Doppler Evaluation of Changing Cardiac Dynamics during Cheyne-Stokes Respiration: Discussion
Of these, a simply analyzed and consistent abnormality is the relationship of the peak velocity of the LV rapid filling phase (E peak) to that of the peak velocity occurring with the atrial contraction phase (A peak). With impairment of LV compliance, the peak velocity of rapid filling decreases (E peak) and the peak velocity of the atrial contraction phase increases (A peak), ie, a change and possible reversal of the E/A ratio occurs. Interpretation of the results suggests that possibly diastolic dysfunction becomes progressively worse during the apneic period with the greatest restriction to filling occurring at the end of this phase. During the breathing phase of the cycle, the ventricular relaxation properties return towards normal. It is prudent to recognize that these Doppler changes may be due to altered LV loading conditions and need not necessarily reflect diastolic dysfunction. Another possible explanation is that an increase in Pco2 during the apneic phase may increase pulmonary vascular resistance lowering preload and stroke volume, whereas during the hyperpneic phase, pulmonary vascular resistance is reduced with resultant increase in left ventricular preload and increase in stroke volume. Click Here
A similar cyclical change is observed with regard to the left ventricular outflow velocity. Information about stroke volume and cardiac output can be derived from analysis of this velocity pattern. The decreased velocity of flow noted at the end of the apneic phase as compared to the velocity at the end of the hypemeic phase suggests a 25 percent reduction in stroke volume assuming an unchanged LV outflow area. The subsequent increase in velocity would suggest an increase in stroke volume. The reduction in cardiac output is temporally associated with an apparent impairment of left ventricular diastolic filling or reduction in preload.