Effects of oral alcohol on superior mesenteric artery blood flow in normal man, horizontal and tilted

Quantitative evaluation of choroidal and retinal microvasculature post-alcohol consumption: A pilot study

PURPOSE

The aim of this study was to assess the impact of acute, heavy alcohol consumption on the ocular microvasculature, providing insight into the largely unexplored response of microvascular structures to excessive drinking.

METHODS

Healthy volunteers in this prospective pilot study were tasked with consuming spirits, wine, and water at different times. Alcohol intake was measured according to body weight (g/kg). The ocular microvascular parameters primarily including choroidal volume (CV) and choroidal vessel volume (CVV) reflecting arteriolovenularity, and choroidal capillary density (CCD) reflecting capillary, were evaluated using swept-source optical coherence tomography angiography at baseline and 0.5-, 1-, 2-, and 3-hour post-consumption.

RESULTS

A total of 34 eyes underwent 170 successful examinations in this study. After consuming spirits or wine, we observed significant decreases in CV and CVV values (all P < 0.01 for 0.5-, 1-, 2-, and 3-hour post-consumption), along with significant increase in CCD (P < 0.05 at 0.5-, 1-, 2-hour post-spirits consumption and 1-hour post-wine consumption). The most pronounced changes occurred 1-hour after spirits or wine consumption (all P < 0.001 in both univariate and multivariate model). However, post-consumption changes in the ocular microvasculature showed no significant differences between spirits and wine (P > 0.05). Additionally, no significant differences were observed in any parameters after water intake (all P > 0.05).

CONCLUSIONS

Excessive alcohol consumption leads to ocular arteriolovenular vasoconstriction and capillary vasodilation, most evident 1-hour post-consumption of spirits and wine. Our research provides insight into alcohol's immediate ocular microvascular effects, hinting at systemic microvascular effects.

Effect of alcohol on blood pressure

BACKGROUND

Alcohol is consumed by over 2 billion people worldwide. It is a common substance of abuse and its use can lead to more than 200 disorders including hypertension. Alcohol has both acute and chronic effects on blood pressure. This review aimed to quantify the acute effects of different doses of alcohol over time on blood pressure and heart rate in an adult population.

OBJECTIVES

Primary objective To determine short-term dose-related effects of alcohol versus placebo on systolic blood pressure and diastolic blood pressure in healthy and hypertensive adults over 18 years of age. Secondary objective To determine short-term dose-related effects of alcohol versus placebo on heart rate in healthy and hypertensive adults over 18 years of age.

SEARCH METHODS

The Cochrane Hypertension Information Specialist searched the following databases for randomised controlled trials up to March 2019: the Cochrane Hypertension Specialised Register; the Cochrane Central Register of Controlled Trials (CENTRAL; 2019, Issue 2), in the Cochrane Library; MEDLINE (from 1946); Embase (from 1974); the World Health Organization International Clinical Trials Registry Platform; and ClinicalTrials.gov. We also contacted authors of relevant articles regarding further published and unpublished work. These searches had no language restrictions.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing effects of a single dose of alcohol versus placebo on blood pressure (BP) or heart rate (HR) in adults (≥ 18 years of age).

DATA COLLECTION AND ANALYSIS

Two review authors (ST and CT) independently extracted data and assessed the quality of included studies. We also contacted trial authors for missing or unclear information. Mean difference (MD) from placebo with 95% confidence interval (CI) was the outcome measure, and a fixed-effect model was used to combine effect sizes across studies.  MAIN RESULTS: We included 32 RCTs involving 767 participants. Most of the study participants were male (N = 642) and were healthy. The mean age of participants was 33 years, and mean body weight was 78 kilograms. Low-dose alcohol (< 14 g) within six hours (2 RCTs, N = 28) did not affect BP but did increase HR by 5.1 bpm (95% CI 1.9 to 8.2) (moderate-certainty evidence). Medium-dose alcohol (14 to 28 g) within six hours (10 RCTs, N = 149) decreased systolic blood pressure (SBP) by 5.6 mmHg (95% CI -8.3 to -3.0) and diastolic blood pressure (DBP) by 4.0 mmHg (95% CI -6.0 to -2.0) and increased HR by 4.6 bpm (95% CI 3.1 to 6.1) (moderate-certainty evidence for all).  Medium-dose alcohol within 7 to 12 hours (4 RCTs, N = 54) did not affect BP or HR. Medium-dose alcohol > 13 hours after consumption (4 RCTs, N = 66) did not affect BP or HR. High-dose alcohol (> 30 g) within six hours (16 RCTs, N = 418) decreased SBP by 3.5 mmHg (95% CI -6.0 to -1.0), decreased DBP by 1.9 mmHg (95% CI-3.9 to 0.04), and increased HR by 5.8 bpm (95% CI 4.0 to 7.5). The certainty of evidence was moderate for SBP and HR, and was low for DBP. High-dose alcohol within 7 to 12 hours of consumption (3 RCTs, N = 54) decreased SBP by 3.7 mmHg (95% CI -7.0 to -0.5) and DBP by 1.7 mmHg (95% CI -4.6 to 1.8) and increased HR by 6.2 bpm (95% CI 3.0 to 9.3). The certainty of evidence was moderate for SBP and HR, and low for DBP. High-dose alcohol ≥ 13 hours after consumption (4 RCTs, N = 154) increased SBP by 3.7 mmHg (95% CI 2.3 to 5.1), DBP by 2.4 mmHg (95% CI 0.2 to 4.5), and HR by 2.7 bpm (95% CI 0.8 to 4.6) (moderate-certainty evidence for all).  AUTHORS' CONCLUSIONS: High-dose alcohol has a biphasic effect on BP; it decreases BP up to 12 hours after consumption and increases BP > 13 hours after consumption. High-dose alcohol increases HR at all times up to 24 hours. Findings of this review are relevant mainly to healthy males, as only small numbers of women were included in the included trials.

