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At least 865 records · Page 48Linked to original sources
PubMed1989

The effects of hyperventilation on cerebral blood flow in the rat with an open and closed carotid-jugular fistula.

Perturbations in cerebral hemodynamics at the time of ablation of an arteriovenous shunt have been regarded as important in the pathogenesis of swelling and hemorrhage complicating resection of arteriovenous malformations (AVMs). A carotid-jugular fistula model in the rat had previously been investigated and found to simulate in part the nonhemorrhagic pathophysiology of a large cerebral arteriovenous fistula. Utilizing this model and measuring cerebral blood flow in 14 regions with a [14C]iodoantipyrine autoradiographic technique, the effects of hypocapnea on the cerebral circulation in opened and closed fistulas were investigated. Regional cerebral blood flow (rCBF) in control animals ranged from a median of 53 to 64 ml/100 g/min at a partial arterial carbon dioxide pressure (PaCO2) of 28 +/- 2 mm Hg and 85 to 112 ml/100 g/min at a PaCO2 of 40 +/- 5 mm Hg. In animals with an open carotid-jugular fistula created 12 weeks before the study, these median rCBF values at comparable PaCO2 levels ranged, respectively, from 15 to 39 ml/100 g/min and 50 to 68 ml/100 g/min (the 25th percentile for the open fistula in the hypocapneic group was 15 ml/100 g/min in 5 of the 14 regions studied). In contrast, median rCBF in the closed fistula group ranged from 73 to 100 ml/100 g/min in hypocapneic animals and from 118 to 187 ml/100 g/min in normocapneic animals. These results demonstrate the preservation of CO2 reactivity; hypoperfusion in the presence of a carotid-jugular fistula, hyperemia on fistula occlusion, and the potential to induce cerebral ischemia with hyperventilation in this model of a cerebral arteriovenous fistula.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Effect of short-duration hyperventilation during endotracheal suctioning on intracranial pressure in severe head-injured adults.

A repeated measures randomized within-group design was used to determine the effectiveness of controlled short-duration hyperventilation (HV) in blunting the increase of intracranial pressure (ICP) during endotracheal suctioning (ETS). A multimodal continuous real-time computerized data acquisition procedure was used to compare the effects of two HV ETS protocols on ICP, arterial pressure, cerebral perfusion pressure (CPP), heart rate, and arterial oxygen saturation in severe head-injured adult patients. The results indicated that short-duration HV for 1 minute, which decreases the PaCO2, reduced ETS-induced elevations in ICP while maintaining CPP. However, it is not clear whether short-duration HV is neuroprotective, particularly in ischemic regions of the brain. Therefore, before a change in practice is implemented on the use of short-duration HV as a prophylactic treatment against ETS-induced elevations in ICP, additional questions on cerebral oxygen delivery and uptake need to be answered.

Adolescent↗
PubMedDate not supplied

Psychophysiological assessment of respiratory function in panic disorder: evidence for a hyperventilation subtype.

OBJECTIVE: Previous research has found differences in respiratory function between panic disorder and other anxiety disorder populations. These differences have been explained as reflecting either a) a specific feature of panic disorder, b) merely a sign of increased general arousal, or c) a result of population sampling error. The current study addressed the question of such differences by using improved methodology over previous research. A preliminary evaluation of respiratory symptoms during panic attacks was undertaken as a means of identifying a respiratory-sensitive subtype of the panic patient. METHOD: Seventeen panic disorder patients (PD), 18 patients with generalized anxiety disorder (GAD), and 20 normal control (NC) subjects were administered a psychophysiological evaluation composed of baseline, stressor, and recovery phases. Panic patients were measured for the severity of respiratory symptoms during panic attacks. End-tidal CO2 (EtCO2) and respiration rate were measured throughout the psychophysiological evaluation. RESULTS: PDs demonstrated significantly lower baseline EtCO2 levels than the GADs and NCs, in spite of being equivalent to GADs on baseline anxiety levels. Moreover, panic patients reporting a high level of respiratory symptoms during panic attacks seemed to account for the bulk of observed differences. CONCLUSIONS: These findings lend support to a group of studies showing differences in respiratory function between panic disorder and other anxiety disorder populations. In addition, this study provides preliminary support for the presence of a distinct "hyperventilation subtype" of panic disorder. The implications of these findings for future research and treatment are discussed.

