No abstract

We have previously shown that activation of muscle receptors by passive stretch (PS) increases heart rate (HR) with little change in blood pressure (BP). We proposed that PS selectively inhibits cardiac vagal activity. We attempted to test this by performing PS during experimental alterations in vagal tone. Large decreases in vagal tone were induced using either glycopyrrolate or mild rhythmic exercise. Milder alterations in vagal tone were achieved by altering carotid baroreceptor input: neck pressure (NP) or neck suction (NS). PS of the triceps surae was tested in 14 healthy human volunteers. BP, ECG and respiration were recorded. PS alone caused a significant decrease (P < 0.05) in R-R interval (962 ± 76 ms at baseline compared to 846 ± 151 ms with PS), and showed a reduction in HR variability, which was not significant. The decrease in R-R interval with PS was significantly less (P < 0.05, n = 3) following administration of glycopyrrolate (−8.1 ± 4.5 ms) compared to PS alone (−54 ± 11 ms), and also with PS during handgrip (+10 ± 10 ms) compared with PS alone (−74 ± 15 ms) (P < 0.05, n = 5). Milder reductions in vagal activity (NP) resulted in a small but insignificant further decrease in R-R interval in response to PS (−107 ± 17 ms compared to PS alone −96 ± 13 ms, n = 5). Mild increases in vagal activity (NS) during PS resulted in smaller decreases in R-R interval (−39 ± 5.5 ms) compared to PS alone (−86 ± 17 ms) (P < 0.05, n = 8). BP was not significantly changed by stretch in any tests. The results indicate that amongst muscle receptors there is a specific group activated by stretch that selectively inhibit cardiac vagal tone to produce tachycardia.

No abstract

Brown adipose tissue (BAT) function is greatest in children but the main factors influencing it remain to be determined. Our study was, therefore, designed to determine whether body mass index (BMI) centile influenced skin temperature overlying BAT depots in the supraclavicular region (SCR) of healthy children. Infrared thermography was used to assess SCR skin temperature at baseline and following exposure to a mild cool stimulus (single hand immersion in water at 20.1°C) over a period of 5 minutes in young children aged 6–11 years (n=55). There was a clear difference in SCR temperature between age matched healthy subjects who were either of low, or high, BMI. The primary indicator of baseline and stimulated SCR temperature was BMI centile for which there was an inverse relationship (R2 = 0.26; P = 0.009). Ethnicity was also a significant predictor of SCR temperature. We have demonstrated an inverse relationship between the temperature of the SCR, co‐locating with the primary region of BAT, and BMI centile. Future studies aimed at determining the primary factors regulating BAT function in healthy children could be used to prevent excess white adipose tissue deposition in early life.