The effect of a meal on cardiac output in man at rest and during moderate exercise

Effect of food intake on echocardiographic measurements in healthy elderly

OBJECTIVE

This study evaluates whether food intake affects systolic and diastolic echocardiographic measurements in healthy seniors.

METHODS

Thirty healthy subjects 65-70 years of age were investigated with echocardiography, at fasting and then 30, 90, and 180 min after a meal.

RESULTS

After 30 min the biggest changes were seen in left ventricular wall stress and myocardial performance index with a decrease of 45% and 33%, respectively, compared to fasting values. Significant (p < .05) increases also were seen in left ventricular stroke volume, left ventricular cardiac output, left ventricular cardiac index, left ventricular outflow velocity-time integral, peak of early diastolic (E) and late diastolic (A) mitral flow velocities, the E/A ratio, pulsed tissue Doppler peak systolic (s') and early (e') and late (a') diastolic velocities, pulmonary vein peak velocities in systole (S) and diastole (D), mitral annular plane systolic excursion (MAPSE), tricuspid annular plane systolic excursion (TAPSE), and global longitudinal strain (GLS) (increases ranging 6%-19%). After 90 min there remained a decrease in wall stress and myocardial performance index of 31% and 17%, respectively, and smaller, but still significant, changes could be seen in left ventricular stroke volume, left ventricular outflow velocity-time integral, MAPSE (lateral), TAPSE, GLS, and a few pulsed tissue Doppler peak systolic velocities and late diastolic velocities. An increase also could be seen in deceleration time of E-wave (DT). After 180 min, all variables except DT were back at baseline or below. No significant changes were seen in S/D ratio, lateral early diastolic velocity (e' lateral) and E/e'ratio.

CONCLUSIONS

This study shows that food intake affects commonly used echocardiographic parameters, both systolic and diastolic, in healthy seniors. With a few exceptions, the changes seen in the older population were less pronounced than previous studies in younger subjects.

Feeding Induces Left Atrial Compression and Impedes Cardiac Filling in Patients With Large Hiatal Hernia

BACKGROUND

Patients with large hiatal hernias (HH) frequently experience postprandial dyspnea. The aim of this study was to evaluate whether feeding induced cardiac compression in these patients using echocardiography.

METHODS

Transthoracic echocardiography was performed during fasting and 30 min after feeding (300 g rice pudding) in patients with HHs (n = 32; mean age, 72 ± 9 years). A subset of patients (n = 15; mean age, 76 ± 6 years) were evaluated postoperatively.

RESULTS

Preoperatively, feeding decreased left atrial (LA) volumes (maximal 27.4 ± 11.3 vs 19.2 ± 9.7 mL/m², P < .001; minimal 13.1 ± 7.0 vs 6.9 ± 5.1 mL/m², P < .001), and increased LA inflow velocities (systolic wave 0.62 ± 0.14 vs 0.77 ± 0.17 m/sec, P < .01; diastolic wave 0.46 ± 0.13 vs 0.59 ± 0.13 m/sec, P < .01), mitral inflow velocities (E wave 0.79 ± 0.17 vs 0.94 ± 0.19 m/sec, P < .01; A wave 0.93 ± 0.20 vs 1.05 ± 0.22 m/sec, P < .01), and E/E' ratio (12.1 ± 2.7 vs 13.7 ± 3.9, P < .01). Cardiac output (6.3 ± 1.6 vs 7.24 ± 2.0 L, P < .01) increased postprandially by marked heart rate augmentation (68.8 ± 7.0 vs 84.2 ± 8.4 beats/min, P < .01), with modest stroke volume increase (88.5 ± 16.7 vs 94.3 ± 19.5 mL, P = .03). After HH surgery, feeding did not change LA volumes (maximal 52.9 ± 13.6 vs 53.4 ± 12.5 mL, P = .89; minimal 28.6 ± 12.2 vs 27.4 ± 8.7 mL, P = .59) or E/E' ratio (10.9 ± 2.1 vs 11.3 ± 2.3) and induced more modest alterations in LA inflow (systolic wave 0.58 ± 0.17 vs 0.68 ± 0.16 m/sec, P = .01; diastolic wave 0.41 ± 0.12 vs 0.47 ± 0.13 m/sec, P = .01) and mitral inflow (E wave 0.69 ± 0.15 vs 0.80 ± 0.13 m/sec, P < .01; A wave 0.92 ± 0.13 vs 1.01 ± 0.18 m/sec, P = .02). Postoperatively, feeding increased cardiac output by substantial stroke volume augmentation (81.9 ± 16.5 vs 90.8 ± 16.0 mL, P = .01), with only modest increase in heart rate (69.8 ± 9.1 vs 75.9 ± 10.5 beats/min, P < .01).