The Effect of Acute Ethanol Consumption on the Human Retinal Circulation: A Study in Diabetic and Non-Diabetic Subjects

The effects of acute ethanol consumption on retinal haemodynamics and retinal vascular autoregulation to oxygen in the human retinal circulation were studied in 10 diabetic (mean age +/- SD: 38.2 +/- 11.1) and 16 non-diabetic (mean age +/- SD: 32.4 +/- 8.8) subjects. Subjects drank 0.5 g of ethanol, as vodka, per kg of body weight, diluted in sugar-free orange juice. Retinal blood flow was determined using laser Doppler velocimetry and computerised image analysis. The effect of ethanol on oxygen reactivity, as a measure of autoregulation, was also determined after 60% oxygen inhalation. All subjects demonstrated a significant fall in mean arterial blood pressure (control group 3.3%, p = 0.04, diabetic subjects 5.7%, p = 0.05), after ethanol intake. Ethanol caused no significant change in retinal blood flow. Oxygen reactivity was found to be 38.3% (22.4-47.7, median and interquartile range) in the non-diabetic subjects at baseline, and 30.7% (10.8-42.1) after ethanol ingestion. In diabetic subjects, the oxygen reactivity was 33.2% (19.8-46.8) at baseline and 24.5% (21.1-32.1) after ethanol. In this study ethanol did not significantly affect retinal blood flow or impair autoregulation. These results suggest that the retinal circulation may be able to autoregulate despite the presence of ethanol, in contrast to other vascular beds where ethanol changes flow.

Systematic and regional haemodynamic effects of caffeine and alcohol in fasting subjects

It is well established that caffeine and alcohol can have acute effects on heart rate and blood pressure, but it is not known whether cardiac output and peripheral blood flow are also affected. Such information is needed before any possible effects of caffeine or alcohol on the haemodynamic responses to food can be assessed. Thus, the present study determined the haemodynamic effects of caffeine or alcohol. Eight healthy young subjects were studied in the fasting state before and after ingestion of water (200 ml), coffee containing caffeine (3.5 mg/kg in 200 ml) or alcohol (0.5 g/kg made up to 200 ml) , in random order on three separate occasions. All of the subjects had abstained from both caffeine and alcohol for at least 12 h. Measurements of blood pressure (BP), heart rate (HR), cardiac output (CO), superior mesenteric artery blood flow (SMABF) and calf blood flow (CBF) were made at baseline and for 2 h after each drink. With the alcohol drink, blood alcohol levels estimated using breath measurement peaked at 18.8 mmol/l. HR fell slightly after water but increased after alcohol (+ 7 beats/min) and after caffeine (+ 16 beats/min, group × time interaction analysis of variance, p < 0.03), with peak responses at 40-60 min and a return to baseline by 120 min. Systolic BP increased significantly with time after all three drinks , with no significant differences between the drinks. CBF rose slightly after the drink of water, more so after alcohol but fell slightly after caffeine (group × time interaction analysis of variance, p < 0.01). Total peripheral resistance rose slightly after water and alcohol but much more markedly after caffeine (group effect analysis of variance, p < 0.001). There were no significant effects of alcohol or caffeine on the other variables. Thus, caffeine and alcohol themselves have haemodynamic effects which might interact with the effects of food.

