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D O Warner

Publications and source records attributed to D O Warner.

At least 73 records · Page 4Linked to original sources
PubMed1994

Effects of halothane on the relationship between cytosolic calcium and force in airway smooth muscle.

The mechanism of the direct relaxing effect of halothane on airway smooth muscle may involve a decrease in 1) cytosolic calcium concentration ([Ca2+]i) and/or 2) the force produced for a given [Ca2+]i (i.e., the "sensitivity" of the myofibrillar contractile system to Ca2+). This study was conducted to test the hypothesis that halothane reduces the sensitivity of the myofibrillar contractile system to Ca2+ during muscarinic receptor stimulation of canine tracheal smooth muscle. Isolated smooth muscle strips were mounted in a photometric superfusion system, stretched to their optimal length for force development, and loaded with the fluorescent Ca2+ indicator, fura 2, for simultaneous recording of fura 2 fluorescence and isometric force. Emission fluorescence intensities due to excitation at 340 (F340)- and 380 (F380)-nm wavelengths were measured and F340/F380 was used as an index of [Ca2+]i. After superfusion with Ca(2+)-free physiological salt solution (PSS) containing 1 or 100 microM acetylcholine (ACh), two consecutive cumulative concentration-response curves to CaCl2 (0.01-2.4 mM) were generated for each strip; one curve was generated in the presence of halothane. In strips stimulated with 1 (n = 6) or 100 (n = 6) microM ACh, the cumulative addition of CaCl2 to the Ca(2+)-free PSS caused concentration-dependent increases in both F340/F380 and force. In strips stimulated with 1 microM ACh, 2.4 +/- 0.3% halothane proportionally attenuated increases in both F340/F380 and force.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1994

Is nitric oxide involved in cutaneous vasodilation during body heating in humans?

The neurotransmitter responsible for neurogenic vasodilation in human skin during body heating is unknown. We sought to determine whether the vasodilating substance nitric oxide (NO) is involved in this phenomenon. Six subjects were heated for 50 min by use of a water-perfused suit while forearm blood flow (FBF) was measured with plethysmography and skin blood flow (SkBF) was measured by the laser-Doppler method in both arms. In one forearm, NG-monomethyl-L-arginine (L-NMMA), an NO synthase blocker, was infused into the brachial artery. Bolus doses of L-NMMA (< or = 4 mg/min) for 5 min were given to blunt NO-mediated vasodilator responses to acetylcholine (ACh, 64 micrograms/min). A continuous infusion of L-NMMA (< or = 1.0 mg/min) was used during body heating to maintain NO synthase blockade. In the forearm receiving L-NMMA, FBF was 1.8 +/- 0.3 ml.100 ml-1.min-1 before drug infusion and rose to 9.5 +/- 1.3 ml.100 ml-1.min-1 with ACh. After L-NMMA infusion, FBF was 1.3 +/- 0.2 ml.100 ml-1.min-1 and rose to 2.6 +/- 0.4 ml.100 ml-1.min-1 with ACh (both P < 0.05 vs. pre-L-NMMA). Similar changes in SkBF were seen with ACh and L-NMMA, confirming that the drugs reached cutaneous vessels. With body heating, oral temperature increased by 1.2 degrees C, heart rate increased by 34 beats/min, and mean arterial pressure remained constant at approximately 75 mmHg. FBF in the treated forearm rose to 11.5 +/- 2.1 vs. 12.6 +/- 1.7 ml.100 ml-1.min-1 in the control forearm (P > 0.05, control vs. treated response).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1994

Anesthesia and chest wall function in dogs.

