Budesonide added to modified porcine surfactant Curosurf may additionally improve the lung functions in meconium aspiration syndrome

Severe meconium aspiration syndrome (MAS) in newborns is often treated by exogenous surfactant. Because its efficacy is reduced by meconium-induced inflammation, glucocorticoid budesonide was added into surfactant preparation Curosurf to enhance efficacy of the surfactant therapy in experimental model of MAS. Oxygen-ventilated rabbits were intratracheally given meconium (25 mg/ml, 4 ml/kg) to induce respiratory failure. Thirty minutes later, animals were treated by intratracheal budesonide (0.25 mg/kg) or surfactant lung lavage (10 ml/kg, 5 mg phospholipids/ml) repeated twice, followed by undiluted Curosurf (100 mg phospholipids/kg) or by the above mentioned surfactant treatment with the last surfactant dose fortified with budesonide (0.25 mg/kg) or were untreated. Animals were ventilated for additional 5 hours and respiratory parameters were measured regularly. After sacrificing animals, wet-dry lung weight ratio was evaluated and plasma levels of interleukins (IL)-1beta, -6, -8, and TNF-alpha were measured by ELISA method. Efficacy of the given therapies to enhance lung functions and to diminish lung edema formation and inflammation increased from budesonide-only and surfactant-only therapy to surfactant+budesonide therapy. Combined therapy improved gas exchange from 30 min of administration, and showed a longer-lasting effect than surfactant-only therapy. In conclusions, budesonide additionally improved the effects of exogenous surfactant in experimental MAS.

Do the oscillations of cardiovascular parameters persist during voluntary apnea in humans?

The aim of this study was to ascertain the persistence of heart rate and blood pressure oscillations at the onset of voluntary apnea in humans and to assess the dependence of the fluctuations parameters on the chemoreceptor activity. In 24 young subjects (10 males, 14 females, mean age 20.4 years) heart rate (represented by its reciprocal value--RR-intervals), systolic blood pressure (SBP) and diastolic blood pressure (DBP) during controlled breathing (CB) of atmospheric air and oxygen followed by apnea were recorded continuously. The cosine functions were then fitted by nonlinear regression analysis to the heart rate, SBP and DBP oscillations during CB and at the onset of apnea. The parameters of oscillations were different during atmospheric air breathing compared to oxygen breathing. During oxygen breathing there was an increase of the RR-interval oscillations--relative bradycardia and enhanced magnitude of respiratory sinus arythmia. During apnea, the base level of the blood pressure oscillations was higher after breathing of atmospheric air compared to oxygen breathing. At least one cosine-like wave oscillation was present at the onset of apnea in the heart rate, SBP and DBP and the second wave was present in all assessed parameters in at least 70% of recordings. The oscillations in RR-intervals are, to some extent, independent of blood pressure oscillations. No significant gender differences were found either in the duration of breath holding or in the RR and SBP oscillations parameters.

'Respiratory' oscillations of cardiovascular parameters during voluntary apnea

The aim of this study was to ascertain the persistence of heart rate and blood pressure oscillations at the onset of voluntary apnea in humans. In 24 young subjects (10 males, 14 females, mean age 20.4 years) RR intervals, systolic blood pressure (SBP) and diastolic blood pressure (DBP) during controlled breathing (CB) of atmospheric air followed by voluntary apnea on FRC level were recorded continuously. The cosine functions were then fitted by nonlinear regression analysis to heart rate, SBP and DBP oscillations during CB and at the onset of apnea. During apnea, the changes of base of RR intervals indicate primary tachycardic reaction followed by a decrease in heart rate. The base of the blood pressure oscillations was higher (hypertensive reaction) in apnea. At least one cosine-like wave oscillation was present at the onset of apnea in heart rate, SBP and DBP and the second wave was present in all assessed parameters at least in 70% of recordings. There were no significant gender differences neither in the duration of breath holding nor in the RR and SBP oscillations parameters.

