The cutaneous vasodilation and sweating responses of prepubertal children to heat stress were examined. Seven prepubertal boys (9-11 years old) and 9 young men (20-24 years old) were seated wearing only swimming trunks while the air temperature (T(a)) was linearly increased from 28 degrees C to 40 degrees C over 50 min and then maintained at 40 degrees C for an additional 10 min. Skin temperature, cutaneous vascular conductance (CVC), and local sweating rate (m(sw)) were measured at multiple sites on the body. The boys had a significantly greater mean surface area-to-mass ratio compared with the young men. The rectal temperature did not change in either group with increasing T(a), although it was significantly higher in the boys. During the first half of the exposure period, when T(a) was less than the mean skin temperature (T(sk)), the boys had significantly higher CVC on the chest and significantly lower m(sw) on the chest and thigh as compared with the young men. During the latter half of the exposure, when heat stress was increased as T(a) exceeded mean T(sk), the boys had significantly higher mean T(sk), greater CVC on the chest and finger, greater rate of increase in the CVC on the forehead and finger, lower m(sw) on the chest and thigh, greater increase in heart rate, and higher thermal sensation. The mean body temperature at the onset of sweating was significantly greater in the boys than in the men. These results suggest that, compared with young men, prepubertal boys manifest greater physiological and perceptual strain under heat stress induced by T(a) exceeding mean T(sk), which is most probably attributable to a combination of lower evaporative heat loss, as evidenced by lower m(sw), and greater heat gain owing to a larger surface area-to-mass ratio. The maturation-related differences in heat loss responses vary according to body site.
To elucidate the mechanisms that underlie the greater decline of skin temperature on the limbs in prepubertal boys as compared to young men, we compared cutaneous vascular conductance (CVC) of the boys and men in response to a reduced ambient temperature (T (a)). The boys had a greater surface area-to-mass ratio (A (D)/mass) and a lower mean skinfold thickness on the trunk but not on the limbs compared to the men. As T (a) decreased from 30 to 17 degrees C over 60 min, the skin temperature (T (sl)) on the limbs (as represented by forearm, finger and thigh) decreased significantly more in the boys than in the men; while T (sl) on the trunk (chest, back and abdomen) and forehead decreased to the same extent. The CVC decreased at all body sites in all subjects, but regional difference existed in age-related alterations in CVC responses despite the similar rectal and mean body temperatures of the groups. The decline in the finger CVC was greater for the boys than for the men, suggesting that greater vasoconstriction and greater A (D)/mass on the fingers may have contributed to the lower finger T (sl) of the boys. However, thigh CVC in the boys was similar to that in the men over the 60-minute exposure, indicating that the lower thigh T (sl) of the boys may be the result of greater heat loss owing to the greater A (D)/mass on the limbs of the boys (but not to greater vasoconstriction or subcutaneous fat). The CVC on the chest and back was greater in the boys over the cold exposure, suggesting that similar T (sl )on the chest and back of the boys and men may result from greater cooling owing to the larger A (D)/mass being offset by combination of less vasoconstriction and more conductive heat transfer in the presence of less subcutaneous fat. These results suggest that the age-related difference in T (sl) in response to mild cold stress may not directly reflect that in cutaneous vasoconstriction alone owing to the differences in anthropometric characteristics (such as greater A (D)/mass and lower subcutaneous fat on trunk) between boys and men.
Introduction: A residual gradient and repeat septal reduction therapy are more likely to occur with alcohol seplta ablation (ASA) than with surgical myectomy. We evaluated a cohort of patients treated with ASA to identify predictive factors of repeat ASA. Methods: Of 157 patients who underwent ASA, 19 (Group R) who underwent repeat ASA procedures remained after excluding those with planned staged ablation and isolated mid-ventricular obstruction. The median time interval between both procedures was 2.1 years. We compared Group R with patients not requiring repeat procedures (n = 105, Group S) in terms of clinical characteristics, ASA procedures, and morphological cardiac magnetic resonance (CMR), which was used to diagnose regional hypertrophy (thickness ≥ 15 mm) for each left ventricular myocardial segment. Results: Compared with group S, group R had a higher peak creatine phosphokinase value at the first ASA (1250 ± 522 vs. 1028 ± 520 IU/L, p = 0.046) and number of hypertrophic segments in the basal left ventricular level (segments 0-6, 2.8 ± 1.7 vs. 1.7 ± 0.8, p = 0.009). In multivariate analysis, diuretics use [adjusted odds ratio, 9.3 (95%CI: 1.6-56.2)] and the number of extended hypertrophy segments (except the anteroseptal region at the basal left ventricular level) were independent predictors of a repeat ASA procedure (adjusted odds ratio, 6.8 (95%CI: 1.5-32.1)/segment, p = 0.010). The repeat ASA rate was only 5% (1/21) among patients without non-anteroseptal hypertrophy, and 3% (1/29) among those without posteroseptal hypertrophy; however, patients with ≥2 segments of non-anteroseptal hypertrophy had an extremely high rate (50%, 7/14). Conclusions: CMR morphological analysis elucidated the characteristics of regional hypertrophic patterns in patients who underwent repeat ASA and found non-anteroseptal extended hypertrophy (≥ 2 segments) to be a crucial predictor of repeat ASA.
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