Effect of meal induced splanchnic arterial vasodilatation on renal arterial haemodynamics in normal subjects and patients with cirrhosis

Tissue Drug Concentration

Blood flow enables the delivery of oxygen and nutrients to the different tissues of the human body. Drugs follow the same route as oxygen and nutrients; thus, drug concentrations in tissues are highly dependent on the blood flow fraction delivered to each of these tissues. Although the free drug concentration in blood is considered to correlate with pharmacodynamics, the pharmacodynamics of a drug is actually primarily commanded by the concentrations of drug in the aqueous spaces of bodily tissues. However, the concentrations of drug are not homogeneous throughout the tissues, and they rarely reflect the free drug concentration in the blood. This heterogeneity is due to differences in the blood flow fraction delivered to the tissues and also due to membrane transporters, efflux pumps, and metabolic enzymes. The rate of drug elimination from the body (systemic elimination) depends more on the driving force of drug elimination than on the free concentration of drug at the site from which the drug is being eliminated. In fact, the actual free drug concentration in the tissues results from the balance between the input and output rates. In the present paper, we develop a theoretical concept regarding solute partition between intravascular and extravascular spaces; discuss experimental research on aqueous/non-aqueous solute partitioning and clinical research on microdialysis; and present hypotheses to predict in-vivo elimination using parameters of in-vitro metabolism.

Oral Glucose Load and Human Cutaneous Microcirculation: An Insight into Flowmotion Assessed by Wavelet Transform

Simple Summary

There is increasing evidence to suggest that microcirculation becomes dysfunctional earlier than large blood vessels or the heart in several diseases. In diabetes mellitus, a disease characterized by chronic hyperglycemia, microvascular impairment is well-established; on the contrary, the effect of acute hyperglycemia in microcirculation remains unclarified. Our aim was to investigate the microvascular effect of an oral glucose load (OGL) using laser Doppler flowmetry (LDF) as a perfusion quantification technique, coupled with wavelet transform (WT) to perform a spectral decomposition of the LDF signal. On two distinct occasions (pre-load and post-load), sixteen healthy subjects drank either a standard glucose solution or water. Perfusion was assessed by LDF and WT while resting and during post-occlusive reactive hyperemia (PORH), evoked by a transient three-min occlusion of the brachial artery, in the forearm and the finger pulp. The OGL affected microcirculation in both sites compared to water, significantly blunting the PORH response in the forearm. The WT revealed significant differences in the cardiac and sympathetic components after OGL between the pre-load and post-load periods. These results suggest that an OGL induces a short-term subtle microvascular impairment, probably involving a modulation of the sympathetic nervous system.

Abstract

Microcirculation in vivo has been assessed using non-invasive technologies such as laser Doppler flowmetry (LDF). In contrast to chronic hyperglycemia, known to induce microvascular dysfunction, the effects of short-term elevations in blood glucose on microcirculation are controversial. We aimed to assess the impact of an oral glucose load (OGL) on the cutaneous microcirculation of healthy subjects, quantified by LDF and coupled with wavelet transform (WT) as an interpretation tool. On two separate occasions, sixteen subjects drank either a glucose solution (75 g in 250 mL water) or water (equal volume). LDF signals were obtained in two anatomical sites (forearm and finger pulp) before and after each load (pre-load and post-load, respectively), in resting conditions and during post-occlusive reactive hyperemia (PORH). The WT allowed decomposition of the LDF signals into their spectral components (cardiac, respiratory, myogenic, sympathetic, endothelial NO-dependent). The OGL blunted the PORH response in the forearm, which was not observed with the water load. Significant differences were found for the cardiac and sympathetic components in the glucose and water groups between the pre-load and post-load periods. These results suggest that an OGL induces a short-term subtle microvascular impairment, probably involving a modulation of the sympathetic nervous system.

Postprandial Changes in Gastrointestinal Hormones and Hemodynamics after Gastrectomy in Terms of Early Dumping Syndrome

Purpose

This study aimed to examine the early postprandial changes in gastrointestinal (GI) hormones and hemodynamics in terms of early dumping syndrome after gastrectomy for gastric cancer.

