Exercise physiology of the left atrium: quantity and timing of contribution to cardiac output

While the phases of left atrial (LA) function at rest have been studied, the physiological response of the LA to exercise is undefined. This study defines the exercise behavior of the normal left atrium by quantitating its volumetric response to graded effort. Healthy subjects (n=131) were enrolled from the Health eHeart cohort. Echocardiograms were obtained at baseline and during ramped supine bicycle exercise. Left ventricular volume index, stroke volume index (LVSVI), left atrial end-systolic volume index (LAESVI), end-diastolic volume index (LAEDVI), emptying fraction (LAEF), reservoir and conduit fraction were analyzed. The LVSVI increased with low exercise, but did not increase further with peak exercise; cardiac output increased through the agency of heart rate. The LAESVI and LAEDVI decreased and the LAEF increased with exercise. As a result, LA reservoir volume index was static throughout exercise. The reservoir fraction decreased from 46% at rest to 40% with low exercise (p<0.001) in association with increased LVSVI, and remained similar at peak exercise. The conduit volume index increased from 20 mL/m2 at rest to 24 mL/m2 at low exercise and stayed the same at peak exercise. Similarly, the conduit fraction increased from 54% at rest to 60% at low exercise (p<0.001) and did not change further with peak exercise. Although atrial function increased with exercise, the major contribution to the augmentation of LV SV is LA conduit fraction, a marker of active ventricular relaxation. Furthermore, the major determinant of raising cardiac output during high level exercise is heart rate.

Evaluation of least significant changes of pulse contour analysis-derived parameters

Background Many maneuvers assessing fluid responsiveness (minifluid challenge, lung recruitment maneuver, end-expiratory occlusion test, passive leg raising) are considered as positive when small variations in cardiac index, stroke volume index, stroke volume variation or pulse pressure variation occur. Pulse contour analysis allows continuous and real-time cardiac index, stroke volume, stroke volume variation and pulse pressure variation estimations. To use these maneuvers with pulse contour analysis, the knowledge of the minimal change that needs to be measured by a device to recognize a real change (least significant change) has to be studied. The aim of this study was to evaluate the least significant change of cardiac index, stroke volume index, stroke volume variation and pulse pressure variation obtained using pulse contour analysis (ProAQT®, Pulsion Medical System, Germany). Methods In this observational study, we included 50 mechanically ventilated patients undergoing neurosurgery in the operating room. Cardiac index, stroke volume index, pulse pressure variation and stroke volume variation obtained using ProAQT® (Pulsion Medical System, Germany) were recorded every 12 s during 15-min steady-state periods. Least significant changes were calculated every minute. Results Least significant changes statistically differed over time for cardiac index, stroke volume index, pulse pressure variation and stroke volume variation (p < 0.001). Least significant changes ranged from 1.3 to 0.7% for cardiac index, from 1.3 to 0.8% for stroke volume index, from 10 to 4.9% for pulse pressure variation and from 10.8 to 4.3% for stroke volume variation. Conclusion To conclude, the present study suggests that pulse contour analysis is able to detect rapid and small changes in cardiac index and stroke volume index, but the interpretation of rapid and small changes of pulse pressure variation and stroke volume variation must be done with caution.

Influence of Preoperative Antioxidant-Antihypoxant Infusion on the Indices of Central Hemodynamics in Elderly Patients during Anesthesia and Surgical Intervention for Femur Fracture

The problem of the safety of elderly patients at surgical intervention for femur fracture is broached. Different types of anesthesia (regional and general) exert both direct and indirect influence on hemodynamics parameters. Ninety patients (mean age 68±4.2 years) were divided into 2 groups depending on the type of anesthesia: epidural and general anesthesia based on proforol and sevoflurane with caudal block. In every group different infusion solutions (Ringer’s solution, 10% Refortan, Mafusol, Cardioxipin) were used prior to anesthesia. The following parameters of central hemodynamics were studied: mean arterial pressure, heart rate, cardiac output and cardiac index, stroke volume index, total vascular resistance. The least changes in hemodynamics were observed when general anesthesia based on proforol and sevoflurane in combination with ropovicain caudal block and cardioxipin preinfusion were used.

