Inhaled furosemide greatly alleviates the sensation of experimentally induced dyspnea

Mechanisms of dyspnea in chronic lung disease

PURPOSE OF REVIEW

To discuss three emerging areas of research triggering new hypotheses for mechanisms of dyspnea.

RECENT FINDINGS

There has been an emphasis on the importance of lung volumes in evaluating symptoms and lung function in patients with chronic obstructive pulmonary disease. Dyspnea intensity seems to more closely correlate with measures of hyperinflation than airflow limitation, highlighting the importance of neuromechanical dissociation in the development of dyspnea. Inhaled furosemide has demonstrated a beneficial effect in laboratory-induced dyspnea, and the sensation of air hunger has been ameliorated by this therapy, possibly via activation of pulmonary stretch receptors. There appear to be distinct affective and sensory components of dyspnea, and the affective dimension may be modifiable, although this has not been fully studied.

SUMMARY

Dyspnea in chronic obstructive pulmonary disease is clearly related to hyperinflation, and lung volumes are valuable for characterizing disease. It remains unclear whether a limitation in tidal volume due to dynamic hyperinflation is the key factor in exertional dyspnea in this disease. Research of inhaled furosemide demonstrates the importance of afferent sensory input in modifying dyspnea, and deserves further study. The contributions of the affective and sensory components of dyspnea remain unclear, but should be studied further.

Nebulized furosemide for the management of dyspnea: does the evidence support its use?

Dyspnea is a common and distressing symptom associated with multiple chronic illnesses and high levels of burden for individuals, their families and health care systems. The subjective nature dyspnea and a poor understanding of pathophysiological mechanisms challenge the clinician in developing management plans. Nebulized furosemide has been identified as a novel approach to dyspnea management. This review summarizes published studies, both clinical and experimental, reporting the use of nebulized furosemide. The search criteria yielded 42 articles published in the period 1988 to 2004. Although nebulized furosemide appeared to have a positive influence on dyspnea and physiological measurements, caution must be taken with the results primarily coming from small-scale clinical trials or observation trials. Despite the limitations of the studies reported, given the range of conditions reporting effectiveness of nebulized furosemide, further investigation of this potential novel treatment of dyspnea is warranted.

Breathlessness in cancer patients

Breathlessness (or dyspnoea) is a common symptom experienced by cancer patients. It may be iatrogenic and is often caused or aggravated by co-morbidity. Recent studies have elucidated the neural and chemical controls of breathing which may be involved in the production of dyspnoea. A rational approach involves making a diagnosis of aetiology and treating reversible causes wherever possible. The main approaches for palliation of dyspnoea include anti-cancer treatments; drugs; oxygen and airflow; non-medical approaches. Further research is needed to clarify the best pharmacological regimens and the place of more invasive interventions.

Furosemide inhalation in dyspnea of mustard gas-exposed patients: a triple-blind randomized study

Dyspnea is the hallmark symptom of some respiratory diseases such as chronic obstructive pulmonary disease and bronchiolitis and is a major reason for which these patients seek medical attention. We performed a randomized triple-blind controlled crossover clinical trial in which we compared the efficacy of inhaled furosemide (4 ml equal to 40 mg in 10 min) with placebo (4 ml of 0.9% saline solution) in 41 mustard gas-exposed patients. Dyspnea index, visual analog scale (VAS), and pulmonary function test results were obtained before and 4 h after treatments. Results showed that both furosemide and placebo significantly decreased VAS and dyspnea index and increased FEV(1), FVC, and FEV(1)/FVC, while there was no difference between the two drugs in these effects (p values .23, .61, .81, .36, and .27, respectively). Our results failed to address the previously reported effects of inhaled furosemide on dyspnea. In fact, we suggest that patients with a previous exposure to sulfur mustard, in which chronic bronchitis and bronchiolitis are the most suggested underlying mechanisms, may not benefit from furosemide to alleviate their dyspnea.