Materials and Methods

Forty patients who underwent gastrectomy for gastric cancer and 18 controls without previous abdominal surgery were enrolled. Before and 20 minutes after liquid meal ingestion, blood glucose, glucagon-like peptide-1 (GLP-1), and GLP-2 concentrations and superior mesenteric artery (SMA) and renal blood flow were measured. The patients' heart rates were recorded at 5-minute intervals. All subjects were examined for dumping syndrome using a questionnaire based on Sigstad's clinical diagnostic index.

Results

The postprandial increases in blood glucose, GLP-1, and GLP-2 levels as well as SMA blood flow and heart rate were greater in patients who underwent gastrectomy than in controls (all P<0.010). Patients who underwent gastrectomy showed a significantly decreased renal blood flow (P<0.001). Among patients who underwent gastrectomy, distal gastrectomy was a significant clinical factor associated with a lower risk of early dumping syndrome than total gastrectomy (hazard ratio, 0.092; 95% confidence interval, 0.013–0.649; P=0.017). Patients who underwent total gastrectomy showed a greater postprandial increase in blood glucose (P<0.001), GLP-1 (P=0.030), and GLP-2 (P=0.002) levels as well as and heart rate (P=0.013) compared to those who underwent distal gastrectomy.

Conclusions

Early postprandial changes in GI hormones and hemodynamics were greater in patients who underwent gastrectomy than in controls, especially after total gastrectomy, suggesting that these changes play a crucial role in the pathophysiology of early dumping syndrome.

Comprehensive MRI assessment of the cardiovascular responses to food ingestion in Fontan physiology

In univentricular (Fontan) physiology, peripheral and splanchnic vascular tone may be raised to counteract reduced cardiac output (CO) and elevated central venous pressure and thus maintain vital organ perfusion. This could negatively affect the normal cardiovascular response to food ingestion, where mesenteric vasodilation and a concurrent rise in CO are central. We sought to elucidate this using rapid cardiovascular MRI. Thirty fasting subjects (50% controls, 40% women and 60% men) ingested a standardized meal. Responses over ~50 min in mean arterial pressure (MAP), CO, and blood flow in all major aortic branches were measured, and regional vascular impedance (Z0) was calculated. Differences from baseline and between groups were assessed by repeated-measures mixed models. Compared with the control group, the Fontan patient group had greater fasting Z0 of the legs and kidneys, resulting in greater systemic Z0 and similar MAP. They further had similar blood flow to the digestive organs at baseline, despite larger variation in mesenteric resistance. Postprandially, blood flow to the legs decreased in the control group but not in the Fontan patient group. Increases in CO and superior mesenteric blood flow were similar in both groups, but the celiac response was blunted in the Fontan patient group. No significant differences in MAP responses were observed. In conclusion, alterations in vascular tone to counteract adverse hemodynamics and raised hepatic afterload may blunt vasoreactivity in the legs and the celiac axis in Fontan physiology. Further study is needed to determine whether blunted celiac or mesenteric vasoreactivity is linked to deteriorating hemodynamics and poor prognosis in Fontan patients.NEW & NOTEWORTHY Novel data on cardiovascular physiology in response to a meal in Fontan patients are presented. Using a previously validated dynamic MRI protocol, we demonstrated that the usual increase in cardiac output and the dilation of the superior mesenteric artery are preserved in clinically well Fontan patients. In contrast, vasoconstriction of the legs may have prevented redistribution of blood flow from this region in response to the meal. This may also affect responses to other types of stress. Celiac vasodilation was also absent in Fontan patients. This may be due to abnormal hepatic circulation. The proposed protocol may be used to study Fontan complications secondary to abnormal regional hemodynamics.

