Cold-water face immersion per se elicits cardiac parasympathetic activity.

BACKGROUND: Cold-water face immersion (FI) is known to produce physiological changes, including bradycardia, by stimulating the parasympathetic system. However, other factors such as sympathetic activity, intrapleural pressures, and changes in chemical mediators may also contribute to these changes. METHODS AND RESULTS: Eight healthy volunteers underwent a series of experiments designed to observe the effects of FI on heart rate and its variability, as detected using wavelet transformation. Each subject was instructed to bend over and put the entire face into an empty basin with and without breathing (protocols 1 and 2, respectively), and then perform FI in warm-water (protocols 3 and 4, respectively) and cold-water (protocols 5 and 6, respectively) while breathing and breath holding. Change in the R-R interval with FI was only significantly greater for protocol 6 than for the control procedure (protocol 1). Also, changes in the natural logarithm of high-frequency power with FI were significantly greater for protocols 5 and 6 than the protocol 1. CONCLUSIONS: Bradycardia associated with cold-water FI is mainly attributed to cardiac vagal activity, which is independent of both the change in body position caused by bending over a basin and breath holding.

Is the chronotropic index applicable to children and adolescents?

BACKGROUND: The aim of the present study was to investigate whether the chronotropic index (CRI) is independent of age, sex, stage of exercise testing, functional capacity and resting heart rate in children, as it is in adult populations. METHODS AND RESULTS: A total of 129 normal children and adolescents underwent maximal treadmill exercise testing according to the Bruce protocol. Submaximal chronotropic response was assessed by the CRI at the end of stages 1, 2, 3, and 4 of Bruce treadmill exercise testing. The CRI assessed at each exercise stage was independent of sex, maximal oxygen uptake and resting heart rate. The CRI was independent of age when measured at stages 3 and 4 in boys and at stage 4 in girls, but was weakly correlated with age when measured at stages 1 and 2 in boys and at stages 1, 2 and 3 in girls. There was a significant effect of exercise intensity on the CRI: multiple comparisons revealed that, in girls, CRI assessed at stage 1 was greater than that assessed at stage 4. Also, lower exercise stages resulted in rather large variations in the measurement. CONCLUSION: The results essentially confirm the potential applicability of the CRI for children and adolescents, although care should be taken in evaluating measurements of the CRI in the early stages of exercise testing to avoid misinterpretation of the results.

Effect of exercise testing protocol on the relationship between minute ventilation and carbon dioxide production.

BACKGROUND: The effect of exercise protocol on the slope of the relationship between minute ventilation and carbon dioxide production (deltaVE/deltaVCO2) has not fully been studied. METHODS: Twenty-five healthy volunteers performed two sessions of incremental bicycle exercise, one with a rapidly increasing staged (RIS: 25W every minute) protocol and another with a slowly increasing staged (SIS: 25W every 3 minutes) protocol to calculate the deltaVE/deltaVCO2. Six of the subjects also participated in sessions of steady state exercise (SSE) test various work rates. RESULTS: The deltaVE/deltaVCO2 was significantly lower when the RIS protocol was used than when the SIS protocol was used (23.3 +/- 2.3 vs. 24.9 +/- 1.8, p < 0.001). Data from the subjects who also underwent SSE sessions revealed that the deltaVE/deltaVCO2 from the SSE protocols was greater than that from the RIS protocol and identical with that from the SIS protocol (125.1 +/- 3.7. 20.6 +/- 1.7, and 24.0 +/- 2.7, respectively, p < 0.05), while arterial partial pressure of carbon dioxide during exercise was not different between the protocols (43.0 +/- 3.3. 39.9 +/- 2.1, and 40.8 +/- 2.6, respectively, n.s.). C ONCLUSIONS: Care must be taken in the interpretation of the values of deltaVE/deltaVCC2, as they are influenced by the difference in exercise protocol.