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. 2016 Oct 5;35(1):24.
doi: 10.1186/s40101-016-0110-x.

Suppression of Vagal Cardiac Modulation by Blue Light in Healthy Subjects

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Free PMC article

Suppression of Vagal Cardiac Modulation by Blue Light in Healthy Subjects

Emi Yuda et al. J Physiol Anthropol. .
Free PMC article

Abstract

Background: In the contemporary life environments, our body is increasingly exposed to various sources of colored light, which may affect our physiological functions as non-image-forming effects. We examined the impacts of colored lights on the autonomic functions by the analysis of heart rate variability (HRV).

Methods: A lighting device consisting of four organic light-emitting diode (OLED) modules (55 × 55 mm2) with adjustable red-green-blue color was secured 24 cm above the eyes of subject lying supine in a light-shielded laboratory. Following a 15-min supine rest, electrocardiogram and respiration were measured continuously during 3-min darkness, 6-min colored OLED illumination, and 3-min darkness under paced breathing (15 breath/min). The measurements were repeated at a 45-min interval for red, green, and blue lights with melanopsin-stimulating photon flux density (MSPFD) of 0.00, 0.10, and 0.20 μmol/m2/s, respectively, in 12 healthy subjects (23 ± 2 years, two females). Additionally, the effects of blue lights with 0.20, 0.10, and 0.04 μmol/m2/s MSPFD were examined in four healthy subjects (25-39 years, two females). HRV was analyzed for low-frequency (LF, 0.04-0.15 Hz) and high-frequency (HF, 0.20-0.30 Hz) power and LF-to-HF ratio (LF/HF).

Results: Compared to darkness before lighting, HF power decreased (P < 0.001) and LF/HF increased (P = 0.024) during lighting on average of all color lights, whereas HF power showed a greater decrease with blue light than with red and green lights (P < 0.05 for both). The decrease in HF power lasted even during darkness after lighting (P < 0.001). HF power decreased with blue light with 0.20 μmol/m2/s MSPFD (P < 0.001) but not with that with 0.10 or 0.04 μmol/m2/s (P = 0.1 and 0.9, respectively).

Conclusions: Vagal cardiac modulation is suppressed by OLED blue light in healthy subjects most likely through melanopsin-dependent non-image-forming effect.

Keywords: Blue light; Heart rate variability; Intrinsically photosensitive retinal ganglion cell; Melanopsin; Non-image-forming vision; Organic light-emitting diode.

Figures

Fig. 1
Fig. 1
Lighting device with organic light-emitting diode (OLED). The device consists of four OLED panels (55 × 55 mm2) with adjustable red-green-blue color and brightness. The panels are linearly aligned and two panels at the both sides incline inward with an angle of 40°
Fig. 2
Fig. 2
Spectral irradiance distributions of colored OLED lights (a) and melanoptic spectral efficiency curve adjusted for human pre-receptoral filtering (b). a Data were measured at the place of the subject’s eyes, i.e., 24 cm below the surface of OLED lighting module. b Generated from data in reference [8]. Vertical dashed lines in both panels indicate the position of λmax of the adjusted melanoptic spectral efficiency (490 nm)
Fig. 3
Fig. 3
Experimental schedule of dark and illumination conditions. Measurement sessions with three different color lights (red, green, and blue) were performed in all subjects with different orders randomized among subjects at an interval of 45 min
Fig. 4
Fig. 4
Heart rate and heart rate variability (HRV) indices in individual subjects before, during, and after exposures to red, green, and blue OLED lights. HF high-frequency component, LF low-frequency component, LF/HF LF-to-HF ratio in power
Fig. 5
Fig. 5
Average changes in heart rate and HRV indices from before to during OLED lighting. Error bars represent standard error of mean. *Significantly different from values for red and green with multiple comparisons (P < 0.05)
Fig. 6
Fig. 6
Average changes in heart rate and HRV indices from before to after OLED lighting. Error bars represent standard error of mean
Fig. 7
Fig. 7
Heart rate and HRV indices in individual subjects before, during, and after exposures to blue OLED lights with 10, 5, and 2 lx

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