Meal Ingestion and Hemodynamic Interactions Regarding Renal Blood Flow on Duplex Sonography: Potential Diagnostic Implications

Splanchnic blood flow changes dramatically after meal ingestion. The present study evaluated physiologic interactions between meal ingestion and hemodynamics with respect to renal blood flow on duplex sonography, assessing the possible influence on Doppler parameters used as diagnostic criteria for renal artery stenosis. Subjects comprised 26 healthy young men (mean age: 22 ± 2 y). Sonographic measurements were made shortly after breakfast and every 1 h thereafter and were compared with values measured before the meal. Peak systolic velocity in the renal artery was elevated post-prandially, peaking at 1 h (90 ± 12 cm/s), compared with pre-prandially (73 ± 10 cm/s, p < 0.01). Similarly, acceleration time at the intra-renal segmental artery shortened to a minimum at 1 h (45 ± 5 ms) compared with baseline (51 ± 6 ms, p < 0.01). The present study indicates that renal blood flow is altered for a few hours after meal ingestion. Attention should be paid to the interpretation of data measured after meals on duplex sonography for diagnosis of renal artery stenosis.

Systematic review: the impact of exercise on mesenteric blood flow and its implication for preoperative rehabilitation

BACKGROUND

Exercise in the preoperative period, or prehabilitation, continues to evolve as an important tool in optimising patients awaiting major intra-abdominal surgery. It has been shown to reduce rates of post-operative morbidity and length of hospital stay. The mechanism by which this is achieved remains poorly understood. Adaptations in mesenteric flow in response to exercise may play a role in improving post-operative recovery by reducing rates of ileus and anastomotic leak.

AIMS

To systematically review the existing literature to clarify the impact of exercise on mesenteric arterial blood flow using Doppler ultrasound.

METHODS

PubMed, EMBASE and the Cochrane library were systematically searched to identify clinical trials using Doppler ultrasound to investigate the effect of exercise on flow through the superior mesenteric artery (SMA). Data were extracted including participant characteristics, frequency, intensity, timing and type of exercise and the effect on SMA flow. The quality of each study was assessed using the Downs and Black checklist.

RESULTS

Sixteen studies, comprising 305 participants in total, were included. Methodological quality was generally poor. Healthy volunteers were used in twelve studies. SMA flow was found to be reduced in response to exercise in twelve studies, increased in one and unchanged in two studies. Clinical heterogeneity precluded a meta-analysis.

CONCLUSION

The weight of evidence suggests that superior mesenteric arterial flow is reduced immediately following exercise. Differences in frequency, intensity, timing and type of exercise make a consensus difficult. Further studies are warranted to provide a definitive understanding of the impact of exercise on mesenteric flow.

Comprehensive assessment of the global and regional vascular responses to food ingestion in humans using novel rapid MRI

Ingestion of food is known to increase mesenteric blood flow. It is not clear whether this increased flow demand is compensated by a rise in cardiac output (CO) alone or by redistribution of blood flow from other organs. We used a new comprehensive imaging method to assess the human cardiovascular response to food ingestion. Following a 12-h fast, blood flow in segments of the aorta and in organ-specific arteries, and ventricular volumes were assessed in 20 healthy adults using MRI at rest and following ingestion of a high-energy liquid meal. Systemic vascular resistance (SVR) fell substantially and CO rose significantly. Blood pressure remained stable. These changes were predominantly driven by a rapid fall in mesenteric vascular resistance, resulting in over four times more intestinal blood flow. Renal vascular resistance also declined but less dramatically. No changes in blood flow to the celiac territory, the brain, or the limbs were observed. In conclusion, this is the first study to fully characterize systemic and regional changes in vascular resistance after food ingestion in humans. Our findings show that the postprandial drop in SVR is fully compensated for by increased CO and not by redistribution of blood from other organs. With the exception of a modest increase in renal blood flow, there was no evidence of altered blood flow to nondigestive organs. The proposed oral food challenge protocol can be applied safely in an MRI environment and may be useful for studying the involvement of the gut in systemic or cardiovascular disease.

Vascular Doppler ultrasonographic indices in cirrhosis: a case-control study with emphasis on the common carotid arteries

PURPOSE

To compare vascular Doppler waveform indices, particularly in the common carotid arteries, between cirrhotic and healthy subjects.

