Flow limitation and dynamic hyperinflation during exercise in COPD patients after single lung transplantation

STUDY OBJECTIVE

Using the negative expiratory pressure (NEP) method, we have previously shown that patients receiving single lung transplantation (SLT) for COPD do not exhibit expiratory flow limitation and have little dyspnea at rest. In the present study, we assessed whether SLT patients exhibit flow limitation, overall hyperinflation, and dyspnea during exercise.

METHODS

Expiratory flow limitation assessed by the NEP method and inspiratory capacity maneuvers used to determine end-expiratory lung volume (EELV) and end-inspiratory lung volume (EILV) were performed at rest and during symptom-limited incremental cycle exercise in eight SLT patients.

RESULTS

At the time of the study, the mean (+/- SD) FEV(1), FVC, functional residual capacity, and total lung capacity (TLC) amounted to 55 +/- 14%, 67 +/- 12%, 137 +/- 16%, and 110 +/- 11% of predicted, respectively. At rest, all patients did not experience expiratory flow limitation and were without dyspnea. At peak exercise, the maximal mechanical power output and maximal oxygen consumption amounted to 72 +/- 20% and 65 +/- 8% of predicted, respectively, with a maximal dyspnea Borg score of 6 +/- 3. All but one patient exhibited flow limitation and dynamic hyperinflation; the EELV and EILV amounted to 74 +/- 5% and 95 +/- 9% TLC, respectively. The patient who did not exhibit flow limitation during exercise had the lowest dyspnea score.

CONCLUSION

Most SLT patients for COPD exhibit expiratory flow limitation and dynamic hyperinflation during exercise, whereas maximal dyspnea is variable.

A comparison of two long-acting beta-agonists, oral bambuterol and inhaled salmeterol, in the treatment of moderate to severe asthmatic patients with nocturnal symptoms. The French Bambuterol Study Group

This multicentre study was set up to compare the efficacies of two long-acting beta 2-agonists, oral bambuterol (20 mg nocte) and inhaled salmeterol (50 micrograms b.i.d.), for the treatment of moderate to severe asthmatics who were considered to be on optimal steroid/bronchodilator therapy, but continued to have troublesome nocturnal symptoms. The study was of double-blind, parallel-group design and comprised a 2-week run-in on previous maintenance therapy followed by a 6-week study treatment period. There were 117 randomized asthmatic patients aged 20-70 years (65 women and 52 men with a mean age of 45 and predicted FEV1 of 64%), who had been taking 800-2000 micrograms inhaled steroid and/or up to 20 mg oral steroid per day for at least 4 weeks. They were asked to complete daily diary cards, recording morning and evening PEF, daily symptoms, nocturnal awakenings, rescue medication and subjective tremor. There was a significant increase in both morning and evening PEF respectively, on bambuterol (28 l min-1, 20 l min-1, P < 0.05) and salmeterol (29 l min-1, P < 0.001; 23 l min-1, P < 0.01) when compared with run-in. The mean percentage fall in overnight PEF was reduced by 8.3% (P < 0.001) on bambuterol and by 6.8% (P < 0.001) on salmeterol. Nocturnal awakenings and daytime symptoms due to asthma were significantly lowered by both treatments, as was the consumption of rescue bronchodilator. Tremor scores were very low during both run-in and study treatments. No significant treatment difference between bambuterol and salmeterol was detected for any of the above variables. Once-daily oral bambuterol provides a highly effective alternative to twice-daily inhaled salmeterol for relief of nocturnal symptoms in patients with moderate to severe asthma.

Expiratory flow limitation in stable asthmatic patients during resting breathing

Application of negative pressure at the mouth during tidal expiration (NEP) provides a simple, rapid, noninvasive method for detecting expiratory flow limitation during spontaneous breathing. Patients in whom NEP elicits an increase in flow throughout expiration are not flow-limited (FL). In contrast, patients in whom application of NEP does not elicit an increase in flow during most or part of tidal expiration are considered FL. We have used the NEP technique to assess the prevalence of expiratory flow limitation during resting breathing in sable asthmatic patients in both the seated and supine positions. In patients in the sitting position, we have also assessed flow limitation with the conventional method, based on comparison of tidal and maximal expiratory flow-volume (MEFV) curves. We studied 13 patients (FEV1 range: 48 to 94% predicted) with both the NEP and conventional techniques. According to the NEP technique, none of the patients was FL in the seated and only two were FL in the supine position. By contrast, on the basis of the conventional method, six of the patients would have been classified as FL in the sitting position. We conclude that: (1) most stable asthmatic patients do not exhibit tidal expiratory flow limitation during resting breathing; and (2) the conventional method for assessing flow limitation may lead to erroneous conclusions.

[Lung volume reduction surgery in emphysema]

Lung volume reduction surgery in emphysema has, as an objective, the reduction of dyspnoea and an increase in the exercise tolerance in patients with respiratory insufficiency suffering from diffuse emphysema. In principle the resection of the most diseased areas of emphysema leads to improvement in the mechanical properties of the emphysematous lung and correct pulmonary hyperinflation. The respiratory function benefits both objective and subjective, produced by surgery are real but transitory and inconstant depending in particular on the evolutionary profile of the emphysematous disease. The indications should be further refined and an objective comparison of different surgical techniques has not been achieved. The impact on the quality of life for these patients is unknown.

Expiratory flow limitation in COPD patients after single lung transplantation

Expiratory flow limitation and dyspnea during resting breathing are common in patients with severe chronic obstructive pulmonary disease (COPD). Although single lung transplantation (SLT) is used to treat end-stage COPD, its effects on flow limitation and dyspnea are not well established. We assessed expiratory flow-limitation and dyspnea in 13 COPD patients after SLT at rest in the sitting and supine positions by applying negative pressure at the mouth during tidal expiration (negative expiratory pressure [NEP] technique). If NEP increases flow throughout the control tidal volume (VT), flow limitation is absent (not flow limited [NEL]). If NEP does not increase flow during part of the control VT, flow limitation is present. After SLT, lung function improved in all but one patient. Twelve patients were NFL during resting breathing in both positions studied. The patient whose lung function did not improve after SLT was flow-limited (FL) both when seated and supine. This patient also exhibited moderately severe chronic dyspnea (Medical Research Council [MRC] score = 3). In the nine other patients in whom dyspnea was assessed, it was slight (MRC score = 1). In conclusion, after SLT for end-stage COPD, expiratory flow limitation at rest is uncommon in both the seated and supine positions. This is consistent with the finding that after SLT the degree of chronic dyspnea is generally slight.

