Percent Change In Cardiac Output Research Articles

Cardiovascular and autonomic effects of water ingestion during postexercise circulatory occlusion

As with water ingestion, the activation of the muscle metaboreflex leads to heightened muscle sympathetic nerve activity. Thus, we hypothesized that water ingestion might enhance the pressor effect of the muscle metaboreflex activation. We examined the effect of water ingestion (50 vs. 500 mL) on the cardiovascular and autonomic responses to static handgrip followed by postexercise circulatory occlusion (PECO) in 19 healthy participants (29.2 ± 8.6 years). Beat-to-beat blood pressure, baroreflex sensitivity (BRS), and R-R intervals were recorded in both conditions (pre- and postingestion). Changes in stroke volume and cardiac output were assessed using Modelflow. Cardiac autonomic regulation was investigated by spectral heart rate variability (HRV); baroreflex control of heart rate was assessed by the sequence method. Water ingestion did not increase the pressor effect induced by PECO. Even though 500 mL of water elicited an overall bradycardia, paired by an increase in the high-frequency HRV, there were no differences between conditions for the decrease in BRS or the resetting of the baroreflex to operate at higher blood pressure. Nevertheless, after the ingestion of 500 mL of water, there were no significant correlations between the percent change in cardiac output and that of BRS, from rest to PECO. This contrasts with that seen in the 50 mL condition (r = -0.68, p < 0.05). Contrasting with our hypothesis, 500 mL of water did not increase the pressor effect induced by PECO. Nevertheless, we found that water ingestion may influence the mechanisms by which the muscle metaboreflex elicits an increased cardiac output during PECO.

Hemodynamic Design Requirements for In-Series Thoracic Artificial Lung Attachment in a Model of Pulmonary Hypertension

Recent thoracic artificial lung (TAL) prototypes have impedances lower than the natural lung. With these devices, proximal pulmonary artery (PA) to distal PA TAL attachment may be possible in patients without right ventricular dysfunction. This study examined the relationship between pulmonary system impedance and cardiac output (CO) to create TAL design constraints. A circuit with adjustable resistance and compliance (C) was attached in a PA-PA fashion with the pulmonary circulation of seven sheep with chronic pulmonary hypertension. The pulmonary system zeroth harmonic impedance modulus (Z(0)) was increased by 1, 2.5, and 4 mmHg/(L/min) above baseline. At each Z(0), C was set to 0, 0.34, and 2.1 ml/mmHg. The change in pulmonary system zeroth and first harmonic impedance moduli (ΔZ(0) and ΔZ(1)), the percent change in CO (%ΔCO), and the inlet and outlet anastomoses resistances were calculated for each situation. Results indicate that ΔZ(0) (p < 0.001) but not ΔZ(1) (p = 0.5) had a significant effect on %ΔCO and that %ΔCO = -7.45*ΔZ(0) (R(2) = 0.57). Inlet and outlet anastomoses resistances averaged 0.77 ± 0.16 and 0.10 ± 0.19 mmHg/(L/min), respectively, and the relationship between %ΔCO and TAL resistance, R(T), in mmHg/(L/min) was determined to be %ΔCO = -(7.45f)×(R(T) + 0.87), in which f = the fraction of CO through the TAL. Thus, newer TAL designs can limit %ΔCO to less than 10% if f < 0.75.

The Relationship Between Pulmonary System Impedance and Right Ventricular Function in Normal Sheep

Right ventricular (RV) afterload is a key determinant of RV function and is increased in many cardiopulmonary pathologies. Pulmonary circulation input impedance has been used to quantify afterload previously but due to its complexity has not been widely applied. This study examines the effect of a subset of the impedance spectrum, the zeroth and first harmonic impedance moduli (Z (0), Z (1)), on RV performance in large animals. An artificial circuit with adjustable resistance and compliance (C) was implanted into the pulmonary circulation of five sheep. Resistance was varied to increase Z (0) in increments of 2 mmHg/(L/min) until Z (0) was 8 mmHg/(L/min) above baseline. At each Z (0), C was adjusted between 0, 0.5 and 2 mL/mmHg or 0, 1, and 5 mL/mmHg. Fourier transforms of the pulmonary artery pressure and flow in each situation were used to calculate the pulmonary impedance. Results show that the percent change in cardiac output (%DeltaCO) is linearly related to the change in Z (0) (DeltaZ (0)). Increases in Z (1) (DeltaZ (1)) decreased %DeltaCO but to a much smaller degree, with the effect of DeltaZ (1) increasing with DeltaZ (0). Regression of these results produce the equation: %DeltaCO = (-0.0829DeltaZ (1) - 3.65)DeltaZ (0) - 9.02 (R (2) = 0.69). Blood flow and pressure moduli are small at harmonics higher than the first and are unlikely to affect RV function. Therefore, during acute, high afterload states, Z (0) is the primary determinant of CO, while the effect of Z (1) is minor.