MATERIALS AND METHODS

A total of 60 patients with Class-B cirrhosis and 60 healthy matched counterparts were enrolled in this prospective study. Vascular Doppler waveform parameters including resistance and/or pulsatility indices (RI and PI, respectively) were obtained from the common carotid, renal, celiac, superior mesenteric, femoral and brachial arteries.

RESULTS

Compared to patients, healthy subjects had significantly higher mean PI and RI obtained from the common carotid (1.53 ± 0.20 vs. 1.43 ± 0.14, p = 0.03; 0.75 ± 0.02 vs. 0.72 ± 0.02, p < 0.001, respectively) and celiac arteries (2.00 ± 0.36 vs. 1.81 ± 0.34, p = 0.03; 0.80 ± 0.03 vs. 0.78 ± 0.02, p < 0.001, respectively). Both the mean PI and RI derived from the renal arteries, in contrast, were significantly higher in patients compared to that in controls (1.05 ± 0.13 vs. 1.11 ± 0.07, p = 0.03; 0.59 ± 0.03 vs. 0.63 ± 0.03, p < 0.001, respectively). The mean vascular impedance values obtained from the remaining arteries were comparable between the two groups.

CONCLUSIONS

Blood flow increases in the common carotid and celiac arteries of Class-B cirrhotic patients with elevated renovascular impedance.

The effect of glucagon-like peptide-2 on arterial blood flow and cardiac parameters

BACKGROUND

Glucagon-like peptide-2 (GLP-2) is known to increase mesenteric blood flow. The aim of the study was to evaluate the effect of GLP-2 on blood flow in different vascular sites, and dynamic changes in cardiac parameters.

METHODS

10 healthy volunteers were given 450 nmol subcutaneous (SC) GLP-2 or isotonic saline (5 subjects) in a single blinded manner. During the following 90 min, blood flow in the superior mesenteric artery (SMA), celiac artery (CA), renal artery (RA), common carotid artery (CCA) was measured using Doppler ultrasound (US), and cardiovascular variables were measured by impedance cardiography and finger plethysmography. Plasma GLP-2 was measured at times 0, 30 and 60 min.

RESULTS

Compared to the placebo group, GLP-2 elicited a 27% decrease in the resistance index (RI) and a 269.4% increase in Time Averaged Maximal Velocity (TAMV) in the SMA (P<0.01). CA, RA and CCA: There were no significant changes in RI or TAMV in the GLP-2 or placebo group, and no change in CA diameter. Cardiac parameters: GLP-2 increased cardiac output (CO), stroke volume (SV) and heart rate (HR) compared to baseline (respectively: 15.3, 4.81 and 8.2% (P<0.001, P<0.01 and P<0.01)). The CO, SV and HR changes were not significantly different from the placebo group. Mean plasma GLP-2 serum levels in the placebo group at times 0, 30 and 60 min were 22.8, 23.4 and 23.2 pmol/l. In the GLP-2 group 20.3, 1273 and 1725 pmol/l.

CONCLUSION

SC GLP-2 increased SMA blood flow, as previously shown, but elicited no changes in other vascular sites. CO and HR increased significantly, presumably due to the increased mesenteric blood flow.

The role of Doppler sonography in predicting severity of acute pancreatitis

PURPOSE

To investigate the role of Doppler sonography (DUS) examination of major abdominal arteries in predicting severity of acute pancreatitis (AP).

METHODS

Twenty-nine patients diagnosed with AP and 14 controls were blindly and prospectively evaluated with Doppler sonography. Disease severity was defined clinically according to acute physiology and chronic health evaluation (APACHE II) score and was classified as severe for APACHE II score > or =8. DUS examination included the measurement of peak systolic velocity (PSV), end diastolic velocity (EDV), pulsatility index (PI), and resistance index (RI) of the celiac artery (CA) and superior mesenteric artery (SMA). Statistical analysis included Mann-Whitney U test, Student t test, and receiver operating characteristic curve analysis.