Influence of Preoperative Antioxidant-Antihypoxant Infusion on the Indices of Central Hemodynamics in Elderly Patients during Anesthesia and Surgical Intervention for Femur Fracture

The problem of the safety of elderly patients at surgical intervention for femur fracture is broached. Different types of anesthesia (regional and general) exert both direct and indirect influence on hemodynamics parameters. Ninety patients (mean age 68±4.2 years) were divided into 2 groups depending on the type of anesthesia: epidural and general anesthesia based on proforol and sevoflurane with caudal block. In every group different infusion solutions (Ringer’s solution, 10% Refortan, Mafusol, Cardioxipin) were used prior to anesthesia. The following parameters of central hemodynamics were studied: mean arterial pressure, heart rate, cardiac output and cardiac index, stroke volume index, total vascular resistance. The least changes in hemodynamics were observed when general anesthesia based on proforol and sevoflurane in combination with ropovicain caudal block and cardioxipin preinfusion were used.

Early Anti-Coagulation after Ischemic Stroke due to Atrial Fibrillation is Safe and Prevents Recurrent Stroke

Background: Patients with acute cardio-embolic stroke from atrial fibrillation (AF) are at risk for recurrence with up to 50% of recurrent stroke occurring within two weeks of the index event. Anti-coagulation with heparinoids within 48 hours of stroke has been shown to increase risk of symptomatic intracranial hemorrhage (ICH) with no clear benefit on early stroke recurrence. Methods: This study was a retrospective chart review of consecutive patients who were admitted to the stroke service at the Foothills Medical Centre between 2009 and 2011. All patients with an acute stroke with a cardio-embolic etiology and a diagnosis of atrial fibrillation were reviewed. We hypothesized that anti-coagulation within two weeks of stroke, appropriately begun because of a diagnosis of AF, decreased rates of recurrent stroke without causing an increase in rates of symptomatic ICH. Results: Between 2009-2011, 324 patients were identified with cardio-embolic stroke secondary to AF. Within two weeks of stroke onset 61.4% (199/324) of patients were therapeutic on anti-coagulation. Patients who were anti-coagulated had a smaller median index stroke volume (3.2 ml vs 18.4 ml). Three (0.9%) patients suffered a clinically significant ICH. Recurrent stroke occurred in 11 patients (3.4%) within the two-week period. Therapeutic anti-coagulation within two weeks of initial stroke was associated with a decreased risk of recurrent stroke (RR 0.1, 95% CI 0.03-0.64). Conclusions: Anti-coagulation within two weeks of acute stroke in patients with AF appears to be safe among patients with smaller infarcts and prevents early recurrent infarction.

The sex-specific impact of systolic hypertension and systolic blood pressure on arterial-ventricular coupling at rest and during exercise

In healthy subjects the arterial system and the left ventricle (LV) are tightly coupled at rest to optimize cardiac performance. Systolic hypertension (SH) is a major risk factor for heart failure and is associated with structural and functional alterations in the arteries and the LV. The effects of SH and resting systolic blood pressure (SBP) on arterial-ventricular coupling ( EaI/ ELVI) at rest, at peak exercise, and during recovery are not well described. We noninvasively characterized EaI/ ELVI as end-systolic volume index/stroke volume index in subjects who were normotensive (NT, n = 203) or had SH (brachial SBP ≥140 mmHg, n = 79). Cardiac volumes were measured at rest and throughout exhaustive upright cycle exercise with gated blood pool scans. EaI/ ELVI reserve was calculated by subtracting peak from resting EaI/ ELVI. At rest, EaI/ ELVI did not differ between SH and NT men but was 23% ( P = 0.001) lower in SH vs. NT women. EaI/ ELVI did not differ between SH and NT men or women at peak exercise or during recovery. Nevertheless, EaI/ ELVI reserve was 61% ( P < 0.001) lower in SH vs. NT women. Similarly, resting SBP (as a continuous variable) was not associated with EaI/ ELVI in men (β = −0.12, P = 0.17) but was inversely associated with EaI/ ELVI in women (β = −0.47, P < 0.001). SH and a higher resting brachial SBP are associated with a lower EaI/ ELVI at rest in women but not in men, and SH women have an attenuated EaI/ ELVI reserve. Whether a smaller EaI/ ELVI reserve leads to functional limitations warrants further examination.

