Differences in fish communities on natural versus artificial temperate reefs, groundfish conservation applications in British Columbia

Human-made marine habitats such as artificial reefs are used to mitigate marine habitat degradation and aid conservation of species at risk. We used ROV and sonar to survey threatened rockfish (Sebastes spp.) and other groundfish species associated with 18 artificial and natural reefs along the south coast of BC, Canada. Using an information-theoretic approach, we found that community composition significantly differed between natural and artificial reefs. Artificial reefs had high variability in rockfish abundance, some supporting very high or low relative abundance. Natural reefs consistently supported intermediate rockfish abundances. Groundfish diversity was significantly greater on natural reefs than artificial reefs. Depth and relief were significant predictors for both abundance and species richness. Interestingly, rockfish abundance was negatively associated with proximity to nearest rockfish conservation area. This research is a first step in understanding causal mechanisms leading to differences between fish communities on artificial reefs in our study system, and which reef attributes may facilitate successful contributions to conservation. Though artificial reefs show promise in the conservation of some threatened species, the maintenance of diverse fish communities depends on protection of heterogenous natural reef communities.

CO(2) rebreathing: an undergraduate laboratory to study the chemical control of breathing

The Read CO2 rebreathing method (Read DJ. A clinical method for assessing the ventilatory response to carbon dioxide. Australas Ann Med 16: 20-32, 1967) provides a simple and reproducible approach for studying the chemical control of breathing. It has been widely used since the modifications made by Duffin and coworkers. Our use of a rebreathing laboratory to challenge undergraduate science students to investigate the control of breathing provided 8 yr of student-generated data for comparison with the literature. Students (age: 19-22 yr, Research Ethics Board approval) rebreathed from a bag containing 5% CO2 and 95% O2 (to suppress the peripheral chemoreflex to hypoxia). Rebreathing was performed, and ventilation measured, after hyperventilation to deplete tissue CO2 stores and enable the detection of the central chemoreflex threshold. We analyzed 43 data sets, of which 10 were rejected for technical reasons. The mean threshold and ventilatory sensitivity to CO2 were 43.3 ± 3.8 mmHg and 4.60 ± 3.04 l·min(-1)·mmHg(-1) (means ± SD), respectively. Threshold values were normally distributed, whereas sensitivity was skewed to the left. Both mean values agreed well with those in the literature. We conclude that the modified rebreathing protocol is a robust method for undergraduate investigation of the chemical control of breathing.

OVA-induced airway hyperresponsiveness alters murine heart rate variability and body temperature

Altered autonomic (ANS) tone in chronic respiratory disease is implicated as a factor in cardiovascular co-morbidities, yet no studies address its impact on cardiovascular function in the presence of murine allergic airway (AW) hyperresponsiveness (AHR). Since antigen (Ag)-induced AHR is used to model allergic asthma (in which ANS alterations have been reported), we performed a pilot study to assess measurement feasibility of, as well as the impact of allergic sensitization to ovalbumin (OVA) on, heart rate variability (HRV) in a murine model. Heart rate (HR), body temperature (T_B), and time- and frequency-domain HRV analyses, a reflection of ANS control, were obtained in chronically instrumented mice (telemetry) before, during and for 22 h after OVA or saline aerosolization in sensitized (OVA) or Alum adjuvant control exposed animals. OVA mice diverged significantly from Alum mice with respect to change in HR during aerosol challenge (P < 0.001, Two-Way ANOVA; HR max change Ctrl = +80 ± 10 bpm vs. OVA = +1 ± 23 bpm, mean ± SEM), and displayed elevated HR during the subsequent dark cycle (P = 0.006). Sensitization decreased the T_B during aerosol challenge (P < 0.001). Sensitized mice had decreased HRV prior to challenge (SDNN: P = 0.038; Low frequency (LF) power: P = 0.021; Low/high Frequency (HF) power: P = 0.042), and increased HRV during Ag challenge (RMSSD: P = 0.047; pNN6: P = 0.039). Sensitized mice displayed decreased HRV subsequent to OVA challenge, primarily in the dark cycle (RMSSD: P = 0.018; pNN6: P ≤ 0.001; LF: P ≤ 0.001; HF: P = 0.040; LF/HF: P ≤ 0.001). We conclude that implanted telemetry technology is an effective method to assess the ANS impact of allergic sensitization. Preliminary results show mild sensitization is associated with reduced HRV and a suppression of the acute T_B-response to OVA challenge. This approach to assess altered ANS control in the acute OVA model may also be beneficial in chronic AHR models.

Vascular defects in gain-of-function fps/fes transgenic mice correlate with PDGF- and VEGF-induced activation of mutant Fps/Fes kinase in endothelial cells

BACKGROUND

Fps/Fes is a cytoplasmic tyrosine kinase that is abundantly expressed in the myeloid, endothelial, epithelial, neuronal and platelet lineages. Genetic manipulation in mice has uncovered potential roles for this kinase in hematopoiesis, innate immunity, inflammation and angiogenesis.

OBJECTIVE

We have utilized a genetic approach to explore the role of Fps/Fes in angiogenesis.

METHODS

A hypervascular line of mice generated by expression of a 'gain-of-function' human fps/fes transgene (fps(MF)) encoding a myristoylated variant of Fps (MFps) was used in these studies. The hypervascular phenotype of this line was extensively characterized by intravital microscopy and biochemical approaches.

RESULTS

fps(MF) mice exhibited 1.6-1.7-fold increases in vascularity which was attributable to increases in the number of secondary vessels. Vessels were larger, exhibited varicosities and disorganized patterning, and were found to have defects in histamine-induced permeability. Biochemical characterization of endothelial cell (EC) lines derived from fps(MF) mice revealed that MFps was hypersensitive to activation by vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF).

CONCLUSIONS

MFps mediates enhanced sensitization to VEGF and PDGF signaling in ECs. We propose that this hypersensitization contributes to excessive angiogenic signaling and that this underlies the observed hypervascular phenotype of fps(MF) mice. These phenotypes recapitulate important aspects of the vascular defects observed in both VEGF and angiopoietin-1 transgenic mice. The fps/fes proto-oncogene product therefore represents a novel player in the regulation of angiogenesis, and the fps(MF) line of mice constitutes a unique new murine model for the study of this process.

G protein-coupled receptor kinase 5 regulates airway responses induced by muscarinic receptor activation

G protein-coupled receptors (GPCRs) transduce extracellular signals into intracellular events. The waning responsiveness of GPCRs in the face of persistent agonist stimulation, or desensitization, is a necessary event that ensures physiological homeostasis. GPCR kinases (GRKs) are important regulators of GPCR desensitization. GRK5, one member of the GRK family, desensitizes central M(2) muscarinic receptors in mice. We questioned whether GRK5 might also be an important regulator of peripheral muscarinic receptor responsiveness in the cardiopulmonary system. Specifically, we wanted to determine the role of GRK5 in regulating muscarinic receptor-mediated control of airway smooth muscle tone or regulation of cholinergic-induced bradycardia. Tracheal pressure, heart rate, and tracheal smooth muscle tension were measured in mice having a targeted deletion of the GRK5 gene (GRK5(-/-)) and littermate wild-type (WT) control mice. Both in vivo and in vitro results showed that the airway contractile response to a muscarinic receptor agonist was not different between GRK5(-/-) and WT mice. However, the relaxation component of bilateral vagal stimulation and the airway smooth muscle relaxation resulting from beta(2)-adrenergic receptor activation were diminished in GRK5(-/-) mice. These data suggest that M(2) muscarinic receptor-mediated opposition of airway smooth muscle relaxation is regulated by GRK5 and is, therefore, excessive in GRK5(-/-) mice. In addition, this study shows that GRK5 regulates pulmonary responses in a tissue- and receptor-specific manner but does not regulate peripheral cardiac muscarinic receptors. GRK5 regulation of airway responses may have implications in obstructive airway diseases such as asthma or chronic obstructive pulmonary disease.