RESULTS

Twelve patients had severe AP and 17 had mild AP. PSV, EDV, and PI of the CA and RI of the SMA were higher in the severe AP group than in the mild AP and control groups (p < 0.001 and p < 0.0001, respectively). The sensitivity and specificity were 100% and 94%, respectively, for a 87 cm/second CA PSV cutoff value, 75% and 100%, respectively, for a 22 cm/second CA EDV cutoff value, 92% and 82%, respectively, for a 1.29 CA PI cutoff value, and 100% and 100%, respectively, for a 0.86 SMA RI cutoff value.

CONCLUSION

DUS can be useful in predicting the severity of AP in the early period of admission phase of the disease.

Different haemodynamic effects of a single dose of long-acting isosorbide-5-mononitrate in healthy subjects and patients with cirrhotic portal hypertension

BACKGROUND

The action pathways of nitrates are hypothesised to be deranged in cirrhosis.

AIM

In order to confirm it, the acute haemodynamic effects of isosorbide-5-mononitrate in cirrhotic patients and controls was investigated.

PATIENT

Nine cirrhotics and nine healthy controls.

METHODS

Evaluation in the fasting state, 90 min after isosorbide-5-mononitrate or placebo (double-blind on two different days) and then 30 and 120 min after eating a standard meal. Various systemic and splanchnic haemodynamic parameters, including arterial impedance, assessed as Doppler pulsatility index, were measured.

RESULTS

isosorbide-5-mononitrate reduced arterial pressure and increased heart rate and mesenteric pulsatility index both in controls and in cirrhotics, whereas the following parameters behaved differently in the two groups (P < 0.05): hepatic pulsatility index decreased (-9%) and the portal velocity increased (+13%) in controls, whereas hepatic pulsatility increased (+18%) and portal velocity decreased (-18%) in cirrhotics. The two groups presented a similar pattern of changes in most variables under placebo after a meal. In controls, the administration of isosorbide-5-mononitrate blunted the postprandial mesenteric vasodilation and related changes in splanchnic and systemic circulation, expected at 30 min, in comparison to those observed under placebo. In cirrhotics, instead, the postprandial pattern was similar under placebo and isosorbide-5-mononitrate.

CONCLUSIONS

The acute administration of isosorbide-5-mononitrate produces different haemodynamic effects in healthy and diseased livers, both in the fasting state and after a meal, consistent with the hypothesis of a deranged response of the intrahepatic microcirculation to nitrates in cirrhosis.

Ultrasonographic splanchnic arterial flow measurement in severe acute pancreatitis

INTRODUCTION

Duplex ultrasonographic technology is now capable of detecting flow signals in the various splanchnic vessels and calculating the concomitant flow velocities using fast-Fourier transformation.

AIM

To use Doppler sonography to investigate how splanchnic hemodynamics vary during the early stage of severe acute pancreatitis.

METHODOLOGY

Six patients with severe acute pancreatitis (age, 59.0 +/- 6.57 years; four men, two women) and seven with mild to moderate acute pancreatitis (age, 60.1 +/- 7.41 years; five men, two women) were examined with Doppler sonography immediately after disease onset. The maximum velocity, minimum velocity, mean velocity, pulsatility index, and resistive index were determined from the Doppler spectra from the proper hepatic artery, celiac artery, and superior mesenteric artery. We also examined 15 healthy subjects (age, 59.3 +/- 4.60 years; 10 men, five women) as controls.

RESULTS

The maximum velocity of the proper hepatic artery in patients with severe acute pancreatitis was significantly higher than that in patients with mild to moderate acute pancreatitis (p = 0.011) and in control subjects (p = 0.0047). Similarly, significant increases in both the minimum velocity and the mean velocity of the proper hepatic artery were observed in patients with severe acute pancreatitis. Neither pulsatility index nor resistive index of the proper hepatic artery showed a significant difference among the three groups. There were no significant differences among the three groups with respect to the flow velocity of the superior mesenteric artery. In contrast, the pulsatility index of the superior mesenteric artery in patients with severe acute pancreatitis was significantly lower than that in patients with mild to moderate acute pancreatitis (p = 0.0058) or in control subjects (p = 0.0024). For patients with acute pancreatitis, a significant inverse correlation was obtained between the maximum velocity of the proper hepatic artery and the pulsatility index of the superior mesenteric artery (r = -0.658, p = 0.0145).

