Effect of burn injury size on cardiovascular responses to exercise in the heat.

We tested the hypothesis that due to well recognized thermoregulatory impairments, resulting in greater thermal strain, adults with well healed burn injuries will have heightened cardiovascular responses to exercise in the heat. Adults with burn injuries covering 20-40% body surface area (n = 10), > 40% body surface area (n = 11), and non-burned controls (n = 10) performed 1 h of treadmill walking at a fixed rate of metabolic heat production (~ 4.5 w/kg) in the heat (39 °C, 40% relative humidity). Core temperature, heart rate, stroke volume, and blood pressure were obtained at rest and during exercise. The increase in core temperature was 0.89 ± 0.40 °C for control, 0.92 ± 0.43 °C for 20-40%, and 1.30 ± 0.58 °C for > 40% (interaction: p = .08). Ending heart rate was greater in > 40% compared to control (142 ± 27 vs 118 ± 9 bpm; p = .03), however there was no difference between 20-40% and control (128 ± 24 vs 118 ± 9 bpm; p = .44). Ending rate pressure product was higher in the > 40% compared to control (21,326 ± 4327 vs 15,971 ± 2156 mmHg*bpm; p = .007), however there was no difference between 20-40% and control (18,698 ± 3741 vs 15,971 ± 2156 mmHg*bpm; p = .16). At 45-min into exercise, cardiac minute work was higher in the > 40% compared to control (577 ± 102 vs 467 ± 63 L/min*mmHg/m²; p = .02), but there was no difference between 20-40% and control (513 ± 82 vs 467 ± 63 L/min*mmHg/m²; p = .36). These findings show that well-healed burn survivors with large burn injuries, such as those covering > 40% of total body surface area, have increased cardiovascular strain during exercise heat stress.