Medical Sciences (Anatomy, Physiology, Pharmacology etc.):

2603409_cardio_questions_1 x

Medical Sciences (Anatomy, Physiology, Pharmacology etc.)

 

Show all working and be careful to fully evaluate and state the units.

Q2.

a) Explain how the presence of formed particles (i.e. red cells) in blood makes its apparent viscosity around four times that of plasma. Explain also why this apparent viscosity should depend on flow rate.

b) In order to prepare a plasma sample, whole bood is centrifuged at 1200 rpm (20 revolutions per second). Given that the centrifugal acceleration is given by rω2 (ω= 2πf) and that the equivalent radius r is 10 cm, estimate how long blood samples should be centrifuged to ensure that the red blood cells will have packed down to the bottom of tubes in which the height of fluid is 5 cm. (Assume that the red blood cells obey Stoke’s law).

c) Explain some of the problems in measuring whole blood viscosity and why some methods are more reliable than others.

Q4.

(a) Injection of 10 ml of saline at 200 C into the right atrium gives rise to a momentary fall in Swan Ganz catheter tip temperature, which is positioned in the right pulmonary artery. This fall in temperature can be approximated to a triangle, with a maximum fall of 0.50 C and a duration2 of 7 seconds. See elsewhere for physical properties of blood and saline. Assume the initial temperature of the blood is 37.00 C. Estimate Cardiac Output in l/min.

(b) Cardiac output can also be estimated non-invasively by using radioactive substances or by high frequency electric current. Explain ONE of these methods explaining advantages and disadvantages compared to the method in (a).

(c) What factors lead to myocardial ischaemia (MI) and how can the risk of a life-threatening MI be reduced through surgical procedures?

Q28.

a) Describe the Swan Ganz catheter, explaining what other measurements than cardiac output can be measured using this, and what the clinical significance of these measurements is.

b) Cardiac Output is estimated by injecting 4 ml of saline at 200 C into the Right Atrium via a Swan Ganz catheter. Figure 1 shows a trace of the resultant fall in temperature in the Pulmonary Artery. Calculate Cardiac Output in l/min.

c) What is % Oxygen Saturation (SaO2) defined as?

d) This can be estimated optically by measuring the reflectance of blood at two wavelengths, 650 nm and 805 nm (approximately). Why are two wavelengths used and what is the significance of these particular wavelengths?

e) How can SaO2 measurements assist in the diagnosis of heart abnormalities (give 2 examples)?