Three anesthetics (pentobarbital, halothane, and isoflurane) were studied in six mongrel dogs to systematically compare their effects on chest wall function during spontaneous breathing. Each dog received each anesthetic on separate occasions. Electrical activities of several respiratory muscles were measured with chronically implanted electrodes, and chest wall motion was assessed by high-speed three-dimensional computed tomography scanning. Phasic expiratory muscle activity was markedly depressed by volatile anesthetics halothane and isoflurane compared with pentobarbital. In contrast, inspiratory activity in parasternal intercostal muscles was relatively well preserved during anesthesia with these volatile agents. The contribution of expiratory muscles to tidal volume was diminished during halothane and isoflurane compared with pentobarbital anesthesia. As anesthesia was deepened, expiratory muscle activity was unchanged during pentobarbital anesthesia, enhanced in some dogs during isoflurane anesthesia, and remained absent during halothane anesthesia. Activity in parasternal intercostal muscle was depressed as inspired concentration of halothane or isoflurane was increased, whereas diaphragmatic activity was unchanged. Depression of expiratory muscle activity by halothane persisted when breathing was stimulated by positive end-expiratory pressure, with significant mechanical consequences for chest wall configuration. Many of these findings are in contrast with previous observations in humans and suggest that the dog is not a suitable model for the study of the effects of anesthetic drugs on the pattern of human respiratory muscle activity.

Abdominal Muscles↗
PubMed1994

Halothane and pertussis toxin-sensitive G proteins in airway smooth muscle.

We hypothesized that halothane-induced depression of airway smooth muscle (AWSM) contractility is caused, in part, by an effect on pertussis toxin-sensitive guanosine triphosphate (GTP)-binding regulatory proteins (G proteins). To determine the effect of G protein inactivation on the ability of halothane to relax AWSM, isolated strips of canine tracheal smooth muscle were contracted with the muscarinic agonist acetylcholine and relaxed by halothane (0.2 to 1.6 minimum alveolar anesthetic concentration [MAC]). Half of the strips were treated with pertussis toxin 10 micrograms/mL. Because a pertussis toxin-sensitive G protein mediates muscarinic inhibition of adenylyl cyclase, depression of G protein function by halothane might also enhance the relaxing effects of beta-adrenoreceptor agonists. To test this possibility, in another series of experiments, the effect of pretreatment with 1.6 MAC halothane on the ability of isoproterenol to relax strips contracted with acetylcholine was studied; the converse order of drug presentation was also performed. Treatment with pertussis toxin did not affect the ability of halothane to relax AWSM; 1.6 MAC halothane produced a 42% +/- 8% (mean +/- SD) and 38% +/- 8% decrease in force in treated and untreated strips, respectively. Exposure to 1.6 MAC halothane did not significantly affect the dose-response relationship between isoproterenol and force. Conversely, exposure to isoproterenol (0.036 +/- 0.033 micron) did not significantly affect the dose-response relationship between halothane and force. These results do not support the presence of a significant effect of halothane on the function of pertussis toxin-sensitive G proteins.

Acetylcholine↗
PubMed1994

Anaesthesia and chest wall function.

The effects of anaesthesia and surgery on the chest wall may be responsible for impaired gas exchange and other pulmonary complications during the perioperative period. Current evidence supports the following sequence of events. Anaesthesia changes the shape and motion of the chest wall, either by changing the amount of tonic and phasic activity of the respiratory muscles (anaesthesia with spontaneous breathing) or by eliminating the activity entirely (paralysis with mechanical ventilation). These primary changes in chest wall function lead to secondary changes in lung function, including the formation of dependent lung atelectasis. Recent advances in imaging of the thorax have called into question traditional understanding of the mechanisms by which anaesthesia alters chest wall function. For example, it is now apparent that anaesthesia reduces the functional residual capacity not by changing the position of the diaphragm, but rather by affecting the rib cage, and, perhaps, the volume of intrathoracic blood. The effects of anaesthesia and surgery on postoperative chest wall function may be lessened by regional analgesia and the use of laparoscopic surgical techniques. However, it is not yet clear that this improvement is associated with a reduction in the incidence of pulmonary complications.

Anesthesia↗
PubMed1993

Factors influencing the direct actions of volatile anesthetics on airway smooth muscle.

