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Biomedical subjects

M G Clement

Publications and source records attributed to M G Clement.

At least 37 records · Page 2Linked to original sources
PubMed1994

In pigs, inhaled nitric oxide (NO) counterbalances PAF-induced pulmonary hypertension.

In 6 anesthetized mechanically ventilated pigs we have studied the effects of inhalation of 80 ppm of nitric oxide (NO) before and after platelet-activating factor (PAF) administration (50 ng/kg iv). Our results show that NO inhalation causes a decrease in pulmonary arterial pressure and in heart rate without affecting other circulatory parameters. PAF administration causes a pulmonary hypertension and a prompt and brief decrease in systemic pressure. Inhalation of NO reduces the pulmonary hypertension, without completely reversing PAF-dependent vasoconstriction. PAF administration to pigs pretreated with indomethacin produces a lesser increase in pulmonary vascular pressure. In this case, NO inhalation can restore to baseline values. Pretreatment of 3 of the 6 pigs with NG-nitro-L-arginine-methyl-ester did not prevent the prompt and brief PAF-induced systemic hypotension. In conclusion, our results show that NO reduces basal pulmonary vascular tone, acts as a pulmonary vasodilator on PAF-preconstricted vessels and is not involved in the brief systemic hypotension consequent to PAF administration.

Administration, Inhalation↗
PubMed1992

PAF and the role of the vagus nerve in the breathing pattern of the pig.

In 14 anesthetized, spontaneously breathing pigs we examined the changes in breathing pattern, in respiratory mechanics and in systemic and pulmonary vascular parameters after i.v. PAF administration. In another 3 pigs, the effects of PAF were also examined after bilateral vagotomy. In intact pigs, PAF induces apnea, bronchoconstriction, pulmonary hypertension and systemic hypotension. Our results also show that administration of PAF alters the phasic vagal activity, modifying the slope of VT vs TI and TE vs TI relationships and the TI0/TI ratio. These effects and apnea are vagus-dependent. The central excitatory timing effect of PAF on inspiratory duration (TI0) was correlated with a decrease in passive compliance but not with active compliance. We postulate that the activation by vagal input strengthens the mechanisms that counteract the bronchoconstrictor effect of PAF.

Animals↗
PubMed1992

Inspiratory timing regulation of PGF2 alpha in newborn pigs.

In intact and vagotomized anesthetized, spontaneously breathing piglets, we investigated the regulation of inspiratory timing evoked by i.v. administration of prostaglandin (PG) F2 alpha. The inspiratory time was evaluated from the flow trace as an index of mechanical inspiratory time (Ti) and from costal and crural diaphragmatic EMG (TiEMG) as an index of neural inspiratory time. Our results under control conditions showed that TiEMG was shorter than Ti. Vagotomy abolished the difference, inducing a change in the power spectrum without modifying the centroid frequency (Cf). PGF2 alpha lengthened TiEMG, causing a postinspiratory diaphragmatic discharge to appear, while mechanical inspiratory time decreased significantly. Postvagotomy i.v. administration of PGF2 alpha did not cause any significant changes in inspiratory time and did not evoke the postinspiratory discharge. The i.v. administration of PGF2 alpha before and after vagotomy did not change the centroid frequency in spite of recruitment of new motor units synchronized with those that are active under control conditions.

Animals↗
PubMed1991

Effects of PGF2 alpha on the EMG of costal and crural parts of the diaphragm of the newborn pig.

We investigated the effects of PGF2 alpha on the breathing patterns and electric activity of costal and crural parts of the diaphragm in 9 anesthetized newborn pigs. The change in diaphragmatic tension was evaluated as the change in transdiaphragmatic pressure. Because PGF2 alpha induces bronchoconstriction and an increase in respiratory resistances, the changes induced by prostaglandin were evaluated as differences between bronchoconstriction after PGF2 alpha and resistive load obtained by applying gradual occlusion to the inspiratory line of the breathing circuit. Our results show that PGF2 alpha decreased respiratory frequency with lengthening of expiratory time, while the resistive load increased both respiratory phases. The changes in breathing pattern were associated with different electrical activities of the diaphragm. While resistive load did not significantly change the EMG power spectrum, PGF2 alpha recruited new motor units. Furthermore, resistive load induced synchronization of the inspiratory time discharge of the costal and crural parts of the diaphragm, while after PGF2 alpha infusion there was an early inspiratory discharge of the crural part.