Large-Artery Hemodynamics After Acute Alcohol Administration in Young, Healthy Volunteers

The objective of the present study was to investigate the acute effects of alcohol on blood flow volume and velocity, on wall motion of superficial large arteries, and on systemic hemodynamics in humans. In 10 healthy volunteers small doses of alcohol were administered either orally (0.3 g/kg in 250 mL water) or intravenously (7.5 mg/kg/minute in 250 mL saline in 40 minutes). The effects of alcohol were compared with those of saline 250 mL infused for 40 minutes (6.25 mL/min). Blood velocity and systodiastolic changes of wall diameter were measured in the common carotid, femoral, and brachial arteries simultaneously with cardiac output and finger blood pressure. Skin temperature was measured at the cheek, hand, and toe. Ethanol administration caused a transitory blood pressure increase accompanied by a rise in peripheral resistances at 20 minutes. Arterial blood flow was not changed by either mode of alcohol administration at any of the measurement sites. However, this result was achieved through different compensatory mechanisms in each artery. In fact, mean carotid diameter increased after both oral and intravenous ethanol administration but remained unchanged at the brachial and femoral level. Mean blood velocity was reduced after alcohol administration at the carotid but was unchanged at the brachial and femoral level after oral or intravenous alcohol administration. Skin temperature increased 20 minutes after alcohol administration at all sites. This study shows that although acute alcohol administration does not change blood flow in superficial large arteries, it causes different autoregulatory local responses of vessel walls.

The acute effects of alcohol on cerebral hemodynamic changes induced by the head-up tilt test in healthy subjects

BACKGROUND

Alcohol is a known triggering factor for orthostatic dysfunction, increasing the risk of neurally-mediated syncope. Since orthostatic tolerance may be affected by both systemic and cerebral hemodynamic changes, our aim was to investigate the acute effects of alcohol on cerebral vasoreactivity measured during the head-up tilt (HUT) test in 20 healthy subjects.

METHODS

Mean arterial blood pressure (mBP), heart rate, and flow parameters in both middle cerebral arteries (MCAs) were continuously recorded in the supine and during a 10-minute HUT positions before and after alcohol intake.

RESULTS

The HUT test resulted in a more prominent decline of adjusted mBP at the level of MCAs (mBPMCA) and a significantly larger decrease of MCA mean flow velocities (MFVMCA) in the post-alcohol period than before alcohol intake. During the HUT phase, the relative decrease in MFVMCA was significantly smaller than the reduction in mBPMCA before drinking alcohol, while these changes were similar after alcohol ingestion. The cerebrovascular resistance index (CVRi) decreased during the HUT phase in the control period, however, it increased after alcohol intake.

CONCLUSION

The similar decrease in mBPMCA and MFVMCA during orthostatic stress after alcohol ingestion together with the increased CVRi indicated the impairment of the compensatory vasodilation of cerebral resistance vessels, i.e. impaired cerebral autoregulation. These findings suggest that alcohol may contribute to impaired orthostatic tolerance not only by a hypotensive response but also by the alteration of cerebral blood flow regulation.

Dose-related effects of red wine and alcohol on hemodynamics, sympathetic nerve activity, and arterial diameter

The cardiovascular benefits of light to moderate red wine consumption often have been attributed to its polyphenol constituents. However, the acute dose-related hemodynamic, vasodilator, and sympathetic neural effects of ethanol and red wine have not been characterized and compared in the same individual. We sought to test the hypotheses that responses to one and two alcoholic drinks differ and that red wine with high polyphenol content elicits a greater effect than ethanol alone. Thirteen volunteers (24–47 yr; 7 men, 6 women) drank wine, ethanol, and water in a randomized, single-blind trial on three occasions 2 wk apart. One drink of wine and ethanol increased blood alcohol to 38 ± 2 and 39 ± 2 mg/dl, respectively, and two drinks to 72 ± 4 and 83 ± 3 mg/dl, respectively. Wine quadrupled plasma resveratrol ( P < 0.001) and increased catechin ( P < 0.03). No intervention affected blood pressure. One drink had no heart rate effect, but two drinks of wine increased heart rate by 5.7 ± 1.6 beats/min; P < 0.001). Cardiac output fell 0.8 ± 0.3 l/min after one drink of ethanol and wine (both P < 0.02) but increased after two drinks of ethanol (+0.8 ± 0.3 l/min) and wine (+1.2 ± 0.3 l/min) ( P < 0.01). One alcoholic drink did not alter muscle sympathetic nerve activity (MSNA), while two drinks increased MSNA by 9–10 bursts/min ( P < 0.001). Brachial artery diameter increased after both one and two alcoholic drinks ( P < 0.001). No beverage augmented, and the second wine dose attenuated ( P = 0.02), flow-mediated vasodilation. One drink of ethanol dilates the brachial artery without activating sympathetic outflow, whereas two drinks increase MSNA, heart rate, and cardiac output. These acute effects, which exhibit a narrow dose response, are not modified by red wine polyphenols.