Adult↗
PubMed1998

A case of shock subsequent to treatment of intracranial hypertension by mannitol injection combined with hyperventilation.

This report describes a sudden decrease in blood pressure after conservative treatment of acute intracranial hypertension. A 63-year-old woman with acute hydrocephalus after undergoing clipping of an aneurysm of the right supracerebellar artery developed increased intracranial pressure, necessitating surgical management. On the operating table, the patient developed Cushing's reflex. Mannitol injection combined with hyperventilation was begun immediately to reduce her intracranial pressure. Fifteen minutes later, a sudden and prolonged suppression of circulation was observed (blood pressure 65/35-85/40 mmHg, heart rate 90-100 beats/min). Postoperatively, computed tomography of the head showed compression of the brain stem. We believe that this patient's blood pressure decrease was related to a sudden reduction of intracranial pressure and that mannitol injection was principally responsible for this occurrence.

Diuretics, Osmotic↗
PubMed1987

Vasospastic angina assessed by hyperventilation-thallium-201 myocardial scintigraphy.

The response to prolonged hyperventilation (HVT) was evaluated by electrocardiography (HVT-ECG) and thallium-201 myocardial scintigraphy (HVT-Tl-Sc) in 40 patients suspected of vasospastic angina. Both tests showed ischaemic changes in 16 patients and no changes in 20 patients. Two patients had abnormal HVT-ECG and normal HVT-Tl-Sc, and the reverse combination was found in two patients. Prolonged HVT was performed in 14 patients during coronary angiography (CAG). Nine developed transient total or subtotal occlusion in one of the major coronary arteries, all of whom had ischaemic HVT-ECG and eight had abnormal HVT-Tl-Sc. In the five patients without spasm at CAG four had normal HVT-ECG and all five normal HVT-Tl-Sc. Our data suggest that HVT-ECG and HVT-Tl-Sc have essentially the same sensitivity and specificity in detecting vasospastic angina.

Adult↗
PubMed1995

Severe hyperventilation and respiratory alkalosis during pressure-support ventilation: report of a hazard.

A 53-year-old woman with a flaccid quadriparesis developed severe hyperventilation and respiratory alkalosis during pressure-support ventilation. A gas leak in the ventilator system caused a loss of positive end-expiratory pressure and autocycling of the ventilator. Large ventilator breaths were then delivered because a high level of pressure support was set in a patient with low respiratory impedance. The complication is rare and its occurrence requires a combination of patient and equipment factors. Awareness of the responsible factors will promote detection and prevention of the hazard.

Alkalosis, Respiratory↗
PubMed1985

Effects of verapamil and sodium cromoglycate on bronchoconstriction induced by isocapnic hyperventilation.

Twenty-four patients who were known to develop bronchoconstriction in response to isocapnic hyperventilation (IH) took part in a double-blind, placebo-controlled trial to assess the effects of verapamil (5 mg) and sodium cromoglycate (SCG) 20 mg in the prevention of IH-induced bronchoconstriction. Both drug and placebo were inhaled in dry powder form and responses were assessed by serial measurements of forced expiratory volume in 1 sec (FEV1). Sodium cromoglycate was shown to offer significant protection whereas verapamil powder provoked bronchoconstriction in over 40% of patients and these patients appeared to be those with more marked degrees of bronchial reactivity.

Asthma, Exercise-Induced↗
PubMed1987

Effects of salbutamol and hyperventilation on the rise in serum potassium after succinylcholine administration.