Animals↗
PubMed1991

The effect of level of contraction on the electromyographic power spectrum of the diaphragm in pigs.

We investigated the relationship between the frequency components of myoelectric power spectra of the diaphragm and the level of diaphragmatic contraction in seven anaesthetized spontaneously breathing pigs. Electromyographic activity of the costal and crural portions of the diaphragm were recorded with fish-hook electrodes and the frequency-power spectra during inspiration were computed and expressed in terms of centroid frequency (fc). Diaphragmatic force was indirectly assessed as transdiaphragmatic pressure (Pdi) which was measured with balloon-catheter systems placed in the abdomen and oesophagus. The relationships between Pdi and costal and crural fc were assessed during brief (2 min) and incremental increases in diaphragmatic contraction, achieved by gradual occlusion of the inspiratory line of the breathing circuit. When Pdi was increased to 128, 191, 287 and 421% of the value measured during unobstructed breathing, costal and crural fc rose significantly in all animals because of an increase in the power of high-frequency components and a decline in the power of low-frequency components. Both costal and crural fc returned to control values within 5 min of the release of inspiratory occlusion. Our results indicate that the level of contraction is an important determinant of the diaphragmatic myoelectric power spectrum and should be taken into consideration when using power spectral analysis to diagnose diaphragmatic mechanical failure.

Animals↗
PubMed1990

PGF2 alpha and breathing pattern in newborn pigs.

The effect of PGF2 alpha has been evaluated in 11 unanaesthetized unrestrained piglets and in 3 anaesthetized piglets (2-3 days old) using a barometric-plethysmographic technique. PGF2 alpha (mg 0.25/pig) was administered as aerosol for 5 min. In 3 of the unanaesthetized newborn pigs the effect of PGF2 alpha aerosol has been evaluated after indomethacin (mg 1/Kg i.v.). The vagal dependent activity of the prostaglandin was also evaluated after atropine (mg 0.08/Kg i.m.). Our results show that PGF2 alpha in newborn pigs causes hypoventilation due to a decrease in respiratory rate and to a lengthening in TE. The changes in TE are due to an increase in the incidence and duration of apneic events characterizing the respiratory activity at birth. After indomethacin PGF2 alpha does not change the breathing pattern. Atropine only partially reduces the effects of PGF2 alpha while, after anaesthesia, prostaglandin does not change the breathing pattern. Consequently our results show that PGF2 alpha in newborn animals similar to other prostaglandins acts as a depressant of respiratory activity.

Aerosols↗
PubMed1987

Lung reflexes affecting the larynx in the pig, and the effect of pulmonary microembolism.

Laryngeal airflow resistance was measured in anaesthetized pigs during stimulation of lung vagal reflexes by injection of phenylbiguanide and of capsaicin, before and during pulmonary microembolism due to intravenous injection of hardened red blood cells; the microembolism caused pulmonary hypertension. The Breuer-Hering reflex was also assessed before and after pulmonary microembolism. Phenylbiguanide and capsaicin caused apnoea followed by rapid shallow breathing, hypertension, bradycardia and laryngeal constriction in inspiration and expiration. Most of these effects were abolished by bilateral cervical vagotomy. Pulmonary microembolism caused only small changes in breathing pattern, mainly a decrease in inspiratory time. After microembolism the Breuer-Hering reflex was enhanced, and injections of phenylbiguanide and capsaicin caused longer apnoeas by a vagal reflex. The changes in pattern of breathing and in lung reflexes after lung microembolism and during the associated pulmonary hypertension are consistent with an enhancement of pulmonary stretch receptor activity in this condition, but do not indicate any important role for C fibre reflexes.

Animals↗
PubMed1986

Effects of vagotomy on respiratory mechanics in newborn and adult pigs.

