Post-prandial cardiovascular responses in man after ingestion of carbohydrate, protein or fat

Sex-dependent impact of a short rest after lunch on hemodynamics as assessed by Doppler sonography

PURPOSE

Taking a short rest after lunch suppresses increases in blood flow to the digestive organs and maintains blood flow to the brain in the afternoon, possibly providing beneficial effects in preventing post-prandial drowsiness. The present study investigated sex-dependent influences on changes in hemodynamics produced by taking a short rest after lunch.

METHODS

Subjects comprised 20 healthy young adults (10 men, 10 women; mean age 21 ± 1 years). Doppler sonography was performed to measure blood flow in the superior mesenteric artery (SMA) and common carotid artery (CCA) before and after lunch every hour on each day, with and without a 15-min rest with eyes closed after lunch. Blood pressure and heart rate (HR) were also measured.

RESULTS

For both men and women, peak systolic velocity (PSV) in the SMA was suppressed by taking a rest. PSV in the CCA in men was increased at 0.5 h after lunch in the resting condition but was decreased in the non-resting condition (median 109%, interquartile range [IQR] 102-120% vs. median 98%, IQR 90-107%; P = 0.037). No such differences were observed in women. Although post-prandial increases in HR were observed in women, a similar increase was only found for men in the resting condition.

CONCLUSION

An increase in CCA blood flow was observed only in men. The present study suggests that a short rest after lunch could better promote the maintenance of blood flow to the brain in men than in women.

The Influence of Food Intake and Preload Augmentation on Cardiac Functional Parameters: A Study Using Both Cardiac Magnetic Resonance and Echocardiography

(1) Background: To investigate how food intake and preload augmentation affect the cardiac output (CO) and volumes of the left ventricle (LV) and right ventricle (RV) assessed using cardiac magnetic resonance (CMR) and trans-thoracic echocardiography (TTE). (2) Methods: Eighty-two subjects with (n = 40) and without (n = 42) cardiac disease were assessed using both CMR and TTE immediately before and after a fast infusion of 2 L isotonic saline. Half of the population had a meal during saline infusion (food/fluid), and the other half were kept fasting (fasting/fluid). We analyzed end-diastolic (EDV) and end-systolic (ESV) volumes and feature tracking (FT) using CMR, LV global longitudinal strain (GLS), and RV longitudinal strain (LS) using TTE. (3) Results: CO assessed using CMR increased significantly in both groups, and the increase was significantly higher in the food/fluid group: LV-CO (ΔLV-CO: +2.6 ± 1.3 vs. +0.7 ± 1.0 p < 0.001), followed by increased heart rate (HR) (ΔHR: +12 ± 8 vs. +1 ± 6 p < 0.001). LV and RV achieved increased stroke volume (SV) through different mechanisms. For the LV, through increased contractility, increased LV-EDV, decreased LV-ESV, increased LV-FT, and GLS were observed. For the RV, increased volumes, increased RV-EDV, increased RV-ESV, and at least for the fasting/fluid group, unchanged RV-FT and RV-LS were reported. (4) Conclusions: Preload augmentation and food intake have a significant impact on hemodynamic and cardiac functional parameters. This advocates for standardized recommendations regarding oral intake of fluid and food before cardiac assessment, for example, TTE, CMR, and right heart catheterization. We also demonstrate different approaches for the LV and RV to increase SV: for the LV by increased contractility, and for the RV by volume expansion.

Effects of Fermented Garlic Extract Containing Nitric Oxide Metabolites on Blood Flow in Healthy Participants: A Randomized Controlled Trial

Aged or fermented garlic extract (FGE) is a natural remedy that improves vascular function through increasing vascular nitric oxide (NO) bioavailability. This is because nitrite (NO2-), a NO metabolite, can be produced through bioconversion with macrobacteria during the fermentation of foods like garlic. We aimed to evaluate the effects of NO2- in FGE on blood flow (BF), blood pressure (BP), velocity of the common carotid artery (CCA) and internal carotid artery (ICA), regional cerebral BF (rCBF), and peripheral BF (PBF). The study was divided into two parts: (1) Thirty healthy adults were divided into FGE and placebo groups to compare BP and velocity of the CCA and ICA; and (2) Twenty-eight healthy adults were divided into FGE and placebo groups to compare rCBF and PBF and determine changes before/after ingestion. Significant changes were noted in BP and the velocity of both CCA 30-60 min after FGE ingestion. FGE ingestion resulted in significant increases in rCBF and increases in body surface temperature through alterations in PBF. No detectable clinical side effects were noted. Overall, oral administration of NO2- containing FGE demonstrated acute positive effects in upregulating BF, including the CCA, BP, rCBF, and PBF. Follow-up studies with larger sample sizes and long-term ingestion may be needed.

Possible effects of short rest after lunch on hemodynamics in the afternoon

PURPOSE

Drowsiness is often experienced in the afternoon after lunch. Decreases in blood flow to the brain secondary to increases in blood flow to the digestive organs after food intake could represent an underlying cause. As various beneficial effects of short rests on mental activities have been reported, the present study investigated hemodynamics using Doppler sonography of the common carotid artery (CCA) and superior mesenteric artery (SMA) after lunch, comparing resting and non-resting cases.

METHODS

Subjects comprised 24 healthy young adults (10 men, 14 women; mean age 22 ± 1 years). Sonography was performed to measure blood flow before and after lunch on each day, with and without a 15-min lying rest with eyes closed after lunch in each subject.

RESULTS

The timing of the peak velocity-time integral in the SMA in resting cases was delayed to 1.5 h after lunch compared to 0.5 h in non-resting cases. Although end-diastolic velocity in the CCA decreased after lunch, this decrease was suppressed in resting cases compared to non-resting cases even 4.5 h after lunch (median 96%, interquartile range [IQR] 83-102% vs. median 87%, IQR 77-92%; P = 0.037). Mean velocity (MV) in the CCA maintained unchanged after lunch in resting cases (P = 0.318), whereas non-resting cases showed decreased MV after lunch (P < 0.001).

CONCLUSION

These findings suggest that a short lying rest with eyes closed suppresses increases in blood flow to the digestive organ and maintains blood flow to the brain after lunch. These hemodynamic changes might help explain the benefits of afternoon rests.

Effects of age on blood pressure and heart rate responses to whey protein in younger and older men

BACKGROUND

Postprandial falls in blood pressure (BP) are more common in older compared to younger individuals. The effects of protein compared to carbohydrates and fat on postprandial BP, and the relation to gastric emptying rates, are poorly studied.