Calcium-independent contraction and sensitization of airway smooth muscle by p21-activated protein kinase

In Triton-skinned phasic ileal smooth muscle, constitutively active recombinant p21-activated kinase (PAK3) has been shown to induce Ca(2+)-independent contraction, which is accompanied by phosphorylation of caldesmon and desmin (Van Eyk JE, Arrell DK, Foster DB, Strauss JD, Heinonen TY, Furmaniak-Kazmierczak E, Cote GP, and Mak AS. J Biol Chem 273: 23433-23439, 1998). In the present study, we investigated whether PAK has a broad impact on smooth muscle in general by testing the hypothesis that PAK induces Ca(2+)-independent contractions and/or Ca(2+) sensitization in tonic airway smooth muscle and that the process is mediated via phosphorylation of caldesmon. In the absence of Ca(2+) (pCa > 9), constitutively active glutathione-S-transferase-murine PAK3 (GST-mPAK3) caused force generation of Triton-skinned canine tracheal smooth muscle (TSM) fibers to approximately 40% of the maximal force generated by Ca(2+) at pCa 4.4. In addition, GST-mPAK3 enhanced Ca(2+) sensitivity of contraction by increasing force generation by 80% at intermediate Ca(2+) concentrations (pCa 6.2), whereas it had no effect at pCa 4.4. Catalytically inactive GST-mPAK3(K297R) had no effect on force production. Using antibody against one of the PAK-phosphorylated sites (Ser(657)) on caldesmon, we showed that a basal level of phosphorylation of caldesmon occurs at this site in skinned TSM and that PAK-induced contraction was accompanied by a significant increase in the level of phosphorylation. Western blot analyses show that PAK1 is the predominant PAK isoform expressed in murine, rat, canine, and porcine TSM. We conclude that PAK causes Ca(2+)-independent contractions and produces Ca(2+) sensitization of skinned phasic and tonic smooth muscle, which involves an incremental increase in caldesmon phosphorylation.

A new method to perform quantitative measurement of bronchoscopic images

Bronchoscopy is a commonly used clinical tool that provides a direct image of the bronchial lumen. However, bronchoscopy has seen little use as a quantitative measurement tool, mainly because of the wide-angle lens which distorts the image. The present authors have tested the ability of numerical algorithms and commercial software to correct for this distortion. Test objects of known size were imaged with four different bronchoscopes. Commercial image analysis software was used to measure the size of features in the images before and after applying distortion correction algorithms. The technique was then applied by measuring airway narrowing in anaesthetized pigs during vagal stimulation. Without correction, object size near the edge of the field of view is underestimated by approximately 40%. The error in measured diameter of concentric circles was dependent on the radius of the circle, increasing to 25% for circles occupying 90% of the field. Third order polynomial functions were required to correct these errors. After correction, errors were independent of object size or location in the image. Correction for lens distortion was independent of the distance between bronchoscope and object. The authors conclude that modern image processing software can correct for the distortion produced by wide-angle bronchoscope lenses.

Role of vagal C-fiber afferents in the bronchomotor response to lactic acid in the newborn dog

We addressed the hypothesis that vagal C-fiber afferents and cyclooxygenase products are the mechanisms responsible for lactic acid (LA)-induced bronchoconstriction in the newborn dog. Perineural capsaicin and indomethacin were used to block conduction of vagal C fibers and production of cyclooxygenase products, respectively. Perineural capsaicin eliminated (85%) the increase in lung resistance (Rl; 45 ± 5.6%) due to capsaicin (25 μg/kg), whereas the increase in Rl (54 ± 6.9%) due to LA (0.4 mmol/kg) was only inhibited by 37 ± 4.7% ( P < 0.05). Atropine reduced LA-induced bronchoconstriction (42 ± 2.1%) by an amount similar to that obtained with perineural capsaicin. However, inhibition was significantly increased when atropine was combined with indomethacin (61 ± 2.7%; P < 0.05), implicating cyclooxygenase products in the LA-induced bronchoconstrictor response. We conclude that the mechanisms responsible for LA-induced bronchoconstriction in the newborn are 1) activation of vagal C-fibers, which, through projections to medullary respiratory centers, leads to activation of vagal cholinergic efferents; 2) production of cyclooxygenase products, which cause bronchoconstriction independent of medullary involvement; and 3) an unknown bronchoconstrictor mechanism, putatively tachykinin mediated. On the basis of our data, pharmaceutical targeting of pulmonary afferents would prevent multiple downstream mechanisms that lead to airway narrowing due to inflammatory lung disease.

Altered airway and cardiac responses in mice lacking G protein-coupled receptor kinase 3

Contraction and relaxation of airway smooth muscles is mediated, in part, by G protein-coupled receptors (GPCRs) and dysfunction of these receptors has been implicated in asthma. Phosphorylation of GPCRs, by G protein-coupled receptor kinase (GRK), is an important mechanism involved in the dampening of GPCR signaling. To determine whether this mechanism might play a role in airway smooth muscle physiology, we examined the airway pressure time index and heart rate (HR) responses to intravenous administration of the cholinergic agonist methacholine (MCh) in genetically altered mice lacking one copy of GRK2 (GRK2 +/-), homozygous GRK3 knockout (GRK3 -/-), and wild-type littermates. (GRK2 -/- mice die in utero.) GRK3 -/- mice demonstrated a significant enhancement in the airway response to 100 and 250 microgram/kg doses of MCh compared with wild-type and GRK2 +/- mice. GRK3 -/- mice also displayed an enhanced sensitivity of the airway smooth muscle response to MCh. In addition, GRK3 -/- mice displayed an altered HR recovery from MCh-induced bradycardia. Although direct stimulation of cardiac muscarinic receptors measured as vagal stimulation-induced bradycardia was similar in GRK3 -/- and wild-type mice, the baroreflex increase in HR associated with sodium nitroprusside-induced hypotension was significantly greater in GRK3 -/- than wild-type mice. Therefore, these data demonstrate that in the mouse, GRK3 may be involved in modulating the cholinergic response of airway smooth muscle and in regulating the chronotropic component of the baroreceptor reflex.

Mechanisms of capsaicin- and lactic acid-induced bronchoconstriction in the newborn dog

1. Capsaicin activation of the pulmonary C fibre vanilloid receptor (VR1) evokes the pulmonary chemoreflex and reflex bronchoconstriction. Among potential endogenous ligands of C fibre afferents, lactic acid has been suggested as a promising candidate. We tested the hypotheses that (a) lactic acid behaves as a stimulant of C fibre receptors in the newborn dog to cause reflex bronchoconstriction, and (b) lactic acid causes reflex bronchoconstriction via the same pulmonary C fibre receptor mechanism as capsaicin using the competitive capsaicin/VR1 receptor antagonist capsazepine. 2. Right heart injection of lactic acid caused a significant increase (47 +/- 8.0 %) in lung resistance (RL) that was atropine sensitive (reduced by 75 %; P < 0.05), consistent with reflex activation of muscarinic efferents by stimulation of C fibre afferents. 3. Infusion of the competitive capsaicin antagonist capsazepine caused an 80 % reduction (P < 0.01) in the control bronchoconstrictor response (41 +/- 8.5 % increase in RL) to right heart injections of capsaicin. The effects of capsazepine are consistent with reversible blockade of the VR1 receptor to abolish C fibre-mediated reflex bronchoconstriction. 4. Lactic acid-evoked increases in RL were unaffected by VR1 blockade with capsazepine, consistent with a separate lactic acid-induced reflex mechanism. 5. We conclude that (a) putative stimulation of C fibres with lactic acid causes reflex bronchoconstriction in the newborn dog, (b) capsazepine reversibly antagonizes reflex bronchoconstriction elicited by right heart injection of capsaicin, presumably by attenuating capsaicin-induced activation of the C fibre 'capsaicin' receptor (VR1), and (c) capsazepine resistance of lactic acid-induced bronchoconstriction indicates that lactic acid evokes reflex bronchoconstriction by a separate mechanism, possibly via the acid-sensing ionic channel.