CONCLUSIONS

Feeding produces marked LA compression in patients with HHs, inducing compensatory exaggerated responses in cardiac inflow and hemodynamic status. These compensatory mechanisms improve postoperatively following resolution of LA compression, likely explaining the debility noted preoperatively.

Carbohydrate ingestion induces differential autonomic dysregulation in normal-tension glaucoma and primary open angle glaucoma

Background

It is reported that glaucoma may be associated with vascular dysregulation. Normal tension glaucoma (NTG) and primary open angle glaucoma (POAG), which feature different intraocular pressure levels, may manifest differential features of systemic autonomic dysregulation.

Methods and results

We investigated autonomic regulation to carbohydrate ingestion and postural change in 37 glaucoma patients (19 NTG and 18 POAG) and 36 controls. Subjects were age and gender-matched, normotensive, and had normal comparable insulin sensitivity. Continuous finger arterial pressure and ECG was recorded in supine and standing positions before and after carbohydrate ingestion. Low frequency (LF, 0.04–0.15Hz) and high frequency (HF, 0.15–0.4Hz) spectral power of heart rate and systolic blood pressure variability (HRV and SBPV) were calculated to estimate sympathovagal function. Overall comparison glaucoma (N = 37) and controls (N = 36) showed an increased sympathetic excitation, vagal withdrawal and unstable mean arterial pressure after carbohydrate ingestion in glaucoma patients. Glaucoma severity by retinal nerve fibre layer (RNFL) thickness is positively correlated to autonomic responses (HRV LF power and HF power in normalised units (nu), and HRV LF/HF ratio) after carbohydrate ingestion. Early (30 minutes) following carbohydrate ingestion, SBP LF power and HRV parameters remained unchanged in controls; while POAG showed abnormal autonomic responses, with a paradoxical vagal enhancement (increased HRV HF power in nu) and sympathetic inhibition (decreased HRV LF power nu and HRV LF/HF ratio), and associated hypotension. Later (60–120 minutes) following carbohydrate ingestion, HRV parameters remained unaltered in controls; whereas NTG manifested vagal withdrawal (reduced HRV HF power nu) and sympathetic hyper-responsiveness (increased HRV LF power nu and HRV LF/HF ratio), despite increased SBP LF power in both controls and NTG. Both NTG and POAG exhibited attenuated autonomic responses to postural stress.

Conclusions

NTG and POAG both manifest some systemic autonomic cardiovascular dysregulation. However, the two forms of glaucoma respond differentially to carbohydrate ingestion, irrespective of insulin resistance.

Effect of food intake on myocardial performance index

Background

Myocardial performance index (MPI) has been investigated in a variety of populations, but the effect of food intake has not been evaluated. We assessed whether myocardial performance index is affected by food intake in healthy subjects.

Methods

Twenty-three healthy subjects aged 25.6 ± 4.5 years were investigated. MPI was measured before, 30 min after, and 110 min after a standardized meal.

Results

MPI decreased significantly (P < 0.05) from fasting values 30 min after the meal, and had almost returned to baseline after 110 min. MPI decreased from 0.28 ± 0.06 (fasting) to 0.20 ± 0.07 30 min after eating. At 110 min after eating the index value was almost back to the baseline value 0.26 ± 0.06. (P = 0.15).

Conclusions

This study shows that myocardial performance index is affected by food intake in healthy subjects.

