Standard Cigarette Smoke Research Articles

Abstract 13349: The Effect of Chronic Standard Cigarette Smoke Exposure Compared to Chronic Electronic Cigarette Exposure With or Without Nicotine on Blood Pressure

Background: While the acute exposure to electronic cigarette (e-C) vapor has been associated with an increase in blood pressure, the chronic effect of e-C vapor on blood pressure compared to standard cigarette smoke has not been extensively studied. We determined the effect of chronic e-C exposure versus standard cigarette smoke on blood pressure and other cardiac functional measures. Methods: Sprague Dawley rats (both sexes) were randomly exposed to air (n=34), e-C with nicotine (e-Cn; n=30), e-C without nicotine (e-C; n= 28) or standard cigarette smoke (SCS; n=27) for 12 weeks. After 12 weeks of exposure hemodynamics were determined by Millar catheter, echocardiography, and thermodilution catheter, a few days after their last exposure. Results: As shown in the Table, SCS was associated with higher systolic, diastolic and mean blood pressures and peak LV systolic pressure compared to air or e-Cn or e-C groups. Neither fractional shortening or cardiac output differed among the groups. dp/dt min, a measure of diastolic LV function, was lowest in the e-C group. Tau, a measure of LV relaxation was worse in this group as well. Conclusions: Standard cigarette smoke exposure was associated with an increase in blood pressure when blood pressure was tested at 12 weeks. Neither electronic cigarette smoke with or without nicotine caused an increase in blood pressure compared to air. However, e-C was associated with worse diastolic function. Standard cigarettes may be associated with a greater sympathetic surge causing elevated blood pressure compared to electronic cigarettes.

Effects of Electronic Cigarette Exposure on Myocardial Infarction and No-Reflow, and Cardiac Function in a Rat Model.

We investigated the effects of exposure to electronic cigarettes (E-cig) vapor on the sizes of the no-reflow and myocardial infarction regions, and cardiovascular function compared to exposure to purified air and standard cigarette smoke. Sprague Dawley rats (both male and female, 6 weeks old) were successfully exposed to filtered air (n = 32), E-cig with nicotine (E-cig Nic+, n = 26), E-cig without nicotine (E-cig Nic-, n = 26), or standard cigarette smoke (1R6F reference, n = 31). All rats were exposed to inhalation exposure for 8 weeks, prior to being subjected to 30 minutes of left coronary artery occlusion followed by 3 hours of reperfusion. Exposure to E-cig vapor with or without nicotine or exposure to standard cigarettes did not increase myocardial infarct size or worsen the no-reflow phenomenon. Exposure to E-cig Nic+ reduced the body weight gain, and increased the LV weight normalized to body weight and LV wall thickness and enhanced the collagen deposition within the LV wall. E-cig exposure led to cardiovascular dysfunction, such as reductions in cardiac output, LV positive and negative dp/dt, suggesting a reduction in contractility and relaxation, and increased systemic arterial resistance after coronary artery occlusion and reperfusion in rats compared to air or cigarette exposure. E-cig exposure did not increase myocardial infarct size or worsen the no-reflow phenomenon, but induced deleterious changes in LV structure leading to cardiovascular dysfunction and increased systemic arterial resistance after coronary artery occlusion followed by reperfusion.

Abstract 13324: Impact of Chronic Electronic Cigarette Vapor Exposure on the Recovery of Cardiovascular Function in Experimental Rat Myocardial Ischemia/Reperfusion Model

Background: The impact of long-term electronic cigarettes (E-cig) vaping on cardiovascular function in rats were investigated. Methods: Sprague Dawley rats (both sex, 6 weeks old) were randomly exposed to filtered air (n=32), E-cig with nicotine (E-cig Nic + , n=26), E-cig without nicotine (E-cig Nic - , n=26), or standard cigarette smoke (n=31). After exposure to inhalation exposure for 8 weeks, the rats were subjected to 30 minutes of left coronary artery occlusion followed by 3 hours of reperfusion. Cardiovascular function was measured with intracavitary Millar catheters and echocardiography during the surgical procedure. Results: As the data shown in the Table, at 2.5 hours after coronary artery reperfusion, heart rate, cardiac output and positive/negative LV dp/dt were lower in the E-cig Nic + group compared to the air and/or cigarette group. LVFS in the cigarette group was higher than compared to E-cig Nic + or air group. There was a significantly higher systemic arterial resistance in the E-cig Nic + group compared to the cigarette group. Conclusions: Chronic E-cig Nic + exposure impairs the cardiovascular function recovery during the phase of coronary artery reperfusion after heart attack, indicated by reductions of heart rate, cardiac output, LV positive and negative dp/dt (suggesting a reduction in contractility and relaxation); and increase in systemic arterial resistance in the setting of experimental acute myocardial infarction compared to air and/or standard cigarette smoke.

