Today I would like to bring to your attention the following
paper:
Tsuji B, Honda Y, Fujii N, Kondo N, Nishiyasu T.
Comparison of hyperthermic hyperventilation during passive
heating and prolonged light and moderate exercise in the heat
J Appl Physiol. 2012 Nov; 113(9):1388-97
The aim of the study was to investigate the still little understood
(in terms of its physiological significance) mechanism behind the increase in
ventilation observed both at rest and during exercise, as a result of a rise in
core temperature. The results of the study indicate that the core temperature
threshold for hyperthermic hyperventilation and the hyperventilatory response
to increasing core temperature in passively heated subjects differs from that
in exercising subjects, irrespective of whether the exercise is moderate or
light.
The topic of “hyperthermic hyperventilation” is one of the
key interests of Dr Nishiyasu’s Lab at the University of Tsukuba (Japan), and the
present work was conducted by Dr Bun Tusji, whom I had the opportunity and
great pleasure to work with during the 5 weeks I recently spent in Japan as a
visiting PhD student in Dr Nishiyasu’s Lab.
Dr Nishiyasu (first on the right), Dr Tsuji (second on the left), and I (first on the left) during my time at the University of Tsukuba
During my time in Japan, I collaborate with Dr Tsuji and Dr Nishiyasu on a
study looking into the effects of restoring end-tidal carbon dioxide tension (PETCO2)
on middle cerebral artery blood velocity (MCA Vmean) during
hyperthermic hyperventilation resulting from passive heating.
A view of the experimental setting of the study I collaborated to while in Japan
It has been proposed that hyperthermic
hyperventilation is a thermoregulatory response aimed at selectively cooling the
brain.
In support of selective brain cooling in hyperthermic humans, White et al. (2010) suggests that vasodilation of the cerebral vasculature
exists, which in turn increases cranial perfusion and maintains the
arterial-venous temperature difference.
However, as a counterpoint, Crandall et al. (2011), suggest
that Whites et al. ‘s argument ignores the potent effects of changes in carbon
dioxide partial pressures on cerebral perfusion, with hypercapnia increasing
and hypocapnia decreasing cerebral blood flow, respectively. In support of this
concept, in their work, Tsuji et al. (2012) suggest that hyperventilation
reportedly leads to hypocapnia and a reduction in cerebral blood flow, which
would increase brain temperature due to a reduction in heat exchange.
Thus, the physiological significance of the human hyperthermic hyperventilation remains uncertain.
For more info on this interesting topic see the Journal of
Applied Physiology:
Humans do/do not demonstrate selective brain cooling
during hyperthermia.
J Appl Physiol. 2011 Feb;110(2):575-80.
Davide Filingeri
PhD Researcher
Environmental Ergonomics Research Centre
Loughborough University, UK
J Appl Physiol. 2012 Nov;113(9):1388-97. doi: 10.1152/japplphysiol.00335.2012. Epub 2012 Aug 23.
Comparison of hyperthermic hyperventilation during passive heating and prolonged light and moderate exercise in the heat.
Source
Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.
Abstract
Elevation of core temperature leads to increases in ventilation in both resting subjects and those engaged in prolonged exercise. We compared the characteristics of the hyperthermic hyperventilation elicited during passive heating at rest and during prolonged moderate and light exercise. Twelve healthy men performed three trials: a rest trial in which subjects were passively heated using hot-water immersion (41°C) and a water-perfused suit and two exercise trials in which subjects exercised at 25% (light) or 50% (moderate) of peak oxygen uptake in the heat (37°C and 50% relative humidity) after first using water immersion (18°C) to reduce resting esophageal temperature (T(es)). This protocol enabled detection of a T(es) threshold for hyperventilation during the exercise. When minute ventilation (Ve) was expressed as a function of T(es), 9 of the 12 subjects showed T(es) thresholds for hyperventilation in all trials. The T(es) thresholds for increases in Ve during light and moderate exercise (37.1 ± 0.4 and 36.9 ± 0.4°C) were both significantly lower than during rest (38.3 ± 0.6°C), but the T(es) thresholds did not differ between the two exercise intensities. The sensitivity of Ve to increasing T(es) (slope of the T(es)-Ve relation) above the threshold was significantly lower during moderate exercise (8.7 ± 3.5 l · min(-1) · °C(-1)) than during rest (32.5 ± 24.2 l · min(-1) · °C(-1)), but the sensitivity did not differ between light (10.4 ± 13.0 l · min(-1) · °C(-1)) and moderate exercise. These results suggest the core temperature threshold for hyperthermic hyperventilation and the hyperventilatory response to increasing core temperature in passively heated subjects differs from that in exercising subjects, irrespective of whether the exercise is moderate or light.
- PMID:
- 22923504
- [PubMed - indexed for MEDLINE]
References for this post
Tsuji B, Honda Y, Fujii N, Kondo N, Nishiyasu T. Comparison of hyperthermic hyperventilation during passive heating and prolonged light and moderate exercise in the heat. J Appl Physiol. 2012 Nov;113(9):1388-97. doi: 10.1152/japplphysiol.00335.2012. Epub 2012 Aug 23. PubMed PMID: 22923504.
White MD, Greiner JG, McDonald PL. Point: humans do demonstrate selective brain cooling during hyperthermia. J Appl Physiol. 2011 Feb;110(2):569-71; discussion 581-2. doi: 10.1152/japplphysiol.00992.2010. Epub 2010 Aug 26. PubMed PMID: 20798268.
Crandall CG, Brothers RM, Zhang R, Brengelmann GL, Covaciu L, Jay O, Cramer MN, Fuller A, Maloney SK, Mitchell D, Romanovsky AA, Caputa M, Nordström CH, Reinstrup P, Nishiyasu T, Fujii N, Hayashi K, Tsuji B, Flouris AD, Cheung SS, Vagula MC, Nelatury CF, Choi JH, Shrivastava D, Gordon CJ, Vaughan JT. Comments on point:counterpoint: humans do/do not demonstrate selective brain cooling during hyperthermia. J Appl Physiol. 2011 Feb;110(2):575-80. doi:10.1152/japplphysiol.01375.2010. PubMed PMID: 21304015.
hmmm...wow... nice link this is most article good
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