Quantitative densitometry of proteins stained with coomassie blue using a Hewlett Packard scanjet scanner and Scanplot software

In the present study we evaluated the performance of a software/scanner system that employed the Hewlett Packard (HP) ScanJet Plus and Scanplot Software for densitometric quantification of protein loads stained with Coomassie Brilliant Blue following sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Gels with bovine serum albumin (BSA) standards, ranging from 0.125 to 10 micrograms, were scanned using reflectance densitometry with 127 microns step size in both the x and y directions and a resolution of 200 dots per inch. Densitometric volume was calculated for each protein band from scanner output in the tagged image file format (TIFF) by a customized software package, Scanplot V. 4.05 (Cunningham Engineering). Protein loads between 0.125 and 10.0 micrograms vs. volume were fit by a second-order regression: Volume = -0.58 x protein load2 + 16.82 x protein load + 7.87 (r = 0.991, p < 0.01). The same gels were scanned and quantified using a transmittance laser densitometer; densitometric volumes measured by both systems were highly correlated (r2 = 0.981, p < 0.01). Additional gels of BSA, smooth muscle myosin heavy chain (myosin), and actin displayed linear relationships between protein loads up to 4.0 micrograms and densitometric volume reflecting unique dye binding properties. We conclude that accurate and reproducible quantitative densitometry of SDS-PAGE can be performed using the HP ScanJet Plus scanner and Scanplot software.

Quantitative videobronchoscopy: a new technique to assess airway caliber

Quantitative assessment of airway caliber is generally confined to indirect physiologic methods or to radiographic techniques. Fiberoptic bronchoscopy provides a direct view of airways, permitting quantification of airway caliber by image analysis. We investigated the characteristics of a bronchoscopic imaging system, determined its limitations in quantification and the corrections necessary for accurate assessment of image dimension, validated the methodology with airway models, and applied the technique to airways in vivo. The system comprised a bronchoscope, videocamera, videocassette recorder (VCR), computer with a frame grabber, and image-analysis program. Image quantification was affected by two sources of distortion: (1) Distance distortion: a loss of image resolution with increasing distance between the object and bronchoscope, requiring determination of the operational distance range. (2) Radial distortion: a progressive reduction in image size from the center to the periphery of the bronchoscopic field of view (FOV), requiring correction of airway dimension according to airway size and location in FOV. Validation of the methodology with different sized airway models indicated an underestimation of measured diameters, which normalized with distortion correction. We provide an example of quantitative videobronchoscopy with measurements of in vivo airway narrowing due to vagal stimulation in the anesthetized dog. Measurements of airway narrowing made with videobronchoscopy were also compared with those made with high-resolution computer-assisted tomography (HRCT) which suggested that the two technologies provide unique but complementary perspectives on airway dimensions. We conclude that videobronchoscopy and image analysis provide a novel and accurate method for the quantification of airway caliber.

Cardiopulmonary actions of muscarinic receptor subtypes in the newborn dog

We addressed the role of muscarinic receptor subtypes in neurally mediated bronchoconstriction in vivo and airway smooth muscle contraction in vitro in the newborn dog. The in vivo dose-response effects of "selective" muscarinic antagonists on changes in lung resistance (RL) and heart rate (HR) in response to electrical stimulation of the vagus nerves were obtained in four groups of newborns. Each group was exposed to a different muscarinic antagonist: M1-selective pirenzepine (pir), M2-selective AF-DX 116 (11-[2-[(diethylamino)methyl]-1-piperidinyl]acetyl-5,11-dihydro-6H-pyrid o- [2,3-b]-[1,4]-benzodiazepine-6-one), M3-selective p-F-HHSiD (p-fluoro-hexahydro-sila-difenidol), and nonselective atropine (atr). In vitro concentration-response effects of pir and AF-DX 116 were obtained for neurally induced contractions of tracheal smooth muscle, elicited by electrical field stimulation. In a separate series of experiments we measured the bronchoconstrictor response to the muscarinic agonist acetylcholine delivered by right heart injection. Muscarinic antagonists reduced RL and HR responses to vagal stimulation in a dose-dependant fashion; however, ED50 values and selectivity for airway and cardiac responses (HR/RL ED50 ratio) were significantly different between antagonists. The rank order of potencies for inhibition of the increase in RL was atr > pir, M1 > p-F-HHSiD, M3 > AF-DX 116, M2, while that for HR was atr > AF-DX 116 > pir > p-F-HHSiD. AF-DX 116 preferentially inhibited the HR response, as reflected by the lowest HR/RL ED50 ratio (p < 0.001). The remaining antagonists preferentially inhibited RL, with the highest HR/RL ED50 ratio seen for p-F-HHSiD. These data suggest that muscarinic receptor subtypes are differentiated at birth and mediate cardiac and airway responses to vagal stimulation. We did not find autoinhibitory actions of airway M2 receptors on either the in vivo bronchoconstrictor response or the in vitro contractile response to electrical field stimulation. This suggests that neonatal airway M2 receptors, but not myocardial M2 receptors, are reduced in number or weakly coupled to muscarinic signal transduction mechanisms. Direct activation of airway smooth muscle by acetylcholine caused dose-dependent increases in RL that reached a plateau at approximately 200% at 100 micrograms, similar to values reported for vagal stimulation.

Hering-Breüer reflexes in high-altitude infants

1. Pulmonary ventilation was found to be similar in high-altitude and low-altitude newborn infants, but the breathing pattern was deeper and slower at high altitude (Mortola, J.P., Frappell, P.B., Frappell, D.E., Villena-Cabrera, N., Villena-Cabrera, M., Peña, F., Am Rev Respir Dis 1992, 46: 1206-9). We questioned the contribution of vagal reflexes to these differences in breathing pattern. 2. Measurements were performed on high-altitude (La Paz, Bolivia, 3600-4050 m, inspired O2 pressure approximately 92 mmHg, n = 34) and low-altitude infants (Santa Cruz, Bolivia, 400 m, PIO2 approximately 141 mmHg, n = 26). The strength of the Hering-Breüer inspiratory inhibitory reflex was estimated from the inspiratory time during a respiratory effort against airways closed at end-expiration (Tloccl). The strength of the Hering-Breüer expiratory facilitatory reflex was estimated from the expiratory duration when airways were occluded during expiration (TEoccl). 3. Tloccl was significantly longer than the open-airways TI at both low and high altitude, but significantly more so (approximately 14%) at high altitude. TEoccl was longer than open-airways TE in both groups of infants, but significantly less so at high altitude, whether TEoccl was compared between occlusions of similar tidal volume (on average, TEoccl at high altitude was 79% of that at low altitude) or similar airway pressure (87%). 4. The results suggest that at high altitude the contribution of the phasic volume-dependent vagal input to the inspiratory off-switch threshold is higher, and that the tonic vagal expiratory facilitation is lower, than at low altitude, presumably because of hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

[Physiological basis for the use of muscarine antagonists in bronchopulmonary dysplasia]