BACKGROUND: The authors hypothesized that the ability of volatile anesthetics to relax airway smooth muscle (AWSM) depends on: 1) the agonist used to produce muscle contraction, 2) the preexisting level of contraction, and 3) the volatile anesthetic used. METHODS: To test the first hypothesis, isolated strips of canine trachealis muscle were precontracted with acetylcholine (ACh), McN-A-343 (McN, another muscarinic agonist), 5-hydroxytryptamine (5HT, a different receptor agonist), or potassium chloride (KCl, which induces contraction by cell depolarization) to 50% of maximal force, then exposed to halothane (0.2-1.6 MAC). To test the second and third hypotheses, other strips were precontracted to 25, 50, 75, and 100% of maximal force with ACh, or to 10, 30, or 50% of maximal force with KCl, and were then exposed to halothane or isoflurane (0.2-1.6 MAC). RESULTS: For AWSM contracted to 50% of maximal force, the amount of relaxation produced by halothane depended on the agonist used to elicit contraction in the following manner: 5HT = McN > ACh; the muscles contracted with KCL did not relax. For ACh-induced contractions, the absolute amount of relaxation produced by halothane did not depend on the level of precontraction. In muscles contracted with KCl, the volatile anesthetics caused significant relaxation only in muscles contracted to 10% of maximal force. Overall, halothane had a significantly greater relaxing effect as compared with isoflurane during ACh-mediated contractions; the effects of the two agents did not differ significantly during KCl-mediated contractions. CONCLUSIONS: When canine AWSM tone is increased by contractile agonists in vitro, the absolute amount of relaxation produced by halothane depends on the agonist used to elicit contraction, but not the degree of precontraction. In addition, there are small but significant differences between the effects of halothane and isoflurane on ACh-mediated contractions.

(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethy↗
PubMed1993

Halothane alters cytosolic calcium transient in tracheal smooth muscle.

Halothane is a potent bronchodilator that attenuates vagally mediated constriction of canine airways, in part by a direct action on the smooth muscle cell. In tracheal smooth muscle, acetylcholine (ACh) produces a transient peak increase in cytosolic ionized calcium concentration ([Ca2+]i), which declines to a sustained plateau concentration that is higher than that of the unstimulated muscle, and a sustained increase in force. The transient peak [Ca2+]i is caused primarily by Ca2+ release from the sarcoplasmic reticulum (SR), whereas the plateau [Ca2+]i is caused primarily by influx of extracellular Ca2+ across the plasma membrane. This study was conducted to investigate the effects of halothane on the 1) transient peak [Ca2+]i during force development (i.e., developed force) and 2) plateau [Ca2+]i during force maintenance (i.e., sustained force) induced by ACh in isolated strips of canine tracheal smooth muscle. Changes in [Ca2+]i were measured with the photoprotein, aequorin. In muscle strips contracted after incubation with 1.1 (n = 5) or 1.5 (n = 5) minimum alveolar concentration (MAC) halothane, halothane significantly attenuated the transient peak aequorin luminescence (AL) and developed force and significantly prolonged the time necessary to reach peak AL and developed force; these effects were not dose dependent. In muscle strips (n = 3) contracted with ACh, addition of halothane caused a reduction in sustained force but no decrease in plateau AL.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1993

Epidural anesthesia and intrathoracic blood volume.

To investigate how epidural anesthesia changes intrathoracic gas volume, high epidural anesthesia was administered to five pentobarbital-anesthetized dogs lying supine, and the total intrathoracic volume at end-expiration was measured with a high-speed three-dimensional x-ray scanner. The amount of gas in the lungs at end-expiration [the functional residual capacity (FRC)] was measured with a nitrogen washout technique, and the intrathoracic tissue volume, including the intrathoracic blood volume, was calculated as the difference between intrathoracic volume at end-expiration and FRC. High epidural anesthesia with the local anesthetic etidocaine to a T-1 myotomal level significantly (P < 0.05) increased intrathoracic volume at end-expiration [76 +/- 35 mL (M +/- SD)] by significantly increasing both intrathoracic tissue volume (33 +/- 15 mL) and FRC (43 +/- 26 mL). Increases in intrathoracic tissue volume were probably caused by increases in intrathoracic blood volume. We conclude that increases in FRC caused by epidural anesthesia in anesthetized dogs lying supine may be minimized by a concurrent increase in intrathoracic blood volume. These results suggest that measurements of thoracic gas volume alone may be insufficient to describe chest wall responses to epidural anesthesia.

