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One type of heart disease is diastolic heart failure (DHF). A study was carried out to see if DHF
was related to abnormalities in the diastolic properties of the left ventricle. Two groups
of patients, one with DHF and the other the control group with no symptoms of DHF,
were assessed to compare:

changes in left ventricular diastolic pressure and volume

and stiffness of muscles leading to resistance of the left ventricle to stretch under
increasing pressure.
Graph 1 shows the mean lowest pressure in the left ventricle during diastole after the
opening of the atrio-ventricular valve. Graph 2 shows individual stiffness constants.
M R Zile et al., “Diastolic heart failure: Abnormalities in active relaxation and passive stiffness of the left
ventricle”, New England Journal of Medicine (2004), vol. 350, issue 19, pp. 1953–1959.
Copyright ©1994 Massachusetts Medical Society. All rights reserved
(a)
Identify the left ventricular diastolic volumes in patients and the control group that
correspond to a pressure of 5 mm Hg.
Patients:
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Control group:
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(1)
(b)
Compare the diastolic pressure-volume relationship of patients with DHF and the
control group.
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(2)
(c)
Distinguish between the stiffness constants in the two groups of patients.
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(1)
(d)
(i)
Suggest why in patients with DHF there is little or no increase in blood
volume pumped out of the left ventricle with each contraction during
exercise.
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(1)
(ii)
Deduce how patients with DHF would respond to heavy exercise.
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(1)
(Total 6 marks)
Explain the role of the SA (sinoatrial) node in the cardiac cycle.
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(Total 6 marks)
(a)
The pumping of blood is a vital process. Explain the roles of the atria and ventricles in
the pumping of blood.
(4)
(b)
Explain how the structure of an artery allows it to carry out its function efficiently.
(5)
(a)
Draw a labelled diagram of the heart showing the chambers, associated blood vessels and
valves.
(4)
(a)
patients: 42 ( 2 ) ml
control group: 73 (2 ) ml
Both answers must be correct to receive [1].
(b)
both show increase in ventricular pressure as volume increases / positive
correlation;
in DHF patients as diastolic volume increases diastolic pressure increases
more rapidly than in the control group / the control group shows a gradual /
almost linear increase while patients with DHF show very rapid / exponential
increase in pressure;
controls have relatively low pressure at large volumes whereas the DHF
patients have higher pressure with a lower maximum volume;
1
2
(c)
DHF patients all (but one) have stiffer left ventricles;
control all have stiffness constant below 0.015 while patients with DHF all have
stiffness constant above 0.014;
DHF patients show wider range of stiffness;
1 max
(d)
(i)
stiff ventricle unable to stretch / increase in volume and fill optimally
(ii)
insufficient (oxygenated) blood would reach the tissues;
heart rate increases due to increase carbon dioxide / decrease blood pH;
cramp due to lactic acid build up;
fatigue due to insufficient oxygenated blood reaching the tissues;
1 max
1
[6]
SA node is located in the wall of right atrium of heart muscle;
has characteristics of both nerve and muscle tissue;
SA node initiates each impulse;
acts as pacemaker of the heart;
no nerve impulses needed for contraction / myogenic;
connected to nerves which slow/accelerate heart rate;
impulses spread out in all directions through walls of atria;
stimulates atrial systole/contraction;
fibres in walls of atria prevent impulses from reaching ventricles;
impulses reach AV node (after atrial contraction);
6 max
[6]
(a)
atria collect blood from veins (vena cava/pulmonary);
collect blood while ventricles are contracting;
atria pump blood into ventricles/ensure ventricles are full;
ventricles pump blood into arteries/out of the heart;
ventricles pump blood at high pressure because of their thicker,
muscular walls;
mention of heart valves working with atria and ventricles to keep
blood moving;
left ventricle pumps blood to systems and right ventricle pumps
blood to lungs;
Both left and right ventricles with correct function required for
mark to be awarded.
(b)
(a)
4 max
thick wall to withstand high blood pressures/avoid bursting/leaks;
many muscle fibres to help pump blood;
many elastic fibres to stretch and pump blood after each heart beat;
narrow lumen to maintain high pressure/because blood flows along
rapidly;
thick outer layer of collagen to give strength/prevent aneurism;
no valves as pressure is high enough to prevent backflow;
endothelium/smooth inner lining to reduce friction;
5 max
Award [1] for each structure clearly drawn and correctly labelled.
Schematic diagrams are acceptable.
right and left ventricles — not connected shown larger than atria;
right and left atrium — not connected, thinner walls than ventricles;
right ventricle has thinner walls than left ventricle / vice versa;
atrio-ventricular valves / tricuspid and bicuspid valves — shown between
atria and ventricles;
aorta and pulmonary artery — shown leaving the appropriate ventricle
with semilunar valves shown;
pulmonary vein and vena cava — shown entering appropriate atrium;
Vessels must join unambiguously to correct chamber.
4 max