Consequences of Electroencephalographic-suppressive Doses of Propofol in Conjunction with Deep Hypothermic Circulatory Arrest

Background Some patients who undergo cerebral aneurysm surgery require cardiopulmonary bypass and deep hypothermic circulatory arrest. During bypass, these patients often are given large doses of a supplemental anesthetic agent in the hope that additional cerebral protection will be provided. Pharmacologic brain protection, however, has been associated with undesirable side effects. These side effects were evaluated in patients who received large doses of propofol. Methods Thirteen neurosurgical patients underwent cardiopulmonary bypass and deep hypothermic circulatory arrest to facilitate clip application to a giant or otherwise high-risk cerebral aneurysm. Electroencephalographic burst suppression was established before bypass with an infusion of propofol, and the infusion was continued until the end of surgery. Hemodynamic and echocardiographic measurements were made before and during the prebypass propofol infusion and again after bypass. Emergence time also was determined. Results Prebypass propofol at 243 +/- 57 micrograms.kg-1.min-1 decreased vascular resistance from 34 +/- 8 to 27 +/- 8 units without changing heart rate, arterial or filling pressures, cardiac index, stroke volume, or ejection fraction. Propofol blood concentration was 8 +/- 2 micrograms/ml. Myocardial wall motion appeared hyperdynamic at the end of cardiopulmonary bypass, and all patients were weaned therefrom without inotropic support. After bypass, vascular resistance decreased further, and cardiovascular performance was improved compared to baseline values. Nine of the 13 patients emerged from anesthesia and were able to follow commands at 3.1 +/- 1.4 h. Three others had strokes and a fourth had cerebral swelling. Conclusions Propofol infused at a rate sufficient to suppress the electroencephalogram does not depress the heart or excessively prolong emergence from anesthesia after cardiopulmonary bypass and deep hypothermic circulatory arrest.

Ultradian rhythms of autonomic, cardiovascular, and neuroendocrine systems are related in humans

Autonomic, cardiovascular, and neuroendocrine activities were monitored for 5-6 h in 10 normal adult resting humans (8 males, 2 females). The nasal cycle, a measure of lateralized autonomic tone, was measured at 4 Hz. Impedance cardiography (BoMed NCCOM3) was used to measure cardiac output, thoracic fluid index, heart rate, ejection velocity index, stroke volume, and ventricular ejection time (averages of 12 heart beats). Systolic, diastolic, and mean arterial pressures were measured with an automated cuff at 7.5-min intervals. Separate blood samples were taken every 7.5 min simultaneously from both arms with the use of indwelling venous catheters. Assays for adrenocorticotropic hormone, luteinizing hormone, norepinephrine, epinephrine, and dopamine were performed on samples from each arm. Time-series analysis, using the fast orthogonal search method of Korenberg, was used to detect variance structure. Significant spectral periods were observed in five windows at 220-340, 170-215, 115-145, 70-100, and 40-65 min. The greatest spectral power was observed in the lower frequencies, but periods at 115-145, 70-100, and 40-65 min were common across variables. Significant correlation coefficients for linear regressions of all paired variables in each subject were observed in 38.87% of the comparisons (subject range, 18.05-48-9.70%) with r > 0.30. These results suggest that either a common oscillator (the hypothalamus) or mutually entrained oscillators regulate these systems.

A Rapid Radioisotope Dilution Technique for the Accurate Determination of the Cardiac Output

SummaryA pair of printing scalers was used to record the information obtained by external monitoring of the isotope dilution curve following the intravenous injection of radioiodinated human serum albumin. The first scaler gives the differential count rate of the curve at increments of one second, whereas the second integrates continuously the isotope dilution curve. This recording device enabled cardiac output determinations to be calculated rapidly at the bedside without any loss in accuracy.Using this method in 15 normal individuals, the cardiac output was found to be 6.13 ± 0.73 liters/minute (Mean ± 1 S.D.), with a cardiac index of 3.36 ± 0.35 liters/minute/m2. In the same group of normals, the stroke index (stroke volume/surface area) amounted to 50 ± 7.3 ml/beat/m2.Comparison of the results of this method with those obtained by integration of the entire isotope dilution curve by an IBM 1620 computer showed excellent agreement, proving the validity of the suggested technique.