A feasibility study of the use of UmbiFlow™ to assess the impact of heat stress on fetoplacental blood flow in field studies

Vulnerable to heat stress: gaps in international standard metric thresholds

Exposure time to heat is increasing with climate change. Heat exposure thresholds are important to inform heat early warning systems, and legislation and guidance for safety in the workplace. It has already been stated that thresholds can be lower for vulnerable groups, including the elderly, pregnant women, children, and those with pre-existing medical conditions due to their reduced ability to thermoregulate their temperature or apply cooling strategies. However, the Wet Bulb Globe Temperature (WBGT) proposed by the international standard organisation (ISO 7243:2017), only takes into account thresholds based on acclimatization status. Therefore in this study we carried out a PRISMA systematic keyword search of "Wet Bulb Globe Temperature" of the Scopus abstract and citation database in August 2023 and a meta-analysis of text extracted from the identified 913 international studies published between December 1957 and July 2023, to investigate heat stress thresholds for different population groups. We find that different thresholds are considered as an indication of heat stress for different population groups. However, critical gaps were identified for the most vulnerable populations, and there are lower numbers of studies on women. Most studies researched adult populations between the ages of 18 and 55 (n = 491), failing to include the youngest and oldest members of society. Based on these findings, we call for targeted investigations to inform effective heat action policies and set early warning thresholds to ensure the safety and wellbeing of the entire population.

Pathomorphological characteristics of heat stress in the experiment

AIM

The purpose of this research was to explore some morphological, physiological, and biochemical changes in female and fetal Wistar rats under heat stress.

METHODS

The experiment involved 30 animals, including two experimental groups (pregnant and nonpregnant females) kept under heat stress at 32°C and one control group consisting of healthy individuals kept in standard vivarium conditions. After dissection, fixation, dehydration, and primary processing, tissue samples were embedded in a mixture of paraffin and lanolin to obtain material for sections. Sections were made using a freezing and angular microtome and stained with hematoxylin and fuchsine solutions. Changes in morphology were assessed by microscopy using a Leitz DIAPLAN system.

RESULTS

As a result of heat stress, an increase in linear cell size, capillary network area, and adrenal mass was observed; adipocytes lost lipid vacuoles; prismatic thyroid cells were replaced by flat cells; hypothyroidism; an increase in the number of osteocyte lacunae; and increased osteoclast activity in bone tissue; interstitial and intracellular oedema and caryopycnosis of ventricular cardiomyocytes; reduction in the diameter of skeletal muscle fibers and replacement of tissue with collagen fibers; water loss in the structure of myofibrils; destructive local changes, hyperchromatosis and caryopycnosis of the hippocampus.

CONCLUSIONS

The data obtained allows predicting the possible consequences of prolonged overheating of tissues of other vertebrates and the human body.

Increased risk of preterm birth due to heat exposure during pregnancy: Exploring the mechanism of fetal physiology

BACKGROUND

Heat exposure during pregnancy can increase the risk of preterm birth (PTB) through a range of potential mechanisms including pregnancy complications, hormone secretion and infections. However, current research mainly focuses on the effect of heat exposure on pathophysiological pathways of pregnant women, but ignore that maternal heat exposure can also cause physiological changes to the fetus, which will affect the risk of PTB.

OBJECTIVE

In this study, we aimed to explore the mediating role of fetal heart rate (FHR) in the relationship between maternal heat exposure and PTB incidence.

METHODS

We assigned heat exposure to a multi-center birth cohort in China during 2015-2018, which included all 162,407 singleton live births with several times FHR measurements during the second and third trimesters. We examined the associations between heat exposure, FHR and PTB in the entire pregnancy, each trimester and the last gestational month. The inverse odds ratio-weighted approach applied to the Cox regression was used to identify the mediation effect of heat exposure on PTB and its clinical subtypes via FHR.

FINDINGS

Exposure to heat significantly increased the risk of PTB during the third trimester and the entire pregnancy, hazard ratios and 95 % CIs were 1.266 (1.161, 1.379) and 1.328 (1.218, 1.447). Heat exposure during the third trimester and entire pregnancy increased FHR in the third trimester by 0.24 bpm and 0.14 bpm. The proportion of heat exposure mediated by FHR elevation on PTB and its subtype ranged from 3.68 % to 24.06 %, with the significant mediation effect found for both medically indicated PTB and spontaneous PTB.

CONCLUSIONS

This study suggests that heat exposure during pregnancy has an important impact on fetal health, and FHR, as a surrogate marker of fetal physiology, may mediate the increased risk of PTB caused by extreme heat. Monitoring and managing physiological changes in the fetus would constitute a promising avenue to reduce adverse birth outcomes associated with maternal heat exposure.

An expert review of environmental heat exposure and stillbirth in the face of climate change: Clinical implications and priority issues

Exposure to extreme heat in pregnancy increases the risk of stillbirth. Progress in reducing stillbirth rates has stalled, and populations are increasingly exposed to high temperatures and climate events that may further undermine health strategies. This narrative review summarises the current clinical and epidemiological evidence of the impact of maternal heat exposure on stillbirth risk. Out of 20 studies, 19 found an association between heat and stillbirth risk. Recent studies based in low- to middle-income countries and tropical settings add to the existing literature to demonstrate that all populations are at risk. Additionally, both short-term heat exposure and whole-pregnancy heat exposure increase the risk of stillbirth. A definitive threshold of effect has not been identified, as most studies define exposure as above the 90th centile of the usual temperature for that population. Therefore, the association between heat and stillbirth has been found with exposures from as low as >12.64°C up to >46.4°C. The pathophysiological pathways by which maternal heat exposure may lead to stillbirth, based on human and animal studies, include both placental and embryonic or fetal impacts. Although evidence gaps remain and further research is needed to characterise these mechanistic pathways in more detail, preliminary evidence suggests epigenetic changes, alteration in imprinted genes, congenital abnormalities, reduction in placental blood flow, size and function all play a part. Finally, we explore this topic from a public health perspective; we discuss and evaluate the current public health guidance on minimising the risk of extreme heat in the community. There is limited pregnancy-specific guidance within heatwave planning, and no evidence-based interventions have been established to prevent poor pregnancy outcomes. We highlight priority research questions to move forward in the field and specifically note the urgent need for evidence-based interventions that are sustainable.

Extreme climatic events and human biology and health: A primer and opportunities for future research

Extreme climatic events are increasing in frequency, leading to hotter temperatures, flooding, droughts, severe storms, and rising oceans. This special issue brings together a collection of seven articles that describe the impacts of extreme climatic events on a diverse set of human biology and health outcomes. The first two articles cover extreme temperatures extending from extreme heat to cold and changes in winter weather and the respective implications for adverse health events, human environmental limits, well-being, and human adaptability. Next, two articles cover the effects of exposures to extreme storms through an examination of hurricanes and cyclones on stress and birth outcomes. The following two articles describe the effects of extreme flooding events on livelihoods, nutrition, water and food insecurity, diarrheal and respiratory health, and stress. The last article examines the effects of drought on diet and food insecurity. Following a brief review of each extreme climatic event and articles covered in this special issue, I discuss future research opportunities-highlighting domains of climate change and specific research questions that are ripe for biological anthropologists to investigate. I close with a description of interdisciplinary methods to assess climate exposures and human biology outcomes to aid the investigation of the defining question of our time - how climate change will affect human biology and health. Ultimately, climate change is a water, food, and health problem. Human biologists offer a unique perspective for a combination of theoretical, methodological, and applied reasons and thus are in a prime position to contribute to this critical research agenda.