Expiratory Resistance Research Articles

Changes in lung function and tidal airflow patterns after increasing extrathoracic airway resistance

The aim of this study was to determine what changes occur in previously described tidal expiratory flow patterns when extrathoracic resistance is added. A total of 16 subjects with normal lung function and 15 patients with chronic COPD, were studied. The following measurements were made before and after the addition of an extrathoracic expiratory resistance (EER; 0.89 kPa/L s at a flow of 0.5 L/s) during uncoached tidal breathing: expiratory time (tE), frequency (f), expiratory time to maximum flow/total expiratory time (tPTEF/tE), tidal maximum expiratory flow (PEF(TIDAL)), and time constant of the respiratory system calculated from the passive portion of tidal expiration (trs(TIDAL)). Post peak profiles were categorized as convex, linear or concave and time for flow to fall to 80% and 20% of maximum (t80 and t20) were measured. Tidal indices tE, f and PEF(TIDAL), were similar in the two groups, but tPTEF/tE was greater and trs(TIDAL) was less in the normal subjects than in the COPD patients. Addition of EER in both groups caused PEF(TIDAL) to decrease and trs(TIDAL), t80 and the percentage of convex profiles to increase. tPTEF/tE increased in the COPD patients but was unchanged in the control group. After addition of EER during tidal breathing, expiratory flow in COPD patients resembled that seen in normal subjects.

Pattern of lung emptying and expiratory resistance in mechanically ventilated patients with chronic obstructive pulmonary disease

Pattern of lung emptying and expiratory resistance in mechanically ventilated patients with chronic obstructive pulmonary disease

Normobaric hypoxia, ozone therapy and respiratory exercise with expiratory resistance in rehabilitation of patients with chronic bronchitis and bronchial asthma

Normobaric hypoxia, ozone therapy and respiratory exercise with expiratory resistance in rehabilitation of patients with chronic bronchitis and bronchial asthma

Model-Based Prediction of Expiratory Resistance Index in Patients with Asthma

Develop a sensitive algorithm and index for detection of asthma patients using forced expiratory flow curves. A lumped-parameter model of forced expiration was developed. The model can predict the flow-volume curve during forced expiratory maneuver. The flow-volume curves generated by the model depend on values of resistance parameters (FER). Use of flow-volume curves recorded from normal subjects and from patients with asthma before and after ventolin inhalation as inputs for the inverse model, yielded the resistance parameters for each case. These parameters are based on the entire information presented in the flow-volume curve and on the reduction in flow at all lung volumes. Forced Expiratory Resistance (FER(N)) indices were estimated at different percent of lung volumes using the inverse model. The index was significantly affected by inhalation of ventolin in asthmatic patients and was insensitive to ventolin inhalation in normal patients. In asthmatic patients, the FER index at five lung volumes (out of eight), was two--five times greater than in normal subjects with p < 0.05 (three of them with p < 0.01). The estimated parameters were sensitive indicators of the degree of lung function impairment and were able to accurately distinguish between healthy and asthmatic patients.

Evaluation of the lung function test in reversible glottis-dilating operations.

Our aim was to obtain an objective evaluation of the airway before and after reversible glottis-dilating operations using the lung function test. Bilateral abductor vocal cord paralysis remains mostly a complication of thyroid surgery. After thyroid surgery, the paralysis is potentially reversible, and the patient has a chance for recovery mostly in the first 6 months. According to these considerations, a reversible vocal cord laterofixation procedure was used instead of tracheostomy. The operations were performed endoscopically using high-frequency JET ventilation and the special endo-extralaryngeal suture technique by Lichtenberger. This technique was used in 92 cases. The pre- and postoperative data of reversible glottis-dilating techniques could be compared in 23 non-selected patients. Lung function tests that were performed were forced inspiratory volume (FIV1), forced expiratory volume (FEV1), peak inspiratory flow rate (PIF), peak expiratory flow rate (PEF) and resistance of the airways (Raw). For the evaluation of the functional results, we used the body-pletysmograph. Our aim was to obtain a quantitative evaluation of the results. These values allow us to compare the results achieved by using different glottis-dilating methods. The FEV1 (forced expiratory volume) improved 25%, and the FIV1 (forced inspiratory volume) improved 39% after the operations on average. PEF (peak expiratory flow rate) and PIF (peak inspiratory flow rate) improved 37 and 45% after glottis-dilating surgery on average. The Raw (resistence of airways) was 271.5% on average before the operations, and after reversible glottis-dilating operations decreased to a level of 200.6%.

