Effect of passive heat stress on arterial stiffness in smokers versus non-smokers.

In non-smokers, passive heat stress increases shear stress and vasodilation, decreasing arterial stiffness. Smokers, who reportedly have arterial dysfunction, may have similar improvements in arterial stiffness with passive heat stress. Therefore, we examined the effects of an acute bout of whole-body passive heat stress on arterial stiffness in smokers vs. non-smokers. Thirteen smokers (8.8 ± 5.5 [median = 6] cigarettes per day for > 4 years) and 13 non-smokers matched for age, mass, height, and exercise habits (27 ± 8 years; 78.8 ± 15.4 kg; 177.6 ± 6.7 cm) were passively heated to 1.5 °C core temperature (T C) increase. At baseline and each 0.5 °C T C increase, peripheral (pPWV) and central pulse wave velocity (cPWV) were measured via Doppler ultrasound. No differences existed between smokers and non-smokers for any variables (all p > .05), except cPWV slightly increased from baseline (526.7 ± 81.7 cm · s(-1)) to 1.5 °C ΔT C (579.7 ± 69.8 cm · s(-1); p < 0.005), suggesting heat stress acutely increased central arterial stiffness. pPWV did not change with heating (grand mean: baseline = 691.9 ± 92.9 cm · s(-1); 1.5 °C ΔT C = 691.9 ± 79.5 cm · s(-1); p > 0.05). Changes in cPWV and pPWV during heating correlated (p < 0.05) with baseline PWV in smokers (cPWV: r = -0.59; pPWV: r = -0.62) and non-smokers (cPWV: r = -0.45; pPWV: r = -0.77). Independent of smoking status, baseline stiffness appears to mediate the magnitude of heating-induced changes in arterial stiffness.

24-h Void number as an indicator of hydration status.

BACKGROUND/OBJECTIVES: Few user-friendly hydration assessment techniques exist for the general population to use on a daily basis. The present study evaluated void number over 24 h as a potential hydration assessment tool. SUBJECTS/METHODS: Male and female subjects collected urine for 24 h while adequately hydrated (n=44; 22 ± 4 years, 168 ± 16 cm, 73 ± 15 kg) or fluid restricted (n=43; 22 ± 3 years, 175 ± 10 cm, 81 ± 24 kg). As a control, participants were asked to void when feeling the 'first urge to void' on a commonly used urge scale and noted the volume of each void. For each sample, 24-h urine volume, osmolality (U(OSM)), specific gravity (U(SG)) and color were measured in the laboratory. RESULTS: As designed, the level of urge upon voiding was consistent throughout the study (2 ± 0; 'first urge to void'). Samples were classified by U(SG) as either euhydrated (U(SG)<1.020) or hypohydrated (U(SG) ⩾ 1.020). Grouping by U(OSM) did not change results. Euhydrated versus hypohydrated individuals had greater 24-h urine volume (1933 ± 864 versus 967 ± 306 ml, respectively) and lower urine color (2 ± 1 versus 5 ± 1), U(SG) (1.012 ± 0.004 versus 1.025 ± 0.004) and UOSM (457 ± 180 versus 874 ± 175 mOsm/kg H2O; all P<0.001). Euhydrated individuals voided more than hypohydrated individuals over the 24-h period (5 ± 2 versus 3 ± 1 voids; P<0.001). Additionally, void number inversely correlated with hydration status as identified by U(SG) (r=-0.50; P<0.05) and U(OSM) (r=-0.56; P<0.05). CONCLUSIONS: In conclusion, over 24 h, individuals with a higher void number were euhydrated (that is, had less concentrated hydration biomarkers) than those with a lower void number. Based on these data, void number might be utilized as a simple and feasible hydration assessment for the general public, as it utilizes no equipment or technical expertise.