Circulation
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Clinical Trial Controlled Clinical Trial
Blood pressure modulation by central venous pressure and respiration. Buffering effects of the heart rate reflexes.
Despite constant fluctuations in cardiac preload caused by the effects of respiration and changes in posture on venous return to the heart, arterial blood pressure remains remarkably constant. The effects of instantaneous lung volume (ILV) and variations of central venous pressure (CVP) on blood pressure (BP) were studied by use of frequency domain techniques to quantify the contribution of heart rate (HR) reflexes to attenuation of the effects of changes in right ventricular preload on arterial pressure. ⋯ Both slow changes of BP (< 0.08 Hz) induced by variations of CVP and more rapid changes induced by ILV are actively buffered by heart rate reflexes. During blockade, the mechanical properties of interposed cardiopulmonary structures limit CVP-induced fluctuations of BP. These findings have implications for BP regulation in pathological conditions associated with impairment of HR control.
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Left ventricular (LV) twist, the longitudinal gradient of circumferential rotation about the LV long axis, may play an important role in the storage of potential energy at end systole and its subsequent release as elastic recoil during early diastole; however, the effects of load and inotropic state on LV systolic twist and diastolic untwist in human subjects have not previously been characterized. ⋯ In conscious human transplant patients, (1) pressure and volume loading do not affect systolic LV twist; (2) dobutamine augments systolic twist and early diastolic untwisting, suggesting more end-systolic potential energy storage and early diastolic elastic recoil with enhanced inotropic state; (3) volume loading decreases early diastolic untwisting, possibly reflecting diminished recoil forces after preload augmentation associated with larger end-systolic volumes (ESV); and (4) M(ear)-dia correlates strongly with ESV (in an inverse fashion), and less strongly, but directly, with LV dP/dtmax.
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Comparative Study
Asymptomatic arrhythmias in patients with symptomatic paroxysmal atrial fibrillation and paroxysmal supraventricular tachycardia.
Paroxysmal atrial fibrillation and paroxysmal supraventricular tachycardia are recognized clinically when patients seek treatment for symptoms due to recurrent arrhythmias; atrial fibrillation also increases the risk of stroke. The frequency with which asymptomatic arrhythmias occur in patients with these arrhythmias is unknown. ⋯ In a group of patients with paroxysmal atrial fibrillation, sustained asymptomatic atrial fibrillation occurs far more frequently than symptomatic atrial fibrillation. However, it is not known whether asymptomatic atrial fibrillation is a potential risk factor for stroke even when patients are not having symptomatic arrhythmias.
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The outcome of the Fontan operation largely depends on patient selection because this procedure is a physiological correction. Among the several selection criteria for the Fontan operation, the importance of adequate size of the pulmonary artery remains controversial. To clarify whether or not pulmonary artery size is indispensable as one of the selection criteria for the Fontan operation, we considered the physiological importance of pulmonary artery size and investigated how pulmonary artery size influenced postoperative hemodynamics of the Fontan operation. ⋯ The smaller pulmonary artery size is hemodynamically disadvantageous after the Fontan operation, with resultant rise in peak control venous pressure and increased afterload to the single ventricle.
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Pressure-volume relations have been established as useful measures of left ventricular (LV) performance. Application of these methods to the intraoperative setting have been limited because of difficulties acquiring LV volume data. Transesophageal echocardiographic automated border detection can measure LV cross-sectional area as an index of volume, which can be coupled with pressure data to construct pressure-area loops on-line. The purpose of this study was to evaluate intraoperative LV performance in patients undergoing coronary bypass surgery before and immediately after cardiopulmonary bypass using on-line pressure-area relations. ⋯ Intraoperative pressure-area loops may be acquired and displayed on-line using transesophageal echocardiographic automated border detection and readily analyzed in a manner similar to pressure-volume loops. LV performance was depressed immediately after cardiopulmonary bypass compared with before. On-line pressure-area relations may be clinically useful to assess LV performance in patients undergoing cardiac surgery in whom load and contractility may be expected to vary rapidly.