The multiple dimensions of dyspnea: review and hypotheses

Although dyspnea is a common and troubling symptom, our understanding of the neurophysiology of dyspnea is woefully incomplete. Most measurements of dyspnea treat it as a single entity. Although the multidimensional dyspnea concept has been mentioned for many decades, only recently has the concept been the subject of experimental tests. Emerging evidence has begun to favor the hypothesis that dyspnea comprises multiple dimensions or components that can be measured as different entities. Most recently, studies have begun to show that there is a separable 'affective dimension' (i.e. unpleasantness and emotional impact). Understanding of the multidimensional measurement of pain is far in advance of dyspnea, and has enabled progress in the neurophysiology of pain, including identification of separate neural structures subserving various elements of pain perception. We propose here a multidimensional model of dyspnea based on a state-of-the-art pain model, and review existing evidence in the light of this model.

The etiology and management of intractable breathlessness in patients with advanced cancer: a systematic review of pharmacological therapy

Intractable breathlessness is a common, devastating symptom of advanced cancer causing distress and isolation for patients and families. In advanced cancer, breathlessness is complex and usually multifactorial and its severity unrelated to measurable pulmonary function or disease status. Therapeutic advances in the clinical management of dyspnea are limited and it remains difficult to treat successfully. There is growing interest in the palliation of breathlessness, and recent work has shown that a systematic, evidence-based approach by a committed multidisciplinary team can improve lives considerably. Where such care is lacking it may be owing to therapeutic nihilism in clinicians untrained in the management of chronic breathlessness and unaware that there are options other than endurance. Optimum management involves pharmacological treatment (principally opioids, occasionally oxygen and anxiolytics) and nonpharmacological interventions (including use of a fan, a tailor-made exercise program, and psychoeducational support for patient and family) with the use of parenteral opioids and sedation at the end of life when appropriate. Effective care centers on the patient's needs and goals. Priorities in breathlessness research include studies on: neuroimaging, the effectiveness of new interventions, the efficacy, safety, and dosing regimens of opioids, the contribution of deconditioning, and the effect of preventing or reversing breathlessness.

Inhaled furosemide in hospitalized infants with viral bronchiolitis: a randomized, double-blind, placebo-controlled pilot study

OBJECTIVE

To evaluate the short and long-term clinical effects and the treatment-feasibility of inhaled-furosemide (IF) as compared with placebo via hood in hospitalized infants with viral-bronchiolitis (VB).

STUDY-DESIGN

A randomized, double-blind, placebo-controlled pilot-study was performed in previously healthy infants (0-12 months). Enrolled infants were randomized to receive either IF (2 mg/kg), or placebo nebulized by hood three times daily throughout the hospitalization. Clinical assessment (respiratory distress assessment instrument [RDAI]) was performed before, 30 and 60 min after the 1st daily inhalation. The short-term effects were evaluated by the RDAI, respiratory assessment change score (RACS) and oxygen requirement and the long-term effects by time to be weaned off oxygen, time to full enteral feeding, length of stay, and "ready to discharge" time.

RESULTS

Both groups (16 infants each) had comparable characteristics at study entry. Mean (+/-SD) age was 72 +/- 43 days, and 29/32 infants were RSV positive. Oxygen requirement (FiO(2)) decreased significantly at 30 min post-inhalation (30 +/- 9.2% to 26 +/- 7.1%, P < 0.05) only in the IF group. RACSs and long-term effects of both groups were comparable. Analysis of IF particles generated by the hood-nebulizer demonstrated that 36% and 49% of the particles were <3 and 5 microm, respectively. No side effects were observed during IF treatment.

CONCLUSION

Based on our pilot study, IF has no significant clinical effects in hospitalized infants with VB. IF via hood seems to be feasible and safe.

