Inflation of antishock trousers increases bronchial response to methacholine in healthy subjects

Role of small airway dysfunction in unexplained exertional dyspnoea

Background

Isolated small airway abnormalities may be demonstrable at rest in patients with normal spirometry; however, the relationship of these abnormalities to exertional symptoms remains uncertain. This study uses an augmented cardiopulmonary exercise test (CPET) to include evaluation of small airway function during and following exercise to unmask abnormalities not evident with standard testing in individuals with dyspnoea and normal spirometry.

Methods

Three groups of subjects were studied: 1) World Trade Center (WTC) dust exposure (n=20); 2) Clinical Referral (n=15); and Control (n=13). Baseline evaluation included respiratory oscillometry. Airway function during an incremental workload CPET was assessed by: 1) tidal flow versus volume curves during exercise to assess for dynamic hyperinflation and expiratory flow limitation; and 2) post-exercise spirometry and oscillometry to evaluate for airway hyperreactivity.

Results

All subjects demonstrated normal baseline forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC). Dyspnoea was reproduced during CPET in WTC and Clinical Referral groups versus Control without abnormality in respiratory pattern and minute ventilation. Tidal flow-volume curves uncovered expiratory flow limitation and/or dynamic hyperinflation with increased prevalence in WTC and Clinical Referral versus Control (55%, 87% versus 15%; p<0.001). Post-exercise oscillometry uncovered small airway hyperreactivity with increased prevalence in WTC and Clinical Referral versus Control (40%, 47% versus 0%, p<0.05).

Conclusions

We uncovered mechanisms for exertional dyspnoea in subject with normal spirometry that was attributable to either small airway dysfunction during exercise and/or small airway hyperreactivity following exercise. The similarity of findings in WTC environmentally exposed and clinically referred cohorts suggests broad relevance for these evaluations.

Interpretation of the "positive" methacholine challenge

BACKGROUND

A methacholine challenge may be used in confirming the diagnosis of asthma, occupational asthma, or reactive airways dysfunction syndrome (RADS) through identification of bronchial hyperreactivity (BHR). While sensitivity of the test in diagnosing clinically significant asthma is excellent, specificity of the test is poor. Since there are many conditions which have been associated with BHR, a positive test must be interpreted cautiously.

METHODS

This paper reviews potential causes of a positive methacholine challenge other than asthma or RADS which have been reported in the medical literature.

RESULTS

Factors which may be associated with a positive methacholine test include test methodology, normal variation of BHR in the general population, and numerous medical conditions.

CONCLUSIONS

In cases of inhalation exposure evaluations, alternative explanations must be considered when determining whether a causal association exists between the exposure and a positive methacholine test result.

Alterations in upper airway cross-sectional area in response to lower body positive pressure in healthy subjects

BACKGROUND

Fluid accumulation in the neck during recumbency might narrow the upper airway (UA) and thereby contribute to its collapse in patients with obstructive sleep apnoea (OSA). It is hypothesised that acute fluid shifts from the legs to the upper body in healthy subjects would increase neck circumference and reduce the cross-sectional area of the UA (UA-XSA).

METHODS

In 27 healthy non-obese subjects of mean (SE) age 39 (3) years and body mass index 23.2 (0.6) kg/m2 studied while supine, leg fluid volume was measured using bioelectrical impedance, neck circumference using a mercury strain gauge and mean UA-XSA between the velum and the glottis using acoustic pharyngometry at end expiration. Measurements were made at baseline after which subjects were randomly assigned to a 5 min time control period or to a 5 min application of lower body positive pressure (LBPP) at 40 mm Hg by anti-shock trousers, separated by a 15 min washout period. Subjects then crossed over to the opposite arm of the study.

RESULTS

Compared with control, application of LBPP significantly reduced leg fluid volume (p<0.001) and increased neck circumference (p<0.001), both at 1 min and 5 min, and reduced UA-XSA after both 1 min (-0.15 cm2; 95% CI -0.23 to -0.09, p<0.001) and 5 min (-0.20 cm2; 95% CI -0.33 to -0.09, p<0.001).

CONCLUSION

In healthy subjects, displacement of fluid from the legs by LBPP causes distension of the neck and narrowing of the UA lumen. Fluid displacement from the lower to the upper body while recumbent may contribute to pharyngeal narrowing and obstruction to airflow in patients with OSA. This may have particular pathological significance in oedematous states such as heart and renal failure.

Simulated obesity-related changes in lung volume increases airway responsiveness in lean, nonasthmatic subjects

STUDY OBJECTIVE

To determine if obesity-related changes in lung volume might contribute to airway reactivity, we investigated the effects of simulated mild obesity-related lung volume reductions on airway responsiveness in lean, nonasthmatic subjects.

