A rapid and sensitive method for the determination of the amount of theophylline in blood spots.

Monitoring of drugs (such as theophylline) with a narrow therapeutic window could be simplified if patients were able to submit blood spots for analysis. This could reduce clinic attendance for venous blood sampling and save staff time. A rapid sensitive method utilizing liquid chromatography-mass spectrometry has been developed to determine the amount of theophylline in blood spots. The lowest level of theophylline analysed in a blood spot was 15 ng extracted into 250 microL and this was still considerably above the limit of quantification (3 ng in 250 microL). The levels of theophylline in blood spots correlated well with theophylline levels in plasma samples obtained from the same patients. The assay might be of use in therapeutic drug monitoring of theophylline and blood spot sampling could be applied to other drugs where therapeutic monitoring is required.

The effect of acute alteration in oxygen tension on the bronchodilator response to salbutamol in vitro and in vivo in man.

These studies examine the effect of acute hypoxia on airway smooth muscle relaxation in response to salbutamol in vitro in human isolated bronchi from non-asthmatics and in vivo in-patients with asthma. Isometric responses were measured from rings of human bronchi pre-constricted with methacholine under oxygen tensions of 95% (hyperoxia), 20% (normoxia) and 4% (hypoxia). Once contractions had plateaued, concentration - response curves were conducted to salbutamol (10(-9)-10(-4)m). Twelve stable asthmatic patients were studied in a randomised double blind fashion. On two study days following baseline measurements, patients were randomised to receive either oxygen (FiO(2)1.0) or a hypoxic gas mixture (FiO(2)0.15) followed by three incremental doses of nebulised salbutamol at 15 min intervals. On two further study days nebulised saline was administered instead of salbutamol. In isolated bronchi, salbutamol-induced relaxations were significantly (P< 0.001) greater in hyperoxia and normoxia (P< 0.01) when compared to hypoxia. Among patients with asthma no significant differences were found in the mean maximum % change in forced expiratory volume (FEV(1)) from baseline between the hypoxic and hyperoxic study days on which nebulised salbutamol was administered. We conclude that acute hypoxia attenuates airway smooth muscle relaxation in response to salbutamol in vitro but has no effect on salbutamol-induced bronchodilation in in-patients with asthma.

Early discharge for patients with exacerbations of chronic obstructive pulmonary disease: a randomized controlled trial.

BACKGROUND: We have previously reported the use of a hospital based respiratory nurse service (Acute Respiratory Assessment Service, ARAS) to support home treatment of patients with exacerbations of chronic obstructive pulmonary disease (COPD). A controlled trial was undertaken to compare early discharge with home treatment supported by respiratory nurses with conventional hospital management of patients admitted with exacerbations of COPD. METHODS: Patients with COPD admitted as emergencies were identified the next working day. They were eligible for inclusion in the study if the differential diagnosis included an exacerbation of COPD, but were excluded if other medical conditions or acidotic respiratory failure required inpatient investigation or management. Of 360 patients reviewed, 209 were being assessed for other active medical problems and were excluded, 33 potential participants were already involved in research studies and so were ineligible, and 37 did not wish to participate in the study. Eighty one patients were randomised to receive conventional inpatient care (n=40) or to planned early discharge the next working day (n=41). Those discharged early continued treatment at home under the supervision of specialist respiratory nurses. Outcome measures were readmission, additional hospital days, and deaths within 60 days of initial admission. Process measures included number of visits, duration of follow up by the respiratory nurse, and additional treatment provided to support early discharge. RESULTS: On an intention to treat basis, a policy of early discharge reduced inpatient stay from a mean of 6.1 (range 1-13) days with conventional management to 3.2 (1-16) days with an early discharge policy. Twelve patients (30% conventional management, 29.3% early discharge) were readmitted in each group giving a mean difference in readmission of 0.7% (95% CI of the difference -19.2 to 20.6). In the conventional management group readmitted patients spent a mean of 8.75 additional days in hospital compared with 7.83 days in the early discharge group, giving a mean difference of 0.92 days (95% CI of the difference -6.5 to 8.3). There were two deaths (5%) in the conventional management group and one (2.4%) in the early discharge group, a mean difference of 2.6% (95% CI of the difference -5.7 to 10.8). CONCLUSIONS: Patients with acute exacerbations of COPD uncomplicated by acidotic respiratory failure or other medical problems can be discharged home earlier than is current practice with support by visiting respiratory nurses. No difference was found in the subsequent need for readmission.

Endothelin-1 levels in induced sputum samples from asthmatic and normal subjects.