Cardiac Output During High Afterload Artificial Lung Attachment

Attachment of thoracic artificial lungs (TALs) can increase right ventricular (RV) afterload and decrease cardiac output (CO) under certain conditions. However, there is no established means of predicting the extent of RV dysfunction. The zeroth harmonic impedance modulus, Z0, was thus examined to determine its effectiveness at predicting CO during high afterload TAL attachment. The MC3 Biolung was attached in four adult sheep groups based on baseline (BL) pulmonary vascular resistance and TAL attachment mode: normal, parallel (n=7); normal, series (n=7); chronic pulmonary hypertension, parallel (n=5), and chronic pulmonary hypertension, series (n=5). The resistance of each attachment mode was increased incrementally and instantaneous pulmonary system hemodynamic data were acquired at each increment. The change in Z0 from BL, DeltaZ0, and percent change in CO (DeltaCO%) were then calculated to determine their relationship. The DeltaCO% varied significantly with DeltaZ0 (p<10(-40)) and DeltaZ02 (p<10(-4)) but not with the attachment and pulmonary hemodynamics group. The relationship between the variables for all sheep groups was DeltaCO%=0.215DeltaZ0(2)-7.14DeltaZ0+2.94 (R2=0.82) for DeltaZ0 in mm Hg/(L/min). Therefore, Z0 is an effective index for determining the CO during TAL attachment in both attachment modes with and without elevated pulmonary vascular resistance.

Comparison of FloTrac™ cardiac output monitoring system in patients undergoing coronary artery bypass grafting with pulmonary artery cardiac output measurements

Arterial pulse waveform analysis has been proposed for cardiac output (CO) determination and monitoring without calibration or thermodilution (FloTrac/Vigileo; Edwards Lifesciences, Irvine, CA, USA). The accuracy and clinical applicability of this technology has not been fully evaluated. We designed this prospective study to compare the accuracy of the FloTrac system (CO(FT)) vs. pulmonary artery catheter standard bolus thermodilution (CO(PAC) ) in patients undergoing coronary artery bypass grafting. We studied 11 patients referred for coronary artery bypass grafting. CO(FT) and CO(PAC) were determined at six time points in the operating room including before and 5 min after volume expansion (500 mL 6% hetastarch). Measurements were performed on arrival in the intensive care unit and every 4 h afterwards. Bland-Altman analysis was used to assess the agreement between CO(FT) and CO(PAC). CO(PAC) ranged from 2.0 to 7.6 L min-1 and CO(FT) ranged from 1.9 to 8.2 L min-1. There was a significant relationship between CO(PAC) and CO(FT) (r = 0.662; P < 0.001). Agreement between CO(PAC) and CO(FT) was -0.26 +/- 0.87 L min-1. Volume expansion induced a significant increase in both CO(PAC) and CO(FT) (from 3.4 +/- 0.8 to 4.4 +/- 1.0 L min-1; P < 0.001 and from 3.9 +/- 1.2 to 5.0 +/- 1.1 L min-1; P < 0.001, respectively) and there was a significant relationship between percent change in CO(PAC) and CO(FT) following volume expansion (r = 0.722; P = 0.01). We found clinically acceptable agreement between CO(FT) and CO(PAC) in this setting. This new device has potential clinical applications.