PARTICIPANTS AND METHODS

We simulated the lung volume reductions of class 1 obesity in eight lean, nonasthmatic subjects by externally mass loading the chest wall and abdomen, and shifting blood volume into the lung with lower limb compression (LLC). Airway responsiveness was assessed by measuring FEV(1) before and after methacholine challenge tests (1, 2.5, 5, 10, and 25 mg/mL) with the following: (1) no intervention (control); (2) external chest loading (CL); (3) LLC; and (4) CL and LLC (COMB) on separate days. Lung function was measured before and after CL, LLC, and COMB were applied.

RESULTS

The application of CL, LLC, and COMB decreased expiratory reserve volume, functional residual capacity, and total lung capacity compared with baseline. FVC and FEV(1) decreased significantly with CL and COMB, while FEV(1)/FVC did not change compared to baseline. The maximal response to the methacholine challenge increased with CL, LLC, and COMB, with a mean maximal fall of FEV(1) of 9%, 11%, and 18%, respectively, compared to a 6% fall with control.

CONCLUSIONS

We conclude that decreases in lung volume increase airway responsiveness and may account for the increased propensity for increased airway responsiveness in the obese.

Asthma and maternal body mass index are related to pediatric body mass index and obesity: results from the Third National Health and Nutrition Examination Survey

OBJECTIVE

Clinical research has shown an increased prevalence of obesity in children with asthma. This study was designed to assess the relationship between asthma and pediatric body mass index (BMI) in a national database and to examine factors that may modify this relationship.

DESIGN

The cross-sectional relationship between asthma and pediatric BMI and obesity (BMI > or = 85th percentile) was studied. Variables that may influence the relationship between asthma and pediatric BMI, such as race/ethnicity and television watching were included in the model for the total sample. A smaller sample of 3,009 white and African American youth were studied in regression models including maternal BMI.

STUDY POPULATION

A nationally representative cross-sectional sample of 5154 children and adolescents of 6 to 16 years of age from the Third National Health And Nutrition Examination Survey.

RESULTS

In the full sample, asthma and television watching were related to BMI, accounting for 3% of the variance in BMI. When maternal BMI was included in the non-Hispanic sample, television watching, maternal BMI, and the interaction of maternal BMI and asthma were related to youth BMI, accounting for 15% of the variance. The standardized BMI z-score for those youth without asthma and no maternal obesity was 0.06, which increased to 0.33 if the youth had asthma, to 0.70 if the youth did not have asthma but the mother was obese, and to 1.71 if the youth had asthma and the mother was obese. Asthma, television watching, and maternal BMI were independent predictors of youth obesity.

CONCLUSIONS

BMI and prevalence of obesity is higher in youth with asthma. Pediatric BMI, but not obesity, is also related to the interaction of asthma and maternal BMI in white and African American youth. Comorbidity of asthma and obesity may complicate treatment of either condition, and prevention of obesity should be encouraged for asthmatic children.

Expiratory flow limitation as a determinant of orthopnea in acute left heart failure

OBJECTIVES

To assess the contribution of expiratory flow limitation (FL) in orthopnea during acute left heart failure (LHF).

BACKGROUND

Orthopnea is typical of acute LHF, but its mechanisms are not completely understood. In other settings, such as chronic obstructive pulmonary disease, dyspnea correlates best with expiratory FL and can, therefore, be interpreted as, in part, the result of a hyperinflation-related increased load to the inspiratory muscles. As airway obstruction is common in acute LHF, postural FL could contribute to orthopnea.

METHODS

Flow limitation was assessed during quiet breathing by applying a negative pressure at the mouth throughout tidal expiration (negative expiratory pressure [NEP]). Flow limitation was assumed when expiratory flow did not increase during NEP. Twelve patients with acute LHF aged 40-98 years were studied seated and supine and compared with 10 age-matched healthy subjects.

RESULTS

Compared with controls, patients had rapid shallow breathing with slightly increased minute ventilation and mean inspiratory flow. Breathing pattern was not influenced by posture. Flow limitation was observed in four patients when seated and in nine patients when supine. In seven cases, FL was induced or aggravated by the supine position. This coincided with orthopnea in six cases. Only one out of the five patients without orthopnea had posture dependent FL. Control subjects did not exhibit FL in either position.

CONCLUSIONS

Expiratory FL appears to be common in patients with acute LHF, particularly so when orthopnea is present. Its postural aggravation could contribute to LHF-related orthopnea.