BACKGROUND: Endothelin-1 (ET-1) is a potent bronchoconstrictor which may have a role in the pathogenesis of asthma. The levels of ET-1 in saliva, induced sputum, and plasma from asthmatic and non-asthmatic subjects were compared. METHODS: Sputum induction was performed on 28 asthmatic subjects and nine normal volunteers. ET-1 levels were measured in plasma, saliva, and sputum samples and reversed phase high performance liquid chromatography (RP-HPLC) was performed on saliva and sputum samples. RESULTS: ET-1 was present in the following order of concentration in both normal and asthmatic subjects: saliva > sputum > plasma (saliva, median 30.1 and 23.9 pg/ ml, respectively; sputum, median 15.5 and 11.2 pg/ml; plasma, median 3.1 and 3.6 pg/ ml). There were no differences between asthmatic and normal subjects in the levels of ET-1 in each fluid. The levels of ET-1 in asthmatic subjects were not influenced by whether or not they were taking inhaled steroids. RP-HPLC of sputum and saliva confirmed the presence of ET-1 in these fluids. CONCLUSIONS: Levels of ET-1 can be measured in saliva and sputum obtained by sputum induction in asthmatic and healthy subjects and, although no difference was found in basal levels of ET-1 in sputum, saliva and plasma between normal subjects and asthmatics without bronchoconstriction, it is apparent that ET-1 is produced or released locally within the respiratory tract in concentrations higher than those in plasma.

Effect of acute alterations in inspired oxygen tension on methacholine induced bronchoconstriction in patients with asthma.

BACKGROUND: Recent in vitro and in vivo studies in animals have suggested that ambient oxygen tension may influence airway responsiveness to bronchoconstrictor stimuli. These observations may have relevance to the management of acute exacerbations of asthma. The present studies were designed to examine the influence of inspired oxygen tension (Fio2 1.0, 0.21, 0.15) on methacholine-induced broncho-constriction in patients with asthma. METHODS: In a dual study two groups of asthmatic patients performed methacholine inhalation challenges breathing either air (Fio2 0.21) or a hypoxic gas mixture (Fio2 0.15) in study 1 and air (Fio2 0.21) or hyperoxia (Fio2 1.0) in study 2. The gases were administered through a closed breathing circuit in a randomised double blind fashion. The PC20 values (dose of methacholine causing a 20% fall in forced expiratory volume in one second (FEV1) were calculated after each methacholine challenge by linear interpolation from the logarithmic dose response curve. Plasma catecholamine levels were measured before and after methacholine challenges as well as heart rate, oxygen saturation, and percentage end tidal carbon dioxide levels. RESULTS: The geometric mean PC20 value for methacholine was significantly lower on the hypoxic study day than on the normoxic day in study 1 (mean difference in PC20 values 2.88 mg/ml (95% CI 1.4 to 5.3); p < 0.05), but there was no significant difference in the geometric mean PC20 value for methacholine between the hyperoxic and normoxic study days in study 2 (mean difference in PC20 values 1.45 mg/ ml (95% CI 0.83 to 2.51)). CONCLUSIONS: Acute hypoxia potentiates methacholine induced bronchoconstriction and acute hyperoxia has no effect in mild to moderate patients with stable asthma.

Investigations on the renin-angiotensin system in acute severe asthma.

The renin-angiotensin system is activated in acute severe asthma. The precise mechanism of activation is at present unknown, but may involve, beta2-agonists, catecholamines or proteases released in airway inflammation. This study aims to identify potential factors involved in the activation of the renin-angiotensin system in acute asthma. Forty asthmatics with severe exacerbations of asthma, assessed by measurement of peak expiratory flow rate (mean (SD) 35 (18)% predicted), oxygen saturation (94 (4)%) and pulse rate (108 (16) beats x min(-1)) were recruited. Nineteen (48%) asthmatics had elevated plasma angiotensin II levels (median (interquartile range) 10.9 (4.3-23.5) pg x mL(-1) (normal range 3-12 pg x mL(-1))) and 10 (25%) had elevated plasma renin concentration (22.0 (10.0-50.0) microU x mL(-1) (normal range 9-50 microU x mL(-1))). Plasma renin and angiotensin II correlated strongly, implying renin-dependent angiotensin II formation. No correlation was found between plasma salbutamol, adrenaline, nor-adrenaline, endothelin-1, histamine, eosinophilic cationic protein, serum angio-tensin-converting enzyme (ACE) activity, total immunoglobulin E (IgE), urea and electrolytes, indicators of the severity of the attack, atopic status, blood pressure and renin or angiotensin II levels. We conclude that although a subpopulation of asthmatics appear to have raised renin and angiotensin II during attacks of acute, severe asthma, the mechanism of activation of the renin-angiotensin system remains unclear.

Effect of angiotensin II on histamine-induced bronchoconstriction in the human airway both in vitro and in vivo.