CONCLUSION

The increase in the hepatic arterial flow velocity and the decrease in the superior mesenteric arterial pulsatility index may represent early events of the severe type of acute pancreatitis.

Changes in renal artery resistance after meal-induced splanchnic vasodilatation in cirrhotic patients

PURPOSE

A relationship between vasomotor tone changes in mesenteric and renal vessels in cirrhotic patients has been suspected but remains controversial. The aim of this study was to assess by duplex Doppler sonography the changes in the circulatory resistance of the renal arteries and superior mesenteric artery (SMA) following meal-induced splanchnic vasodilatation.

METHODS

Twenty-seven cirrhotic patients and 15 healthy volunteers with no hepatic or renal dysfunction were prospectively included in the study. The resistance index (RI) of the SMA and of the right and left renal arteries was measured by duplex Doppler sonography before and 30 minutes after ingestion of a standard 400-kcal balanced liquid meal. Values in controls and patients and values before and after the meal were compared, and correlations between RIs, Child-Pugh class (liver function), and creatinine clearance were assessed in cirrhotic patients.

RESULTS

The fasting renal artery RI was greater in cirrhotic patients than in controls (p < 0.0001), but there was no difference in fasting SMA RIs. After the meal, there was a significant decrease in the SMA RI in controls (0.85 +/- 0.04 before versus 0.74 +/- 0.03 after meal, p = 0.0001) and in cirrhotic patients (0.85 +/- 0.04 before versus 0.77 +/- 0.04 after, p = 0.0001) and a significant increase in the renal artery RI (0.57 +/- 0.06 before versus 0.62 +/- 0.05 after in controls, p = 0.001; 0.68 +/- 0.07 before versus 0.70 +/- 0.07 after in cirrhotic patients, p = 0.001). No correlation was found in cirrhotic patients between the changes in renal artery RI and the postprandial SMA RI decrease, the Child-Pugh class, or the creatinine clearance.

CONCLUSIONS

Meal-induced SMA vasodilatation (RI decrease) is associated with a marked increase in the renal artery RI, worsening the renal vasoconstriction in cirrhotic patients.

Effect of transcatheter arterial chemoembolization on kidney hemodynamics and function in patients with cirrhosis and hepatocellular carcinoma

BACKGROUND/AIMS

Transcatheter arterial chemoembolization (TACE) may have deleterious effect on the kidney in patients with cirrhosis and hepatocellular carcinoma. The aim of the study was to test this hypothesis.

METHODS

Twenty-four patients with cirrhosis and hepatocellular carcinomas were included. They consisted of 16 patients undergoing a single TACE and eight patients undergoing diagnostic angiography. Doppler ultrasonography was used to measure hepatic artery pulsatility index (HA-PI) and renal artery pulsatility index (RA-PI) before and 1 day and 10 days after the procedure. Similarly, kidney function was assessed by measuring creatinine clearance. In addition, plasma renin activity, noradrenaline, and endothelin-1 were also measured.

RESULTS

In patients receiving diagnostic angiography, no significant changes in HA-PI were observed after the procedure. In contrast, HA-PI increased significantly 1 day after the procedure (19%, p<0.01) in patients undergoing TACE, although it returned to baseline value 10 days after the procedure. In patients undergoing diagnostic angiography, no significant changes in RA-PI were observed after the procedure. Similarly, no detectable changes in RA-PI were noted in patients undergoing TACE. A transient small reduction in creatinine clearance was noted after the procedure in patients undergoing diagnostic angiography (-12%, p<0.05) and in those undergoing TACE (-11%, p<0.05). However, the effect was similar in the two groups (two-way ANOVA, p=0.72). No significant changes in plasma renin activity, noradrenaline, and endothelin-1 were observed after either diagnostic angiography or TACE.

CONCLUSIONS

These results suggest that TACE per se has no deleterious effect on the kidney hemodynamics and function in patients with cirrhosis and hepatocellular carcinoma.