Table 1 Characteristics of reports and individual effect estimates included in meta-analysis

From: Meta-analysis of heat-induced changes in cardiac function from over 400 laboratory-based heat exposure studies

Variable

All studies

k = 400

Stratified by heating modalitya

Climate chamber

k = 82

Water-perfused suit

k = 197

Hot water immersion

k = 88

Sauna

k = 36

Individual effect estimatesb

 Total effect estimates, no.

586

124

264

139

59

 Effect estimates per study, no. (%)

   1

281 (69.2%)

55 (67.1%)

147 (74.6%)

54 (61.4%)

21 (58.3%)

   2

87 (21.8%)

19 (23.2%)

38 (19.3%)

23 (26.1%)

9 (25.0%)

   3

13 (3.2%)

2 (2.4%)

7 (3.6%)

3 (3.4%)

1 (2.8%)

   4+

23 (5.8%)

6 (7.3%)

5 (2.5%)

8 (9.1%)

5 (13.9%)

 Total participant-exposures, no.

6856

1887

2812

1464

695

Sample demographics

 Sample size, n

10 (8–13)

10 (9–16)

10 (8–12)

10 (8–12)

10 (8–12)

 Age, years

26 (23-31)

27 (24–38)

27 (24–32)

24 (22–27)

23 (21–26)

 Sex, proportion females

0.00 (0.00–0.44)

0.00 (0.00–0.38)

0.25 (0.00–0.45)

0.00 (0.00–0.38)

0.00 (0.00–0.42)

 Height, cm

173 (169–177)

173 (169–177)

173 (171–177)

172 (168–175)

176 (167–181)

 Mass, kg

71.7 (65.3–77.0)

72.7 (67.2–78.7)

73.0 (67.0–77.0)

68.0 (62.5–74.5)

73.0 (64.9–77.8)

 Body mass index, kg/m2

23.5 (22.4–24.9)

24.3 (23.0–25.4)

24.0 (22.8–25.0)

22.7 (21.6–23.7)

22.9 (21.8–24.5)

 Body surface area, m2

1.85 (1.76–1.94)

1.87 (1.79–1.95)

1.87 (1.77–1.94)

1.80 (1.70–1.91)

1.89 (1.74–1.95)

Study characteristics

 Duration of heating, min

60 (40–79)

92 (60–128)

58 (45–71)

52 (31–60)

30 (20–45)

Posture, no. (%)

  Seated

312 (57.1%)

91 (85.8%)

48 (18.7%)

119 (93.7%)

54 (96.4)%

  Supine

34 (42.9%)

15 (14.2%)

209 (81.3%)

8 (6.3%)

2 (3.6%)

Clothing insulation, no. (%)c

  Low (e.g., summer clothing)

576 (98.3%)

115 (92.7%)

263 (99.6%)

139 (100.0%)

59 (100.0%)

  Medium (e.g., work uniform)

10 (1.7%)

9 (7.3%)

1 (0.4%)

0 (0.0%)

0 (0.0%)

Köppen climate class, no. (%)

  Temperate

427 (72.9%)

73 (58.9%)

198 (75.0%)

113 (81.3%)

43 (72.9%)

  Continental

148 (25.3%)

41 (33.1%)

66 (25.0%)

25 (18.0%)

16 (27.1%)

  Arid

7 (1.2%)

6 (4.8%)

0 (0.0%)

1 (0.7%)

0 (0.0%)

  Polar

4 (0.7%)

4 (3.2%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

Body temperature measurementd

 End-heating Tcore, °C

37.8 (37.3–38.2)

37.4 (37.2–37.7)

37.8 (37.3–38.1)

37.9 (37.4–38.5)

38.2 (38.0–38.7)

Tcore measurement site, no. (%)

  Direct, slow-responding

313 (53.4%)

79 (63.7%)

131 (49.6%)

78 (56.1%)

25 (42.4%)

  Direct, fast-responding

156 (26.6%)

14 (11.3%)

86 (32.6%)

43 (30.9%)

13 (22.0%)

  Indirect

117 (20.0%)

31 (25.0%)

47 (17.8%)

18 (12.9%)

21 (35.6%)

End-heating Tskin, °C

37.6 (36.1–38.5)

36.2 (35.0–37.2)

38.2 (37.4–38.7)

36.0 (35.3–38.0)

37.8 (36.5–39.2)

End-heating Tbody, °C

37.7 (37.3–38.1)

37.4 (36.9–37.6)

37.8 (37.4–38.2)

37.5 (37.3–38.2)

37.8e

  1. Data presented as median (interquartile range) or no. (%) of available effect-level data. Not all studies provided information on each variable listed in the table; see supplemental Table S17 for reporting rates (pp 70).
  2. aThe number of studies across all heating modalities (k = 403) is slightly higher than the total number of studies included in the review (k = 400) since some studies supplied effect estimates for more than one heating modality.
  3. bIndividual effect estimates (unit of analysis) refer to the change in heart rate from pre-heating baseline values to the end of heating. The number of participant-exposures was calculated by summing the sample sizes across effect estimates.
  4. cClothing insulation was classified as low if participants were nude, semi-nude, or wearing summer attire. Clothing was classified as medium if participants wore a work or military uniform. Clothing insulation level was assumed to be low for studies not reporting this information. Studies employing high levels of clothing insulation (e.g., nuclear biological chemical suit) were excluded from analysis.
  5. dData are distributions of sample means for core temperature (Tcore), mean skin surface temperature (Tskin), and mean body temperature (weighted average of core and skin temperatures, Tbody) reported at end-heating (when cardiac outcomes were measured). The body site at which core temperature was measured was classified as i) direct, fast-responding (pulmonary artery, esophagus, tympanic membrane), direct, slow-responding (rectum, gastrointestinal tract), or indirect (aural canal, oral cavity, other).
  6. eonly k = 1 studies reported end-heating mean body temperature in a sauna.
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