Expiratory changes in pressure: flow ratio during sleep in patients with sleep-disordered breathing.

The size of the upper airway is smallest during sleep, at the end of expiration. This may favor upper-airway collapse in patients with obstructive sleep apnea. In the respiratory cycles preceding obstructive events during sleep, our hypothesis is that upper-airway resistance (UAR) increased earlier during expiration prior to changes occurring during inspiration. We analyzed the pharyngeal pressure-to-flow ratios in order to determine variations in UAR for both inspiration and expiration during stable respiration and the 4 consecutive breaths preceding upper-airway obstructive events in stage 2 sleep. To assess the variation of resistance throughout the within-breath period during stable respiration and the 4 breaths preceding obstructive events, results were expressed as the instantaneous resistance at fixed points 10%, 30%, 50%, 70%, and 90% of time values of inspiration and expiration. Global inspiratory and expiratory UARs during wakefulness and sleep in stable respiration were expressed by the median of instantaneous UAR values. Tertiary-care academic medical center. Eleven patients with moderate to severe sleep-disordered breathing. None. During stable respiration, both inspiratory and expiratory resistance increased during sleep, compared to values while awake. The difference between inspiratory and expiratory UAR increased when sleep deepened. During the respiratory cycle, the increase in the end-expiratory UAR occurred earlier than during inspiration; during stable respiration, UAR was much aggravated during the last three breaths preceding an obstructive event. Increases in the expiratory UAR occurred earlier than during inspiration in the cycles preceding upper-airway collapse in patients with sleep apnea. This finding suggested an important role of the expiratory phase in promoting upper-airway collapse and is in accordance with the inspiratory pharyngeal instability occurring when lowering the expiratory pressure in patients with obstructive sleep apnea.

Pediatric laryngeal paralysis: a new proposed surgical therapy.

The cricothyroid muscle (CTM) has a separate innervation from that of intrinsic laryngeal muscles; therefore, its action may contribute to airflow resistance in children with laryngeal paralysis (LP) secondary to recurrent laryngeal nerve (RLN) palsy. We proposed removal of the CTM as a means of indirectly widening the paralyzed neonatal glottis. A prospective study was conducted using a piglet animal model to simulate LP and evaluate the proposed treatment's outcome. LP was induced via bilateral RLN sectioning in seven piglets. The CTMs were then removed. Animals acted as their own controls. Outcome measures consisted of serial inspiratory and expiratory airflow resistance measurements taken (1) with no intervention, (2) after RLN sectioning, and (3) after CTM removal. Several animals were awakened to assess their clinical responses to the interventions. The paired Student's t-test was used for statistical analysis. Inspiratory airflow resistance was significantly increased by RLN sectioning (p = .0062) and then significantly decreased after subsequent CTM removal (p = .0005). Clinical responses to the interventions mirrored the measured findings. Removal of the CTM significantly decreases inspiratory airway resistance in piglets with induced LP. This proposed surgical therapy for pediatric bilateral LP warrants further investigation.

