Biomedical subjects

N J Rehrer

Publications and source records attributed to N J Rehrer.

At least 19 recordsLinked to original sources

PubMed2005

Effect of carbohydrate on portal vein blood flow during exercise.

Effects of carbohydrate ingestion and exercise on portal vein blood flow were studied. Flow was measured by pulsed-electronic Doppler. Eight male subjects performed four tests after a standardised breakfast and 5 h fast. Beverages were CHO (10 % glucose, 30 mmol . l (-1) NaCl) and W (water, 30 mmol . l (-1) NaCl). Exercise experiments comprised a resting measurement, 10 min warm-up and 60 min 70 % VO(2)max cycling. Every 10 min subjects stopped cycling briefly (approximately 30 s) for measurements. Beverage was consumed after warm-up (500 ml) and at 20 and 40 min (250 ml). Similar tests were done at rest. Blood samples were taken concurrently with flow measurements for hormonal concentrations. Exercise decreased blood flow (repeated measures ANOVA, p < 0.0001) and carbohydrate ingestion increased flow (p = 0.015). At rest, flow was greater with CHO than with W at 20 (177 +/- 31; 101 +/- 25 %, resp.) (mean +/- SE), 30 (209 +/- 37; 120 +/- 20 %), 40 (188 +/- 32; 108 +/- 12 %), and 60 min (195 +/- 19; 112 +/- 12 %) (1-way ANOVA, Fisher's PLSD, p < 0.05). Flow was similar during exercise with CHO and W, with a tendency for CHO to maintain flow better, at 10 (124 +/- 27; 77 +/- 21 %), 20 (81 +/- 10; 60 +/- 13 %), 30 (106 +/- 26; 56 +/- 10 %), 40 (109 +/- 28; 54 +/- 8 %), 50 (85 +/- 17; 54 +/- 13 %), and 60 min (61 +/- 15; 47 +/- 7 %). A positive correlation between glucagon and flow and an inverse correlation between noradrenaline and flow were observed. Exercise reduces, and carbohydrate increases, portal vein flow. Changes in plasma concentrations suggest that noradrenaline and glucagon, respectively, may play a role in modulating flow.

Adult↗

PubMed2001

Effect of exercise on portal vein blood flow in man.

PURPOSE: Doppler pulsed flow and electronic scanning allow for instantaneous measurement of portal vein flow. This method was used to monitor alterations in splanchnic blood flow during exercise. METHODS: Measurements of portal vein blood flow were performed in eight healthy males at rest and at 10-min intervals during cycle ergometry at 70% of maximal aerobic capacity. Subjects stopped cycling briefly (approximately 30 s) and stopped breathing while measurements were made. Flow was calculated from values obtained for velocity of red blood cell passage and cross-sectional area of the vessel. RESULTS: Cross-sectional area decreased during exercise, resulting in a significant decrease in flow over time (P = 0.0001 by ANOVA). The flow within the portal vein had decreased by 80% after 60 min of exercise (absolute flow, 0.63 +/- 0.13 L x min(-1) at rest and 0.13 +/- 0.04 L x min(-1) at 60 min). CONCLUSION: Electronic Doppler flow measurement of portal vein flow is a viable, noninvasive technique that can be used to measure splanchnic blood flow. Values obtained as a result of intensive exercise are in line with earlier results obtained with other techniques.

Adult↗

PubMed2001

Fluid and electrolyte balance in ultra-endurance sport.

