Splanchnic venous pressure-volume relation during experimental acute ischemic heart failure. Differential effects of hydralazine, enalaprilat, and nitroglycerin

Role of splanchnic circulation in the pathogenesis of heart failure: State-of-the-art review

A hallmark of heart failure (HF), whether it presents itself during rest or periods of physical exertion, is the excessive elevation of intracardiac filling pressures at rest or with exercise. Many mechanisms contribute to the elevated intracardiac filling pressures, and notably, the concept of volume redistribution has gained attention as a cause of the elevated intracardiac filling pressures in patients with HF, particularly HF with preserved ejection fraction, who often present without symptoms at rest, with shortness of breath and fatigue appearing only during exertion. This phenomenon suggests cardiopulmonary system non-compliance and inappropriate volume distribution between the stressed and unstressed blood volume components. A substantial proportion of the intravascular blood volume is in the splanchnic vascular compartment in the abdomen. Preclinical and clinical investigations support the critical role of the sympathetic nervous system in modulating the capacitance and compliance of the splanchnic vascular bed via modulation of the greater splanchnic nerve (GSN). The GSN activation by stressors such as exercise causes excessive splanchnic vasoconstriction, which may contribute to the decompensation of chronic HF via volume redistribution from the splanchnic vascular bed to the central compartment. Accordingly, for example, GSN ablation for volume management has been proposed as a potential therapeutic intervention to increase unstressed blood volume. Here we provide a comprehensive review of the role of splanchnic circulation in the pathogenesis of HF and potential novel treatment options for redistributing blood volume to improve symptoms and prognosis in patients with HF.

Prospective Evaluation of Venous Excess Ultrasound for Estimation of Venous Congestion

BACKGROUND

Venous excess ultrasound (VExUS) is a novel ultrasound technique previously reported as a noninvasive measure of venous congestion and predictor of cardiorenal acute kidney injury.

RESEARCH QUESTION

Are there associations between VExUS grade and cardiac pressures measured by right heart catheterization (RHC) and cardiac biomarkers and clinical outcomes in patients undergoing RHC?

STUDY DESIGN AND METHODS

We conducted a prospective cohort study at the Denver Health Medical Center from December 20, 2022, to March 25, 2023. All patients undergoing RHC underwent a blinded VExUS assessment prior to their procedure. Multivariable regressions were conducted to assess relationships between VExUS grade and cardiac pressures, biomarkers, and changes in weight among patients with heart failure, a proxy for diuretic success. Receiver operating characteristic curve and area under the curve (AUC) were derived for VExUS, inferior vena cava (IVC) diameter, and IVC collapsibility index (ICI) to predict right atrial pressure (RAP) > 10 and < 7 mm Hg.

RESULTS

Among 81 patients, 45 of whom were inpatients, after adjusting for age, sex, and Charlson Comorbidity Index, there were significant relationships between VexUS grade of 2 (β = 4.8; 95% CI, 2.6-7.1; P < .01) and 3 (β = 11; 95% CI, 8.9-14; P < .01) and RAP, VExUS grade of 2 (β = 6.8; 95% CI, 0.16-13; P = .045) and 3 (β = 15; 95% CI, 7.3-22; P < .01) and mean pulmonary artery pressure, and VExUS grade of 2 (β = 7.0; 95% CI, 3.9-10; P < .01) and 3 (β = 13; 95% CI, 9.5-17; P < .01) and pulmonary capillary wedge pressure. AUC values for VExUS, IVC diameter, and ICI as predictors of RAP > 10 mm Hg were 0.9 (95% CI, 0.83-0.97), 0.77 (95% CI, 0.68-0.88), and 0.65 (95% CI, 0.52-0.78), respectively. AUC values for VExUS, IVC diameter, and ICI as predictors of RAP < 7 mm Hg were 0.79 (95% CI, 0.70-0.87), 0.74 (95% CI, 0.64-0.84), and 0.62 (95% CI, 0.49-0.76), respectively. In a subset of 23 patients with heart failure undergoing diuresis, there was a significant association between VExUS grade 3 and change in weight between time of RHC and discharge (P = .025).

INTERPRETATION

Although more research is required, VExUS has the potential to increase diagnostic and therapeutic capabilities of physicians at the bedside and increase our understanding of the underappreciated problem of venous congestion.