OBJECTIVES

To determine the effects of a whey protein compared to a control drink on systolic BP (SBP) and diastolic BP (DBP), and heart rate (HR) in healthy younger and older men, and to relate these effects to gastric emptying.

DESIGN

A pooled analyses of two randomized, double-blind, cross-over studies.

SETTING

Two acute clinical intervention studies with identical study design.

PARTICIPANTS

Nineteen older (age: 74 ± 1 years, body mass index: 26 ± 1 kg/m² ) and 13 younger (23 ± 1 years, 24 ± 1 kg/m² ) healthy men.

INTERVENTION

A 70 g/280 kcal whey-protein or control (water with diet cordial, ~2 kcal) drink (450 ml).

MEASUREMENTS

BP and HR were assessed with an automated device immediately before and at 3-min intervals after drink ingestion (0-180 min). Gastric emptying of the drinks was measured using 3D ultrasonography (0-180 min).

RESULTS

Older versus younger men exhibited a greater fall in SBP (-23 ± 2 vs -15 ± 2 mmHg, p = 0.001) after whey-protein versus control, as BP did not change after the two drinks in younger men (p > 0.05). The nadir in SBP occurred later in the older than younger men (114 ± 11 vs 62 ± 14 min; p < 0.001), with SBP still apparently declining 180 min after whey-protein ingestion in the older men. The magnitude of the rise in HR was greater (p < 0.05) in the younger than older men.

CONCLUSION

Following ingestion of 70 g whey protein, healthy older men exhibited a sustained fall in BP, despite an increase in HR, whereas in younger men there was no change in BP. BP may need to be monitored after high protein meals in older people at risk of postprandial hypotension.

A high-protein meal does not improve blood pressure or vasoactive biomarker responses to acute exercise in humans

Blood pressure (BP) responses to exercise yield prognostic information beyond resting BP. While habitual higher dietary protein intake is associated with reduced resting BP, few studies have assessed the impact of high-protein meals on acute BP and vasoactive biomarker responses to exercise. To test the hypothesis that consuming a higher-protein, lower fat meal (HP; 30 g protein, 17 g fat, 52 g carbohydrate) would attenuate the BP response to exercise and result in a more robust post-exercise hypotensive response compared to a lower-protein, higher-fat meal (LP; 13 g protein, 25 g fat, 54 g carbohydrate), we recruited 31 pre-hypertensive subjects to complete this randomized, double-blind, cross-over acute feeding study. One hundred sixty-five minutes after consuming the test HP or LP meal, subjects exercised on a cycle ergometer at 70% VO₂ max for 30 minutes. Blood pressure was measured prior to the meal and periodically before, during, and after exercise for a 315-minute period. Blood samples were periodically collected to quantify plasma arginine, arginine metabolites (asymmetric dimethylarginine, symmetric dimethylarginine; ADMA, SDMA), endothelin-1, nitrates, and nitrites in a subset of subjects (n = 15) as shown in Supplemental Table S1. Consuming the HP meal did not influence the BP responses to exercise, including the post-exercise return to baseline BP or systolic BP area under the curve. While the HP meal resulted in greater postprandial plasma arginine concentrations, ADMA, SDMA, endothelin-1, nitrates, and nitrites were unaltered. These results suggest that consuming a higher-protein, lower-fat meal does not influence BP or vasoactive biomarker responses to exercise compared to a lower-protein, higher-fat meal.

High-glucose mixed-nutrient meal ingestion impairs skeletal muscle microvascular blood flow in healthy young men

Oral glucose ingestion leads to impaired muscle microvascular blood flow (MBF), which may contribute to acute hyperglycemia-induced insulin resistance. We investigated whether incorporating lipids and protein into a high-glucose load would prevent postprandial MBF dysfunction. Ten healthy young men (age, 27 yr [24, 30], mean with lower and upper bounds of the 95% confidence interval; height, 180 cm [174, 185]; weight, 77 kg [70, 84]) ingested a high-glucose (1.1 g/kg glucose) mixed-nutrient meal (10 kcal/kg; 45% carbohydrate, 20% protein, and 35% fat) in the morning after an overnight fast. Femoral arterial blood flow was measured via Doppler ultrasound, and thigh MBF was measured via contrast-enhanced ultrasound, before meal ingestion and 1 h and 2 h postprandially. Blood glucose and plasma insulin were measured at baseline and every 15 min throughout the 2-h postprandial period. Compared with baseline, thigh muscle microvascular blood volume, velocity, and flow were significantly impaired at 60 min postprandial (-25%, -27%, and -46%, respectively; all P < 0.05) and to a greater extent at 120 min postprandial (-37%, -46%, and -64%; all P < 0.01). Heart rate and femoral arterial diameter, blood velocity, and blood flow were significantly increased at 60 min and 120 min postprandial (all P < 0.05). Higher blood glucose area under the curve was correlated with greater MBF dysfunction (R² = 0.742; P < 0.001). Ingestion of a high-glucose mixed-nutrient meal impairs MBF in healthy individuals for up to 2 h postprandial.

Cardiovascular and Orthostatic Responses to a Festive Meal Associated With Alcohol in Young Men

Aim: Sharing a festive meal associated with alcohol is quite common. While the cardiovascular changes occurring after meal ingestion of different nutrient composition has been well-established, the effects of ingesting a festive versus a standard meal accompanied with alcohol are less clear. Here, we compared the postprandial hemodynamics, cutaneous and psychomotor performance responses after ingestion of a classical Swiss festive meal [cheese fondue (CF)] versus a light ready-meal [Nasi Goreng (NG)], both accompanied with white wine.

Methods: In a randomized cross over design, we examined in 12 healthy young men, the continuous cardiovascular, cutaneous, and reaction time responses to ingestion of cheese fondue versus a standard meal at rest (sitting position) and hemodynamic changes in response to orthostatic challenge (active standing) in pre- and postprandial phases.

Results: Breath alcohol concentration after wine ingestion was similar after both meal types. Compared to the standard meal, consumption of CF induced higher increases in heart rate (HR), cardiac output (CO), double product (DP) and cardiac power output (CPO), greater vasodilation, and rises in skin blood flow and skin temperature. Greater increases in HR, DP, and mean blood pressure (MBP) were observed during orthostatic challenges with CF compared to NG. A two-choice reaction time task revealed similar reaction times with both meals, suggesting no influence of meal composition on psychomotor performance.

