Table 1

Baseline population characteristics and measurements

Day workers Shift workers p Value
Population characteristics:
 Age (y, mean (SD))29.3 (5.3)30.4 (6.7)0.4
 Sex (% female)9110.81-150
 Smoking habits (%):
  Never smoker48410.41-150
  Current smoker2640
 Education (%):
Baseline frequency of premature complexes:
 PAC (beats/h, median)0.540.47NA
 PAC (respondents with >1/h, %)30.938.70.41-151
 PVC (beats/h, median)0.0430.042NA
 PVC (respondents with >0.1/h, %)25.823.40.81-151
Baseline heart rate variability:
 Heart rate (beats/min)71.6 (8.4)75.3 (8.4)0.04
 SDNNi (ms)89.1 (28.7)74.6 (20.7)0.01
 Loglow (log ms)−2.67 (0.18)−2.76 (0.21)0.03
 Loghigh (log ms)−2.98 (0.35)−3.15 (0.30)0.03
 % lf65.1 (10.8)68.4 (8.1)0.2
  • 1-150 p value by χ2 test.

  • 1-151 p value by Wilcoxon two sample test.

  • PAC=premature atrial complexes; PVC=premature ventricular complexes; SDNNi=mean of all 5 minute SDs of NN intervals; Loglow=power in the low frequency range (0.05–015 Hz) in logarithmic units; Loghigh=power in the high frequency range (0.15–0.40 Hz) in logarithmic units; % lf=low frequency power (0.05–0.15 Hz) in normalised units.