We have examined breathing patterns and respiratory mechanics in anesthetized tracheostomized newborn piglets and adult pigs and the changes determined by cervical bilateral vagotomy. Piglets had a respiratory system compliance and resistance, on a per kilogram basis, respectively, higher and smaller than the adults. After vagotomy neither variable changed in the newborn, but resistance dropped in the adult. This may suggest that efferent vagal control of bronchomotor tone is more pronounced in the adult. Respiratory system time constant was longer in newborns both before and after vagotomy. The distortion of the chest wall, examined as the ratio between the volume inhaled spontaneously and the passive volume for the same abdominal motion, was more marked in newborns, reflecting their higher chest wall compliance. The work per minute, computed from the pressure and volume changes, was larger in piglets. After vagotomy the external work per minute was not different; however, the larger tidal volumes were accompanied by a larger chest distortion. This may indicate that vagal control of the breathing pattern, by limiting the depth of inspiration and hence the amount of chest distortion, has implications on the energetics of breathing.

Animals↗
PubMed1983

[Technical variations in abdominal heterotransplants of the heart].

The Authors describe the innovations by them introduced in a series of 15 experiments of abdominal heart heterotopic transplantation done in the Institute of Veterinary Physiology and Biochemistry University of Milano. Particularly they recommend the use of cardioplegia and the prolene as suture's material to reduce the ischemic time. Also they signal the importance of a new position of the transplanted heart with the apex looking at the head of the recipient. They think this position should be the best to preserve the anatomical connections between the great vessels of the guest heart.

Animals↗
PubMed1983

The cardiorespiratory impairment in cirrhosis and sepsis. An experimental interpretation using octopamine infusion.

The effects of octopamine on systemic and pulmonary circulation and on respiratory parameters have been studied in ten O2 100% breathing pigs. A rise in cardiac index (CI) due to an increase in the dynamics of the left ventricle and a progressive hypoxemia, notwithstanding the hyperventilation, was found. The decrease in arterial O2 tension was due to a rise in the pulmonary shunt fraction (QS/QT). The statistical analysis of cardiorespiratory parameters demonstrated that the high flow state linked with a non-Starling mechanism was the causing factor of a ventilation: perfusion ratio (VA/QT) decrease, which led to the rise in QS/QT. Also, a decrease in the lung compliance simultaneous to the increased blood flow was observed. It is suggested that octopamine may play a role in the pathogenesis of the cardiorespiratory hemodynamic impairment of cirrhosis and sepsis where high levels of this false neurotransmitter were observed.

Animals↗
PubMed1981

Prostacyclin effect on blood pressure in pig with aortic obstruction.

Cardiovascular effects of infused prostacyclin (PGI2) were investigated in hypertensive anesthetized pigs in the steady state and at 1,2,3,4,5,10,15,20 and 30 min after the beginning of the infusion. PGI2 were perfused at the rate of 2 microgram/Kg/min for 4 min before and after vagosympathectomy. We measured the mean arterial pressure, heart rate, cardiac output, stroke volume, mean pulmonary arterial pressure, mean pulmonary wedge pressure and calculated total systemic resistance and total pulmonary resistance. Our findings suggest that prostacyclin lowers pulmonary and systemic blood pressure in hypertensive animal by vasodilatation. The decrease in mean arterial pressure does not produce any change in heart rate probably because the substance also has a vagal effect. Finally, it might reduce venous return by dilatation of capacitance vessels. PGI2 appears to be a powerful vasodilator agent acting both afterload and preload without influencing heart rate or stroke volume.

Animals↗
PubMed1981

Effects of PGI2 on pattern of breathing in the pig during aortic obstruction.

We studied the effects of prostacyclin on pattern in six anaesthetized pigs with aortic obstruction. PGI2 causes a rightward displacement of VT/TI relationship (Hering-Breuer threshold curve) without a corresponding change in inspiratory flow. With airways occluded at the end respiratory level, we analyze how PGI2 affects the central respiratory rhythm in the absence of the phasic lung volume-related vagal loop. Infusion of prostacyclin causes leftward displacement of the TE/TI relationship and an increase in TTOTo correlated with the hypotensive action. The change in the bulbo-pontine pacemaker is caused by a marked increase in TEo and this suggests that PGI2 can modulate the central respiratory rhythm, independently of the blood pressure level.