Conclusion: In sitting position, CF ingestion induced a more important cardiovascular load compared to NG. Although the dose of alcohol and the festive meal used here did not lead to orthostatic hypotension, eating CF induced a greater cardiometabolic load suggesting that hemodynamic reserves have been encroached during active standing. This may impede the cardiovascular capacity during physical exercise or stress situations, particularly in elderly subjects who are at greater risk for postprandial hypotension and cardiovascular diseases.

Influence of breakfast on hemodynamics after lunch - a sonographic evaluation of mesenteric and cervical blood flows

Hemodynamics is subject to change after eating meals, which may be related to various postprandial physical statuses such as hypotension or daytime sleepiness. Previous studies have shown that blood flow in the superior mesenteric artery (SMA) increases after meals, but conflicting results have been reported regarding blood flow in the common carotid artery (CCA). In those studies, the fasting interval before the meal was not taken into account. For example, eating breakfast shortly before lunch may affect hemodynamics in these vessels. The present study therefore investigated hemodynamics in the CCA and SMA after lunch, comparing cases with and without breakfast. Subjects comprised 24 healthy young adults (mean age, 22 ± 1 years). Duplex Doppler sonography was performed to measure blood flow values for calculating flow volume (FV) before and after lunch until 3 h postprandially, on each day with breakfast and without breakfast, respectively, in every subject. Net FV after lunch did not differ between cases with and without breakfast, either in the SMA or in the CCA. Blood FV in the SMA was significantly increased after eating lunch regardless of whether breakfast was eaten (P<0·05 each). However, FV in the CCA was significantly decreased until 1 h after lunch compared with the preprandial state in cases without breakfast (P<0·05), but not in cases with breakfast. In conclusion, a sudden decrease in FV in the CCA from the preprandial state is seen after lunch when breakfast is skipped.

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.

Oral glucose challenge impairs skeletal muscle microvascular blood flow in healthy people

Skeletal muscle microvascular (capillary) blood flow increases in the postprandial state or during insulin infusion due to dilation of precapillary arterioles to augment glucose disposal. This effect occurs independently of changes in large artery function. However, acute hyperglycemia impairs vascular function, causes insulin to vasoconstrict precapillary arterioles, and causes muscle insulin resistance in vivo. We hypothesized that acute hyperglycemia impairs postprandial muscle microvascular perfusion, without disrupting normal large artery hemodynamics, in healthy humans. Fifteen healthy people (5 F/10 M) underwent an oral glucose challenge (OGC, 50 g glucose) and a mixed-meal challenge (MMC) on two separate occasions (randomized, crossover design). At 1 h, both challenges produced a comparable increase (6-fold) in plasma insulin levels. However, the OGC produced a 1.5-fold higher increase in blood glucose compared with the MMC 1 h postingestion. Forearm muscle microvascular blood volume and flow (contrast-enhanced ultrasound) were increased during the MMC (1.3- and 1.9-fold from baseline, respectively, P < 0.05 for both) but decreased during the OGC (0.7- and 0.6-fold from baseline, respectively, P < 0.05 for both) despite a similar hyperinsulinemia. Both challenges stimulated brachial artery flow (ultrasound) and heart rate to a similar extent, as well as yielding comparable decreases in diastolic blood pressure and total vascular resistance. Systolic blood pressure and aortic stiffness remained unaltered by either challenge. Independently of large artery hemodynamics, hyperglycemia impairs muscle microvascular blood flow, potentially limiting glucose disposal into skeletal muscle. The OGC reduced microvascular blood flow in muscle peripherally and therefore may underestimate the importance of skeletal muscle in postprandial glucose disposal.

Comparative effects of small intestinal glucose on blood pressure, heart rate, and noradrenaline responses in obese and healthy subjects

Meal consumption leads to an increase in sympathetic output to compensate for hemodynamic changes and maintain blood pressure (BP). Obesity is associated with a blunting of the sympathetic response to meal ingestion, but interpretation of studies investigating these responses is compromised by their failure to account for the rate of gastric emptying, which is an important determinant of postprandial cardiovascular and sympathetic responses and, in both health and obesity, exhibits a wide interindividual variation. We sought to determine the effects of intraduodenal glucose infusion, bypassing gastric emptying, on BP, heart rate (HR), and noradrenaline responses in obese and healthy control subjects. 12 obese subjects (age 36.6 ± 3.9 years, body mass index (BMI) 36.1 ± 1.3 kg/m2 ) and 23 controls (age 27.8 ± 2.4 years, BMI 22.4 ± 0.5 kg/m2 ) received intraduodenal infusions of glucose at 1 or 3 kcal/min, or saline, for 60 min (t = 0-60 min), followed by intraduodenal saline (t = 60-120 min). BP and HR were measured with an automatic cuff, and blood samples collected for measurement of plasma noradrenaline. Intraduodenal glucose at 1 kcal/min was associated with a fall in diastolic BP in the control subjects only (P < 0.01), with no change in systolic BP, HR or noradrenaline in either group. In both groups, intraduodenal glucose at 3 kcal/min was associated with a fall in diastolic (P < 0.01), but not systolic, BP, and rises in HR (P < 0.001) and plasma noradrenaline (P < 0.01), with no difference in responses between the groups. We conclude that cardiovascular and sympathetic responses to intraduodenal glucose infusion are comparable between obese and control subjects, and dependent on the rate of glucose delivery.

Comparative effects of glucose and water drinks on blood pressure and cardiac function in older subjects with and without postprandial hypotension

Postprandial hypotension (PPH) occurs frequently and is thought to reflect an inadequate increase in cardiac output to compensate for the rise in splanchnic blood flow after a meal. Gastric distension by water attenuates the postprandial fall in blood pressure (BP). Cardiac hemodynamics (stroke volume (SV), cardiac output (CO), and global longitudinal strain (GLS)) have hitherto not been measured in PPH We sought to determine the comparative effects of water and glucose drinks on cardiac hemodynamics in healthy older subjects and individuals with PPH Eight healthy older subjects (age 71.0 ± 1.7 years) and eight subjects with PPH (age 75.5 ± 1.0 years) consumed a 300 mL drink of either water or 75 g glucose (including 150 mg ¹³C-acetate) in randomized order. BP and heart rate (HR) were measured using an automatic device, SV, CO, and GLS by transthoracic echocardiography and gastric emptying by measurement of ¹³CO₂ In both groups, glucose decreased systolic BP (P < 0.001) and increased HR, SV, and CO (P < 0.05 for all). The fall in systolic BP was greater (P < 0.05), and increase in HR less (P < 0.05), in the PPH group, with no difference in SV or CO Water increased systolic BP (P < 0.05) in subjects with PPH and, in both groups, decreased HR (P < 0.05) without affecting SV, CO, or GLS In subjects with PPH, the hypotensive response to glucose and the pressor response to water were related (R = -0.75, P < 0.05). These observations indicate that, in PPH, the hypotensive response to oral glucose is associated with inadequate compensatory increases in CO and HR, whereas the pressor response to water ingestion is maintained and, possibly, exaggerated.

