A controlled chamber study of effects of exposure to diesel exhaust particles and noise on heart rate variability and endothelial function

Figures & data

Figure 1. Time line for exposure and HRV and PAT registration in all scenarios.

Figure 2. The setup for the chamber exposure studies.

Figure 3. Typical particle number size distribution during the diesel exhaust exposure.

Table 1. Summary of exposure characteristics (mean ± standard deviation) of exposures during each exposure scenario.

Type of exposure	Particle mass concentrations (PM1)	Particle number concentrations (10–500 nm)	CMD	GSD	NO	NO2	CO	CO2	Noise	Temp
	µg/m^3	Particles/cm^3	nm		ppb	ppb	ppm	ppm	dB (A)	°C
Reference	2 ± 2	<100	117	2.1	3	1	0.3	940	46	22.6
		± 10	± 15	± 0.5	± 1	± 1	± 0.1	± 60		± 0.9
Diesel (only)	271	384,000	86	2.0	9720	1460	7.9	1970	46	22.7
	± 31	± 44,000	± 9	± 0.1	± 920	± 460	± 1.6	± 70		± 0.8
Noise (only)	2 ± 2	<100	117	2.1	3	1	0.3	940	75	22.6
		± 20	± 15	± 0.2	± 1	± 0	± 0.1	± 80		± 0.7
Combined (diesel + noise)	280	392,000	92	1.9	9840	1240	6.3	1920	75	22.7
	± 23	± 56,000	± 8	± 0.1	± 1110	± 400	± 2.5	±170		± 0.6

PM₁: Particulate matter with aerodynamic diameter less than 1 μm; CMD: count median diameter; GSD: geometric standard deviation; NO: nitrogen oxide; NO₂: nitrogen dioxide; CO: carbon oxide; CO₂: carbon dioxide; Temp: temperature.

Table 2. Descriptive statistics (medians and ranges) of HRV and endothelial function parameters for each exposure scenario.

	Parameters	Time points	Exposure scenarios
			Reference	Diesel	Noise	Combined
Heart rate variability	HF	Before exposure	287 (97, 2030)	496 (21, 1979)	370 (97, 1587)	321 (102, 1642)
		30 min into exposure	339 (110, 2492)	355 (26, 1763)	262 (101, 1369)	375 (78, 1941)
		90 min into exposure	242 (40, 1719)	214 (17, 1837)	180 (20, 2151)	187 (12, 1770)
		150 min into exposure	301 (41, 1832)	322 (14, 1896)	207 (19, 1597)	217 (19, 1585)
	LF	Before exposure	427 (97, 1279)	516 (126, 862)	405 (74, 1146)	350 (90, 1295)
		30 min into exposure	595 (145, 1425)	529 (159, 1329)	412 (110, 1232)	517 (93, 1708)
		90 min into exposure	367 (58, 1753)	306 (31, 1283)	461 (92, 1493)	374 (71, 1193)
		150 min into exposure	571 (90, 1279)	437 (97, 1126)	314 (60, 1164)	429 (79, 1260)
	TP	Before exposure	1784 (496, 4301)	1802 (657, 4032)	1885 (626, 3583)	2204 (640, 4480)
		30 min into exposure	1972 (1084, 5073)	1843 (748, 4348)	1964 (771, 3969)	2215 (849, 4027)
		90 min into exposure	1510 (986, 4039)	1848 (347, 3730)	1725 (467, 3663)	2120 (380, 4005)
		150 min into exposure	1978 (580, 4292)	1723 (397, 4289)	1839 (449, 3838)	2009 (381, 4730)
Endothelial function^a	RHI	After exposure	2.45 (1.28, 3.12)	1.97 (1.36, 3.4)	2.32 (1.19, 3.2)	2.27 (1.19, 4.31)
	Baseline pulse amplitudes^b	After exposure	6.01 (4.42, 6.97)	6.23 (4, 6.85)	5.98 (4.01, 6.98)	6.28 (4.5, 6.87)
	AI@75	After exposure	−4.92 (−23.3, 31.7)	−4.98 (−22.4, 17.3)	−6.73 (−18.8, 28.6)	−6.6 (−18.8, 19.4)
Heart rate		Before exposure	57 (44, 76)	58 (47, 87)	59 (47, 72)	57 (43, 77)
		30 min into exposure	56 (44, 75)	55 (45, 84)	59 (47, 70)	57 (45, 76)
		90 min into exposure	61 (49, 84)	63 (49, 98)	64 (50, 91)	62 (49, 92)
		150 min into exposure	60 (45, 82)	63 (50, 93)	63 (53, 84)	62 (47, 86)

HF: High frequency band; LF: low frequency band; TP: total power; RHI: Reactive Hyperemia Index; AI@75: the Augmentation Index normalized to a heart rate of 75 beats per minute.