Clinical Review of Hypertensive Acute Heart Failure

Although acute heart failure (AHF) is a common disease associated with significant symptoms, morbidity and mortality, the diagnosis, risk stratification and treatment of patients with hypertensive acute heart failure (H-AHF) still remain a challenge in modern medicine. Despite great progress in diagnostic and therapeutic modalities, this disease is still accompanied by a high rate of both in-hospital (from 3.8% to 11%) and one-year (from 20% to 36%) mortality. Considering the high rate of rehospitalization (22% to 30% in the first three months), the treatment of this disease represents a major financial blow to the health system of each country. This disease is characterized by heterogeneity in precipitating factors, clinical presentation, therapeutic modalities and prognosis. Since heart decompensation usually occurs quickly (within a few hours) in patients with H-AHF, establishing a rapid diagnosis is of vital importance. In addition to establishing the diagnosis of heart failure itself, it is necessary to see the underlying cause that led to it, especially if it is de novo heart failure. Given that hypertension is a precipitating factor of AHF and in up to 11% of AHF patients, strict control of arterial blood pressure is necessary until target values are reached in order to prevent the occurrence of H-AHF, which is still accompanied by a high rate of both early and long-term mortality.

Preload Reduction Therapies in Heart Failure

Preload reserve represents an important concept in the normal physiologic responses of the body to meet the changing metabolic demands. The recruitment of preload in healthy patients leads to an increase in effective circulating blood volume with a concomitant increase in cardiac output. However, in the setting of heart failure (HF), preload augmentation may precipitate HF decompensation. In this review, we focus on the role of splanchnic nerve modulation and pharmacological therapeutic interventions to prevent HF decompensation through preload reduction. Furthermore, we explore the emerging device-based approaches for cardiac preload reduction while reviewing the ongoing clinical trials.

Splanchnic Nerve Modulation Effects on Surrogate Measures of Venous Capacitance

Background Splanchnic nerve modulation (SNM) is an emerging procedure to reduce cardiac filling pressures in heart failure. Although the main contributor to reduction in cardiac preload is thought to be increased venous capacitance in the splanchnic circulation, supporting evidence is limited. We examined changes in venous capacitance surrogates pre- and post-SNM. Methods and Results This is a prespecified analysis of a prospective, open-label, single-arm interventional study evaluating the effects of percutaneous SNM with ropivacaine in chronic heart failure with elevated filling pressures at rest and with exercise. Patients underwent cardiopulmonary exercise testing with invasive hemodynamic assessment pre- and post-SNM. Blood pressure changes with modified Valsalva maneuver and hemoconcentration, pre- and post-SNM were compared using a repeated measures model. Inferior vena cava diameter and collapsibility (>50% decrease in size with inspiration), and presence of bendopnea pre- and post-SNM were also compared. Fifteen patients undergoing SNM (age 58 years, 47% women, 93% with left ventricular ejection fraction ≤35%) were included. After SNM, changes in systolic blood pressure during Valsalva (peak-to-trough) were greater (41 versus 48 mm Hg, P=0.025). Exercise-induced hemoconcentration was unchanged (0.63 versus 0.43 g/dL, P=0.115). Inferior vena cava diameter was reduced (1.59 versus 1.30 cm, P=0.034) with higher collapsibility (33% versus 73%, P=0.014). Bendopnea was less (47% versus 13%, P=0.025). Conclusions SNM resulted in increased venous capacitance, associated decreased cardiac preload, and decreased bendopnea. Minimally invasive measures of venous capacitance could serve as markers of successful SNM. Long-term effects of SNM on venous capacitance warrant further investigation for heart failure management. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT03453151.

Effect of nitroglycerin on splanchnic and pulmonary blood volume

BACKGROUND

Sublingual nitroglycerin (SL NTG) is useful for treating acute decompensated heart failure, possibly by increasing splanchnic capacitance and reducing left ventricular (LV) preload. We evaluated a radionuclide method to study these effects, initially in subjects without heart failure.