Effects of Helium and 40% O2 on Graded Exercise With Self-Contained Breathing Apparatus

Maximal exercise performance is decreased when breathing from a self-contained breathing apparatus (SCBA), owing to a ventilatory limitation imposed by the increased expiratory resistance. To test the hypothesis that decreasing the density of the breathing gas would improve maximal exercise performance, we studied 15 men during four graded exercise tests with the SCBA. Participants breathed a different gas mixture during each test: normoxia (NOX; 21% O2, 79% N2), hyperoxia (HOX; 40% O2, 60% N2), normoxic helium (HE-OX; 21% O2, 79% He), and hyperoxic helium (HE-HOX; 40% O2, 60% He). Compared to NOX, power output at the ventilatory threshold and at maximal exercise significantly increased with both hyperoxic mixtures. Minute ventilation was increased at peak exercise with both helium mixtures, and maximal aerobic power (VO2max) was significantly increased by 12.9 +/- 5.6%, 10.2 +/- 6.3%, and 21.8 +/- 5.6% with HOX, HE-OX, and HE-HOX, respectively. At peak exercise, the expired breathing resistance imposed by the SCBA was significantly decreased with both helium mixtures, and perceived respiratory distress was lower with HE-HOX. The results show that HE-OX improved maximal exercise performance by minimizing the ventilation limitation. The performance-enhancing effect of HOX may be explained by increased arterial oxygen content. Moreover, HE-HOX appeared to combine the effects of helium and hyperoxia on VO2max.

Breathing around the clock: an overview of the circadian pattern of respiration.

This article reviews human and animal studies about the circadian patterns of physiological variables involved with the respiratory function. Some measures reflecting the mechanical properties of the lungs, such as functional residual capacity, forced expiratory volumes and airway resistance, change periodically with the time of the day. Also resting pulmonary ventilation (V(E)), tidal volume, and breathing rate follow circadian patterns. In humans, these patterns occur independently of the daily changes in activity, whereas, to some extent, they are linked to changes in the state of arousal. Differently, in some rodents, the circadian oscillations of the breathing pattern occur independently of the daily rhythms of either activity or state of arousal. Recent measurements of the breathing pattern for unlimited periods of time in undisturbed animals have indicated that the circadian changes occur in close temporal phase with those of oxygen consumption, carbon dioxide production, and body temperature. However, none of these variables can fully explain the circadian pattern of breathing, the origin of which remains unclear. Both in humans and in rats the V(E) responses to hypercapnia or hypoxia differ at various times of the day. In rats, the daily differences in V(E) responses are buffered by changes in metabolic rate, such that, unlike humans, the hyperventilation (defined as the increase in ventilation-metabolism ratio) remains constant throughout the 24 h. The presence of a biological clock is a major advantage in the adaptation to the environment, although it forces some variables to deviate periodically from their mean value. In humans, these deviations become apparent in conditions of hypoxia. Hence, a daily time-window exists in which the respiratory system is less capable of responding to challenges, a factor which may contribute to the findings that some cardio-respiratory symptoms and diseases peak at particular times of the day.

Pulmonary function tests in preschool children with asthma.

Pulmonary function tests are seldom performed in preschool children with asthma. The aim of this multicenter study was to compare pulmonary function in 74 preschool children with asthma (height of 90-130 cm) and 84 healthy control subjects. Functional residual capacity (helium dilution technique) and expiratory interrupter resistance (interrupter technique) were measured. As compared with control children, children with asthma had a significantly higher resistance (0.77 +/- 0.20 vs. 0.92 +/- 0.22 kPa. L-1. second, p < 0.001) and significantly lower specific expiratory interrupter conductance (p < 0.005) values. Resistance values were significantly higher in children with asthma with than without symptoms on exertion (p < 0.05). The effect of bronchodilator administration, expressed as the percentage of baseline and predicted resistance values, was significantly greater in children with asthma than in control subjects (-18.6 +/- 13.6% vs. -11.2 +/- 15.2%, p </= 0.001, and -23.2 +/- 19.2% vs. -12.6 +/- 17.8%, p < 0.001), respectively. A 35% decrease in resistance after bronchodilation expressed as the percentage of predicted values had a likelihood ratio of 3 for separating the bronchodilator response in children with asthma from that in healthy control subjects. Pulmonary function tests that do not require active cooperation may help in the management and follow-up of preschool children with asthma who are unable to perform forced expiratory maneuvers.