[Pulmonary surfactant in the respiratory tract]

Pulmonary surfactant is a surface active material able to reduce surface tension at the alveolar and bronchiolar air-liquid interface. It plays an important role in conductive as well in peripheral airways and that is why surfactant dysfunction is thought to contribute to pathomechanisms of pulmonary diseases with bronchial obstruction. Airway surfactant originates mainly from alveoli and some components (specific proteins SP-A, SP-B and SP-D) are synthetized and secreted also by non-ciliated cells of the airway mucosa. In comparison to alveolar surfactant the bronchiol one has the same composition, with lower amount of surfactant proteins. Surfactant has following functions in airways: stabilisation of small airways, role in mucociliary and non-ciliary transport, immunomodulation, barrier function and antiedematous function. Ability of pulmonary surfactant to influence wall thickness and diameter of airways indicates possible role of its quantitative and/or qualitative changes in the pathogenesis of asthma, chronic obstructive pulmonary disease and others.

Changes in parameters of mechanics of breathing during high-frequency jet ventilation: what is the cause?

In experiments on 51 healthy anaesthetized and paralyzed rabbits the changes in parameters of mechanics of breathing during high frequency jet ventilation (HFJV) were determined and the mechanisms responsible for these changes were investigated. In the first series of experiments with two groups of animals ventilated by HFJV with relative inspiratory time ti=0.5 and ti=0.7 airway resistance (Raw) after 5 h of HFJV in the ti=0.5 group increased from 1.14+/-0.05 to 2.31+/-0.09 kPal(-1) x s (P < or = 0.001), in the ti=0.7 group from 1.22+/-0.04 to 1.78+/-0.08 kPal(-1) x s (P < or = 0.01). Dynamic compliance (Cdyn) decreased in the ti=0.5 group from 0.041+/-0.004 to 0.017+/-0.001 l x kPa(-1) (P < or = 0.01) and in the ti=0.7 group from 0.034+/-0.003 to 0.022+/-0.002 l x kPa(-1) (P < or = 0.01). In the second series of experiments a group of animals was ventilated by HFJV after cervical vagotomy. The deterioration of Raw and Cdyn was significantly reduced in vagotomized rabbits in comparison to the controls without vagotomy. Finally, the study of phospholipid content in bronchoalveolar lavage fluid revealed no significant differences after 5 h of artificial ventilation or spontaneous breathing. These data indicate that HFJV results in changes in the parameters of mechanics of breathing in healthy lungs, which may be attenuated, but not fully eliminated, by bilateral cervical vagotomy. The decrease in Cdyn and increase in Raw are probably not due to changes in the pulmonary surfactant content.

Biophysical and physiological properties of a modified porcine surfactant enriched with surfactant protein A

Surfactant protein A (SP-A), a major protein component of natural pulmonary surfactant, is absent in exogenous surfactants currently used in clinical practice. We investigated the physical and physiological properties of one of these modified natural surfactants (Curosurf) after enrichment with 5% SP-A (SP-A-Curosurf). A pulsating bubble system was used for in vitro assessments and ventilated newborn rabbits for evaluation of in vivo effects. In the presence of various potential inhibitors (meconium 5 mg.mL-1, fibrinogen 5 mg.mL-1, albumin 25 mg.mL-1, or whole serum proteins 25 mg.mL-1), Curosurf at a concentration of 5 mg.mL-1 was inactivated while SP-A-Curosurf and natural porcine surfactant at the same concentration had normal maximum and minimum surface tension. This protective effect of SP-A was calcium dependent. In immature newborn rabbits, the improvement of lung-thorax compliance observed after treatment with 100 mg.kg-1 of SP-A-Curosurf was equivalent to that obtained with 200 mg.kg-1 of Curosurf. Similarly, in near-term newborn rabbits with respiratory failure induced by instillation of fibrinogen via the airways, the increase in compliance after administration of 100 mg.kg-1 of SP-A-Curosurf corresponded to that seen after treatment with 200 mg.kg-1 of Curosurf, whereas Curosurf at a dose of 100 mg.kg-1 had no substantial effect. Our data thus indicate that surfactant protein A increases the resistance of Curosurf to inactivation under in vivo conditions.