METHODS AND RESULTS

Red blood cells were labelled by an in vitro method. Abdominal and chest images were obtained at rest, showing relative regional blood volumes. The abdomen was then re-imaged during progressive escalation of intrathoracic pressure using continuous positive airway pressure to assess baseline splanchnic capacitance (pressure-volume relationship, PVR) and compliance (slope of PVR). The procedure was repeated after 0.6 mg SL NTG, followed by chest images. Relative splanchnic blood volume increased at rest after SL NTG (P < .002), signifying an increase in splanchnic capacitance. The slope of the splanchnic PVR decreased in proportion to the baseline PVR (P = .0014), signifying increased compliance. The relative pulmonary blood volume decreased in proportion to the increase in splanchnic blood volume (P = .01).

CONCLUSIONS

A semi-quantitative radionuclide method demonstrated the effect of SL NTG for increasing splanchnic capacitance and compliance, with a proportional decrease in pulmonary blood volume. These data may be applied to quantitatively evaluate the importance of splanchnic vasodilation as a mechanism of LV preload reduction in the treatment of heart failure.

CLINICAL TRIALS REGISTRATION

NCT02425566.

Venous Tone and Stressed Blood Volume in Heart Failure: JACC Review Topic of the Week

A number of pathologic processes contribute to the elevation in cardiac filling pressures in heart failure (HF), including myocardial dysfunction and primary volume overload. In this review, we discuss the important role of the venous system and the concepts of stressed blood volume and unstressed blood volume. We review how regulation of venous tone modifies the distribution of blood between these 2 functional compartments, the physical distribution of blood between the pulmonary and systemic circulations, and how these relate to the hemodynamic abnormalities observed in HF. Finally, we review recently applied methods for estimating stressed blood volume and how they are being applied to the results of clinical studies to provide new insights into resting and exercise hemodynamics and therapeutics for HF.

Targeting Preload in Heart Failure: Splanchnic Nerve Blockade and Beyond

Preload augmentation represents a critical mechanism for the cardiovascular system to increase effective circulating blood volume to increase cardiac filling pressures and, subsequently, for the heart to increase cardiac output. The splanchnic vascular compartment is the primary source of vascular capacity and thus the primary target for preload recruitment in humans. Under normal conditions, sympathetic stimulation of these primary venous vessels promotes the shift of blood from the splanchnic to the thoracic compartment and elevates preload and cardiac output. However, in heart failure, since filling pressures may be elevated at rest due to decreased venous capacitance, incremental recruitment of preload to enhance cardiac output may exacerbate congestion and limit exercise capacity. Accordingly, recent attention has focused on therapies designed to regulate splanchnic vascular redistribution to improve cardiac filling pressures and patient-centered outcomes such as quality of life and exercise capacity in patients with heart failure. In this review, we discuss the relevance of splanchnic circulation as a venous reservoir, the contribution of stressed blood volume to heart failure pathogenesis, and the implications for pharmacological therapeutic interventions to prevent heart failure decompensation. Further, we review emerging device-based approaches for cardiac preload reduction such as partial/complete occlusion of the superior vena cava or the inferior vena cava.

Splanchnic nerve modulation in heart failure: mechanistic overview, initial clinical experience, and safety considerations

Volume recruitment from the splanchnic compartment is an important physiological response to stressors such as physical activity and blood loss. In the setting of heart failure (HF), excess fluid redistribution from this compartment leads to increased cardiac filling pressures with limitation in exercise capacity. Recent evidence suggests that blocking neural activity of the greater splanchnic nerve (GSN) could have significant benefits in some patients with HF by reducing cardiac filling pressures and improving exercise capacity. However, to date the long-term safety of splanchnic nerve modulation (SNM) in the setting of HF is unknown. SNM is currently used in clinical practice to alleviate some forms of chronic abdominal pain. A systematic review of the series where permanent SNM was used as a treatment for chronic abdominal pain indicates that permanent SNM is well tolerated, with side-effects limited to transient diarrhoea or abdominal colic and transient hypotension. The pathophysiological role of the GSN in volume redistribution, the encouraging findings of acute and chronic pilot SNM studies and the safety profile from permanent SNM for pain provides a strong basis for continued efforts to study this therapeutic target in HF.

Splanchnic Nerve Block Mediated Changes in Stressed Blood Volume in Heart Failure

OBJECTIVES

The authors estimated changes of stressed blood volume (SBV) induced by splanchnic nerve block (SNB) in patients with either decompensated or ambulatory heart failure with reduced ejection fraction (HFrEF).

