Peripheral airway involvement in asthma assessed by single-breath SF6 and He washout

The aim of the study was to assess how deep into the acinar region the airway response to cold dry-air hyperventilation challenge (CACh) reaches in subjects with asthma of different severity. Peripheral airway function was measured using a single-breath sulphur hexafluoride (SF6) and helium (He) washout test and overall airway function by forced expiratory volume in one second (FEV1) at rest, after CACh and beta2-therapy in 55 adults with a history of asthma. The normalised phase-III slopes (SnIII) for SF6 and He were used to assess peripheral airway obstruction and the (SF6-He) SnIII difference to indicate where obstruction occurred. While a greater He versus SF6 slope increase indicates a response close to the acinar entrance, the reverse indicates a response deeper into the acinar airspaces. Twelve subjects had a major fall in FEV1 (> or = 20%) after CACh, 16 a minor fall (10-19%), and 27 did not react. Resting He and SF6 SnIII were significantly greater in major responders with respect to minor and nonresponders, while resting FEV1 did not differ between the three groups. The major responders showed marked increases of He and SF6 SnIII after CACh, with greater increase for He resulting in a negative (SF6-He) SnIII difference. To conclude, airways close to the acinar entrance participate in the overall airway response to cold-air challenge in asthmatic adults with marked airway hyperresponsiveness to cold, dry air.

[Tetany as a difficult diagnostic problem in the neurological outpatient department]

The paper presents a model of diagnostic and therapeutic management of tetany, with special attention paid the role of magnesium and to psychotherapy or psychiatric treatment. Two types of tetany are distinguished: manifest and latent (spasmophilia). The former, due to hypocalcemia, is relatively rare and usually postoperative (parathyroid tetany), while the mechanism of the much more common latent tetany or spasmophilia involves hyperventilation and magnesium deficiency. Latent tetany affects particularly young women. There are many signs of spasmophilia, but none is specific, so this pathology is difficult to diagnose.

Treatment of space-occupying cerebral infarction

OBJECTIVE

Patients with a hemispheric infarct accompanied by massive edema have a poor prognosis; the case fatality rate may be as high as 80%, and most survivors are left severely disabled. Various treatment strategies have been proposed to limit brain tissue shifts and to reduce intracranial pressure, but their use is controversial. We performed a systematic search of the literature to review the evidence of efficacy of these therapeutic modalities.

DATA SOURCES

Literature searches were carried out on MEDLINE and PubMed.

STUDY SELECTION

Studies were included if they were published in English between 1966 and February 2002 and addressed the effect of osmotherapy, hyperventilation, barbiturates, steroids, hypothermia, or decompressive surgery in supratentorial infarction with edema in animals or humans.

DATA SYNTHESIS

Animal studies of medical treatment strategies in focal cerebral ischemia produced conflicting results. If any, experimental support for these strategies is derived from studies with animal models of moderately severe focal ischemia instead of severe space-occupying infarction. None of the treatment options have improved outcome in randomized clinical trials. Two large nonrandomized studies of decompressive surgery yielded promising results in terms of reduction of mortality and improvement of functional outcome.

CONCLUSIONS

There is no treatment modality of proven efficacy for patients with space-occupying hemispheric infarction. Decompressive surgery might be the most promising therapeutic option. For decisive answers, randomized, controlled clinical trials are needed.

[A case of coronary vasospasm treated with stent placement]

We report about a 49 year old woman with repeated chest pain at rest. During hyperventilation significant ST-segment elevation in leads V1-V5 appeared. Bicycle stress test did not provoke any ECG changes. Coronary angiography showed a significant stenosis of the left anterior descending coronary artery. Successful balloon angioplasty followed by stent implantation was performed. After an uneventful course of twelve months, hyperventilation could provoke neither chest pain nor ECG changes again without any antispastic medical treatment. Impact of fixed atherosclerotic lesions for the occurrence of coronary vasospasm, usefulness of hyperventilation as a non-invasive provocation test and therapy are discussed.

Hyperventilation-induced limb shaking TIA in Moyamoya disease

The authors present a case of hyperventilation-induced left upper limb shaking from an underlying Moyamoya disease. Video EEG monitoring and SPECT study were performed. Leptomeningeal collateral circulation was investigated by conventional angiography and by SPECT study with acetazolamide. Limb shaking in Moyamoya disease may result from a transient hypoperfusion of the contralateral frontoparietal cortex rather than basal ganglia.

