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Hydration

Hydration and Physical Activity

Citation:

Greenleaf JE, Jackson R, Geelen G, Keil LC, Hinghofer-Szalkay H, Whittam JH. Plasma Volume Expansion with Oral Fluids in Hypohydrated Mean at Rest and During Exercise.  Aviation, Space, and Environmental Medicine, 1998 69(9):837-844.

PubMed ID: 9737753
 
Study Design:
Non-Randomized Controlled Trial
Class:
C - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

To evaluate oral rehydration fluid formulations of various osmotic and carbohydrate contents which could be used by astronauts to increase extracellular (plasma and interstitial) fluid volume in preparation for extravehicular activity (EVA) in microgravity (exercise experiment).

To determine whether the plasma sodium or osmotic content was the most important variable for increasing plasma volume .

Inclusion Criteria:

Pass comprehensive medical exam

Exclusion Criteria:

None specified

Description of Study Protocol:
  • Four experimental drinks:  1) water; 2) 19.6 meq Na+ beverage; 3) 157 meq Na+ beverage; 4) 19.6 meq Na+ + glucose (9.7% total CHO)
  • Two commercial beverages:  1)  Shaklee Performance (shaklee Technica, San Francisco CA) ( ~ 20 meq Na+; 9.7% total CHO);  2) Power Surge (Perc Products, Moscow, PA) (~20 meq Na+, 9.7% total CHO)
  • Two groups:  Rest (RE) or Exercise (EE) at 71 + 1% of peak VO2 for 70 min
  • Protocol: 
    • Subjects dehydrated for 24 hr prior to test
    • 45 min resting control period prior to drinking
    • Drink volume = 12 mL ·kg-1 (898-927 mL); drinking time=2.3 to 6.2 min (mean + SE = 4.8+0.4 min during RE and 3.2 + 0.2 min with EE
Data Collection Summary:

Timing of Measurements

  • Pre-testing (-45 min): weight and urine
  • -15, -5, +3, +9, +15, +30, +70 min:  blood
  • Post-tesing(+70 min): weight and urine

Dependent Variables

  •  Blood paramenters
    • Percent change blood volume: calculated with the Hb-Hct transformation equation
    • Plasma osmolaltiy
  • Urinary measurements
    • Urinary volume: [pre-testing control vs posst-test (+70 min)] was time and measured in graduated cylinders
    • Urinary osmotic concentration (Uosm)
    • Urinary flow (V): ml/min
    • Urinary osmotic clearance (Cosm): urine osmotic excretion (Uosm·V)/plasma osmolality
    • Free water clearance (CH2O was V·Cosm)

Independent Variables

  • Exercise condition: RE (resting) or EE (Exercise) (supine)
  • Hydration beverage

   

Description of Actual Data Sample:

Initial N:  7 males (2 subjects participated in both conditions

Attrition (final N):  Final N=7

Age: (mean + s.d.)  RE:  (n=5) 32+7 years ;  EE (n=4):  35+7 years

Anthropometrics:

  • Weight (kg):  RE = 78.00 + 8.15;  EE = 74.91 + 8.09
  • Height (m2):  RE= 1.94 + 0.11;  EE = 1.87 + 0.13
  • Peak VO2:  EE = 34.8 + 12.0 ml ·min-1 ·kg-1

Location:  NASA, Ames Research Center, California

Summary of Results:

REST Experiment:
    After drinking/ first 15 min. of rest:

  • Plasma Volume:
    • No change in PV with 157 meq Na+ and Power [20 meq Na+]
    • Decrease in PV by .3-4%% with Water, 19.6meq  Na+, 19.6 meq Na++glu, and Performance [20 meq Na+] (P<.05)
  • Plasma osmotic changes
    • Resting osmolality and change osmolality were lowest with Water (P<.05)
    • Small increasing  trend (NS) of change osmolality within 5 min with all drinks exept Water that returned by baseline (Zero) by 70 min.
    • No change in PV with 157 meq Na+ and Power [20 meq Na+]
    • Decrease in PV by .3-4%% with Water, 19.6 meq Na+, 19.6 meq Na++glu, and Performance [20 meq Na+] (P<.05)  

    15 + minutes of rest:

  • Plasma Volume:
    • all PV shifts had returned to zero
    • Changes with Water, 19.6 meq Na+, 19.6 meq Na++glu, and Power [20 meq Na+ tended to increase to only +1% (NS)
  • Plasma osmotic concentration and content:
    • Plasma osmolality of Performace [20 meq Na+] @ 15 min and 157 meq Na+ at 30 min. were higher (P<.05) compared with Water.  