Anesthesia, Epidural↗
PubMed1992

Halothane alters the response of isolated airway smooth muscle to carbon dioxide.

Rings of canine bronchi were studied in vitro to determine the effects of halothane on the responses of airway smooth muscle to hypercapnia and hypocapnia. Bronchi were first contracted to 50% of maximal active force with acetylcholine (ACh), 5-hydroxytryptamine (5HT), potassium chloride (KCl), or the muscarinic agonist McN-A-343 (McN). The CO2 concentration of the bathing solution was then changed from 6% to either 1% (hypocapnia) or 10% (hypercapnia). In the absence of halothane, changes in CO2 concentration had no significant effect on muscles contracted with ACh. With all other contractile agonists, increasing the CO2 concentration caused bronchial relaxation, while decreasing the CO2 concentration caused contraction. In the presence of 2 MAC halothane, hypocapnia relaxed bronchi contracted with the muscarinic agonists ACh or McN; the responses to hypocapnia of bronchi contracted with KCl and 5HT were not significantly changed by halothane. Halothane had no effect on the responses of the bronchi to hypercapnia. We conclude that airway smooth muscle contracted with cholinergic agonist relaxes in response to hypocapnia when exposed to 2 MAC halothane; this mechanism may contribute to the depression of hypocapnic bronchoconstriction caused by halothane in vivo.

Animals↗
PubMed1992

Halothane changes the relationships between lung resistances and lung volume.

The authors hypothesized that relaxation of airway smooth muscle by halothane lessens the dependence of airway resistance on lung volume, and that halothane alters the relationship between pulmonary resistance and lung volume by changing both the airway and tissue components of pulmonary resistance. The relationship among airway resistance, tissue resistance, and lung volume was examined in mongrel dogs before and during the administration of halothane, both in airways with reduced smooth muscle tone (after vagotomy) and during moderate increases in smooth muscle tone caused by vagus nerve stimulation (VNS). Resistance were measured at several levels of positive end-expiratory pressure (PEEP, 4-15 cmH2O) using an alveolar capsule technique. Before halothane administration, airway resistance increased at low PEEP; VNS accentuated this increase. Tissue resistance increased at low PEEP only during VNS. Halothane had no significant effect on any resistance before VNS. During VNS, halothane markedly blunted increases in airway resistance and tissue resistance as PEEP decreased. The authors conclude that during stimulation of airway smooth muscle in dogs, halothane attenuates increases in airway resistance and tissue resistance with reductions in lung volume in dogs. Thus, moderate changes in lung volume have little effect on these resistances during halothane anesthesia under these conditions.

Airway Resistance↗
PubMed1992

Sympathetic modulation of blood flow and O2 uptake in rhythmically contracting human forearm muscles.

