Stimulus response latency of cough and expiration reflex depends on breathing in the rabbit.

Expiration reflex and cough may have distinct afferent pathways and/or central integrative mechanisms that may both result in different stimulus response latencies. A newly described method that uses a punctuate mechanical tracheal stimulus to provoke defensive ventilatory reflexes should allow the stimulus response latency to be calculated with reasonable accuracy. The aim of the study was to test whether cough and expiration reflex have different stimulus response latencies. Four hundred and sixty one mechanical tracheal stimulations (50-300 msec) were performed in 21 anesthetized, tracheotomized rabbits. Twenty three percent stimulations (108) provoked a cough reflex and 37% an expiration reflex (171). The individual mean stimulus response latency was computed for each reflex, calculated from stimulus onset to earliest detectable change in ventilatory flow. Cough reflex latency was significantly shorter in inspiration compared to expiration (257±19 msec vs 391±61 msec; p=0.01). In contrast, the expiration reflex latency was significantly shorter in expiration compared to inspiration (210±11 msec vs 329±29 msec, p=0.003). It is concluded that the within breath dependence of the difference in stimulus response latency between cough and expiration reflex is more likely to express different brainstem mechanisms but difference in afferent fibres may not be excluded.

Cough threshold and reactivity to mechanical stimulation of the trachea in the rabbit preliminary observations.

OBJECTIVES: The aim of the study was to characterise mechanically induced cough threshold and reactivity by exposing the trachea to stimuli of variable duration in rabbit. BACKGROUND: Long lasting mechanical stimulation is widely used in experimental protocols studying cough reflex. The cough threshold and reactivity to chemical agents is known to change due to e.g. airway inflammation but similar evidence for mechanical stimulation has not been reported. METHODS: The tracheal provocation was realized in two anesthetized tracheotomized rabbits with a rotating probe actuated by a small electrical motor with mechanical stimulus times (ST) lasting 50, 150, 300 and 600 ms. Cough reflex was evaluated from tidal volume and airflow signals. RESULTS: The incidence of cough reflex (single or multiple) increased from 8% (ST 50 ms) to 84% (ST 600 ms). With the lengthening of stimulus, the rate of multiple responses increases. CONCLUSION: The technique developed here may prove useful to standardize the protocols of mechanical cough in the experimental animal using an approach similar to chemical tussigenic agents. The cough threshold could be defined as minimal ST (STmin) capable to elicit 1 cough and cough reactivity obtained by interpolation as ST that provokes 50 % of cough responses (STso) (Tab. 1, Fig. 3, Ref. 27).

Cerebrospinal fluid outflow and intracranial pressure in hydrocephalic patients with external ventricular drainage.

BACKGROUND AND PURPOSE: The aim of this study was to monitor the 24 h cerebrospinal fluid (CSF) outflow and intracranial pressure (ICP) in hydrocephalic adult patients with external ventricular drainage (EVD). PATIENTS AND METHODS: Twelve patients (5M/7F) aged 30-69 years suffering from acute hydrocephalus requiring EVD were admitted in the neuro-intensive care unit. The CSF collecting bag was continuously weighted using a high-precision scale, the filtered output of which was fed at 1 Hz to a computer and converted to flow (Q'ext(csf)). ICP was also recorded. RESULTS: One patient was excluded because more than 80% of the Q'ext(csf) data were rejected by the system. The mean +/- SD Q'ext(csf) and ICP were respectively 7.5 +/- 3.4 ml/h (range 1.6-12.1 ml/h) and 12.4 +/- 2.7 mmHg. Two patterns of Q'ext(csf) were identified: a continuous profile and a discontinuous one with numerous bursts frequently associated with manoeuvres such as cough or chest physiotherapy. The short-term variations of Q'ext(csf) and ICP were usually unrelated. CONCLUSION: The study stresses the important inter and intra-subject variability of Q'ext(csf) in patients with EVD. The mean Q'ext(csf) is lower than the reference production rate (21 ml/h), raising the question of persistent CSF absorption and/or depressed secretion. The independent changes of Q'ext(csf) and ICP on the short term is likely to be explained by the pressure-volume characteristics of the intracranial space.

In Vivo Documentation of Stimulus Velocity Tuning of Mechanically Induced Reflex Cough.