Comparative effects of helium-oxygen and external positive end-expiratory pressure on respiratory mechanics, gas exchange, and ventilation-perfusion relationships in mechanically ventilated patients with chronic obstructive pulmonary disease

To compare the effects of He/O(2) and external PEEP (PEEPe) on intrinsic PEEP (PEEPi), respiratory mechanics, gas exchange, and ventilation/perfusion (V(A)/Q) in mechanically ventilated COPD patients. Prospective, interventional study in the intensive care unit of a university hospital. Ten intubated, sedated, paralyzed, mechanically ventilated COPD patients studied in the following conditions: (a) baseline settings made by clinician in charge, air/O(2), ZEEP; (b) He/O(2), ZEEP; (c) air/O(2), ZEEP; (d) air/O(2), PEEPe 80% of PEEPi. Measurements at each condition included V(A)/Q by the multiple inert gas elimination technique (MIGET). PEEPi and trapped gas volume were comparably reduced by He/O(2) (4.2+/-4 vs. 7.7+/-4 cmH(2)O and 98+/-82 vs. 217+/-124 ml, respectively) and PEEPe (4.4+/-1.3 vs. 7.8+/-3.6 cmH(2)O and 120+/-107 vs. 216+/-115 ml, respectively). He/O(2) reduced inspiratory and expiratory respiratory system resistance (15.5+/-4.4 vs. 20.7+/-6.9 and 19+/-9 vs. 28.8+/-15 cmH(2)O l(-1)s(-1), respectively) and plateau pressure (13+/-4 vs. 17+/-6 cmH(2)O). PEEPe increased airway pressures, including total PEEP, and elastance. PaO(2)/FIO(2) was slightly reduced by He/O(2) (225+/-83 vs. 245+/-82) without significant V(A)/Q change. He/O(2) and PEEPe comparably reduced PEEPi and trapped gas volume. However, He/O(2) decreased airway resistance and intrathoracic pressures, at a small cost in arterial oxygenation. He/O(2) could offer an attractive option in COPD patients with PEEPi/dynamic hyperinflation.

Tidal off-line exhaled nitric oxide measurements in a pre-school population.

Exhaled nitric oxide (ENO) is used as a non-invasive marker of airway inflammation. The aim of this study was to measure ENO in a pre-school population using a relatively novel method, the off-line tidal breathing method, and to investigate differences in ENO between subjects with different presentations of wheezing. ENO was measured in 129 children (median age 4.4 years, quartiles 4.0-4.8 years) through a mouth mask attached to a two-way valve with an expiratory resistance of 5 cm H(2)0. Mean tidal ENO concentration (tENO) was calculated from triplicate measurements. Mean +/- SEM tENO for 89 control subjects was 13+/-0.4 ppb (95%CI 11.8-13.7 ppb); this level was significantly different from tENO in 15 children with a history of recurrent wheezing (18.6+/-1.9 ppb; 95%CI 14.5-22.7 ppb; t-test P<0.0001). Mean tENO in 16 children with a single wheezing episode was 11.4+/-1.0 ppb (95%CI 9.2-13.6 ppb) and thus significantly different from the recurrent wheezing group (t-test P=0.0024). The off-line tidal breathing method is a feasible and appealing method for measuring exhaled nitric oxide in pre-school children. With this method, higher tidal exhaled nitric oxide levels were found in children with recurrent wheezing.