It is known that circulating catecholamines stimulating beta 2-receptors and the acid-base balance play important roles in the regulation of serum potassium (K+). The present study was undertaken to investigate the effect of salbutamol (SB), a highly selective beta 2 agonist, and hyperventilation (HV)-induced alkalosis on the change in serum K+ after succinylcholine (SCh) administration in dogs. Pretreatment with SB (0.4 microgram.kg-1.min-1 for 30 min) produced sustained decreases in serum K+ and mean arterial pressure, and transient increases in cardiac output and serum insulin concentration. Maintaining respiratory alkalosis with HV (PaCO2 = 2.6-3.3 kPa) produced sustained decreases in serum K+ and cardiac output. Although both pretreatment with SB and HV-induced alkalosis significantly reduced the absolute increases in serum K+ after SCh, the effect of SB was more remarkable than that of HV. These results suggest that the degree of beta 2-receptor activity can strongly modulate the change in serum K+ after SCh administration.

Albuterol↗
PubMed1982

Hyperinflation on hyperventilation-a simple test to detect early airway disease.

The hypothesis was raised that an increased end-expiratory lung volume when switching over from normal to hyperventilation (positive delta FRC) can be used as a criterion of early obstructive lung disease. In 20 normal subjects and in 24 patients with suspect or manifest lung disease delta FRC at breathing frequencies of 40, 60 and 80 min-1, forced expiratory volume in one second (FEV1), vital capacity (VC), maximal expiratory flow at 50 and 25% of VC (MEF50 and MEF25) and closing volume (CV) were determined. FEV% (FEV1 X VC-1 X 100) and CV% (CV X VC-1 X 100) were calculated. delta FRC40 correlated negatively with FEV%, MEF50 and MEF25 for normals and patients separately with no difference between the groups. The residual standard deviation of delta FRC40 on FEV% was significantly reduced when MEF50 and MEF25 was included. delta FRC40 did not correlate with CV or CV%. delta FRC60 and delta FRC80 did not correlate with MEF50 and MEF25. The reproducibility of delta FRC40 was of the same order as the other variables studied. A delta FRC40 of +0.31 corresponded to MEF50 and MEF25 values 2 SD below the reference value. This suggests that a positive delta FRC40 of more than 0.31 indicates airway obstruction.

Adolescent↗
PubMedDate not supplied

Hyperventilation activation on EEG recording in childhood.

In 66 children with no neurologic symptoms, we analyzed EEG slowing quantitatively during standardized hyperventilation (HV) activation [respiration rate (RR) of 30/min, threefold increase of VE, and 4-min duration]. Changes in cerebral blood flow (CBF) and velocity were also monitored in right common carotid artery by Doppler ultrasonic method. Decreases in PCO2 and CBF were the fundamental factors producing EEG slowing during HV. The degree of EEG slowing was greater in younger children and well proportional to age with such standardized HV. The decrease in CBF was much greater in younger children at the beginning of HV and may be related to the significant EEG slowing. EEG slowing was not related to the degree of decrease in CBF. The age difference in EEG response to HV in children and adults may be due to the differences in the decrease in the CBF volume and sensitivity of the CNS to the change in CBF.

Adolescent↗
PubMedDate not supplied

Altered responsiveness during hyperventilation-induced EEG slowing: a non-epileptic phenomenon in normal children.

The relation between hyperventilation (HV)-induced high-amplitude rhythmical slowing (HIHARS) and altered responsiveness without generalized spike and wave activity has not been clearly defined. To test whether altered responsiveness is a nonspecific physiologic response rather than a symptom of generalized epilepsy, we assessed verbal recall ability and motor response testing in 12 healthy nonepileptic children (mean age 9.6 years). Both tasks were administered as a baseline before HV, during HV but before onset of EEG slowing, and during HIHARS. Verbal recall and motor responsiveness remained unchanged during baseline and HV before onset of slowing. During HIHARS, all children exhibited impaired verbal recall (p < 0.005) and 8 of 12 failed to respond to repeated auditory clicks (p < 0.005). Our findings indicate that in a normal setting, responsiveness may be impaired during HV in healthy nonepileptic children.

Acoustic Stimulation↗
PubMed2001

Effect of hyperventilation on cerebral blood flow velocity in preeclamptic pregnancies: is there evidence for an altered cerebral vasoreactivity?