It is well known that fluid and electrolyte balance are critical to optimal exercise performance and, moreover, health maintenance. Most research conducted on extreme sporting endeavour (>3 hours) is based on case studies and studies involving small numbers of individuals. Ultra-endurance sportsmen and women typically do not meet their fluid needs during exercise. However, successful athletes exercising over several consecutive days come close to meeting fluid needs. It is important to try to account for all factors influencing bodyweight changes, in addition to fluid loss, and all sources of water input. Increasing ambient temperature and humidity can increase the rate of sweating by up to approximately 1 L/h. Depending on individual variation, exercise type and particularly intensity, sweat rates can vary from extremely low values to more than 3 L/h. Over-hydration, although not frequently observed, can also present problems, as can inappropriate fluid composition. Over-hydrating or meeting fluid needs during very long-lasting exercise in the heat with low or negligible sodium intake can result in reduced performance and, not infrequently, hyponatraemia. Thus, with large rates of fluid ingestion, even measured just to meet fluid needs, sodium intake is vital and an increased beverage concentration [30 to 50 mmol/L (1.7 to 2.9 g NaCl/L) may be beneficial. If insufficient fluids are taken during exercise, sodium is necessary in the recovery period to reduce the urinary output and increase the rate of restoration of fluid balance. Carbohydrate inclusion in a beverage can affect the net rate of water assimilation and is also important to supplement endogenous reserves as a substrate for exercising muscles during ultra-endurance activity. To enhance water absorption, glucose and/or glucose-containing carbohydrates (e.g. sucrose, maltose) at concentrations of 3 to 5% weight/volume are recommended. Carbohydrate concentrations above this may be advantageous in terms of glucose oxidation and maintaining exercise intensity, but will be of no added advantage and, if hyperosmotic, will actually reduce the net rate of water absorption. The rate of fluid loss may exceed the capacity of the gastrointestinal tract to assimilate fluids. Gastric emptying, in particular, may be below the rate of fluid loss, and therefore, individual tolerance may dictate the maximum rate of fluid intake. There is large individual variation in gastric emptying rate and tolerance to larger volumes. Training to drink during exercise is recommended and may enhance tolerance.

Alcohol Drinking↗

PubMed1999

Glycaemic control, muscle glycogen and exercise performance in IDDM athletes on diets of varying carbohydrate content.

The aim of this study was to examine the effects of a high carbohydrate diet on glycaemic control, resting muscle glycogen levels and exercise performance in athletes with insulin dependent diabetes (IDDM). Seven trained (mean +/- S.D., VO2max 50.3 +/- 7.4 ml/kg/min) IDDM males consumed a high carbohydrate diet (HCD) or a normal mixed diet (NMD) for 3 week periods in a randomised crossover trial with a one week wash-out. Carbohydrate provided 59% or 50% of total energy intake, respectively, on the two diets. Fasting plasma lipids, mean blood glucose (over 96 h), fructosamine and muscle glycogen were measured and insulin use recorded. Exercise performance was evaluated by a 15 min time trial following a 50 min pre-loading block. Statistical significance was assessed using two tailed paired Student t-tests. Mean blood glucose was 10% higher on HCD than NMD (p = 0.005), fructosamine levels were 375 +/- 54 and 353 +/- 51 (mol/L on HCD and NMD, resp., p = 0.04) and daily insulin requirements were 15% higher on HCD than NMD (p = 0.02). Fasting blood lipids were similar on the two diets. Muscle glycogen was significantly lower on HCD than NMD (88.2 +/- 19.2 and 95.6 +/- 14.6 mmol/kg ww, respectively, p = 0.02). Exercise completed during the time trial was 6% less on HCD than on NMD (p = 0.007). An increased carbohydrate intake for three weeks, in IDDM athletes, is associated with a deterioration in glycaemic control, increased insulin requirements, decreased muscle glycogen and reduced exercise performance. These data do not support recommendations for IDDM athletes to consume a high carbohydrate diet, at least not when glycaemic control worsens upon following this advice, as was observed in this short-term study.

Adolescent↗

PubMed1999

Sodium-free fluid ingestion decreases plasma sodium during exercise in the heat.