Incorporation of the Time-Varying Postprandial Increase in Splanchnic Blood Flow into a PBPK Model to Predict the Effect of Food on the Pharmacokinetics of Orally Administered High-Extraction Drugs

Following a meal, a transient increase in splanchnic blood flow occurs that can result in increased exposure to orally administered high-extraction drugs. Typically, physiologically based pharmacokinetic (PBPK) models have incorporated this increase in blood flow as a time-invariant fed/fasted ratio, but this approach is unable to explain the extent of increased drug exposure. A model for the time-varying increase in splanchnic blood flow following a moderate- to high-calorie meal (TV-Q _Splanch) was developed to describe the observed data for healthy individuals. This was integrated within a PBPK model and used to predict the contribution of increased splanchnic blood flow to the observed food effect for two orally administered high-extraction drugs, propranolol and ibrutinib. The model predicted geometric mean fed/fasted AUC and C _max ratios of 1.24 and 1.29 for propranolol, which were within the range of published values (within 1.0-1.8-fold of values from eight clinical studies). For ibrutinib, the predicted geometric mean fed/fasted AUC and C _max ratios were 2.0 and 1.84, respectively, which was within 1.1-fold of the reported fed/fasted AUC ratio but underestimated the reported C _max ratio by up to 1.9-fold. For both drugs, the interindividual variability in fed/fasted AUC and C _max ratios was underpredicted. This suggests that the postprandial change in splanchnic blood flow is a major mechanism of the food effect for propranolol and ibrutinib but is insufficient to fully explain the observations. The proposed model is anticipated to improve the prediction of food effect for high-extraction drugs, but should be considered with other mechanisms.

Effects of meal ingestion on blood pressure and regional hemodynamic responses after exercise

This study investigated the combined effects of consuming a meal during postexercise hypotension (PEH) on hemodynamics. Nine healthy young male subjects performed each of three trials in random order: 1) cycling at 50% of heart rate reserve for 60 min, 2) oral ingestion of a carbohydrate liquid meal (75 g glucose), or 3) carbohydrate ingestion at 40 min after cycling exercise. Blood pressure, heart rate, cardiac output, and blood flow in the superior mesenteric (SMA), brachial, and popliteal arteries were measured continuously before and after each trial. Regional vascular conductance (VC) was calculated as blood flow/mean arterial pressure. Blood pressure decreased relative to baseline values ( P < 0.05) after exercise cessation. Blood flow and VC in the calf and arm increased after exercise, whereas blood flow and VC in the SMA did not. Blood pressure did not change after meal ingestion; however, blood flow and VC significantly decreased in the brachial and popliteal arteries and increased in the SMA for 120 min after the meal ( P < 0.05). When the meal was ingested during PEH, blood pressure decreased below PEH levels and remained decreased for 40 min before returning to postexercise levels. The sustained increase in blood flow and VC in the limbs after exercise was reduced to baseline resting levels immediately after the meal, postprandial cardiac output was unchanged by the increased blood flow in the SMA, and total VC and SMA VC increased. Healthy young subjects can suppress severe hypotension by vasoconstriction of the limbs even when carbohydrate is ingested during PEH.

Differential acute effects of carbohydrate- and protein-rich drinks compared with water on cardiac output during rest and exercise in healthy young men

The acute effects of drinks rich in protein (PRO) versus carbohydrate (CHO) on cardiovascular hemodynamics and reactivity are uncertain. A randomized crossover design was used to compare 400-mL isoenergetic (1.1 MJ) drinks containing whey protein (PRO; 44 g) or carbohydrate (CHO; 57 g) versus 400 mL of water in 14 healthy men. The primary and secondary outcomes were changes in cardiac output, blood pressure, systemic vascular resistance (SVR) and digital volume pulse measured prior to and 30 min following consumption at rest, during 12 min of multi-stage bicycle ergometry, and 15 min postexercise. The mean change (95% confidence interval (CI)) in resting cardiac output at 30 min was greater for CHO than for PRO or water: 0.7 (0.4 to 1.0), 0.1 (-0.2 to 0.40), and 0.0 (-0.3 to 0.3) L/min (P < 0.001), respectively; the higher cardiac output following CHO was accompanied by an increase in stroke volume and a lower SVR. The mean increments (95% CI) in cardiac output during exercise were CHO 4.7 (4.4 to 5.0), PRO 4.9 (4.6 to 5.2), and water 4.6 (4.3 to 4.9) L/min with the difference between PRO versus water being significant (P < 0.025). There were no other statistically significant differences. In summary, a CHO-rich drink increased cardiac output and lowered SVR in the resting state compared with a PRO-rich drink or water but the effect size of changes in these variables did not differ during or after exercise between CHO and PRO. Neither protein nor carbohydrate affected blood pressure reactivity to exercise.

Acute effects of a mixed meal on arterial stiffness and central hemodynamics in healthy adults

BACKGROUND

Elevated central pressures and arterial stiffness are associated with increased peripheral resistance and higher sympathetic nervous system activity. Additionally, consumption of a meal is known to be sympathoexcitatory. However, the acute effects of a meal on aortic wave reflection and stiffness are unknown. Therefore, we tested the hypothesis that aortic wave reflection and stiffness would increase after a meal.

METHODS

We examined these effects using high-fidelity radial arterial pressure waveforms and carotid-femoral pulse wave velocity measured noninvasively by applanation tonometry before and 60 and 180 minutes after ingestion of a liquid mixed meal (Ensure; 40% of daily energy expenditure) in 17 healthy adults (9 men/8 women; aged 29 ± 2 years). Additionally, we measured sympathetic activity by microneurography at baseline and up to 60 minutes after the meal.

