Effect of acute ambient temperature exposure on cardio-pulmonary and respiratory kinetics in men

Figures & data

Figure 1. Work rate protocol for exercise testing for the three different ambient temperatures. Gray horizontal bars indicate time periods for mean value calculations during rest (30 s), at low and high constant phases (30 s), during the PRBS phases (300 s) and at the end of the WR steps of 100, 125 and 150 W (30 s each). PRBS: pseudorandom binary sequence.

Table 1. Ambient conditions in the climatic chamber during the exercise tests (mean ± SD).

N = 13	15 °C	25 °C	35 °C	Sig
Temperature (°C)	15.1 ± 0.3	24.5 ± 1.3	35.4 ± 0.3	a, b, c
Pressure (mbar)	997 ± 7	968 ± 8	973 ± 8	b, c, d
Relative humidity (%)	34 ± 2	33 ± 2	33 ± 5	n.s.

SD: standard deviation; Sig: significant difference.

n.s.: Not significantly different, p > 0.05.

^a Significant difference between 15 °C and 25 °C, p < 0.01 (2-tailed).

^b Significant difference between 25 °C and 35 °C, p < 0.01 (2-tailed).

^c Significant difference between 35 °C and 15 °C, p < 0.01 (2-tailed).

^d Significant difference between 15 °C and 25 °C, p < 0.05 (2-tailed).

Figure 2. Test procedure time line. See text for details.

Table 2. Peak responses (mean ± SD) during exercise for 15 °C, 25 °C and 35 °C ambient temperatures.

N = 13	15 °C	25 °C	35 °C	Sig
Peak power output (W)	237 ± 35	244 ± 31	231 ± 29	a
Peak power output (W·kg^−1)	2.9 ± 0.6	3.0 ± 0.4	2.8 ± 0.4	n.s.
Peak oxygen uptake (L·min^−1)	3.8 ± 0.8	3.8 ± 0.8	3.4 ± 0.7	a
Peak oxygen uptake (mL·min^−1·kg^−1)	48 ± 12	47 ± 9	42 ± 9	a
Peak heart rate (min^−1)	161 ± 16	167 ± 9	164 ± 10	n.s.
Peak core body temperature (°C)	39.2 ± 0.6	39.0 ± 0.4	37.9 ± 0.3	b, c
Gas exchange threshold (L·min^−1)	1.6 ± 0.4	1.7 ± 0.5	1.6 ± 0.4	n.s.
Exercise time (s)	1389 ± 88	1404 ± 74	1367 ± 69	a

SD: standard deviation; Sig: significant difference.

n.s.: not significantly different, p > 0.05.

^a significant difference between 25 °C and 35 °C, p < 0.05 (2-tailed).

^b significant difference between 15 °C and 35 °C, p < 0.001 (2-tailed).

^c significant difference between 25 °C and 35 °C, p < 0.001 (2-tailed).

Figure 3. (a,b) Absolute values of HR (mean ± SE, 3a) and CBT (mean ± SE, 3b) as function of WR across the ambient temperatures (15 °C, 25 °C and 35 °C). CBT: core body temperature; HR: heart rate; SE: standard error of the mean; WR: work rate.

Figure 4. (a–c) Relative changes of HR (ΔHR, mean ± SE, 4a), CBT (ΔCBT; mean ± SE, 4b) and PSI (mean ± SE, 4c) based on the resting values as function of work rate across the ambient temperatures. CBT: core body temperature; HR: heart rate; PSI: physiological strain index; SE: standard error of the mean.

Figure 5. (a–c) Means (±SE) of the cross-correlation functions (CCF) of WR with HR (5a), pulmonary (V̇O₂pulm 5 b) and muscular (V̇O₂musc, 5c) oxygen uptake, respectively, for the different ambient temperatures. The grey triangle displays the ACF of WR. The upper right enhanced graphs display the mean values (± SE) at specific lag times (−20, −10, 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110 and 120 s) for a comparison applying a two-way ANOVA with factors Lag and Posture. Significant differences for factor Lag are not displayed graphically to avoid overloading the figure. See text for further explanation. ACF: auto-correlation function; ANOVA: analysis of variance; HR: heart rate; SE: standard error of the mean; WR: work rate.

Figure 6. Mean (±SE) of the CCF [maxima and lags (CCF_max, CCF_lag)] of work rate with HR, pulmonary (V̇O₂pulm) and muscular (V̇O₂musc) oxygen uptake, respectively, for 15 °C, 25 °C and 35 °C ambient temperatures. The grey line illustrates the auto-correlation function of WR (in part). Data points that are close to or on this line represent therefore possible assumptions of a linear first-order response of the physiological system or parameter behind the computational rational. CCF: cross-correlation function; HR: heart rate; SE: standard error of the mean.

Table 3. Means and SD of model parameter estimates and time-series analysis between HR, muscular (V̇O₂musc) and pulmonary (V̇O₂pulm) oxygen uptake for 15 °C, 25 °C and 35 °C ambient temperatures.

					HR		V̇O2pulm		V̇O2musc
N = 13		Vv (mL)	Q̇rem (mL·min^−1)	V̇O2rem (L·min^−1)	CCFmax (a.u.)	CCFlag (s)	CCFmax (a.u.)	CCFlag (s)	CCFmax (a.u.)	CCFlag (s)
Temperature	Sig	*	n.s.	n.s.	n.s.	n.s.	n.s.	n.s.	n.s.	n.s.
15 °C	Mean	3446	3580	0.28	0.440	10	0.331	32	0.432	13
	SD	584	1606	0.06	0.116	3	0.056	7	0.093	4
25 °C	Mean	3319	3831	0.27	0.420	11	0.339	36	0.446	13
	SD	556	1347	0.06	0.102	4	0.045	4	0.091	4
35 °C	Mean	2962	4404	0.27	0.417	10	0.325	32	0.409	12
	SD	597	1740	0.06	0.118	3	0.054	6	0.081	3

HR: heart rate; Q̇_rem and V̇O₂rem: perfusion and oxygen uptake for the remainder of the body; SD: standard deviation; Sig: significant difference; V_v: venous blood volume between the exercising muscles and the lungs.

n.s.: not significantly different, p > 0.05.

* Tendency for factor Temperature, 0.10 > p > 0.05.

Figure 8. SDS of HR, muscular (V̇O₂musc) and pulmonary oxygen uptake kinetics [V̇O₂pulm, without and with lag-correction (+20 s)]. The deviance is calculated between simulated CCF courses derived from the corresponding CCF_max value and the measured or estimated parameter (from lags −20 to 180 s, see Figure 7). Smaller values indicate better agreements with first-order system properties. CCF: cross-correlation function; HR: heart rate; SDS: sum of deviation squares.