Table 5. Comparison of means ± SE of changes in heart rate variation indexes and respiration rates in three levels of tasks under different ambient air temperatures .

Variables( Mean differences)	18°C	22°C	26°C	30°C	Repeated measure ANOVA result
					Heat P-value	Task P-value	Heat•Task P-value	Heat ƒ	Task ƒ	Heat•TasK ƒ	ε
HR, n=1 (beat/min)	-1.11±1.07	-2.41±1.34	1.96±0.778	2.71±1.08	‏**	‏**	0.835	0.169	0.421	0.012	0.781
HR, n=2 (beat/min)	2.18±0.923	-0.16±0.996	5.13±1.38	5.91±1.23
HR, n=3 (beat/min)	2.44±0.885	2.10±0.508	5.51±1.50	7.35±1.32
SDNN, n=1 (ms)	-17.13±10.56	-0.34±14.25	-5.43±8.43	-8.66±7.87	0.80		0.917	0.010	0.114	0.005	0.461
SDNN, n=2 (ms	-19.18±13.58	-8.37±8.93	-17.53±12.53	-19.85±8.04
SDNN, n=3 (ms)	-23.30±14.25	-12.33±47.79	-18.34±12.73	-21.81±8.68
RMMSN, n=1 (ms)	-13.56±13.24	-0.23±7.30	-6.85±10.79	-9.05±6.55	0.816	0.147	0.998	0.006	0.055	0.001	0.491
RMMSD, n=2 (ms)	-19.91±15.21	-7.80±10.66	-11.89±19.00	-13.91±7.14
RMMSD, n=3 (ms)	-20.93±12.10	-8.26±10.55	-13.86±19.46	-16.43±7.15
LF/HF ratio, n=1	2.04±1.17	0.43±1.19	1.35±0.558	1.57±0.521	‏**	0.051	0.428	0.481	0.10	0.019	0.241
LF/HF ratio, n=2	2.78±1.15	054±1.04	1.84±0.680	2.29±0.528
LF/HF ratio, n=3	5.28±1.07	0.93±1.13	2.39±0.537	6.63±4.55
RSP, n=1 (bpm)	2.24±0.557	1.01±0.760	2.40±0.495	3.44±0.843	‏**	‏**	0.995	0.105	0.277	0.003	0.906
RSP, n=2 (bpm)	2.51±0.727	1.12±0.855	2.70±0.499	4.04±0.527
RSP, n=3 (bpm)	3.57±0.679	2.05±0.807	3.54±0.574	4.88±0.365

HR: Heart rate changes as compared with the baseline‚ SDNN: Changes standard deviation of normal-to-normal intervals as compared with the baseline‚ RMSSD: Changes root of the mean squared difference between adjacent normal heart beat (N-N) intervals as compared with the baseline‚ LF/HF: LF/HF: Change in LF to HF ratio as compared with the baseline‚ RSP: change in respiratory as compared with the baseline‚ n=1, n = 2 and n = 3, respectively, low workload‚ medium workload, and high workload.