The renin-angiotensin system is activated in acute severe asthma. Angiotensin II causes bronchoconstriction in mild asthmatics and potentiates methacholine-evoked bronchoconstriction both in vitro and in vivo. To evaluate the effect of angiotensin II on histamine-induced bronchoconstriction, human bronchial rings (n = 6) were obtained from lung tissue at thoracotomy and were prepared in organ baths. Contractions were measured isometrically and cumulative concentration-response curves obtained to angiotensin II alone and to histamine in the presence and absence of threshold concentrations of angiotensin II. Eight asthmatic patients with bronchial hyper-reactivity to histamine were challenged with histamine during intravenous infusion of placebo, angiotensin II 1 ng kg-1 min-1 and angiotensin 2 ng kg-1 min-1 administered in a randomized, double-blind fashion, FEV1 was measured prior to, during the infusion and during the histamine challenge. Angiotensin II (3 x 10(-7)M and 10(-6)M) alone evoked small contractions (< 0.25 g) of human bronchi in vitro, but pre-incubation with threshold concentrations of angiotensin II (10(-7)M, 3 x 10(-7)M and 10(-6)M) had no effect on histamine-evoked contractions. In asthmatic patients, angiotensin II alone had no effect on baseline FEV1 at the low levels infused and did not affect the response to nebulized histamine as measured by the PC20 histamine: Geometric mean (range) PC20 histamine (mg ml-1) screening day 3.58 (1.26-7.75), placebo infusion 2.67 (0.89-9.57), angiotensin II 1 ng kg-1 min-1 2.45 (0.42-6.97) and angiotensin II 2 ng kg-1 3.09 (0.8-10.78). It is concluded that, in contrast to its potentiating effect on methacholine-induced bronchoconstriction, angiotensin II has no effect on histamine-evoked bronchoconstriction in human bronchi in vitro or in vivo.

Effect of acute hyperoxia on the bronchodilator response to salbutamol in stable asthmatic patients.

BACKGROUND: Recent animal studies have suggested that changes in oxygen tension may alter airway responses to bronchoconstrictor and bronchodilator stimuli. These effects may have relevance to the management of acute exacerbations of asthma but have not been well studied in man. This study was designed therefore to examine the effect of acute hyperoxia (Fio2 1.0) on the bronchodilator response to salbutamol in stable asthmatic patients. METHODS: Twelve stable adult asthmatic patients (three women) were studied using a randomised double blind placebo controlled crossover design. On two study days following baseline measurements patients breathed either air (Fio2 0.21) or oxygen (Fio2 1.0) for 10 minutes alone and then in combination with three incremental doses of nebulised salbutamol administered at 15 minute intervals. The same protocol was employed on two further study days using nebulised saline instead of salbutamol. RESULTS: The mean absolute change in forced expiratory volume in one second (FEV1) from baseline after salbutamol was similar on the normoxic and hyperoxic study days but significantly greater than the study days on which nebulised saline was administered. CONCLUSION: Acute hyperoxi does not potentiate the immediate bronchodilator response to salbutamol in stable asthmatic patients.

Vasoconstrictor effects of angiotensin II on the pulmonary vascular bed.

The systemic pressor effects of angiotensin II (ANGII) are well described, whereas relatively little is known regarding its effects on the pulmonary circulation in humans. Doppler echocardiographic measurements were performed in eight normal volunteers after a 30-min control infusion (baseline), after sequential 30 min stepwise infusions of ANGII (2, 4, and 6 ng/kg/min), and again 30 min after stopping ANGII therapy. There were significant dose-related increases in mean pulmonary arterial pressure and total pulmonary vascular resistance, with values returning to baseline after stopping ANGII therapy. However, the increase in vascular resistance was proportionately greater for the pulmonary compared with systemic vascular bed, and the difference was significant at all doses of ANGII. Thus, the pulmonary vasculature exhibited greater sensitivity to the vasoconstrictor effects of ANGII in comparison with the systemic vasculature.

Comparative effects of angiotensin II on Doppler parameters of left and right heart systolic and diastolic blood flow.

1. The purpose of the study was to investigate the effects of angiotensin II on Doppler parameters of right ventricular systolic and diastolic blood flow, and to compare these with effects on the left heart, in normal subjects. 2. Pulsed-wave Doppler measurements were made in eight normal volunteers: after a 30 min control i.v. infusion of dextrose, after 30 min stepwise infusions of angiotensin II (2, 4 and 6 ng kg-1 min-1), and finally 30 min after stopping the 6 ng kg-1 min-1 dose of angiotensin II. Aortic (Ao) and pulmonary (Po) systolic ejection parameters, as well as mitral (Mi) and tricuspid (Tc) diastolic filling parameters were measured. 3. Ao and Po maximal velocity were both significantly reduced by angiotensin II, whereas there were significant opposite effects on Ao (reduced) and Po (increased) mean acceleration. There was a dose-related fall in Po acceleration time with angiotensin II, whilst Ao acceleration time remained unchanged. 4. Mi and Tc early diastolic filling velocities were not significantly altered by angiotensin II compared with baseline, although there was a significant rebound increase in both Mi and Tc early filling after cessation of angiotensin II infusion. Mi and Tc pressure half-times were not significantly changed. 5. In conclusion, angiotensin II produced changes in Po ejection parameters consistent with a pressor response in the pulmonary vascular bed. Neither right nor left ventricular diastolic filling were directly affected by angiotensin II. The differential effects of angiotensin II on Po and Ao ejection parameters might be due to inherent differences in basal pulmonary and systemic vascular tone.