RESULTS

Although sympathetic activity increased after the meal, both peripheral and central pressures were reduced at 180 minutes from baseline (all P < 0.05). Contrary to our hypothesis, augmentation index (14% ± 3% vs. 2% ± 3% vs. 8% ± 3%), augmentation index normalized for heart rate (8% ± 3% vs. -3% ± 3% vs. 3% ± 3%), augmented pressure (5 ± 1 mm Hg vs. 1 ± 1 mm Hg vs. 3 ± 1 mm Hg), and pulse wave velocity (7.1 ± 0.2 m/s vs. 6.7 ± 0.2 m/s vs. 6.7 ± 0.1 m/s) were substantially reduced at 60 and 180 minutes after the meal (all P < 0.05).

CONCLUSIONS

Taken together, our results suggest that a liquid mixed meal acutely decreases central hemodynamics and arterial stiffness in healthy adults, which may be a result of meal-related increases in insulin and/or visceral vasodilation.

The effect of endogenously released glucose, insulin, glucagon-like peptide 1, ghrelin on cardiac output, heart rate, stroke volume, and blood pressure

Background

Ingestion of a meal increases the blood flow to the gastrointestinal organs and affects the heart rate (HR), blood pressure and cardiac output (CO), although the mechanisms are not known. The aim of this study was to evaluate the effect of endogenously released glucose, insulin, glucagon-like peptide 1 (GLP-1), ghrelin on CO, HR, stroke volume (SV), and blood pressure.

Methods

Eleven healthy men and twelve healthy women ((mean ± SEM) aged: 26 ± 0.2 y; body mass index: 21.8 ± 0.1 kg/m²)) were included in this study. The CO, HR, SV, systolic and diastolic blood pressure, antral area, gastric emptying rate, and glucose, insulin, GLP-1 and ghrelin levels were measured.

Results

The CO and SV at 30 min were significantly higher, and the diastolic blood pressure was significantly lower, than the fasting in both men and women (P < 0.05). In men, significant correlations were found between GLP-1 level at 30 min and SV at 30 min (P = 0.015, r = 0.946), and between ghrelin levels and HR (P = 0.013, r = 0.951) at 110 min. Significant correlations were also found between the change in glucose level at 30 min and the change in systolic blood pressure (P = 0.021, r = -0.681), and the change in SV (P = 0.008, r = -0.748) relative to the fasting in men. The insulin 0-30 min AUC was significantly correlated to the CO 0-30 min AUC (P = 0.002, r = 0.814) in men. Significant correlations were also found between the 0-120 min ghrelin and HR AUCs (P = 0.007, r = 0.966) in men. No statistically significant correlations were seen in women.

Conclusions

Physiological changes in the levels of glucose, insulin, GLP-1 and ghrelin may influence the activity of the heart and the blood pressure. There may also be gender-related differences in the haemodynamic responses to postprandial changes in hormone levels. The results of this study show that subjects should not eat immediately prior to, or during, the evaluation of cardiovascular interventions as postprandial affects may affect the results, leading to erroneous interpretation of the cardiovascular effects of the primary intervention.

Trial registration number

NCT01027507

Relationship between postprandial changes in cardiac left ventricular function, glucose and insulin concentrations, gastric emptying, and satiety in healthy subjects

Background

The digestion of food is known to alter the hemodynamics of the body significantly. The purpose of this study was to study the postprandial changes in stroke volume (SV), cardiac output (CO) and left ventricular (LV) longitudinal systolic and diastolic functions measured with tissue Doppler imaging, in relation to gastric emptying rate (GER), satiety, and glucose and insulin concentrations in healthy subjects.

Methods

Twenty-three healthy subjects were included in this study. The fasting and postprandial changes at 30 min and 110 min in CO, heart rate (HR) and blood pressure were measured. Moreover, tissue Doppler imaging systolic (S'), early (E') and late (A') mitral annular diastolic velocities were measured in the septal (s) and lateral (l) walls. Glucose and insulin concentrations, and satiety were measured before and 15, 30, 45, 60, 90, and 120 min after the start of the meal. The GER was calculated as the percentage change in the antral cross-sectional area 15-90 min after ingestion of the meal.

Results

This study show that both CO, systolic longitudinal ventricular velocity of the septum (S's) and lateral wall (S'l), the early diastolic longitudinal ventricular velocity of the lateral wall (E'l), the late diastolic longitudinal ventricular velocity of the septum (A's) and lateral wall (A'l) increase significantly, and were concomitant with increased satiety, antral area, glucose and insulin levels. The CO, HR and SV at 30 min were significantly higher, and the diastolic blood pressure was significantly lower, than the fasting. The satiety was correlated to HR and diastolic blood pressure. The insulin level was correlated to HR.

Conclusions

This study shows that postprandial CO, HR, SV and LV longitudinal systolic and diastolic functions increase concomitantly with increased satiety, antral area, and glucose and insulin levels. Therefore, patients should not eat prior to, or during, cardiac evaluation as the effects of a meal may affect the results and their interpretation.

Trial Registration

ClinicalTrials.gov: NCT01027507

Decreases in splanchnic vascular resistance contribute to hypotensive effects of L-serine in hypertensive rats

l-Serine administration reduces mean arterial pressure (MAP) in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats rendered hypertensive by chronic oral treatment with the nitric oxide synthase inhibitor N(omega)-nitro-l-arginine methyl ester (l-NAME). To determine if the fall in MAP was due to decreases in vascular resistance or cardiac output (CO), and to record regional hemodynamic effects, we measured the distribution of fluorescent microspheres to single bolus intravenous injections of l-serine (1 mmol/kg) in 14-wk-old male WKY, SHR, and l-NAME-treated WKY rats. MAP and total peripheral resistance (TPR) were significantly higher (P < 0.01), whereas CO was lower in l-NAME-treated WKY (P < 0.01) and SHR (P < 0.05). l-Serine administration led to a rapid fall in MAP (WKY 22%, l-NAME-WKY 46%, SHR 34%,) and TPR (WKY 24%, l-NAME-WKY 68%, SHR 53%), whereas CO was elevated. In WKY rats, l-serine induced an increase in blood flow only in the small intestine (53%) while it was more profound in several vascular beds of hypertensive rats [l-NAME-WKY: small intestine (238%), spleen (184%), diaphragm (85%), and liver (65%); SHR: small intestine (217%), spleen (202%), diaphragm (116%), large intestine (105%), pancreas (96%), and liver (93%)]. Pretreatment with a combination of apamin (a small calcium-activated potassium channel inhibitor) and charybdotoxin (an intermediate calcium-activated potassium channel inhibitor) abolished the l-serine-induced changes in blood flow and TPR. l-Serine acts predominantly on apamin- and charybdotoxin-sensitive potassium channels in the splanchnic circulation to increase blood flow, thereby contributing to the fall in TPR and the pronounced blood pressure-lowering effect of l-serine in hypertensive rats.

