Acute Effects of Electronic Cigarette Aerosol Inhalation on Vascular Function Detected at Quantitative MRI

Abstract

Background Previous studies showed that nicotinized electronic cigarettes (hereafter, e-cigarettes) elicit systemic oxidative stress and inflammation. However, the effect of the aerosol alone on endothelial function is not fully understood. Purpose To quantify surrogate markers of endothelial function in nonsmokers after inhalation of aerosol from nicotine-free e-cigarettes. Materials and Methods In this prospective study (from May to September 2018), nonsmokers underwent 3.0-T MRI before and after inhaling nicotine-free e-cigarette aerosol. Peripheral vascular reactivity to cuff-induced ischemia was quantified by temporally resolving blood flow velocity and oxygenation (SvO2) in superficial femoral artery and vein, respectively, along with artery luminal flow-mediated dilation. Precuff occlusion, resistivity index, baseline blood flow velocity, and SvO2 were evaluated. During reactive hyperemia, blood flow velocity yielded peak velocity, time to peak, and acceleration rate (hyperemic index); SvO2 yielded washout time of oxygen-depleted blood, rate of resaturation, and maximum SvO2 increase (overshoot). Cerebrovascular reactivity was assessed in the superior sagittal sinus, evaluating the breath-hold index. Central arterial stiffness was measured via aortic pulse wave velocity. Differences before versus after e-cigarette vaping were tested with Hotelling T2 test. Results Thirty-one healthy never-smokers (mean age, 24.3 years ± 4.3; 14 women) were evaluated. After e-cigarette vaping, resistivity index was higher (0.03 of 1.30 [2.3%]; P < .05), luminal flow-mediated dilation severely blunted (-3.2% of 9.4% [-34%]; P < .001), along with reduced peak velocity (-9.9 of 56.6 cm/sec [-17.5%]; P < .001), hyperemic index (-3.9 of 15.1 cm/sec2 [-25.8%]; P < .001), and delayed time to peak (2.1 of 7.1 sec [29.6%]; P = .005); baseline SvO2 was lower (-13 of 65 %HbO2 [-20%]; P < .001) and overshoot higher (10 of 19 %HbO2 [52.6%]; P < .001); and aortic pulse wave velocity marginally increased (0.19 of 6.05 m/sec [3%]; P = .05). Remaining parameters did not change after aerosol inhalation. Conclusion Inhaling nicotine-free electronic cigarette aerosol transiently impacted endothelial function in healthy nonsmokers. Further studies are needed to address the potentially adverse long-term effects on vascular health. © RSNA, 2019 Online supplemental material is available for this article.

Figures

Graphical abstract

Figure 1:

Flowchart of participant enrollment and exclusion, completed assessments, and test-retest repeatability. aPWV = aortic pulse wave velocity, BMI = body mass index, CVR = cerebrovascular reactivity, PVR = peripheral vascular reactivity.

Figure 2:

Response to cuff occlusion in the femoral circulation. A, Vessel-wall images of the superficial femoral artery (SFA) at different points (60 seconds [A60], 90 seconds [A90], and 120 seconds [A120]) as indicated by crosses in B during reactive hyperemia. The dashed circles represent the lumen area at baseline. B, Superficial femoral vein (SFV) oxygen saturation (SvO2) at baseline (green line) and during hyperemia. C, SFA blood flow velocity (V). D, Axial image obtained with MRI in the thigh, with SFA and SFV indicated in red and blue, respectively. Sample data shown for a representative participant. ΔSvO2 = peak-to-peak SvO2, HI = hyperemic index, PFR = peripheral flow reserve, RI = resistivity index, TFF = time of forward flow, TP = time to peak, TW = washout time, Vb = baseline velocity, VP = peak hyperemic velocity, Vr = retrograde velocity during early diastole, Vs = systolic velocity.

Figure 3a:

Neurovascular response to breath hold. (a) Magnitude image intensity of superior sagittal sinus (SSS, box). Insets show velocity maps at different points of the velocity time-course (40 seconds [t40], 50 seconds [t50], and 70 seconds [t70]). (b) Sample SSS blood flow velocity time-course (red line) shown for a representative participant. The thick black line is linear fit during breath holds, the slope of which is the breath-hold index (BHI). ΔVSSS = post–breath hold relative velocity increase.