The rationale for the use of muscarinic antagonists in bronchopulmonary dysplasia (BPD) is based on the physiology and pharmacology of airway smooth muscle, the pathology of BPD, and the response of infants with BPD to bronchodilators, in vivo and in vitro studies of airway smooth muscle of newborn animals and humans indicate that vagal efferent airway innervation and/or muscarinic receptors are functional at birth, as well as early in gestation. Current concepts regarding muscarinic receptor subtypes suggest that M3 receptors mediate airway smooth muscle contraction, M2 receptors are autoinhibitory and limit vagally-mediated bronchoconstriction, and M1 receptors may play a facilitatory role in ganglionic transmission. Muscarinic receptor subtypes appear to be functionally expressed at birth but may undergo developmental regulation. Infants with BPD have an elevated pulmonary resistance that is accompanied by hypertrophy of airway smooth muscle, b2-agonists cause bronchodilation in BPD as does atropine in infants recovering from severe BPD. The synthetic congener of atropine, ipratropium bromide (IPB) causes bronchodilation in ventilator-dependent infants with BPD in a dose-dependent fashion. Nebulized IPB causes a decrease in respiratory resistance that reaches a maximum of 20% at 175 mg. The bronchodilation seen with muscarinic antagonists suggests that part of the elevated resistance associated with BPD is due to increased muscarinic tone, presumably vagal in origin. When IPB is combined with salbutamol (0.04 mg) the response is increased in magnitude and duration; reaching a slightly larger decreases in resistance (26%) that is now accompanied by an increase in compliance (20%).(ABSTRACT TRUNCATED AT 250 WORDS)

Bronchomotor responses to hypoxia and hypercapnia in decerebrate cats

Decerebrate animals are often used in investigations of the control of breathing because anesthesia-induced depression of respiratory reflexes is absent. We therefore investigated the level of tone and responsiveness of airway smooth muscle in seven decerebrate, paralyzed, and ventilated cats. Specifically, we measured the changes in pulmonary resistance (RL) and dynamic pulmonary compliance (CLdyn) in response to hypoxia and hypercapnia. All cats responded to hypoxia (approximately 10% O2 in N2) with significant increases (mean 49%, range 5-156%) in RL from a mean control value of 0.0197 +/- 0.0081 (SD) cmH2O.ml-1.s. During inhalation of 5% CO2 in O2, RL increased significantly (mean 59%, range 16-135%) from a mean control value of 0.0190 +/- 0.0056 cmH2O.ml-1.s. Decreases in CLdyn during hypoxia and hypercapnia were much smaller, averaging -9 and -11%, respectively. After atropine was administered, average control RL fell 50%, from 0.0269 to 0.0134 cmH2O.ml-1.s (P < 0.05; n = 4). Hypoxic and hypercapnic gas mixtures did not affect pulmonary mechanics after atropine was administered. In three cats, oscillations of RL were synchronized to phrenic activity but only at low respiratory frequencies (approximately 12 cycles/min), indicating that airway smooth muscle responded slowly to vagal input. Pentobarbital sodium, like atropine, reduced control RL in three cats. These cats lost their bronchoconstrictor response to hypercapnia but had augmented responses to hypoxia compared with preanesthetic responses. We conclude that decerebrate cats possess resting bronchomotor tone and retain their responsiveness to hypoxia and hypercapnia. Thus the decerebrate cat is a useful model for studying the control of tracheobronchial smooth muscle.

Epithelial modulation of neonatal and fetal porcine bronchial contractile responses

We tested the hypothesis that bronchial epithelium of newborn and fetal pigs exerts an inhibitory effect on bronchial contractile function. In vitro studies were performed on 13 isolated bronchial segments from seven neonatal pigs (12 h to 4 d old) and on 9 bronchial segments from five late-term pig fetuses (105 d gestation, term = 115 d). This preparation keeps the lumen of the airway physiologically intact and separate from the serosal aspect. Stem bronchi of the right and left lung were mounted horizontally at 6 cm H2O in a chamber containing oxygenated Kreb's solution. One bronchus was intact while the other had the epithelium removed with a cotton-tipped applicator soaked in Kreb's solution. Removal of epithelium was confirmed histologically. The lumen pressure of the mounted bronchi was measured at constant volume after the luminal application of acetylcholine (ACh) or K2SO4 (80 mM/L in place of NaCl), after serosal applications of these two substances at the peak of the luminal response, and after serosal application of ACh alone (newborn only). ACh (1, 10, and 100 microM) in the lumen of intact airways of neonatal pigs caused contractions of 0.1 +/- 0.07 (SEM), 0.4 +/- 0.14, and 0.9 +/- 0.18 cm H2O, respectively; in airways denuded of epithelium, ACh caused contractions of 3.9 +/- 1.1, 15.5 +/- 2.94, and 2.95 +/- 4.97 cm H2O (p < 0.001 versus intact airways). Luminal contractions were 2.9 +/- 2.2%, 2.6 +/- 0.9%, and 2.8 +/- 0.7% of the luminal+serosal values for intact segments, as compared with 65.5 +/- 4.6%, 58.8 +/- 7.7%, and 75.1 +/- 6.2% for denuded segments (p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

The integrity of the epithelium is a major determinant of the responsiveness of the dog bronchial segment to mucosal provocation

The intact bronchial segment of the dog was used to investigate the role of the epithelium in modulating bronchial responsiveness: firstly, because it retains many of the properties of the airway wall including the separation of the mucosal and adventitial surfaces; and secondly, because airway tissue from dogs has been principally used in advancing evidence for epithelial relaxant substances. The development of tone by the airway smooth muscle was measured as an increase in luminal pressure of the isovolumic segment. Cholinergic excitatory and sympathetic inhibitory responses were obtained to electrical field stimulation. Responses to acetylcholine (ACh), carbachol, depolarizing K+ solution and vanadate (VO3-) applied to the mucosal surface were greatly attenuated both in sensitivity and reactivity compared with their effect on the adventitial surface. Mechanical removal of the epithelium greatly augmented these responses to agents in the lumen (ACh sensitivity increased 100-fold) to equal those by adventitial stimulation. The latter were unaffected by epithelial removal. No functional evidence for epithelial-derived inhibitory factors could be demonstrated. It is concluded that the impermeable nature of the epithelium acts as a barrier to diffusion of hydrophilic and charged molecules thereby producing large concentration gradients across the airway wall. A breach in the integrity of the epithelium enables molecules to gain access to the smooth muscle.

Capsaicin-induced reflex bronchoconstriction in the newborn

Although bronchoconstriction in response to C-fibre stimulation has been reported to be weak or absent in the newborn, pulmonary resistance and compliance have not been measured. We tested the hypothesis that capsaicin reflexly activates pulmonary efferent outflow to airway smooth muscle in the newborn. We measured breath-by-breath responses of inspiratory lung resistance (RLi) and dynamic compliance (CLdyn) in 13 newborn dogs and 4 newborn pigs during right heart injections of saline, capsaicin (25-50 micrograms/kg) and acetylcholine (ACh). Repeat capsaicin injections at 5 min intervals were made to test for desensitization in the newborn dog. All newborn dogs and 2 of 4 newborn pigs displayed a brisk bronchoconstriction; in the dog, RLi increased maximally by 97% +/- 13 (SE) and CLdyn decreased maximally by 32% +/- 2. In both species, initial capsaicin injections (CAP1) caused a long latency (time to peak heart rate 26.8 +/- 2 and 20 sec +/- 2.5) increase in heart rate (40% +/- 11 and 20.1% +/- 8.2 for the newborn dog and pig respectively). In the dog, but not the pig, capsaicin responses after the ACh trial (CAP2 and CAP3) caused a short latency bradycardia while the long latency tachycardia continued to be expressed in both species. The maximal changes in RLi and CLdyn, and the bradycardia, were reduced (i.e. desensitized) by 36%, 53% and 63% respectively if capsaicin injection was repeated within 5 min. Muscarinic blockade with atropine abolished the bronchoconstrictor and bradycardia responses to capsaicin but had no effect on the tachycardia. We conclude that the newborn possesses the neural circuitry to mount a bronchoconstrictor response to C-fibre stimulation. We speculate that the response is designed to reduce dead space and stabilize highly compliant airways of the newborn during the rapid shallow breathing that is typically associated with C-fibre stimulation.