Latent pulmonary function abnormalities in children with Crohn's disease

Recently, latent pulmonary involvement has been described in adult patients with inflammatory bowel disease. It is unknown, however, whether this also occurs in children, and whether the pulmonary abnormalities differ between the acute phase and remission. The incidence of pulmonary abnormalities has been investigated in 26 children with acute or quiescent Crohn's disease in terms of the following parameters: clinical pulmonary symptoms, chest roentgenograms and pulmonary function tests, including lung transfer factor for carbon monoxide (TLCO). One child had a severe digital clubbing. Chest radiographs were normal in all subjects. No significant differences were found between acute and quiescent phase for pulmonary volumes and expiratory flows, but TLCO (% predicted) was significantly decreased during the active phase of the disease as compared to remission (53 +/- 15 vs 81 +/- 19% predicted). These data suggest that latent pulmonary involvement is also present in a paediatric population with active Crohn's disease, despite a short disease history and absence of smoking. Although the nature of this abnormality remains unclear, this extradigestive epiphenomenon should be taken into account with respect to the aetiopathogenesis of Crohn's disease.

Diaphragmatic function in severely malnourished patients with anorexia nervosa. Effects of renutrition

The effects of malnutrition and refeeding on nutritional indices, pulmonary function, and diaphragmatic contractile properties were studied in severely malnourished patients with anorexia nervosa. Fifteen patients were evaluated upon hospital admission (Day 0) and on Days 7, 30, and 45 after starting feeding. Spirometry, lung volumes, and arterial blood gases were measured at each time interval, as were contractile properties of the diaphragm as assessed by transdiaphragmatic pressure generated during electrical phrenic nerve stimulation (Pdistim) and a maximal sniff maneuver (Pdisniff). Anthropomorphic and biochemical measurements were performed at each time interval. Patients were severely malnourished upon admission; mean body weight was 37.1 +/- 4.7 kg (63% ideal body weight). During nutritional support, body weight increased significantly to 42.9 +/- 4.6 kg on Day 45 (p < 0.01), as did muscle mass: 11.2 +/- 4.1 kg on Day 0, to 16.6 +/- 4.9 kg on Day 45 (p < 0.01). Vital capacity and FEV1 increased significantly by Day 30 (p < 0.05). Lung volumes were unchanged. Mean arterial blood gas values were also within the normal range at Day 0; PaO2, 92.6 +/- 2.4 mm Hg and PacO2, 41.0 +/- 1.5 mm Hg. Four patients, however, had an increased PacO2 (> 42 mm Hg) at Day 0, which returned to normal by Day 30. Diaphragmatic contractility was severely depressed initially; Pdistim, 15.9 +/- 1.4 cm H2O; Pdisniff, 65.4 +/- 5 cm H2O; but it significantly increased with nutritional support by Day 30 to 22.5 +/- 1.9 and 84.6 +/- 4.7 cm H2O, respectively. We conclude that diaphragmatic function is severely impaired in malnuorished patients free of other coexisting

Acute effects of zolpidem, triazolam and flunitrazepam on arterial blood gases and control of breathing in severe COPD

Patients with severe chronic obstructive pulmonary disease (COPD) commonly complain of insomnia, but hypnotic drugs are generally not recommended due to their depressant effect on the respiratory centres. The aim of this study was, therefore, to compare the effects of a single dose of the benzodiazepine hypnotics, triazolam 0.25 mg and flunitrazepam 1 mg, and a new imidazopyridine compound, zolpidem 10 mg, in hypercapnic COPD patients. Twelve stable COPD patients (mean +/- SD arterial oxygen tension (PaO2) 9.3 +/- 0.8 kPa and arterial carbon dioxide tension (PaCO2) 5.9 +/- 1.9 kPa) were included in the study. The following measurements were performed before and 2 h after drug administration: PaO2 and PaCO2, minute ventilation (VE), mouth occlusion pressure (P0.1), rebreathing CO2 tests with ventilatory response to carbon dioxide stimulation (delta VE/delta PACO2) and mouth occlusion pressure response to carbon dioxide stimulation (delta P0.1/delta PACO2). The measurements were performed in a randomized, double-blind fashion, each patient receiving a single dose of each drug on three different days, separated by a one week interval. No difference was noted between control measurements and those taken 2 h after administration of zolpidem in the following parameters: PaCO2, PaCO2, VE, P0.1, delta VE/delta PACO2 and delta P0.1/PACO2. Two hours after administration of triazolam and flunitrazepam, a significant difference was noted in VE for triazolam and for flunitrazepam. After flunitrazepam administration, a significant decrease in PaCO2 (6 +/- 1.8 at baseline versus 7 +/- 0.4 kPa), and delta VE/PACO2 (0.44 +/- 0.20 at baseline versus 0.31 +/- 0.21 l.min-1 x kPa) were observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute effects of zolpidem, triazolam and flunitrazepam on arterial blood gases and control of breathing in severe COPD

Patients with severe chronic obstructive pulmonary disease (COPD) commonly complain of insomnia, but hypnotic drugs are generally not recommended due to their depressant effect on the respiratory centres. The aim of this study was, therefore, to compare the effects of a single dose of the benzodiazepine hypnotics, triazolam 0.25 mg and flunitrazepam 1 mg, and a new imidazopyridine compound, zolpidem 10 mg, in hypercapnic COPD patients. Twelve stable COPD patients (mean +/- SD arterial oxygen tension (PaO2) 9.3 +/- 0.8 kPa and arterial carbon dioxide tension (PaCO2) 5.9 +/- 1.9 kPa) were included in the study. The following measurements were performed before and 2 h after drug administration: PaO2 and PaCO2, minute ventilation (VE), mouth occlusion pressure (P0.1), rebreathing CO2 tests with ventilatory response to carbon dioxide stimulation (delta VE/delta PACO2) and mouth occlusion pressure response to carbon dioxide stimulation (delta P0.1/delta PACO2). The measurements were performed in a randomized, double-blind fashion, each patient receiving a single dose of each drug on three different days, separated by a one week interval. No difference was noted between control measurements and those taken 2 h after administration of zolpidem in the following parameters: PaCO2, PaCO2, VE, P0.1, delta VE/delta PACO2 and delta P0.1/PACO2. Two hours after administration of triazolam and flunitrazepam, a significant difference was noted in VE for triazolam and for flunitrazepam. After flunitrazepam administration, a significant decrease in PaCO2 (6 +/- 1.8 at baseline versus 7 +/- 0.4 kPa), and delta VE/PACO2 (0.44 +/- 0.20 at baseline versus 0.31 +/- 0.21 l.min-1 x kPa) were observed.(ABSTRACT TRUNCATED AT 250 WORDS)

The respiratory response to CO2 and O2 in patients with coma due to voluntary intoxication with barbiturates and carbamates

We have investigated the respiratory response to CO2 and to O2 in comatose subjects self intoxicated with barbiturates and carbamates. The chemical drive of 12 such patients with coma was compared with that of comparable normal subjects. The ventilatory response to CO2 was depressed but the P0.1 response was of the same order of magnitude as in normals. O2 had little effect on the ventilatory parameters and occlusion pressure. There was no difference between the two groups of patients, indicating that the respiratory changes observed were more dependent on the intensity of the intoxication than on the nature of the drugs. In addition, mechanical factors seem mainly responsible for the depressed ventilatory response to CO2.

