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PubMed1985

Pulmonary gas exchange and diaphragmatic position. Effect of tonic phrenic stimulation compared with that of increased airway pressure.

The influence of diaphragmatic position on abnormal gas exchange has been examined to investigate the theory that the impairment in gas exchange in anaesthetized man is caused by disturbance of diaphragmatic mechanics, resulting in abnormalities of dependent lung ventilation. A gas exchange abnormality, probably caused by airway closure in the dependent regions of the lung, was induced in anaesthetized rabbits by reducing lung volume to residual volume and allowing passive re-expansion. The effects on gas exchange of increases in lung volume produced by two methods--the application of positive end-expiratory pressure (PEEP) and phrenic nerve stimulation (PNS)--were compared. Both methods were adjusted to give the same increase in lung volume. PNS was found to produce greater caudal movement of the diaphragm than PEEP, particularly in the dependent regions. PNS also improved gas exchange significantly more than PEEP. These findings support the theory that alterations in diaphragmatic mechanics during anaesthesia contribute to the gas exchange impairment in man.

Animals↗
PubMed1990

Congenital diaphragmatic hernia: impact of prostanoids in the perioperative period.

A prospective study of 10 neonates with congenital diaphragmatic hernia and five controls to determine the importance of prostanoid concentrations perioperatively and the relation with persistent pulmonary hypertension (PPH) is reported. In neonates with congenital diaphragmatic hernia postoperative concentrations of the vasoconstrictor thromboxane B2 rose significantly and were higher during episodes of PPH; this rise may provoke PPH and subsequent right to left shunting.

6-Ketoprostaglandin F1 alpha↗
PubMed1996

Regulation of ventilatory muscle blood flow.

The ventilatory muscles perform various functions such as ventilation of the lungs, postural stabilization, and expulsive maneuvers (e.g., coughing). They are classified in functional terms as inspiratory muscles, which include the diaphragm, parasternal intercostal, external intercostal, scalene, and sternocleidomastoid muscles; and expiratory muscles, which include the abdominal muscles, internal intercostal, and triangularis sterni. The ventilatory muscles require high-energy phosphate compounds such as ATP to fuel the biochemical and physical processes of contraction and relaxation. Maintaining adequate intracellular concentrations of these compounds depends on adequate intracellular substrate levels and delivery of these substrates by arterial blood flow. In addition to the delivery of substrates, blood flow influences muscle function through the removal of metabolic by-products, which, if accumulated, could exert negative effects on several excitatory and contractile processes. Skeletal muscle substrate utilization is also dependent on the ability to extract substrates from arterial blood, which, in turn, is accomplished by increasing the total number of perfused capillaries. It follows that matching perfusion to metabolic demands is critical for the maintenance of normal muscle contractile function. In this article, I review the factors that influence ventilatory muscle blood flow. Major emphasis is placed on the diaphragm because a large number of published reports deal with diaphragmatic blood flow. The second reason for focusing on the diaphragm is because it is the largest and most important inspiratory muscle.

Animals↗
PubMed1998

Reproducibility of twitch mouth pressure, sniff nasal inspiratory pressure, and maximal inspiratory pressure.

Twitch mouth pressure (Pmo,tw) during magnetic phrenic nerve stimulation and sniff nasal inspiratory pressure (SNIP) were recently proposed as alternative noninvasive methods for assessing inspiratory muscle strength. This study aimed to compare their reproducibility with maximal inspiratory pressure (MIP) in normal subjects. Ten healthy subjects were studied at functional residual capacity in semirecumbent position. Cervical magnetic phrenic nerve stimulation was performed during gentle expiration against an occlusion incorporating a small leak. Constancy of stimulation was controlled by recording diaphragmatic electromyogram. Within and between-session reproducibility of pressure were studied for Pmo,tw, SNIP, and MIP. The subjects were studied during a session of 10 manoeuvres repeated after 1 day and 1 month. The mean values were 16 cmH2O for Pmo,tw, 118 cmH2O for SNIP, and 115 cmH2O for MIP. For the three tests, the within subject variation was small in relation to between-subject variation, with the intraclass correlation coefficient ranging 0.79-0.90 for Pmo,tw, 0.85-0.92 for SNIP, and 0.88-0.92 for MIP. At 1 day interval, the coefficient of repeatability (2 SD of differences) was 3.6 cmH2O for Pmo,tw, 32 cmH2O for SNIP and 28 cmH2O for MIP. At 1 month interval, the coefficient of repeatability was 5.8 cmH2O for Pmo,tw, 23 cmH2O for SNIP and 21 cmH2O for MIP. We conclude that the within session reproducibility of the new tests twitch mouth pressure and sniff nasal inspiratory pressure is sufficient to be clinically useful. For sniff nasal inspiratory pressure, the between session reproducibility established after 1 day was maintained after 1 month. For twitch mouth pressure, the between session reproducibility declined slightly after 1 month. These characteristics should be considered when using these methods to follow an individual patient over time.

Adult↗
PubMed1976

Differences between right and left lateral chest radiographs.

Differences between 150 normal right lateral chest teleroentgenographs and 150 left laterals (infants, children, and adults) were evaluated and determined to be greater than has been generally appreciated. On the left lateral view the left leaf is distinguished from the right leaf by the following generalizations: anteriorly the left leaf is lower; posteriorly it is higher as is its costrophrenic sulcus; it intersects the relatively flattened right leaf near the posterior heart border; the stomach bubble and/or colon are immediately subjacent; there is no segmental obliteration by the inferior vena cava as there often is with the right leaf; in adults the outline of the left leaf is often sharper. When both major fissures can be identified, the left almost always intersects its diaphragmatic leaf posterior to and more vertically than the right fissure.

Adult↗
PubMed2004

[A successful weaning from mechanical ventilation by diaphragmatic plication for unilateral diaphragmatic paralysis].

A patient with unilateral diaphragmatic paralysis (UDP) after cardiac surgery, commonly extubated without any troubles, encounters a serious fetal respiratory complication in a rare case. We had a case of a 68-year-old man under long term mechanical ventilation (MV) because of UDP and phrenic nerve injuries after the replacement of the ascending aorta. After this operation he suffered from mediastinal infection and needed MV for a few days. Thereafter, he was extubated successfully and returned to the ward, but his chest X-p showed right diaphragmatic elevation. Two days after returning to the ward, he developed dyspnea and tachypnea and received MV for two months. We decided to perform diaphragmatic plication (DP) because of long term MV and difficulty in respiratory weaning. The patient was successfully weaned from MV on the 4th postoperative day of the right DP. Pulmonary function test was improved dramatically. In a case of long term MV due to UDP, DP can be one of effective treatments.

Aged↗
PubMed1998

VATS plication of diaphragmatic eventration.

Diaphragmatic eventration in the adult may be associated with dyspnoea. Video-assisted thoracoscopic surgery (VATS) techniques have been applied to the plication of diaphragmatic eventration in three adult patients. Symptoms and spirometry improved in all patients. Ventilation and perfusion of the affected lung was also improved.

Diaphragmatic Eventration↗
PubMed1982

End-expiratory volume in the rat: effects of consciousness and body position.

Functional residual capacity (FRC), tidal volume (VT), and frequency (f) were compared in 23 rats while either awake and unrestrained or anesthetized. FRC was determined from gas compression with closed airway inside a cone-shaped body plethysmograph. In the awake state (mean +/- SD), FRC was 1.02 +/- 0.22 ml/100 g, VT was 0.38 +/- 0.06 ml/100 g, and f was 142 +/- 22 breaths/min. During anesthesia, FRC decreased (P less than 0.01) to 52.9% of awake values, VT increased (P less than 0.01) to 147.4%, and f decreased (P less than 0.01) to 71.8%, leaving minute ventilation almost unchanged. An additional seven rats were used to examine postural effects on FRC during anesthesia, and in another seven animals pleural pressure changes were monitored. Dynamic lung compliance (0.80 ml . kg-1 X cmH2O-1) was not altered by anesthesia, but the pressure-volume curve was shifted 6 cmH2O higher. Thoracic compression, followed by a time-dependent effect of volume history, may account for the major change in FRC. The remainder of the decrease in FRC may be due to lower breathing frequency, loss of inspiratory muscle activity, and/or less airway resistance after anesthesia. Peak diaphragmatic electromyogram per unit VT was shown to increase almost linearly with FRC, indicating that diaphragmatic efficiency was decreased as lung volume was elevated.

Anesthesia, General↗
PubMed1985

Respiratory load compensation in chronic airway obstruction.

To assess respiratory neuromuscular function and load compensating ability in patients with chronic airway obstruction (CAO), we studied eight stable patients with irreversible airway obstruction during hyperoxic CO2 rebreathing with and without a 17 cmH2O X l-1 X s flow-resistive inspiratory load (IRL). Minute ventilation (VE), transdiaphragmatic pressure (Pdi), and diaphragmatic electromyogram (EMGdi) were monitored. Pdi and EMGdi were obtained via a single gastroesophageal catheter with EMGdi being quantitated as the average rate of rise of inspiratory (moving average) activity. Based on the effects of IRL on the Pdi response to CO2 [delta Pdi/delta arterial CO2 tension (PaCO2)] and the change in Pdi for a given change in EMGdi (delta Pdi/delta EMGdi) during rebreathing, two groups could be clearly identified. Four patients (group A) were able to increase delta Pdi/delta PaCO2 and delta Pdi/delta EMGdi, whereas in the other four (group B) the IRL responses decreased. All group B patients were hyperinflated having significantly greater functional residual capacity (FRC) and residual volume than group A. In addition the IRL induced percent change in delta Pdi/delta PaCO2, and delta VE/delta PaCO2 was negatively correlated with lung volume so that in the hyperinflated group B the higher the FRC the greater was the decrease in Pdi response due to IRL. In both groups the greater the FRC the greater was the decrease in the ventilatory response to loading. Patients with CAO, even with severe airways obstruction, can effect load compensation by increasing diaphragmatic force output, but the presence of increased lung volume with the associated shortened diaphragm prevents such load compensation.

Diaphragm↗
PubMed1991

Effect of dexamethasone on diaphragmatic and soleus muscle morphology and fatigability.

In spite of the extensive use of corticosteroids, its myopathic effect on respiratory muscle is unknown with relation to the dose and duration of therapy. The present study examined the effects of dexamethasone on the morphology and function of respiratory (diaphragm) as compared to skeletal (soleus) muscle. Control rats were compared to those that received low, high and prolonged doses of dexamethasone. Body mass was reduced proportionally to the dose and duration of therapy. Atrophy of the diaphragm was greater than that of the soleus when normalized to body mass. Absolute tension and tension as a function of cross sectional area was significantly (P less than 0.05) less in the diaphragm and soleus at the high and prolonged dosages. Dexamethasone had no effect on fatigability except in the soleus after prolonged treatment. Furthermore, after prolonged therapy, it had converse effects on the Pt and 1/2RT in the diaphragm as compared to the soleus muscle. Dexamethasone improved the recovery times in the diaphragm alone. Our data suggest that dexamethasone weakens the diaphragm and soleus by reducing its mass and apparently also through some effect on the intrinsic contractile apparatus.

Animals↗
PubMed2000

Roles of periaqueductal gray and nucleus tractus solitarius in cardiorespiratory function in the rat brainstem.

Periaqueductal gray (PAG) and nucleus tractus solitarius (NTS) are important centres for regulation of cardiorespiratory function in cats. We aimed to study the effects of specific PAG stimulation on cardiorespiratory parameters in the rat. Microinjection of D, L-homocysteic acid (DLH) into dorsolateral PAG of anaesthetised rats, led to: marked increases in respiratory frequency (RF) and amplitude of diaphragmatic electromyogram, decreases in inspiratory and expiratory durations, and increased blood pressure and heart rate. Following injection of propranolol (150 pmol, 30 nl), a beta-adrenergic antagonist, into the commissural subnucleus of NTS, the DLH-induced increase in RF was markedly attenuated. Inspiratory neurones (late I cells) in NTS were excited upon stimulation of PAG and their increased activity was accompanied by increased RF. The changes in activity of the late I cells in response to stimulation of dorsolateral PAG provide physiological evidence of a link, possibly noradrenergic, between the two nuclei and involvement of the NTS in control of respiratory functions orchestrated by the PAG.

Animals↗
PubMed1999

Abdominal weight and inspiratory resistance: their immediate effects on inspiratory muscle functions during maximal voluntary breathing in chronic tetraplegic patients.

OBJECTIVE: To study the immediate effects of maximal voluntary (MV) breathing, with and without abdominal weight (AW) or inspiratory resistance (IR), on inspiratory muscle functions in chronic tetraplegic patients. DESIGN: A crossover trial design. SETTING: Rehabilitation department of a university hospital. PARTICIPANTS: Nine tetraplegic men injured at the C4 to T1 levels, with a mean duration of injury of 72.8 months. INTERVENTIONS: Each subject performed MV breathing without and with AW load (AWMV breathing) and IR load (IRMV breathing) separately. MAIN OUTCOME MEASURES: Electromyographic (EMG) activity of the inspiratory muscles, mouth pressure, inspiratory flow, and inspiratory volume. RESULTS: AWMV breathing evoked greater diaphragmatic EMG activity, inspiratory flow, and inspiratory volume than did IRMV breathing, although the increase of diaphragmatic EMG activity was not statistically significant. Conversely, IRMV breathing produced greater sternocleidomastoid EMG activity and negative mouth pressure than did AWMV breathing. Both AWMV and IRMV breathing evoked greater inspiratory muscle EMG activity than did MV breathing. CONCLUSION: AW and IR loads have differential immediate effects on the inspiratory muscle functions during MV breathing in patients with chronic tetraplegia, suggesting that these two breathing maneuvers may have dissimilar mechanisms of training in such patients. The muscle EMG activity evoked during MV breathing with AW or IR is greater than that without a mechanical load, implying that mechanically loaded training in tetraplegic patients results in load compensatory adjustments via their respiratory motor output to improve respiratory function.

Abdomen↗
PubMed1994

Determinants of maximal transdiaphragmatic pressure in adults with cystic fibrosis.

To investigate whether diaphragmatic strength could be reduced in cystic fibrosis (CF), and to examine possible mechanisms leading to diaphragmatic weakness, we measured transdiaphragmatic pressure (Pdi), together with lung mechanics, including dynamic "intrinsic" positive end-expiratory pressure (PEEPi,dyn), ventilation, lung volumes, and nutritional status in 15 adult patients with CF in stable clinical condition. Diaphragmatic strength was assessed as the maximum Pdi (Pdimax). Nutritional assessment included the calculation of weight as a percentage of ideal weight for height (Wt/Ht). On average, our 15 CF patients had airway obstruction (FEV1 = 59 +/- 28% predicted) and a small PEEPi,dyn (1 +/- 0.7 cm H2O). Functional residual capacity average 52 +/- 9% of the predicted total lung capacity. The Wt/Ht was normal on average (95%), but with a large range from malnutrition to a good nutritional status (76 to 109%). We found that Pdimax decreased with increasing FRC/TLC percent predicted (r = 0.55, p < 0.05), but more significantly with decreasing Wt/Ht (r = 0.76, p < 0.001). The multiple linear regression analysis for these factors was significant (R2 = 0.70, p < 0.05); however, the partial regression coefficient was significant only for Wt/Ht (p < 0.01). These results suggest that in CF patients, diaphragmatic strength decreases with the progression of the disease, increasing lung volume and worsening nutritional status, and that malnutrition is the strongest determinant of diaphragmatic weakness.

Adolescent↗
PubMed1983

Load compensation in obese patients during quiet tidal breathing.

Seventeen eucapnic massively obese patients and eight normal subjects had their respiratory cycle parameters studied while breathing room air at rest. Despite large variations in the degree of obesity, our patients demonstrated normal mean inspiratory and expiratory flow rates, duty cycles, and minute ventilation. The maintenance of normal mean inspiratory flow rates was found to be dependent on an augmentation of neuromuscular drive (P0.1); furthermore, a strong positive correlation between percentage ideal body weight (i.e., the degree of obesity) and P0.1 was present. The obese were found to partition their tidal volume preferentially to their rib cage compartment, choosing to leave the abdominal compartment relatively immobile. Analysis of the diaphragmatic electromyogram revealed a persistence of activity into early expiration, the length of which also depended on the degree of obesity. These findings suggest that the diaphragm's volume-generating function in the obese is reduced, and furthermore the persistence of its activity in expiration serves to attenuate the rate of expiratory flow. No significant difference in any respiratory cycle parameter was found between simple obesity patients and formerly hypercapnic obese patients.

Adult↗
PubMed1999

Respiratory disturbances during sleep in syringomyelia and syringobulbia.

OBJECTIVE: To determine the frequency and types of abnormalities of respiratory control during sleep in syringomyelia and syringobulbia and to provide a basis to predict patients at risk of sudden death. METHODS: Thirty patients (15 male and 15 female; mean age 39.0 +/- 12.6 years) with communicating syringomyelia were divided into two groups: those with evidence of syringobulbia (17 patients) and those without compromise of the medulla or syringomyelia (13 patients). Patients were studied with pulmonary function studies and polysomnography. Respiratory center sensitivity to CO2 (rebreathing technique) was measured in 9 patients. RESULTS: Severely affected patients had mild-to-moderate restriction and individual patients had bilateral diaphragmatic or vocal cord palsy, abnormal respiratory rhythm, prolonged inspiratory time, or an abnormal respiratory response to CO2. Very prolonged central, obstructive, and mixed sleep apneas with low O2 saturation values and a fixed heart rate were recorded in most patients with syringobulbia. Five patients developed severe respiratory complications and died during a follow-up period of 10 years. Respiratory abnormalities failed to correlate with syrinx size. CONCLUSIONS: Severe abnormalities in respiratory rhythm generation during sleep occur in patients with syringobulbia. The respiratory disturbances are not due to muscle weakness and they are not correlated with the size of the cavity. The combination of dysphagia and dysphonia in patients with longstanding syringomyelia and syringobulbia predicted likelihood of respiratory disturbances during sleep.

Adolescent↗
PubMed1992

Pleural determinants of restrictive lung function and respiratory symptoms in an asbestos-exposed population.

To further define the relationship between asbestos-induced pleural fibrosis and restrictive lung function, we investigated the pleural determinants of respiratory symptoms and restrictive physiology in 1,211 sheet metal workers. We evaluated the relationship between specific components of pleural fibrosis (costophrenic angle involvement, diaphragmatic plaques, width and length of pleural fibrosis, pleural calcification, and the type of fibrosis-circumscribed plaque or diffuse pleural thickening) and both forced vital capacity and respiratory symptoms. We found that costophrenic angle involvement, the width and length of pleural fibrosis, and the presence of either circumscribed plaque or diffuse pleural thickening were each significantly associated with a lower FVC. No consistent relationship was observed between FVC and either diaphragmatic plaques or pleural calcification. However, since the pleural abnormalities were highly collinear, none of these abnormalities alone or in combination predicted the reduction in FVC significantly better than a model that included circumscribed plaques and diffuse pleural thickening. We also investigated the relationship of each component of pleural fibrosis with cough, dyspnea, and chest pain. After controlling for appropriate confounders, a trend toward significance was observed between increased width and length of fibrosis and dyspnea with exertion. Otherwise, these pleural abnormalities were not consistently related to any of the three respiratory symptoms. Our results indicate that although pleural plaques and diffuse pleural thickening and their components are independently associated with a lower FVC, these components of pleural fibrosis do not substantially improve the previously defined relationship between FVC and both circumscribed plaques and diffuse pleural thickening. In addition, a trend toward significance was observed between the width and length of the pleural abnormality and dyspnea while hurrying.

Asbestosis↗