Effects of intraduodenal glucose, fat, and protein on blood pressure, heart rate, and splanchnic blood flow in healthy older subjects

BACKGROUND

Postprandial hypotension frequently occurs in the elderly. The hypotensive response to a meal is triggered by the interaction of nutrients with the small intestine; information relating to the effects of different macronutrients on blood pressure (BP) is limited and inconsistent.

OBJECTIVE

The objective of the study was to determine the effects of intraduodenal glucose, fat, and protein on BP, heart rate (HR), and superior mesenteric artery (SMA) blood flow in healthy older subjects.

DESIGN

Eight subjects received intraduodenal glucose (64 g), fat (10% oil emulsion), protein (72 g whey), or saline (0.9%) at a rate of 2.7 mL/min for 90 min, followed by intraduodenal saline for 30 min. BP, HR, and SMA blood flow were measured.

RESULTS

The falls in systolic BP during infusions of glucose, fat, and protein did not differ significantly (P=0.97); however, the fall occurred significantly earlier during the glucose infusion; (18+/-3.0 min) than during the fat (46+/-11.0 min; P=0.02) and protein 33+/-7 min; P=0.04) infusions. The increases in HR during glucose, fat, and protein infusions (P<0.0001 for all) did not differ significantly. SMA blood flow increased significantly after all infusions (P<0.001 for all), but the increase was significantly (P<0.05) lower after protein than after the other infusions.

CONCLUSIONS

Intraduodenal glucose, fat, and protein decrease systolic BP in healthy older subjects, but the onset of the hypotensive response is earlier after glucose, and the effect of protein on SMA blood flow is less than that of the other nutrients.

Periprandial changes of the sympathetic-parasympathetic balance related to perceived satiety in humans

Food intake regulation involves various central and peripheral mechanisms. In this study the relevance of physiological responses reflecting the autonomic nervous system were evaluated in relation to perceived satiety. Subjects were exposed to a lunch-induced hunger-satiety shift, while profiling diverse sensory, physiological, and biochemical characteristics at 15 min intervals. Sensory ratings comprised questionnaires with visual analogues scales about their feeling of satiety, desire to eat, fullness, and hunger. Physiological characteristics included heart rate, heart rate variability, and blood pressure, while biochemical markers such as cortisol levels and α-amylase activity were monitored in saliva. The four sensory ratings correlated with heart rate and salivary α-amylase suggesting a higher sympathetic tone during satiety. Furthermore, heart rate variability was associated with age and waist-to-hip ratio and cortisol levels negatively correlated with body mass index. Finally, neither chewing nor swallowing contributed to a heart rate increase at food consumption, but orosensory stimulation, as tested with modified sham feeding, caused a partial increase of heart rate. In conclusion, after meal ingestion critical physiological alterations reveal a elevated sympathetic tone, which is a potential measure of satiety.

Effects of acute hypobaric hypoxia on resting and postprandial superior mesenteric artery blood flow

Reduced blood flow to the gut may contribute to weight loss and gastrointestinal symptoms of acute mountain sickness (AMS) at altitude. A study in humans tested the hypothesis that acute hypobaric hypoxia (ALT) would attenuate the normal postprandial hyperemia in the superior mesenteric artery (SM). Blood pressure, cardiac output (CO), and (SM) were measured with previously validated noninvasive Doppler ultrasonic flowmetry in 9 (3 women) healthy young adults (mean age: 23; range: 18-33 yr) residing at 1700 m. Baseline measurements were made after 2 h at ALT in a chamber at 430 mmHg (asymptotically equal to 4800 m = 15,750 ft) after 10-12-h fasting, and the next day the control (CON) measurements were made at 615 mmHg (1850 m). Postprandial measurements were made 45 to 60 min after ingesting a 1000-cal liquid meal under both conditions. At ALT, 5 of the 9 subjects had AMS by the Lake Louise score criteria of headache > or =1 and total score > or =3. ALT significantly reduced fasting, baseline SM relative to CON by 15%, and increased CO by 16%. The postprandial CO increase was not different between ALT and CON, but (SM) increased 115% at CON, but only 75% at ALT, the attenuation being significant (p < 0.006). Neither the diminution of fasting (SM) at ALT nor the attenuation of the postprandial increase in (SM) correlated significantly with AMS symptom scores. These results suggest that baseline and postprandial gut blood flow are altered during acute altitude exposure because of increased intestinal sympathetic tone, inferred from increased local resistance, and may be related to reduced energy intake if sustained during prolonged exposure.

Mechanisms behind the postprandial increase in cardiac output: a clue obtained from transplanted hearts

Consumption of a meal is followed by an increase in cardiac output (CO) which appears to be closely related to the concomitant increase in blood flow to the gastrointestinal organs. To gain information on the mechanism behind this increase in CO we have previously used Doppler ultrasound technique to record circulatory responses to a standardized meal in five patients with recently transplanted and thus denervated hearts. We obtained the surprising result that they reacted to the consumption of a meal with a greater increase in CO than did five matched normal controls. The patients also presented above-normal levels of heart rate (HR) and CO at rest. The same five patients have now been tested 18 months later to re-examine their remarkable cardiac response to ingestion of a meal. The hearts of two patients showed some signs of reinnervation, whereas the hearts of the other three were apparently still fully denervated. However, all five patients once again evolved a marked cardiac response to ingestion of a meal. Postprandial CO reached significantly higher levels in the patients than in the controls. The persistence of such a pronounced postprandial augmentation of CO in transplanted and largely denervated hearts strengthens the assumption that the heart is induced to increase its postprandial performance through the action of a humoral agent of some sort, possibly one of the hormones from the duodenal-pancreatic region.