Nonadrenergic noncholinergic neurotransmitter of feline trachealis: VIP or nitric oxide?

We tested the hypothesis that vasoactive intestinal peptide (VIP) or nitric oxide (NO) is the nonadrenergic noncholinergic (NANC) neurotransmitter in feline trachealis. Isometric tension was measured in trachealis (open or closed tracheal rings) in vitro. Propranolol (10 microM) and atropine (1 microM) were present throughout the experiment, and smooth muscle tone was increased to 60-90% maximal with 5-hydroxytryptamine. We used three methodologies to reduce the relaxation function of VIP, which in turn should reduce NANC-mediated relaxation. 1) The putative VIP antagonist peptide T (10 microM) did not affect VIP concentration-response curves or electrical field stimulation- (EFS) induced NANC responses. 2) Incubation of tissue in specific VIP antiserum (16 h at 4 degrees C) did not reduce EFS-induced NANC relaxations relative to tissue incubated in normal rabbit serum (P > 0.05). On the basis of our passive immunization techniques, it is not possible to absolutely reject VIP as the NANC transmitter. We speculate that nonspecific peptidases present in normal serum and VIP antiserum reduce EFS-induced responses similarly. 3) VIP desensitization, confirmed by a significant rightward shift (P < 0.01) in the VIP concentration-response curve, was achieved by exposing tissues (n = 11) to 1.0 microM VIP for 30 min. Desensitization did not reduce the EFS-induced NANC relaxatory response (P < 0.05) compared with control tissues, suggesting that VIP is not the NANC mediator.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of vagal stimulation on the distribution of inspired gas in the lungs

We investigated the direct effects of efferent vagal activity on the distribution of inspired gas by stimulating the vagus nerve of one lung and measuring the topographic distribution of a radioactive tracer (133Xe) to both lungs. The distribution of inspired (133Xe) boli was measured with NaI scintillation detectors placed apex-base over each posterior lung of intubated, paralyzed, anesthetized dogs. In 7 supine dogs vagal stimulation reduced the distribution of rapidly insufflated 133Xe boli (flow greater than 2.5 L/s) to the test lung (P less than 0.02), but not when boli were insufflated slowly (flow less than 0.5 L/s), suggesting that vagal stimulation affects pulmonary gas distribution primarily by increasing airway resistance and not through changes in lung compliance. The effect of vagal stimulation on the regional apex-base distribution of inspired gas (greater than 2.5 L/s) was measured in 7 supine and 5 upright dogs. In the supine position, vagal stimulation did not change the uniform apex-base bolus distribution, whereas in the upright position less of the bolus was distributed to the middle and lower lung regions (P less than 0.043), compared to control measurements. This indicates that the regional effects of vagal stimulation on the distribution of inspired gas are uniform in the supine position, but that vagal stimulation alters the distribution of inspired gas when the apex-base pleural pressure gradient is increased.

Airway smooth muscle contraction at birth: in vivo versus in vitro comparisons to the adult

It is clear from the literature that considerable postnatal development occurs in the contractile properties of skeletal and cardiac muscle. Nevertheless, few studies have focused on developmental changes in airway smooth muscle or on the functional capabilities of airway innervation in the newborn. Conclusions about force generation, based on measurements of pulmonary mechanics during stimulation of the vagus nerves, suggest that the newborn possesses a reduced capability to narrow airway diameter relative to the adult. This reduced in vivo response is accompanied by a reduction in maximal force generating capabilities when compared on the basis of force per unit tissue cross-sectional area (stress) in vitro. However, studies of porcine airways suggest that such a finding may simply reflect a reduction in the relative amount of contractile protein (myosin heavy chain) as seen in fetal or preterm smooth muscle. Thus, comparisons based on force normalized per cross-sectional area of myosin alter conclusions from one in which fetal tracheal smooth muscle generates less maximal force than the adult, to one in which the fetal trachea has greater contractile capabilities. Interestingly, comparisons of maximal isometric force in bronchial smooth muscle between different age groups remain unaffected when myosin heavy chain normalization is applied. Finally, there appears to be an age at which maximal force is significantly greater than at any other age, independent of the amount of smooth muscle (determined morphologically), smooth muscle myosin content, or myosin isoform. Whether this enhanced in vitro response is reflected in vivo, or is counteracted by other physiological mechanisms, remains to be seen.

Dexamethasone therapy for bronchopulmonary dysplasia: improved respiratory mechanics without adrenal suppression

The purpose of the present study was to examine the pattern of changes in respiratory system mechanics induced by dexamethasone (Dex) in infants with bronchopulmonary dysplasia (BPD) and to determine whether dosages that produce these changes induce adrenal suppression. We examined mechanics in seven ventilator-dependent premature infants (age, 33 +/- 4.8 days) with BPD, before and daily during Dex therapy. Dex (0.5 mg/kg/day) was given intravenously for 7 days unless complications necessitated early termination. Respiratory system resistance (Rrs) and compliance (Crs) were measured by the passive expiratory flow-volume technique during the course of dexamethasone therapy or until extubation. Adrenocorticotrophic hormone (ACTH) stimulation tests were done at baseline and following Dex therapy to evaluate adrenal function. Dex therapy caused a 77 +/- 18% increase in Crs (from 0.97 +/- 0.09 SEM mL/cmH2O to 1.6 +/- 0.16 mL/cmH2O; P less than 0.025) and a 33 +/- 5% decrease in Rrs (from 0.20 +/- 0.02 cmH2O/mL/s to 0.14 +/- 0.01 cmH2O/mL/s; P less than 0.01). Concurrently, ventilator rate, mean airway pressure, and FIO2 all decreased significantly (P less than 0.025). Extubation occurred later in infants with the lowest Crs and highest Rrs at baseline. At extubation, all Crs values were greater than 1.33 mL/cmH2O and Rrs values were less than 0.15 cmH2O/mL/s. Systolic blood pressure increased from 61 +/- 6.3 mmHg to 84 +/- 17 mmHg, 72-96 h after the start of Dex (P less than 0.025). There were no episodes of culture-positive sepsis. Neither basal nor ACTH-stimulated levels of cortisol were suppressed as a result of Dex therapy (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Bronchodilator response to ipratropium bromide in infants with bronchopulmonary dysplasia

Although the muscarinic antagonist Ipratropium bromide is used clinically as a bronchodilator in infants ventilated because of bronchopulmonary dysplasia (BPD), no studies have compared the response or efficacy of different dosages or its effectiveness in combination with beta-adrenergic agonists. We measured the response of respiratory system mechanics in 10 ventilated infants (25 +/- 2 days of age) to 75, 125, and 175 micrograms ipratropium bromide (IB), 125 micrograms IB plus 0.04 mg salbutamol (SAL), 175 micrograms IB plus 0.04 mg SAL, and saline vehicle, delivered via nebulizer into the ventilator circuit. Respiratory system resistance (Rrs) and compliance (Crs) were measured by the passive flow-volume technique. Rrs and Crs were measured before and at 1 to 2 h and at 4 h after delivery of the five drug dosages or saline. All six studies were completed within a 72-h period. Saline had no significant effect on mechanics. Significant responses to ipratropium alone were seen only after 175 micrograms where Rrs decreased 20 +/- 3% (SEM) (p less than 0.05) at 1 to 2 h and 16 +/- 5% (p less than 0.05) at 4 h. After 125 micrograms IB + SAL and 175 micrograms IB + SAL, Rrs was significantly decreased both at 1 to 2 h and at 4 h, and Crs was significantly increased 20 +/- 6% and 20 +/- 4%, respectively, at 1 to 2 h. The greatest decrease in Rrs (26 +/- 6%) was seen 1 to 2 h after 175 micrograms IB + salbutamol.(ABSTRACT TRUNCATED AT 250 WORDS)

