PubMed Health⌕ Search

Biomedical subjects

V E Thomas

Publications and source records attributed to V E Thomas.

9 recordsLinked to original sources
PubMed1996

Capsaicin cough sensitivity increases during upper respiratory infection.

The mechanism of cough associated with upper respiratory infection (URI) is poorly understood. This paper reports a study of the role of altered sensitivity of capsaicin-sensitive airway nerves. In a prospective study, baseline (B) capsaicin-induced cough and methacholine-induced airway responsiveness were measured in 103 healthy volunteers. During the following year, 31 subjects reattended for challenge testing during URI (I) and after recovery (R). The log concentration of capsaicin required to elicit two coughs (C2) was significantly lower during infection than recovery but not baseline [median (interquartile range) B = 0.59 (0.28-1.20), I = 0.27 (0-0.89), R = 0.89 (0.28-1.49)]. Log C5 (concentration causing five coughs) was lower during infection than baseline and recovery [B = 1.79 (1.20-2.70), I = 1.49 (0.89-2.08), R = 1.79 (1.20-2.40)]. FEV1 and PC15 methacholine values were unchanged during infection compared to baseline. Subjects with dry cough (n = 14) had lower C5 values during infection than both baseline and recovery, and lower C2 values during infection than recovery; in these subjects, increase in capsaicin sensitivity correlated with cough severity score. Subjects with productive cough or no cough showed no consistent changes during infection. Twenty-six control subjects who reattended without URI showed no change in capsaicin sensitivity. Upper respiratory infection may cause cough as a result of increased sensitivity of capsaicin-sensitive afferent airway nerves without affecting airway calibre or responsiveness.

Administration, Inhalation↗
PubMed1994

Effect of clonidine on induced cough and bronchoconstriction in guinea pigs and healthy humans.

We examined the effects of the alpha 2-receptor agonist clonidine, administered orally and by inhalation, on citric acid- and capsaicin-induced reflexes in guinea pigs and healthy human subjects. In groups (n = 8-10) of conscious guinea pigs, oral clonidine (10 and 100 micrograms/kg) was without effects, whereas inhaled clonidine (10-1,000 microM) caused a concentration-dependent inhibition of citric acid-induced cough (coughs during 3 min: control, 6.5 +/- 0.9; 1,000 microM clonidine, 1.7 +/- 1.0; P < 0.05) and reflex bronchoconstriction (time to onset of bronchoconstriction: control, 191 +/- 24 s; 1,000 microM clonidine, 317 +/- 33 s; P < 0.05). The inhibitory effect of inhaled clonidine on both reflexes was completely reversed by pretreatment with yohimbine but not with prazosin. In 12 healthy human volunteers, oral clonidine (150 mg) caused a significant fall in supine and erect systolic blood pressure and a significant increase in drowsiness as measured on a visual analogue scale 1 and 2 h after administration. Despite these effects, oral clonidine had no effect on capsaicin-induced cough or reflex bronchoconstriction in humans. In contrast to the effects in guinea pigs, inhaled clonidine (281 microM) had no effect on capsaicin-induced cough or reflex bronchoconstriction in humans. These data suggest that peripheral alpha 2-receptors exert an inhibitory effect on sensory neurotransmission in the guinea pig but not in the healthy human airway, indicating an important difference between the two species.

Administration, Inhalation↗
PubMed1994

Capsaicin cough sensitivity decreases with successful treatment of chronic cough.

To assess the role of enhanced cough sensitivity in the pathogenesis of cough, we measured cough severity on a visual analogue scale (VAS) and capsaicin cough sensitivity (the concentration required to elicit two [C2] and five [C5] coughs) in 87 consecutive patients referred with chronic cough. Measurements were repeated after complete investigation and treatment, when patients were entered into one of four study groups: (1) treatment success (primary cause of cough successfully treated with elimination of the cough, n = 48); (2) primary treatment failure (treatment of potential primary cause of cough unsuccessful, n = 12); (3) cough treatment failure subgroup A (potential primary cause of cough identified and successfully treated but no improvement in cough, n = 8); and (4) cough treatment failure subgroup B (no potential primary cause of cough identified, n = 19). All patients in groups 3 and 4 were nonsmokers, had normal chest radiography and negative histamine challenge test, and failed to respond to intensive empirical treatment for rhinitis and gastroesophageal reflux. The VAS cough severity was lower and log C2 and C5 higher after treatment compared with initial values in the treatment success group but not in the other three groups. Enhanced sensitivity of airway nerves that mediate cough is important in the pathogenesis of nonproductive cough, and successful treatment is associated with a reduction in cough sensitivity. While enhanced sensitivity of airway nerves is usually present in patients with identifiable causes of chronic nonproductive cough, it is also found in other patients in whom the cause of cough is unknown.

Adult↗
PubMed1993

Effect of topical beclomethasone on histamine-induced increases in nasal airflow resistance and secretion in perennial rhinitis.

The effects of topical beclomethasone dipropionate on changes in nasal resistance and secretion induced by topical histamine were studied in eight patients with perennial rhinitis. Patients were studied at enrollment, after 3 weeks of beclomethasone (100 micrograms spray to each nasal cavity twice daily), and after 3 weeks of placebo (saline) treatment administered in a double-blind cross-over trial. Nasal airflow resistance (Rnaw) and total protein, albumin, lysozyme and glycoconjugate secretion in nasal lavage fluids were measured after topical application of histamine to the nasal mucosa. Resistance measurements and secretory parameters were similar for the initial study and after placebo treatment. In those studies, histamine (1 and 10 mg) increased both nasal resistance and secretion of total protein, albumin and glycoconjugates. After beclomethasone treatment the rise in respiratory resistance in response to histamine was significantly attenuated (delta Rnaw, +11.57 cm H2O/l/s with placebo, +5.80 with beclomethasone, P < 0.05). Beclomethasone had no effect on histamine-induced secretion. Because nasal resistance is determined mainly by vascular processes, beclomethasone treatment appears to have a prominent action on the vascular bed to reduce mediator-induced vasodilatation in perennial rhinitis.

Administration, Intranasal↗
PubMed1992

Ipratropium bromide delivered orally by metered dose inhaler does not decrease salivary flow in normal subjects.

A randomised placebo-controlled cross-over group study was conducted to ascertain the occurrence and duration of xerostomia induced by 240 micrograms (high dose) and 120 micrograms (low dose) of ipratropium bromide (IPB) delivered by metered dose inhaler (MDI) into the mouth in normal subjects. Salivary output was higher with both doses of IPB than with placebo though the differences were not statistically significant. IPB was less palatable than placebo as indicated on visual analogue scale (VAS) and the taste of the drug may have caused a reflex increase in salivary output from the major salivary glands which would have masked any possible local effect of the drug on the smaller submucosal glands of the mouth. IPB delivered into the oral cavity by MDI is therefore not a suitable treatment for hypersalivation.

Administration, Inhalation↗
PubMed1975

Comparison of three methods for determining oxygen saturation in arterial blood.

Oxygen saturation was determined by direct measurement with the Van Slyke method, an oximeter, and by indirect measurement with a pO2 electrode with conversion of oxygen tension to oxygen saturation. All three methods correlated well when the oxygen saturation was above 94 per cent. Below this value both the oximeter measurement and the saturation value calculated from the oxygen tension significantly overestimated the oxygen saturation as determined by the Van Slyke method. It appears from our data that when the saturation is less than 94 per cent, the absolute values for O2 saturation continue to be accurately determined with a Van Slyke, but the other two methods in this range are, at best, only useful in detecting gross changes in oxygen saturation.

Electrodes↗