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Biomedical subjects

M L Riedesel

Publications and source records attributed to M L Riedesel.

At least 19 recordsLinked to original sources
PubMed1996

Pre-exercise glycerol hydration improves cycling endurance time.

The effects of glycerol ingestion (GEH) on hydration and subsequent cycle ergometer submaximal load exercise were examined in well conditioned subjects. We hypothesized that GEH would reduce physiologic strain and increase endurance. The purpose of Study I (n = 11) was to determine if pre-exercise GEH (1.2 gm/kg glycerol in 26 ml/kg solution) compared to pre-exercise placebo hydration (PH) (26 ml/kg of aspartame flavored water) lowered heart rate (HR), lowered rectal temperature (Tc), and prolonged endurance time (ET) during submaximal load cycle ergometry. The purpose of Study II (n = 7) was to determine if the same pre-exercise regimen followed by carbohydrate oral replacement solution (ORS) during exercise also lowered HR, Tc, and prolonged ET. Both studies were double-blind, randomized, crossover trials, performed at an ambient temperature of 23.5-24.5 degrees C, and humidity of 25-27%. Mean HR was lower by 2.8 +/- 0.4 beats/min (p = 0.05) after GEH in Study I and by 4.4 +/- 1.1 beats/min (p = 0.01) in Study II. Endurance time was prolonged after GEH in Study I (93.8 +/- 14 min vs. 77.4 +/- 9 min, p = 0.049) and in Study II (123.4 +/- 17 min vs. 99.0 +/- 11 min, p = 0.03). Rectal temperature did not differ between hydration regimens in both Study I and Study II. Thus, pre-exercise glycerol-enhanced hyperhydration lowers HR and prolongs ET even when combined with ORS during exercise. The regimens tested in this study could potentially be adapted for endurance activities.

Adult↗
PubMed1995

Sustained hyperhydration with glycerol ingestion.

Heavy exercise lasting more than three hours tends to result in dehydration, as the fluid intake is less than fluid loss by sweat and urine. Dehydration as small as one percent of body weight has been reported to decrease work capacity. In present and previous studies insensible water loss and sweat are assumed to be the same in both control and experimental conditions. Fluid intake less urine volume is utilized as an indicator of euhydration, hypohydration, or hyperhydration. Previous studies involving glycerol intake describe hyperhydration for 4.5 to 8 hours. The objective of this study was to keep subjects hyperhydrated (retention of water) for 32 or 49 hours. The experimental protocol involved ingestion of a large volume of fluid (39.2 or 51.1 ml/kg/d) with glycerol (2.9 to 3.1 g/kg/d) and without glycerol. In both Series I (49 h) and Series II (32 h) experiments, the intake of glycerol resulted in smaller urine volumes. This study demonstrates it is possible to keep human subjects hyperhydrated for extended periods of time and thereby reduce the amount of fluid consumption necessary just prior to or during bouts of negative fluid balance situations.

Administration, Oral↗
PubMed1995

Simultaneous cerebrovascular and cardiovascular responses during presyncope.

BACKGROUND AND PURPOSE: Presyncope, characterized by symptoms and signs indicative of imminent syncope, can be aborted in many situations before loss of consciousness occurs. The plasticity of cerebral autoregulation in healthy humans and its behavior during this syncopal prodrome are unclear, although systemic hemodynamic instability has been suggested as a key factor in the precipitation of syncope. Using lower body negative pressure (LBNP) to simulate central hypovolemia, we previously observed falling mean flow velocities (MFVs) with maintained mean arterial blood pressure (MABP). These findings, and recent reports suggesting increased vascular tone within the cerebral vasculature at presyncope, cannot be explained by the classic static cerebral autoregulation curve; neither can they be totally explained by a recent suggestion of a rightward shift in this curve. METHODS: Four male and five female healthy volunteers were exposed to presyncopal LBNP to evaluate their cerebrovascular and cardiovascular responses by use of continuous acquisition of MFV from the right middle cerebral artery with transcranial Doppler sonography, MABP (Finapres), and heart rate (ECG). RESULTS: At presyncope, MFV dropped on average by 27.3 +/- 14% of its baseline value (P < .05), while MABP remained at 2.0 +/- 27% above its baseline level. Estimated cerebrovascular resistance increased during LBNP. The percentage change from baseline to presyncope in MFV and MABP revealed consistent decreases in MFV before MABP. CONCLUSIONS: Increased estimated cerebrovascular resistance, falling MFV, and constant MABP are evidence of an increase in cerebral vascular tone with falling flow, suggesting a downward shift in the cerebral autoregulation curve. Cerebral vessels may have a differential sensitivity to sympathetic drive or more than one type of sympathetic innervation. Future work to induce dynamic changes in MABP during LBNP may help in assessing the plasticity of the cerebral autoregulation mechanism.