Vagal cholinergic innervation of the airways in newborn cat and dog

Although several studies have examined the pulmonary response to muscarinic agonists in the newborn, none has addressed the functional capabilities or "maturity" of vagal innervation to airway smooth muscle in the newborn. The purpose of the present study was to provide a quantitative analysis of the ability of vagal excitatory innervation (encompassing the pre- and postganglionic fibers, airway ganglia, and airway smooth muscle) to alter pulmonary mechanics in the newborn. We measured the changes in pulmonary mechanics elicited by electrical stimulation of the vagus nerves in 20 newborn cats and 18 puppies anesthetized with chloralose urethan. Animals were tracheotomized and ventilated (chest open), and the cervical vagus nerves were sectioned and placed on stimulating electrodes. Animals were placed in a flow plethysmograph, and mean inspiratory resistance (RL,I) and dynamic compliance were measured on a breath-by-breath basis. In each animal RL,I increased, dynamic compliance decreased, and heart rate slowed during 10 s of vagal stimulation at frequencies ranging from 2 to 20 pulses/s. At each stimulus frequency there was a spectrum of responses with respect to the percent change in RL,I. At 15 pulses/s there was a fourfold difference in the RL,I response of the most- and least-sensitive animals. In both species, higher stimulus frequencies caused greater increases in RL,I; at 2 pulses/s RL,I increased on average approximately 40%, compared with approximately 250% at 20 pulses/s. The increase in RL,I was similar in the kitten and puppy at stimulus frequencies of 6 and 15 pulses/s but was less in the kitten at 2 pulses/s (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Compliance of the respiratory system in infants born at high altitude

Populations living at high altitude are known to have a number of distinctive physiologic traits, including an increase in lung volume and compliance. We asked whether the factors that result in the increased compliance of high altitude natives were sufficiently expressed in utero that an increase in respiratory system compliance (Crs) could be detected at birth. Measurements were performed at about 1 day after birth on 34 infants born in La Paz, Bolivia (3,600 m, Pb about 495 mm Hg) and 36 born in Santa Cruz (400 m, Pb about 735 mm Hg). All infants were full-term and healthy, with body weights of at least 2,700 g. We measured Crs from expirations within the tidal volume range by the multiple occlusion method. Breathing pattern was measured from the spirometric record, and an index of chest wall distortion was obtained from the ratio of volume and abdominal displacement during spontaneous breathing and relaxations against closed airways. Rib cage and abdomen dimensions did not differ between the two groups. Crs values in Santa Cruz were similar to those previously obtained in Montreal and in other Caucasian infant populations at low altitudes. Crs was 33% and Crs/kg 37% greater (p less than 0.001) in the high altitude group, which included equal numbers of Amerindians and Mestizos of European ancestry. Dynamic elevation of the end-expiratory level was similar in both groups. Ventilation/kg and the distortion ratio were slightly yet significantly higher in the high altitude infants, suggesting an increased ventilatory drive.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of subfornical organ stimulation on respiration in the anesthetized rat

The studies reported here have demonstrated that electrical stimulation in the subfornical organ of the urethane-anesthetized rat elicits augmented breaths in over 90% of animals tested. Similar stimulation in immediately adjacent anatomical regions such as the hippocampal commissure was without effect. Detailed analysis of respiratory timing revealed no other significant respiratory effects of such subfornical stimulation.

Muscle-fiber architecture, innervation, and histochemistry in the diaphragm of the cat

Previous anatomical descriptions of the diaphragm have contained several contradictory findings. To validate and extend the previous work, diaphragmatic architecture, histochemistry, and end-plate distribution were examined by use of a combination of anatomical methods, including fiber microdissections, cholinesterase staining, and enzyme histochemistry. Microdissections showed that muscle-fiber fascicles throughout the diaphragm contain both long fibers that run from origin to insertion and shorter fibers with intrafascicular terminations. Fibers with intrafascicular terminations were particularly common in the costal diaphragm, where they accounted for the majority of sampled fibers. The heterogeneity of fiber length was reflected in the pattern of end-plate banding. Cholinesterase studies showed that fiber fascicles in cat and kitten diaphragms were crossed by two to four end-plate bands distributed in discontinuous arrays across the width of the muscle. A similar pattern of multiple banding was also demonstrated in the adult and neonatal dog. However, rat and rabbit diaphragms had only a single, continuous end-plate band. Histochemical studies of fiber types in different parts of the feline diaphragm showed that costal, crural, and sternal subregions had similar overall proportions of fiber types. However, type SO (slow oxidative) fibers were distributed more densely on the thoracic than the abdominal surface of costal and crural, but not sternal subregions. Type SO fibers were also concentrated in fiber fascicles bordering the esophageal hiatus.

Nonadrenergic inhibitory innervation to the airways of the newborn cat

Vagal, nonadrenergic inhibitory system (NAIS) innervation to airway smooth muscle has been demonstrated in adults of several species, including humans. However, the functional status of this system in newborns is not known. The NAIS of intestinal smooth muscle has been demonstrated in newborns and develops in parallel with cholinergic innervation (14). Since the lung is derived embryologically from the foregut and cholinergic innervation is operative at birth, we tested the hypothesis that NAIS innervation to the airways is functional in newborn cats. Nineteen cats (2-11 days of age) were anesthetized with chloralose-urethan, and a tracheal cannula was inserted. The chest was opened and the animals were mechanically ventilated. The cervical vagus nerves were separated from the sympathetics, cut, and placed on stimulating electrodes. Mean inspiratory resistance (RL, I) and dynamic compliance (Cdyn, L) were measured on a breath-by-breath basis. Atropine and propranolol were administered (2 mg/kg iv) to block cholinergic and adrenergic pathways, respectively. Subsequently, serotonin infusion was used to increase RL, I approximately 150%. Stimulation (10 s) at frequencies ranging from 2 to 20/s caused a slow-onset (30 s to peak) long-lasting decrease in RL, I and a much smaller increase in Cdyn, L. The magnitude and duration of the bronchodilation increased with stimulus frequency to a plateau at approximately 15/s. At a stimulus frequency of 2/s, RL, I decreased 11 +/- 1.9 vs 36 +/- 4.8% (SE) at 20/s, whereas Cdyn, L increased 2 +/- 1.1 vs. 6 +/- 1.7%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Motor unit territories supplied by primary branches of the phrenic nerve

Recent studies have demonstrated that, under certain circumstances, the diaphragm does not contract as a homogeneous unit. These observations suggest that motor units may not be randomly distributed throughout the muscle but confined to localized subvolumes. In the present study, electromyographic (EMG) and glycogen depletion methods were combined to investigate the organization of motor units supplied by the primary branches of the phrenic nerve in the cat. Four primary branches are generally present, one branch to the crus and three branches to the sternocostal region. The gross motor-unit territory of each of the four phrenic primary branches was determined by stimulating each nerve separately, while recording from nine EMG electrodes distributed over the hemidiaphragm. Stimulation of the crural branch evoked activity in the ipsilateral crus, whereas stimulation of each of the remaining branches evoked activity in discrete but overlapping areas of the sternocostal diaphragm. A more precise analysis of the distribution and borders of the motor territories was obtained by mapping regions depleted of muscle glycogen due to stimulation of each primary branch for 90 min. Glycogen depletion results closely matched the EMG findings of a localized distribution of motor units served by single primary branches. Stimulation of the crural branch typically caused depletion of the ipsilateral crus, whereas the sternocostal branches each served a striplike compartment. In the majority of cases, the borders of the sternocostal compartments were relatively abrupt and consisted of a 1- to 2-mm transition zone of depleted and nondepleted fibers. These studies demonstrate that motor unit territories of the primary branches of the phrenic nerve are highly delineated. This compartmentalization provides the central nervous system with the potential for a more precise regional motor control of costal and crural diaphragm than previously suspected.

