Facilitation-independent response of the diaphragm to cortical magnetic stimulation

Neural diseases are often associated with respiratory muscle disorders. Assessment of the motor pathway from the central nervous system to the diaphragm is therefore highly clinically relevant from a diagnosis and follow-up point of view. Cortical magnetic stimulation (CxMS) combined with surface diaphragm electromyogram (EMGdi) has to date been limited in this application by the need of an underlying voluntary contraction to obtain a diaphragm response (facilitation). This study was performed to verify this point with high-powered stimulators and to describe the pattern of diaphragm response to CxMS. In nine subjects, EMGdi was compared with EMG of the abductor pollicis brevis (APB). CxMS was applied on relaxed muscles. The effects of its decreasing intensity and those of a voluntary contraction were studied. In three subjects, transdiaphragmatic pressure was also measured. CxMS consistently provoked a contraction of the relaxed diaphragm (16.06 +/- 0.64 ms, mean +/- SD). Decreasing stimulation intensity decreased the amplitude and increased the latency of this response. Underlying contractions had opposite effects. Respective behaviors of the diaphragm and APB were similar. It is concluded that CxMS gives access to central motor conduction to the diaphragm without the need for subject cooperation.

Assessment of the motor pathway to the diaphragm using cortical and cervical magnetic stimulation in the decision-making process of phrenic pacing

BACKGROUND

Phrenic nerve pacing is a recognized substitute to positive pressure ventilation via tracheotomy in patients with high cervical cord lesions or central hypoventilation. Although its indications are infrequent, reliable strategies need to be used in the determinations of patients who may benefit from this treatment; contraindications should be carefully respected.

STUDY OBJECTIVES

To determine whether modern and noninvasive means to study the motor pathway to the diaphragm, namely cortical magnetic stimulation (CxMS) and cervical magnetic stimulation (CMS), can contribute to the selection of patients who may benefit from phrenic pacing.

DESIGN AND SETTING

Prospective study (18 months), on a consecutive basis, of patients referred for possible phrenic pacing to a 10-bed ICU associated with a respiratory neurophysiology laboratory.

PATIENTS

Seven patients (high cervical cord injury, n = 5; central hypoventilation following neurosurgery, n = 1; idiopathic acquired central hypoventilation, n = 1). INTERVENTION, MEASUREMENTS, AND RESULTS: Electromyography of the diaphragm and transdiaphragmatic pressure were assessed in response to CxMS and CMS. In three cases, no interruption of the corticodiaphragmatic pathway was evidenced, the decision of pacing was postponed, and the patients eventually recovered a spontaneous breathing activity. In two cases, the diagnosis of irreversible peripheral phrenic dysfunction was reached and pacing was denied. In two cases, complete interruption of the corticodiaphragmatic pathway and integrity of peripheral conduction led to the decision of phrenic pacemaker implantation.

CONCLUSION

CxMS and CMS can be used to refine the assessment of patients proposed for phrenic pacing. CxMS can possibly identify those in whom there is a possibility for eventual recovery, and therefore substantiate a decision to postpone the pacing.

Impairment of central motor conduction to the diaphragm in stroke

Respiratory complications are common in patients with stroke, but the involvement of the diaphragm in this setting is not completely understood. The purpose of this study was to assess corticodiaphragmatic pathways in patients with vascular hemiplegia. Fifteen patients were studied, nine with a capsular type of hemiplegia. Seven age-matched subjects served as the control group, and eight healthy young volunteers were studied to validate the methods by comparison with the literature. Diaphragm electromyogram was recorded bilaterally, using surface electrodes. Abductor pollicis brevis electromyogram was also recorded. After having checked the integrity of peripheral conduction, corticofugal pathways were studied using cortical magnetic stimulation, a reproducible and patient-independent stimulus. Left and right conduction times to the diaphragm were symmetrical in the control subjects, the young volunteers, and the six patients with hemiplegia but without capsular lesion (16.5 to 20.1 ms). Conversely, they were markedly asymmetrical in patients with capsular hemiplegia, diaphragm response on the plegic side being abolished or markedly delayed. Although the clinical impact of these findings remains to be determined, this study confirms that "central diaphragm paralysis" can be present in stroke. It also indicates that there is no bilateral motor representation of each hemidiaphragm.