Abstract 12922: Detection of the Effect of Nicotine Delivered by E-Cigarettes or Standard Cigarettes on Cardiovascular System From a Carotid Waveform Using a Physics-Based Machine Learning Approach

Introduction: We have recently shown (Alavi et al. Circulation, (2021)144: A13745-A13745) that adverse effects of nicotine delivered chronically by electronic cigarette (EC) vapor or standard cigarettes on left ventricular systolic function can be captured using intrinsic frequency (IF) method applied on carotid waveforms. Here, we propose a hybrid IF-machine learning (ML) method to detect nicotine effect on cardiovascular system using a carotid waveform. Methods: Total number of n=117 young healthy adult male and female Sprague Dawley rats (49% (n=57) female, weight ~200-250 g) were randomized and exposed to: 1) purified air, n=32; 2) EC vapor without nicotine (EC NIC-), n=26; 3) EC vapor plus nicotine (EC NIC+), n=27; and 4) standard cigarette smoke from reference combustion cigarettes (3R4F), n=32. All the exposures (nose-only) took place for duration of 5 hours/day, 4 days/week for total of 8 weeks. Third-generation type EC from VaporFi, tank model: Volt 2 was used. E-liquid was tobacco flavored with a 50/50 propylene glycol/glycerin ratio. Similar nicotine amount as the standard cigarette was delivered to the rats of EC NIC+ group. After 8 weeks of exposure, IFs were computed from invasively measured carotid waveforms. A support vector machine (SVM) classifier with radial basis function kernel was trained using IF data from 83 rats to detect (non)-nicotine groups. The k -fold cross-validation ( k =10) was used to avoid overfitting. The remaining rats were used for generalization test (n=14) and stratified blind test (n=20). Results: Our SVM model showed positive and negative predictive values of 66.7% and 76.9%, respectively. Sensitivity and specificity were 82.4% and 58.8% for test data (Fig1). Conclusions: Our results suggest that nicotine delivered by ECs or cigarettes can be detected by a physics-based ML model from a single carotid waveform. This method can potentially be used for detecting adverse effect of nicotine on cardiovascular system noninvasively.

Abstract 13745: Nicotine Delivered by Electronic Cigarette Vapor or Standard Cigarettes Adversely Affects Left Ventricular Systolic Function Measured by Cardiovascular Intrinsic Frequency in Rats

Introduction: Cardiovascular intrinsic frequency (IF) is a systems approach for the analysis of left ventricle (LV) function, arterial dynamics, and LV-arterial coupling. It was shown in a recent Framingham Heart Study (Hypertension 2021, 77(2):338-346) that higher values of the first IF (ω 1 ) (derived from carotid pressure waveforms) are associated with higher risk for incident heart failure and composite CVD events. Here, we examined the effect of chronic exposure to E-cigarette and standard cigarette on ω 1 in rats. Methods: Adult male and female Sprague Dawley rats were exposed to: 1) Purified air ( n =6); 2) E-cigarette vapor without nicotine ( n =6); 3) E-cigarette vapor plus nicotine (similar amount of nicotine as the standard cigarette, n =6); and 4) Standard nicotine-containing cigarette smoke ( n =9). E-cigarette was a 3rd generation type E-cigarette from VaporFi, tank model: Volt 2. Rats were placed into a nose-only exposure system. The exposures took place for 5 hours/day, 4 days/week for a total of 8 weeks. The E-liquid was a 50/50 propylene glycol/glycerin mixture with a tobacco flavor additive. After 8 weeks of exposure, the rats were anesthetized to measure the hemodynamics including invasive carotid pressure waveforms. IF parameters were computed from pressure waveforms with similar cardiac cycles. Results: There was no difference in ω 1 between purified air and E-cigarette vapor without nicotine; there was no significant difference in ω 1 between E-cigarette vapor with nicotine versus standard nicotine-containing cigarette smoke. ω 1 was significantly higher (P<0.005) in the nicotine-containing groups versus the non-nicotine containing groups (Fig.1). Conclusions: Our results suggest that nicotine delivered either by standard cigarette smoke or E-cigarette vapor adversely affects the LV systolic function, and ω 1 measured from the carotid waveform alone (that can be measured non-invasively with an iPhone app), can capture these negative effects.