Figure 3b:

Neurovascular response to breath hold. (a) Magnitude image intensity of superior sagittal sinus (SSS, box). Insets show velocity maps at different points of the velocity time-course (40 seconds [t40], 50 seconds [t50], and 70 seconds [t70]). (b) Sample SSS blood flow velocity time-course (red line) shown for a representative participant. The thick black line is linear fit during breath holds, the slope of which is the breath-hold index (BHI). ΔVSSS = post–breath hold relative velocity increase.

Figure 4:

Measurement of aortic pulse wave velocity. A, Sagittal view of the aortic arch with path length of the flow wave between the ascending aorta (Aa) and descending aorta (Da; Δs). B, Axial view showing Aa and Da, and the time course of the, C, complex difference (CD) signals during three cardiac cycles. D, CD signal intensity averaged across the aorta width during a single cardiac cycle (the transit time [t] is indicated). Sample data shown for a representative participant. t = time.

Figure 5a:

MRI-derived vascular parameters before and after e-cigarette vaping. Box-and-whisker plots for the strongest effects observed show (a) SvO2 during baseline (SvO2b), (b) SvO2 washout time (TW), (c) SvO2 overshoot, (d) luminal flow-mediated dilation (FMDL), (e) peak hyperemic blood flow velocity (VP), and (f) hyperemic index (HI). P values were derived on the basis of paired t tests. The boxes represent inner quartiles; horizontal lines within the box indicate the median and crosses (X) indicate the mean.

Figure 5b:

MRI-derived vascular parameters before and after e-cigarette vaping. Box-and-whisker plots for the strongest effects observed show (a) SvO2 during baseline (SvO2b), (b) SvO2 washout time (TW), (c) SvO2 overshoot, (d) luminal flow-mediated dilation (FMDL), (e) peak hyperemic blood flow velocity (VP), and (f) hyperemic index (HI). P values were derived on the basis of paired t tests. The boxes represent inner quartiles; horizontal lines within the box indicate the median and crosses (X) indicate the mean.

Figure 5c:

MRI-derived vascular parameters before and after e-cigarette vaping. Box-and-whisker plots for the strongest effects observed show (a) SvO2 during baseline (SvO2b), (b) SvO2 washout time (TW), (c) SvO2 overshoot, (d) luminal flow-mediated dilation (FMDL), (e) peak hyperemic blood flow velocity (VP), and (f) hyperemic index (HI). P values were derived on the basis of paired t tests. The boxes represent inner quartiles; horizontal lines within the box indicate the median and crosses (X) indicate the mean.

Figure 5d:

MRI-derived vascular parameters before and after e-cigarette vaping. Box-and-whisker plots for the strongest effects observed show (a) SvO2 during baseline (SvO2b), (b) SvO2 washout time (TW), (c) SvO2 overshoot, (d) luminal flow-mediated dilation (FMDL), (e) peak hyperemic blood flow velocity (VP), and (f) hyperemic index (HI). P values were derived on the basis of paired t tests. The boxes represent inner quartiles; horizontal lines within the box indicate the median and crosses (X) indicate the mean.

Figure 5e:

MRI-derived vascular parameters before and after e-cigarette vaping. Box-and-whisker plots for the strongest effects observed show (a) SvO2 during baseline (SvO2b), (b) SvO2 washout time (TW), (c) SvO2 overshoot, (d) luminal flow-mediated dilation (FMDL), (e) peak hyperemic blood flow velocity (VP), and (f) hyperemic index (HI). P values were derived on the basis of paired t tests. The boxes represent inner quartiles; horizontal lines within the box indicate the median and crosses (X) indicate the mean.

Figure 5f:

MRI-derived vascular parameters before and after e-cigarette vaping. Box-and-whisker plots for the strongest effects observed show (a) SvO2 during baseline (SvO2b), (b) SvO2 washout time (TW), (c) SvO2 overshoot, (d) luminal flow-mediated dilation (FMDL), (e) peak hyperemic blood flow velocity (VP), and (f) hyperemic index (HI). P values were derived on the basis of paired t tests. The boxes represent inner quartiles; horizontal lines within the box indicate the median and crosses (X) indicate the mean.

Figure 6:

Electronic cigarette components. Photograph shows the superior envelope (1), mouthpiece (2), light emitting diode (3), cylindrical 3.7-V lithium battery (4), wick and filament (5), thick wire (6), inner fibers (7), and outer fibers (8).