Adolescent↗
PubMed1994

Simultaneous transcranial Doppler and arterial blood pressure response to lower body negative pressure.

Microgravity induces fluid shifts which can alter the cardiovascular responses of astronauts both during space flight and on return to Earth. The decrease in orthostatic tolerance in astronauts returning from a weightless environment can be modelled in ground-based studies using lower body negative pressure (LBNP). This study examined the physiological changes induced by LBNP and determined a reliable method of predicting the onset of presyncope to enable evaluation of countermeasures for loss of orthostatic tolerance, such as glycerol-induced hyperhydration. Six healthy male subjects, aged 18 to 45 years, were each subjected to two LBNP tests, with or without glycerol ingestion. Continuous, non-invasive measurements of middle cerebral artery blood flow velocities (CBF) by transcranial Doppler, arterial blood pressure (Finapres ABP), ECG and LBNP box pressures were recorded during each test. Negative pressure was increased in three minute intervals until symptoms of presyncope were observed. An increase in heart rate (HR), a relatively constant mean ABP and a steady decline in mean CBF were consistently observed as the box pressure was decreased. The continuous on-line measurements clearly showed consistent dynamic changes in both CBF and ABP waveforms in response to changes in LBNP. At the onset of presyncope, sudden drops in mean ABP, HR and mean CBF were typically noted, the latter providing the earliest indication of presyncope. The time required to re-establish original baseline values of CBF and ABP after release of box pressure varied widely from six to over ten minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Glycerol-induced hyperhydration: its effects on fluid compartments in the rat.

Glycerol solutions are a safe, effective means to achieve a long-term state of hyperhydration. The effects of glycerol-induced hyperhydration (GIH) on the total body water (TBW), extracellular fluid (ECF), plasma volume (PV), intracellular fluid (ICF), and interstitial fluid (ISF) were investigated in the rat. Ten rats were intragastrically administered either 20 ml/kg of water or 5% glycerol. The TBW, ECF, and PV were determined by 3H2O, 14C-inulin and dye dilution, respectively at 2 h postingestion. Urine volumes and fluid retention were measured throughout the experiment. Fluid retention was increased by 50% with the 5% glycerol solution when compared to water. When the fluid compartment data at 2 h are expressed in terms of percent of body weight, the TBW and ICF of the glycerol-treated rats exceeds that of the water-treated rats, and the values for the ECF, PV, and ISF were similar after the glycerol solution and water regimens. Glycerol solutions appear to have a greater effect in expanding TBW and ICF than equal volumes of water.

Analysis of Variance↗
PubMed1990

Effects of glycerol-induced hyperhydration prior to exercise in the heat on sweating and core temperature.

Hypohydration reduces exercise performance and thermoregulatory capacity in the heat. Hyperhydration prior to exercise may decrease, delay, or eliminate the detrimental effects of hypohydration. The rapid clearance of excess fluid makes hyperhydration of subjects with common beverages difficult. Glycerol, a natural metabolite which is rapidly absorbed, has osmotic action, and is evenly distributed within the body fluid compartments, was tested as a possible hyperhydrating agent. In six subjects, the following fluid regimens at time 0 were randomly administered on three separate days: in trial 1, glycerol (1 g.kg-1 body weight) plus water (21.4 ml.kg-1 body weight); in trial 2, water (21.4 ml.kg-1); and in trial 3, water (3.3 ml.kg-1) was ingested at time 0. The subjects performed moderate exercise (equivalent to 60% VO2max in a comfortable environment) in a hot dry environment. The exercise started at 2.5 h after the fluids were ingested. The urine volume prior to exercise was decreased when glycerol was ingested, thus resulting in glycerol-induced hyperhydration. During the exercise following the glycerol-induced hyperhydration, there was elevated sweat rate and lower rectal temperature during the moderate exercise in the heat. There were no changes in hemoglobin, hematocrit, or serum electrolyte concentrations following glycerol intake. These data support the hypothesis that glycerol-induced hyperhydration reduces the thermal burden of moderate exercise in the heat.