This study tested the effects of sympathetically mediated changes in blood flow to active muscles on muscle O2 uptake (VO2) in humans. Four minutes of graded (15-80% of maximum voluntary contraction, MVC) rhythmic handgrip exercise were performed. Forearm blood flow (FBF) (plethysmography) and deep vein O2 saturation were measured each minute. Forearm O2 uptake was calculated using the Fick principle. In protocol 1, exercise was performed while supine and again while upright to augment sympathetic outflow to the active muscles. Standing reduced FBF at rest from 3.6 to 2.2 ml.100 ml-1.min-1 (P < 0.05). During light exercise (15-40% MVC) FBF was unaffected by body position. Standing reduced FBF (P < 0.05) from 36.0 to 25.2 ml.100 ml-1.min-1 and forearm VO2 from 38.2 to 28.1 ml.kg-1.min-1 during the final work load. In protocol 2, exercise was performed while supine before and after local anesthetic block of the sympathetic nerves to the forearm. Sympathetic block increased FBF at rest from 3.1 to 8.9 ml.100 ml-1.min-1 (P < 0.05), and FBF was higher during all work loads At 70-80% of MVC sympathetic block increased FBF from 35.4 to 50.7 ml.100 ml-1.min-1 (P < 0.05), and forearm VO2 from 45.5 to 54.2 ml.kg-1.min-1 (P < 0.05). These results suggest that in humans sympathetic nerves modulate blood flow to active muscles during light and heavy rhythmic exercise and that this restraint of flow can limit O2 uptake in muscles performing heavy rhythmic exercise.

Adolescent↗
PubMed1992

Electrical activation of expiratory muscles increases with time in pentobarbital-anesthetized dogs.

Although the pentobarbital-anesthetized dog is often used as a model in studies of respiratory muscle activity during spontaneous breathing, there is no information regarding the stability of the pattern of breathing of this model over time. The electromyograms of several inspiratory and expiratory muscle groups were measured in six dogs over a 4-h period by use of chronically implanted electrodes. Anesthesia was induced with pentobarbital sodium (25 mg/kg iv), with supplemental doses to maintain constant plasma pentobarbital concentrations. Phasic electrical activity increased over time in the triangularis sterni, transversus abdominis, and external oblique muscles (expiratory muscles). The electrical activity of the costal diaphragm, crural diaphragm, and parasternal intercostal muscles (inspiratory muscles) was unchanged. These changes in electrical activity occurred despite stable plasma levels of pentobarbital and arterial PCO2. They were associated with changes in chest wall motion and an increased tidal volume with unchanged breathing frequency. We conclude that expiratory muscle groups are selectively activated with time in pentobarbital-anesthetized dogs lying supine. Therefore the duration of anesthesia is an important variable in studies using this model.

Anesthesia↗
PubMed1992

Limitation of maximal bronchoconstriction in living dogs.

Fourteen dogs were studied to determine whether (1) interdependence between airways and parenchyma can limit maximal bronchoconstriction under static conditions in vivo, and (2) stretching of airway smooth muscle during tidal breathing can attenuate muscle shortening and account for the limited bronchoconstriction previously observed in response to increasing doses of methacholine (MCh). In six dogs the left lung was ventilated while 50% MCh was nebulized into the airways of the right lower lobe (RLL) held at constant transpulmonary pressures (PL). Airway closure, as assessed by an alveolar capsule technique during small oscillations in lobar volume, occurred at PL less than or equal to 7.5 cm H2O. To assess the effects of tidal breathing, pulmonary resistance (RL) was measured in four dogs after MCh nebulization into the RLL during tidal breathing while the left lung was separately ventilated. In another four dogs the whole lung was challenged with MCh. At each MCh concentration, RL values in the RLL were much higher than in the whole lungs (30-fold at the highest MCh concentration), showing that maximal bronchoconstriction in response to MCh is much greater in the RLL than in the whole lung. We conclude that neither interdependence nor tidal breathing can fully explain limited maximal bronchoconstriction in living dogs.

Airway Resistance↗
PubMed1991

Halothane, enflurane, and isoflurane depress the peripheral vagal motor pathway in isolated canine tracheal smooth muscle.

