Biomedical subjects

A G Thin

Publications and source records attributed to A G Thin.

4 recordsLinked to original sources

PubMed2004

Effect of respiratory rate on airway deadspace ventilation during exercise in cystic fibrosis.

Gas exchange during exercise in patients with cystic fibrosis (CF) is characterised by an elevated physiological deadspace to tidal volume ratio. While this has been attributed to alveolar ventilation perfusion mismatch, there are other potential causes of the high proportion of wasted ventilation, including factors relating to the volume and the ventilation of the airway deadspace. CF (n = 6, F = 1, FEV1 26-63% pred) and control (n = 6, F = 2) subjects completed steady-state exercise on a cycle ergometer. Gas exchange was measured breath-by-breath and the volume of the airway deadspace (V(Daw)) determined using the equal areas method. Exercise data were interpolated to a CO2 output of 0.7 l/min. V(Daw) was similar in the two groups both at rest and during exercise. However, the airway deadspace ventilation (V(Daw)) (median (inter-quartile range)), patients, 6.8 (5.1-7.1) l/min; controls, 4.9 (3.5-5.6) l/min, P < 0.05) was significantly greater in the CF group due to a greater respiratory frequency. These results indicate that in CF patients, abnormally increased V(Daw) is an important contributor to the total (physiological) deadspace ventilation. Exercise performance in CF might be enhanced by efforts directed at facilitating an increase in exercise tidal volume and therefore the adoption of a more efficient pattern of breathing.

Adult↗

PubMed2004

Models for estimating the change-point in gas exchange data.

In subjects undertaking an incremental exercise test to exhaustion, the onset of metabolic acidosis can be detected by an increased rate of carbon dioxide output (VCO2) relative to the rate of increase of oxygen uptake (VO2). To locate the change-point (the gas exchange threshold) in such subjects, a two-line regression model relating these two quantities has been used, where the location of the change-point is unknown. We argue that statistical models where the change-point is set on time (rather than VO2) are more appropriate. This is because VO2 is not monotone in time. We use novel statistical methodology of hidden Markov models to demonstrate the existence of the change-point. We use time series models, to estimate the position of the change-point. In these models distributions other than the multivariate normal are considered. For some subjects, the variance of VCO2 increases with time because of increasing ventilation and this is also modelled. The results are illustrated using gas exchange data on three healthy subjects who performed a 20 W min(-1) workrate ramp test.

Acid-Base Equilibrium↗

PubMed2001

Glucocorticoid treatment reduces exhaled nitric oxide in cystic fibrosis patients.

In cystic fibrosis (CF), low concentrations of exhaled nitric oxide (NO) and reduced expression of inducible nitric oxide synthase (iNOS) in airway epithelium have been reported. However, abundant iNOS expression has been found in the subepithelial tissues and elevated concentrations of NO metabolites in breath condensate and sputum. These conflicting results may be explained by increased scavenging of NO by superoxide radicals, resulting in rapid conversion to peroxynitrite, so that only a small proportion of the NO produced in the lung tissue reaches the airway lumen. If iNOS were active in the CF lung, exhaled NO would be further reduced by glucocorticoid treatment. CF patients (n = 13) were recruited to a double-blind, placebo-controlled study with crossover. Treatment comprised prednisolone or placebo for 5 days with a 9 day washout. After each treatment, exhaled NO was measured, spirometry performed and blood collected for measurement of serum nitrogen dioxide/nitrous oxide (NO2/NO3). Ten patients (8 male) completed the study. Following prednisolone treatment (mean +/- SD) exhaled NO concentration (3.1 +/- 1.6 parts per billion (ppb)) was significantly reduced versus placebo treatment (4.9 +/- 4.2 ppb; p<0.05, Wilcoxon signed-rank test). Spirometric indices and serum NO2/NO3 concentration were unchanged. These findings support the hypothesis that glucocorticoids suppress nitric oxide production in cystic fibrosis airways by reducing inducible nitric oxide synthase expression or by inhibiting recruitment of neutrophils, cells which express inducible nitric oxide synthase.

Adult↗

PubMed1999

Lactate determination in exercise testing using an electrochemical analyser: with or without blood lysis?

The practical use of lactate electrochemical analysers in exercise testing has not been adequately examined. Initial studies have reported differences in lactate concentration between that measured spectrophotometrically and that measured electrochemically. The study described here was undertaken to compare, using the statistical technique of Bland and Altman (1986), two widely available methods of measuring lactate using lysed and non-lysed blood samples and the lactate thresholds derived from the measured lactate values using a log-log transform technique. Thirteen normal, healthy young adults (11 male) undertook progressive exercise tests to exhaustion. Arterialised venous blood samples were taken each minute and the lactate concentration therein was measured both spectrophotometrically and electrochemically and either with or without lysis of the blood samples. The lactate concentrations measured in lysed blood using both methods (182 pairs) were in close agreement. The electrochemical values obtained using non-lysed blood were systematically lower than spectrophotometric values (206 pairs), the difference becoming progressively greater at higher lactate concentrations. Results for the lactate threshold comparisons are given as mean difference (limits of agreement with 95% probability). Lactate thresholds (12 pairs) derived from lysed blood lactate concentrations measured spectrophotometrically and electrochemically were not significantly different -30 (240) ml O2 x min(-1). Lactate thresholds (11 pairs) derived from lysed spectrophotometric and non-lysed electrochemical measurements were also not significantly different + 20 (250) ml O2 x min(-1). Thus, despite the difference in the measured lactate concentrations, the derived lactate thresholds are in agreement and, therefore, electrochemical analysers can be used for lactate threshold determination using the log-log transform technique without sample lysis.

Adult↗