BACKGROUND

The splanchnic vascular capacity is a major determinant of the SBV, which in turn determines cardiac filling pressures and may be modifiable through SNB.

METHODS

We analyzed data from 2 prospective, single-arm clinical studies in decompensated HFrEF (splanchnic HF-1; resting hemodynamics) and ambulatory heart failure (splanchnic HF-2; exercise hemodynamics). Patients underwent invasive hemodynamics and short-term SNB with local anesthetics. SBV was simulated using heart rate, cardiac output, central venous pressure, pulmonary capillary wedge pressure, systolic and diastolic systemic arterial and pulmonary artery pressures, and left ventricular ejection fraction. SBV is presented as ml/70 kg body weight.

RESULTS

Mean left ventricular ejection fraction was 21 ± 11%. In patients with decompensated HFrEF (n = 11), the mean estimated SBV was 3,073 ± 251 ml/70 kg. At 30 min post-SNB, the estimated SBV decreased by 10% to 2,754 ± 386 ml/70 kg (p = 0.003). In ambulatory HFrEF (n = 14) patients, the mean estimated SBV was 2,664 ± 488 ml/70 kg and increased to 3,243 ± 444 ml/70 kg (p < 0.001) at peak exercise. The resting estimated SBV was lower in ambulatory patients with HFrEF than in decompensated HFrEF (p = 0.019). In ambulatory patients with HFrEF, post-SNB, the resting estimated SBV decreased by 532 ± 264 ml/70 kg (p < 0.001). Post-SNB, with exercise, there was no decrease of estimated SBV out of proportion to baseline effects (p = 0.661).

CONCLUSIONS

The estimated SBV is higher in decompensated than in ambulatory heart failure. SNB reduced the estimated SBV in decompensated and ambulatory heart failure. The reduction in estimated SBV was maintained throughout exercise. (Splanchnic Nerve Anesthesia in Heart Failure, NCT02669407; Abdominal Nerve Blockade in Chronic Heart Failure, NCT03453151).

Blood Pressure Reduction in Hypertensive Acute Heart Failure

PURPOSE OF REVIEW

To review the key clinical and research questions regarding blood pressure (BP) reduction with vasodilators in the early management of hypertensive acute heart failure (H-AHF).

RECENT FINDINGS

Despite numerous AHF vasodilator clinical trials in the past two decades, virtually none has studied a population where vasoconstriction is the predominant physiology, and with the agents and doses most commonly used in contemporary practice. AHF patients are remarkably heterogenous by vascular tone, and this heterogeneity is not always discernible through BP or clinical exam. Emerging data suggest that diastolic BP may be a stronger correlate of vascular tone in AHF than systolic BP, despite the latter historically serving as a key inclusion criterion for vasodilator clinical trials. Existing data are limited. A clinical trial that evaluates vasodilators in a manner of use consistent with contemporary practice, specifically within the subpopulation of patients with true H-AHF, is greatly needed. Until then, observational data supports long-standing vasodilators such as nitroglycerin, administered by IV bolus, and with goal reduction of SBP ≤25% as a safe first-line approach for patients with severe H-AHF presentations.

Extracardiac Abnormalities of Preload Reserve: Mechanisms Underlying Exercise Limitation in Heart Failure with Preserved Ejection Fraction, Autonomic Dysfunction, and Liver Disease

While many of the cardiac limitations to exercise performance are now well-characterized, extracardiac limitations to exercise performance have been less well recognized but are nevertheless important. We propose that abnormalities of cardiac preload reserve represents an under-recognized but common cause of exercise limitations. We further propose that mechanistic links exist between conditions as seemingly disparate as heart failure with preserved ejection fraction, nonalcoholic fatty liver disease, and pelvic venous compression/obstruction syndromes (eg, May-Thurner). We conclude that extracardiac abnormalities of preload reserve serve as a major pathophysiologic mechanism underlying these and other disease states.