Brain diffusion during hyperventilation: diffusion-weighted MR-monitoring in patients with temporal lobe epilepsy and in healthy volunteers

Hyperventilation (HV) can be used to provoke epileptiform activity and occasionally seizures in generalised and in focal epilepsies. Based on the hypothesis that HV might alter brain diffusion in the epileptogenic areas of patients with temporal lobe epilepsy (TLE), we examined these alterations using quantitative diffusion MR imaging (DI) in four patients with TLE and unilateral hippocampal sclerosis (TLE-HS) and six patients with TLE without hippocampal sclerosis (TLE-pure), and in 10 healthy volunteers. Brain diffusion was measured at baseline and immediately after 4 min of HV. In all patients with TLE HV was repeated two times, 4 min each, followed by subsequent DI. The apparent diffusion coefficient (ADC) was quantified in predefined regions of interest. In controls, the ADC did not differ between baseline and HV and between right and left side. Compared to controls TLE-HS patients showed significantly higher ADC at baseline in the hippocampus of the ictogenic side (111+/-13 vs. 87.5+/-4.26 x 10(-5) mm(2)/s, P=0.029). During HV ADC decreased significantly in the ictogenic hippocampus compared to controls (-17.3+/-7.1 vs. -3.34+/-8.7, P=0.004). In TLE-pure patients ADC of the ictogenic hippocampus was higher than in normals (99.3+/-14.2 vs. 87.5+/-4.26 x 10(-5) mm(2)/s, P=0.031) but there was no significant decrease during HV. Serial HV did not further enhance this decrease. No significant HV-induced changes were seen in other brain areas. In conclusion, our results show that HV can induce dynamic changes of brain diffusion in patients with sclerotic hippocampi but not in non-sclerotic hippocampi. These findings may be utilized for lateralisation of the epileptogenic hippocampus during presurgical evaluation of TLE.

[Characteristics of mental status of patients with neurocirculatory dystonia]

AIM

To specify forms of severity of mental disorders in neurocirculatory asthenia (NCA) for more precise differentiation between NCA as a nosological entity and syndrome.

MATERIAL AND METHODS

The examination including specially-designed interview, ECG, echo-CG, orthostatic and hyperventilation tests, bicycle exercise, consultation of the psychiatrist, psychological tests covered 80 NCA patients (31 men, 49 women, mean age 29.2 +/- 9.08 years).

RESULTS

NCA is characterized by the absence of a clear link with psychoemotional stress, seasonal disease aggravations, weakness, dizziness, negative results of orthostatic and hyperventilation tests. Among NCA criteria, dominating are "additional signs". Patients with anxio-fobic, panic, anxio-depressive neurotic disorders are characterized by strong relations between manifestation, subsequent disease exacerbations with psychogenia; attack-like NCA manifestation, prevalence of "basic signs" among diagnostic criteria (cardialgia, pulse and blood pressure lability, nonspecific alterations of T wave, positive orthostatic and hyperventilation tests).

CONCLUSION

NCA presents at least with two variants. In the first variant NCA picture is characterized by hereditary or early acquired vegetative stigmation and secondary neurotic disorders; the second variant presents as a clinically formed illness in which NCA symptoms manifest as a syndrome which is a leading component of a mental disease.

Heparin inhibits hyperventilation-induced late-phase hyperreactivity in dogs

Inhalation of heparin attenuates hyperventilation-induced bronchoconstriction in humans and dogs. The purpose of this study was to determine whether heparin inhibits the late-phase response to hyperventilation, which is characterized by increased peripheral airway resistance (RP), eicosanoid mediator production, neutrophilic/ eosinophilic inflammation, and airway hyperreactivity (AHR) at 5 h after dry air challenge (DAC). Fiberoptic bronchoscopy was used to record RP and airway reactivity (DeltaRP) to aerosol and intravenous histamine before and 5 h after DAC. Bronchoalveolar lavage fluid (BALF) cells and eicosanoid mediators were also measured approximately 5 h after DAC. DAC of vehicle-treated bronchi resulted in late-phase airway obstruction (approximately 120% increase over baseline RP), inflammation, increased BALF concentrations of leukotriene (LT) C(4), LTD(4), and LTE(4) and prostaglandin (PG)D(2), and AHR. Pretreatment with aerosolized heparin attenuated late-phase airway obstruction by approximately 50%, inhibited eosinophil infiltration, reduced BALF concentrations of LTC(4), LTD(4), and LTE(4) and PGD(2), and abolished AHR. We conclude that heparin inhibits hyperventilation-induced late-phase changes in peripheral airway function, and does so in part via the inhibition of eosinophil migration and eicosanoid mediator production and release.