Heat stress redistributes blood flow in arteries of the brain during dynamic exercise

We hypothesized that heat stress would decrease anterior and posterior cerebral blood flow (CBF) during exercise, and the reduction in anterior CBF would be partly associated with large increase in extracranial blood flow (BF). Nine subjects performed 40 min of semirecumbent cycling at 60% of the peak oxygen uptake in hot (35°C; Heat) and thermoneutral environments (25°C; Control). We evaluated BF and conductance (COND) in the external carotid artery (ECA), internal carotid artery (ICA), and vertebral artery (VA) using ultrasonography. During the Heat condition, ICA and VA BF were significantly increased 10 min after the start of exercise ( P < 0.05) and thereafter gradually decreased. ICA COND was significantly decreased ( P < 0.05), whereas VA COND remained unchanged throughout Heat. Compared with the Control, either BF or COND of ICA and VA at the end of Heat tended to be lower, but not significantly. In contrast, ECA BF and COND at the end of Heat were both higher than levels in the Control condition ( P < 0.01). During Heat, a reduction in ICA BF appears to be associated with a decline in end-tidal CO2 tension ( r = 0.84), whereas VA BF appears to be affected by a change in cardiac output ( r = 0.87). In addition, a change in ECA BF during Heat was negatively correlated with a change in ICA BF ( r = −0.75). Heat stress resulted in modification of the vascular response of head and brain arteries to exercise, which resulted in an alteration in the distribution of cardiac output. Moreover, a hyperthermia-induced increase in extracranial BF might compromise anterior CBF during exercise with heat stress.

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.

Effect of food intake on left ventricular wall stress

Objective

Left ventricular wall stress has been investigated in a variety of populations, but the effect of food intake has not been evaluated. We assessed whether left ventricular wall stress is affected by food intake in healthy subjects.

Methods

Twenty-three healthy subjects aged 25.6 ± 4.5 years were investigated. Meridional end-systolic wall stress (ESS) and circumferential end-systolic wall stress (cESS) were measured before, 30 minutes after, and 110 minutes after a standardised meal.

Results

Both ESS and cESS decreased significantly (P < 0.001) from fasting values 30 minutes after the meal, and had not returned to baseline after 110 minutes. ESS decreased from 65 ± 16 kdynes/cm² (fasting) to 44 ± 12 kdynes/cm² 30 minutes after, and to 58 ± 13 kdynes/cm² 110 minutes after eating. cESS decreased from 98 ± 24 kdynes/cm² to 67 ± 18 kdynes/cm² 30 minutes after, and to 87 ± 19 kdynes/cm² 110 minutes after the meal.

Conclusion

This study shows that left ventricular wall stress is affected by food intake in healthy subjects.

Peripheral circulation

Blood flow (BF) increases with increasing exercise intensity in skeletal, respiratory, and cardiac muscle. In humans during maximal exercise intensities, 85% to 90% of total cardiac output is distributed to skeletal and cardiac muscle. During exercise BF increases modestly and heterogeneously to brain and decreases in gastrointestinal, reproductive, and renal tissues and shows little to no change in skin. If the duration of exercise is sufficient to increase body/core temperature, skin BF is also increased in humans. Because blood pressure changes little during exercise, changes in distribution of BF with incremental exercise result from changes in vascular conductance. These changes in distribution of BF throughout the body contribute to decreases in mixed venous oxygen content, serve to supply adequate oxygen to the active skeletal muscles, and support metabolism of other tissues while maintaining homeostasis. This review discusses the response of the peripheral circulation of humans to acute and chronic dynamic exercise and mechanisms responsible for these responses. This is accomplished in the context of leading the reader on a tour through the peripheral circulation during dynamic exercise. During this tour, we consider what is known about how each vascular bed controls BF during exercise and how these control mechanisms are modified by chronic physical activity/exercise training. The tour ends by comparing responses of the systemic circulation to those of the pulmonary circulation relative to the effects of exercise on the regional distribution of BF and mechanisms responsible for control of resistance/conductance in the systemic and pulmonary circulations.

Effect of food intake on commonly used pulsed Doppler and tissue Doppler measurements

OBJECTIVE

This study evaluates the effect of food intake on commonly used pulsed Doppler and tissue Doppler measurements.

METHODS

Twenty-three healthy subjects aged 25.6 ± 4.5 years were investigated. A wide selection of pulsed Doppler and tissue Doppler variables were measured before a standardized meal as well as and 30 and 110 minutes afterwards.