Volatile anesthetics are potent bronchodilators, but the site of action for the dilation is unclear. To determine the site of action of halothane, enflurane, and isoflurane on the peripheral vagal motor pathway, isolated strips of canine trachealis muscle were stimulated before and during exposure to halothane at 0.3, 1.0, 1.7, or 2.4 MAC, enflurane at 1 MAC, or isoflurane at 1 MAC. The sites and methods of stimulation were: 1) postsynaptic nicotinic cholinergic receptors in the intramural parasympathetic ganglia, with 1,1-dimethyl-4-phenyl-piperazinium iodide (DMPP); 2) postganglionic cholinergic nerve fibers, with electrical field stimulation (EFS); and 3) muscarinic cholinergic receptors of the smooth muscle, with acetylcholine (ACh). The concentration-response curve to DMPP was significantly shifted to the right by 0.3 MAC halothane, whereas 0.3 MAC halothane had no significant effect on the concentration-response curves to ACh and EFS. At concentrations greater than 1 MAC of halothane, enflurane, or isoflurane, concentration-response curves to all three stimuli were shifted significantly to the right; i.e., the contractile responses to ACh, EFS, and DMPP were reduced. At all concentrations of halothane the force of contraction was significantly more reduced during stimulation with DMPP than during stimulation with ACh, and at halothane concentrations greater than or equal to 1.7 MAC the response to EFS was significantly more reduced than that to ACh. We conclude that halothane, enflurane, and isoflurane attenuated airway constriction by several mechanisms, including 1) reduced excitability of the postsynaptic nicotinic receptors of the intramural parasympathetic ganglia and 2) an effect on the smooth muscle and/or on the muscarinic receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Bronchodilation by halothane is not modulated by airway epithelium.

Halothane relaxes airway smooth muscles. To test the hypothesis that this relaxation is modulated by airway epithelium, we studied the effects of halothane on isolated second- and third-order canine bronchial rings and second-order canine bronchial segments. Paired rings or segments were examined, with the epithelium removed from one ring or segment of each pair. The bronchial rings were suspended in organ chambers and contracted with 10(-8)-10(-3) M acetylcholine (ACh), 10(-8)-10(-5) M 5-hydroxytryptamine (5HT), or 0.5-16 Hz electrical field stimulation (EFS, 15 V, 0.5-ms pulse duration). The tissue was contracted in the absence of halothane and during exposure to 1 and 2 MAC halothane. The bronchial segments were perfused intraluminally with physiologic salt solution (PSS) and contracted with 10(-6) M carbachol added to the tissue-bath PSS. One or 2 MAC halothane was then added to the perfusate. In the absence of halothane, epithelium removal increased the sensitivity of the bronchial rings to ACh and 5HT but not to EFS. Addition of 1 or 2 MAC halothane to the bathing fluid of the rings with or without epithelium decreased the sensitivity of the rings to ACh and 5HT. One MAC halothane decreased the sensitivity of the rings with and without epithelium to EFS. The decrease in sensitivity caused by halothane was not significantly different in rings with or without epithelium for any method of stimulation. In the bronchial segments, relaxations evoked by 1 or 2 MAC were not different in segments with or without epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1991

Chest wall motion during epidural anesthesia in dogs.

To determine the relative contribution of rib cage and abdominal muscles to expiratory muscle activity during quiet breathing, we used lumbar epidural anesthesia in six pentobarbital sodium-anesthetized dogs lying supine to paralyze the abdominal muscles while leaving rib cage muscle motor function substantially intact. A high-speed X-ray scanner (Dynamic Spatial Reconstructor) provided three-dimensional images of the thorax. The contribution of expiratory muscle activity to tidal breathing was assessed by a comparison of chest wall configuration during relaxed apnea with that at end expiration. We found that expiratory muscle activity was responsible for approximately half of the changes in thoracic volume during inspiration. Paralysis of the abdominal muscles had little effect on the pattern of breathing, including the contribution of expiratory muscle activity to tidal breathing, in most dogs. We conclude that, although there is consistent phasic expiratory electrical activity in both the rib cage and the abdominal muscles of pentobarbital-anesthetized dogs lying supine, the muscles of the rib cage are mechanically the most important expiratory muscles during quiet breathing.

Anesthesia, Epidural↗