A Low Plasma Volume in Formerly Preeclamptic Women Predisposes to the Recurrence of Hypertensive Complications in the Next Pregnancy

Formerly preeclamptic women with a subnormal plasma volume (PV) have an increased risk to develop a hypertensive disorder in a subsequent pregnancy as compared to women with normal PV. In the current study we tested the hypothesis that formerly preeclamptic women who develop recurrent disease in their next pregnancy differ from their counterparts with an uneventful next pregnancy by a lower pre-pregnant PV, a lower venous capacitance, smaller rises in these indices in early pregnancy, a lower renal adaptive response, and a lower response to mild exercise. We enrolled 33 formerly preeclamptic women in this study. Only 14 conceived within the study period, with seven of them developing a recurrent hypertensive disorder in their next pregnancy (RECUR), while seven had an uneventful next pregnancy (NORM). Before pregnancy and at 12 weeks of gestational age, we compared the following variables between these subgroups: PV, venous capacitance, effective renal plasma flow (ERPF), glomerular filtration rate (GFR), and the responses in stroke volume (SV) and heart rate (HR) to mild exercise. To estimate venous capacitance, we infused 500 mL of a modified gelatine solution in 30 minutes while recording the change in cardiac output (pulse contour analysis). The ratio of percent change in blood volume to percent change in cardiac output in response to a standardized small volume load provides an estimate for venous capacitance. RECUR differed from NORM by a 20% lower pre-pregnant PV (P <.02) and venous capacitance (0.29 [0.11-0.55] vs 0.86 [0.64-2.03] P = .002). NORM and RECUR were comparable with respect to pregnancy-induced rise in PV, renal hemodynamics and function, and response to mild exercise at 12 weeks. Newborn weight correlated positively with pre-pregnancy PV (R(2) = 0.53 and P = .04). Formerly preeclamptic women with a recurrent hypertensive disorder in their next pregnancy differed from their counterparts with an uneventful next pregnancy by a lower pre-pregnant PV and a lower venous capacitance, the latter two indices correlating also inversely with the incidence of fetal growth restriction. The preserved acute response to volume-related stimuli in women with a low pre-pregnant PV supports the view that the predisposition of low pre-pregnant PV to adverse pregnancy outcome may result from a concomitant, PV-dependent change setpoint and/or gain in the stimulus/response interrelation of the volume regulatory system.

A Subnormal Plasma Volume in Formerly Preeclamptic Women is Associated with a Low Venous Capacitance

Pregnancy induces a smaller rise in plasma volume in formerly preeclamptic women with a pre-existent subnormal plasma volume than in their counterparts with a normal plasma volume. These women also have a three times higher recurrence rate of pregnancy-induced hypertensive disorders. In this study we tested the hypothesis that a subnormal plasma volume in these women is related to a lower capacitance of their venous compartment. In 31 nonpregnant formerly preeclamptic women with a subnormal plasma volume and eight parous controls, we infused intravenously 500 mL of a modified gelatin solution over 30 minutes. Before and after infusion we measured the circulating levels of alpha-atrial natriuretic peptide (alpha-ANP) and active plasma renin concentration (APRC). During volume loading, we recorded the change in heart rate, stroke volume, and cardiac output using pulse contour analysis. We measured the ratio of percent change in blood volume and percent change in cardiac output during volume loading as a marker for venous capacitance. During volume loading, patients differed from controls by a larger rise in alpha-ANP, pulse rate, and cardiac output, and by a lower estimated venous capacitance. The concomitant response of stroke volume and APRC did not differ appreciably between groups. Formerly preeclamptic women with a subnormal plasma volume differ from controls with a normal plasma volume by a reduced venous capacitance. These results support our hypothesis that, in these women, a subnormal plasma volume indicates the presence of a subnormal venous capacitance.

Correlation of the tei index with invasive measurements of ventricular function in a porcine model

Background The Doppler myocardial performance (Tei) index has been reported to be clinically useful in assessing left ventricular systolic and diastolic function in both adults and children. However, there are limited data to compare the Tei index with invasive measurements of ventricular function. We used a porcine model to directly correlate the Tei index with invasive indices of systolic and diastolic function. Methods Pressure volume loops were obtained from 10 pigs (32-45 kg). A micromanometer and a conductance catheter were placed in the left ventricle to record pressure and volume, respectively. A flow probe was placed around the ascending aorta to record cardiac output. Baseline pressure volume loops were generated during preload reduction through caval occlusion. Epicardial echocardiograms were performed just before the caval occlusion. Invasive indices including preload recruitable stroke work, ventricular stiffness constant, and cardiac output were assessed, as were noninvasive echocardiographic indices including Tei index and ejection fraction. An ischemic insult, ventricular fibrillation, was induced to alter ventricular function. After cardioversion and 40 minutes of reperfusion, echocardiographic and invasive measurements were repeated. Results There was a statistically significant inverse relationship between the percent change in Tei and the percent change in preload recruitable stroke work after ventricular fibrillation ( r = −0.70, P = .02), although the correlation between the actual values of Tei and preload recruitable stroke work were not statistically significant. There was a statistically significant inverse relationship between the percent change in Tei and the percent change in cardiac output ( r = −0.65, P = .03). There was a direct correlation between the value of Tei and the ventricular stiffness constant at baseline ( r = 0.63, P < .05). As anticipated, the value of Tei was inversely related to ejection fraction by epicardial echocardiogram at baseline ( r = −0.85, P < .001). The percent change in Tei was inversely related to the percent change in ejection fraction as well ( r = −0.69, P < .05). Conclusions This animal model is one of the first studies to demonstrate a direct correlation between the Tei index and systolic and diastolic invasive measurements of ventricular function. This supports the clinical use of this index as a measure of global ventricular function.