This study assessed whether replacing sweat losses with sodium-free fluid can lower the plasma sodium concentration and thereby precipitate the development of hyponatremia. Ten male endurance athletes participated in one 1-h exercise pretrial to estimate fluid needs and two 3-h experimental trials on a cycle ergometer at 55% of maximum O2 consumption at 34 degrees C and 65% relative humidity. In the experimental trials, fluid loss was replaced by distilled water (W) or a sodium-containing (18 mmol/l) sports drink, Gatorade (G). Six subjects did not complete 3 h in trial W, and four did not complete 3 h in trial G. The rate of change in plasma sodium concentration in all subjects, regardless of exercise time completed, was greater with W than with G (-2.48 +/- 2.25 vs. -0.86 +/- 1.61 mmol. l-1. h-1, P = 0.0198). One subject developed hyponatremia (plasma sodium 128 mmol/l) at exhaustion (2.5 h) in the W trial. A decrease in sodium concentration was correlated with decreased exercise time (R = 0.674; P = 0.022). A lower rate of urine production correlated with a greater rate of sodium decrease (R = -0. 478; P = 0.0447). Sweat production was not significantly correlated with plasma sodium reduction. The results show that decreased plasma sodium concentration can result from replacement of sweat losses with plain W, when sweat losses are large, and can precipitate the development of hyponatremia, particularly in individuals who have a decreased urine production during exercise. Exercise performance is also reduced with a decrease in plasma sodium concentration. We, therefore, recommend consumption of a sodium-containing beverage to compensate for large sweat losses incurred during exercise.

Adult↗

PubMed1996

Muscle glycogen recovery after exercise during glucose and fructose intake monitored by 13C-NMR.

The purpose of this study was to examine muscle glycogen recovery with glucose feeding (GF) compared with fructose feeding (FF) during the first 8 h after partial glycogen depletion using 13C-nuclear magnetic resonance (NMR) on a clinical 1.5-TNMR system. After measurement of the glycogen concentration of the vastus lateralis (VL) muscle in seven male subjects, glycogen stores of the VL were depleted by bicycle exercise. During 8 h after completion of exercise, subjects were orally given either GF or FF while the glycogen content of the VL was monitored by 13C-NMR spectroscopy every second hour. The muscular glycogen concentration was expressed as percentage of the glycogen concentration measured before exercise. The glycogen recovery rate during GF (4.2 +/- 0.2%/h) was significantly higher (P < 0.05) compared with values during FF (2.2 +/- 0.3%/h). This study shows that 1) muscle glycogen levels are perceptible by 13 C-NMR spectroscopy at 1.5 T and 2) the glycogen restoration rate is higher after GF compared with after FF.

Adult↗

PubMed1994

The maintenance of fluid balance during exercise.

Fluid supplementation is necessary for exercise in which fluid losses must be offset by intake to avoid the negative effects of hypohydration on health and performance. Several aspects of gastrointestinal function have been studied to gain information concerning the assimilation of ingested fluids to maintain fluid balance during exercise. Research results with regards to gastric emptying and secretion, intestinal absorption and secretion, and aspects of fluid retention, including urine production and plasma volume changes, can be utilised to formulate an appropriate fluid supplementation regimen. Increasing the volume of ingestate and decreasing the carbohydrate concentration promote gastric emptying of fluids. By maintaining a low osmolality secretion is reduced, thus leading to a greater rate of net fluid absorption. Adding sodium and carbohydrate (up to approximately 7%) increases the net intestinal absorption rate. Increasing carbohydrate concentration above this level begins to have a deleterious effect on intestinal absorption of fluid. Sodium also promotes retention of ingested fluids and leads to an increased plasma volume response during rehydration. The primary goal of supplementation should be considered, fluid vs carbohydrate provision, and the beverage composition altered accordingly. Beverage composition to maximise fluid provision will not maximise carbohydrate availability.

Dehydration↗

PubMed1993

1H editing of 2-deuterated exogenous and natural endogenous D-glucose in biological samples.

A spin-echo based 1H homonuclear pulse sequence, enabling the selective editing of homonuclear first-order J-multiplet types, is presented and analyzed. Its effectiveness in quantification applications is assessed. Its potential usefulness in the quantitative distinction between 2-deuterated and natural D-glucose in biological samples is briefly discussed, with emphasis on studies of hexose metabolism conducted in vitro.

Absorption↗

PubMed1993

Breath 13CO2 background enrichment during exercise: diet-related differences between Europe and America.

