4 The wall thickness of an essentially spherical left ventri

4. The wall thickness of an essentially spherical left ventricle can be considered constant at 1.5 cm throughout the cardiac cycle. Measured transmural pressures are as follows: 19 mm Hg as the AV valve opens, 24 mm Hg as the AV valve closes, 71 mm Hg as the semilunar valve opens, 80 mm Hg as the semilunar valve closes, and maximally, 99 mm Hg when 80% of the stroke volume has been ejected. Suppose that the ventricular end diastolic volume (EDV) is 362 mls and the cardiac output is 4.9 L/min at a heart rate of 75 bpm.

A) The left ventricular stroke volume (SV) = _________

B) The left ventricular preload in mm Hg = __________. (Hint: preload is the same as wall stress, which can be calculated using LaPlace’s Law. Radius of ventricle = 4 cm).

Solution

(A) :- Stroke Volume can be calculated by:

SV = cardiac output(mL/min) / heart rate(bpm)

= 4900/75

= 65 mL.

(B) :- Preload or wall stress can be calculated as:-

Wall stress or wall tension of essentially spherical is equal to the

= pressure x radius / 2

where pressure is the pressure exerted by the blood to the wall of left ventricle

radius is the radius of the ventricle

= 99 x 4 /2

= 396/2

= 198 mm Hg.