^aBased on 63 recordings from 16 participants, after excluding 9 unreliable recordings.

^bCalculated as the mean value of the natural logarithm of baseline pulse amplitudes in both fingers.

Table 3. Percentage changes in HRV parameters during the different exposure scenarios compared to the reference exposure.

	Percentage change HF (ΔHF%)			Percentage change TP (ΔTP%)			Percentage change LF/HF (ΔLF/HF%)
Exposure scenario	Estimated means (95%CI)^a	β (95% CI)^a	p^a	Estimated means (95% CI)^a	β (95% CI)^a	p^a	Estimated means (95% CI)^a	β (95% CI)^a	p^a
Reference^b	−1.43 (−17.d, 14.7)	Ref	Ref	11.0 (−8.35, 30.3)	Ref	Ref	57.4 (21.6, 93.2)	Ref	Ref
Diesel	−23.1 (−39.4, −6.85)	−21.7 (−40.3, −3.10)	0.022	1.46 (−18.0, 21.0)	−9.53 (−30.7, 11.7)	0.37	53.2 (17.1, 89.3)	−4.16 (−49.3, 41.0)	0.85
Noise	−13.3 (−30.0, 3.1)	−11.8 (−30.4, 6.70)	0.21	3.48 (−16.1, 23.0)	−7.51 (−28.7, 13.6)	0.48	68.0 (32.0, 104)	10.6 (−33.6, 54.8)	0.63
Combined	−19.3 (−35.4, −3.16)	−17.9 (−36.4, 0.66)	0.059	−5.72 (−25.1, 13.6)	−16.7 (−37.8, 4.35)	0.12	77.8 (42.2, 113)	20.4 (−21.4, 62.3)	0.34

HF: High frequency band; TP: total power; LF/HF: the ratio of low frequency to high frequency band.

^aEstimated mean, beta with 95%CI and p value were derived from linear mixed model: HRV = α_i + β₁ × exposures + β₂ × time points + β₃ × exposure order + ɛ_ij. β in the table were corresponded to β₁ in the model.

^bThe comparisons between the other exposures and the reference exposure were based on the average percentage changes in HRV from three recordings during the exposure.

Table 4. Reactive Hyperemia Index (RHI), Augmentation Index, and baseline pulse amplitudes after the different exposure scenarios compared to the reference exposure, after exclusions (n = 16).

	RHI			Baseline pulse amplitudes^a			AI@75
Exposure scenario	Estimated means (95% CI)^b	β (95% CI)^b	p^b	Estimated means (95%CI)^b	β (95% CI)^b	p^b	Estimated means (95% CI)^b	β (95% CI)^b	p^b
Reference	2.22 (1.89, 2.55)	Ref	Ref	5.90 (5.47, 6.32)		Ref	−2.98 (−9.05, 3.09)	Ref	Ref
Diesel	2.14 (1.81, 2.48)	−0.08 (−0.39, 0.23)	0.61	5.85 (5.41, 6.28)	−0.05 (−0.41, 0.31)	0.78	−2.48 (−8.62, 3.66)	0.50 (−3.83, 4.82)	0.82
Noise	2.29 (1.96, 2.61)	0.07 (−0.24, 0.37)	0.67	5.79 (5.36, 6.21)	−0.11 (−0.47, 0.25)	0.54	−2.38 (−8.47, 3.71)	0.60 (−3.68, 4.88)	0.78
Combined	2.34 (2.01, 2.66)	0.12 (−0.18, 0.42)	0.44	5.93 (5.51, 6.36)	0.03 (−0.31, 0.38)	0.84	−3.67 (−9.74, 2.4)	−0.69 (−4.9, 3.52)	0.74

RHI: Reactive Hyperemia Index; AI@75: the Augmentation Index normalized to a heart rate of 75 beats per minute.

^aBaseline pulse amplitudes was calculated as the mean value of the natural logarithm of baseline pulse amplitudes in both fingers.

^bEstimated mean, beta with 95%CI and p value were derived from linear mixed model: Endothelial function parameters = α_i + β₁ × exposures + β₂ × exposure order + ɛ_i. β in the table were corresponded to β₁ in the model.