[Chest pains in the dental environment]

Chest pain does not necessarily indicate cardiac disease. The most common causes of acute chest pain encountered in dental situations include hyperventilation, pulmonary embolism, angina pectoris and myocardial infarction. Stress and fear often cause rapid breathing or hyperventilation. This usually occurs in young adults and although the hyperventilating patient often complains of chest pain, this is rarely a manifestation of cardiac disease. Pulmonary embolism usually indicates the occlusion of a pulmonary artery causing severe chest pain. The primary clinical manifestation of angina pectoris is chest pain. Although most instances of anginal pain are easily terminated, the dentist must always consider the possibility that the supposed anginal attack is actually a sign of acute myocardial infarction (AMI). AMI is a clinical syndrome caused by a deficient coronary arterial blood supply to a region of myocardium that results in cellular death. There is a high incidence of mortality among AMI with death often occurring within 2 hours of the onset of signs and symptoms. The initial clinical manifestations of all types of chest pain can be similar. Therefore the dentist must develop proficiency in constituting a differential diagnosis and an efficient management protocol. As in most medical situations prevention is the most powerful tool. However, if chest pains do occur, measures such as airway management, oxygen supplementation, coronary artery dilation, analgesis and in extreme cases, cardiopulmonary resuscitation and evacuation to the emergency room, may be necessary.

Eicosanoids modulate hyperpnea-induced late phase airway obstruction and hyperreactivity in dogs

A canine model of exercise-induced asthma was used to test the hypothesis that the development of a late phase response to hyperventilation depends on the acute production of pro-inflammatory mediators. Peripheral airway resistance, reactivity to hypocapnia and aerosol histamine, and bronchoalveolar lavage fluid (BALF) cell and eicosanoid content were measured in dogs approximately 5 h after dry air challenge (DAC). DAC resulted in late phase obstruction, hyperreactivity to histamine, and neutrophilic inflammation. Both cyclooxygenase and lipoxygenase inhibitors administered in separate experiments attenuated the late phase airway obstruction and hyperreactivity to histamine. Neither drug affected the late phase inflammation nor the concentrations of eicosanoids in the BALF obtained 5 h after DAC. This study confirms that hyperventilation of peripheral airways with unconditioned air causes late phase neutrophilia, airway obstruction, and hyperreactivity. The late phase changes in airway mechanics are related to the hyperventilation-induced release of both prostaglandins and leukotrienes, and appear to be independent of the late phase infiltration of inflammatory cells.

Hyperventilation in traumatic brain injury patients: inconsistency between consensus guidelines and clinical practice

BACKGROUND

This study assessed patients with traumatic brain injury (TBI) to determine whether prehospital and community hospital providers employed hyperventilation therapy inconsistent with consensus recommendation against its routine use.

METHODS

This prospective analysis of 37 intubated TBI patients without herniation, undergoing helicopter transport to an urban Level I center, entailed flight crews' noting of assisted ventilation rate (AVR) and end-tidal carbon dioxide (ETCO2) upon their arrival at trauma scenes or community hospitals. A priori-set levels of AVR and ETCO2 were used to assess frequency of guideline-inconsistent hyperventilation, and Fisher's exact and Kruskal-Wallis tests assessed association between guideline-inconsistent hyperventilation and manual vs. mechanical ventilation mode.

RESULTS

Inappropriately high AVR and low ETCO2 were seen in 60% and 70% of patients, respectively. Manual ventilation was associated with guideline-inconsistent hyperventilation assessed by AVR (p = 0.038) and ETCO2 (p = 0.022).

CONCLUSION

Prehospital and community hospital hyperventilation practices are not consistent with consensus recommendations for limitation of hyperventilation therapy.

Acute lung injury and lung transplantation influence in vitro subtype conversion of pulmonary surfactant

The effects of surfactant treatment on surfactant subtype conversion after lung injury were examined. Dogs were subjected to hyperventilation for 8 h with or without surfactant treatment. Lungs were stored for 17 h, and the right lung was transplanted and reperfused for 6 h. Conversion of large aggregate (LA) surfactant to small aggregates was investigated using in vitro surface area cycling. LA from transplanted lungs (Transplant-LA) from the nontreated group converted more rapidly than Transplant-LA from the treated group. Transplant-LA from both groups converted more rapidly than LA from normal lungs. Calculations based on [(3)H]dipalmitoylphosphatidylcholine in the administered surfactant [bovine lipid extract surfactant (BLES)] showed that the endogenous component of Transplant-LA converted more rapidly than the exogenous component. This indicates exogenous BLES did not equilibrate completely with endogenous surfactant. LA from hyperventilated, stored donor right lungs and from the recipients' native lungs from the nontreated group converted more rapidly than corresponding LA in the BLES-treated group. Similar relative conversions were observed with exogenous components from all lungs. Relative conversion of endogenous component from Transplant-LA was more rapid than that from LA from donor's stored right lung or from the recipient's native right lung. Low levels of phenylmethylsulfonyl fluoride inhibited conversion of Transplant-LA to a greater extent than normal LA. LA from all experimental groups had similar protein levels. These studies show acute lung injury, transplant, ischemia-reperfusion, and surfactant treatment have major effects on surfactant subtype integrity.

A case of effective gastrostomy for severe abdominal distention due to breathing dysfunction of Rett's syndrome: a treatment of autonomic disorder

We report a case of 13-year-old-girl with Rett's syndrome and effectiveness of gastrostomy for severe paradoxical respiration, seizures and abdominal distention. Since the age of 3, she was observed to have typical hand-washing movement and autistic behavior. At the age of 8, she began to have hyperventilation and seizures in awake stage. Her symptoms were worse from year to year. At the age of 13, gastrostomy was done to treat severe abdominal distention. Her symptoms were improve dramatically by the gastric air removal through gastrobutton.

Cerebral vasoconstriction in vasovagal syncope: any link with symptoms? A transcranial Doppler study

BACKGROUND

Cerebral vasoconstriction has been described previously in vasovagal syncope (VVS). This phenomenon appears paradoxical in view of the well-known decrease of systemic vascular resistances taking places during VVS. We aimed to assess (1) whether cerebral vasoconstriction in VVS is an independent paradoxical phenomenon and (2) whether cerebral vasoconstriction has any link with symptoms and/or VVS onsets.

METHODS AND RESULTS

Seven young patients with recurrent VVS participated in the study. Each patient underwent monitoring of heart rate, blood pressure, cerebral blood flow velocity (by means of transcranial Doppler), end-tidal PCO(2), peripheral oximetry, respiratory rate, and tidal volumes both at rest and during head-up tilt. All the subjects experienced tilt-induced VVS. A significant increase of respiratory tidal volumes was observed in each subject >/=160 seconds before VVS. This deep breathing induced a PCO(2) decrease and, consequently, also a decrease in cerebral blood flow velocity and increase in cerebrovascular resistance (expressed by the increase of the pulsatility index). Within 40 seconds, 5 subjects started complaining of discomfort, in the absence of any significant blood pressure drop.

CONCLUSIONS

Cerebral vasoconstriction is not a paradoxical phenomenon when it occurs before tilt-induced VVS but rather is only the physiological consequence of the hyperventilation-induced hypocapnia that occurs in habitual fainters. The large lag between the onset of syncope and cerebral vasoconstriction excludes the hypothesis that VVS is dependent on abnormal behavior of cerebral hemodynamics.

Hyperventilation facilitates induction of supraventricular tachycardia: a novel method and the possible mechanism

INTRODUCTION

Hyperventilation has been demonstrated to alter autonomic function. Sympathomimetic drugs (isoproterenol) and parasympatholytic drugs (atropine) may be needed to facilitate induction of supraventricular tachycardia (SVT). The aim of this study was to test the clinical utility and mechanisms of hyperventilation to facilitate SVT initiation.

METHODS AND RESULTS

Fourteen patients with clinically documented SVT (9 AV nodal reentrant tachycardia and 5 AV reciprocating tachycardia) but noninducible during baseline electrophysiologic study were included. Immediately after hyperventilation test (at least 30 respirations/min) for 2 minutes, systolic blood pressure, sinus cycle length, anterograde and retrograde 1:1 conduction, and induced SVT were measured. Arterial blood gas, pH, and heart rate variability before and after hyperventilation were measured. Seven of nine patients with AV nodal reentrant tachycardia and 3 of 5 patients with AV reciprocating tachycardia could be induced immediately after the hyperventilation test. After hyperventilation, anterograde AV and retrograde VA 1:1 conduction were improved, sinus cycle length was decreased, and heart rate variability were decreased in both groups.

