People with Respiratory Illnesses Should Use Caution in Heat & Humidity

The summer months can spell trouble for some older adults with respiratory ailments. As outdoor temperatures rise, so does the risk of landing in the hospital, says a team of Johns Hopkins researchers in a new study.

Older adults generally have more difficulty adjusting to rising outdoor temperatures than younger people do. As we age, we become less efficient at thermoregulation—the body's ability to keep itself in a healthy temperature range. Plus, older adults are more likely to have conditions such as heart failure, diabetes, heart disease and obesity, which heat can worsen, and take prescription drugs like diuretics, beta blockers, antidepressants and anticholinergics, which can interfere with the ability to cool off and perspire.

Hot weather can be especially hard on people with respiratory disorders. In their study, the Hopkins researchers uncovered a correlation between rising temperatures and the number of emergency hospital admissions for chronic obstructive pulmonary disease (COPD) and respiratory tract infections among people 65 and older.

Emergencies rise with temps

Using data collected from approximately 12.5 million Medicare beneficiaries, the researchers found that, for every 10-degree increase in daily outdoor temperature, same-day respiratory-related emergency hospitalizations of older men and women rose 4.3 percent. To reach their conclusions, the researchers measured the number of hospitalizations for respiratory disorders and the daily temperatures from May to December over 10 years through 2008 in 213 urban U.S. counties.

The association with emergency hospitalization risk remained, even after the study authors accounted for air quality, most notably pollution and ozone levels, and seasonal trends. Hospitalization risk was strongest on the day of heat exposure but still significant on the day after.

Past studies have shown a link between exposure to outdoor heat and respiratory-related deaths, but this study is the first wide-ranging look at the association between outdoor heat and respiratory-related emergency hospitalization among an older population that's not limited to residents of major U.S. and European cities. The Hopkins study was published online in March 2013 by the American Journal of Respiratory and Critical Care Medicine.

Respiratory responses to heat

Since this was an observational study—which can establish only a relationship, not a direct cause—the researchers couldn't say for sure why the risk of hospitalizations for respiratory distress increased with rising temperatures. Although they couldn't definitively determine the mechanisms behind heat's effects on respiratory health, the researchers suggest that the poor respiratory responses are likely due to breathing in hot air.

Inhaling hot air can exacerbate respiratory disorders like COPD and promote airway inflammation. For example, a person with COPD who suddenly inhales hot air may experience a bronchospasm. A bronchospasm contracts the airways, making it harder to breathe, and causes shortness of breath. This may also explain why just a few minutes of heat exposure can trigger a respiratory response. And breathing hot air may also aggravate existing respiratory infections, some of which may be initiated by summertime irritants like pollen or mold.

The researchers suggest that impaired thermoregulation may also play a partial role in respiratory response to heat. When the body can't cool itself off, the result is hyperthermia, which includes a variety of heat illnesses such as heat cramps, heat exhaustion and heatstroke. Hyperthermia can cause a rapid heartbeat and increased blood flow to the skin, leaving blood needed for vital organs in short supply.

The body demands more oxygen as it works to stay cool, which can lead to decreased lung function. This can result in abnormally rapid or deep breathing, a condition called hyperpnea. The good news is that, if you liv' in an area with high average summer temperatures, your thermoregulatory response may be acclimated to hotter weather. That’s because your body's ability to thermoregulate improves with repeated heat exposure, whereas people not used to long-term heat have a harder time adjusting. As a result, you may be less likely to be hospitalized for a heat-related respiratory emergency.

Access to air conditioning plays a big role in breathing easy during summer months, too. A study published in July 2012 in Epidemiology suggests that people who live in areas with typically mild summers reside in homes that aren't equipped with air conditioning or built to stay cool when the weather gets unexpectedly warmer, denying them much-needed relief.

Source: Prepared by the Editors of The Johns Hopkins Medical Letter: Health After 50

Publication Review By: the Editorial Staff at

Published: 17 Jul 2013

Last Modified: 12 Aug 2013