     70 min. rest:

  • Plasma volume:
    • PV changes of 157 meq Na+ and Performance [20 meq Na+] (both with greater ionic content) increased to +7.6% and +4.6% at 70 min. of rest (P<.05)
  • Plasma Osmotic concentration and content:
    • Plasma  Osmotic concentration and content:
      • % change PV increased at 70 min with Performance [20 meq Na+](P<.05) and 157  meq Na+(P<.05) (higher osmotic contents)
      • No consistent relationship between total osmolality, change osmolality, and % change in osmotic content.
      • Osmotic content of all drinks except 157 meq Na+ and Performance [20 meq Na+]responded similarly with Water. Drink total osmolality was: Water-30; 19.6 meq Na+ -70; 157 meq Na+: -320; 19.6 meq Na++glu -650; Performance -380 and Power -390.


EXERCISE experiment
    After drinking/first 15 min exercise:

  • Plasma volume:
    • PV with all drinks decreased significantly (P<.05) between 3-15 min. of exercise

15+ min exercise:

    • No recovery of PV to control level with any drink.

70 min exercise:

  • Plasma volume:
  • % change PV 70 min. values= -5.2% (NS) with 19.6 meq Na++glu to -13.5% (P<.05) with Power [20 meq Na+] and -14.2% (P<.05) with Water.

    • Greater sustained decreases in PV with Water and Power [20 meq Na+]
    • After drinking Water and Power [20 meq Na+], exercise hypovolemic response at 70 min decreased by 12-14% units (similar to comparable exercise with no prior fluid intake).
    • 19.6 meq Na+ and 19.6 meq Na++glu and 157 meq Na+ resulted in somewhat attenuated levels (NS) of hypovolemia during exercise.
    • Drinks 19.6 meq Na+, 157 meq Na+, 19.6 meq Na++glu, and Performance [20 meq Na+] provided 5-9% units of PV restoration when compared with Water.
       
  • Plasma osmotic concentration and content:
    • -8% with Water and Power (P=.05); comparable decrease in exercise PV
    • 157 meq Na+and Performance resulted in the highest or least attenuated content change (NS) , associated with lesser attenuated comparable negative changes in exercise PV, suggesting that higher osmotic content maintains PV
       

Urinary parameters - rest and exercise experiments

  • Average urinary exertion rates
    • RE:  101 +0.1 ml ·min-1  (Normal = 1.0 ml ·min-1)
    • EE: 1.2+0.2 ml·min-1
  • Increase in excretion 2.0 + 0.5 ml·min-1 in 19.6 meq Na+ (P<.05)
  • No differences between rest and exercise in average mean free water clearance or other osmotic clearances

Other Findings

  • Rest (control) systolic/diastolic blood pressures(BP) and heart rate (HR) were within normal range of 110-120/80-90 mmHg and 60-70 bpm
  • Drink composition had no effect on rest or exercise BP or heart rate responses: Steady state levels of BPs (158 -166/72-75 mm Hg) and HR (124-151 bpm) were reached at 60-70 min of exercise.
Author Conclusion:

Drink formulation cation (mainly sodium) content is more important than its total osmotic content for inducing hypervolemia in resting subjects.  Formulations with greater hypervolemic action at rest are not as effective during exercise;  therefore, different formulations will probably be necessary to attenuate hypovolemia during exercise.

Funding Source:
Government: NASA
Reviewer Comments:
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? ???
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? ???
  2.2. Were criteria applied equally to all study groups? ???
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? ???
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) No
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? ???
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? N/A
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? Yes
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? ???
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? N/A
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? N/A
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes