Smoking and pulmonary function

Systematic review of the evidence relating FEV1 decline to giving up smoking

BACKGROUND

The rate of forced expiratory volume in 1 second (FEV1) decline ("beta") is a marker of chronic obstructive pulmonary disease risk. The reduction in beta after quitting smoking is an upper limit for the reduction achievable from switching to novel nicotine delivery products. We review available evidence to estimate this reduction and quantify the relationship of smoking to beta.

METHODS

Studies were identified, in healthy individuals or patients with respiratory disease, that provided data on beta over at least 2 years of follow-up, separately for those who gave up smoking and other smoking groups. Publications to June 2010 were considered. Independent beta estimates were derived for four main smoking groups: never smokers, ex-smokers (before baseline), quitters (during follow-up) and continuing smokers. Unweighted and inverse variance-weighted regression analyses compared betas in the smoking groups, and in continuing smokers by amount smoked, and estimated whether beta or beta differences between smoking groups varied by age, sex and other factors.

RESULTS

Forty-seven studies had relevant data, 28 for both sexes and 19 for males. Sixteen studies started before 1970. Mean follow-up was 11 years. On the basis of weighted analysis of 303 betas for the four smoking groups, never smokers had a beta 10.8 mL/yr (95% confidence interval (CI), 8.9 to 12.8) less than continuing smokers. Betas for ex-smokers were 12.4 mL/yr (95% CI, 10.1 to 14.7) less than for continuing smokers, and for quitters, 8.5 mL/yr (95% CI, 5.6 to 11.4) less. These betas were similar to that for never smokers. In continuing smokers, beta increased 0.33 mL/yr per cigarette/day. Beta differences between continuing smokers and those who gave up were greater in patients with respiratory disease or with reduced baseline lung function, but were not clearly related to age or sex.

CONCLUSION

The available data have numerous limitations, but clearly show that continuing smokers have a beta that is dose-related and over 10 mL/yr greater than in never smokers, ex-smokers or quitters. The greater decline in those with respiratory disease or reduced lung function is consistent with some smokers having a more rapid rate of FEV1 decline. These results help in designing studies comparing continuing smokers of conventional cigarettes and switchers to novel products.

The effect of passive smoking on the incidence of airway complications in children undergoing general anaesthesia

The aim of this study was to assess whether passive smoking affected the frequency of airway complications in children undergoing general anaesthesia. One hundred and twenty-five children undergoing general anaesthesia for elective daycase surgery were monitored for adverse respiratory events and desaturation during induction, intra-operatively and in the recovery room. Oxygen saturation was monitored throughout and a venous sample was taken for estimation of carboxyhaemoglobin levels. Parents were asked to fill in a questionnaire detailing their smoking habits. Sixty-three of the children were passive smokers with a potential daily exposure varying from 5-130 cigarettes. There was no difference in the frequency of respiratory events between passive smokers and those not exposed to cigarette smoke at induction or intra-operatively. However, in the recovery room, desaturation was significantly more common in passive smokers (p < 0.02). This was related to the cumulative number of cigarettes smoked by individuals to whom the child was exposed (p < 0.05). Neither carboxyhaemoglobin levels nor domiciliary address were predictive of desaturation. This study suggests that passive smoking contributes to postoperative arterial oxygen desaturation following general anaesthesia in children.

Changes in arterial oxygen saturation in cigarette smokers following general anaesthesia

The effect of cigarette smoking on postoperative arterial oxygen saturation was evaluated in 45 adult patients using pulse oximetry. Patients were divided into a smoking group (n = 20) and a non-smoking group (n = 25) based on current smoking habits up until the time of surgery. The two groups were similar with respect to sex, ASA physical status, surgical procedure, duration of anaesthesia, narcotic and anaesthetic use and recovery characteristics. The non-smoking group was, however, significantly (P less than 0.05) older than the smoking group. Postoperative oxygen saturation (SaO2) decreased (P less than 0.001) during transport of both groups of patients from the Operating Room to the Recovery Room; a decrease which was significantly greater in the smoking group. The severity of hypoxaemia was also significantly greater in the smoking group than in the non-smoking group. This study suggests that cigarette smoking contributes to postoperative arterial oxygen desaturation following general anaesthesia and that supplemental oxygen should be administered to these patients during postoperative transport.

Oral N-acetylcysteine speeds reversal of cigarette smoke-induced mucous cell hyperplasia in the rat

We set out to determine whether or not the "mucolytic" drug N-acetylcysteine would speed the reversal of cigarette smoke-induced secretory-cell hyperplasia to normal, similar to that found previously for two nonsteroidal antiinflammatory drugs. Cigarette smoke alone significantly (p less than 0.01) increased the number of secretory cells in seven out of eight airway levels studied and maintained a significant increase in five of the levels at least 3 weeks after cessation of exposure. Treatment of rats with N-acetylcysteine, as 1% of their drinking water during the recovery period, reduced the time taken for secretory cell number to return to normal to between 4 days and 3 weeks, depending on airway level.

Indomethacin and flurbiprofen speed recovery of rat bronchial epithelium after exposure to cigarette smoke

The cigarette smoke-induced rat model of chronic bronchitis was used to study the time course of the return of cigarette smoke-induced secretory cell hyperplasia to the normal and the capacity of two non-steroidal anti-inflammatory drugs to speed this recovery. Cigarette smoke alone significantly increased (P less than 0.05) the number of secretory cells in all of the eight airway levels studied to between 52-225% above control values. After cessation of exposure, recovery was complete by 9 days in the trachea, between 10-21 days in 'proximal' intrapulmonary airways and 43-84 days in distal bronchioli. Indomethacin and flurbiprofen, given by intraperitoneal injection at 4 mg/kg body weight for 21 days of the recovery period, significantly reduced the time taken for recovery to between 4 and 9 days in intrapulmonary airways but had no effect in the trachea.

Decrease in ventilatory capacity between ages of 50 and 54 in representative sample of Swedish men

The ventilatory capacity, including flow-volume curves of 313 men, all 50 years old, was examined in 1963 and 1967. The group as a whole, which included persons with chronic bronchitis, with "other respiratory symptoms," and without respiratory symptoms, showed the same absolute decrease in ventilatory capacity.Vital capacity, forced expiratory volume, and maximum expiratory flow all dropped more for the smokers than for either the non-smokers or the ex-smokers. In those who had stopped smoking for four years or less, however, ventilatory capacity did not decline significantly less than in those who continued to smoke.