Rob Meade

Promoting targeted heat early warning systems for at-risk populations - Nature Climate Change Extreme heat poses a growing threat to vulnerable urban populations, and the existing heat early warning system usually operates at population level. Pairing emerging individualized and population ear...

Our new comment published in @natclimate.nature.com advocating for the addition of more personalised early warning systems for the most in need during extreme heat ☀️🥵🌡️ www.nature.com/articles/s41... @griffith.edu.au

Just a note on the study - the technique we validated evaluates the upper limit for thermoregulation, above which core temperature will increase to dangerous levels over a relatively short period.

The thresholds are much higher than those for discomfort and (likely) impacts on focus, learning etc.

1/11 Sport and exercise science is moving into an era of excellent work regarding evidence synthesis and the application of advances in meta-analytical modeling to make the most of the typically inferentially weak studies that make up the field... #theory #science #philsci #metasci

Data driven != Evidence driven

Let me know if you have any Qs 😁

Abstract Recent projections suggest that large geographical areas will soon experience heat and humidity exceeding limits for human thermoregulation. The survivability limits modeled in that research were based on laboratory studies suggesting that humans cannot effectively thermoregulate in wet bulb temperatures (Twb) above 26 to 31 °C, values considerably lower than the widely publicized theoretical threshold of 35 °C. The newly proposed empirical limits were derived from the Twb corresponding to the core temperature inflection point in participants exposed to stepped increases in air temperature or relative humidity in a climate-controlled chamber. Despite the increasing use of these thermal-step protocols, their validity has not been established. We used a humidity-step protocol to estimate the Twb threshold for core temperature inflection in 12 volunteers. To determine whether this threshold truly demarcates the Twb above which thermoregulation is impossible, each participant was subsequently exposed to Twb above (~33.7 °C, Tabove) and below (~30.9 °C, Tbelow) their respective inflection point (~32.3 °C, Twb) for up to 9 h (in random order). Core temperature rose continuously in Tabove. It was projected that core temperatures associated with heat stroke (40.2 °C) would occur within 10 h. While Tbelow was also uncompensable, the core temperature rate of rise was considerably lower than in Tabove such that it would take >24 h to reach 40.2 °C. Our study supports thermal-step protocols as an effective technique for evaluating survivability limits for heat exposure and provides a direct assessment of the limits of human thermoregulation.

This seems bad. Over time, what people have assumed was the physical limit of human heat tolerance keeps going down. It used to be thought it was a wet-bulb of 35C, now it seems it's more like 32C for resting humans and 27C for people doing minimal physical activity.

www.pnas.org/doi/10.1073/...

For all intents and purposes, human skin has a max temperature of ~35C. Since sweat evaporation is our primary mode of heat loss, a wet bulb temp of 35C - equivalent to 35C air temp with 100% humidity - means that there is no vapour pressure gradient for skin-environ evaporation and thus no cooling

Understanding how thermoregulation differs between these areas and those experiencing the greatest increases in humid heat is critical for future heat warnings and adaptation planning.

Looking into the future, there is a need to evaluate upper limits in a wider range of populations, as thermal step protocols have been employed primarily in laboratories from temperate areas.

Thermal step protocols are an effective and efficient method for estimating upper limits for thermoregulation. This is great news, as they are widely used and being increasingly incorporated into large scale #climate #modelling.

We exposed young adults for 9 hours to conditions just above or below the core temperature inflection point and found that thermal step protocols work extremely well.

However, despite being around for over 50 years, thermal step protocols have never been validated.

There are increasing concerns that #heatwaves of the future will be so hot and humid that they exceed the limits of human heat tolerance. Recent laboratory research using “thermal-step protocols” has argued that these limits are likely lower than once thought.

Our latest daylong heat exposure trial – Validating new limits for human thermoregulation – is out today in
@pnas.org!

www.pnas.org/doi/10.1073/...

Only on Canadians! The purpose of the study was to validate the technique used to assess upper limits for thermoregulation. Turns out that technique works quite well, but you are absolutely right that there is a need to expand research to a wider range of populations/contexts (which we discuss)

New study validates lower limits of human heat tolerance A study from the University of Ottawa's Human and Environmental Physiology Research Unit (HEPRU) has confirmed that the limits for human thermoregulation—our ability to maintain a stable body temperature in extreme heat—are lower than previously thought.

New findings indicate that human heat tolerance limits are lower than previously estimated, highlighting the need for updated health policies as climate change intensifies extreme heat conditions. doi.org/g9bdv8

Meta-analysis of heat-induced changes in cardiac function from over 400 laboratory-based heat exposure studies - Nature Communications Understanding heat-induced changes in cardiac function has come primarily from laboratory studies employing encapsulated, water-based heating modalities. Here, the authors show that these studies over...

Your heart rate increases 26 beats per minute per degree increase in your body's core temperature, and other cool tidbits about how heat stresses our bodies in a meta-analysis that looked at over 400 lab studies on heat stress www.nature.com/articles/s41...

Incredible new @nature.com Communications paper 📃 by Meade et al. in which they synthesize the findings from over 400 laboratory-based heat exposure studies to improve understanding of the effects of heat stress on cardiac responses 🥵

www.nature.com/articles/s41...

Meta-analysis of heat-induced changes in cardiac function from over 400 laboratory-based heat exposure studies - Nature Communications Understanding heat-induced changes in cardiac function has come primarily from laboratory studies employing encapsulated, water-based heating modalities. Here, the authors show that these studies over...

New in @naturecomms.bsky.social from @robertdmeade.bsky.social and all-star cast 🤩:

Meta-analysis of heat-induced changes in cardiac function from over 400 laboratory-based heat exposure studies 👇

www.nature.com/articles/s41...

Current prioritizing projects by guilt.