RESULTS

The following variables increased significantly (P < 0.05) 30 minutes after food intake: left ventricular stroke volume, left ventricular cardiac output, left ventricular outflow velocity-time integral, peak of early diastolic (E) and late diastolic (A) mitral flow velocities, pulmonary vein peak velocities in systole (S) and in diastole (D), S/D, pulsed tissue Doppler peak systolic velocities, and late diastolic velocities. Deceleration time of E-wave decreased significantly (P < 0.05). The change in measured variables between fasting and 30 minutes after the food intake ranged from 7% to 28%. There were no significant (P > 0.05) changes in E/A, early diastolic tissue Doppler velocities (e'), and E/e'. Most, but not all variables returned to baseline values 110 minutes after food intake.

CONCLUSIONS

This study shows that food intake affects several echocardiographic variables used to routinely assess diastolic function and hemodynamics. Further studies are warranted in older healthy subjects and in patients with various cardiac diseases to determine whether the findings are reproducible in such populations.

Handgrip contraction induces a linear increase in arterial pressure by peripheral vasoconstriction, increased heart rate and a decrease in stroke volume

AIM

The hypothesis that isometric handgrip induces a progressive increase in arterial pressure and a linear increase in setpoint for arterial pressure control was tested.

METHODS

The continuous time course of changes in heart rate (HR), stroke volume (SV) and mean arterial pressure (MAP) was recorded during a 2-min handgrip contraction of 40% of maximal voluntary contraction force. Twice during the development of the handgrip-induced, gradual pressure increase of ∼25 mmHg, additional, transient changes in arterial pressure were mechanically induced. The subsequent baroreflex responses to these additional pressure changes were studied. The additional steep increase in arterial pressure (∼10 mmHg) was induced both after 70 and 100 s of handgrip contraction, by inflating bilateral thigh cuffs to suprasystolic pressure. Cuff pressure was released after 10s, thus introducing a steep decrease in MAP.

RESULTS

During the development of the handgrip-induced pressure increase, HR increased, SV decreased, cardiac output (CO) increased slightly and total peripheral conductance (TPC=CO/MAP) increased (i.e. peripheral vasoconstriction). The circulatory responses to the additional, sudden increase and subsequent decrease in arterial pressure after 70 and 100 s perfectly adjusted arterial pressure back to the linear increase in MAP, indicating an effective baroreflex response.

CONCLUSION

The increase in MAP which characterizes handgrip-induced pressure response can be regarded as a result of a gradual increase in the set point of the arterial baroreflexes, with no change in the time course and magnitude of the baroreflex responses to additional, induced changes in MAP.

Postprandial lipaemia does not affect resting haemodynamic responses but does influence cardiovascular reactivity to dynamic exercise

Postprandial lipaemia impairs endothelial function, possibly by changes in oxidative stress, but whether this affects cardiac output and/or systemic vascular resistance (SVR) at rest and in response to dynamic exercise remains uncertain. The present study set out to investigate the effects of a high-fat meal (HFM) v. a low-fat, high-carbohydrate meal (HCM) on cardiac output and SVR. A HFM (50 g fat) and an isoenergetic HCM (5 g fat) were randomly fed to thirty healthy adults using a crossover design. Cardiac output, heart rate and blood pressure (BP) were measured, and stroke volume and SVR were calculated over a 3 h rest following the meal, during exercise 3 h postprandially and for 45 min post-exercise. Blood samples were collected at fasting, 3 h postprandially and immediately post-exercise. Plasma TAG increased by 63.8 % 3 h following the HFM, and NEFA fell by 94.1% 3 h after the HCM. There was a 9.8% rise in plasma 8-isoprostane-F2alpha concentration following the HFM, and a 6.2% fall following the HCM. Cardiac output increased postprandially, but the difference between meals at rest or exercise was not statistically significant. The HFM resulted in a 3.2 mmHg (95% CI 0.7, 5.7) smaller increase in exercise mean arterial BP compared with the HCM due to a greater fall in exercise SVR. Postprandial lipaemia induced by a HFM does not affect cardiac output and/or SVR at rest, but it blunts the increase in BP during exercise.