The respiratory response to CO2 and O2 in patients with coma due to voluntary intoxication with barbiturates and carbamates

We have investigated the respiratory response to CO2 and to O2 in comatose subjects self intoxicated with barbiturates and carbamates. The chemical drive of 12 such patients with coma was compared with that of comparable normal subjects. The ventilatory response to CO2 was depressed but the P0.1 response was of the same order of magnitude as in normals. O2 had little effect on the ventilatory parameters and occlusion pressure. There was no difference between the two groups of patients, indicating that the respiratory changes observed were more dependent on the intensity of the intoxication than on the nature of the drugs. In addition, mechanical factors seem mainly responsible for the depressed ventilatory response to CO2.

The transition between apnoea and spontaneous ventilation in patients with coma due to voluntary intoxication with barbiturates and carbamates

We have investigated the transition from apnoea to spontaneous breathing in five comatose patients self intoxicated with barbiturates and carbamates. All patients were apnoeic on admission, and were studied throughout the course of recovery. The transition between the first respiratory movements and a stable and nearly normal ventilation (stable respiratory activity) ranged from 15 to 105 min, a very short time compared to the duration of the apnoeic state that lasted 6 to 72 h from admission. Minute ventilation and occlusion pressure during the first respiratory movements were 6.3 +/- 2.7 l.min-1 and 1.35 +/- 0.45 kPa, respectively. These values increased by roughly 50 and 100% by the time stable respiratory activity was achieved. The increase in minute ventilation was entirely due to an increased inspiratory flow, in relation to a proportionate increase in occlusion pressure, and without significant changes in the respiratory times or in the effective elastance. We conclude that the transition between apnoea and stable respiratory activity is characterized by its rapidity, by the fact that respiratory times are fixed throughout the recovery process, and by the fact that effective elastance is high.

The transition between apnoea and spontaneous ventilation in patients with coma due to voluntary intoxication with barbiturates and carbamates

We have investigated the transition from apnoea to spontaneous breathing in five comatose patients self intoxicated with barbiturates and carbamates. All patients were apnoeic on admission, and were studied throughout the course of recovery. The transition between the first respiratory movements and a stable and nearly normal ventilation (stable respiratory activity) ranged from 15 to 105 min, a very short time compared to the duration of the apnoeic state that lasted 6 to 72 h from admission. Minute ventilation and occlusion pressure during the first respiratory movements were 6.3 +/- 2.7 l.min-1 and 1.35 +/- 0.45 kPa, respectively. These values increased by roughly 50 and 100% by the time stable respiratory activity was achieved. The increase in minute ventilation was entirely due to an increased inspiratory flow, in relation to a proportionate increase in occlusion pressure, and without significant changes in the respiratory times or in the effective elastance. We conclude that the transition between apnoea and stable respiratory activity is characterized by its rapidity, by the fact that respiratory times are fixed throughout the recovery process, and by the fact that effective elastance is high.

A randomized, controlled trial of theophylline in patients with severe chronic obstructive pulmonary disease

To assess the effects of theophylline in chronic obstructive pulmonary disease, we conducted a randomized, placebo-controlled, double-blind, crossover trial in 60 patients with severe but stable disease. The patients (mean age, 61 years) were studied before and after two months of placebo and two months of treatment with a sustained-release preparation of theophylline (10 mg per kilogram of body weight per day), administered orally. The two treatments were administered in a random order and separated by an eight-day washout period. After taking theophylline for two months (mean plasma concentration, 14.8 mg per liter), as compared with the two months of placebo, the patients had significant improvements in dyspnea, pulmonary gas exchange (partial pressure of arterial oxygen, 66 vs. 61 mm Hg [P less than 0.0001]; partial pressure of arterial carbon dioxide, 44 vs. 49 mm Hg [P less than 0.0001]), vital capacity (63 percent vs. 58 percent of the predicted value [P less than 0.0001]), and forced expiratory volume in one second (36 percent vs. 32 percent of the predicted value [P less than 0.0001]), with no significant change in airway resistance or functional residual capacity. Minute ventilation increased by a mean of 18 percent (P less than 0.0001) in the patients taking theophylline because of increased tidal volume, with no change in respiratory frequency. The respiratory-muscle performance of the patients taking theophylline improved by approximately 29 percent (P less than 0.0001), as indicated by a decline in the ratio of inspiratory pleural pressure during quiet breathing to maximal pleural pressure. We conclude that theophylline improves respiratory function and dyspnea in patients with severe chronic obstructive pulmonary disease and that these improvements are probably due to better respiratory-muscle performance.

Dopamine effects on diaphragmatic strength during acute respiratory failure in chronic obstructive pulmonary disease

STUDY OBJECTIVE

To assess the effects of dopamine, which has an inotropic effect on the myocardium and increases renal and splanchnic blood flow, on diaphragmatic contraction.

DESIGN AND PATIENTS

We studied the changes in transdiaphragmatic pressure during electrical bilateral supramaximal stimulation of the phrenic nerves in eight patients with chronic obstructive pulmonary disease during acute respiratory failure. In three patients, changes in diaphragmatic blood flow were also evaluated.

METHODS

All patients were intubated and artificially ventilated. Stimulated transdiaphragmatic pressure, cardiac output, evaluated with a Swan Ganz catheter, and diaphragmatic blood flow, evaluated by timed volume collections of left phrenic venous effluent (a catheter was introduced into the right femoral vein and advanced into the left inferior phrenic vein) were measured before dopamine infusion, every 10 minutes after the onset of dopamine infusion (10 micrograms/kg body weight.min during 30 minutes) and 15 minutes after the end of dopamine infusion. Arterial blood gases and pH were measured before and at the end of dopamine infusion.

MEASUREMENTS AND MAIN RESULTS

Arterial blood gases and pH were maintained within normal range by mechanical ventilation throughout the study. With dopamine infusion, heart rate increased by 17% (P less than 0.001) and cardiac output by 40% (P less than 0.001) on the average. The increase in cardiac output was accompanied by a marked increase in diaphragmatic blood flow (30% on the average) in the three patients in whom it was measured (P less than 0.001). Diaphragmatic strength also increased significantly during dopamine administration. Transdiaphragmatic pressure for an identical phrenic stimulation increased by 30% (P less than 0.001) on the average. The changes in cardiac output, diaphragmatic blood flow, and transdiaphragmatic pressure persisted throughout the infusion period; all values returned to control values 15 minutes after the end of dopamine administration.

