Relative cardiac cost and physical, mental and psychological work load among a group of post-operative care personnel

Maximal tachycardia and high cardiac strain during night shifts of emergency physicians

PURPOSE

To compare tachycardia and cardiac strain between 24-hour shifts (24hS) and 14-hour night shifts (14hS) in emergency physicians (EPs), and to investigate key factors influencing tachycardia and cardiac strain.

METHODS

We monitored heart rate (HR) with Holter-ECG in a shift-randomized trial comparing a 24hS, a 14hS, and a control day, within a potential for 19 EPs. We also measured 24-h HR the third day (D3) after both shifts. We measured perceived stress by visual analog scale and the number of life-and-death emergencies.

RESULTS

The 17 EPs completing the whole protocol reached maximal HR (180.9 ± 6.9 bpm) during both shifts. Minutes of tachycardia >100 bpm were higher in 24hS (208.3 ± 63.8) than in any other days (14hS: 142.3 ± 36.9; D3/14hS: 64.8 ± 31.4; D3/24hS: 57.6 ± 19.1; control day: 39.2 ± 11.6 min, p < .05). Shifts induced a cardiac strain twice higher than in days not involving patients contact. Each life-and-death emergency enhanced 26 min of tachycardia ≥100 bpm (p < .001), 7 min ≥ 110 bpm (p < .001), 2 min ≥ 120 bpm (p < .001) and 19 min of cardiac strain ≥30% (p = .014). Stress was associated with greater duration of tachycardia ≥100, 110 and 120 bpm, and of cardiac strain ≥30% (p < .001).

CONCLUSION

We demonstrated several incidences of maximal HR during shifts combined with a high cardiac strain. Duration of tachycardia were the highest in 24hS and lasted several hours. Such values are comparable to those of workers exposed to high physical demanding tasks or heat. Therefore, we suggest that EPs limit their exposure to 24hS. We, furthermore, demonstrated benefits of HR monitoring for identifying stressful events. ClinicalTrials.gov identifier: NCT01874704.

Estimating relative physical workload using heart rate monitoring: a validation by whole-body indirect calorimetry

Measuring physical workload in occupational medicine is fundamental for risk prevention. An indirect measurement of total and relative energy expenditure (EE) from heart rate (HR) is widely used but it has never been validated. The aim of this study was to validate this HR-estimated energy expenditure (HREEE) method against whole-body indirect calorimetry. Twenty-four-hour HR and EE values were recorded continuously in a calorimetric chambers for 52 adult males and females (19-65 years). An 8-h working period was retained, comprising several exercise sessions on a cycloergometer at intensities up to 65% of the peak rate of oxygen uptake. HREEE was calculated with reference to cardiac reserve. A corrected HREEE (CHREEE) was also calculated with a modification to the lowest value of cardiac reserve. Both values were further compared to established methods: the flex-HR method, and the use of a 3rd order polynomial relationship to estimate total and relative EE. No significant difference was found in total EE when measured in a calorimetric chamber or estimated from CHREEE for the working period. A perfect linear and identity relationship was found between CHREEE and energy reserve values for intensities ranging from 15% to 65%. Relative physical workload can be accurately assessed from HR recordings when expressed in CHREEE between 15% to 65%, and EE can be accurately estimated using the CHREEE method.