Assessment of the voluntary activation of the diaphragm using cervical and cortical magnetic stimulation

The twitch occlusion technique is a promising tool for use in accessing central drive to the diaphragm and determining maximal transdiaphragmatic pressure (Pdi) from submaximal efforts. It clinical use is limited by difficulties inherent to bilateral electrical stimulation (BES) of the phrenic nerves. This study was designed to revisit the technique using cervical magnetic stimulation (CMS). In addition, the effects of a voluntary contraction on diaphragm response to magnetic stimulation of the cortex (CxMS) were studied. Seven volunteers aged 23-33 yrs were studied. Pdi was determined at relaxed functional residual capacity (FRC) in response to BES (Pdi,P-ES) and CMS (Pdi,p-CMS), and the effects of an increasing voluntary contraction (Pdi, vol) were assessed, The same procedure was applied to CxMS. Pdi,p-CMS at relaxed FRC was 27.5 +/- 2.2 cmH2O (mean+/-SEM), about 20% higher than Pdi,p-ES, and reported previously. Pd,p-CMS linearly decreased with Pdi, vol, and six out of seven subjects were capable of producing voluntary contractions sufficient to extinguish the twitch. More complex patterns were observed with CxMS. Cervical magnetic stimulation provides diaphragmatic twitch occlusion data very similar to bilateral electrical phrenic stimulation. Magnetic stimulation, be it cervical or cortical, could probably be helpful for the assessment of central and peripheral mechanisms of diaphragmatic dysfunction in the clinical setting.

Chronic hiccups and sleep

To explore the effect of sleep on hiccups, we studied eight patients aged 20-81 years, all males with chronic hiccups lasting 7 days to 7 years, by means of overnight polysomnography. The incidence of new bouts of hiccups and the likelihood of hiccups being present were both highest in wakefulness and became progressively lower through stages I-IV of slow wave sleep (SWS) to rapid eye movement sleep (REMS). There was a significant tendency for hiccups to disappear at sleep onset and REMS onset. Of all 21 bouts of hiccups that were observed to stop, 10/21 did so during an apnea or hypopnea. Frequency of hiccups within a bout slowed progressively from wakefulness through the stages of SWS to REMS. For the whole group, mean frequency decreased significantly from wakefulness [(25.6 +/- 12.1), (mean +/- SD)] to sleep onset or stage I (22.3 +/- 12.2). Sleep latency was increased from 8 +/- 16.3 minutes when hiccups were absent to 16.35 +/- 19.9 minutes when it was present. Sleep efficiency was poor because of long waking periods, and there were deficiencies of both SWS and REMS. Hiccups themselves were not responsible for any arousals or awakenings. We conclude that neural mechanisms responsible for hiccups are strongly influenced by sleep state and that hiccups disrupt sleep onset but not established sleep.

[Tools for the assessment of tobacco dependence: comparison with questionnaires and marker assays]

Fagerström Tolerance Questionnaire has been questioned in some respects for the purpose of the evaluation of tobacco dependence. In a sample of 208 smokers attempting to quit, we measured on urinary samples the levels of nicotine metabolites via their thiobarbituric acid derivatives comparatively to the levels of nicotine and cotinine by high performance liquid chromatography. Urinary concentration of nicotine metabolites was 77.1 +/- 50.0 mumol/l. Nicotine and cotinine levels were respectively 8.2 +/- 12.0 mumol/l and 12.9 +/- 9.8 mumol/l. Spearman correlation coefficients were used to examine the relationships among various measures of exposure to cigarette smoke, tobacco markers and tobacco addiction scores obtained through the Fagerström Questionnaire and a Simplified Questionnaire. Nicotine metabolites are correlated with the score obtained with the Simplified Questionnaire (rho = 0.39) better than with the score of Fagerström (rho = 0.28) (p < 0.01). These moderate correlations suggest that the measurement of tobacco markers provide a more valuable information than questionnaires for the appreciation of the depth of tobacco intake. The questionnaires should not serve as a substitute for tobacco markers determination.