CONCLUSIONS

Dopamine has a potent effect on diaphragmatic strength generation and diaphragmatic blood flow in patients with chronic obstructive pulmonary disease during acute respiratory failure. It is possible to improve diaphragmatic contraction in these patients by administering pharmacologic agents that augment diaphragmatic blood flow.

Effects of sepsis on diaphragmatic function in rats

The effects of a 3-day pneumococcal infection on diaphragmatic strength and endurance capacity were studied in an in vivo rat model. Thirty-four rats were divided into a control (C) (n = 17) or a septic (S) group (n = 17). Animals were inoculated subcutaneously with 10(11) Streptococcus pneumoniae (S), or sterile culture media (C). All rats were studied 3 days after inoculation. Diaphragmatic strength and endurance capacity were studied in 11 animals of each group. Diaphragmatic strength was assessed by measuring transdiaphragmatic pressure (Pdi) generated during electrical stimulation of the phrenic nerves at different frequencies (0.5, 10, 20, 30, 50, and 100 Hz). Endurance index was calculated as the ratio of Pdi generated after 30 s of phrenic nerve stimulation at 10 Hz divided by the initial force. Measurements of lung weights and lung histologic examinations were performed in the 6 remaining rats from each group. S animals were hyperthermic (39 to 40 degrees C rectal temperature). There was no evidence of pneumonia at histologic examination in Group S. No differences in wet weight of the lung and in the dry-to-wet weight ratio were noted in Group S as compared with Group C. However, S. pneumoniae was isolated from blood and lungs of S animals. Diaphragmatic weight was not different between S and C groups, whereas the weights of the extensor digitorium longus (EDL), tibialis anterior (TA), and soleus muscles were significantly reduced in Group S as compared to Group C.(ABSTRACT TRUNCATED AT 250 WORDS)

Tracheal occlusion pressure: a simple index to monitor respiratory muscle fatigue during acute respiratory failure in patients with chronic obstructive pulmonary disease

STUDY OBJECTIVE

To assess respiratory muscle fatigue in acute respiratory failure in patients with chronic obstructive pulmonary disease and evaluate its influence on weaning patients from mechanical ventilation.

DESIGN AND PATIENTS

We studied the time course of tracheal occlusion pressure (P0.1) and high-to-low ratio of the diaphragmatic electromyogram in 16 patients in acute respiratory failure with chronic obstructive pulmonary disease.

METHODS

All patients were intubated and studied during a 15-minute weaning period from ventilation. Minute ventilation (VE), arterial blood gases, P0.1 and high-to-low ratio of the diaphragm were measured every day from the onset to the end of acute failure (before extubation) at 5 and 15 minutes into the weaning period. The diaphragmatic electromyogram was recorded with an esophageal electrode and the high-to-low ratio of the electrical signal analyzed to assess diaphragmatic fatigue.

MEASUREMENTS AND MAIN RESULTS

In all patients P0.1 was markedly increased (7.1 +/- 2.4 cm H2O, mean +/- SE) on the first day of acute failure and did not change during weaning. In 11 patients, P0.1 had decreased to 4.7 +/- 1.8 cm H2O (P less than or equal to 0.002) before extubation (which was done after 5 to 9 days). In these patients, the high-to-low ratio of the diaphragm decreased rapidly-during the first minutes of weaning on the first day of acute failure and remained low throughout weaning, whereas before extubation no decrease in high-to-low ratio was seen during weaning. In 5 patients, P0.1 did not change significantly from the onset of acute failure and the high-to-low ratio remained low before extubation. These 5 patients had to be reintubated within 2 to 6 days. In both groups of patients, VE did not change significantly from the first to last day of acute failure (10.3 +/- 3 compared with 10.7 +/- 2.1 min-1), whereas blood gases during room air breathing improved significantly from the first to last day of acute failure, respectively, in each group (arterial oxygen pressure [PaO2], 33.5 +/- 1.5 compared with 44 +/- 9 mm Hg (P less than or equal to 0.05) and PaO2 56 +/- 2.3 compared with 49 +/- 2 mm Hg (P less than 0.005).

CONCLUSIONS

Extubation should not be done in patients with respiratory muscle fatigue despite improvement in arterial blood gases and clinical status; and P0.1 provides a valid and simple index to assess the likelihood of respiratory muscle fatigue.

Effects of Ca2+ withdrawal on diaphragmatic fiber tension generation

The effects of extracellular Ca2+ withdrawal were studied on isolated diaphragmatic muscle fibers and compared with the effects on the papillary, soleus, and extensor digitorum longus (EDL) contractility, using the same in vitro model. Diaphragmatic fibers were obtained from 15 rats, and papillary muscles, soleus, and EDL were obtained from 10 animals. Isometric force generated in response to 1-Hz supramaximal electrical stimulation was measured with a highly sensitive photoelectric transducer. After control measurements, perfusion with a Krebs solution depleted of calcium (0 Ca2+) was started while the fibers were continuously stimulated (4 times/min) and twitches recorded. For the papillary fibers, perfusion with zero Ca2+ was followed by an immediate decrease in twitch tension, complete twitch abolition occurring within 3 +/- 1 min after zero-Ca2+ exposure. Diaphragmatic fibers behaved similarly, although twitch abolition was delayed (10 +/- 3 min after 0-Ca2+ exposure). For the soleus fibers, the twitch amplitude amounted to 38 +/- 10% of control (62% decrease on the average) after 30 min of zero-Ca2+ exposure, no twitch abolition being noted even after 1 h of Ca2+-free exposure. The twitch amplitude of the EDL fibers amounted to 75 +/- 7% of control (25% decrease) after 30 min of zero-Ca2+ exposure. The recovery kinetics for the four fiber types after reexposure to Ca2+-containing solution were also different, with papillary and diaphragmatic fibers recovering completely within 2.5 +/- 0.5 and 4 +/- 0.5 min, respectively. By contrast, neither the soleus nor the EDL showed complete recovery after 30 min.(ABSTRACT TRUNCATED AT 250 WORDS)

[Action of aminophylline on the strength of contraction of the diaphragm in patients with chronic obstructive respiratory insufficiency]

The effect of a sustained-release aminophylline preparation on diaphragmatic contractility was investigated in patients with stable chronic obstructive lung disease (FEV1 = 22.6% of predicted value). Ten such patients were tested before (control) and after a week's course of oral aminophylline. Diaphragmatic contractility was evaluated by measuring the transdiaphragmatic pressure generated at residual functional capacity by bilateral electrical stimulation of the phrenic nerves. The nerves were stimulated supramaximally at 1 Hz, using needle electrodes. Plasma aminophylline levels (12.5 +/- 0.9 mg/l) were within therapeutic range in all patients. After treatment with aminophylline, for each stimulation the transdiaphragmatic pressure increased significantly from 14 +/- 1.3 to 17 +/- 1.3 cm H2O (+21%; P less than 0.005). These results confirm that aminophylline increases the force of contraction of the diaphragmatic fibres electively tested by the technique used. Long-term treatment with theophylline in therapeutic doses may be of interest in such patients, as it might improve their diaphragmatic contractility and result in better control of both respiratory muscle fatigue and episodes of acute respiratory failure.

