Podcast Summary: The New Yorker Radio Hour – How Extreme Heat Affects the Body

Date: August 26, 2025
Host: Evan Osnos (substituting for David Remnick)
Guests: Dhruv Kullar (New Yorker staff writer, physician), Dr. Douglas Casa (CEO, Korey Stringer Institute, Professor of Kinesiology, University of Connecticut)

Overview of Episode Theme

This episode delves into the science of how extreme heat affects the human body, a topic of growing urgency as global temperatures reach record highs. The show follows New Yorker contributor and physician Dhruv Kullar as he participates in experiments at a specialized heat lab and discusses the mechanics, dangers, and strategies for coping with extreme heat, informed by both personal and expert insights from Dr. Douglas Casa, a leading researcher on heat illnesses.

Key Discussion Points & Insights

1. Experiencing Extreme Heat in the Lab

• Dhruv Kullar visits the University of Connecticut Heat Lab to undergo tests that simulate intense heat exposure common to athletes, soldiers, and laborers.
  • Physical Test: Kullar walks on a treadmill in an environmental chamber set to 104°F and 40% humidity, while monitored for physiological data (03:09).
  • Immediate Physical Effects:
    • “Just feel extremely puffy everywhere… you’d have to cut my finger off to get my wedding ring off right now.” — Dhruv Kullar (02:45-02:51)
    • Develops a headache and describes how hard it is to imagine physical labor in such conditions (02:57-03:08)
  • Fluid Loss:
    • Kullar loses over 2.2 pounds in 90 minutes, almost entirely sweat (03:37-03:43).
  • Sweat Analysis:
    • Lab technicians conduct a “reverse Gatorade” test, washing off sweat to analyze the loss of sodium, magnesium, and chloride (03:54-04:28).

2. The Science of Heat’s Impact on the Body

Dr. Douglas Casa’s Background

• Suffered exertional heat stroke as a 16-year-old athlete, which profoundly affected his career path (05:03-05:48).

Mechanics of Heat Stress

• Divided Blood Supply:
  • “When you do intense exercise in the heat… the blood or the fluid in your body has to now be shared by three main entities. So your skin…your heart…[and] your muscles.” — Dr. Douglas Casa (06:44-07:06)
  • Heat exposure creates a bottleneck in cooling, heart function, and performance. Dehydration amplifies these stresses.

Types of Heat Illness

• Exertional Heat Stroke: Occurs during intense activity; body overheats faster than it can cool (08:03).
• Classic Heat Stroke: A failure of the thermoregulatory system, especially in infants, the elderly, or people with comorbidities in hot environments (08:03-09:04).

Demographics at Risk

• Children, elderly, people with chronic illnesses, and any group forced to be in hot environments for prolonged periods—such as athletes, the military, and outdoor laborers.

3. Recognizing & Treating Heat Illness

Immediate Cooling Is Critical

• Key Principle: “Cool first, transport second.” — Dr. Douglas Casa (09:19)
  • Cold water immersion is the fastest, most effective way to cool someone suffering from heat stroke (09:34).
  • Time to critical: Survivability is tied to lowering body temperature within 30 minutes; delays can be deadly (09:34-09:49).

Temperature Measurement

• Rectal temperature is essential for accuracy:
  • Oral, tympanic (ear), and skin measurements can be grossly inaccurate during intense heat; only rectal temps offer reliable data for treatment decision-making (10:49-11:07).

Humidity as a Danger Multiplier

• Evaporation of sweat is the main cooling mechanism, and high humidity prevents sweat from evaporating, dramatically increasing risk (11:24-12:13).
  • Most exertional heat stroke deaths in the US happen in humid, southeastern states.

4. Extreme Heat, Climate Change, and Public Health

Historical Context

• Until recently, heat stroke awareness was mostly relevant to specific high-risk groups. Recent climate trends have made it a public health crisis for everyone (12:56-13:59).

Real-World Impacts

• Case study: Phoenix, AZ
  • A study shows that a heat wave coinciding with a power outage could send nearly half the city to seek medical care (13:59).
  • “Having air conditioning, really—it’s a lifesaver. But in a lot of places… they don’t have a lot of air conditioning,” notes Kullar (14:03-14:10).
• Mass-casualty events in Europe
  • In France’s 2003 heat wave, 12,000 died in one week; in 2022, over 61,000 heat deaths across Europe (14:26).

Practical Prevention and Coping Strategies

• Four key steps to protect oneself during extreme heat (15:24):
  1. Always have cold fluids nearby and hydrate when needed.
  2. Use cooling strategies (cold wet towels, shade, etc.).
  3. Adjust work/rest cycles based on how hot it is.
  4. Use heat acclimatization (gradually increase activity over 1-2 weeks).

Notable Quotes & Memorable Moments

• On the immediacy of risk:
  “You have 30 minutes to get the patient’s temperature to under 104 if you want to assure survivability with an exertional heat stroke.” — Dr. Douglas Casa (09:34)
• On the challenge of changing perceptions:
  “It seems to be so complicated to get people to do the right thing…the concept of cool first, transport second.” — Dr. Douglas Casa (09:19)
• On modern climate vulnerability:
  “Now this is making it affect so many people, even just during daily living, daily workouts, daily things that they're trying to do, but now they have to face the extreme heat.” — Dr. Douglas Casa (13:40-13:59)

Timestamps for Important Segments

• [01:27] Dhruv Kullar introduces the lab experiment
• [02:43] First-person account of the physical effects of heat
• [03:49] Kullar describes extended recovery after heat exposure
• [04:26] Sweat analysis: “Reverse Gatorade”
• [05:03] Dr. Casa recounts personal experience with heat stroke
• [06:44] Mechanism of heat stress and blood supply
• [08:03] Explanation of types of heat stroke
• [09:19] Importance of immediate cooling: “Cool first, transport second”
• [10:49] Why rectal temperature is essential for accurate diagnosis
• [11:30] Humidity’s role in increasing risk
• [12:56] Evolution of heat illness awareness amidst climate change
• [13:59] Mass-casualty case studies and risks of power outages
• [15:24] Four critical strategies for coping with extreme heat

Tone & Speaker Attributions

• Evan Osnos: Engaging, slightly wry introduction/hosting
• Dhruv Kullar: Scientific yet personal; combines human experience and medical expertise
• Dr. Douglas Casa: Deeply knowledgeable, passionate, and direct, reflecting on decades of experience and lessons learned

Conclusion

This episode powerfully blends firsthand experience, medical expertise, and the urgency of adapting to a hotter world. Listeners come away with a clear understanding of what heat does to the human body, why it is so dangerous, who is at greatest risk, and concrete, actionable advice to stay safe as temperatures continue to rise.