Physical examination of the adult patient with respiratory diseases: inspection and palpation

Inspection of the thorax identifies the breathing position adopted by the patient, the shape of the thorax, the dynamics of respiration (breathing pattern, symmetry of expansion, mechanics and synchrony of rib cage and abdominal movements). Inspection of the neck adds useful information, particularly with respect to the dynamics of breathing. Palpation ascertains the signs suggested by inspection with respect to the mechanics of breathing. It also assesses the state of the pleura and pulmonary parenchyma by studying the tactile fremitus. It integrates extrarespiratory signs, such as enlarged lymph nodes or breast abnormalities. Extrathoracic respiratory signs should also be systematically looked for, including cyanosis, finger deformation, pulsus paradoxus, and pursed lips breathing. Interobserver agreement about respiratory signs has repeatedly been studied, and generally found to be low, as are clinical-functional correlations. However, some data on chronic obstructive pulmonary disease (COPD), asthma or pulmonary embolism are available. From the description of some signs and the current knowledge about their operative values, it appears that much clinical research remains necessary to better define the precise diagnostic value of a given sign. The impact of training on diagnostic performance also has to be defined. Both of these aspects should allow clinicians to optimize the way in which they use their hands and eyes to conduct respiratory diagnosis, as well as the way they teach respiratory symptomatology.

Physical examination of the adult patient with respiratory diseases: inspection and palpation

Inspection of the thorax identifies the breathing position adopted by the patient, the shape of the thorax, the dynamics of respiration (breathing pattern, symmetry of expansion, mechanics and synchrony of rib cage and abdominal movements). Inspection of the neck adds useful information, particularly with respect to the dynamics of breathing. Palpation ascertains the signs suggested by inspection with respect to the mechanics of breathing. It also assesses the state of the pleura and pulmonary parenchyma by studying the tactile fremitus. It integrates extrarespiratory signs, such as enlarged lymph nodes or breast abnormalities. Extrathoracic respiratory signs should also be systematically looked for, including cyanosis, finger deformation, pulsus paradoxus, and pursed lips breathing. Interobserver agreement about respiratory signs has repeatedly been studied, and generally found to be low, as are clinical-functional correlations. However, some data on chronic obstructive pulmonary disease (COPD), asthma or pulmonary embolism are available. From the description of some signs and the current knowledge about their operative values, it appears that much clinical research remains necessary to better define the precise diagnostic value of a given sign. The impact of training on diagnostic performance also has to be defined. Both of these aspects should allow clinicians to optimize the way in which they use their hands and eyes to conduct respiratory diagnosis, as well as the way they teach respiratory symptomatology.

Inferences about respiratory muscle use after cardiac surgery from compartmental volume and pressure measurements

BACKGROUND

After upper abdominal surgery, patients have been observed to have alterations in respiratory movements of the rib cage and abdomen and respiratory shifts in pleural and abdominal pressure that suggest dysfunction of the diaphragm. The validity of making such deductions about diaphragm function from these observations is open to discussion.

METHODS

In eight adult patients, American Society of Anesthesiologists physical status 2, scheduled for elective cardiac surgery, we measured respiratory rate, tidal volume, rib cage and abdominal cross-section changes, and esophageal (Pes) and gastric (Pga) pressures preoperatively, 1 day postoperatively, and 5 days postoperatively. These data were analyzed in detail by following the variables through each respiratory cycle.

RESULTS

Mean delta Pga/delta Pes decreased from 0.73 preoperatively to -0.56 1 day postoperatively and recovered to 0.47 5 days postoperatively. Plots of Pes against Pga and rib cage against abdominal expansion (Konno-Mead diagrams) were constructed. Six patients showed a postoperative pattern of breathing similar to that seen in patients who have undergone abdominal surgery: a decrease in the ratio of delta Pga/delta Pes and a shift toward rib cage expansion, with an increase in breathing rate and a decrease in tidal volume. This change was accomplished in most cases by the use of abdominal muscles in expiration with an increase in inspiratory intercostal muscle action without an increase in diaphragm activation, that is, a shift in the normal balance of respiratory muscle use in favor of muscles other than the diaphragm. A different ventilatory pattern was observed in the other two patients, consisting of minimal rib cage excursion and a large abdominal excursion. In these cases tidal volume was generated largely by contraction and relaxation of abdominal muscles with probable reduction in diaphragm activity. In addition, five patients exhibited positive changes in Pes at the end of inspiration that corresponded to closure of the upper airway, relaxation of inspiratory muscles, and subsequent opening of the airway with sudden exhalation, producing a grunt.