Autonomic influence on cardiovascular performance in diabetic subjects

Cardiomyopathy, coronary artery atherosclerosis, or autonomic neuropathy may affect the cardiovascular performance of the diabetic patient. To evaluate the role of parasympathetic nervous system activity on cardiovascular performance, 25 diabetic subjects who lacked symptoms, signs, or objective measurements of ischemia or cardiomyopathy were studied. Diabetic subjects were classified according to their RR variation, an index of cardiac parasympathetic nervous system activity. Fourteen diabetic subjects had a normal RR variation of greater than 30 (D-NOR), and 11 diabetic patients had an abnormal RR variation of less than 20 (D-ABN). Fifteen age- and weight-matched, healthy, nondiabetic subjects (NOR) constituted the control group. All subjects had oxygen consumption, multigated acquisition determination of cardiac output, and work product measured before and during supine bicycle maximum exercise testing. There was no difference in the resting cardiac output among the groups. Resting work product, however, was greatest in the D-ABN group when compared with performance in the other two groups (D-ABN: 11,500 +/- 800; D-NOR: 9,000 +/- 600; NOR: 8,700 +/- 400; p less than 0.0025). This was due to an increase in both heart rate (p less than 0.025) and systolic blood pressure (p less than 0.015). In the diabetic subjects, there was an inverse relationship between the RR variation and resting work product (r = 0.47, n = 25, p less than 0.005). In response to exercise, the percent increase in cardiac output at matched percent maximum oxygen uptake was greatest in the NOR, D-NOR, and D-ABN groups, respectively (analysis of variance, p less than 0.01). In the diabetic subjects, there was a significant relationship between the RR variation and the maximum percent change in cardiac output (r = 0.41, n = 25, p less than 0.02). Compared with the NOR group, the maximum increase in work product was impaired in diabetic subjects (p less than 0.002) and not different between the D-NOR and D-ABN groups. The increase in resting work product and the poor cardiac output responses to exercise in the D-ABN group are due to a decrease in cardiac parasympathetic nervous system activity and can be suggested by an abnormal RR variation. This index of parasympathetic nervous system activity can help the physician identify that subset of diabetic patients that may need special consideration when exercise training is prescribed.

Mechanisms for attenuated pressor responses to α-agonists in ovine pregnancy

Attenuated pressor responses to angiotensin II and α-agonists normally occur during ovine pregnancy; however, for α-agonists it is not known to what extent this reflects alterations in cardiac output. We therefore compared peripheral and cardiac responses to α-agonists in pregnant (n = 6) and nonpregnant (n = 6) sheep, measuring mean arterial pressure, heart rate, and cardiac output before and during steady-state dose responses to norepinephrine (0.458 to 45.84 μg/min) and phenylephrine (1.29 to 129 μg/min). Both α-agonists caused dose-dependent increases in mean arterial pressure and systemic vascular resistance, more so in nonpregnant than pregnant sheep (p < 0.01), and decreases in cardiac output and heart rate (p < 0.01). In both nonpregnant and pregnant sheep the percent change in systemic vascular resistance generally exceeded the percent change in mean arterial pressure, reflecting decreases in cardiac output; however, at equivalent increases in percent change in mean arterial pressure and percent change in systemic vascular resistance, the fall in the percent change in cardiac output was greatest in pregnant sheep (p < 0.05). Also, at similar increases in mean arterial pressure the percent change in heart rate was greatest in pregnant sheep (p < 0.01). In contrast to angiotensin II, the attenuated pressor responses to α-agonists observed during ovine pregnancy are partly a result of reflex decreases in cardiac output mediated mainly through falls in heart rate.