Assessment of central venous physiology of Fontan circulation using peripheral venous pressure

OBJECTIVE

Elevated central venous pressure is a major cause of morbidity and mortality after the Fontan operation. The difference between mean circulatory filling pressure and central venous pressure, a driving force of venous return, is important in determining dynamic changes in central venous pressure in response to changes in ventricular properties or loading conditions. Thus, noninvasive central venous pressure and mean circulatory filling pressure estimation may contribute to optimal management in patients undergoing the Fontan operation. We tested the hypothesis that central venous pressure and mean circulatory filling pressure in those undergoing the Fontan operation can be simply estimated using peripheral venous pressure and arm equilibrium pressure, respectively.

METHODS

This study included 30 patients after the Fontan operation who underwent cardiac catheterization (median 8.6, 3.4-42 years). Peripheral venous pressure was measured at the peripheral vein in the upper extremities. Mean circulatory filling pressure was calculated by the changes of arterial pressure and central venous pressure during the Valsalva maneuver. Arm equilibrium pressure was measured as equilibrated venous pressure by rapidly inflating a blood pressure cuff to 200 mm Hg.

RESULTS

Central venous pressure and peripheral venous pressure were highly correlated (central venous pressure = 1.6 + 0.68 × peripheral venous pressure, R = 0.86, P < .0001). Stepwise multivariable regression analysis showed that only peripheral venous pressure was a significant determinant of central venous pressure. Central venous pressure was accurately estimated using regression after volume loading by contrast injection (R = 0.82, P < .0001). In addition, arm equilibrium pressure measurements were highly reproducible and robustly reflected invasively measured mean circulatory filling pressure (mean circulatory filling pressure = 9.1 + 0.63 × arm equilibrium pressure, R = 0.88, P < .0001).

CONCLUSIONS

Central venous pressure and mean circulatory filling pressure can be noninvasively estimated by peripheral venous pressure and arm equilibrium pressure, respectively. This should help clarify unidentified Fontan pathophysiology and the mechanisms of Fontan failure progression, thereby helping construct effective tailor-made approaches to prevent Fontan failure.

A novel framework of circulatory equilibrium

A novel framework of circulatory equilibrium was developed by extending Guyton's original concept. In this framework, venous return (COV) for a given stressed volume (V) was characterized by a flat surface as a function of right atrial pressure (PRA) and left atrial pressure (PLA) as follows: COV= V /W − GSPRA− GPPLA, where W, GS, and GPdenote linear parameters. In seven dogs under total heart bypass, COV, PRA, PLA, and V were varied to determine the three parameters in each animal with use of multivariate analysis. The coefficient of determination ( r2= 0.92–0.99) indicated the flatness of the venous return surface. The averaged surface was COV= V/0.129 − 19.61PRA− 3.49PLA. To examine the invariability of the surface parameters among animals, we predicted the circulatory equilibrium in response to changes in stressed volume in another 12 dogs under normal and heart failure conditions. This was achieved by equating the standard surface with the individually measured cardiac output (CO) curve. In this way, we could predict CO [ y = 0.90 x + 5.6, r2= 0.95, standard error of the estimate (SEE) = 8.7 ml·min−1·kg−1], PRA( y = 0.96 x, r2= 0.98, SEE = 0.2 mmHg), and PLA( y = 0.89 x + 0.5, r2= 0.98, SEE = 0.8 mmHg) reasonably well. We conclude that the venous return surface accurately represents the venous return properties of the systemic and pulmonary circulations. The characteristics of the venous return surface are invariable enough among animals, making it possible to predict circulatory equilibrium, even if those characteristics are unknown in individual animals.

Effects of estrogen on venous function in rats with chronic heart failure

The effect of 17beta-estradiol on venous function was investigated in ovariectomized rats with heart failure. Rats (50-60 days old) were ovariectomized and implanted with 60-day-release pellets that contain 17beta-estradiol (1.5 mg) or vehicle. The left coronary artery was ligated 7 days later. Another group of ovariectomized rats was given vehicle pellets and then a sham operation was performed. The rats were studied while under pentobarbital anesthesia at 7 wk after ligation. Ligated rats, relative to sham groups, had lower mean arterial pressure (MAP, -34 mmHg) and cardiac output (CO, -38%); higher arterial resistance (R(A), +12%) and venous resistance (R(V), +116%); mean circulatory filling pressure (MCFP, +40%) and left ventricular end-diastolic pressure (LVEDP, +11 mmHg); and similar cardiovascular responses to norepinephrine (NE). Treatment of ligated rats with 17beta-estradiol increased CO (+16%); reduced R(A) (-16%), R(V) (-35%), MCFP (-23%), and LVEDP (-3 mmHg); and augmented MAP, R(V,) and MCFP responses to NE. Therefore, 17beta-estradiol reduced MCFP, and this reduced preload (LVEDP). 17beta-Estradiol decreased R(V), which, along with decreased R(A) (afterload), led to an increase in CO. 17beta-Estradiol likely augmented vasoconstriction to NE through an improvement on the cardiovascular status.