CONCLUSIONS

Indirect measurements of respiratory muscle action based on pressure and chest wall motion are easier than are assessments based on implanted electromyogram electrodes and sonomicrometers that measure electric activity and muscle length, respectively, directly. Interpretation requires numerous assumptions and detailed analysis of phase relations among the variables. In patients after thoracic surgery, however, these measurements strongly point to a shift in the distribution of motor output toward muscles other than the diaphragm.

[Physiopathology of COPD (steady-state)]

Chronic obstructive pulmonary disease (COPD) have several pathophysiological characteristics in common, the main one being an increased airways resistance (raw). It is the result of bronchial abnormalities and reduced parenchymal elasticity, and is influenced by lung volume. Raw decreases with increasing lung volume, and increases with decreasing lung volume. Such expiratory events are generally compensated on the inspiratory side. Inspiration is shortened to prolong expiration, and breathing takes place at higher lung volume to take benefit of the higher lung recoil. This inspiratory load is associated to an increased inspiratory drive, and contributes to put inspiratory muscles at disadvantage. However, with time, adaptative changes take place that restore their force at a shorter length. Chronic fatigue, often suspected in this setting, is therefore not currently demonstrated. Bronchial and parenchymal abnormalities lead to ventilation-perfusion mismatch, that contribute to hypoxemia and hypercapnia through deadspace and shunt effects. Hypercapnia can also correspond in part to protective mechanisms, if the energy requirements for its maintenance are too high.

Baclofen therapy for chronic hiccup

Chronic hiccup is a rare but potentially severe condition, that can be symptomatic of a variety of diseases, or idiopathic. Many therapeutic interventions have been reported, most often as case reports. Among other drugs, baclofen has been suggested as a therapy for chronic hiccup. In a large series of patients, we have evaluated its therapeutic position. In patients with chronic hiccup, defined as hiccup spell or recurring hiccup attacks lasting more than 7 days, investigation of the upper gastro-oesophageal tract (fibroscopy, manometry, and pH monitoring) was systematically performed. Most patients had tried numerous drugs in the past, without success. Baclofen was used as a first treatment in patients without evidence of any gastro-oesophageal disease (n = 17), and was undertaken only after full treatment of such disease (n = 55) had failed to solve the hiccup problem (n = 20). Baclofen has, therefore, been administered to 37 patients with chronic hiccup (average duration 4.6 yrs). Baclofen produced a long-term complete resolution (18 cases) or a considerable decrease (10 cases) of hiccups in 28 of the 37 patients. There was no significant difference between patients with or without gastro-oesophageal disease. We conclude that so-called idiopathic chronic hiccup often results from gastro-oesophageal abnormalities. Also, if controlled studies confirm our encouraging results, baclofen can be a major element in the treatment of chronic hiccup that is idiopathic, or that cannot be helped by treatment of gastro-oesophageal diseases.

[Chemotherapy of small cell bronchial cancers. Prognostic importance of complete response (1,280 patients). Groupe Petites Cellules]

OBJECTIVE

Pretherapeutic prognostic factors for patients given chemotherapy for small cell lung carcinoma have been widely studied. We evaluated response to chemotherapy in patients included in 4 multicentric trials with less restrictive entry criteria in order to determine the contribution of clinical outcome as a predictive factor.

METHODS

Pretherapeutic and therapeutic prognostic factors were assessed in 1280 patients included in 4 successive multicentric therapeutic trials on chemotherapy for small cell lung carcinoma conducted from January 1, 1983 to April 1, 1992. Logrank test for univariate analysis and Cox's stepwise method for multivariate analysis were used to evaluate the results.

