Biomedical subjects

G Dechman

Publications and source records attributed to G Dechman.

8 recordsLinked to original sources

PubMed1995

Time course of histamine-induced bronchoconstriction and its adrenergic and H2 modulation.

We characterized the complete time course of histamine-induced bronchoconstriction and its modulation via the release of endogenous catecholamines and by its actions on H2-receptors in anesthetized, tracheostomized, paralyzed, and artificially ventilated mongrel dogs. Respiratory resistance (R) and elastance (E) were estimated continuously with a recursive least squares estimator. Three protocols were followed in which multiple histamine bolus injections were given 1 h apart. We found that the time courses of E and R had consistent patterns (transient peak that returned to baseline within 1000 sec) even in cases of low mean arterial pressure (MAP). Indomethacin pre-treatments prevented tachyphylaxis to repeated i.v. challenges. beta-blockade produced a mild increase in baseline and a potentiation of the histamine-induced response in E and these effects were not altered with further alpha-or H2-blockade. Blockade of alpha-receptors increased the time to recovery in both E and MAP presumably by decreasing blood flow. Finally, we suggest that preventing the H2-receptor induced increase in bronchial blood flow may have increased the time to maximal E without affecting the recovery time.

Animals↗

PubMed1995

On the use of the alveolar capsule technique to study bronchoconstriction.

Using the alveolar capsule technique, we studied the time courses of respiratory mechanical parameters at various sites on the lung surface during bronchoconstriction. Six mongrel dogs were anesthetized, tracheostomized, paralyzed and artificially ventilated (12-25 ml/kg, 19-22 breaths/min). Sternotomy was performed and alveolar capsules were glued to various parts of the lungs. Tracheal pressure and flow and alveolar pressure were measured continuously for 25 min after i.v. bolus injections of histamine (0, 0.05, 0.5, 5.0, 50.0 mg). The challenges were spaced 1 h apart. Estimates of lung tissue resistance and elastance were obtained with our recursive least-squares estimator (Lauzon and Bates, J. Appl. Physiol., 1159-1165, 1991). We found that the time courses of the parameters of most capsules were initially uniform but quickly diverged as bronchoconstriction developed. Also, we found that the differences in time course of mechanics between alveolar regions either developed randomly with step-like features presumably reflecting intermittent opening and closing of the airways leading to the various alveolar capsules, or in a progressive dose-dependent manner, possibly reflecting a gradual but structurally pre-set pattern of bronchoconstriction, or with a combination of these two patterns. We explain our results in terms of inhomogeneous mechanical properties of the lungs and examine some artifacts introduced by the alveolar pressure measurement technique.

Animals↗

PubMed1995

Considerations when testing and training the respiratory muscles.

The purpose of this review is to describe the muscles of respiration, mechanisms that lead to their dysfunction, and unique features of the respiratory muscles that should be considered when designing testing and training protocols for patients with respiratory compromise. The diaphragm's unique shape is an important determinant of its function. Respiratory pathophysiology combined with systemic abnormalities may result in inspiratory muscle weakness, fatigue, and injury. The specificity of training principle, as it applies to respiratory muscle training in patients with respiratory compromise, will be described. Precautions related to this type of training will also be outlined. In conclusion, a better understanding of the mechanisms contributing to inspiratory muscle dysfunction will assist physical therapists in designing the most appropriate training programs. This article, along with the other articles in this focus on respiratory muscle training, will provide therapists with scientifically based guidelines for rehabilitation of patients with impaired respiratory muscle function.

Breathing Exercises↗

PubMed1994

Mechanical behaviour of the canine respiratory system at very low lung volumes.

We studied the changes in dynamic elastance and resistance of the respiratory system in 6 supine, anaesthetized, paralysed, tracheostomised and open chested dogs. Tracheal pressure (Ptr), tracheal flow (V) and 3 alveolar pressures (Palv by alveolar capsule) were measured continuously for 20 min at 5 levels of positive end expiratory pressure (PEEP) between 0.1 and 0.5 kPa. The lungs were inflated to total lung capacity (TLC) at the start of each recording period. Lung elastance (EL) and resistance (RL) were estimated by fitting the equation Ptr = RLV + ELV + K to the measured data for each breath by multiple linear regression (V = volume, K = constant). Airway resistance (Raw) was obtained from the difference between Ptr and Palv. EL increased progressively in the 20 min following lung inflations. The increase in EL over this time was about 45% of its baseline value at a PEEP of 0.1 kPa compared to an increase of only about 10% at a PEEP of 0.5 kPa. In contrast, RL changed very little over the recording period at all levels of PEEP. At low levels of PEEP Palv often bore no resemblance to Ptr indicating that significant airway obstruction or closure had occurred. These results suggest that the increase in EL at low PEEP was primarily due to the accretion of airspace closure, and that nonlinear tissue mechanical properties were responsible for the lack of change in RL.