The hypotensive response to oral fat is comparable but slower compared with carbohydrate in healthy elderly subjects

The objective of the present study was to determine the comparative hypotensive responses to drinks containing predominantly fat and carbohydrate (CHO) in healthy elderly subjects. Using a randomised, cross-over study, the participants, twelve elderly subjects, six of them female (72.2 (sd 5.7) years), were investigated. On three separate days, blood pressure (BP) and heart rate were measured following ingestion of 300 ml drinks containing: (1) CHO (75 g glucose and 93 g Polyjoule (CHO polymer) providing 2732 kJ (653 kcal)); (2) 88 % fat (cream blended with milk providing 2732 kJ (653 kcal)); (3) water. Systolic BP decreased following the CHO drink (P<0.001) and the high-fat drink (P<0.001) but not water; there was no difference in the magnitude of the decrease between the CHO drink and the drink containing fat (13.4 v. 15.6 mmHg). However, the onset of the fall was slower after the fat-containing drink (13.0 v. 26.5 min (P=0.01); area under the curve for 0-30 min for CHO drink -6.5 v. fat-containing drink 125.4 mmHg x min (P=0.043)). We conclude that ingestion of a high-fat drink results in a comparable fall in BP to a CHO drink although the onset is relatively slower. These observations may have implications for the management of postprandial hypotension.

Factors affecting the quantitative liver-spleen scan in normal individuals

The quantitative liver-spleen scan (QLSS) can estimate the functional hepatic mass and the organ volumes by precise measurement of sulfur colloid (SC) distribution. The normal range determined in prior studies was estimated from patients with absence of chronic liver disease in which intense fasting appeared to produce slightly abnormal values. This study was to determine the effect of fasting or fed status and colloid particle size on quantitative measurements from the QLSS in a small cohort of normal individuals. Twelve persons without any medical problems had QLSS taken twice, 2 weeks apart, one fasting and one postprandial. Patients were scanned after injection of 5-6 mCi of SC; six patients were given solution A (5- to 12-microm particle size) and six patients solution B (2- to 12-microm particle size). SPECT and planar analysis were performed. SC distribution of total counts between the liver and the spleen {[L/(L + S)]t ratio}, liver-spleen index (LSI), and liver-bone marrow index (LBI) were calculated. The perfused hepatic mass (PHM) is the average of the LSI and LBI. Spleen and liver volumes are expressed as milliliters per pound ideal body weight (IBW). Results showed that the liver and spleen volumes (solution B postprandial, 9.27 +/- 2.48 and 1.47 +/- 0.57 ml/lb IBW, respectively) and LBI were not affected by the type of SC solution or by ingestion status. L/(L + S) total and pixel count ratios were significantly higher for solution B and postprandial studies. [L/(L + S)]t, LSI, and PHM increased significantly (P < 0.05) from fasting to postprandial for solution A (0.71 +/- 0.13 vs 0.79 +/- 0.08, 80 +/- 14 vs 91 +/- 8, and 102 +/- 10 vs 106 +/- 8, respectively) and for solution B (0.81 +/- 0.05 vs 0.90 +/- 0.02, 86 +/- 4 vs 95 +/- 3, and 101 +/- 5 vs 110 +/- 3). Neither fasting nor postprandial LSI and PHM were significantly different between solution A and solution B. We conclude the following. (1) The QLSS functional indices in "true" normal patients fall within the previously reported normal range. (2) Calculated liver and spleen volumes are not altered by fasting or sulfur colloid particle size. (3) Fasting significantly decreased the [L/(L + S)]t, LSI, and PHM. (4) A postprandial scan may be preferable since the normal values for [L/(L + S)]t, LSI, and PHM are greater, with a narrower range, than fasting values.

Postprandial hypotension

Postprandial hypotension is a prevalent condition in the elderly population and seems to be more common in frail elderly individuals who may be more susceptible to complications such as syncope and falls. Diagnosis is relatively easy and may be reversible in many cases. The epidemiology and pathophysiology of postprandial hypotension are not defined fully; however, a number of pathologic processes likely are involved, including abnormal sympathetic function, baroreceptor function, and vasoactive peptide release and activity. The precise relationship between symptoms and postprandial reductions in blood pressure is unclear. Blood pressure maintenance after a meal may depend on the interaction of some or all of the mechanisms outlined previously to compensate for the increase in bowel blood volume. The impairment of one or more of these mechanisms could result in inadequate compensation that leads to hypotension. If so, the presence of symptoms depends on that individual patient's ability to exercise adequate compensatory cerebral autoregulation. A hypertensive elderly patient may experience symptoms with only a small reduction in blood pressure, whereas a patient with autonomic failure may require a much larger fall in blood pressure to occur before they become symptomatic. The current definition of postprandial hypotension uses a threshold of 20 mm Hg as a cut off for diagnosis, but this may not be relevant to the presence or absence of symptoms. Further epidemiologic data are needed. Additionally, there is a lack of controlled trial evidence for the drugs that are used to treat this condition, and treatment often is carried out on a trial-and-error basis. Further research must be performed to identify the specific pathophysiology in certain patient groups, such as elderly hypertensive patients and those with autonomic failure, and to identify effective pharmacologic therapies that can be supported by randomized, placebo-controlled trials.

Circulatory responses to a meal in patients with a newly transplanted heart

It is well established that consumption of a meal releases a gradually developing and quite marked increase in blood flow to the gastrointestinal organs and a similar and simultaneous increase in cardiac output (CO). It is not known through which mechanism the pumping of the heart adjusts so accurately to the gastrointestinal flow increase. We have approached this problem by serving a standardized, mixed meal to five patients with recently transplanted and thus denervated hearts and to five sex- and age-matched controls. Pre- and postprandial levels of CO and blood flow in the superior mesenteric artery (SMA) were recorded with Doppler ultrasound technique. The patients with transplanted hearts had significantly higher preprandial levels of heart rate (HR) and CO than the controls. With a timing similar to that seen in the controls did all five patients develop considerable and synchronous postprandial increases in superior mesenteric arterial flow and in CO. Increases in superior mesenteric arterial flow were significantly greater than the controls. Also, COs, high even before meals were given, increased further and to the same relative extent as in the control persons. The marked postprandial increase in CO, probably secondary to the increase in intestinal blood flow, could hardly come about through any sort of nervous reflex to the recently transplanted and denervated hearts. It appears more likely that a humoral connection of some sort exists between the two circulatory events.

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.