Cardiorespiratory parameters and respiratory reflexes in rabbits during hyperthermia

The effects of different body temperature (BT) on the respiratory and cardiovascular parameters and respiratory reflexes were studied in 33 anaesthetized adult rabbits. Hyperthermia elicited panting with mean panting respiratory rate 199 +/- 14 x min-1 in all anaesthetized rabbits. Significant correlations between BT and frequency of breathing (positive), heart rate (positive) or tidal volume (negative) were found. Cooling was accompanied by considerable arterial hypotension. Duration of the Hering-Breuer reflex (HB) was reduced by the rise of BT. Intensity of the reflex (assessed as the ratio of the apnoeic pause to the mean duration of the previous 5 breaths) was unchanged up to the body temperature eliciting panting (41.15 +/- 0.08 degrees C) when it was greatly diminished. Defensive airway reflexes were also changed in hyperthermia. The duration as well as the intensity of nasal apnoea (Kratschmer's reflex) and laryngeal chemoreflex apnoea were decreased. The intensities of respiratory efforts in sneezing and laryngeal coughing were reduced. The expulsive reactions evoked by mechanical stimulation of the larynx were replaced by very shortlasting inhibition of breathing during panting. The results indicate that reflex control of breathing via the Hering-Breuer reflex and the ability to eliminate irritants from the airways are diminished during hyperthermia and panting in anaesthetized rabbits.

Defensive reflexes of the respiratory system in anaesthetized rabbits during high frequency jet ventilation

The defensive airway reflexes during high frequency jet ventilation (HFJV) were studied in anaesthetized, non-vagotomized (n = 16) and vagotomized (n = 11) rabbits. The animals were ventilated by a high frequency jet ventilator. Sneezing and coughing were evoked by mechanical stimulation of the airways. During HFJV spontaneous breathing was inhibited only in the non-vagotomized rabbits. Mechanical stimulation of the airways during HFJV evoked sneezing and coughing, in which the inspiratory component was inhibited. This inhibition occurred not only in defensive reflexes evoked from the regions with increased pressure (trachea, bronchi), but also from the nose. Vagotomy diminished but did not fully eliminate the changes in sneezing accompanying HFJV. The intensity of maximum expiratory efforts was not significantly affected by HFJV in both subgroups.

[The pulmonary surfactant factor. Current knowledge, research trends and use in clinical practice]

Investigation of the composition and significance of individual components of the surfactant indicated that besides phospholipids an important role is played also by surfactant proteins. They aid not only the reduction of the surface tension of the lungs (SP-B, SP-C), but serve also in regulation of surfactant secretion (SP-A) and in local defense and immune responses in the lungs (SP-A and SP-D). Impairments of surfactant were discovered not only in RDS, but also in cases of meconium aspiration, congenital diaphragmatic hernia, pneumonia, pulmonary edema, idiopathic fibrosis of the lungs, alveolar proteinosis, pneumothorax, and bronchial asthma. Therapy by means of exogenous surfactant was proved effective in therapy of RDS. Occasional cases of exogenous surfactant therapy in other pulmonary diseases are auspicious, it is necessary, though, to develop and produce a sufficient amount of exogenous surfactant of high quality and at an acceptable price and to find an optimal manner of surfactant administration into the lungs. A significant perspective is anticipated to utilization of intrapulmonary administration of the exogenous surfactant as a carrier of further active substances for local administration into the lungs. (Ref. 36.)

[Mechanisms of thermoregulation in fetuses and children]

In the submitted review the authors discuss the problem of thermoregulation in foetuses and children. Attention is devoted in particular to the action of thermoregulating nervous and hormonal mechanisms.