Sleep, respiratory physiology, and nocturnal asthma

The nocturnal worsening of asthma is a common feature of this disease that recently has received extensive investigation. Most recent efforts have focused on the role of circadian biorhythms that could promote a nocturnal increase in airway inflammation, leading to a subsequent increase in airflow obstruction and asthma symptoms. However, definitive studies remain lacking. As discussed in this review, there is also substantial evidence that sleep itself may play a direct role in the nocturnal worsening of asthma. Potential mechanisms for such a sleep-related effect could include the supine posture, alterations in sympathetic and parasympathetic "balance," sleep-associated reductions in lung volume, intrapulmonary pooling of blood, and sleep-associated upper airway narrowing, both with and without snoring and obstructive sleep apnea (OSA). These potential contributors to this troublesome phenomenon deserve further consideration when investigating mechanisms of nocturnal asthma.

Sympathetic vascular control of the laryngeo-tracheal, bronchial and pulmonary circulation in the pig: evidence for non-adrenergic mechanisms involving neuropeptide Y

Neuropeptide Y (NPY) and noradrenaline (NA) are co-stored in sympathetic perivascular nerves of the airway mucosa and lung. THe superior laryngeal, bronchial and pulmonary vascular responses were therefore studied in anaesthetized pigs after systemic injections of NPY and NA and after stimulation (2 or 10 Hz, 15 V, 5 ms) of the cranial and caudal portions of hte cervical sympathetic trunk or the stellate ganglia. NPY and NA increased vascular resistance, suggesting vasoconstriction in all three vascular beds. Stimulation of the cervical sympathetic trunk in the cranial direction caused clear-cut vasoconstriction and a decrease in the superficial blood flow in the laryngeal and tracheal circulation supplied by the superior laryngeal artery. This vascular response may be related to release of NA at 2 Hz and possibly also NPY at 10 Hz, since a remaining vasoconstrictor response at 10 Hz was present in reserpinized preganglionically transected pigs when tissue content of NA but not NPY was depleted. The decrease in superficial blood flow in the tracheal mucosa on sympathetic stimulation was absent after reserpine, however. Stimulation of the cervical sympathetic trunk in caudal direction provoked vasoconstriction in the bronchial and pulmonary vascular beds in control pigs. The basal tone of these two vascular beds was not influenced on electrical stimulation after reserpine pretreatment, however, suggesting involvement of NA and possibly aslo NPY, which were both depleted by reserpine. Electrical stimulation of the stellate ganglia also evoked reserpine-sensitive vasoconstriction in both the bronchial and pulmonary vascular beds. The left stellate ganglion dominated the vasomotor response in the bronchial circulation, whereas the right side mainly influenced the pulmonary circulation and the heart.

Influence of posture on expiratory flows and airway responsiveness to methacholine in asthma

This study looked at the effects of posture on the morning/evening expiratory flows and airway responsiveness to methacholine. Fourteen nonsmoking subjects with stable asthma (eight men, six women) were included in the study. Subjects were randomly allocated to spend 4 h in the supine or seated position on separate days, in the morning from 8 to 12 AM and in the evening from 8 to 12 PM. The FEV1 was measured hourly in the assigned position. Before and after each 4-h period, a methacholine inhalation test was done in the sitting position. In the morning study, baseline FEV1 measurements on the supine and seated days were not different. There was no significant difference between the baseline and postsession FEV1 on both days (baseline and postsession FEV1 percent predicted +/- SEM; seated: 83.6 +/- 2.9, 83.8 +/- 3.3; supine: 85.8 +/- 2.8, 85.4 +/- 3.7; n = 13). delta FEV1 (baseline/postsession) was not different between the two sessions. In the evening study, baseline FEV1 measurements on the supine and seated days were similar. FEV1 decreased after both sessions, although this difference reached statistical significance only in the supine position (baseline and postsession FEV1 percent predicted +/- SEM; seated: 90.0 +/- 4.1, 84.9 +/- 4.1, p = 0.08; supine: 90.7 +/- 3.1, 82.9 +/- 4.5, p = 0.02; n = 8). delta FEV1 (baseline/postsession) was not different between the two evening sessions. In the morning, after the seated position, PC20 methacholine was unchanged (mean PC20 [mg/ml]: beginning = 1.00, end = 1.02) while after the supine position it was slightly reduced from a mean of 0.97 to 0.73 mg/ml. This last reduction was mainly observed in the most hyperresponsive subjects and its magnitude was significantly correlated with baseline PC20 (r = 0.637, p = 0.024). The increase in methacholine response (delta PC20) after the supine session was significantly higher than after the seated session. In the evening study, there was a slight reduction in PC20 after both sessions, but this was only significant after the supine position (mean PC20 baseline and postsession [mg/ml]: seated: 0.63, 0.47, p = 0.08; supine: 0.62, 0.44, p = 0.04). No difference was found between delta PC20 of the two sessions. We conclude that the supine position does not have persistent effects on FEV1, but it may increase airway responsiveness in the most hyperreactive subjects.