The effect of acute exposure to hyperbaric oxygen on respiratory system mechanics in the rat

Cardiorespiratory alterations in patients undergoing hyperbaric oxygen therapy

OBJECTIVE

To evaluate cardiorespiratory alterations due to a single session of hyperbaric oxygen therapy.

METHOD

Randomized study with patients: a control group and hyperbaric oxygen therapy. Evaluations occurred in the beginning, during, and after exposure to pure oxygen above atmosphere for 2 hours. Systemic blood pressure, peripheral oxygen saturation, pulse rate, lung volume and lung capacity, and maximal inspiratory and expiratory pressures were evaluated. Peripheral oxygen saturation, pulse rate, and systemic blood pressure were evaluated during the pressurizing in the first hour. Data were evaluated by means of ANOVA, Mann-Whitney, and independent t-test (p<0.05).

RESULTS

A total of 14 adult patients were evaluated. In the group under therapy (seven subjects), aged: 49.57±14.59 years, there was a decrease in the pulse rate of 16 beats per minute after 35 minutes of therapy (intragroup analysis), and the peripheral oxygen saturation was higher within the same period compared to the control group.

CONCLUSION

The hyperbaric oxygen therapy promotes cardiorespiratory alterations with the increase of the peripheral oxygen saturation and decrease of the pulse rate, without altering blood pressure levels and the strength, volumes, and respiratory capacities.

Environmental Physiology and Diving Medicine

Man's experience and exploration of the underwater environment has been recorded from ancient times and today encompasses large sections of the population for sport enjoyment, recreational and commercial purpose, as well as military strategic goals. Knowledge, respect and maintenance of the underwater world is an essential development for our future and the knowledge acquired over the last few dozen years will change rapidly in the near future with plans to establish secure habitats with specific long-term goals of exploration, maintenance and survival. This summary will illustrate briefly the physiological changes induced by immersion, swimming, breath-hold diving and exploring while using special equipment in the water. Cardiac, circulatory and pulmonary vascular adaptation and the pathophysiology of novel syndromes have been demonstrated, which will allow selection of individual characteristics in order to succeed in various environments. Training and treatment for these new microenvironments will be suggested with description of successful pioneers in this field. This is a summary of the physiology and the present status of pathology and therapy for the field.

The effects of nifedipine on respiratory mechanics investigated by theend-inflation occlusion method in the rat

CONTEXT

Calcium channel blockers may theoretically exhibit relaxing effects not only on vascular smooth muscle but also on airway smooth muscle.

OBJECTIVE

To investigate possible effects of nifedipine on respiratory mechanics in the rat.

METHODS

Respiratory system mechanical parameters were measured by the end-inflation occlusion method in the rat in vivo before and after the intraperitoneal administration of nifedipine.

RESULTS

We found that nifedipine affects respiratory mechanics, inducing a reduction of airway resistance and of respiratory system elastance, probably because of a relaxing action on airway and parenchimal smooth muscle cells.

CONCLUSION

Should these results be further confirmed by human investigations, a possible role of nifedipine in pharmacological respiratory system's diseases treatment may be suggested.

A review of the effects of some endocrinological factors on respiratory mechanics

CONTEXT

Endocrinological factors have been recently described to affect respiratory mechanics.

OBJECTIVE

To review recent literature data, most of all obtained by the end-inflation occlusion method, describing the effects of molecules of endocrinological interest such as endothelin, erythropoietin and renin-angiotensin, on respiratory mechanics parameters.

METHODS

The papers considered in this review were found by inserting in Pubmed/Medline the following indexing terms: hormones, endothelin, erythropoietin, angiotensin and respiratory mechanics.

RESULTS

It was found that the above cited molecules, beside their well known physiological main effects, exhibit influences on respiratory mechanics, most of all on the airflow resistance, which was described to be increased by endothelin and angiotensin, and decreased by erythropoietin.

CONCLUSIONS

A number of molecules of biological interest exhibit unexpected influences on respiratory mechanics. The clinical effects depend on the consequences of modified inspiratory pressure values the respiratory muscles have to perform for a given breathing pattern.

The Effects of Prone with Respect to Supine Position on Stress Relaxation, Respiratory Mechanics, and the Work of Breathing Measured by the End-Inflation Occlusion Method in the Rat

PURPOSE

The working hypothesis is that the prone position with respect to supine may change the geometric configuration of the lungs inside the chest wall, thus their reciprocal mechanical interactions, leading to possible effects on stress relaxation phenomena and respiratory mechanics.

METHOD

The effects of changing body posture from supine to prone on respiratory system mechanics, particularly on stress relaxation, were investigated in the rat by the end-inflation occlusion method.

RESULTS

In the prone with respect to supine position, an increment of the frictional resistance of the airway (from 0.13 ± 0.01 to 0.19 ± 0.02 cm H2O/l sec(-1), p < 0.05) and a decrement of the stress relaxation-linked pressure dissipation (from 0.51 ± 0.05 to 0.45 ± 0.05 cm H2O/l sec(-1), p < 0.01) were found. Respiratory system elastance and total resistive pressure dissipation did not change significantly. Accordingly, a significant increase of the frictional "ohmic" mechanical inspiratory work of breathing and a decrease of the visco-elastic work of inspiration were demonstrated, while no significant changes occurred for the total mechanical work of breathing and its total resistive and elastic components.