Histamine induces postprandial tachycardia through a direct effect on cardiac H2-receptors in pythons

The intrinsic heart rate of most vertebrates studied, including humans, is elevated during digestion, suggesting that a nonadrenergic-noncholinergic factor contributes to the postprandial tachycardia. The regulating factor, however, remains elusive and difficult to identify. Pythons can ingest very large meals, and digestion is associated with a marked rise in metabolism that is sustained for several days. The metabolic rise causes more than a doubling of heart rate and a fourfold rise in cardiac output. This makes the python an interesting model to investigate the postprandial tachycardia. We measured blood pressure and heart rate in fasting Python regius, and at 24 and 48 h after ingestion of a meal amounting to 25% of body wt. Digestion caused heart rate to increase from 25 to 56 min, whereas blood pressure was unchanged. The postprandial rise in heart rate was partially due to a doubling of intrinsic heart rate. The H2-antagonist did not affect heart rate of fasting snakes but decreased heart rate by 15–20 min at 24 h into digestion, whereas it had no effects at 48 h. Thus, the histaminergic tone on the heart rose from none to 30% at 24 h but vanished after 48 h. In anesthetized snakes, histamine caused a systemic vasodilatation and a marked increase in heart rate and cardiac output mediated through a direct effect on H2- receptors. Our study strongly indicates that histamine regulates heart rate during the initial phase of digestion in pythons. This study describes a novel regulation of the vertebrate heart.

Hemodynamic consequences of rapid changes in posture in humans

Tolerance to +G z gravitational stress is reduced when +G z stress is preceded by exposure to hypogravity (fraction, 0, or negative G z). For example, there is an exaggerated fall in eye-level arterial pressure (ELAP) early on during +G z stress (head-up tilt; HUT) when this stress is immediately preceded by −G z stress (head-down tilt; HDT). The aims of the present study were to characterize the hemodynamic consequences of brief HDT on subsequent HUT and to test the hypothesis that an elevation in leg vascular conductance induced by −G z stress contributes to the exaggerated fall in ELAP. Young healthy subjects ( n = 3 men and 4 women) were subjected to 30 s of 30° HUT from a horizontal position and to 30 s of 30° HUT when HUT was immediately preceded by 20 s of −15° HDT. Four bouts of HDT-HUT were alternated between five bouts of HUT in a counterbalanced designed to minimize possible time effects of repeated exposure to gravitational stress. One minute was allowed for recovery between tilts. Brief exposure to HDT elicited an exaggerated fall in ELAP during the first seconds of the subsequent HUT (−17.9 ± 1.4 mmHg) compared with HUT alone (−12.4 ± 1.2 mmHg, P <0.05) despite a greater rise in stroke volume (Doppler ultrasound) and cardiac output over this brief time period in the HDT-HUT trials compared with the HUT trials (thereafter stroke volume fell under both conditions). The greater fall in ELAP was associated with an exaggerated increase in leg blood flow (femoral artery Doppler ultrasound) and was therefore largely (70%) attributable to an exaggerated rise in estimated leg vascular conductance, confirming our hypotheses. Thus brief exposure to −G z stress leads to an exaggerated fall in ELAP during subsequent HUT, owing to an exaggerated increase in estimated leg vascular conductance.

What is the role of non-invasive measurements of atherosclerosis in individual cardiovascular risk prediction?

Primary prevention of CVD (cardiovascular disease) is mainly based on the assessment of individual cardiovascular risk factors. However, often, only the most important (conventional) cardiovascular risk factors are determined, and every level of risk factor exposure is associated with a substantial variation in the amount of atherosclerosis. Measuring the effect of risk factor exposure over time directly in the vessel might (partially) overcome these shortcomings. Several non-invasive imaging techniques have the potential to accomplish this, each of these techniques focusing on a different stage of the atherosclerotic process. In this review, we aim to define the current role of various of these non-invasive measurements of atherosclerosis in individual cardiovascular risk prediction, taking into account the most recent insights about validity and reproducibility of these techniques and the results of recent prospective outcome trials. We conclude that, although the clinical application of FMD (flow-mediated dilation) and PWA (pulse wave analysis) in individual cardiovascular risk prediction seems far away, there may be a role for PWV (pulse wave velocity) and IMT (intima-media thickness) measurements in the near future.

