Hot temperatures during the 2019 heatwave in France were closely linked to weight loss in heart failure patients, according to a new study.
The research, published on Wednesday in the journal ESC Heart Failure, calls for better application of telemonitoring technology to look after frail patients as global warming intensifies.
“This study is the first to show a strict relationship between ambient temperature and body weight in heart failure patients,” study author François Roubille of Montpellier University Hospital in France said in a statement.
Weight loss observed in patients with heart failure could lead to low blood pressure, especially when standing up, and renal failure, making it “potentially life-threatening”, found researchers.
“With rising temperatures forecast for the future, clinicians and patients should be ready to reduce the dose of diuretics when weight loss occurs,” Dr Roubille said.
Since the heart does not pump blood efficiently around the body in patients with heart failure, waste products accumulate, causing shortness of breath and fluid build-up in the lungs, legs and abdomen.
Weight gain in these patients is related to congestion and is the main reason for hospital admission so patients are given diuretics to increase urine output and reduce breathlessness and swelling.
Researchers hypothesised in the new study that body weight of patients with heart failure could change during a heatwave.
“When healthy people drink more fluids during hot weather, the body automatically regulates urine output. This does not apply to patients with heart failure because they take diuretics,” Dr Roubille explained.
In the study, researchers assessed 1,420 patients with chronic heart failure for the relationship between body weight in patients and air temperature between 1 June and 20 September 2019 – covering two heatwaves at the end of June and July in France.
They used a telemonitoring system to remotely obtain information on weight and symptoms with patients weighing themselves every day using a connected weighing scale that automatically sent measurements to the clinic.
Patients also reported daily symptoms like fatigue, breathlessness and cough by answering questions on a personal device with their answers sent automatically to the clinic.
Researchers also obtained data on daily temperatures at noon using data from the closest weather station to each patient’s home.
They then analysed the link between patient weight, ambient temperature on the same day and temperature two days prior to weight measurement.
The study found the link between temperature and weight was “very strong” with the patients’ weight dropping as temperature rose.
The strongest association with temperatures, according to the research, was two days prior to the weight measurement.
“The weight loss we observed during the heatwave was clinically relevant. Patients weighing 78kg lost 1.5kg in a short period of time. We were surprised to see that weight dropped with hot temperatures, as we had expected the opposite,” Dr Roubille said.
“For this reason, the telemonitoring system was programmed to alert clinicians when patients gained weight,” he added.
With more heatwaves likely in the climate crisis era, scientists call for telemonitoring systems that alert clinicians of weight loss in heart failure patients.
“For heart failure patients not monitored remotely, a good rule of thumb would be to contact a healthcare professional if weight drops by 2kg during a heatwave for advice on adjusting diuretic medication. Reacting early should help us to prevent complications,” Dr Roubille added.