Intravenous nicorandil prevents thiamylal-fentanyl–induced bronchoconstriction in humans*

Nicorandil has a hybrid property between nitrates and potassium channel openers and has been reported to cause a concentration-dependent relaxation of isolated guinea pig trachealis. Experimental asthma in a guinea pig model was also inhibited by nicorandil. However, no clinical data on the bronchorelaxant effects of this drug have been published. The aim of this study was to investigate whether intravenous nicorandil prevents thiamylal-fentanyl-induced bronchoconstriction. Double-blind, prospective, placebo-controlled, randomized study. A total of 36 patients were randomly allocated to two groups: a control group (n = 18) and a nicorandil group (n = 18). Intravenous administration of nicorandil or a placebo (normal saline). Anesthesia was induced with 5 mg/kg thiamylal and 0.3 mg/kg vecuronium. A continuous infusion of 15 mg x kg(-1) x hr(-1) thiamylal was then used to maintain the anesthesia. Controlled ventilation was maintained, delivering 50% nitrous oxide in oxygen. At 20 mins after the induction of anesthesia, the control group patients were given a 6 mL/hr continuous infusion of normal saline and the nicorandil group patients were given a 6 mg x hr(-1) (6 mL/hr) continuous infusion of nicorandil for 60 mins. At 30 mins after the start of the study, both groups received a 5-microg/kg dose of fentanyl. Systolic and diastolic arterial pressure, heart rate, mean airway resistance, expiratory airway resistance, and dynamic lung compliance were measured for the baseline condition, just before the administration of fentanyl (T30), at three consecutive 6-min intervals after the fentanyl injection (T36, T42, and T48) and 30 mins after the fentanyl injection (T60). Both groups had comparable baseline values for mean airway resistance, expiratory airway resistance, and dynamic lung compliance. In the control group, both mean airway resistance and expiratory airway resistance increased significantly at T36-60, compared with the baseline values, and dynamic lung compliance decreased significantly at T36-60, compared with the baseline value. In the nicorandil group, no changes in mean airway resistance, expiratory airway resistance, or dynamic lung compliance occurred at T36-60. Our observations suggest that the intravenous administration of nicorandil has a bronchodilator effect in humans.

Monitorización de la función respiratoria en el niño con ventilación mecánica (II): complianza, resistencia, hiperinsuflación dinámica, espacio muerto y trabajo respiratorio

Several parameters can be used to study respiratory mechanics in children on mechanical ventilation. Compliance is a measure of the distensibility of the respiratory system. In mechanical ventilation two measures of compliance can be used. Static compliance (pulmonary distensibility) can be measured in volume modes by the application of an inspiratory pause with the respiratory system at rest (sedated patients without inspiratory effort). Dynamic compliance does not require an inspiratory pause and the respiratory system need not be at rest. Compliance can be calculated numerically or expressed graphically in the volume-pressure curve. Many respirators can calculate inspiratory and expiratory airway resistance (including endotracheal tube resistance). Several measures can be used to detect dynamic hyperinflation (intrinsic PEEP, auto-PEEP, trapped air volume) after application of an expiratory pause. The latest respirators can perform these measurements almost automatically. Work of breathing and respiratory effort can also be analyzed by measuring several parameters (pressure-time product, imposed work of breathing, P 0.1, maximum inspiratory pressure). However, these measures have not yet been standardized in children.

Presión positiva continua en la vía aérea por vía nasal en el recién nacido prematuro: estudio comparativo de dos modelos de baja resistencia

To compare the safety and efficacy of two low expiratory resistance models of nasal continuous positive airway pressure (n-CPAP) in preterm infants. A 1-year prospective trial was performed in the Neonatal Intensive Care Unit of La Fe Hospital to compare the Infant Flow (IF) and Medijet (MJ) devices. All preterm infants requiring n-CPAP for respiratory distress at birth (group I), infants weighting less than 1500 g requiring postextubation (group II) and those with apnea-bradycardia syndrome (ABS) (group III) were included. The patients were randomly assigned to IF or MJ. A total of 125 patients received 226 treatments (IF: n 5 126: MJ: n 5 110). The mean gestational age was 29.4 weeks and the mean birth weight was 1340 g.Efficacy. In group I (n 5 73) no difference were found between systems and 6 hours' after initiation of n-CPAP decreases in FiO2, CO2 and respiratory effort were similar. The need for intubation was also similar (IF: 34.6 %; MJ: 24.1 %). In group II (n 5 73) the need for reintubation at 48 hours was similar with both treatments (IF:19 %; MJ: 8 %). In group III (n 5 80) resolution of ABS was similar after 24 hours of n-CPAP (IF: 46 %; MJ: 58 %). The need for intubation was also similar (IF: 26 %; MJ: 10 %).Complications. Air leaks occurred in six preterm infants (IF: 4; MJ: 2). Severe abdominal distension occurred in 5 % with both systems. Five infants had significant nasal lesions (IF: 1; MJ: 4). The efficacy and safety of both systems was similar in the variables studied and no significant differences were found.

