Heart Rate Reserve In Pediatric Patients With Severe Burns - Implications For Exercise Prescription

PURPOSE: Patients with severe burns present with a hypermetabolic state, which is reflected in part by an elevated resting heart rate (rest HR). This condition remains for several years post burn. However, rest HR and peak exercise heart rate (peak HR) are variables used to calculate heart rate reserve (HRR), which is utilized in prescribing exercise and reflects the individual’s level of cardiopulmonary fitness. We hypothesize that the HRR in children with burns would be lower compared to non-burned children, and that their peak oxygen consumption (peak VO2) would be lower. METHODS: We analyzed exercise data from 19 children with burns ≥30% of their total body surface area (TBSA), and age ≥ 7 years. As a comparison group we exercise tested 17 children without burns, matching the same age criteria. All children performed a modified Bruce Treadmill Test with the assessment of rest HR and rest VO2,as well as peak VO2 and peak HR. The HRR was calculated by subtracting the rest HR from the peak HR. Results are presented as means ± SD. Student's t-Tests were performed to assess the significance levels between the groups. Significance was set at p < 0.05. RESULTS: Participants with burns had a mean age of 13.5 ± 2.5 years, while the non-burned children had a mean age of 13.4 ± 2.4 years (p = 0.94). Children with burns had a TBSA of 45 ± 13%. Rest VO2 in children with burns was 6.8 ± 2.4 ml/kg/min, while the non-burned children had a rest VO2 of 4.6 ± 1.5 ml/kg/min (p = 0.002). Peak VO2in children with burns was 24.5 ± 5.9 ml/kg/min, while non-burned children had a peak VO2 of 41.2 ± 9.8 ml/kg/min (p = 0.00002). Rest HR for children with burns was 124 ± 18 beats per minute (bpm) compared to 85 ± 14 bpm in children without burns (p = 0.000002). Peak HR in children with burns was 184 ± 21 bpm, while the peak HR in non-burned children was 193 ± 13 bpm (p = 0.11). Interestingly, the HRR in children with burns was 60 ± 17 bpm compared to 108 ± 13 bpm in non-burned children (p = 0.0000008). CONCLUSIONS: Despite a similar peak HR, burned children show a significantly lower HRR and lower peak VO2 than non-burned children. The lower HRR in children with burns has implications for an effective exercise training program and its prescription. Therefore, we suggest taking these findings into account and aiming to establish methods to reduce the elevated rest HR in order to increase HRR and peak VO2. NIDILRR 90DPBU0003-05-03, NIH R01HD049471-15, Remember the 15 Burns Endowment Fund