A traditional North American diet contains a high percentage of carbohydrates (CHO) derived from C4 plants (maize, sugar cane), whereas a European diet contains primarily CHO derived from C3 plants (potato, sugar beet). The natural 13C enrichment of the first type of CHO is higher than that of the latter type. 13CO2 production from orally ingested C4 plant-derived CHO can, therefore, be used to quantify oxidation rates of orally ingested CHO at rest and during exercise. Recently it has been shown that oxidation rates assessed this way in North Americans should be corrected for an increase in breath background 13CO2 during exercise. We hypothesized that the indicated difference in metabolic origin of CHO would imply that no such correction is required for subjects on a European diet. We therefore studied changes from rest in breath 13CO2 enrichment in Dutch volunteers during cycle ergometry at 65% maximal work load (experiment 1, 2h, 6 subjects) and 70% maximal oxygen uptake (experiment 2, 90 min, 8 subjects) while ingesting water (experiments 1 and 2) and potato starch-derived glucose (experiment 2). Experiment 1 was done before and after careful instruction of the subjects to refrain from nutrient sources potentially containing CHO of C4 metabolic origin. No significant changes from rest 13CO2 enrichment were observed in tests with water and potato-derived glucose ingestion in subjects who excluded CHO of C4 metabolic origin from their diet.

Adipose Tissue↗

PubMed1993

Effects of electrolytes in carbohydrate beverages on gastric emptying and secretion.

Two experiments were done at rest to examine gastric residue and secretion volume and electrolyte composition after ingestion of beverages of varying composition. In the first experiment the effects of two different sport drinks, one isotonic (7% carbohydrate, primarily sucrose) (I) and one hypertonic (18% carbohydrate, primarily maltodextrin) (H), and a control beverage (0.08 g.l-1 aspartame in water) (C) on titratable acid, pH, osmolality, gastric emptying and secretion volume, and Na+, K+, and Cl- content were measured. In a second experiment five solutions were tested all containing 150 g.l-1 maltodextrin, with 28 meq.l-1 Na+ (low Na), 140 meq.l-1 Na+(high Na), 28 meq.l-1 K+(K), or 140 meq.l-1 Na+ and 28 meq.l-1 K+(high NaK). Beverages H and C, and distilled water (W) were also tested. Samples were taken via a nasogastric tube. A dye dilution technique for serial sampling was employed to determine beverage and secretion volumes. After receiving a bolus of 8 ml.kg-1 body weight, samples of gastric residue were taken at 0, 10, 20, 30, 40, 60, and 80 min. Gastric secretion of Na+, K+, and Cl- was fairly constant despite large differences in beverage composition. Changes in gastric residue pH, titratable acid, osmolality, and electrolyte composition reflected the increasing proportion of the residue that was from gastric secretions. The effects of varying concentrations of Na+ and K+ (in a 150 g.l-1 maltodextrin solution) on gastric emptying were not significant. The high carbohydrate concentration and/or the large volume ingested may have overridden any effect of sodium or potassium. No differences were observed between W and C. Secretion was decreased in these two solutions versus all the others. Although nonsignificant, there was a trend for greater secretion in H versus the other carbohydrate containing solutions in experiment 2. This may be a result of the higher pH maintained after ingestion of this beverage.

Adolescent↗

PubMed1992

Physiological changes and gastro-intestinal symptoms as a result of ultra-endurance running.

One hundred and seventy-two competitors of the Swiss Alpine Marathon, Davos, Switzerland, 1988, volunteered for this research project. Of these volunteers 170 (158 men, 12 women) finished the race (99%). The race length was 67 km with an altitude difference of 1,900 m between the highest and lowest points. Mean age was 39 (SEM 0.8) years. Average finishing times were 8 h 18 min (men) and 8 h 56 min (women). Loss of body mass averaged 3.4% body mass [mean 3.3 (SEM 0.2)%; 4.0 (SEM 0.4)%; men and women, respectively]. Blood samples from a subgroup of 89 subjects (6 women and 83 men) were taken prior to and immediately after completion of the race. Changes in haemoglobin (9.3 mmol.l-1 pre-race, 9.7 mmol.l-1 post-race) and packed cell volume (0.44 pre, 0.48 post-race) were in line with the moderate level of dehydration displayed by changes in body mass. Mean plasma volume decreased by 8.3%. No significant changes in plasma osmolality, sodium, or chloride were observed but plasma potassium did increase by 5% (4.2 mmol.l-1 pre-race, 4.4 mmol.l-1 post-race). Mean fluid consumption was 3290 (SEM 103) ml. Forty-three percent of all subjects, and 33% of those who gave blood samples, complained of gastro-intestinal (GI) distress during the race. No direct relationship was found between the quantity or quality of beverage consumed and the prevalence of GI symptoms.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Gastrointestinal complaints in relation to dietary intake in triathletes.

This study examined the relationship between gastrointestinal (GI) symptoms and dietary intake in triathletes. Fifty-five male triathletes (age 31 +/- 6 yrs) were surveyed regarding the most recently completed half Iron Man triathlon. Questions were asked regarding GI symptoms and dietary intake. Fifty-two percent complained of eructation and 48% of flatulence. Other symptoms were abdominal bloating, vomiting urge, vomiting, nausea, stomachache, intestinal cramps, and diarrhea. More symptoms occurred while running than at other times. All individuals who had eaten within 30 min of the start vomited while swimming. Fat and protein intake was greater in those who vomited or had the urge to vomit than in those without these symptoms. Of the former, 93% had consumed a hypertonic beverage. Forty percent of those who drank a hypertonic beverage and only 11% of those who drank an iso- or hypotonic beverage had severe complaints. Four of five individuals with stomachache had consumed a strongly hypertonic beverage. All subjects with intestinal cramps had eaten fiber-rich foods in the prerace meal; only 10% of those without cramps had done so.

Adult↗

PubMed1992

Gastric emptying, absorption, and carbohydrate oxidation during prolonged exercise.

This study was designed to examine aspects of digestive function that may limit assimilation of water and oxidation of orally ingested carbohydrate (CHO) during exercise. Eight males completed a crossover study in which each cycled on four occasions for 80 min at 70% maximal O2 consumption. Beverage was consumed at 0, 20, 40, and 60 min. Beverages were water, 4.5% glucose (4.5G), 17% glucose (17G), and 17% maltodextrin (17MD). CHO beverages contained 20 meq/l NaCl and were 13C enriched to measure exogenous CHO oxidation. Gastric (beverage) volume was measured at 80 min. Water uptake was estimated by including 2H2O in the beverage and measuring 2H accumulation in blood. Jejunal perfusion tests were conducted at rest with the same subjects and beverages. In 60 min, 1,294 +/- 31 (SE) ml were ingested; at 80 min, volumes emptied with H2O (1,257 +/- 32 ml) and 4.5G (1,223 +/- 32 ml) were greater than with 17G (781 +/- 56 ml) and 17MD (864 +/- 71 ml; P less than 0.05). Total CHO oxidized was similar with all beverages, but there was a greater increase in exogenous CHO oxidation over time with 17G and 17MD than with 4.5G; 54, 19, and 18% of the CHO ingested with 4.5G, 17G, and 17MD, respectively, was oxidized. This represents 57, 32, and 27%, respectively, of the CHO emptied from the stomach. 2H accumulation in the blood was more rapid with H2O and 4.5G than with 17G or 17MD. Net jejunal water absorption was greater from 4.5G than from water. Net water absorption was also observed from 17MD, whereas net secretion was observed with 17G.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

[The effect of beverage composition and gastrointestinal function on fluid and nutrient availability during physical exertion: e review].

Intensive exercise affects digestion and absorption. Nevertheless, athletes involved in intensive endurance exercise are advised to ingest fluid and energy supplying nutrients, to compensate for the losses and to delay fatigue. The present review describes the effects of exercise on the gastrointestinal tract and the aspects which determine optimal fluid and nutrient delivery during exercise in different climatological and exercise conditions.

Carbohydrate Metabolism↗

PubMed1991

Biomechanical vibration of the abdominal region during running and bicycling.

The incidence of gastrointestinal (GI) distress reported among long distance runners and not in practitioners of other sports with more gliding movements, such as bicycling, leads one to speculate that there is a difference in concussions and vibration of the GI region and that this may possibly be associated with the disparity in GI disorders. The present experiment was conducted to quantify the difference in vibration (accelerations/decelerations) of the GI region during running as compared to bicycling. An actometer was used which included a piezoelectric sensor. The sensor was placed on the abdomen of six subjects during identical trials of bicycling and running. Movement in three planes was detected by the sensor and recorded. The accelerometer output (AO) is an integral of these measurements. AO was used in making comparisons of the two types of movement, expressed as counts per minute. Mean AO was more than doubled in running, 859.5 +/- 130.1 (SD), versus bicycling, 425.8 +/- 149.5 (SD) (p less than .0001). The common assumption that running results in more body vibrations than bicycling has been substantiated and quantified. Although the differences are large, it can only be speculated that these differences explain the high frequency of GI symptoms among runners.

Abdomen↗

PubMed1991

Daily variation in gastric emptying when using the double sampling technique.

The purpose of this study was to establish the intra-individual variation in the rate of gastric emptying (GE) by using the double sampling technique of George. Eight healthy male volunteers, all familiar with gastric intubation and testing, participated in four GE tests, using an isotonic fluid as a test meal. Conditions were kept constant during all four tests, and each test was separated by at least 48 h. The within-subjects coefficient of variation proved to be 29%. The findings demonstrate that, given standard conditions, GE is reproducible from day to day.

Adult↗

PubMed1991

The importance of volume in regulating gastric emptying.

There is now substantive evidence that the provision of exogenous carbohydrate at high rates (1-2 g. min-1) can enhance performance during prolonged exercise. This finding has revived research into the factors determining the rate of exogenous carbohydrate delivery during exercise. While the rate of muscle oxidation of exogenous carbohydrate could be determined by the rate of gastric emptying or of intestinal carbohydrate absorption or of muscle glucose uptake and oxidation, most physiologists seem to have assumed that gastric emptying is the factor that limits the rate of exogenous carbohydrate delivery during exercise. Furthermore, studies of gastric emptying have suggested that the carbohydrate content of the ingested solution is an important factor determining its rate of gastric emptying. However, the findings of recent studies employing a repeated drinking design suggest that the gastric volume and therefore the pattern of drinking during exercise will have a significant, possibly major, influence on the rate of both carbohydrate and water delivery from any solution. This review considers this evidence and its practical implications for athletes who wish to ingest carbohydrate during exercise and for exercise physiologists designing studies to optimize carbohydrate delivery to muscle during exercise. It is proposed that, if gastric volume is an important determinant of the rate of gastric emptying, a more standardized method for reporting the rates of gastric emptying of different solutions should be adopted.

Beverages↗

PubMed1990

Gastric emptying with repeated drinking during running and bicycling.

The high prevalence of gastrointestinal complaints in long-distance runners makes the movements specific to this type of exercise suspected of causing a disruption of normal gastrointestinal function. Gastric emptying rate is one indicator thereof. In the present study trained volunteers performed similar repeated fluid ingestion tests while running and while bicycling for 80 min at 70% VO2max. Control tests at rest were also conducted. Two drinks containing carbohydrate were tested, one hypertonic, and one isotonic. Artificially sweetened water was used as a control. Gastric emptying rate of the isotonic drink, expressed as a percentage of the volume in the stomach at the beginning of each measurement period, did not differ between cycling and running during the first 40 min and was faster during cycling than during running between 40 and 80 min. With the hypertonic drink no differences between cycling and running were observed. In comparing gastric emptying rates after each sequential bolus, at rest, the isotonic drink was observed to maintain a high emptying rate, equal to that of water, whereas the hypertonic drink emptied more slowly after the first 20-min period. A similar pattern was observed during both running and cycling. The isotonic drink continued to empty quickly after the initial 20 min, whereas GE rate of the hypertonic drink decreased after the initial 20 min.

Adult↗