CONCLUSION

It is concluded that postural changes affect the visco-elastic characteristics of the respiratory system and the related stress relaxation phenomena by influencing the disposition and relation of the lungs inside the chest wall and their relative geometrical configuration, and the interaction phenomena of the constitutive parenchymal structures, i.e., elastin and collagen fibers. Since the prone position resulted in no serious or disadvantageous respiratory system mechanical derangement, it is suggested it may be usefully applied in nursing or for therapeutic goals.

A REVIEW OF THE EFFECTS OF BODY TEMPERATURE VARIATIONS ON RESPIRATORY MECHANICS: MEASUREMENTS BY THE END-INFLATION OCCLUSION METHOD IN THE RAT

The temperature of body fluids is expected to affect tissues mechanical properties, including respiratory system tissues. This is because of the changes in airway smooth muscle tone and contractile properties, influencing airway frictional resistance to airflow, and because of the temperature effects on the stress–strain relationships of elastin and collagen, which determinates the elastic behavior of the lungs as reflected by their pressure–volume relationship. Alveolar surfactant biological and physical properties have also been shown to be affected by temperature changes, suggesting influences on the respiratory system hysteretic properties.

Experimental works describing the effects of body temperature variations on respiratory mechanics are reviewed, including recent findings dealing with investigations on respiratory mechanics carried out by the end-inflation occlusion method in the rat. This method allows to determine, together with the elastance of the respiratory system, its resistive properties too. In particular, both the ohmic airway resistance due to frictional forces in the airway and the additional visco-elastic resistance exerted because of tissues stress-relaxation may be quantified.

The effects of body temperature variations were assessed, and experimentally induced temperature increments and/or decrements allowed to conclude that respiratory system tissues stiffness, both the ohmic and the stress-relaxation linked resistances, and the hysteretic behavior of the respiratory system, decrease with temperature increments. The mechanisms responsible for these effects are analyzed.

Postnatal hyperoxia exposure differentially affects hepatocytes and liver haemopoietic cells in newborn rats

Premature newborns are frequently exposed to hyperoxic conditions and experimental data indicate modulation of liver metabolism by hyperoxia in the first postnatal period. Conversely, nothing is known about possible modulation of growth factors and signaling molecules involved in other hyperoxic responses and no data are available about the effects of hyperoxia in postnatal liver haematopoiesis. The aim of the study was to analyse the effects of hyperoxia in the liver tissue (hepatocytes and haemopoietic cells) and to investigate possible changes in the expression of Vascular Endothelial Growth Factor (VEGF), Matrix Metalloproteinase 9 (MMP-9), Hypoxia-Inducible Factor-1α (HIF-1α), endothelial Nitric Oxide Synthase (eNOS), and Nuclear Factor-kB (NF-kB). Experimental design of the study involved exposure of newborn rats to room air (controls), 60% O₂ (moderate hyperoxia), or 95% O₂ (severe hyperoxia) for the first two postnatal weeks. Immunohistochemical and Western blot analyses were performed. Severe hyperoxia increased hepatocyte apoptosis and MMP-9 expression and decreased VEGF expression. Reduced content in reticular fibers was found in moderate and severe hyperoxia. Some other changes were specifically produced in hepatocytes by moderate hyperoxia, i.e., upregulation of HIF-1α and downregulation of eNOS and NF-kB. Postnatal severe hyperoxia exposure increased liver haemopoiesis and upregulated the expression of VEGF (both moderate and severe hyperoxia) and eNOS (severe hyperoxia) in haemopoietic cells. In conclusion, our study showed different effects of hyperoxia on hepatocytes and haemopoietic cells and differential involvement of the above factors. The involvement of VEGF and eNOS in the liver haemopoietic response to hyperoxia may be hypothesized.

Hyperbaric air exposure at 2.5 ATA does not affect respiratory mechanics and lung histology in the rat

BACKGROUND

We previously demonstrated that the exposure to hyperbaric hyperoxia increased respiratory system elastance and both the "ohmic" and viscoelastic components of inspiratory resistances, probably because of increased oxygen tension toxic effects. We presently investigated the possible consequences of a single exposure to 2.5-atmospheres absolute air (hyperbarism) lasting 90 min.

METHODS

We used the end-inflation occlusion method on anesthetized rats after about 15 min from previous exposure to hyperbarism. The method allows the measurements of respiratory system elastance and of the ohmic and viscoelastic components of airway resistance, which respectively depend on the Newtonian pressure dissipation due to the ohmic airway resistance to airflow and on the viscoelastic pressure dissipation caused by respiratory system tissue stress relaxation. The expressions of inducible NO synthase (iNOS) and endothelial NO synthase (eNOS) in the lung's tissues were also investigated, together with the histological characteristics of lung tissue. Data were compared with those obtained in control animals and in previously studied animals exposed to hyperoxic hyperbarism.

RESULTS

Unlike with hyperoxic hyperbarism, hyperbarism per se did not change significantly the parameters of respiratory mechanics in the control animals (respiratory system elastance and ohmic and viscoelastic resistances were 2.01 ± 0.17 vs. 1.74 ± 0.08 cm H(2)O/ml, and 0.13 ± 0.02 vs. 0.13 ± 0.03 and 0.425 ± 0.04 vs. 0.33 ± 0.03 cm H(2)O/ml s(-1) in control vs. experimental animals, respectively, none significantly different), nor did it induce evident effects on lung histology. An increment of both iNOS and eNOS expressions was documented instead (0.50 ± 0.05 vs. 0.75 ± 0.07 and 1.04 ± 0.1 and 1.4 ± 0.15, respectively).

CONCLUSION

Our results indicate that, at variance with hyperoxic hyperbarism, the acute exposure to only hyperbarism does not affect either the elastic or the resistive respiratory system properties, or lung histology.