RESULTS

Univariate analysis identified pretherapeutic factors as significant for prognosis: Karnofsky index (p < 0.0001), alkaline phosphatase level (p < 0.0002), white cell count (p < 0.0005), age (p = 0.0007), presence of brain metastasis (p = 0.0004), presence of liver metastasis (p = 0.03), initial extension (p = 0.04). Multivariate analysis taking into account pretherapeutic and therapeutic factors demonstrated that complete response after the second and after the sixth treatment session were predictive of longer survival (p = 0.0001). This factor was more powerful than all the pretherapeutic factors including the Karnofsky index, initial extension and brain metastasis.

CONCLUSION

For patients with small cell lung carcinoma, the prognostic value of early response to chemotherapy suggests that high-doses should be used starting at the first session.

History of diaphragm physiology: the achievements of Galen

Galen (129-200 AD) produced a large written output which was to remain one of the major basis of clinical medicine for centuries. His contribution to respiration, reported in his own books and in those of Oribasius, was that of a chest physician and of an experimental physiologist. He described in minute details how to perform a remarkable series of experiments by which he demonstrated the anatomy and function of the respiratory muscles. He described the actions of the diaphragm and how it moves the rib cage, in a series of spinal chord sections and muscle denervations. He investigated the passive or active nature of expiration and made fine observations of lung movements through the exposed pleural space. He described the interaction between the lungs and chest wall and developed the concept of interaction between ribcage and abdominal muscles in maintaining the position of the diaphragm, showing a clear understanding of the principle that the diaphragm can move upward during an isovolume manoeuvre as long as the ribcage is allowed to expand. A skillful clinician, Galen applied his theories of the analysis of problems at the bedside, particularly in patients affected with dyspnoea which he attributed to respiratory muscle dysfunction.

The earliest history of diaphragm physiology

The diaphragm was recognized as a distinct anatomical structure in the earliest Greek writings. However, the precise description of wounds suffered by warriors during the Trojan war by Homer was not tied to any particular function. The diaphragm was assimilated to the region that harbours thought. The first physiologic explanations of respiration by Empedocles in the 5th century BC and the concepts introduced by Plato and Hippocrates did not include a significant participation of the diaphragm. Aristole was the first to link respiration to a particular organ and a specific movement of the thorax. However, he considered that it was the heart which caused the lungs to expand by heating them, and the lungs in turn forced the thorax to dilate, a concept which was to survive until the 17th century. As in Aristole's theory the diaphragm played no role in respiration and was just a fence separating the thorax from the abdomen. A major break through occurred in Alexandria in the 4th and 3rd century BC: Herophilus was the first to recognize that muscles were the agents of movement and Erasistratus performed animal experiments which showed that the respiratory muscles were the agents of respiratory movements, thus opening the way to the later discoveries of Galen.

Inspiratory muscle testing in stable COPD patients

Exploration of inspiratory muscles in stable chronic pulmonary disease patients can be important in the investigation of a respiratory handicap unsatisfactorily explained by alterations of the passive respiratory system, or in the follow-up of patients undergoing treatments that can interfere with muscle function. Compensatory mechanisms tend to counterbalance the deleterious effects of hyperinflation in these patients, and precise clinical data are needed in order to avoid mistakes due to underverified hypotheses. Investigation of inspiratory muscle function requires the study of output data under various states of activity of the system. As outputs, volume displacement lacks specificity, pressure measurements can be more specific but are at times invasive and should be associated with lung volume measurements, electromyography is methodologically complex, nonquantitative and of poor reproducibility. Voluntary manoeuvres depend upon subject co-operation, and do not allow partitioning of output between the action of different muscle groups. Transcutaneous electrical phrenic nerve stimulation is devoid of these inconveniences, but it explores only one muscle (the diaphragm) under conditions that are not "natural" (relaxed rib cage). Recently, perspectives for easier clinical assessment of inspiratory muscle function in chronic obstructive pulmonary disease patients have been opened by cervical magnetic stimulation, better understanding of the meaning of mouth pressure in relationship to phrenic stimulation, and development of noninvasive tests, such as nostril pressure during sniff or phonomyography. If validated, such tests should provide a reasonably limited panel of clinical tools to better appreciate muscle function in this setting.

