercises, stops, and has his/her blood pressure measured as quickly as possible.
Analysis
Regression analysis for the correlation between blood pressure and level of exercise.
Equipment
Exercise bike
Blood pressure recorder