Nicotine Toxicity Secondary to Aftermarket Modifications to a Vaping Device.

Electronic cigarettes continue to rise in popularity as a reportedly safe alternative to standard cigarette smoking. Their use has become common in our society and specifically in our young active duty population. This cigarette smoking alternative has come under recent scrutiny with the discovery of e-cigarette or vaping product use-associated lung injury. However, there is another potential risk associated with vaping: the relative ease at which vaping devices can be modified has allowed a growing community of users to invent novel ways of delivering higher concentrations of nicotine. Here, we describe two cases of active duty patients who presented to an emergency department with clinical nicotine toxicity after using a heavily modified e-cigarette.

Effects of Chronic Electronic Cigarette Vapor Exposure and Standard Cigarette Smoke on Myocardial Infarction and No‐reflow in a Rat Model

Effects of Chronic Electronic Cigarette Vapor Exposure and Standard Cigarette Smoke on Myocardial Infarction and No‐reflow in a Rat Model

Effect of e-cigarettes on nasal epithelial cell growth, Ki67 expression, and pro-inflammatory cytokine secretion.

Upon use, e-cigarette aerosol comes in contact with various mucosal tissues, including the nasal epithelium, which may lead to nasal pathologies. We therefore assessed the effect of e-cigarettes on nasal epithelial cell and tissue behaviours. Human primary nasal epithelial cells and engineered 3D nasal mucosa tissues were exposed or not to either e-cigarette aerosol or standard cigarette smoke. We then evaluated cell viability and lactate dehydrogenase (LDH) activity. With the tissues analysed tissue structure, the expression of Ki67 proliferating marker, and the secretion of pro-inflammatory cytokines by the engineered nasal mucosa. The nasal epithelial cells exposed to e-cigarettes displayed a larger cell size and a faint nucleus following exposure to e-cigarettes. This is supported by the increased levels of LDH activity following exposure to e-cigarettes, compared to that observed in the control. Tissues exposed to e-cigarette aerosol displayed a structural deregulation, with more large-sized cells, fewer Ki67-positive cells, and a reduced proliferation rate, compared to that observed in the non-exposed tissues. Cytokine measurements showed high levels of IL-6, IL-8, TNFα, and MCP-1, demonstrating that e-cigarettes activated pro-inflammatory cytokine responses. E-cigarette aerosol showed adverse effects on nasal epithelial cells and nasal engineered mucosa tissue. These findings indicate that e-cigarettes could be a threat to nasal tissues and may impair the innate immune function of nasal epithelial cells.

Early effects of cigarette smoke extract on human oral keratinocytes and carcinogenesis in head and neck squamous cell carcinoma.

BackgroundCigarette smoking is a major risk factor for head and neck squamous cell carcinoma. Still, the effect of cigarette smoke on the molecular level is unclear. The aim of the present study was to investigate the early effects of cigarette smoke on carcinogenesis of head and neck squamous cell carcinoma.MethodsHuman oral keratinocytes were exposed for 1 week to standardized cigarette smoke extract, and subsequently RT‐quantitative PCR array was performed. Protein expression of dysregulated genes was determined by immunohistochemistry in tissue samples of oral squamous cell carcinoma, oral leukoplakia, and tonsil mucosa.Results RT‐PCR revealed upregulation of ITGA‐2 and MMP‐1, whereas TEK receptor tyrosine kinase was downregulated in human oral keratinocytes. ITGA‐2 and MMP‐1 were significantly overexpressed in tissue samples of oral squamous cell carcinoma in comparison to normal mucosa (P <.01 in all experiments). ConclusionUpregulation of ITGA‐2 and MMP‐1 induced by cigarette smoke contributes significantly to oral carcinogenesis.

Evaluation of Macular Perfusion in Healthy Smokers by Using Optical Coherence Tomography Angiography.

To investigate the macular perfusion changes in healthy smokers by using optical coherence tomography angiography (OCTA). OCTA measurements were taken for the right eyes of 40 smokers (Group 1) and age- and sex-matched control cases (Group 2). Group 1 underwent OCTA scanning with the XR Avanti AngioVue OCTA (Optovue, Fremont, CA) at baseline and at 5 minutes, 30 minutes, and 60 minutes after one standard cigarette smoking. The same scanning protocol was applied without smoking in Group 2. Macular vessel area density, flow index of the choriocapillaris, foveal avascular zone (FAZ), and central macular thickness were evaluated in both groups. Group 1 consisted of 28 men and 12 women with a mean age of 41.2 years ± 9.1 years (range: 24 years to 63 years). The mean age of Group 2 was 42.6 years ± 8.4 years (range: 21 years to 65 years), which consisted of 28 men and 12 women. The mean baseline vessel area density, flow index of the choriocapillaris, FAZ, and central macular thickness showed no statistically significant differences between Groups 1 and 2. Although the flow index of choriocapillaris values were similar at the repetitive OCTA measurements in the control group (P > .05), it was decreased from 1.94 ± 0.06 to 1.89 ± 0.08, 1.90 ± 0.08, and 1.91 ± 0.07 at 5 minutes, 30 minutes, and 60 minutes following smoking, respectively, in Group 1 (P < .001). Smoking causes a significant decrease in the blood flow index of the choriocapillary area by the acute effects of nicotine and other chemical substances in cigarettes on peripheral vascular structure, as evaluated by OCTA. [Ophthalmic Surg Lasers Imaging Retina. 2017;48:617-622.].

A Standardized Method for the Preparation of a Gas Phase Extract of Cigarette Smoke.

The gas phase of cigarette smoke is important from the viewpoint of human health, because it can pass through alveolar epithelium and enter the circulation. There is no standard method for the preparation of a gas phase extract of cigarette smoke (CSE), although CSE is widely used for research instead of whole cigarette smoke. We have established a standard method for the preparation of CSE. One cigarette per trial is continuously combusted under a reduced pressure generated by an aspiration pump with a velocity of 1.050 L/min: the main stream of the smoke is passed through a Cambridge filter to remove tar, and subsequently, bubbled through a glass ball filter (pore size, 20-30 µm) into 15 mL of phosphate-buffered saline (PBS). To express the concentration of CSE, a virtual tar concentration is introduced, which is calculated assuming that tar trapped on the Cambridge filter is dissolved in the PBS. CSEs prepared from smaller numbers of cigarettes (original virtual tar concentration≤15 mg/mL) show similar concentration-response curves for cytotoxicity versus virtual tar concentrations. CSEs prepared from various brands of cigarettes and by different smoking regimes (continuous and puff smoking) show similar cytotoxic potency if the virtual tar concentrations are the same. In conclusion, using the standardized method for CSE preparation in combination with the virtual tar concentration, it becomes possible to simply and rapidly prepare standard CSEs with defined concentrations from any brand of cigarettes, which are toxicologically equivalent to CSE prepared by puff smoking.

Toxicity Mechanisms of Cigarette Smoke on Mouse Fetus Mitochondria.

Maternal smoking has been recognized as a common cause of low birth weight, preterm birth and the decrease of gestational age period. Unfortunately, there is an increasing interest within public especially woman in Iran in the tobacco products consumption. On the other hand, the deleterious effect of maternal smoking on human fetus in pregnancy period especially in the first trimester encouraged us to investigate toxicity mechanisms of cigarette smoke on mouse fetus mitochondria. For this purpose different concentrations (1, 10 and 100%) of standardized cigarette smoke extract (CSE) were administrated on mitochondria isolated from fetus of NMRI mice on the 15 day of gestation. Our results showed a significant increase in ROS (Reactive oxygen species) formation, lipid peroxidation, mitochondrial membrane potential collapse, mitochondrial swelling and finally a decrease in ATP concentration in the CSE-treated isolated fetus mitochondria. Our results suggest that CSE-induced embryo toxicity is the result of disruptive effect on mitochondrial respiratory chain that leads to ROS formation, lipid peroxidation, mitochondrial MMP (mitochondrial membrane potential) decline and decrease of ATP level which starts apoptosis signaling.

