PubMed Health⌕ Search

Biomedical subjects

N Loos

Publications and source records attributed to N Loos.

5 recordsLinked to original sources
PubMed2000

Respiratory and upper airways impedance responses to methacholine inhalation in spontaneously breathing cats.

The upper airways may contribute to the increase in respiratory resistance induced by methacholine (Mch). The aim of this study was to simultaneously assess the Mch response of upper airways and lower respiratory resistances (Rua, Rrs,lo) and reactances (Xua, Xrs,lo), and to test whether the change of total respiratory resistance and reactance after Mch were affected by upper airways mechanisms. Seven cats breathing spontaneously were studied under chloralose, urethane anaesthesia. Forced oscillations were generated at 20 Hz by a loud-speaker connected to the pharyngeal cavity. A pneumotachograph was placed between rostral and caudal extremities of the severed cervical trachea. Pressure drops were measured across the upper airways and across the lower respiratory system. Rua, Xua, Rrs,lo and Xrs,lo were obtained after nebulized normal saline and Mch administered directly through the tracheostomy. The analysis focused on Mch tests showing clear positive upper airways response. Volume and flow dependence of Rrs,lo and Rua were assessed during tidal inspiration using multiple linear regression analysis. After Mch, Rrs,lo increased and became negatively volume dependent, while the increase in Rua was associated with no significant change in volume dependence; Xrs,lo became negative while Xua did not change. The upper airways response to methacholine may thus contribute to the increase in total respiratory resistance but may not account for either its negative volume dependence or the decrease in total resistance. It is surmised that these features more specifically reflect alterations in respiratory mechanics occurring at the level of the intrathoracic airways.

Airway Resistance↗
PubMed2000

[Several aspects of respiratory function testing in children].

Some practical aspects of respiratory function testing (RFT) are reviewed with special interest on applications in preschool children. RFT may be used for diagnostic, management and follow up purposes. Children may benefit from RFT in a variety of pathological situations. Asthma and other obstructive airways diseases certainly represent the most frequent conditions. Vital Capacity and Forced Expiratory Volume in one second (FEV1) may usually be obtained from age 7 on. In smaller children, the forced expiratory manoeuvre is much less successful. Non invasive measurements such as respiratory resistance (Rrs) or specific airway resistance (sRaw) may be used. Rrs is usually measured by the interrupter technique or the forced oscillation technique and sRaw by body plethysmography, not requiring the estimation of thoracic gas volume. Because much variability is introduced by the upper airways, these parameters are less suited than FEV1 to establish the degree of baseline airway obstruction. On the other hand, Rrs and sRaw may quantify reversibility of airway obstruction and/or bronchial hyperresponsiveness. Lung hyperinflation may be identified by the assessment of Functional Residual Capacity (FRC) with a dilution method. More generally lung growth may be followed up in longitudinal studies of FRC even in small children. More work is needed to standardize RFT techniques and indications in the preschool child.

Age Factors↗
PubMed1999

Methacholine-induced volume dependence of respiratory resistance in preschool children.

Enhanced negative volume dependence of airway resistance is associated with bronchoconstriction in tracheostomized paralysed open-chest animals. Significant upper airways responses may be associated with bronchoconstriction and could thereby alter the pattern of volume dependence in spontaneously breathing subjects. The aim of the study was to test whether volume dependence of respiratory resistance (Rrs) could be demonstrated in preschool children undergoing routine methacholine challenge. The volume dependence of respiratory oscillation resistance at 12 and 20 Hz (Rrs,12 and Rrs,20) was examined in eight 4-5.5-yr-old children showing a positive response to methacholine. Multiple linear regression analysis was also used to account for flow dependence during tidal breathing (Rrs,12 or Rrs,20=K1+K2¿V'¿+K3V). Rrs,12 and Rrs,20 yielded similar results. Negative volume dependence was present at baseline and significantly enhanced by methacholine (p<0.01). For instance, the mean+/-SD inspiratory K3 at 20 Hz was 4.1+/-1.3 hPa x s x L(-2) at baseline and -15.0+/-4.3 hPa x s x L(-2) after methacholine, in which case it was also larger on expiration than on inspiration (p<0.05), possibly as a result of upper airway responses. A significant increase in the negative volume dependence of respiratory resistance may thus be shown in preschool children in response to methacholine. The volume dependence (K3) during inspiration may be particularly useful in detecting bronchoconstriction, because it is less likely to be affected by upper airway mechanisms than during expiration.

Aerosols↗
PubMed1998

Mechanisms of ventilatory inhibition by exogenous dopamine in cats.

Intravenous injection of dopamine (DA) has consistently been shown to depress minute ventilation (VE). Whereas at low dosage (</=10 microgram/kg) this effect may be accounted for by inhibition of the carotid sinus nerve chemosensory discharge (CSNCD), other mechanisms appear to be involved with large dosage (>/=50 microgram/kg). The purpose of this study was to elucidate the mechanisms of DA-induced VE depression. The effects of intravenous injection of DA doses ranging from 1 to 200 microgram/kg were studied in 18 anesthetized cats. DA was injected during air and O2 breathing, after alpha-adrenergic blockade by phenoxybenzamine and after baro- and chemodenervation. VE and CSNCD were also simultaneously recorded on four occasions. In contrast to that with use of low-dose DA, VE depression induced by high-dose DA was dissociated from CSNCD, persisted during 100% O2 breathing, and was significantly correlated with the rise in arterial blood pressure. Although blunted, VE depression was still present after complete chemo- and barodenervation but was suppressed by blocking of the concomitant vasoconstriction with phenoxybenzamine. It is concluded that reflexes of circulatory origin contribute to the VE depression induced by large-dose DA, in addition to its effects on arterial chemoreceptors. The contribution of baroreceptor stimulation and peripheral vasoconstriction is discussed.

Action Potentials↗