Category: Cardiology

Although there is no obviously apparent physiologic reason for there to be a spontaneous cyclic variation of cardiac flow, it would seem unreasonable in the light of our inadequate understanding of the pathophysiology of Cheyne-Stokes respiration, to toally discount the cardiac events as being primary rather than secondary to the ventilatory cycle. Respiratory control is regulated by a chemostatic feedback system under the influence of three basic components. These are the respiratory chemoreceptors (controlling system), the arterial, venous and cerebrospinal fluid pH, Po2 and Pco2 (controlled system) and the “loop,” with an inherent time delay, being the circulation transferring information from the lungs to the brain. The controlling system regulates the amount of ventilation depending on the strengths of the various chemical stimuli. …Read the rest of this article

Doppler Evaluation of Changing Cardiac Dynamics during Cheyne-Stokes Respiration: OutcomeAlthough an association of intracardiac with respiratory events is apparent, the initiation and chronologic sequence cannot be definitively established due to the recurrent cyclic, possibly self-perpetuating nature of the events. The mechanism of this series of events must, with our current state of knowledge, remain conjecture. Several factors may be responsible for the genesis of the intracardiac velocity changes seen during the varying phases of Cheyne-Stokes respiration. These include the following: first, changing arterial oxygen saturations during the cyclical phases of respiration. Left ventricular function may be adversely affected during periods of hypoxia. …Read the rest of this article

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. …Read the rest of this article

Doppler Evaluation of Changing Cardiac Dynamics during Cheyne-Stokes Respiration: ResultsMean transmitral velocity and peak early velocity are significantly higher at the end of hyperpnea as compared to the end of apnea. An increase in peak late transmitral filling velocity (A wave) occurs between these two phases. Consequently, the E/A ratio shows a significant decrease from end-hyperpnea to end-apnea (Fig 1). Similarly directed quantitative changes were found with respect to the E integral, A integral, and the ratio. …Read the rest of this article

Patients were examined in the supine or left lateral decubitus position using standard two-dimensional and pulsed Doppler echo-cardiographic techniques. Studies were recorded using commercially available echocardiographs and analyzed with a commercially available graphics analysis system. All studies were performed by one experienced echocardiographer.
Left ventricular inflow velocity profiles were obtained from an apical four-chamber view with the pulsed-Doppler sample volume positioned at the tips of the mitral valve leaflets. …Read the rest of this article

Doppler Evaluation of Changing Cardiac Dynamics during Cheyne-Stokes RespirationAlthough Cheyne-Stokes respiration is a frequent and well-recognized accompaniment of severe cardiac failure and other conditions, the mechanism of the phenomenon of the periodic breathing is not well understood. In patients with congestive heart failure, it has been shown to be a marker of severe hemodynamic derangement.
Cardiovascular changes and derangements occurring during Cheyne-Stokes have been documented both clinically and experimentally; however, only limited insights into the associated hemodynamic changes have been gained. Noninvasive evaluation by Doppler echocardiography provides information about velocities of intracardiac blood flow. Because hemodynamic information can be obtained from Doppler echocardiography with regard to flow velocity profiles, the technique has the capability of providing insight into the cardiovascular changes occurring during Cheyne-Stokes respiration. …Read the rest of this article

On the other hand, it has recently been demonstrated that catecholamines can enhance cell-to-cell mechanical and electrical coupling and attenuate conduction inhomogeneity and desynchronization of cells being a source of fibrillation during ischemia . This was based on the observation of catecholamine-induced increased spread of fluorescent dye between cardiomyocytes under hypoxic conditions and high calcium concentration , and it may provide a further explanation for the suppression of arrhythmias demonstrated in our study.
In this study of the isolated heart we did not explore the relationship between the preconditioning-like anti-arrhythmic effect and changes in hemodynamics. These transient changes in heart rate and perfusion pressure (due to coronary vasoconstriction) may be sufficient to produce a certain degree of demand ischemia leading to preconditioning. On the other hand, we cannot rule out a direct adrenergic effect on the myocardium triggering adaptive processes mediated by the signal transduction system.
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