Hemodynamic and hormonal responses to nicorandil in a canine model of acute ischemic heart failure: a comparison with cromakalim and nitroglycerin

The pharmacologic profiles of nicorandil in the cardiovascular system have been characterized by K-channel opening and nitrate activities. However, the effects of nicorandil on acute heart failure have yet to be elucidated. To investigate the effects of nicorandil under such pathophysiologic conditions, we administered nicorandil intravenously to dogs with acute ischemic heart failure induced by coronary embolization and compared the results with those induced by cromakalim and nitroglycerin. The heart failure in this experiment was demonstrated by a reduction of mean blood pressure (MBP) from 143+/-3 to 129+/-2 mm Hg (p < 0.01); cardiac output (CO) from 2.18+/-0.10 to 1.06+/-0.05 L/min (p < 0.01); stroke volume (SV) from 12.7+/-0.6 to 6.8+/-0.3 ml/min (p < 0.01); Vmax, an index of the contractility of the left ventricle, from 105.5+/-4.4 to 49.9+/-1.8 1/s (p < 0.01), and an increase in right atrial pressure (RAP) from 2.9+/-0.3 to 5.3+/-0.3 mm Hg (p < 0.01); left ventricular end-diastolic pressure (LVEDP) from 2.5+/-0.4 to 26.0+/-1.4 mm Hg (p < 0.01); and T, time constant of left ventricular relaxation, from 38.3+/-0.8 to 62.4+/-2.8 ms (p < 0.01). Furthermore, plasma renin activity (PRA) and plasma atrial natriuretic peptide (ANP) increased (from 1.72+/-0.29 to 5.03+/-0.68 ng AngI/ml/h, p < 0.01; from 103.9+/-5.8 to 411.5+/-29.4 pg/ml, p < 0.01, respectively), whereas brain natriuretic peptide (BNP) remained unchanged (from 23.1+/-2.2 to 26.9+/-1.4 pg/ml). Nicorandil (10-40 microg/kg/min, i.v. infusion for 20 min for each dosing) or cromakalim (0.25-1 microg/kg/min) decreased MBP, systemic vascular resistance (SVR), RAP, and LVEDP, and increased CO, SV, and Vmax. However, the reduction of RAP in cromakalim was significantly smaller than those of nicorandil and nitroglycerin in comparison at similar hypotensive doses. Nitroglycerin (2.5-10 microg/kg/min) decreased MBP, RAP, and LVEDP, and increased Vmax but did not change CO or SV. Increased plasma ANP levels, an index of cardiac filling pressure after induction of acute ischemic heart failure, were decreased significantly by cromakalim and tended to decrease by nicorandil or nitroglycerin. Plasma BNP levels and PRA were not influenced by any of these drugs. These results suggest that nicorandil produces the reduction of both preload and afterload followed by an improvement of cardiac contractility in this model. The increase in CO may be mediated mainly by the drug's K-channel opening activities and the reduction of venous tone by its nitrate properties. Nicorandil may prove to be useful in the treatment of acute ischemic heart failure.

Clinical death and the measurement of stressed vascular volume

OBJECTIVES

To measure stressed vascular volume in humans and to review the concepts of stressed and unstressed vascular volume.

DESIGN

Observational study during surgical procedure.

SETTING

Operating room at a university hospital.

PATIENTS

Five patients undergoing hypothermic circulatory arrest for surgery on major vessels.

INTERVENTION

We measured the volume that drained from the patient to the reservoir of the pump when the pump was turned off.

MEASUREMENTS AND MAIN RESULTS

Stressed volume was 20.2+/-1.0 mL/kg, which is 30% of the predicted blood volume of these patients.

CONCLUSION

The amount of blood volume that determines vascular filling pressure is only about a quarter of the total predicted volume, which means that there is a large reserve of unstressed volume that can be recruited to maintain vascular filling pressure.