Acute risk factors for myocardial infarction

Increased knowledge concerning the triggering of acute cardiovascular diseases has yielded a change in philosophical approach to this field. During the last decade, clinical evidence suggested that the term acute risk factors can be used for the activities and events that suddenly and transiently increase the risk of acute cardiac diseases. External triggers, such as heavy physical activity, emotional stress, eating, cold or heat exposure, coffee or alcohol consumption, cocaine or marijuana use and sexual intercourse are recognized as most important acute risk factors. It is likely that the morning hours may be considered as an endogenous, external triggering independent acute risk factor related to physiological sympathetic arousal. The features of triggering have been best described for an acute myocardial infarction whose moment of onset appears to be the result of a dynamic interaction between an endogenous response to acute risk factors and patient vulnerability. In this article, pathophysiological changes implicated as internal triggering mechanisms are summarized and the terms sympathetic and parasympathetic triggering patterns are introduced. A highly individual approach tailored both to protect against acute risk factors and to reduce patient vulnerability could provide a more complete protection from myocardial infarction and other coronary incidents. Lifestyle modifications, regular physical activity and adequate drug regimens may at least prove able to defer the occurrence of coronary thrombosis, thereby providing time for the development of collateral vessels, plaque stabilization or invasive/surgical treatment.

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.

Meta-analysis of possible external triggers of acute myocardial infarction

BACKGROUND

Although it is well known that the acute myocardial infarction can be triggered by events such as physical activity, emotional stress, sexual activity or eating, the observed frequencies of these events preceding the onset of myocardial infarction vary between published reports.

METHODS

A meta-analysis of 17 seldom population-based studies that included data on frequency of external triggers or onsets during sleep was performed. In each analysis, the data were combined only from the studies reporting on a particular trigger.

RESULTS

Of the 10519 patients, heavy physical activity was recorded before the onset of myocardial infarction in 6.1%, whereas mild-to-moderate physical activity was recorded in 28.6% of 7517 patients. Eating preceded the onset in 8.2% of 4785 patients, various kinds of emotional stress in 6.8% of 2565 (particularly anger in 2.1% of 2283), meteorologic stress in 3.7% of 3371, and sexual activity in 1.1% of 3406 patients. Out of 11778 patients, 20.7% had infarction onset during sleep. Triggers in general (OR = 1.45, 95%CI = 1.21-1.76; p < 0.0001), heavy physical activity (OR = 6.21, 95%CI = 3.77-10.23; p < 0.0001) and eating (OR = 1.70, 95%CI = 1.14-2.53; p = 0.0008) were more likely to precede the infarction onset in men while women were more likely to report emotional stress (OR = 0.66, 95%CI = 0.50-0.86; p = 0.002).

CONCLUSIONS

The present meta-analysis defines the occurrence of possible external triggers before the onset of myocardial infarction in general population, but their actual contribution to the very onset is somewhat less frequent. Future investigation should identify other eventual triggers unrecognized as yet, asses the risk of triggering myocardial infarction among patients with defined levels of ischemic heart disease or plaque vulnerability, and further elucidate the pathophysiologic mechanisms of gender differences and beneficial effect of habitual physical activity.

Dynamic time course of hemodynamic responses after passive head-up tilt and tilt back to supine position

Mechanisms involved in the control of arterial pressure during postural changes were studied by analysis of the dynamic time course of cardiovascular changes during head-up tilt (HUT) and tilt back to supine position (TB). Beat-to-beat values of cardiovascular variables were recorded continuously before, during, and after passive HUT to 30 degrees in seven healthy humans. Left cardiac stroke volume (SV, Doppler ultrasound), mean arterial blood pressure (MAP), heart rate (HR), cardiac output (CO), and total peripheral conductance (TPC) were recorded. During HUT, MAP at the level of the carotid baroreceptors decreased by approximately 5 mmHg. There was a striking asymmetry between the time courses of cardiovascular changes on HUT and on TB. Adjustments generally took up to 30 s after HUT, whereas most changes were completed during the first 10 s after TB. Cardiovascular reflex adjustments of HR and TPC were more symmetrical. After HUT, SV was maintained during the first 4-6 s and then decreased steadily during the next 30 s to a stable level approximately 25% below its pretilt value. However, after TB, SV increased rapidly to its pretilt value in <10 s. This asymmetry in SV dynamics may be explained in part by a more rapid change in left cardiac filling after TB than after HUT. On TB, there must be a rapid inflow of stagnant blood from the legs, whereas venous valves will impede backward filling of veins in the lower body on HUT. In conclusion, we have revealed a characteristic asymmetry in cardiovascular responses to inverse variations in gravity forces in humans. This asymmetry can be explained in part by nonlinear, hydrodynamic factors, such as the one-way effect of venous valves in the lower part of the body.