Lung mechanics and activity of slowly adapting airway stretch receptors

Transpulmonary pressure is thought to be closely associated with slowly adapting mechanoreceptor activity. The transpulmonary pressure required to inflate the lung to a given volume depends on pulmonary compliance: for equal tidal volumes less pressure will be required if compliance is higher. Therefore, an inverse relationship is expected between receptor activity and lung compliance for equal changes in lung volume. We have studied 33 slowly adapting airway stretch receptors (SARs) in anaesthetized, vagotomized, paralysed and artificially ventilated dogs, with the chest open, at constant tidal volume and frequency. After lung compliance had been increased by hyperinflation, all of the ten tracheal receptors studied and fourteen of the 23 intrapulmonary receptors reduced their activity. Of the remaining intrapulmonary receptors five increased their activity and four were unaffected. Our results indicate that, although airway stretch receptor discharge is usually related to transpulmonary pressure, this relationship is not always present in the case of peripherally located endings; this is possibly due to a discrepancy between local transmural pressure and overall transpulmonary pressure. Thus, in addition to the well described independence of SAR discharge frequency from lung volume, the activity of SARs having peripheral locations is not always predictable on the basis of changes in transpulmonary pressure.

Lung mechanics and activity of slowly adapting airway stretch receptors

Transpulmonary pressure is thought to be closely associated with slowly adapting mechanoreceptor activity. The transpulmonary pressure required to inflate the lung to a given volume depends on pulmonary compliance: for equal tidal volumes less pressure will be required if compliance is higher. Therefore, an inverse relationship is expected between receptor activity and lung compliance for equal changes in lung volume. We have studied 33 slowly adapting airway stretch receptors (SARs) in anaesthetized, vagotomized, paralysed and artificially ventilated dogs, with the chest open, at constant tidal volume and frequency. After lung compliance had been increased by hyperinflation, all of the ten tracheal receptors studied and fourteen of the 23 intrapulmonary receptors reduced their activity. Of the remaining intrapulmonary receptors five increased their activity and four were unaffected. Our results indicate that, although airway stretch receptor discharge is usually related to transpulmonary pressure, this relationship is not always present in the case of peripherally located endings; this is possibly due to a discrepancy between local transmural pressure and overall transpulmonary pressure. Thus, in addition to the well described independence of SAR discharge frequency from lung volume, the activity of SARs having peripheral locations is not always predictable on the basis of changes in transpulmonary pressure.

Differential effects of CO2 and hypoxia on bronchomotor tone in the newborn dog

We compared the effects of hypoxia and hypercapnia on pulmonary mechanics in the newborn dog. Animals were anesthetized with a mixture of chloralose/urethane, paralyzed and ventilated with the chest open. Following an inflation to control volume history, mean inspiratory resistance (RLi) and dynamic compliance (CLdyn) were measured on a breath-by-breath basis during ventilation with control (FIO2 = 0.4), hypoxic (FIO2 = 0.1) and hypercapnic (FICO2 = 0.05) gas mixtures. Hypercapnia increased RLi 63% (n = 9) while hypoxia increased RLi in only 1/9 animals. Neither gas mixture changed CLdyn compared to control. The response to hypercapnia and the lone hypoxic response were eliminated by denervation of the airways by atropine administration or vagotomy. Following airway denervation hypoxia caused a small but statistically significant fall in CLdyn compared to the denervated control. These findings demonstrate that the newborn dog is capable of reflexly increasing bronchomotor tone and that vagal efferent innervation to the airways is functional at birth. Our data also suggest that in the newborn, central chemoreceptors are more effective than peripheral chemoreceptors in altering vagal tone to airway smooth muscle. Increased bronchomotor tone with hypercapnia may help to prevent dynamic compression of the airways.

Temporomandibular joint ankylosis in rheumatoid arthritis. A case report

Rheumatoid arthritis can result in ankylosis of the temporomandibular joint. The objectives of treatment are to maintain ascending mandibular ramus height, improve joint function and prevent occlusal-facial deformity. These are achieved by the use of a glenoid fossa-condylar total joint replacement prosthesis.

Effects of hypoxia on lung mechanics in the newborn cat

The present study was designed to investigate the effects of hypoxia on lung mechanics in the newborn cat and to determine if vagal efferent innervation to the airways is involved in the response. We studied 11 animals, aged 2-7 days, anesthetized with a mixture of chloralose-urethane administered intraperitoneally. A tracheal cannula was inserted just below the larynx and following paralysis (pancuronium bromide), mechanical ventilation was initiated. A pneumothorax was created by a midline thoracotomy and an end-expiratory load was applied to maintain functional residual capacity. Animals were placed in a flow plethysmograph from which measurements of transpulmonary pressure, flow, and volume, mean inspiratory resistance, and dynamic compliance of the lung were calculated. The experimental protocol consisted of a series of 8-min trials, each preceded by a controlled volume history. The hypoxia challenge was composed of 1 min of ventilation with 40% O2, followed by 5 min exposure to 10% O2 and 2 min of recovery. In the majority of animals (7 out of 11), hypoxia had no effect on lung mechanics compared with control trials. Four animals responded to hypoxia with an increase in resistance and a decrease in compliance. Resistance remained elevated throughout the hypoxia with an average maximal increase of 47.2 +/- 22.2% (SD). Dynamic compliance was significantly decreased at the 2nd, 3rd, and 4th min only of hypoxia. Bilateral vagotomy abolished the response in the four animals and hypoxia had no effect on mechanics postvagotomy. Our data suggest that in most cases changes in lung mechanics do not play a causal role in the biphasic ventilatory response to hypoxia seen in the newborn.

Laryngeal cold receptors

We have previously demonstrated the presence of specific laryngeal 'flow' receptors activated independently of transmural pressure. This study considers the operational characteristics of these endings. In 15 anesthetized dogs we recorded single unit action potentials from the peripheral cut end of the internal branch of the superior laryngeal nerve. All the 30 laryngeal 'flow' receptors studied showed an inspiratory modulation when the dog was breathing room air at 26 degrees C and 55% relative humidity (laryngeal temperature approximately equal to 34 degrees C) through the upper airway. All the receptors became silent when the temperature of the inspired air was raised to 36-40 degrees C, 100% relative humidity (laryngeal temperature between 35 and 38 degrees C) and increased their activity when the temperature in the larynx was decreased either by lowering the temperature or the humidity of the inspired air. Fourteen laryngeal 'flow' receptors were tested with a steady flow of air, directed through the isolated in vivo larynx, at different temperatures and saturated with water vapor. Their discharge rate was found to be inversely related to laryngeal temperature (from 35 to 25 degrees C) and independent of airflow. Their rate of adaptation indicates a high dynamic sensitivity. In the isolated larynx preparation these receptors were activated by airflow in both inspiratory and expiratory directions provided that laryngeal temperature was lower than 35 degrees C. We conclude that the previously described laryngeal 'flow' receptors operate as thermoreceptors activated by cooling.