The purpose of this study was to investigate cerebral arteriolar vasoreactivity function in preeclampsia. Preeclamptic (n = 26) and healthy pregnant (n = 22) women underwent transcranial Doppler sonography of the middle cerebral artery at rest and after 60 seconds of hyperventilation (HV). Systolic, diastolic, and mean blood flow velocities were recorded. The percentage change of the blood flow velocities after HV was calculated. Mean blood flow velocity of the middle cerebral artery was higher in preeclamptic women as compared with healthy pregnant women. No difference could be detected in percentage change of middle cerebral artery blood flow velocities after HV between the two groups. There is no evidence of a small-vessel vasoconstriction among preeclamptic patients. The role of vasoconstriction of the large cerebral arteries and vasodilation of the resistance arterioles, as well as a combination of these 2 pathomechanisms, in determining cerebral blood flow in preeclampsia and eclampsia should be investigated in further studies.

Adolescent↗
PubMed2006

The validity of a hyperventilation test for an investigation of autonomic failure: assessment in patients with multiple system atrophy and Parkinson's disease.

Although heart rate (HR) responses to hyperventilation (HV) have been used as a cardiovascular autonomic function test, autonomic involvement during HV remains uncertain. To clarify the relationship between autonomic activity and cardiovascular changes during HV, we compared cardiovascular responses during HV among subjects with different autonomic function, namely 16 patients with probable multiple system atrophy (MSA), 16 with possible MSA, 28 with Parkinson's disease (PD) and 28 healthy controls. Abnormalities of cardiovascular responses to head-up postural change and the Valsalva maneuver were definitely present in the order of probable MSA, possible MSA and PD, and abnormal HR and blood pressure (BP) responses during HV were observed in probable MSA and possible MSA, but not in PD. Unlike the significant difference in standard cardiovascular autonomic function tests, the HR and BP responses during HV were equivalent between probable and possible MSA. These findings suggest that cardiovascular control during HV may be affected not only by autonomic activity but also by other factors.

Adult↗
PubMed1980

Changes in cerebral blood flow during hyperventilation and CO2-breathing measured transcutaneously in humans by a bidirectional, pulsed, ultrasound Doppler blood velocitymeter.

We have used a bidirectional pulsed ultrasound doppler system which measures the instantaneous mean velocity across the lumen of a blood vessel in order to determine the relationship between alveolar PCO2 (PACO2) and blood flow in the four arteries supplying the brain in humans. Both high and low PACO2-values were explored. Six subjects, 3 males and 3 females (22-40 years) were studied by use of this non-invasive technique. To increase the PACO2 the subjects were breathing 4, 6 and 8% CO2 in air. PACO2 was reduced by voluntary hyperventilation down to a chosen end-expiratory PCO2 value of about 2.2 kPa. We found a linear relationship between arterial blood flow expressed as a percentage of control level and PACO2 in the range from 3.3 to 7.3 kPa. At the very lowest PACO2 values a levelling off of the response, with flow values of 40 to 45%, was observed. The CO2-reactivities in the 6 persons varied between 28.1 and 30.0%/kPa. The time course and the magnitude of the flow response were similar in all four arteries.

Adult↗
PubMed1966

The effect of beta adrenergic receptor blockade on the vasodilator response in the forearm to voluntary hyperventilation.

1. Blood flow was simultaneously measured by venous-occlusion plethysmography in both forearms of ten healthy men. 2. Voluntary overbreathing to produce about 8 times the resting ventilation caused a vasodilatation similar in both forearms. 3. When one forearm was treated with an intra-arterialinfusion of propranolol, a beta adrenergic blocking agent, the vasodilator response was reduced by an average of 28%, the reduction was significant (P < 0-01). 4. The failure of propranolol to abolish the vasodilator response was not due to incomplete block of beta adrenergic receptors since the dose of propranolol used reversed the vasodilator response to an intravenous infusion of adrenaline. 5. The results suggest that the vasodilator response to voluntary hyperventilation can be explained partly, but not entirely, by the release to the circulation of an adrenaline-like substance.

Adrenergic beta-Antagonists↗