Arterial blood gases in elderly persons with chronic obstructive pulmonary disease (COPD)

With the increasing number of elderly people in developed countries, physicians are often confronted with patients whose arterial oxygen tension, PaO2, is lower than that of normal young adults. The normal values predicted in the literature for very old individuals are generally extrapolated from younger subjects. The purpose of the present study was to obtain PaO2 values from a large population of elderly subjects with normal and obstructive ventilatory function. We measured arterial blood gases in 274 subjects, aged 65-100 yrs (mean 82 yrs), with chronic bronchitis and moderate airways obstruction (mean forced expiratory volume in one second (FEV1), 53% pred). Mean PaO2 was 10.0 +/- 1.4 kPa (75.2 +/- 10.8 mmHg) and mean arterial carbon dioxide tension (PaCO2) was 5.4 +/- 0.8 kPa (40.5 +/- 6.1 mmHg). Both PaO2 and PaCO2 were independent of age. Blood gas abnormalities were associated with airways obstruction: PaO2 was positively correlated to FEV1 and PaCo2 was negatively correlated to FEV1. PaO2 was 10.8 +/- 1.4 kPa (81.5 +/- 10.7 mmHg) in the patients with FEV1 > or = 90% predicted versus 9.5 +/- 1.3 kPa (71.5 +/- 10.1 mmHg) in those with FEV1 < or = 35% pred. These findings suggest that the predicted PaO2 extrapolated from younger normal values are often erroneously underestimated. It is probably more accurate to accept as normal a PaO2 of 10.6-11.3 kPa (80-85 mmHg) for all subjects over 65 yrs, irrespective of their age.

Arterial blood gases in elderly persons with chronic obstructive pulmonary disease (COPD)

With the increasing number of elderly people in developed countries, physicians are often confronted with patients whose arterial oxygen tension, PaO2, is lower than that of normal young adults. The normal values predicted in the literature for very old individuals are generally extrapolated from younger subjects. The purpose of the present study was to obtain PaO2 values from a large population of elderly subjects with normal and obstructive ventilatory function. We measured arterial blood gases in 274 subjects, aged 65-100 yrs (mean 82 yrs), with chronic bronchitis and moderate airways obstruction (mean forced expiratory volume in one second (FEV1), 53% pred). Mean PaO2 was 10.0 +/- 1.4 kPa (75.2 +/- 10.8 mmHg) and mean arterial carbon dioxide tension (PaCO2) was 5.4 +/- 0.8 kPa (40.5 +/- 6.1 mmHg). Both PaO2 and PaCO2 were independent of age. Blood gas abnormalities were associated with airways obstruction: PaO2 was positively correlated to FEV1 and PaCo2 was negatively correlated to FEV1. PaO2 was 10.8 +/- 1.4 kPa (81.5 +/- 10.7 mmHg) in the patients with FEV1 > or = 90% predicted versus 9.5 +/- 1.3 kPa (71.5 +/- 10.1 mmHg) in those with FEV1 < or = 35% pred. These findings suggest that the predicted PaO2 extrapolated from younger normal values are often erroneously underestimated. It is probably more accurate to accept as normal a PaO2 of 10.6-11.3 kPa (80-85 mmHg) for all subjects over 65 yrs, irrespective of their age.

Oral immunization with bacterial extracts for protection against acute bronchitis in elderly institutionalized patients with chronic bronchitis

Acute bronchitis is a major source of morbidity in elderly patients. The purpose of this study was to assess the preventive effects of oral immunisation with a bacterial extract. Three hundred and fifty four patients with chronic bronchitis, living in institutions for the elderly (aged > 65 yrs), were included in a randomized, placebo-controlled, double-blind study. The purpose of the study was to assess preventive effects of OM-85 BV (an immunostimulating agent consisting of lyophilized fractions of eight of the most common pathogens isolated in respiratory tract infections) against acute lower respiratory tract infections. Two hundred and ninety patients completed the study (143 taking placebo and 147 taking OM-85 BV). There was a 28% reduction in the number of lower respiratory tract infections in the patients treated with OM-85 BV; this was entirely due to 40% reduction in the number of episodes of acute bronchitis (p < 0.01), with no difference in the number of episodes of pneumonia and bronchopneumonia. A larger number of patients in the OM-85 BV group were free of acute bronchitis throughout the 6 month study period (96 vs 69) and there was a 28% reduction in the number of antibiotic prescriptions in the OM-85 BV treated group. These results suggest that OM-85 BV has a protective effect against acute bronchitis in elderly patients living in institutions.