Reflex effects and receptor responses to upper airway pressure and flow stimuli in developing puppies

We studied the changes in breathing pattern due to pressure and airflow stimuli applied to isolated upper airway in nine 1- to 14-day-old and six 29- to 35-day-old anesthetized puppies breathing through a tracheostomy. Negative-pressure and flow, both inspiratory and expiratory, altered the breathing pattern only in the 1- to 14-day-old puppies, whereas positive pressure was ineffective in both age groups. Negative pressure caused apnea in 12% of the trials, expiratory flow in 18%, and inspiratory flow in 21%. When apnea did not occur there was a significant prolongation of inspiratory and expiratory time and a decrease of tidal volume of the first breath following the application of negative pressures. Section of the superior laryngeal nerves abolished the responses to pressure and flow. In nine 1- to 14-day-old and four 29- to 35-day-old puppies we recorded the activity of single units of the superior laryngeal nerves. We identified specialized receptors responding to pressure (68.5%), flow (2.7%), and contraction of upper airway muscles (drive, 28.8%). All types of receptors had a prevalent inspiratory-related activity. In the younger age group the discharge rate of pressure receptors at comparable negative pressures was lower than in older puppies. The strong inhibitory influences originating from the upper airway in the early stages of development presumably reflect different integrative properties of the central nervous system.

Respiratory afferent activity in the superior laryngeal nerves

This study evaluates the afferent activity in the superior laryngeal nerve (SLN) during breathing as well as during occluded inspiratory efforts. Experiments were performed in 11 anesthetized and spontaneously breathing dogs. Electroneurographic activity was recorded from the peripheral cut end of the SLN and, in 3 dogs, also from the contralateral vagus nerve. A tracheal cannula with a side arm allowed the bypass of the larynx during breathing and occluded efforts. A clear inspiratory modulation was present in all experimental conditions. Both peak and duration of the SLN activity decreased (87% and 89%) when breathing was diverted from the upper airway to the tracheostomy. Peak and duration of the SLN activity (as % of upper airway breathing) increased during occluded efforts; however, the increase was greater when the larynx was not by-passed (peak = 118% vs 208%, duration = 143% vs 178%). Section of the ipsilateral recurrent laryngeal nerve reduced the inspiratory modulation. Vagal afferent activity increased equally during tracheostomy and upper airway breathing and decreased markedly during tracheal and upper airway occlusions. Our results indicate that collapsing pressure in the larynx is the major stimulus in activating laryngeal afferents.

Laryngeal pressure receptors

We studied the response characteristics of laryngeal pressure receptors in anesthetized dogs, breathing through a tracheal cannula, by recording single unit action potentials from the peripheral cut end of the internal branch of the superior laryngeal nerve. The larynx, with the rest of the upper airway, was isolated and cannulated separately for the application of distending and collapsing pressures. We identified receptors responding to either negative or positive pressure and a few responding to both. All these receptors showed a marked dynamic sensitivity and had the characteristics of slowly adapting mechanoreceptors. The majority of pressure receptors were active at zero transmural pressure and the gain of their response to pressure was higher at lower values, suggesting a role for these receptors in eupnea. Reflex alterations in breathing pattern and upper airway muscle activity during upper airway pressure changes, previously reported, are presumably mediated by the receptors described here. Moreover, these receptors may play a role in certain pathological states, such as obstructive sleep apnea, in which the upper airway is transiently subjected to large collapsing pressure.

Vagal control of the breathing pattern and respiratory mechanics in the adult and newborn rabbit

In an attempt to define the role of SARs on the breathing pattern and respiratory mechanics, we have studied adult rabbits anaesthetised, supine and tracheostomised during air breathing (A), after SO2 breathing (200 ppm for a period long enough to abolish the apnea following lung inflation, 10-30 min) (S), and after bilateral vagotomy (V). Tidal volume and inspiratory time increased, while breathing frequency decreased from A to V. The effects of S depended upon the type of anaesthesia used, with a definite increase in volume and a drop in frequency in the urethane anaesthetized animals and a trend toward opposite changes with barbiturate anaesthesia. Total and lung compliance increased and total pulmonary resistance decreased from A to S; no further changes were observed with V. The combined changes in breathing pattern and mechanics decreased the respiratory work per minute from A to V, suggesting that the primary concern of the vagal afferent information is to regulate the breathing pattern. Finally, in newborn rabbits it was not possible to block the apnea following lung inflation even with SO2 concentration up to 330 ppm for 30 min. From A to V the changes in breathing pattern and compliance were similar to those observed in the adult.

Airway receptor activity in the developing opossum

Characteristics of airway receptor discharge were evaluated in pentobarbital-anesthetized, gallamine-paralyzed, artificially ventilated, open-chest suckling and weanling opossums (Didelphis marsupialis). Animals were tested with single-unit vagal recordings at 20, 30, 55, and 90 days of age; results were compared with previous data from adults. Rapidly adapting airway receptors ( RARs ) comprised a smaller percentage of the sampled population at 20 and 30 days of age than in older groups. The static firing properties of slowly adapting airway receptors (SARs) were examined at 0-20 cmH2O transpulmonary pressure (Ptp). At the higher Ptp levels, average receptor discharge rates increased with increasing age; these results are similar to findings in placental mammals. At 5 cmH2O, however, only the 20-day-old animals exhibited reduced rates of SAR discharge. The dynamic response of SARs in 20- and 30-day-old animals was reduced compared with adult values, as measured by the adaptation of their discharge frequencies; however, the reduction was proportional to the lower receptor firing rates. About 80% of tested SARs were inhibited by CO2 at 20 and 55 days; similar results were obtained in adults. Other results have shown that morphologic development of the vagi in opossums at 50 days of age compares with placental mammals similarly studied at birth. In contrast, the static SAR discharge in the 50-day-old opossum at low Ptp (i.e., 5 cmH2O) is similar to that observed in adults, whereas the newborn placental mammal has a greatly reduced SAR firing rate. This suggests that early utilization of the lungs can contribute to functional maturation of airway receptors.

Laryngeal receptors responding to transmural pressure, airflow and local muscle activity

The larynx has a rich sensory supply which is the main source of several respiratory reflexes. These reflexes, that influence both the patency of the upper airway and the pattern of breathing, are related to transmural pressure and/or airflow in the upper airway. Yet hardly any information is available on the response of laryngeal mechanoreceptors to transmural pressure and airflow. We recorded action potentials from single fibers separated from the superior laryngeal nerve of anesthetized dogs, breathing spontaneously either through a tracheostomy or the upper airway. The airway could be occluded above or below the larynx. On the basis of their behavior during tracheostomy breathing, upper airway breathing, tracheal occlusion and upper airway occlusion, laryngeal mechanoreceptors were classified as pressure receptors, flow receptors or 'drive' receptors (stimulated by the respiratory activity of upper airway muscles). Pressure receptors were encountered most frequently, representing 63.6% of our sample of 110 receptors, 'drive' receptors constituted 21.8% and flow receptors the remaining 14.6%. Our findings indicate that, even though the three types of receptors differ in sensory modality, they concur in exhibiting a predominant activity during inspiration. In fact, 65% of all receptors are active during eupneic inspiration. Moreover, their activity increases markedly during upper airway obstruction.

Neonatal pattern of breathing following cesarean section: epidural versus general anesthesia

We tested the hypothesis that different anesthetic techniques for elective cesarean section would be reflected in the pattern of breathing and its control after birth. The pattern of breathing, including tidal volume, total breath duration (TTOT), minute ventilation, inspiratory (TI) and expiratory times, TI/TTOT ratio, and mouth occlusion pressure, was measured in 27 infants delivered by elective cesarean section during maternal epidural (lidocaine-carbon dioxide-epinephrine, n = 19) or general anesthesia (66% oxygen in N2O and 0.5% halothane, n = 8) at 10, 60, and 90 min and 3-5 days of age. Neonatal acid-base values and Apgar scores were within normal limits in both groups of infants. In general, at any given age the values of the respiratory parameters measured and their variability were similar between the two groups of infants. These findings indicate that the pattern of breathing after birth is not different following epidural or general anesthesia, and on the basis of our measurements, both epidural or general anesthesia appeared equally suitable for elective cesarean section.