Effects of theophylline and enprofylline on diaphragmatic contractility

Experimental data suggest that theophylline (T) enhances diaphragmatic contractility by increasing the influx of calcium at the cell membrane level through an inhibition of adenosine receptors (Aubier et al., J. Appl. Physiol. 54: 460-4, 1983). Enprofylline (E) is a xanthine drug that has poor ability to antagonize physiological actions of adenosine. The aim of this study was to compare the effects on diaphragmatic contractility of T and E in order to determine whether antagonism of adenosine receptors was the underlying mechanism of the inotropic effect of T on diaphragmatic contractility. Ten normal subjects were studied in the sitting position. The contractile properties of the diaphragm were assessed by measuring the transdiaphragmatic pressure (Pdi) generated at functional residual capacity during bilateral electrical stimulation of the phrenic nerves. The subjects were randomized, and after control measurements were performed, they received T or E. This was a double-blind crossover study, the measurements being repeated with the second drug after one week. Both drugs were administered intravenously with a loading dose of 6 and 2 mg/kg administered in 30 min for T and E and a maintenance dose of 0.9 and 0.075 mg.kg-1 X h-1 for T and E, respectively. Measurements were performed before and 60 min after T or E administration. Plasmatic levels of both drugs were also analyzed. In all the subjects, therapeutic levels of T or E were reached (14.8 +/- 0.6 and 3.9 +/- 0.42 mg/l for T and E, respectively, at 30 min).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of digoxin on diaphragmatic strength generation in patients with chronic obstructive pulmonary disease during acute respiratory failure

We studied the effects of digoxin, a compound that has an inotropic effect on the myocardium, on diaphragmatic function in 8 patients with chronic obstructive pulmonary disease. All the patients were in acute respiratory failure and were artificially ventilated. Diaphragmatic strength was assessed by measuring the transdiaphragmatic pressure generated at functional residual capacity during bilateral supramaximal electrical stimulation of the phrenic nerves. The latter were stimulated before and at 45 and 90 min after administration of digoxin (0.02 mg/kg infused for 10 min). In all the patients, cardiac output was measured by the thermodilution technique using a Swan-Ganz catheter placed in the pulmonary artery. Arterial blood gases and pH were maintained within normal range by mechanical ventilation. In all the patients, digoxin plasma levels reached the therapeutic range (mean values, 2.82 +/- 0.17 and 2.90 +/- 0.20 nmol/L at 45 and 90 min, respectively) after digoxin administration. Diaphragmatic strength improves significantly after digoxin administration, the transdiaphragmatic pressure for an identical phrenic stimulation increasing by 19.5% (p less than 0.001) on the average. This increase was noted 45 and 90 min after digoxin administration. We conclude that digoxin has a potent effect on diaphragmatic strength generation that may be beneficial in patients with chronic obstructive pulmonary disease during acute respiratory failure. Furthermore, this inotropic positive effect of digoxin on the diaphragm, as previously observed for the myocardium, emphasizes the similarities between these 2 contractile tissues.

Effects of digoxin on diaphragmatic strength generation

Contrary to hindlimb muscle, extracellular calcium plays an important role in diaphragmatic strength generation (J. Appl. Physiol. 58: 2054-61, 1985). Since the inotropic effect of digitalis appears to be related to cell membrane transport of calcium, we studied the effect of digoxin on diaphragmatic contractility in 20 anesthetized dogs. The diaphragm was electrically stimulated with intramuscular electrodes. The transdiaphragmatic pressure (Pdi) during supramaximal (50 V) 2-s stimulations applied over a frequency range of 10-100 Hz was measured with balloon catheters at functional residual capacity. Cardiac output was measured with a Swan-Ganz catheter and diaphragmatic blood flow (Qdi) by timed volume collections of left inferior venous effluent. The force generated by the sartorius muscle during electrical stimulations was studied concomitantly to Pdi. In 10 dogs (group A) 0.04 mg/kg of digoxin was infused in 10 min. In 10 other dogs (group B) 0.2 mg/kg was administered. All measurements were performed during control and 30, 60, 90, and 120 min after digoxin administration. In group A, digoxin plasmatic level at 60 min reached a therapeutic range in all dogs (1.8 +/- 0.3 ng/ml), whereas in group B, digoxin plasmatic level was higher (8 +/- 1.3 ng/ml). No significant change in cardiac output and Qdi was noted after administration of digoxin, either in the dogs of group A or those of group B.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of theophylline on isolated diaphragmatic fibers. A model for pharmacologic studies on diaphragmatic contractility

An in vitro model of isolated diaphragmatic muscle fibers was developed to study the effects of theophylline on diaphragmatic contractility. The effects of theophylline on this model were compared for each dose with the effects of the drugs on a "classic" hemidiaphragmatic muscle preparation. Diaphragmatic strips obtained from 20 rats were placed into an open topped channel of a plexiglass tissue chamber and perfused with continuously flowing Krebs solution heated to 37 degrees and bubbled with a 95% O2 and 5% CO2 gas mixture so as to maintain pH, PO2, PCO2 constant (7.4, 100, and 35 mmHg, respectively). Isometric force generated in response to 1 Hz supramaximal electrical stimulation was measured with a highly sensitive photoelectric transducer. Graded doses of aminophylline (15 to 75 mg/L) were administered and their effect assessed on diaphragmatic peak twitch tension. On the single diaphragmatic muscle fibers preparation, theophylline produced a dose dependent increase in peak twitch tension, which, at a concentration of theophylline of 15 mg/L, a therapeutic dose, amounted to 111 +/- 1.5% of control (p less than 0.05). At a concentration of 60 mg/L the increase in peak twitch tension averaged 35 +/- 2.5% of control, (p less than 0.001). On the other hand, theophylline had no effect on the hemidiaphragm preparation until a dose of 250 mg/L. These findings suggest that the effects of theophylline on diaphragmatic contractility are due to a direct action of the drug on the contractile properties of the diaphragmatic fibers and also validate the presented in vitro model as a promising one for future pharmacologic studies on diaphragmatic contractility.