Coughing induced by airway irritation modulates the sensation of air hunger

The aim of this study was to clarify whether coughing elicited by airway irritation can modulate the sensation of air hunger. Using a visual analog scale (VAS), we measured air hunger for 30 s following breakpoint of a breath-hold in healthy young subjects who were asked to resume their breathing according to four patterns (free breathing, citric acid inhalation, voluntary cough, and panting) before and/or after airway anaesthesia. We also measured air hunger for citric acid-induced coughing and voluntary coughing without the preceding breath-holding. The free breathing after breakpoint of breath-holding causes an immediate relief of air hunger (VAS median values at 5, 15 and 25 s after breath-hold: 39, 0 and 0), whereas voluntary coughing causes a delay in the relief of air hunger (67, P < 0.05; 17, P < 0.05; and 0, NS) and a slower relief occurred during citric acid-induced coughing (81, P < 0.01; 49, P < 0.05; and 12, P < 0.05). Conversely, the voluntary coughing and citric acid-induced coughing per se failed to induce air hunger. Inhalation of lidocaine aerosol completely abolished the cough response to citric acid inhalation causing an immediate relief of air hunger, whereas airway anaesthesia alleviated only slightly the air hunger during voluntary coughing. The changes in air hunger during the panting were similar to those during the voluntary coughing observed before airway anaesthesia and were not affected by airway anaesthesia (VAS at 15 s point before versus after anaesthesia: 18 versus 15; NS). Coughing induced by airway irritation per se does not generate the sensation of air hunger but can aggravate it, presumably by vagally mediated mechanisms and/or central mechanisms.

Raising end-expiratory volume relieves air hunger in mechanically ventilated healthy adults

Air hunger is an unpleasant urge to breathe and a distressing respiratory symptom of cardiopulmonary patients. An increase in tidal volume relieves air hunger, possibly by increasing pulmonary stretch receptor cycle amplitude. The purpose of this study was to determine whether increasing end-expiratory volume (EEV) also relieves air hunger. Six healthy volunteers (3 women, 31 ± 4 yr old) were mechanically ventilated via a mouthpiece (12 breaths/min, constant end-tidal Pco2) at high minute ventilation (V̇e; 12 ± 2 l/min, control) and low V̇e (6 ± 1 l/min, air hunger). EEV was raised to ∼150, 400, 725, and 1,000 ml by increasing positive end-expiratory pressure (PEEP) to 2, 4, 6, and 8 cmH2O, respectively, for 1 min during high and low V̇e. The protocol was repeated with the subjects in the seated and supine positions to test for the effect of shifting baseline EEV. Air hunger intensity was rated at the end of each breath on a visual analog scale. The increase in EEV was the same in the seated and supine positions; however, air hunger was reduced to a greater extent in the seated position (13, 30, 31, and 44% seated vs. 3, 9, 23, and 27% supine at 2, 4, 6, and 8 cmH2O PEEP, respectively, P < 0.05). Removing PEEP produced a slight increase in air hunger that was greater than pre-PEEP levels ( P < 0.05). Air hunger is relieved by increases in EEV and tidal volume (presumably via an increase in mean pulmonary stretch receptor activity and cycle amplitude, respectively).

Inhaled furosemide does not alleviate respiratory effort during flow-limited exercise in healthy subjects

Expiratory muscle loading results in increased perception of respiratory effort; this response is mediated by non-vagal reflexes originating in the chest wall. Furosemide, due to its vagal effect, might not affect the perception of respiratory effort during expiratory flow-limited incremental exercise. In this study, we compared in nine healthy subjects the following determinants of exercise performance such as respiratory effort (Borg), workload (W'), ventilation (V'E), tidal volume (VT), respiratory frequency (f), and mean inspiratory flow (VT/TI), an index of central respiratory drive, during either standard incremental cycling exercise, or expiratory flow-limited incremental exercise. In addition we examined the effect of inhaled placebo, furosemide (40 or 80 mg) on the perception of respiratory effort following standard incremental cycling exercise and expiratory flow-limited incremental exercise. Compared with standard incremental cycling exercise, expiratory flow-limited incremental exercise increased the Borg score and VT/Ti, and decreased W',V'E ,VT, and f in all subjects at iso-workload. Neither placebo nor furosemide modified peak ventilatory variables, slopes, or intercepts of the relationships of the Borg score with W', V'E, VT/TI and VT during expiratory flow-limited incremental exercise. We conclude that (a) compared with standard incremental exercise, expiratory flow limited exercise increases central respiratory drive and perception of respiratory effort, and (b) furosemide does not affect the sensation of respiratory effort under the present conditions of increased drive to the respiratory muscles.

