Perceptual responses in the heat after brief intravenous versus oral rehydration

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158

122

Context: Authors of most field studies have not observed decrements in physiologic function and performance with increases in dehydration, although authors of well-controlled laboratory studies have consistently reported this relationship. Investigators in these field studies did not control exercise intensity, a known modulator of body core temperature.Objective: To directly examine the effect of moderate water deficit on the physiologic responses to various exercise intensities in a warm outdoor setting.Design: Semirandomized, crossover design. Setting: Field setting. Patients or Other Participants: Seventeen distance runners (9 men, 8 women; age 5 27 6 7 years, height 5 171 6 9 cm, mass 5 64.2 6 9.0 kg, body fat 5 14.6% 6 5.5%).Intervention(s): Participants completed four 12-km runs (consisting of three 4-km loops) in the heat (average wet bulb globe temperature 5 26.56C): (1) a hydrated, race trial (HYR), (2) a dehydrated, race trial (DYR), (3) a hydrated, submaximal trial (HYS), and (4) a dehydrated, submaximal trial (DYS).Main Outcome Measure(s): For DYR and DYS trials, dehydration was measured by body mass loss. In the submaximal trials, participants ran at a moderate pace that was matched by having them speed up or slow down based on pace feedback provided by researchers. Intestinal temperature was recorded using ingestible thermistors, and participants wore heart rate monitors to measure heart rate.Results: Body mass loss in relation to a 3-day baseline was greater for the DYR (24.30% 6 1.25%) and DYS trials (24.59% 6 1.32%) than for the HYR (22.05% 6 1.09%) and HYS (22.0% 6 1.24%) trials postrun (P , .001). Participants ran faster for the HYR (53.15 6 6.05 minutes) than for the DYR (55.7 6 7.45 minutes; P , .01), but speed was similar for HYS (59.57 6 5.31 minutes) and DYS (59.44 6 5.44 minutes; P . .05). Intestinal temperature immediately postrun was greater for DYR than for HYR (P , .05), the only significant difference. Intestinal temperature was greater for DYS than for HYS postloop 2, postrun, and at 10 and 20 minutes postrun (all: P , .001). Intestinal temperature and heart rate were 0.226C and 6 beats/min higher, respectively, for every additional 1% body mass loss during the DYS trial compared with the HYS trial.Conclusions: A small decrement in hydration status impaired physiologic function and performance while trail running in the heat.Key Words: environmental physiology, dehydration, rehydration, core temperature, heart rate Key Points N The physiologic and performance decrements associated with dehydration that exist in laboratory settings also exist in field settings. N Methodologic challenges in the field setting make isolating these effects difficult.

Section: Submaximal Running (Hys and Dys)mentioning

confidence: 99%

mentioning

confidence: 99%

Influence of Hydration on Physiological Function and Performance During Trail Running in the Heat

Casa

Stearns

Lopez

et al. 2010

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158

122

“…4 Oral REHY provides oropharyngeal stimulation, important for perceptual and some physiologic responses. [28][29][30] Bypassing this reflex with IV REHY, however, eliminates the potential disadvantage of delayed gastric emptying or intestinal fluid absorption or discomfort. [31][32][33] Direct comparisons are obviously contingent upon OR fluid tolerance, which can be impaired during significant dehydration.…”

Section: Discussionmentioning

confidence: 99%

Thermoregulation and Stress Hormone Recovery After Exercise Dehydration: Comparison of Rehydration Methods