[Moderate alcohol consumption and cardiovascular diseases]

While excessive ethanol consumption can result in higher rate of morbidity and mortality resulting from several diseases including cancer and cirrhosis, epidemiological studies suggest that moderate alcohol ingestion reduces the risk of cardiovascular diseases. However, the precise mechanisms by which moderate alcohol consumption protects against coronary heart disease (CHD) is not fully understood. Epidemiological studies suggest that alcohol consumption influences several risk factors for CHD including blood pressure, plasma cholesterol levels, platelet function, and fibrinolytic parameters, preventing both vascular thrombosis and occlusion. Turning to molecular and cellular levels, ethanol has been shown to act on several signal transduction mechanisms involve in the inhibition of smooth muscle cells proliferation and migration and in the activation of the release of vasoactive factors from vascular cells such as nitric oxide (NO). The latter is of importance since NO has been shown to possess antioxidant, antiaggregant properties, to regulate vascular tone and to inhibit both proliferation of smooth muscle cells and adhesion of leukocytes. Altogether, the above mentioned beneficial properties of moderate concentration of ethanol might help to explain the cardio- and vascular protection induced by ethanol. This review compels several bibliographic data concerning the cardiovascular effect of moderate alcohol consumption.

Alcohol potentiates orthostatic hypotension : implications for alcohol-related syncope

BACKGROUND

Alcohol consumption may be linked to syncopal events. The mechanisms by which alcohol may induce syncope are unknown. Impairment of the response to orthostatic stress may be involved. Using a double-blind, randomized, placebo-controlled study, we tested the hypothesis that short-term alcohol intake causes orthostatic hypotension because of an impairment in the vasoconstrictor response to orthostatic stress.

METHODS AND RESULTS

We examined the effects of alcohol on blood pressure, heart rate, and forearm vascular resistance (FVR) during orthostatic stress achieved by stepwise increases in lower-body negative pressure (LBNP) in 14 healthy young volunteers. During the placebo session, blood pressure did not change significantly during LBNP at -5, -10, and -20 mm Hg. A significant decrease in blood pressure was evident only at -40 mm Hg. In contrast, blood pressure fell significantly at all levels of LBNP during the alcohol session. Compared with placebo, alcohol potentiated the hypotensive responses to LBNP, particularly at -40 mm Hg, when the decrease in systolic blood pressure after alcohol intake (-14 mm Hg) was double that after placebo intake (-7 mm Hg). FVR increased with LBNP after placebo. However, after alcohol intake, FVR did not increase during LBNP despite the potentiated decrease in blood pressure. FVR responses during LBNP were reduced during alcohol compared with placebo consumption (P=0.04).

CONCLUSIONS

Short-term alcohol consumption elicits hypotension during orthostatic stress because of impairment of vasoconstriction. These findings have implications for the understanding of the hemodynamic effects of alcohol and, in particular, for understanding syncopal events that occur in association with alcohol intake.

Understanding gastrointestinal perfusion in critical care: so near, and yet so far

An association between abnormal gastrointestinal perfusion and critical illness has been suggested for a number of years. Much of the data to support this idea comes from studies using gastric tonometry. Although an attractive technology, the interpretation of tonometry data is complex. Furthermore, current understanding of the physiology of gastrointestinal perfusion in health and disease is incomplete. This review considers critically the striking clinical data and basic physiological investigations that support a key role for gastrointestinal hypoperfusion in initiating and/or perpetuating critical disease.

Efficacy of compression of different capacitance beds in the amelioration of orthostatic hypotension

Orthostatic hypotension (OH) is the most disabling and serious manifestation of adrenergic failure, occurring in the autonomic neuropathies, pure autonomic failure (PAF) and multiple system atrophy (MSA). No specific treatment is currently available for most etiologies of OH. A reduction in venous capacity, secondary to some physical counter maneuvers (e.g., squatting or leg crossing), or the use of compressive garments, can ameliorate OH. However, there is little information on the differential efficacy, or the mechanisms of improvement, engendered by compression of specific capacitance beds. We therefore evaluated the efficacy of compression of specific compartments (calves, thighs, low abdomen, calves and thighs, and all compartments combined), using a modified antigravity suit, on the end-points of orthostatic blood pressure, and symptoms of orthostatic intolerance. Fourteen patients (PAF, n = 9; MSA, n = 3; diabetic autonomic neuropathy, n = 2; five males and nine females) with clinical OH were studied. The mean age was 62 years (range 31-78). The mean +/- SEM orthostatic systolic blood pressure when all compartments were compressed was 115.9 +/- 7.4 mmHg, significantly improved (p < 0.001) over the head-up tilt value without compression of 89.6 +/- 7.0 mmHg. The abdomen was the only single compartment whose compression significantly reduced OH (p < 0.005). There was a significant increase of peripheral resistance index (PRI) with compression of abdomen (p < 0.001) or all compartments (p < 0.001); end-diastolic index and cardiac index did not change. We conclude that denervation increases vascular capacity, and that venous compression improves OH by reducing this capacity and increasing PRI. Compression of all compartments is the most efficacious, followed by abdominal compression, whereas leg compression alone was less effective, presumably reflecting the large capacity of the abdomen relative to the legs.

Pharmacological manipulation of human gastrointestinal blood flow

The splanchnic circulation is one of the largest vascular regions in man. In the past, this has been difficult to study because of methodological problems. The adapting of noninvasive Doppler techniques has made it possible to develop reproducible measurements of coeliac and superior mesenteric artery blood flow, which are the main contributors to the gastrointestinal vasculature. This has resulted in the further understanding of neurogenic and humoral control of this region in a number of physiological and pathophysiological states, and has contributed towards the knowledge of its pharmacological control. These studies are of relevance to cardiovascular homeostasis and, in particular, systemic blood pressure control which depends upon various factors including responses in different vascular regions. In this review the key physiological factors which influence pharmacological studies on this circulation will be discussed. Examples will be provided, in subjects with cardiovascular and neurological disorders, of how administration of endogenous and exogenous substances, including drugs with specific pharmacological effects, alter human gastrointestinal blood flow. These will include insulin, alcohol, the somatostatin analogue octreotide, the central acting sympatholytic clonidine and the angiotensin II-converting inhibitor captopril. The relevance of these studies to subjects with postural hypotension due to sympathetic denervation and to primary hypertension, in particular, will be discussed.

Role of magnesium and calcium in alcohol-induced hypertension and strokes as probed by in vivo television microscopy, digital image microscopy, optical spectroscopy, 31P-NMR, spectroscopy and a unique magnesium ion-selective electrode

It is not known why alcohol ingestion poses a risk for development of hypertension, stroke and sudden death. Of all drugs, which result in body depletion of magnesium (Mg), alcohol is now known to be the most notorious cause of Mg-wasting. Recent data obtained through the use of biophysical (and noninvasive) technology suggest that alcohol may induce hypertension, stroke, and sudden death via its effects on intracellular free Mg2+ ([Mg2+]i), which in turn alter cellular and subcellular bioenergetics and promote calcium ion (Ca2+) overload. Evidence is reviewed that demonstrates that the dietary intake of Mg modulates the hypertensive actions of alcohol. Experiments with intact rats indicates that chronic ethanol ingestion results in both structural and hemodynamic alterations in the microcirculation, which, in themselves, could account for increased vascular resistance. Chronic ethanol increases the reactivity of intact microvessels to vasoconstrictors and results in decreased reactivity to vasodilators. Chronic ethanol ingestion clearly results in vascular smooth muscle cells that exhibit a progressive increase in exchangeable and cellular Ca2+ concomitant with a progressive reduction in Mg content. Use of 31P-NMR spectroscopy coupled with optical-backscatter reflectance spectroscopy revealed that acute ethanol administration to rats results in dose-dependent deficits in phosphocreatine (PCr), the [PCr]/[ATP] ratio, intracellular pH (pHi), oxyhemoglobin, and the mitochondrial level of oxidized cytochrome oxidase aa3 concomitant with a rise in brain-blood volume and inorganic phosphate. Temporal studies performed in vivo, on the intact brain, indicate that [Mg2+]i is depleted before any of the bioenergetic changes. Pretreatment of animals with Mg2+ prevents ethanol from inducing stroke and prevents all of the adverse bioenergetic changes from taking place. Use of quantitative digital imaging microscopy, and mag-fura-2, on single-cultured canine cerebral vascular smooth muscle, human endothelial, and rat astrocyte cells reveals that alcohol induces rapid concentration-dependent depletion of [Mg2+]i. These cellular deficits in [Mg2+]i seem to precipitate cellular and subcellular disturbances in cytoplasmic and mitochondrial bioenergetic pathways leading to Ca2+ overload and ischemia. A role for ethanol-induced alterations in [Mg2+]i should also be considered in the well-known behavioral actions of alcohol.