CONCLUSION

Hyperventilation can facilitate induction of SVT. Improvement of conduction properties and changes of autonomic function are the possible mechanisms.

A simple apparatus for accelerating recovery from inhaled volatile anesthetics

Hyperpnea increases anesthetic elimination but is difficult to implement with current anesthetic circuits without decreasing arterial PCO2. To circumvent this, we modified a standard resuscitation bag to maintain isocapnia during hyperpnea without rebreathing by passively matching inspired PCO2 to minute ventilation. We evaluated the feasibility of using this apparatus to accelerate recovery from anesthesia in a pilot study in four isoflurane-anesthetized dogs. The apparatus was easy to use, and all dogs tolerated being ventilated with it. Under our experimental conditions, isocapnic hyperpnea reduced the time to extubation by 62%, from an average of 17.5 to 6.6 min (P = 0.012), but not time from extubation to standing unaided. This apparatus may provide a practical means of applying isocapnic hyperpnea to shorten recovery time from volatile anesthetics.

IMPLICATIONS

A simple modification to a standard resuscitation bag allows one to increase ventilation without decreasing blood carbon dioxide levels. In dogs, we confirmed that this circuit can be used to accelerate the elimination of and recovery from volatile anesthetics.

Is periventricular leucomalacia a result of hypoxic-ischaemic injury? Hypocapnia and the preterm brain

Decrease in the arterial partial pressure of carbon dioxide (PaCO(2)) causes a reduction in cerebral blood flow in humans and in most animal species; in adults as well as in newborns and even in fetal life. Severely decreased PaCO(2) increases cerebral lactate production, modifies spontaneous electric brain activity, and may decrease the metabolic rate of oxygen. A relation between very low PaCO(2) and brain injury, however, has not been shown in adult humans or full-term newborn infants, nor in perinatal animals. In contrast, an association between low PaCO(2) and cerebral palsy and white matter injury in preterm infants has been reported repeatedly. A cause-and-effect relation is suggested by data from the immature rat: brain damage induced by ligation of a carotid artery can be reduced by adding CO(2) to the inspired gas and hence avoiding the consequences of spontaneous hyperventilation. This may be relevant for the clinical care of preterm infants, since PaCO(2) to a large extent is a function of respiratory management. The questions to be addressed are whether hypocapnia sensitizes the brain to hypoxaemia, and also whether the escape mechanisms are less effective in the preterm human brain.

The relation between hyperventilation and pediatric syncope

OBJECTIVE

The objective was to evaluate prospectively the role of hyperventilation in the development of neurocardiogenic syncope in children during head-upright tilt testing (HUTT).

STUDY DESIGN

Tilt testing was performed in 34 children (mean age 10.6 years) with clinical suspicion of syncope. Respiratory rate and end-tidal carbon dioxide pressure were continuously monitored during HUTT.

RESULTS

Tilt test was negative in 12 cases; 3 (25%) patients of this group exhibited hyperventilation any time during the test. In the remaining 22 cases the HUTT was positive, and 15 (68.2%) patients of this group exhibited hyperventilation at the onset of clinical symptoms and during syncope. In the positive HUTT group, the mean time elapsed from the tilt to the onset of syncope and the mean time elapsed from the onset of clinical symptoms to syncope (latency time) were significantly longer for patients who hyperventilated than for those who did not hyperventilate, (21.8 vs 11.5 minutes) (P =.002) and (78 vs 51 seconds) (P =.04), respectively.

CONCLUSIONS

Spontaneous hyperventilation could play a relevant role in the pathophysiology of pediatric neurocardiogenic syncope, and it could point out a specific subtype of response to orthostatic stress in susceptible patients. We suggest the inclusion of capnography in tilt-test protocols could improve the assessment of syncope in children.

Medical emergencies in the oral health care setting

On any given day a patient seen by the dental hygienist has the potential of experiencing a life-threatening medical emergency. All dental hygiene practitioners should be aware of potential risks that a patient may present, take steps to prevent life-threatening events from occurring, and plan for problems in advance of their happening. The primary goal of this course is to help dental hygienists carry out the ethical, moral, legal, and professional obligation owed any patient. The course will review the basics of medical emergencies, with particular emphasis on those that are most likely to occur in the dental office. Discussion will center on general aspects of prevention and preparation, and will focus on the recognition and emergency treatment of specific conditions. Vasodepressor syncope, orthostatic hypotension, acute adrenal insufficiency, hyperventilation, asthma, heart failure and acute pulmonary edema, cerebrovascular accident seizures, hyperglycemia, hypoglycemia, myocardial infarction, angina pectoris, and anaphylaxis will be emphasized.