Duplex ultrasound for assessment of superior mesenteric artery blood flow

Duplex ultrasound (DU) is recognised as a valuable tool for the assessment of blood flow in many vascular territories. The application of this technique to the superior mesenteric artery (SMA) has increased rapidly throughout the last decade. The purpose of this review is to collate currently available information on the utility of SMA DU, both in terms of research and clinical practice. Research investigations have revealed low intra- and interobserver variability in the estimation of Doppler variables, while reliable evaluation of B-mode dimensions requires repeated measurements. SMA blood flow velocity has been found to be dependent upon changes in central haemodynamics and in peripheral resistance, which was documented in studies with hypotension, medication and post-prandially. Food intake induces mesenteric vasorelaxation reflected by a 10-fold increase in the diastolic velocity. This feature has been utilised in studies on mesenteric physiology, which confirmed parasympathetic activity during hypovolaemia, and showed that exercise increases splanchnic resistance and reduces its blood flow following a 50% reduction in the hepato-splenic and a 25% reduction in the mesenteric blood flow. Clinical studies have documented high sensitivity and specificity of DU in detection of disease in splanchnic arteries. Diastolic velocity was found to be the most accurate indicator of SMA stenosis, while an absent Doppler signal from a well visualised vessel has been found to be a reliable predictor of occlusion. The high predictive value of DU in the detection of mesenteric artery disease, together with its simplicity and non-invasiveness, suggests that DU should take precedence over arteriography in both clinical practice and laboratory investigations.

Seasonal changes in heart rate and food intake in reindeer (Rangifer tarandus tarandus)

This study tested the hypothesis that the annual cycle in heart rate (HR) in reindeer is, at least in part, a consequence of seasonal fluctuation in voluntary-food intake. Heart rate and daily dry matter voluntary-food intake (DDMVFI) were recorded in two captive female reindeer (Rangifer tarandus tarandus) from April 1995 to August 1996. Heart rate was measured continuously in each animal for 20-24 h for 7 days each month using Polar(R) Sport Testers (PST); DDMVFI was measured in each animal daily for 17 months. Modal daily heart rate (MDHR) and DDMVFI fluctuated seasonally in close synchrony, both reaching maxima in July and minima in January. The relationship between HR and DDMVFI was investigated experimentally by manipulating the level of feeding in a stepwise manner in May, when appetite was low and in August, when DDMVFI was close to maximum. Heart rate showed stepwise changes in close synchrony with the changes in levels of feeding. These results suggest that the seasonal increase in HR in summer is a consequence of increased food intake and, likewise, decreased HR in winter is a consequence of reduced food intake. The observed relationship between food intake and HR presumably reflects changes in cardiac output and/or the rate of flow of blood to the gastrointestinal tract which are influenced by meal size.

Involvement of the human splanchnic circulation in pressor response induced by handgrip contraction

We have analysed the adjustment of blood flow and vascular conductance in the abundantly supplied splanchnic circulation to a generally released pressor reaction. Pressor responses were induced by 2-min periods of standardized, sustained handgrip in seven healthy students. The effects of handgrip tests were followed both in the fasting state and after the consumption of a substantial, mixed meal. In the first of the two sessions, changes in superior mesenteric artery blood flow were recorded and concomitant changes in local vascular conductance derived. In the other session, pressor released cardiac output changes were recorded and changes in total peripheral vascular conductance derived. Both types of flow changes were recorded using ultrasound Doppler technique. Typically, blood flow in the superior mesenteric artery increased two- to threefold after a meal. Handgrip contractions induced an initial rapid increase in heart rate, cardiac output and total peripheral conductance, followed by a gradual decline in total peripheral conductance and stroke volume and a gradual increase in heart rate and mean arterial pressure for the rest of the period. At the end of 2-min pressor periods, total peripheral conductance was only about 10% below the pre-handgrip level, whereas vascular conductance locally in the area of the superior mesenteric artery decreased by some 30%. Thus, it appears that the splanchnic vascular bed contributes markedly to the compound pressor response. Handgrips caused significantly less reduction in local vascular conductance in the post-prandial than in the pre-prandial state, indicating that blood flow to the digesting gastrointestinal tract retains a relatively high priority also in a pressor situation.

Effects of octreotide on postprandial systemic and hepatic hemodynamics in patients with postnecrotic cirrhosis

The effects of octreotide on postprandial hemodynamic responses were evaluated in 20 patients with postnecrotic cirrhosis. They were randomly assigned to receive either a 100-micrograms bolus with a 100-micrograms/h infusion of octreotide or a placebo. Placebo administration did not affect any of the hemodynamic values. However, after a liquid meal of 500 kcal, postprandial increases in the hepatic venous pressure gradient and hepatic blood flow were observed in patients receiving placebo, while the systemic hemodynamic values remained unchanged. In contrast, in patients receiving octreotide, the hepatic blood flow was significantly decreased 30 min after administration, while the hepatic venous pressure gradient and the systemic hemodynamic values were not affected. After ingestion of a meal, the mean values of the hepatic blood flows were not significantly different from basal values. Moreover, the wedged hepatic venous pressure, the hepatic venous pressure gradient and the systemic hemodynamic values were not affected by meal ingestion. However, during octreotide infusion, hepatic blood flow 30 min after the meal had a tendency to increase compared to before the meal. In conclusion, octreotide inhibited the postprandial increase in portal pressure in patients with postnecrotic cirrhosis. In addition, octreotide decreased hepatic blood flow in the fasting state. When given before a meal, the increase in blood flow induced by the meal restored the hepatic blood flow to basal levels.

Priority of blood flow to splanchnic organs in humans during pre- and post-meal exercise

Cardiac output and superior mesenteric arterial flow in five healthy young men were followed using Doppler ultrasound techniques at rest and during 4 min bouts of bicycle exercise in both a pre- and a post-meal situation. The meal given was mixed and heavy, with an energy content (related to body size) of about 1400-1600 kcal (5.9-6.9 MJ). Two levels of exercise, 50-65 W and 150-200 W (about 75% of VO2max), were tested, with the subjects cycling in a reclining position. Superior mesenteric arterial flow increased threefold, to about 1.1 l min-1, after the meal. During exercise in the fasting situation there were only modest changes in splanchnic vascular conductance, and moderate increases in superior mesenteric arterial flow were actually recorded. Exercise in the post-prandial state caused appreciable reductions in splanchnic vascular conductance, and a 38% reduction was observed during the most heavy exercise. However, not even such a decrease in conductance resulted in any definite reduction in superior mesenteric arterial blood flow, which was maintained at the pre-exercise level. Cardiac output increased by about 1.3 l min-1 after the meal. The exercise-induced increases in cardiac output were of the same order in the fasting and in the post-prandial state. Variance analyses showed the high cardiac output levels reached during post-prandial exercise to be no different from levels that would be reached by pure summation of the changes caused by eating alone and by exercise alone. It is concluded that blood flow to the splanchnic organs in reclining man retains its high pre- and post-prandial priority during short exercise bouts of up to 75% of VO2max.