Effect of inhaled furosemide on air hunger induced in healthy humans

Recent evidence suggests that inhaled furosemide relieves dyspnoea in patients and in normal subjects made dyspnoeic by external resistive loads combined with added dead-space. Furosemide sensitizes lung inflation receptors in rats, and lung inflation reduces air hunger in humans. We therefore hypothesised that inhaled furosemide acts on the air hunger component of dyspnoea. Ten subjects inhaled aerosolized furosemide (40 mg) or placebo in randomised, double blind, crossover experiments. Air hunger was induced by hypercapnia (50+/-2 mmHg) during constrained ventilation (8+/-0.9 L/min) before and after treatment, and rated by subjects using a 100 mm visual analogue scale. Subjects described a sensation of air hunger with little or no work/effort of breathing. Hypercapnia generated less air hunger in the first trial at 23+/-3 min after start of furosemide treatment (58+/-11% to 39+/-14% full scale); the effect varied substantially among subjects. The mean treatment effect, accounting for placebo, was 13% of full scale (P=0.052). We conclude that 40 mg of inhaled furosemide partially relieves air hunger within 1h and is accompanied by substantial diuresis.

Na+-K+-2Cl− cotransporters and Cl− channels regulate citric acid cough in guinea pigs

Loop diuretics have been shown to inhibit cough and other airway defensive reflexes via poorly defined mechanisms. We test the hypothesis that the furosemide-sensitive Na+-K+-2Cl− cotransporter (NKCC1) is expressed by sensory nerve fibers innervating the airways where it plays an important role in regulating sensory neural activity. NKCC1 immunoreactivity was present on the cell membranes of most nodose and jugular ganglia neurons projecting to the trachea, and it was present on the peripheral terminals of putative mechanosensory nerve fibers in the airways. In urethane-anesthetized, spontaneously breathing guinea pigs, bolus application of citric acid (1 mM to 2 M) to an isolated and perfused segment of the tracheal mucosa evoked coughing and respiratory slowing. Removal of Cl− from the tracheal perfusate evoked spontaneous coughing and significantly potentiated cough and respiratory slowing reflexes evoked by citric acid. The NKCC1 inhibitor furosemide (10–100 μM) significantly reduced both the number of coughs evoked by citric acid and the degree of acid-evoked respiratory slowing ( P < 0.05). Localized tracheal pretreatment with the Cl− channel inhibitors DIDS or niflumic acid (100 μM) also significantly reduced cough, whereas the GABAA receptor agonist muscimol potentiated acid-evoked responses. These data suggest that vagal sensory neurons may accumulate Cl− due to the expression of the furosemide-sensitive Cl− transporter, NKCC1. Efflux of intracellular Cl−, in part through calcium-activated Cl− channels, may play an important role in regulating airway afferent neuron activity.

Management of Symptoms Other than Pain

Symptom management requires an understanding of the likely cause of the symptom in the individual patient, comprehensive assessment, and evidence-based interventions. This article explores the management strategies for common symptoms encountered in palliative care practice. Stomatitis, xerostomia, dysphagia, nausea and vomiting, anorexia, constipation, dyspnea, and fatigue are among the symptoms reviewed.

The role of vagal afferent nerves in chronic obstructive pulmonary disease

Circumstantial evidence supports the hypothesis that the vagal nervous system is dysregulated in chronic obstructive pulmonary disease. This dysregulation can lead to an increased sensitivity of the cough reflex such that the coughing becomes, at times, "nonproductive" or inappropriate. Vagal dysregulation can also lead to an increase in the activity of the parasympathetic reflex control of the airways, which contributes to greater mucus secretion and bronchial smooth muscle contraction. Indirect evidence indicates that lung disease is accompanied by substantive changes to the entire reflex pathways, including enhanced activity of the primary afferent nerves, increases in synaptic efficacy at secondary nerves in the central nervous system, and changes in the autonomic nerve pathways. Drugs aimed at normalizing neuronal activity may, therefore, be beneficial in chronic obstructive pulmonary disease.

Palliative management of refractory dyspnea in COPD

COPD is a progressive illness with worldwide impact. Patients invariably reach a point at which they require palliative interventions. Dyspnea is the most distressing symptom experienced by these patients; when not relieved by traditional COPD management strategies it is termed "refractory dyspnea" and palliative approaches are required. The focus of care shifts from prolonging survival to reducing symptoms, increasing function, and improving quality of life. Numerous pharmacological and non-pharmacological interventions can achieve these goals, though evidence supporting their use is variable. This review provides a summary of the options for the management of refractory dyspnea in COPD, outlining currently available evidence and highlighting areas for further investigation. Topics include oxygen, opioids, psychotropic drugs, inhaled furosemide, Heliox, rehabilitation, nutrition, psychosocial support, breathing techniques, and breathlessness clinics.

Effects of naloxone on respiratory sensation before and after a removal of severe respiratory stress

Severe respiratory stress causes dyspnea, and a sudden release of this stress frequently accompanies a euphoric sensation. We hypothesized that acute severe respiratory stress may result in an elaboration of endogenous opioids within the central nervous system, and that these opioids may play significant roles in relieving dyspnea and generating euphoric sensation after a sudden removal of the stress. To test this hypothesis, we examined the effects of naloxone (0.04 mg/kg, I.V.) and the placebo (normal saline) on changes in respiratory sensation before and after the release of severe respiratory stress in a double-blind, randomized, crossover study in 14 healthy adults. Acute severe respiratory stress was induced by loaded breathing with a combination of resistive loading and hypercapnia. The subjects rated their changes in sensation by using a bidirectional visual analogue scale. Naloxone pretreatment affected neither the ventilation nor the development of dyspneic sensation during loaded breathing. Naloxone pretreatment only slightly attentuated the euphoric sensation developed after the release of severe respiratory stress. These findings suggest a small role of opioids in relieving dyspnea and in generating euphoria before and after a sudden removal of stress.

Management of dyspnea

Patients with cancer frequently report dyspnea, the uncomfortable awareness of breathing. Lung involvement with cancer does not predict its occurrence. Patients describe it as one of the most frightening and distressing symptoms, and patient self-report is the only reliable measure. Measurements of respiratory rate, oxygen saturation, and arterial blood gases do not measure dyspnea. Opioids in modest doses have been demonstrated to give effective relief of dyspnea, whether or not identifiable reversible causes exist. Medical management of dyspnea can be directed at the underlying cause when the potential benefits outweigh the burdens of such treatment. In rare cases where symptomatic treatment is unable to control dyspnea to the patient's satisfaction, sedation is an effective, ethical option.

Effects of inhaled furosemide on exertional dyspnea in chronic obstructive pulmonary disease

The aim of this study is to investigate the effects of inhaled furosemide on the sensation of dyspnea produced during exercise in patients with stable chronic obstructive pulmonary disease (COPD). In a double-blind, randomized, crossover study we compared the effect of inhaled furosemide on dyspneic sensation during exercise testing with that of placebo. Spirometry and incremental and constant-load exercise testing were performed after inhalation of placebo or furosemide on 2 separate days in 19 patients with moderate or severe COPD. Subjects were asked to rate their sensation of respiratory discomfort using a 100-mm visual analog scale. There was significant improvement in mean FEV1 and FVC after inhalation of furosemide (p = 0.038 and 0.005, respectively) but not after placebo. At standardized exercise time during constant-load exercise testing but not during incremental exercise, the mean dyspneic visual analog scale score was lower after inhalation of furosemide compared with placebo (33.7 +/- 25.2 vs. 42.4 +/- 24.0 mm, respectively, p = 0.014). We conclude that inhalation of furosemide alleviates the sensation of dyspnea induced by constant-load exercise testing in patients with COPD and that there is significant bronchodilation after inhalation of furosemide compared with placebo in these patients.

Effect of nebulized furosemide in terminally ill cancer patients with dyspnea

We evaluated the effect of ultrasonically nebulized furosemide (20 mg) on dyspnea uncontrollable by standard therapy in patients with terminal cancer. Dyspnea was evaluated using the Cancer Dyspnea Scale (CDS) before and 60 min after inhalation. Changes in arterial blood gases, hemoglobin oxygen saturation (SpO2), heart rate (HR), and respiratory rate (RR) also were evaluated. In 12 of 15 patients (80%), total dyspnea scores by CDS improved significantly after inhalation of furosemide (P = 0.007), especially concerning a reduced sense of effort (P = 0.013) and reduced anxiety (P = 0.04). No significant changes were observed in the partial pressure of oxygen in arterial blood (PaO2), the partial pressure of carbon dioxide in arterial blood (PaCO2), SpO2, HR, or RR. Inhalation of nebulized furosemide appears to be effective against dyspnea in terminally ill cancer patients.

Effects of inhaled furosemide on CO(2) ventilatory responsiveness in humans

We previously showed that inhaled furosemide improves experimentally induced dyspnea. In order to test the possibility that inhaled furosemide may alter the CO(2) chemosensitivity and thereby reduce the dyspneic sensation, the effect of inhaled furosemide on CO(2) chemosensitivity was evaluated with a double-blinded, randomized crossover design in 10 healthy subjects. The CO(2) chemosensitivity was measured by the steady-state and rebreathing methods before and after the inhalation of placebo (normal saline) and furosemide aerosols (40 mg). In addition, subjects were asked to rate their sensation of respiratory discomfort using a visual analog scale (dyspneic VAS) during the measurement of CO(2) chemosensitivity with the steady-state method. Our results showed that (1) inhaled furosemide does not affect the breathing patterns of resting breathing, (2) inhaled furosemide does not affect the slope and intercept of the CO(2) response curve, regardless of whether the CO(2) chemosensitivity is measured by the steady-state technique or rebreathing technique and (3) inhaled furosemide improves the dyspneic sensation produced during hypercapnic hyperpnea. These results suggest that the mechanism of the improvement of dyspnea by inhaling furosemide is not associated with the decrease in the ventilatory drive to CO(2).

Effects of ondansetron on respiratory pattern and sensation of experimentally induced dyspnea

CONTEXT

Dyspnea remains a therapeutic challenge, especially in chronic respiratory conditions. Recent studies have shown that the induction of unpleasant dyspnea sensations activates areas in the insular cortex.

OBJECTIVE

This study was designed to investigate the potential effects of ondansetron, a potent anti-serotonin agent, on induced dyspnea sensation.

TYPE OF STUDY

A randomized double blind study.

SETTING

Pulmonary Function Laboratory of Hospital das Clínicas de Ribeirão Preto.

PARTICIPANTS

Ten healthy male volunteers (mean age +/- standard error = 23.1 +/- 0.41 years) without respiratory diseases and showing normal spirometric tests.

INTERVENTIONS

Uncomfortable breathing was induced in the volunteers on two different days, via the use of inspiratory resistors (loads of 0, 7, 14 and 21 cm H2O/l/sec) and breathholding, two hours after taking 8 mg of ondansetron (Ond) or placebo (Plac).

MAIN MEASUREMENTS

Respiratory discomfort during breathing under loading was evaluated on a 100-mm visual analog scale. The maximum length of time of voluntary apnea was measured in seconds.

RESULTS

The mean maximum voluntary apnea time did not differ between the ondansetron and placebo days (Plac = 96 +/- 6.6 sec vs. Ond = 100 +/- 7.9 sec). Ondansetron did not influence the dyspnea sensation induced by different inspiratory loads (0 cm H2O/l/sec: Ond = 1.4 mm +/- 0.44 vs. Plac = 2.1 +/- 0.85 mm; 7 cm H2O/l/sec: Ond = 16.6 +/- 2.74 mm vs. Plac = 13.7 +/- 2.06 mm; 14 cm H2O/l/sec; Ond = 30.5 +/- 4.50 mm vs. Plac = 27.1 +/- 3.44 mm; 21 cm H2O/l/sec: Ond = 50.3 +/- 6.72 mm vs. Plac = 49.4 +/- 6.72 mm). Ondansetron led to significant decreases in tidal volume under basal conditions and when breathing under the highest inspiratory loading (0 cm H2O/l/sec: Ond = 0.83 +/- 0.26 l vs. Plac = 1.0 +/- 0.28 l; 21 cm H2O/l/sec: Ond = 0.86 +/- 0.23 l vs. Plac = 1.1 +/- 0.22 l)

CONCLUSION

The present results suggest that 5-HT3 receptors do not play an important role in the mediation of dyspnea sensations.

Furosemide: progress in understanding its diuretic, anti-inflammatory, and bronchodilating mechanism of action, and use in the treatment of respiratory tract diseases

Accumulated experimental and clinical data suggest that adrenocorticosteroids and/or endogenous ouabain-like substances may play an important role in the mechanism of furosemide diuretic action. It was reported that the drug is highly bound in the adrenals, lungs, kidney, spleen, and liver. In patients with liver cirrhosis, furosemide exerted a markedly decreased natriuretic effect compared with normal subjects, and the plasma levels of circulating endothelin and atrial natriuretic factor (ANF) were significantly elevated. In neonates, after administration of furosemide, the urinary excretion of endothelin-1 and aldosterone increased markedly, and it is known that endothelin may release ANF and aldosterone in a dose-dependent manner. Furosemide was used to stimulate zona glomerulosa, whereas ANF decreased the production of steroids in zona glomerulosa and fasciculata cell culture owing to stimulation by various factors. Because the concomitant use of ANF and furosemide appeared to be diuretically effective in newborns after cardiac surgery, one may suggest that furosemide competes with ANF for its effects on the adrenals. Furosemide administered by inhalation exerted a protective effect on allergic and perennial nonallergic rhinitis and was effective in preventing the postsurgical recurrence of nasal polyposis. The drug can also be used as an antiasthmatic agent. In preterm ventilator-dependent infants with chronic lung disease, aerosolized furosemide improved pulmonary function with no marked effect on diuresis. In adults and children with asthma, furosemide exerted a protective effect against bronchoconstriction induced by several indirect stimuli similar to that of disodium cromoglycate or nedocromil. Aerosolized furosemide had a preventive effect also on bronchoconstriction induced by inhaled lysine acetylsalicylate in patients with aspirin-sensitive asthma. In high-dose beclomethasone-dependent asthma, inhaled lysine acetylsalicylate and furosemide exerted a mutually potentiating antiasthmatic activity, allowing considerable sparing of the inhaled steroid. It is proposed that this effect may be explained by the corticosteroid-sparing action of lysine released from the lysine acetylsalicylate molecule because similar beneficial effects were also obtained after the concomitant use of epsilon-aminocaproic acid (whose chemical structure is almost the same as that of lysine) and prednisone. Furosemide exhibited an anti-inflammatory effect through inhibition of production and release of cytokines interleukin (IL)-6, IL-8, and tumor necrosis factor-alpha from peripheral mononuclear cells, which may have a beneficial effect on local inflamed tissue imbalance in the ratio of different cytokines, thus improving the sensitivity of target cells to endogenous glucocorticosteroids.

Do steroids interfere in dyspnoea sensation?

Dyspnoea remains a remarkable clinical problem and a therapeutic challenge, mainly in chronic respiratory conditions. This study investigated the potential effects of steroids on dyspnoea sensation regardless of their pulmonary anti-inflammatory actions. Sixteen healthy men (mean age +/- SD = 22.5 +/- 1.6 years) developed uncomfortable breathing by the use of inspiratory resistors (loads of 0, 7, 14 and 21 cm H2O/l/s) and breathholding 6 h after taking 40 mg of prednisone (Pred) or placebo (Plac). Respiratory discomfort during breathing with loads was evaluated with a 100 mm visual analog scale. The maximum voluntary apnoea time did not differ between the prednisone and placebo days (Plac = 96 +/- 11.8 s x Pred = 105 +/- 12.2 s) and prednisone did not influence the dyspnoea sensation induced by different inspiratory loads (0 cm H2O/l/s: Pred = 2.8 mm x Plac = 1.9 mm; 7 cm H2O/l/s: Pred = 18.3 mm x Plac = 18.6 mm; 14 cm H2O/l/s; Pred = 33.0 mm x Plac = 34.1 mm; 21 cm H2O/l/s: Pred = 48.1 mm x Plac = 49.6 mm). Prednisone intake was associated with a significant increase in minute ventilation during breathing with no inspiratory loads (Pred = 11.91 +/- 1.28 l/min- x Plac = 9.95 +/- 0.86 l/min). Although steroids certainly may improve respiratory conditions due to anti-inflammatory actions, available evidence does not support any specific beneficial effect of these drugs on these perception of dyspnoea itself.

Pharmacology of airway afferent nerve activity

Afferent nerves in the airways serve to regulate breathing pattern, cough, and airway autonomic neural tone. Pharmacologic agents that influence afferent nerve activity can be subclassified into compounds that modulate activity by indirect means (e.g. bronchial smooth muscle spasmogens) and those that act directly on the nerves. Directly acting agents affect afferent nerve activity by interacting with various ion channels and receptors within the membrane of the afferent terminals. Whether by direct or indirect means, most compounds that enter the airspace will modify afferent nerve activity, and through this action alter airway physiology.

Nebulized furosemide as a novel treatment for dyspnea in terminal cancer patients

Three terminal cancer patients with severe dyspnea were treated with nebulized furosemide. The underlying causes of dyspnea varied. Twenty milligrams of furosemide was nebulized and inhaled four times each day. Dyspnea dramatically improved and could be controlled for weeks. No noticeable side effects were observed. Inhalation of nebulized furosemide seems to be an effective and useful treatment for dyspnea in terminal cancer patients, but these observations need to be confirmed in a randomized controlled trial.

Lack of positive interaction between CO2 and hypoxic stimulation for P(CO2)-VAS response slope in humans

To compare the effect of hypoxia on ventilatory responses and respiratory sensation to carbon dioxide, 29 young adults were examined using a modified Read's rebreathing method with four experimental conditions. We used varying gas mixtures and kept PET(O2) constant at >300, 100, 80 and 60 mmHg for each four rebreathing tests. Respiratory sensation was measured by visual analog scale (VAS). The slope of the CO2-ventilation response curve increased significantly with hypoxia, confirming a positive ventilatory interaction between hypoxia and hypercapnia. However, the slope of the CO2-VAS response curve remained unchanged. The V(E)-VAS relation slope tended to become depressed with advancing hypoxia, i.e. the magnitude of VAS elicited by a given ventilation decreased with hypoxia, signifying that dyspneic sensation was effectively mitigated during hypoxic hyperventilation. We suggest that this relief of dyspneic sensation might be due to the inhibitory respiratory effect from augmented pulmonary stretch receptor (PSR) activity.

Responses of tracheobronchial receptors to inhaled furosemide in anesthetized rats

Inhalation of furosemide, a loop diuretic, has shown favorable effects on experimentally induced cough, bronchoconstriction, and dyspnea. The effect of inhaled furosemide on tracheobronchial receptors was studied in anesthetized, spontaneously breathing rats. Single unit or pauci unit activity was recorded from the right vagus nerve. Tracheobronchial receptors were classified into slowly and rapidly adapting receptors (SARs and RARs, respectively), based on their adaptation index (AI), which was derived from the decrease in spike frequency (sf) over 2 s, expressed as a percentage of the peak firing rate. There were 43 SARs (AI </= 25%) and eight RARs (AI >/= 50%). Inhalation of furosemide (n = 29) increased the slope of airway pressure (Paw) versus sf of SARs from 8.6 to 14.8 Hz/cm H(2)O with an increase in sf at Paw = 0 cm H(2)O from 18.0 to 49.5 Hz, resulting in an upward shift of the line. Neither inhalation of vehicle (n = 9) nor intravenous injection of furosemide (n = 5) changed this relationship. In addition, inhalation of furosemide attenuated the activity of RARs. These findings indicate that SARs are sensitized and RARs desensitized by inhalation of furosemide. We discuss possible mechanisms for this, and its relevance to clinical problems of dyspnea, bronchoconstriction, and cough.