Premium
The effect of fan use and folic acid supplementation on thermal and cardiovascular strain in healthy aged humans during heat exposure
Author(s) -
Gag Daniel,
Romero Steven A,
Ngo Hai,
Poh Paula YS,
Kouda Ken,
Cramer Matthew N,
Jay Ollie,
Crandall Craig
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1290.8
Subject(s) - relative humidity , medicine , sweat , forearm , thermoregulation , vasodilation , zoology , surgery , physics , biology , thermodynamics
Attenuated heat loss and altered cardiovascular adjustments during heat stress are considered important contributing factors to the increased prevalence of death in aged individuals during heat waves. Interventions aimed at reducing thermal and cardiovascular strain during heat stress in the aged are lacking. We therefore examined if fan use (by improving sweat evaporation) or folic acid supplementation (by improving cutaneous vasodilation) can mitigate thermal and cardiovascular strain during heat exposure, as well as modify the limit of thermal compensability in healthy aged humans. Six healthy older individuals (69 ± 3 y, 166 ± 12 cm, 72 ± 16 kg, 2 males/4 females) rested in a thermal chamber at a temperature of 42°C and a relative humidity initially maintained at 30%. After a 30 min baseline period, relative humidity was increased in 2% steps every 5 min until a relative humidity of 70% was reached (100 min). The protocol was performed with no intervention (CON), with a fan that provided ~4 m/s of air velocity (FAN), and following 6 weeks of folic acid supplementation (FOLIC). Esophageal (T es ) and mean skin (T sk ) temperatures, local forearm cutaneous vascular conductance (laser‐Doppler, CVC), forearm vascular conductance (Doppler ultrasound, FVC), local sweat rate (ventilated capsule), heart rate and blood pressure were measured throughout. At 70% relative humidity, fan use and folic acid supplementation both increased CVC relative to control (CON: 1.34 ± 0.24 vs. FAN: 1.95 ± 0.39 vs. FOLIC: 1.81 ± 0.35 units/mmHg, P ≤0.05). However, this did not translate into different FVC responses (CON: 4.86 ± 1.95 vs. FAN: 5.08 ± 1.91 vs. FOLIC: 4.41 ± 1.78 mL/min/mmHg, P >0.05). Fan use also increased local sweat rate (0.84 ± 0.27 mg/min/cm 2 ) relative to CON (0.60 ± 0.26 mg/min/cm 2 , P ≤0.05), whereas FOLIC had no effect (0.62 ± 0.21 mg/min/cm 2 , P =0.64). Relative to CON (T es : 37.62 ± 0.29°C, T sk : 38.41 ± 0.25°C), esophageal and mean skin temperatures were greater during FAN (T es : 37.94 ± 0.63°C, T sk : 38.97 ± 0.55°C, P ≤0.05) but not FOLIC (T es : 37.58 ± 0.21°C, T sk : 38.28 ± 0.25°C, P >0.05). In contrast, heart rate and blood pressure were similar during all conditions (both P >0.05). The critical humidity at which an inflection in esophageal temperature was observed did not differ between conditions (CON: 63 ± 2 vs. FAN: 64 ± 5 vs. FOLIC: 63 ± 4%, P =0.64). Under the conditions employed, fan use results in greater esophageal and mean skin temperatures during extreme heat exposure in healthy aged individuals while folic acid supplementation has no effect. Furthermore, neither intervention reduced cardiovascular strain nor did they modify the limit of thermal compensability. Support or Funding Information Funded by the National Institutes of Health (GM‐068865).