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.

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.

Metabolic and cardiovascular responses to liquid and solid test meals

There is indirect evidence from previous studies that the physiological responses to a liquid test meal may differ from those seen after consumption of a solid meal. The aim of the present study was to determine the metabolic and cardiovascular responses to isoenergetic high-carbohydrate mixed nutrient liquid or solid test meals, providing 2.1 MJ (approximately 70% of which was from carbohydrate), in eight healthy men following an overnight fast. Metabolic rate increased significantly after both meals (P < 0.0001, time effect), but the increase was significantly greater after the solid than after the liquid test meal (0.40 (SE 0.14), 0.26 (SE 0.10) kJ/min respectively, P = 0.001). The respiratory exchange ratio increased significantly after both the liquid and solid test meals, with no significant differences between them. Forearm blood flow increased significantly after the liquid test meal (0.70 (SE 0.33) ml/100 ml per min, P < 0.0001), whilst it decreased after the solid meal (-0.28 (SE 0.16) ml/100 ml per min, P < 0.0001). Heart rate increased on both occasions, but the response was significantly greater after the solid meal (P = 0.02). There were no significant plasma noradrenaline responses, but there were significantly higher increases in serum insulin and blood glucose following the solid meal. Thus, the physical form of a test meal affects the physiological responses to nutrient ingestion.

Systemic and regional (including superior mesenteric) haemodynamic responses during supine exercise while fasted and fed in normal man

The systemic and regional (including superior mesenteric artery, SMA) responses to exercise in the fasting and fed state were studied in ten normal subjects before, during and after 9 min of graded supine bicycle exercise on two separate occasions, when fasted and after a liquid meal. During exercise, blood pressure (BP) and cardiac index rose similarly in both states. Resting SMA blood flow was higher when fed (519 (282-619) versus 240 (133-255) ml/min, p < 0.01). SMA blood flow fell during exercise in both states, to 98 (63-154) ml/min, p < 0.01 when fasted and to 55 (42-149) ml/min, p < 0.01 when fed. SMA vascular resistance rose during exercise in both states, but rose less when fasted by 36 (6-57)% versus 143 (36-240)% (NS). Resting forearm and leg blood flow (FBF and LBF) and vascular resistance (FVR and LVR) were similar fasted and fed. FBF and FVR did not change after exercise in either state. LBF rose and LVR fell similarly in both states. We conclude that in normal subjects, although splanchnic oxygen demand is likely to be greater after food, during light to moderate exercise splanchnic vasoconstriction contributes to maintenance of BP.

The effect of meal size on the cardiovascular responses to food ingestion

Cardiac output (CO; indirect Fick), blood pressure (BP) and heart rate (HR; oscillometry), superior mesenteric artery blood flow (SMABF; Duplex Doppler) and calf blood flow (CBF; venous occlusion plethysmography) were recorded in the fasted state and for 120 min following the ingestion of 1, 2, and 3 MJ, high-carbohydrate meals in eight healthy females. BP was unchanged following food. HR (P < 0.0005) and CO (P < 0.005) rose significantly following all three meals. Integrated increments in CO over the postprandial period were greater after 3 MJ compared with the 1 and 2 MJ meals (P < 0.05). SMABF rose significantly following all three meals. The pattern of blood flow response was significantly different between the 1 and 3 MJ meals (interaction effect P < 0.02, ANOVA), with blood flow after the 3 MJ meal being significantly greater than flow after the 1 MJ meal at 15, 60, and 90 min. Similarly, the pattern of response was significantly different after the 2 and 3 MJ meals (interaction effect P < 0.03, ANOVA), with blood flow being significantly greater at 15 and 90 min after the 3 MJ meal. CBF fell significantly in the first 15 min after the 3 MJ meal and then recovered towards baseline values. No other significant changes in CBF were recorded. There are substantial peripheral and central cardiovascular changes after food in man and there appears to be a relationship between meal size and the extent of these changes.

Superior mesenteric artery blood flow and gastric emptying in humans and the differential effects of high fat and high carbohydrate meals

This study was designed to determine if the differential effect of high fat and high carbohydrate meals on mesenteric blood flow is a result of changed gastric emptying rate. Eight healthy men were studied twice. Superior mesenteric artery blood flow (Doppler ultrasound) was measured before and after a 2.5 MJ meal (either 74% of the energy as carbohydrate or 71% as fat). Emptying of meals was followed by gamma-scintigraphy. The pattern of the superior mesenteric artery blood flow response was different after the two meals (interaction effect p < 0.001 analysis of variance), with a far more sustained response after fat. The time by which half the meal had emptied (t50) was also significantly greater after fat (p < 0.02). Superior mesenteric artery blood flow corresponding to t50 was 449 ml/min after carbohydrate and 592 ml/min after fat. There was a significant curvilinear relation between the superior mesenteric artery blood flow response and gastric emptying after carbohydrate (r2 = 0.94) and no relation at all after fat. This study confirms the finding that ingestion of meals with a high fat content slows gastric emptying compared with meals with a high carbohydrate content in healthy volunteers. A more sustained mesenteric hyperaemia was also recorded after the fat meal compared with the carbohydrate meal. The relation, however, between the volume of meal remaining in the stomach and the mesenteric response was considerably different after the two meals. Further study is required to elucidate the mechanism behind the vascular responses recorded in the mesenteric bed after food in humans.

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

Changes in cardiac output and in superior mesenteric arterial flow were followed with Doppler ultrasound techniques in five young, healthy persons for 2 h after ingestion of medium-sized (4 MJ), fluid meals containing either carbohydrate, protein, fat or water only. Measurements were carried out before meals and at regular post-meal intervals, during which mean arterial blood pressure was also followed. All energy-containing meals caused marked and gradually developing post-prandial increases in cardiac output as well as in superior mesenteric arterial flow. The maximum flow levels were reached in the course of 30-60 min and maintained until the observations ended after 2 h. The intake of water caused no such flow increases. There were considerable interpersonal variations in the size and in the speed of development of the flow increases after the three types of energy-containing meals. The flow-increasing effects of the three meal types were not significantly different, even if the most marked increases (median values about 11 min-1 for both cardiac output and superior mesenteric arterial flow) occurred after carbohydrate meals. The marked effects on circulation of the three food components were also revealed in the calculated, integrated amounts of 'extra' cardiac output and superior mesenteric arterial flow observed in the course of the 2 h following the meal. Values of more than 100 1 for such 'extra' flows were seen after carbohydrate meals. The marked ingestion-released increase in blood flow to the splanchnic organs is apparently partly met by an increase in cardiac output, and partly by some redistribution of flow, which benefits the digestive system.

The effect of meal size on postprandial increase in cardiac output

Heart rate, stroke volume, cardiac output and mean arterial blood pressure were followed from the resting pre-meal situation and for 2 hours after intake of standardized meals in four healthy individuals. Continuous records of stroke volume and cardiac output were achieved with an improved method of Doppler ultrasonography. A smallish meal and one 2 1/2 times larger were both given twice and in random order to each of the four test persons. The consumption of a meal invariably resulted in a cardiac output increase, which developed gradually to reach a maximum level 30 to 60 min after end of the meal. The postprandial cardiac output increase resulted from significant increases in both heart rate and stroke volume. There were distinct and significant differences between the circulatory responses to small and large meals. The increase in cardiac output after a large meal was considerably larger and lasted for longer than the increase after a small meal. Two hours after a small meal cardiac output was nearly or fully back to pre-meal values, while cardiac output was still markedly elevated 2 hours after a large meal. Consequently, the total 'extra' amount of blood delivered by the heart over 2 post-meal hours was significantly--about 100%--larger after the large meal than after the small one. Mean arterial blood pressure either fell or remained almost unchanged in the hour after a meal, so that total peripheral resistance was consistently and significantly reduced in the postprandial period--and considerably more so after a large meal than after a small one.