McDermott

Casa

Lee

et al. 2013

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Context: Athletic trainers recommend and use a multitude of rehydration (REHY) methods with their patients. The REHY modality that most effectively facilitates recovery is unknown.Objective: To compare 5 common REHY methods for thermoregulatory and stress hormone recovery after exercise dehydration (EXDE) in trained participants.Design: Randomized, cross-over, controlled study. Patients or Other Participants: Twelve physically active, non-heat-acclimatized men (age ¼ 23 6 4 years, height ¼ 180 6 6 cm, mass ¼ 81.3 6 3.7 kg,VO 2 max ¼ 56.9 6 4.4 mLÁmin, body fat ¼ 7.9% 6 3%) participated. Intervention(s): Participants completed 20-hour fluid restriction and 2-hour EXDE; they then received no fluid (NF) or REHY (half-normal saline) via ad libitum (AL), oral (OR), intravenous (IV), or combination IV and OR (IV þ OR) routes for 30 minutes; and then were observed for another 30 minutes.Main Outcome Measure(s): Body mass, rectal temperature, 4-site mean weighted skin temperature, plasma stress hormone concentrations, and environmental symptoms questionnaire (ESQ) score.Results: Participants were hypohydrated (body mass À4.23% 6 0.22%) post-EXDE. Rectal temperature for the NF group was significantly greater than for the IV group (P ¼ .023) at 30 minutes after beginning REHY (REHY30) and greater than OR, IV, and IV þ OR (P .009) but not AL (P ¼ .068) at REHY60. Mean weighted skin temperature during AL was less than during IV þ OR at REHY5 (P ¼ .019). The AL participants demonstrated increased plasma cortisol concentrations compared with IV þ OR, independent of time (P ¼ .015). No differences existed between catecholamine concentrations across treatments (P . .05). The ESQ score was increased at REHY60 for NF, AL, OR, and IV (P , .05) but not for IV þ OR (P ¼ .217). The NF ESQ score was greater than that of IV þ OR at REHY60 (P ¼ .012).Conclusions: Combination IV þ OR REHY reduced body temperature to a greater degree than OR and AL REHY when compared with NF. Future studies addressing clinical implications are needed.Key Words: heat stress, heat illness, hypohydration Key PointsA combination of intravenous and oral fluid replacement after exercise dehydration reduced heat-related symptoms more than a single mode of rehydration. If intravenous fluid replacement is warranted, the addition of simultaneous oral rehydration seems to add benefit to an efficient recovery.

“…13 Perceived thirst did not differ among treatment drinks at any point during the 60-minute rehydration period. Scientists 26,27 have observed that the act of drinking, not a decrease in OSM p or [Na þ ] p , is responsible for the rapid satiety of thirst. Additionally, the Na þ content of the fluid consumed appears to have a minimal effect on thirst.…”

Section: Perceptual Indicatorsmentioning

confidence: 99%

Ad Libitum Fluid Intake and Plasma Responses After Pickle Juice, Hypertonic Saline, or Deionized Water Ingestion

Allen

Miller

Albrecht

et al. 2013

Context: Adding sodium (Na þ ) to drinks improves rehydration and ad libitum fluid consumption. Clinicians (~25%) use pickle juice (PJ) to treat cramping. Scientists warn against PJ ingestion, fearing it will cause rapid plasma volume restoration and thereby decrease thirst and delay rehydration. Advice about drinking PJ has been developed but never tested.Objective: To determine if drinking small volumes of PJ, hypertonic saline (HS), or deionized water (DIW) affects ad libitum DIW ingestion, plasma variables, or perceptual indicators.Design: Crossover study. Setting: Laboratory.Patients or Other Participants: Fifteen, euhydrated (urine specific gravity 1.01) men (age ¼ 22 6 2 years, height ¼ 178 6 6 cm, mass ¼ 82.9 6 8.4 kg).Intervention(s): Participants completed 3 testing days (!72 hours between days). After a 30-minute rest, a blood sample was collected. Participants completed 60 minutes of hard exercise (temperature ¼ 36 6 28C, relative humidity ¼ 16 6 1%). Postexercise, they rested for 30 minutes; had a blood sample collected; rated thirst, fullness, and nausea; and ingested 83 6 8 mL of PJ, HS, or DIW. They rated drink palatability (100-mm visual analog scale) and were allowed to drink DIW ad libitum for 60 minutes. Blood samples and thirst, fullness, and nausea ratings (100-mm visual analog scales) were collected at 15, 30, 45, and 60 minutes posttreatment drink ingestion.Main Outcome Measure(s): Ad libitum DIW volume, percentage change in plasma volume, plasma osmolality (OSM p ,) plasma sodium concentration ([Na þ ] p ), and thirst, fullness, nausea, and palatability ratings.Results: Participants consumed more DIW ad libitum after HS (708.03 6 371.03 mL) than after DIW (532.99 6 337.14 mL, P , .05). Ad libitum DIW ingested after PJ (700.35 6 366.15 mL) was similar to that after HS and DIW (P . .05). Plasma sodium concentration, OSM p , percentage change in plasma volume, thirst, fullness, and nausea did not differ among treatment drinks over time (P . .05). Deionized water (73 6 14 mm) was more palatable than HS (17 6 13 mm) or PJ (26 6 16 mm, P , .05).Conclusions: The rationale behind advice about drinking PJ is questionable. Participants drank more, not less, after PJ ingestion, and plasma variables and perceptual indicators were similar after PJ and DIW ingestion. Pickle juice did not inhibit short-term rehydration.