Adult↗
PubMed1987

Hyperhydration with glycerol solutions.

Glycerol was tested as an agent to promote hyperhydration of male and female subjects. Series I experiments involved ingesting 0.5, 1.0, or 1.5 g glycerol/kg body wt and within 40 min drinking 0.1% NaCl, 21.4 ml/kg. In series II, 1.0 g glycerol/kg body wt was ingested at time 0, and 25.7 ml/kg of 0.1% NaCl was ingested over a 3.5-h period. Experiments were of 4-h duration and included controls without glycerol as each subject served as his/her control. Blood samples were taken at 40- or 60-min intervals for hemoglobin (Hb), hematocrit (Hct), plasma osmolality, glycerol, and multiple blood chemistry analyses. Urine was collected at 60-min intervals. Glycerol ingestion increased plasma osmolality for 2 h and reduced the total 4-h urine volume. There were no significant changes in Hb or Hct as a result of the glycerol or excess fluid intake. This study demonstrates that glycerol plus excess fluid intake can produce hyperhydration for at least 4 h.

Adolescent↗
PubMed1983

Body composition of oligo/amenorrheic athletes.

Menstrual dysfunction in athletes may be related to low body weight or low body fat content. To investigate the relationship between body composition and menstrual function, body composition was evaluated by hydrostatic weighing in two groups of women: 14 athletes with oligo/amenorrhea and 28 athletes with regular menstruation. Age and height were similar in the two groups. In all of the weight parameters, including total body weight, percent ideal body weight, Livi Index, percent body fat, fat weight, and lean body weight, athletes with oligo/amenorrhea were significantly lighter than athletes with regular menstruation. We concluded that menstrual dysfunction in athletes is associated with low body weight, which is comprised of smaller amounts of both fat and lean body mass.

Adipose Tissue↗
PubMed1980

Urea recycling in active golden-mantled ground squirrels (Spermophilus lateralis).

In response to fasting or fasting combined with water deprivation urine urea excretion declined sharply in normothermic ground squirrels (Spermophilus lateralis) when compared with laboratory rats. Intraperitoneal injection of urea equivalent to 0.3% of body weight failed to increase blood urea in 12-h fasted ground squirrels, and led to little urine urea excretion when compared with similarly treated rats. Collection of expired CO2 from fasted or fasted water-deprived ground squirrels that were urea loaded and injected with a tracer dose of 14C-tagged urea revealed a 1,000- to 1,500-fold greater 14CO2 expiration than controls. Treatment of fasted squirrels with antibiotics (penicillin, tetracycline, or sulfamethazine) to reduce intestinal microflora reduced expired 14CO2 to control levels. In fasted squirrels, drug treatment also enhanced urine urea excretion with values approaching those of controls. The results of these experiments point to the possibility of urea nitrogen recycling in nutritionally stressed ground squirrels.

Animals↗
PubMed1980

Protein metabolism and urea recycling in rodent hibernators.

A review of the metabolism of hibernators supports the argument that protein utilization is an essential aspect of hibernation. Several lines of evidence in support of this hypothesis are discussed, including (1) the field preferences of some hibernators for a diet rich in protein prior to hibernation, (2) the gluconeogenic maintenance of glycogen stores during hibernation, (3) the maintenance of plasma amino acid levels during hibernation and their elevation during the process of arousal, (4) changes in levels of nonprotein nitrogen with hibernation, (5) the potential for urea recycling by intestinal microflora in active fasted animals, and (6) the lack of correlation between loss of lean body mass and urea recovery during the hibernating season. These data serve to emphasize the contribution of protein metabolism to the overall energetic adjustments required for survival at a lower body temperature.

Amino Acids↗
PubMed1973

Memory and hibernation in Citellus lateralis.

Squirrels learned to escape from a water bath by making a visual discrimination. Twenty-four hours after reaching criterion for learned behavior, the animals were exposed to the first of two 11-day cold exposures. The animals that hibernated had better retention of the learned behavior.

Animals↗