Respiratory response to CO2 in patients with chronic obstructive pulmonary disease in acute respiratory failure

The aim of our study was to determine the importance of chemoreceptor stimulation by carbon dioxide in setting the level of ventilation in patients with chronic obstructive pulmonary disease (COPD) in acute respiratory failure. We studied the ventilatory and mouth occlusion pressure (P0.1) responses to CO2 in 25 COPD patients under treatment for episodes of acute respiratory failure, and in 24 normal subjects. Carbon dioxide rebreathing tests were performed in the spontaneously breathing, intubated patients, after arterial blood gases had been quasi-normalized by mechanical ventilation, which allowed us to compare both groups at similar resting arterial carbon dioxide tension (PaCO2) and acid-base status. The slopes of the ventilatory responses were markedly lower in the patients (mean +/- SEM, 1.28 +/- 0.23 versus 12.53 +/- 1.13 l.min-1.kPa-1). The slopes of the P0.1 responses were lower in the patients (0.27 +/- 0.05 versus 0.45 +/- 0.05 kPa.kPa-1), but the absolute P0.1 values were not significantly different from the normals. Increasing PaCO2 from 5.3 to 8 kPa (40 to 60 mmHg) resulted in a mean increase of 34% in ventilation. These results show that CO2 drive is a major determinant of respiratory stimulation in many COPD patients with acute respiratory failure.

Respiratory response to CO2 in patients with chronic obstructive pulmonary disease in acute respiratory failure

The aim of our study was to determine the importance of chemoreceptor stimulation by carbon dioxide in setting the level of ventilation in patients with chronic obstructive pulmonary disease (COPD) in acute respiratory failure. We studied the ventilatory and mouth occlusion pressure (P0.1) responses to CO2 in 25 COPD patients under treatment for episodes of acute respiratory failure, and in 24 normal subjects. Carbon dioxide rebreathing tests were performed in the spontaneously breathing, intubated patients, after arterial blood gases had been quasi-normalized by mechanical ventilation, which allowed us to compare both groups at similar resting arterial carbon dioxide tension (PaCO2) and acid-base status. The slopes of the ventilatory responses were markedly lower in the patients (mean +/- SEM, 1.28 +/- 0.23 versus 12.53 +/- 1.13 l.min-1.kPa-1). The slopes of the P0.1 responses were lower in the patients (0.27 +/- 0.05 versus 0.45 +/- 0.05 kPa.kPa-1), but the absolute P0.1 values were not significantly different from the normals. Increasing PaCO2 from 5.3 to 8 kPa (40 to 60 mmHg) resulted in a mean increase of 34% in ventilation. These results show that CO2 drive is a major determinant of respiratory stimulation in many COPD patients with acute respiratory failure.

Hiccup in adults: an overview

Hiccup is a forceful, involuntary inspiration commonly experienced by fetuses, children and adults. Its purpose is unknown and its pathophysiology still poorly understood. Short hiccup bouts are mostly associated with gastric distention or alcohol intake, resolve spontaneously or with simple folk remedies and do not require medical attention. In contrast, prolonged hiccup is a rare but disabling condition which can induce depression, weight loss and sleep deprivation. A wide variety of pathological conditions can cause chronic hiccup: myocardial infarction, brain tumour, renal failure, prostate cancer, abdominal surgery etc. Detailed medical history and physical examinations will often guide diagnostic investigations (abdominal ultrasound, chest or brain CT scan...). Gastric and duodenal ulcers, gastritis, oesophageal reflux and oesophagitis are commonly observed in chronic hiccup patients and upper gastrointestinal investigations (endoscopy, pH monitoring and manometry) should be included in the diagnostic evaluation systematically. Etiological treatment is not always available and chronic hiccup treatment has classically relied on metoclopramide and chlorpromazine. Recently, baclofen (LIORESAL) has emerged as a safe and often effective treatment.