Airway Resistance↗

PubMed1994

Assessment of acute pleural effusion in dogs by computed tomography.

We used computed tomography (CT) to examine the effects of infusing 60 ml/kg of saline into the pleural space of four anesthetized paralyzed dogs ventilated with a constant tidal volume at a positive end-expiratory pressure of 0.5 kPa. The dogs were positioned supine, and the thoracic cavity was scanned from apex to base before and immediately after effusate loading. Each CT image was analyzed semi-automatically on a 486 personal computer with custom-designed software. We found that, despite right-side infusion, the effusate was distributed bilaterally no doubt because of the incomplete canine mediastinum. In general, the volume change of the lung was one-third and that of the chest wall was two-thirds that of the total volume infused. Most of the lung volume was contained in the caudal one-third of the lung pre-effusion, and most of the lung volume loss due to effusion was from this same region. Chest wall volume increased and in a more uniform manner post-effusion. The decrease in lung volume resulted in an increase in the mean density of the lung and an increase in its vertical density gradient as the lung was lifted upward toward the sternum by the effusate. The lung lost vertical height while the chest wall increased both its vertical and lateral dimensions after effusate loading. These results suggest that expansion of the chest wall helps preserve lung volume in the presence of acute pleural effusion. We have also demonstrated that CT is a useful tool for assessing changes in volume, shape, and density of the respiratory system.

Animals↗

PubMed1993

Effect of pleural effusion on respiratory mechanics, and the influence of deep inflation, in dogs.

We wished to study how pleural effusion affects dynamic mechanics of the lung and the chest wall. We also determined if these changes could be reversed by deep lung inflations. Pleural effusion was produced by saline infusion into the pleural space. During the infusion and over the following 2 hours, dynamic elastance and resistance of the lungs, the chest wall and the whole respiratory system were recorded. Dynamic elastance and resistance of the lung increased significantly during fluid loading and were partially, and only transiently, reversed by deep inflations. Dynamic elastance and resistance of the chest wall were little affected by these procedures. Thus, pleural effusion can have significant effects on dynamic elastance and resistance of the respiratory system (ERS, RRS). The transient nature of the change in lung parameters after deep inflation suggests that therapies based on periodic lung inflations may be of little benefit to patients with this condition.

Animals↗

PubMed1992

Factors affecting the accuracy of esophageal balloon measurement of pleural pressure in dogs.

Simultaneous measurement of esophageal and tracheal pressures during an occluded inspiratory effort was used to assess the accuracy of the esophageal balloon for measuring pleural pressure in dogs. Esophageal balloons were inserted in five mongrel dogs, and an occlusion test was performed with the balloon tip 5, 10, 15, 20, and 25 cm above the esophageal sphincter; at lung volumes of functional residual capacity (FRC) and FRC + 600 ml; and in supine and right- and left-side lying postures. The protocol was repeated in paralyzed animals. This time the occlusion test was performed by injecting air into a plethysmograph to change the body surface pressure, simulating pressure changes produced by respiratory efforts in spontaneously breathing animals. In 47% of the tests in spontaneously breathing dogs, the slope of esophageal vs. tracheal pressure varied greater than 10% from unity. After paralysis the slope did not vary greater than 5% from unity under any circumstance. These data indicate that the poorer performance of the occlusion test in nonparalyzed dogs is due to active tension in the walls of the esophagus and stress induced in the intrathoracic soft tissues by the descent of the diaphragm during a breathing effort.

Animals↗

PubMed1992

Time course of respiratory mechanics during histamine challenge in the dog.

We studied the dynamics of respiratory mechanical parameters in anesthetized tracheostomized paralyzed dogs challenged with a bolus of histamine injected either venously (venous group) or arterially (arterial group). The venous group was further divided into two groups: the first was bilaterally vagotomized and received hexamethonium bromide (denervated group), and the second also received atropine sulfate (atropine group). In the venous group, tissue resistance (Rti) and tissue elastance (Eti) increased biphasically, whereas airway resistance was monophasic and synchronized with the second rise of the tissue parameters. In the arterial group, Rti, Eti, and airway resistance increased synchronously. The denervated and atropine groups showed dynamics similar to those of the venous group. We postulate that the first phase observed in Rti and Eti in the venous group is due to constriction of the smooth muscles of the peripheral airways and blood vessels distorting the parenchyma. The second and larger phase is then due to histamine reaching the bronchial circulation and constricting the central airways, again distorting the parenchyma. The results from the arterial group support this hypothesis, whereas those from the denervated group ascertain that none of the phases observed in the venous group was due to nervous reflexes.

Airway Resistance↗