Animals↗
PubMed1981

Respiratory modulation by vagal afferents in pigs.

We have studied the role of pulmonary vagal afferents and baroreceptors of the aortic arch on control of breathing in anaesthetized pigs. As in other species (dog, cats and rabbits) the depth and rate of breathing was found to be controlled by a volume-related vagal feed-back loop from pulmonary stretch receptors. Rapid shallow breathing following histamine aerosol and phenyldiguanide i.v. (which are likely to stimulate pulmonary vagal irratant and J receptors) occurred through a decrease in the activation threshold of the inspiratory cut-off mechanism without altering the matching of inspiratory to expiratory time. These results are also similar to those found in cats and rabbits. Histamine caused an increase in pulmonary resistance and a decrease in compliance: these effects were partially vagally mediated and partially due to a direct stimulation of smooth muscles by the drug. It seems, from relating the respiratory to the vascular systemic effect of histamine administration, that pigs have a greater respiratory response than cats or rabbits. A stepwise decrease in blood pressure through haemorrhage under iso-PCO2 and iso-PO2 conditions was found to affect the matching of the expiratory to the inspiratory time without affecting the activation threshold of the inspiratory cut-off mechanism.

Animals↗
PubMed1981

Work of breathing in dog during exercise.

In six dogs trained to wear a mask and to swallow an esophageal balloon, the dynamic work of breathing (Wdyn) was measured while the animals ran on a treadmill at different intensities (7-13 km.h-1,+10%). Wydn (kg.m.min-1) increased with ventilation (VE, 1.min-1) according to Wdyn = 0.308.10(-2) VE2 + 0.0098.10(-2).VE3. However, if the exercise was prolonged so that the body temperature rose above approximately 39 degrees C, Wdyn, for a given ventilation, decreased; and hence Wdyn = 0.253.10(-2).VE2 -- 0.0011.10(-2).VE3. Similar observations have been made on another dog heated from an external source. From this finding it seems that during exercise, when the temperature rises and the ventilation increases to dissipate heat, the airway size, at least in some portion of the respiratory tract, increases markedly and therefore the cost of breathing is greatly diminished. This mechanism would save oxygen for the exercising limb muscles when exercise has to be continued for an extended time.

Airway Resistance↗
PubMed1980

[Evaluation of PO2, PCO2, pH, and B.E. in milking cows in different milking phases].

During one year we studied the acid-base state in the milking cows trying to solve the relationship between the secretion disorders and feeding. THe results confirm that exist a link between the acid-base state and the disorders. These disorders are connected to problems of alimentation. In our experiments it had been possible to observe a change in pH of blood versus alkalosis.

Acid-Base Imbalance↗
PubMed1980

[Modifications of the respiratory mechanism induced by administration of 18, 19, 20-trinor-17-cyclohexyl-13, 14-dehydro PGF 2 alpha methyl ester].

The effects on pattern of breathing, on compliance and respiratory resistances of PGF 22 were investigated in anaesthetized pigs before and after vagosympathectomy. A marked increase in respiratory resistance and a decrease in lung compliance simultaneously with a pulmonary congestion were observed. The respiratory changes were considered secondary both to a vagal reflex and to the hemodynamic impairment.

Airway Resistance↗
PubMed1980

[18,19,20-trinor-17-cyclohexyl-13,14-dehydro PGF 2 alpha methylester as the cause of hypertension in pulmonary circulation].

The hemodynamic effects of a synthetic compound of PGF 2 alpha have been studied before and after vagosympathectomy. Synthetic PGF 2 alpha caused a marked hypertension in the pulmonary circulation linked with the vasoconstrictor action of this substance on the small lung vessels. A slight hypotension was observed in the denervated animal where the highest values of pulmonary pressure were reached. The authors conclude that this fact may be due to an inhibition of the vasoconstrictor systemic tone secondary to the pulmonary hypertensive state.

Animals↗