Have you ever wondered a given chest x-ray is taken in systole or diastole ? We should . . . isn’t ? Statistically chances of a X ray to fall in diastole is 10-20 % more than systole as the later phase is longer . The peculiarity of cardiac anatomy is that , the profile of the heart alters so little between systole and diastole .Still the blood is pumped efficiently into both pulmonary and systemic circulation . The left ventricle shortens by 35% and ejects 65 % of blood . Similarly RV shortens but with lesser quantum.
In a simple and elegant study by Stephen Gammill in 1970 published in Radiology journal,
he concluded the following about the CT ratio between systole and diastole.
- 52 % showed changes of 0.3 cm
- 41 per cent showed alterations of 0.4 to 0.9 cm,
- Only 7 per cent showed a significant variation of 1.0 to 1.7 cm in transverse cardiac diameter.
(I wonder why any follow up studies on this vital issue is scarce !)
In spite both ventricles contracting during systole the radiological transverse cardiac diameter is relatively undisturbed !
Importance of Rotary , Twist ,Torsional and Longitudinal motion
The fact that CT ratio does not alter significantly in most , imply the heart has some other kinetic motion which does not compromise the transverse diameter during systole. They are the rotary , and twist motion .The relative constancy of CT ratio is a good evidence for existence for such alternate motions .We have since confirmed this by sophisticated echocardiographic techniques .
Another evidence for rotary motion recognised in the bed side when the apical impulse hits you in the fingers even as the ventricle is supposed to go away from chest wall during systole . This is the torsional movement of LV apex and adjacent inter ventricular septum .
Reference
http://radiology.rsna.org/content/94/1/115.abstract
Coming soon
Inspiratory and expiratory x ray chest and the effect on cardiac contours .