Toxicity of cigarette smoke on isolated lung, heart, and brain mitochondria: induction of oxidative stress and cytochrome c release

Cigarette smoking is one of the main risk factors for premature human death which is associated with a variety of respiratory and vascular diseases, and cancer due to exposure to hundreds of toxicants. Rat mitochondria were obtained by differential ultracentrifugation and incubated with different concentrations (1%, 10%, or 100%) of standardized cigarette smoke extract (CSE). Our results showed that CSE induced a rise in mitochondrial reactive oxygen species (ROS) formation, lipid peroxidation, and mitochondrial membrane potential (MMP) collapse before mitochondrial swelling ensued in isolated pulmonary mitochondria. Disturbance in oxidative phosphorylation was also confirmed by decrease in ATP concentration in the CSE-treated mitochondria. In addition, collapse of MMP and mitochondrial swelling produced release of cytochrome c via outer membrane rupture or mitochondrial permeability transition (MPT) pore opening. Our results suggested that CSE-induced toxicity in lung tissue is the result of disruptive effect on mitochondrial respiratory chain that leads to ROS formation, lipid peroxidation, MMP decline, and cytochrome c expulsion which results in apoptosis signaling and cell loss.

Cigarette smoke facilitates allergen penetration across respiratory epithelium

The association between cigarette smoke exposure and allergic airway disease is a matter for debate. We sought to investigate in an in vitro system whether active smoking reduces the integrity and barrier function of the respiratory epithelium and thus facilitates allergen penetration. We cultured the human bronchial epithelial cell line 16HBE14o- in a transwell culture system as a surrogate for the intact respiratory epithelium. The cell monolayer was exposed to standardized cigarette smoke extract (CSE). The extent and effects of trans-epithelial allergen penetration were measured using 125I-labelled purified major respiratory allergens (rBet v 1, rPhl p 5 and rDer p 2) and histamine release experiments. Exposure of cells to concentrations of CSE similar to those found in smokers induced the development of para-cellular gaps and a decrease in trans-epithelial resistance. CSE exposure induced a more than threefold increase in allergen penetration. Increased subepithelial allergen concentrations provoked a substantial augmentation of histamine release from sensitized basophils. Our results indicate that cigarette smoke is a potent factor capable of reducing the barrier function of the respiratory epithelium for allergens and may contribute to increased allergic inflammation, exacerbation of allergic disease and boosting of IgE memory.

The parity-related protection against breast cancer is compromised by cigarette smoke during rat pregnancy: observations on tumorigenesis and immunological defenses of the neonate

Early pregnancy is a powerful negative risk factor for breast cancer (BCa) in women. Pregnancy also protects rats against induction of BCa by carcinogens such as N-methyl-N-nitrosourea (MNU), making the parous rat a useful model for studying this phenomenon. Smoking during early pregnancy may lead to an increased risk of BCa in later life, possibly attributable to carcinogens in cigarette smoke (CS), or to reversal of the parity-related protection against BCa. To investigate these possibilities, 50-day-old timed first-pregnancy rats were exposed to standardized mainstream CS (particle concentration = 50 mg/m3) or to filtered air (FA) 4 h/day, Day 2-20 of gestation. Age-matched virgin rats were similarly exposed to CS or FA. At age 100 days, the CS or FA-exposed, parous and virgin rats were injected s.c. with MNU (50 mg/kg body wt), or with MNU vehicle. Mammary tumors (MTs) first appeared in virgin rats 9 weeks post-MNU injection. While no MTs were detected in FA-exposed parous rats until 18 weeks post-MNU, MTs appeared in the CS-exposed parous rats as early as 10 wks (P < 0.02). As no MTs developed in CS-exposed rats not injected with MNU, CS did not act as a direct mammary carcinogen. Serum prolactin concentration on Day 19 of pregnancy in CS-exposed dams was reduced by 50% compared with FA-exposed dams (P < 0.005). CS exposure during a pregnancy may thus 'deprotect' rats, enhancing their vulnerability to MNU-induced BCa. Prenatal CS exposure had no detectable effect on the immune responses of the pups examined at 3, 8 or 19 weeks of age. However, prolactin concentration in stomach contents (milk) of 3-day-old pups suckled by CS-exposed dams was decreased when compared with that of FA-exposed dams (P < 0.032). As milk-borne prolactin modulates development of the central nervous and immune systems of neonatal rats, CS exposure of the dams could adversely affect later maturation of these systems by reducing milk prolactin.