Pulmonary function tests in preschool children with cystic fibrosis.

Pulmonary function tests have rarely been assessed in preschool children with cystic fibrosis (CF). The objective of this multicenter study was to compare pulmonary function in 39 preschool children with CF (height, 90-130 cm; 16 homozygous Delta F508) and in 79 healthy control children. Functional residual capacity (helium dilution technique) and expiratory interrupter resistance (Rint(exp)) (interrupter technique) were measured. As compared with control children, children with CF had significantly higher Rint(exp), expressed as absolute values and as Z-scores (1.05 +/- 0.36 versus 0.80 +/- 0.20 kPa.L(-1). second, p < 0.0001; and 1.31 +/- 1.72 versus 0.19 +/- 0.97, p < 0.0001), and significantly lower specific expiratory interrupter conductance (1.29 +/- 0.34 versus 1.63 +/- 0.43 kPa(-1). second, p < 0.0001). The effect of the bronchodilator salbutamol on Rint(exp) was not significantly different between children with CF and control children. Rint(exp) Z-scores were significantly higher in children with CF who were exposed to passive smoke (n = 8) (p < 0.03). Children with CF and with a history of respiratory symptoms (n = 31) had significantly higher functional residual capacity Z-scores (p < 0.02) and lower specific expiratory interrupter conductance Z-scores (p < 0.04). Genotype did not influence the data. We conclude that Rint(exp) and functional residual capacity measurements may help to follow young children with CF who are unable to perform reproducible forced expiratory maneuvers.

Hyperventilation with He-O2 breathing is not decreased by superimposed external resistance.

The purpose of this study was to determine the effect of imposed external resistance on the ventilatory response to He-O(2) breathing during peak exercise. To accomplish this purpose, separate inspiratory and expiratory external resistances were applied to offset for the decrease in intrapulmonary airway resistance with He-O(2) breathing. Seven men and three women (69+/-3 years, mean+/-S.D.) with normal pulmonary function performed graded cycle ergometry to exhaustion breathing room air, He-O(2) (79% He, 21% O(2)), He-O(2) with imposed expiratory resistance, and He-O(2) with imposed inspiratory resistance. Ventilation (VE), lung mechanics, and PET(CO(2)) were measured during each 1 min increment in work rate and were analyzed by one-way ANOVA for repeated measures at rest, ventilatory threshold (VTh), and peak exercise. In response, VE was increased and PET(CO(2)) was decreased at VTh (P<0.01) and peak exercise (P<0.01) whenever breathing He-O(2). Thus, VE was increased during exercise above VTh with He-O(2) breathing regardless of increases in inspiratory or expiratory external resistance. In conclusion, these data suggest that inspiratory resistive unloading is no more important than expiratory resistive unloading to the increase in VE with He-O(2) breathing during heavy and peak exercise.