Effect of hypophosphatemia on diaphragmatic contractility in patients with acute respiratory failure

We studied the effects of hypophosphatemia on diaphragmatic function in eight patients with acute respiratory failure who were artificially ventilated. Their mean serum phosphorus level was 0.55 +/- 0.18 mmol per liter (normal value, 1.20 +/- 0.10). The contractile properties of the diaphragm were assessed by measuring the transdiaphragmatic pressure generated at functional residual capacity during bilateral supramaximal electrical stimulation of the phrenic nerves. Diaphragmatic function was evaluated in each patient before and after correction of hypophosphatemia, which was achieved by administration of 10 mmol of phosphorus (as KH2PO4) as a continuous infusion for four hours. After phosphate infusion, the mean serum phosphorus level increased significantly (1.33 +/- 0.21 mmol per liter, P less than 0.0001). The increase in serum phosphorus was accompanied by a marked increase in the transdiaphragmatic pressure after phrenic stimulation (17.25 +/- 6.5 cm H2O as compared with 9.75 +/- 3.8 before phosphate infusion, P less than 0.001). Changes in the serum phosphorus level and transdiaphragmatic pressure were well correlated (r = 0.73). These results strongly suggest that hypophosphatemia impairs the contractile properties of the diaphragm during acute respiratory failure, and they emphasize the importance of maintaining normal serum inorganic phosphate levels in such patients.

Effects of hypocalcemia on diaphragmatic strength generation

We studied the effects of hypocalcemia on diaphragmatic force and diaphragm blood flow (Qdi) in 12 anesthetized dogs. The diaphragm was electrically stimulated with intramuscular electrodes surgically implanted in the ventral surface of each hemidiaphragm. The transdiaphragmatic pressure (Pdi) during supramaximal (50 V) 2-s stimulations applied over a frequency range of 10-100 Hz was measured with balloon catheters during tracheal occlusion at functional residual capacity. A catheter was placed via the femoral vein into the left inferior phrenic vein, and Qdi was measured by timed volume collections of left inferior venous effluent. A catheter was introduced in a femoral artery to monitor blood pressure (BP). In five additional dogs, the force generated by the sartorius muscle during electrical stimulation was also studied concomitantly to diaphragmatic force. The animals were mechanically ventilated throughout the experiment, and the arterial blood gases and pH were maintained constant. Hypocalcemia was induced by a continuous infusion of EGTA (70 mg X kg-1 X h-1), which led to a progressive decrease (P less than 0.0001) of ionized calcium plasmatic level from 2.21 +/- 0.4 meq/1 during control to 1.69 +/- 0.06, 1.25 +/- 0.5, and 1.07 +/- 0.5 meq/1 after 30, 60, and 120 min, respectively. Hypocalcemia decreased progressively Pdi, which amounted to 84 +/- 3 (P less than 0.001) and 98 +/- 2% of control values for the low frequencies (10 and 20 Hz) and the high frequencies (50 and 100 Hz), respectively, after 30 min of EGTA infusion and to 74 +/- 5 and 79 +/- 6% for the low and high frequencies, respectively, after 120 min.(ABSTRACT TRUNCATED AT 250 WORDS)

[Hypophosphoremia during mechanical ventilation for chronic obstructive bronchopathies]

Hypophosphoremia may interfere with respiratory function in chronic obstructive pulmonary diseases (COPD) through different mechanisms: muscular exhaustion and weakness. Accordingly, the frequency and magnitude of hypophosphoremia was studied in 36 consecutive patients with acute respiratory failure and mechanical ventilation. Initial phosphoremia was normal (1,32 +/- 0,12 mmol/l) but often and rapidly decreased in all patients after mechanical ventilation had been started (0,54 +/- 0,14 mmol/l after 24 h). After this, phosphoremia remained low, slowly increasing with continued enteral nutrition (2000 Kcal, 276 g of glucides, 33 mmol/l of phosphorus). Four patients had severe hypophosphoremia after 24 h of mechanical ventilation (less than 0,30 mmol/l). Phosphoremia returned to a normal level 36 h after extubation. Hypophosphoremia was closely linked to pH improvement (r = + 0,67, P less than 0,001) and was paralleled by a drop in phosphaturia, suggesting intra-cellular penetration of phosphorus.

[Function of the respiratory muscles in acute cardiac decompensation]

In anesthetized dogs the performance of the respiratory muscles during cardiogenic shock and their influence on its outcome was studied. Shock was induced by cardiac tamponade. Cardiac output during shock amounted to 25-35% of control and was kept constant. Minute ventilation (VE) initially increased and then progressively decreased until respiratory arrest. The latter was due to impairment of respiratory muscle contractility, the pressure generated by the diaphragm (Pdi) decreasing despite a marked increase in the diaphragmatic electromyogram and of the phrenogram. Mechanical ventilation during shock prolonged survival for the same decrease in cardiac output, and also decreased substantially the severity of lactic acidosis. Furthermore, blood flow to the respiratory muscles during shock was different in the animals breathing spontaneously (SB) from that in mechanically ventilated animals (MV). The fraction of cardiac output distributed to the respiratory muscles during control amounted to 1.85% in MV and 2.79% in SB. With shock this decreased to 1.55% in MV while in SB it decreased by 21%, which suggests that mechanical ventilation during shock preserves a large portion of cardiac output used by the respiratory muscles during spontaneous breathing, thus making it available to other organs.

Bilateral phrenic stimulation: a simple technique to assess diaphragmatic fatigue in humans

Transdiaphragmatic pressure (Pdi) and the rate of relaxation of the diaphragm (tau) were measured at functional residual capacity (FRC) in six normal seated subjects during single-twitch stimulation of both phrenic nerves. The latter were stimulated supramaximally with needle electrodes with square-wave impulses of 0.1-ms duration at 1 Hz before and after diaphragmatic fatigue produced by resistive loaded breathing. Constancy of chest wall configuration was achieved by monitoring the diameter of the abdomen and the rib cage with a respiratory inductive plethysmograph system. During control the peak Pdi generated during the phrenic stimulation amounted to 34.4 +/- 4.2 (SE) cmH2O and represented in each subject a fixed fraction (17%) of its maximal transdiaphragmatic pressure. After diaphragmatic fatigue the peak Pdi decreased by an average of 45%, amounting to 18.1 +/- 2.7 cmH2O 5 min after the fatigue run, and tau increased from 55.2 +/- 9 ms during control to 77 +/- 8 ms 5 min after the fatigue run. The decrease in peak Pdi and the increase in tau observed after the fatigue run persisted throughout the 30 min of the recovery period studied, the peak Pdi amounting to 18.4 +/- 2.8 and 18.9 +/- 3.3 cmH2O and tau to 81.3 +/- 5.7 and 88.7 +/- 10 ms at 15 and 30 min after the end of the fatigue run, respectively. It is concluded that diaphragmatic fatigue can be detected in man by bilateral phrenic stimulation with needle electrodes without any discomfort for the subject and that the decrease in diaphragmatic strength after fatigue is long lasting.