In order to clear airways and lungs defensive reflexes are provoked rather by the dynamic phase of mechanical stimulus. It is speculated that provocation of defensive response depends not only on stimulus duration but also on stimulus velocity. Fourteen adult rabbits were anaesthetized and tracheotomized. Mechanical stimulus was provoked by a mechanical probe introduced through the tracheotomy and rotated by a small electrical motor using a rotational velocity of 40 rpm/s and 20 rpm/s. Threshold, incidence and intensity of cough reflex (CR) were analyzed for each animal. Statistical comparisons between two velocities were performed using Friedman nonparametric test for repeated measurements. Results are median (25-75 %). The threshold of CR was significantly increased (p=0.005) from 350 ms (300-500 ms) to 550 ms (350-1150 ms) and the incidence of cough reflex was significantly reduced (p=0.002) from 50 % (19 50 %) to 0 % (0-25 %) when the rotational velocity of the mechanical probe was reduced by half. The findings of this study are of interest as they show that protective reflex cough, an important mechanism that allows clearing airways even during sleep or anesthesia, is tuned by mechanical stimulus velocity.

[An experimental study to evaluate mineralization of vertebral bone by computerized tomography (author's transl)]. / Evaluation de la minéralisation osseuse vertébrale par tomographie computérisée. Etude expérimentale.

Computerized tomography ("tomodensitometry") should, in principle, be able to calculate the linear attenuation coefficient of a compact or spongy bone volume. This coefficient is related to the amount of mineralization, enabling the use of the Scanner X to measure the density of the bone. Thirty vertebrae from the vertebral columns of 14 subjects who died after acute infections were examined by C.T. and by standard methods, and then calcinified. The correlation between ashes weight-Houns-field number was positive but only moderate (r = 0.54), and lower than the result obtained (r = 0.84) with standard methods. Errors occur with presently used apparatuses which are related to: polychromatism, too high an energy of the beam, artefacts, and the effects of "partial volume". Futhermore, the mineral concentration by unit of vertebral volume is very low, and large variations must occur for it to be detectable. Finally, considerable errors arise from the intravertebral bone fat. Suggestions are made with the objective of improving the quality of C.T. as a measuring instrument.

Frequency dependence of capnography in anesthetized rabbits.

Aspirative capnography may be of help to diagnose early childhood asthma, but clinical usefulness in young children is limited by the relatively high respiratory rate. This study aimed to characterize the [Formula: see text] time course during airway constriction in 8 anesthetized rabbits, artificially ventilated at 30, 60 and 80breaths/min. Methacholine was inhaled to double the respiratory resistance measured at 8Hz by the forced oscillation technique. The capnogram shape changed in response to both methacholine and ventilatory frequency. Slope of phase II, the peak of first-order time derivative and trough of the second-order time derivative of the [Formula: see text] signal, were significantly attenuated after methacholine compared with baseline at all breathing rates (p<0.02). Moreover, significant correlations between respiratory reactance and resistance were observed with the phase III slope and the angle described by phase II and phase III (p<0.01). It is concluded that capnography may be useful to identify acute airway changes related to bronchoconstriction, even at high breathing frequencies.

Biphasic airway-lung response to anaphylactic shock in Brown Norway rats.

Bronchospasm may be part of the response to systemic anaphylaxis in humans. The anaphylactic shock has been characterized in allergic rats, but little data are available on the concurrent changes in airway-lung mechanics. The aim was to describe the respiratory resistance (Rrs) and reactance (Xrs) response to ovalbumin (OVA) induced systemic anaphylaxis in allergic rats. Thirty five anesthetized and mechanically ventilated Brown Norway rats were randomly allocated to OVA (n=20) or vehicle (n=15) sensitization and provocation. Rrs and Xrs were obtained by the forced oscillation technique at 20 Hz. Allergic rats showed dramatic and reproducible concurrent Rrs peak and Xrs through within 4 min of OVA injection (p<0.0001). Thereafter, Rrs returned to baseline while Xrs remained significantly more negative (p<0.0001). It is concluded that systemic anaphylaxis in allergic rats is associated with severe early acute inhomogeneous bronchoconstriction followed by pulmonary interstitial/small airspace edema. The model may be of interest to assess treatments targeting the associated bronchoconstriction and/or airway vascular leakage.

Estimation of the bronchodilatory effect of deep inhalation after a free run in children.

The bronchomotor effects of a deep inhalation (DI) may provide relevant information about the mechanisms of exercise-induced airway obstruction in children and may be assessed by respiratory conductance (Grs) measured using the forced oscillation technique. The aims of the present study were to assess the effect of DI on Grs after exercise in relationship to the lung function response to exercise. Grs at 12 Hz using a head generator and spirometric data were measured in 62 children suspected of asthma before and 5 min after a 6-min free run. After exercise, Grs was significantly increased by DI in 38 subjects, who also showed larger Grs and forced expiratory volume in one second (FEV1)/forced vital capacity (FVC) responses to exercise than the 24 nonresponders. Stepwise regression indicated significant correlation between the response of Grs to DI and both Grs and FEV1/FVC responses to exercise. The data are consistent with exercise-induced bronchoconstriction being reversed by deep inhalation.