Effects of Exposure to Standard- and Nicotine-Reduced-Cigarette Smoke on Pharmacokinetics of Theophylline and Cimetidine in Rats

Influences of exposure to standard- (containing nicotine and tar) and nicotine-reduced-cigarette smoke on the pharmacokinetics of theophylline (20 mg/kg, per os) and cimetidine (50 mg/kg, per os) were investigated in rats. Animals were exposed to standard- or nicotine-reduced-cigarette smoke for 8min with a “smoking machine”. In control rats, theophylline concentrations in plasma increased rapidly, peaked 2h later, and then decreased gradually. Concentrations of theophylline in plasma of rats exposed to standard- and nicotine-reduced-cigarette smoke were suppressed in comparison with that of control rats, and the suppressive effect of nicotine-reduced-cigarette smoke was weaker than that of standard-cigarette smoke. The suppression of theophylline concentrations in plasma induced by exposure to cigarette smoke may be due to nicotine and other constituents of the cigarette smoke, even if the effects are slight. For cimetidine, no difference was found between drug concentration in plasma of rats exposed to nicotine-reduced-cigarette smoke and that of control rats; however, the drug concentration in plasma of rats exposed to standard-cigarette smoke was markedly suppressed. These results suggest that the suppression of cimetidine concentrations in plasma may be due solely to nicotine in cigarette smoke.

Effects of Standard Cigarette Smoke and Nicotine-Reduced Cigarette Smoke on Plasma Concentrations of Indomethacin Administered Orally to Rats

The influence of acute exposures to standard (ST) and nicotine-reduced (NR) cigarette smokes on the plasma concentration of orally administered indomethacin (IM, 5 mg/kg) was investigated in rats. IM plasma concentrations in the ST- and NR-groups were lower than those in the nonsmoking control group, while the lowered effect in the NR-group was slightly weaker than in the ST-group. These results suggest that the plasma concentrations of IM administered orally are lowered by the acute exposure of cigarette smoke, and this influence may be attributed largely to constituents other than nicotine in the cigarette smoke as well as slightly attributable to nicotine.

Effects of standard cigarette smoke and nicotine-reduced cigarette smoke on plasma concentrations of indomethacin administered orally to rats.

The influence of acute exposures to standard (ST) and nicotine-reduced (NR) cigarette smokes on the plasma concentration of orally administered indomethacin (IM, 5 mg/kg) was investigated in rats. IM plasma concentrations in the ST- and NR-groups were lower than those in the non-smoking control group, while the lowered effect in the NR-group was slightly weaker than in the ST-group. These results suggest that the plasma concentrations of IM administered orally are lowered by the acute exposure of cigarette smoke, and this influence may be attributed largely to constituents other than nicotine in the cigarette smoke as well as slightly attributable to nicotine.

Effects of Standard Cigarette and Nicotine-Less Cigarette Smoke Inhalings on Nicorandil Plasma Levels in Rats

The influence of cigarette smoke on nicorandil plasma levels at a dose of 10 mg/kg administered orally was investigated in rats. The animals were exposed to standard and nicotine-less cigarette smoke for 8 min using a 'smoking machine'. In nonsmoking control rats, nicorandil plasma levels increased rapidly and reached the maximum (approx. 7.6 micrograms/ml) after 1 h and then decreased gradually. On the other hand, nicorandil plasma levels in the rats inhaling standard cigarette and nicotine-less cigarette smoke reached the maximum (approx. 4.7 and 4.9 micrograms/ml, respectively) after 1-2 h. These results suggest that nicorandil plasma levels after oral administration are influenced not only by standard cigarette smoke but also by nicotine-less cigarette smoke.

Clearance of polonium-210-enriched cigarette smoke from the rat trachea and lung

The distribution and clearance of α radioactivity in the lungs of rats were measured after inhalation of smoke from cigarettes highly enriched in 210Po. Female Fischer rats were exposed daily for 6 months to smoke from cigarettes with 500 times the normal content of 210Po. Control rats were exposed to standard cigarette smoke. Animals were serially withdrawn and killed. After necropsy the trachea, major bronchi, larynx, and nasopharynx were exmined for surface α activity by an etched track technique utilizing cellulose nitrate detectors. Areas of accumulated activity were seen on samples of larynx from rats exposed to the 210Po-enriched cigarettes. No other local accumulations were seen on the airways. The lower lungs were analyzed radiochemically for 210Po. Both radiochemical analysis and track measurements showed highly elevated activity concentrations in rats exposed to the 210Po-enriched cigarettes. Following withdrawal from smoking, both short- and long-term clearance components were seen. The parameters which fit the postexposure data for clearance of the lung burden cannot fit the buildup during the exposure period.