Respiratory alkalosis

Respiratory alkalosis is an extremely common and complicated problem affecting virtually every organ system in the body. This article reviews the various facets of this interesting problem. Respiratory alkalosis produces multiple metabolic abnormalities, from changes in potassium, phosphate, and calcium, to the development of a mild lactic acidosis. Renal handling of the above ions is also affected. The etiologies may be related to pulmonary or extrapulmonary disorders. Hyperventilation syndrome is a common etiology of respiratory alkalosis in the emergency department setting and is a diagnosis by exclusion. There are many cardiac effects of respiratory alkalosis, such as tachycardia, ventricular and atrial arrhythmias, and ischemic and nonischemic chest pain. In the lungs, vasodilation occurs, and in the gastrointestinal system there are changes in perfusion, motility, and electrolyte handling. Therapeutically, respiratory alkalosis is used for treatment of elevated intracranial pressure. Correction of a respiratory alkalosis is best performed by correcting the underlying etiology.

Splanchnic-mesenteric capacitance bed in the postural tachycardia syndrome (POTS)

BACKGROUND

Gastroenterologic symptoms are common in the postural tachycardia syndrome (POTS), and postprandial worsening of orthostatic symptoms often occurs. We, therefore, investigated splanchnic-mesenteric vasoregulation in POTS.

SUBJECTS AND METHODS

Eleven patients with POTS (one man, 10 women, 29.4 +/- 7.7 (S.D.) years) and 10 controls (two men, eight women, 27.9 +/- 5.6 years) participated in this study. The protocol included 5 min of 70 degrees head-up tilt (HUT) before and after a liquid meal, as well as 1.5 min of hyperventilation. Blood pressure (BP), heart rate (HR), endtidal CO2, and cardiovascular indices derived from thoracic electrical bioimpedance were continuously monitored. Superior mesenteric artery (SMA) blood flow was measured by real time Doppler ultrasound and analyzed off-line. Cross-sectional area of SMA (SMA-area) and time-averaged velocity (SMA-TAV) were measured; SMA blood flow (SMA-BF) and vascular resistance (SMA-VR) were derived.

RESULTS

The following significant results were found: at supine rest, the POTS group had higher HR, BP, SMA-TAV and SMA-BF and a lower SMA-VR than the control group. HUT resulted in a reduction of pulse pressure, CO2 level, SMA-area, SMA-TAV and SMA-VF and increment of HR and SMA-VR in both groups. The POTS group underwent greater increment of HR and greater reduction of CO2 than controls. Hyperventilation induced increment of HR and cardiac index (CI) and reduction of SMA-VR in controls; no significant change occurred in POTS. The test meal induced increments of HR, CI, SMA-area, SMA-TAV and SMA-VF and reduction of SMA-VR in patients and controls for both supine rest and HUT.

CONCLUSION

The main novel observations of increased resting SMA-BF, SMA-TAV supine, and reduced SMA-VR when compared with controls support the notion that there is excessive splanchnic capacity (pooling) at rest in POTS.

Pulmonary capillary blood volume in hyperpnea-induced bronchospasm

Reactive hyperemia of the bronchial circulation has been postulated to contribute to the airway narrowing that occurs following exercise or hyperpnea in subjects with asthma with hyperpnea-induced bronchospasm (HIB). Changes in lung parenchymal mechanics also occur in HIB, including increases in peripheral airway resistance. Since the peripheral airways and lung parenchyma are supplied by the pulmonary circulation, and changes in the pulmonary circulation could alter airway resistance or tissue mechanics, we hypothesized that pulmonary capillary blood flow would increase in association with HIB, resulting in increases in pulmonary capillary blood volume (VC). We measured VC by using two test gases of varying oxygen concentration to determine the diffusing capacity of the lung for carbon monoxide (DL(CO)) before and after a period of hyperpnea in 13 subjects with asthma with HIB and 10 control subjects without asthma. Despite subjects with asthma having a significant fall in FEV(1) following hyperpnea compared with control subjects (DeltaFEV(1) = -26 +/- 12 versus -4 +/- 4%, mean +/- SD, p < 0.001), there was no change in the DL(CO) or VC from baseline values. We conclude that pulmonary capillary blood volume does not change following hyperpnea, and therefore that changes in pulmonary blood flow are not associated with HIB.