Effects of posture on the respiratory mechanics of the chick embryo

In the chicken embryo, pulmonary ventilation and pulmonary gas exchange begin approximately one day before the completion of hatching. We asked to what extent the posture inside the egg, and the presence of the eggshell and membranes, may alter the mechanical behaviour of the respiratory system. The passive mechanical properties of the respiratory system were studied in chicken embryos during the internal pipping phase (rupture of the air cell) or the external pipping phase (hole in the eggshell). Tracheal pressure and changes in lung volume were recorded during mechanical ventilation, first, with the embryo curled up inside the egg, then again after exteriorization from the eggshell. In the internal pippers, respiratory system compliance increased and expiratory resistance decreased after exteriorization, whereas the mean inspiratory impedance did not change. In the external pippers, exteriorization had no significant effects on respiratory compliance, resistance, or impedance, and the values were similar to those of newly hatched chicks. We conclude that, in the chicken embryo, at a time when pulmonary ventilation becomes an important mechanism for gas exchange, the curled up posture inside the egg does not provide any significant mechanical constraint to breathing.

Developmental changes in nitric oxide synthase isoform expression and nitric oxide production in fetal baboon lung.

Nitric oxide (NO), produced by NO synthase (NOS), plays a critical role in multiple processes in the lung during the perinatal period. To better understand the regulation of pulmonary NO production in the developing primate, we determined the cell specificity and developmental changes in NOS isoform expression and action in the lungs of third-trimester fetal baboons. Immunohistochemistry in lungs obtained at 175 days (d) of gestation (term = 185 d) revealed that all three NOS isoforms, neuronal NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS), are primarily expressed in proximal airway epithelium. In proximal lung, there was a marked increase in total NOS enzymatic activity from 125 to 140 d gestation due to elevations in nNOS and eNOS, whereas iNOS expression and activity were minimal. Total NOS activity was constant from 140 to 175 d gestation, and during the latter stage (160-175 d gestation), a dramatic fall in nNOS and eNOS was replaced by a rise in iNOS. Studies done within 1 h of delivery at 125 or 140 d gestation revealed that the principal increase in NOS during the third trimester is associated with an elevation in exhaled NO levels, a decline in expiratory resistance, and greater pulmonary compliance. Thus, there are developmental increases in pulmonary NOS expression and NO production during the early third trimester in the primate that may enhance airway and parenchymal function in the immediate postnatal period.

Pulmonary effects of passive smoking: the Indian experience

There are only a few studies done on pulmonary effects of passive smoking from India, which are summarized in this paper. Several vernacular tobacco products are used in India, bidis (beedis) being the commonest form of these. Bidis contain a higher concentration of nicotine and other tobacco alkaloids compared to the standard cigarettes (e.g., the sum of total nicotine and minor tobacco alkaloids was 37.5 mg in bidi compared to 14–16 mg in Indian or American cigarettes in one study). A large study performed on 9090 adolescent school children demonstrated environmental tobacco smoke (ETS) exposure to be associated with an increased risk of asthma. The odds ratio for being asthmatic in ETS-exposed as compared to ETS-unexposed children was 1.78 (95% CI: 1.33–2.31). Nearly one third of the children in this study reported non-specific respiratory symptoms and the ETS exposure was found to be positively associated with the prevalence of each symptom. Passive smoking was also shown to increase morbidity and to worsen the control of asthma among adults. Another study demonstrated exposure to ETS was a significant trigger for acute exacerbation of asthma. Increased bronchial hyper-responsiveness was also demonstrated among the healthy nonsmoking adult women exposed to ETS. Passive smoking leads to subtle changes in airflow mechanics. In a study among 50 healthy nonsmoking women passively exposed to tobacco smoke and matched for age with 50 unexposed women, forced expiratory volume in first second (FEV1) and peak expiratory flow (PEF) were marginally lower among the passive smokers (mean difference 0.13 L and 0.20 L-1, respectively), but maximal mid expiratory flow (FEF25–75%), airway resistance (Raw) and specific conductance (sGaw) were significantly impaired. An association between passive smoking and lung cancer has also been described. In a study conducted in association with the International Agency for Research on Cancer, the exposure to ETS during childhood was strongly associated with an enhanced incidence of lung cancer (OR = 3.9, 95% CI 1.9–8.2). In conclusions several adverse pulmonary effects of passive smoking, similar to those described from the western and developed countries, have been described from India.