Effects of theophylline on diaphragmatic strength and fatigue in patients with chronic obstructive pulmonary disease

We studied the effects of theophylline on diaphragmatic strength and fatigue in 15 patients with severe chronic obstructive pulmonary disease. Diaphragmatic strength was assessed by measurement of the transdiaphragmatic pressure generated at functional residual capacity during a maximal inspiratory effort against closed airways. Diaphragmatic fatigue was induced by resistive loaded breathing. The electrical activity of the diaphragm was recorded with an esophageal electrode during the fatigue runs, and the high-low ratio of the electrical signal was analyzed to assess diaphragmatic fatigue. Studies were performed before and after 7 and 30 days of theophylline administration (mean plasma level, 13 +/- 2 mg per liter). A control group received a placebo instead of theophylline. Theophylline increased maximal transdiaphragmatic pressure by 16 per cent after 7 days of administration (P less than 0.01), and this increase persisted after 30 days. No significant change in maximal transdiaphragmatic pressure was observed in the group given the placebo. Theophylline also suppressed diaphragmatic fatigue in all patients who received it. We conclude that theophylline has a potent and long-lasting effect on diaphragmatic strength and fatigue in patients with fixed airway obstruction.

Effects and mechanism of action of terbutaline on diaphragmatic contractility and fatigue

We studied the effects of intravenously administered terbutaline on diaphragmatic force and fatigue during electrical stimulation of the diaphragm in 17 anesthetized dogs. The diaphragm was stimulated indirectly through the phrenic nerves with electrodes placed around the fifth roots and directly with electrodes surgically implanted in the abdominal side of each hemidiaphragm. Transdiaphragmatic pressure (Pdi) during direct or indirect supramaximal 2-s stimulation applied over a frequency range of 10-100 Hz was measured with balloon catheters during tracheal occlusion at functional residual capacity. In seven dogs the administration of terbutaline (0.5 mg) had no effect on Pdi at any stimulation frequency applied directly or indirectly. The effect of terbutaline (0.5 mg) on diaphragmatic fatigue was then tested in 10 other dogs. Diaphragmatic fatigue was produced by continuous 20-Hz electrical supramaxial stimulation of the phrenic nerves during 30 min. At the end of the fatigue procedure Pdi decreased by 50 +/- 5 and 30 +/- 8% of control values at 10 and 100 Hz, respectively, for either direct or indirect stimulation. The decrease in Pdi for low frequencies of stimulation (10 and 20 Hz) lasted 100 +/- 18 min, whereas it lasted only 40 +/- 10 min for the high frequencies (50 and 100 Hz). When terbutaline (0.5 mg) was administered after the fatiguing procedure, Pdi increased within 15 min by 20 +/- 4% at 10 Hz and by 12 +/- 3% at 100 Hz for either direct or indirect stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of aminophylline on diaphragmatic fatigue during acute respiratory failure

The effects of aminophylline on diaphragmatic fatigue and recovery in the face of hypoxemia and hypercapnic acidosis were studied in anesthetized, spontaneously breathing, dogs. The phrenic nerves were stimulated supramaximally at 10, 20, 50, and 100 Hz during 2 s with electrodes placed around the fifth roots, and the resulting transdiaphragmatic pressure (Pdi) was measured with balloon catheters. The dogs were occluded before the stimulations at functional residual capacity. The latter was monitored by measuring the end-expiratory transpulmonary pressure, which remained constant throughout the experiment. Diaphragmatic fatigue was produced by resistive loaded breathing. At the end of the runs, which lasted 15 +/- 2 min, all the dogs were severely hypoxemic (30 +/- 5 mmHg), hypercapnic (65 +/- 4 mmHg), and acidotic (7.1 +/- 0.05). During the fatigue runs, phrenic stimulation resulted in a marked decrease in Pdi, which amounted at 20 Hz to 70 +/- 8% and 45 +/- 12% of the control values 5 min after the onset of the fatigue runs and at the end, respectively. After recovery (3 h), Pdi and arterial blood gas determinations returned to control values. Identical fatigue runs were repeated with aminophylline infusion (loading dose, 6 mg/kg in 10 min and maintenance dose, 1 mg/kg/h), leading to a plasmatic concentration of 16.4 +/- 2 mg/l. Aminophylline protected the diaphragm against fatigue, and despite the presence of hypoxemia and hypercapnic acidosis, the Pdi generated for a 20 Hz stimulation of the phrenic nerves at identical times of the preceding run amounting to 100 +/- 15% and 85 +/- 10% of control values, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Diaphragmatic contractility enhanced by aminophylline: role of extracellular calcium

We have studied the effects of aminophylline on diaphragmatic contractility in 12 anesthetized dogs. The phrenic nerves were stimulated supramaximally (20 Hz, 0.1 ms) with electrodes placed around the fifth roots, and the transdiaphragmatic pressure (Pdi) generated at functional residual capacity (FRC) was measured with balloon catheters. Constancy of FRC was monitored by measuring the end-expiratory transpulmonary pressure, the dogs being occluded at FRC before the stimulations. The electrical activity of the diaphragm (Edi) during the stimulations was recorded with electrodes inserted in both hemidiaphragms. Phrenic stimulations during an infusion of aminophylline (10 mg/kg in 5 min) increased Pdi by 25 +/- 8% of control values, whereas the Edi remained unchanged. This potentiating effect of aminophylline was abolished when an identical dose was injected during a continuous infusion of a calcium blocker (verapamil, 0.1 mg X kg-1 X min-1). Infusion of another methylxanthine compound, caffeine (10 mg/kg), also increased Pdi for an identical electrical phrenic nerve stimulation by 21 +/- 6% compared with control values. However, the potentiating effect of caffeine was not abolished by verapamil. We conclude that aminophylline in vivo increases diaphragmatic contractility and that extracellular calcium is necessary for this action, a mechanism not shared by another methylxanthine compound, caffeine.