Effects of CGS 21680, a selective A2A adenosine receptor agonist, on cardiac output and vascular resistance in acute heart failure in the anaesthetized rat

1. The effects of CGS 21680, a selective A2A adenosine receptor agonist, on cardiac output, blood pressure, mean circulatory filling pressure (Pmcf), arterial and venous resistances, heart rate and left ventricular end-diastolic pressure were assessed in rats with acute heart failure by means of coronary artery occlusion. 2. Animals (n=6 in each group) were divided into five groups: group I, sham-operated vehicle-treated (0.9% saline; 0.018 mL min(-1)); groups II-V, subject to coronary artery occlusion and treated with vehicle (0.9% saline; 0.018 ml min(-1)) and CGS 21680 (0.1, 0.3 and 1.0 microg kg(-1) min(-1)), respectively. Haemodynamic measurements were taken one hour after completion of surgery, ninety minutes after coronary artery occlusion (except in group I), and fifteen minutes after infusion of saline or CGS 21680. 3. Baseline haemodynamic measurements before occlusion were found not to differ significantly between the different groups of animals. However, after occlusion, cardiac output, rate of rise in left ventricular pressure (+ dP/dt) and blood pressure were significantly reduced when compared to corresponding values in sham-operated animals. In addition, occlusion of the coronary artery resulted in a significant elevation in venous resistance, Pmcf and left ventricular end-diastolic pressure as compared to corresponding values in sham-operated animals. 4. Infusion with CGS 21680 at the highest dose significantly reduced blood pressure, arterial resistance and left ventricular end-diastolic pressure when compared to occluded vehicle-treated animals (group II). Administration of CGS 21680 at the highest dose also significantly increased cardiac output (28%) and heart rate (10%) in comparison to occluded vehicle-treated animals. In addition, the highest dose of CGS 21680 significantly reduced Pmcf (9%) and venous resistance (62%) in comparison to occluded vehicle-treated animals. Administration of CGS 21680 did not significantly affect +dP/dt when compared to occluded vehicle-treated animals. 5. The results from the present investigation indicate that occlusion of the coronary artery in rats results in a state of heart failure characterized by reduced arterial pressure and cardiac output, and increased venous resistance, Pmcf and left ventricular end-diastolic pressure. Administration of CGS 21680 to animals with acute heart failure resulted in increased cardiac output which was due to reduced venous resistance, as well as increased heart rate.

Severe haemorrhage partially reverses moderate haemorrhage-induced decrease in intestinal vascular capacitance

The purpose of the present study was to compare the effect of severe haemorrhage with moderate haemorrhage on intestinal vascular capacitance. In 12 chloralose-anaesthetized pigs, moderate and subsequent severe haemorrhage was induced by removal of 15 and 25% of blood volume, respectively. Six of the animals were vagotomized prior to induction of haemorrhage. The portal vein pressure/intestinal blood volume (P-V) relationship was measured by using blood pool scintigraphy and varying portal vein pressure. Moderate haemorrhage resulted in a leftward shift of the P-V relationship towards the pressure axis with decreases in cardiac output, portal blood flow and arterial pressure, and an increase in heart rate. Severe haemorrhage shifted the P-V relationship back towards the volume axis compared with moderate haemorrhage, with further decreases in cardiac output, portal blood flow and arterial pressure. While moderate haemorrhage reduced intestinal blood volume at a portal vein pressure of 7 mmHg (Vp7) to 81 +/- 3% of the control value (P < 0.01), severe haemorrhage increased Vp7 to 88 +/- 1% of the control value (P < 0.05 compared with moderate haemorrhage). After vagotomy, moderate haemorrhage decreased Vp7 to 84 +/- 4% of the control value (P < 0.01), whereas Vp7 did not change significantly after severe haemorrhage (Vp7 increased to 86 +/- 1% of the control value). Thus, severe haemorrhage is associated with an increase in intestinal vascular capacity compared with moderate haemorrhage. This increase is mediated in part via the cardiac vagal reflex. The attenuation of intestinal venoconstriction during severe haemorrhage probably contributes to further decreases in cardiac output and arterial pressure by redistribution of blood to the peripheral circulation.