The repeatability and validity of respiratory resistance measured by the forced oscillation technique.

Measurement of forced expiratory volume in one second (FEV1) is commonly used in bronchial challenge testing in laboratory and epidemiological studies but has certain disadvantages. We have therefore studied the repeatability and validity of a derived measurement of respiratory resistance (Ros) obtained with the Siregnost FD5 impedance oscillometer (Siemens). Repeatability was estimated in 25 non-asthmatics and 28 asthmatics and compared with that of PEFR, FEV1 and specific conductance. PEFR and FEV1 were the most repeatable. Repeatability for measurements with the oscillometer as measured by the intraclass correlation coefficient for a single measurement was 0.75 for non-asthmatics, but was less good for asthmatics (intraclass correlation coefficient 0.56). To assess the validity of respiratory resistance measured during a histamine bronchial challenge test a sample of 20 hospital personnel was studied on four occasions, FEV1 and Ros both being measured twice. Ros changed at lower doses of histamine than FEV1, but the intraclass correlation coefficient for repeatability of change only reached 0.6 at an absolute dose of 3.41 mumol histamine. The estimated provocation dose of histamine producing a 35% fall in Ros was 8.70 mumol (95% range for a single measurement +/- 1.11 doubling doses), that producing a 10% fall in FEV1 was 8.32 mumol (95% range +/- 1.04 doubling doses) and a 20% fall in FEV1 11.48 mumol (95% range +/- 1.11 doubling doses). Measurements obtained with the Siregnost FD5 oscillometer are repeatable. The use of Ros during bronchial challenge testing is valid, but shows insufficient advantage over FEV1 to support its use in epidemiological studies.

Effect of changing dietary sodium on the airway response to histamine.

The airway response to histamine has been shown to be related to the 24 hour urinary excretion of sodium. To assess whether this relation is likely to represent a direct causal association a randomised double blind crossover trial of slow sodium (80 mmol/day) was compared with placebo in 36 subjects having a low sodium diet. The dose of histamine causing a 20% fall in FEV1 (PD20) was 1.51 doubling doses lower when the men were taking sodium than when they were taking placebo (p less than 0.05). On the basis of PD10 values, the difference in men was 1.66 doubling doses of histamine (p less than 0.05). There was no corresponding effect in women. Regressing PD10 against urinary excretion of electrolytes with data from the two occasions during the trial and the measurements made before the trial showed a significant association with sodium excretion after allowance had been made for any effect associated with potassium or creatinine excretion, the latter being a marker of the completeness of the urine collection. Again there was no corresponding effect among women. These findings are compatible with the differences in regional mortality data for England and Wales, which show a relation between asthma mortality and regional per person purchases of table salt for men but not for women.

Lung abscess and empyema.

Forty-eight patients presenting with lung abscess or empyema were studied between 1976 and 1984. The clinical features, diagnostic techniques and management are discussed. Aerobes were cultured from specimens obtained in 37.5 per cent of cases, both aerobes and anaerobes in 54.2 per cent and anaerobes alone in only 8.3 per cent. Bacteroides fragilis was not isolated. Forty-two per cent of patients had previously received antibiotics, but fully sensitive organisms were grown from 17 of 20 specimens from this group. Forty-five per cent of aerobes and 17.8 per cent of anaerobes were resistant to penicillin. There were no specific clinical features which distinguished the patients with a lung abscess from those with an empyema, nor between those with an underlying abnormality and those in whom the infection arose in a previously normal lung. Lung abscesses should be treated medically with intensive physiotherapy and appropriate antibiotics; penicillin can no longer be considered the antibiotic of choice. If the cavity fails to drain satisfactorily, further investigations should be undertaken to exclude a tumour or other underlying abnormality.

The effect of verapamil and inspired CO2 on the bronchoconstriction provoked by hyperventilation in normal humans.

Two groups of eight normal subjects were investigated in separate studies to demonstrate the effects of changes in end-tidal PCO2, and of pretreatment with the calcium antagonist drug verapamil, on bronchoconstriction provoked by voluntary hyperventilation. Total respiratory resistance (Ros) was measured by the forced oscillation technique before and after 90 s voluntary hyperventilation. End-tidal PCO2 during hyperventilation was varied by altering inspired CO2 concentration. When end-tidal PCO2 fell during hyperventilation, there was a rise in Ros. This did not occur if end-tidal PCO2 was controlled at a normal resting level during hyperventilation. Specific conductance (sGaw) was measured before and after 90 s voluntary hyperventilation of air. Subjects were treated with oral verapamil or placebo for 2 1/2 days and the effect of hyperventilation on sGaw was reassessed. Verapamil reduced significantly the fall in sGaw caused by hyperventilation. Placebo had no effect. In normal humans, bronchoconstriction provoked by hyperventilating air at ambient temperature and humidity is mediated by the fall in PCO2, and is also reduced by verapamil.

Familial abnormalities of thyroxine binding proteins: some problems of recognition and interpretation.

A three generation family study was carried out after inappropriate treatment with radioactive iodine of a 50 year old woman with a raised serum total thyroxine concentration and free thyroxine index. Subsequent investigations showed that she and five members of her family had raised thyroxine binding globulin concentrations. Free thyroxine and free triiodothyronine concentrations were normal. Problems encountered in the recognition of this thyroxine binding protein disorder are discussed. Clinicians and clinical biochemists should be aware of these pitfalls and thus avoid further incorrect treatment on the basis of biochemical findings, even though free hormone estimations are now becoming readily available.