Increased ventilation caused by improved diaphragmatic efficiency during aminophylline infusion

The mechanism underlying the increase in ventilation (VE) observed during aminophylline infusion was investigated in 12 anesthetized spontaneously breathing dogs. Progressive doses of aminophylline were infused every 30 min, leading to plasmatic levels of 10 to 20, 20 to 30, 30 to 50 mg/L. The increase in VE observed while increasing aminophylline plasmatic concentration ranged from 4.2 +/- 6 to 9.5 +/- 1.2 L/min. Concomitantly to VE, we measured an index of the inspiratory neuromuscular output of the diaphragm, the transdiaphragmatic pressure generated at FRC 0.1 s after the onset of a spontaneous inspiration developed against closed airways (Pdi0.1). For each plasmatic level of aminophylline, Pdi0.1 increased as VE (117 +/- 4, 126 +/- 2, 140 +/- 6% of control values for 10 to 20, 20 to 30, 30 to 50 mg/L, respectively). To establish the role played by an improvement in diaphragmatic contractility in the increase in Pdi0.1 with aminophylline, we measured for each plasmatic level of aminophylline the transdiaphragmatic pressure generated at FRC against closed airways during supramaximal stimulation at 10, 20, 50, and 100 Hz of the 2 phrenic nerves (Pdi). Pdi increased while increasing aminophylline plasmatic level for all the frequencies of stimulation. A relationship was found between Pdi and Pdi0.1 at any aminophylline plasmatic level as well as with VE. No change in the mechanical properties of the respiratory system occurred with aminophylline. We conclude that the increase in VE observed after aminophylline administration in our animal model is essentially due to an improvement in diaphragmatic contractility rather than an increase in the central nervous system output.

Comparison of esophageal, tracheal, and mouth occlusion pressure in patients with chronic obstructive pulmonary disease during acute respiratory failure

In 14 acutely ill patients with chronic obstructive pulmonary disease who were either intubated or breathed via a tracheostomy, we measured the pressures generated in the esophagus and trachea during the first 0.1 s of spontaneous inspiratory efforts against closed airway (P0.1). No significant difference was found between P0.1 in the trachea and esophagus, where it was measured at 2 balloon levels (distance from balloon tip to nares: 35 and 45 cm). In 4 of the patients we also compared esophageal and mouth occlusion pressures during mouth breathing, the orifice of tracheostomy being temporarily obstructed. Mouth P0.1 in the 4 patients averaged approximately 47% of the esophageal occlusion pressure (4.4 +/- 1.7 versus 8.9 +/- 3.1 cm H2O, respectively). Because in patients with COPD with upper airways bypassed (tracheostomized or intubated) the changes in esophageal and tracheal pressure during occluded respiratory efforts were similar, it is concluded that the difference between esophageal and mouth occlusion pressure is due to the tissue compliance of the oropharynx.

Effects of airway anesthesia on pattern of breathing and blood gases in patients with chronic obstructive pulmonary disease during acute respiratory failure

To assess the role played by airway receptors in the genesis of rapid and shallow breathing of patients with chronic obstructive pulmonary disease (COPD), we studied the effects of airway anesthesia in 14 patients with COPD during acute respiratory failure. Airway anesthesia was performed by fiberoptic xylocaine administration from the larynx to the subsegmental bronchi, all patients being intubated or tracheostomized. A small decrease in minute ventilation of 6 +/- 1% of the control values occurred after airway anesthesia. This was due to a decrease (p less than 0.01) in respiratory frequency (f) (14.5 +/- 1%). The latter resulted from an increase (p less than 0.0005) in the expiratory time, whereas the inspiratory time did not change significantly. On the other hand, tidal volume increased (p less than 0.02) by 10.1 +/- 0.6%. In all patients, these modifications were accompanied by arterial blood gas deterioration, mean PaO2 and PaCO2 of 42 +/- 3 mmHg and 62 +/- 3 mmHg, respectively, 15 min after xylocaine administration, as compared with 48 +/- 2 mmHg and 54 +/- 2 mmHg, respectively, during the control period. No correlation was found between the changes in minute ventilation and PaO2 or PaCO2. We conclude that (1) activation of airway receptors are involved in the determination of the rapid and shallow breathing observed in patients with COPD during acute respiratory failure, and (2) airway xylocaine anesthesia that worsens arterial blood gases is contraindicated in these patients.

Effects of the administration of O2 on ventilation and blood gases in patients with chronic obstructive pulmonary disease during acute respiratory failure

The effects of the administration of 100% oxygen on minute ventilation (VE) and arterial blood gases were studied in patients with chronic obstructive pulmonary disease during acute respiratory failure. The administration of O2 resulted in an early decrease in VE, which averaged 18% +/- 2 SE of the control VE, and was due to a decrease in both tidal volume (VT) and respiratory frequency (f). This was followed by a slow increase in VE, such that after 15 min of breathing O2, VE rose to 93 +/- 6% of the control room air value, with both VT and f similar to control values. Despite the small difference between VE while breathing room air and that at the fifteenth minute of O2 inhalation, PaCO2 increased by 23 +/- 5 mmHg, and no significant correlation was found between the changes in VE and PaCO2. By the fifteenth minute of O2 inhalation the PaO2 averaged 225 +/- 23 mmHg, and it was concluded that despite the removal of the hypoxic stimulus of O2 inhalation, the activity of the respiratory muscles remained great enough to maintain VE at nearly the same degree as that while breathing room air. Consequently, the changes in PaCO2 after the administration of O2 were mainly due to increased inhomogeneity of VA/Q distribution within the lungs.

Central respiratory drive in acute respiratory failure of patients with chronic obstructive pulmonary disease

Control of breathing was studied in patients with chronic obstructive pulmonary disease, both in the chronic state and during acute respiratory failure. The results were compared to those in a group of age-matched normal subjects. In patients breathing air, minute ventilation was not different during acute and chronic states, and was similar to that in normal subjects. The pattern of breathing, however, was different: acutely ill patients took shorter and smaller breaths, with a breathing frequency higher than that of normal subjects. The pattern of the chronic group was intermediate between that of acutely ill patients and that of normal subjects. Mouth occlusion pressure, an index of neuromuscular respiratory drive, was 5 times greater in acutely ill patients than in normal subjects. Administration of O2 at a flow of 5 L/min caused a small (14%), bus significant, decrease in minute ventilation due to decreased respiratory frequency. The tidal volume did not change, so the decrease in minute ventilation was the result of decreased inspiratory flow. This was associated with a decreased mouth occlusion pressure that was still 3 times greater than that of normal subjects. The increase in arterial PCO2, observed after administration of O2 was not correlated with the decrease in ventilation, indicating that other factors must be responsible for the increase in arterial PCO2. We concluded that (1) despite the poor mechanical advantage of the respiratory muscles in acute respiratory failure, the increased drive to breathe results in high mouth occlusion pressure and inspiratory flow, and (2) the increase in arterial PCO2, observed during administration of O2 is not related solely to changes in respiratory drive.