Does acute hyperventilation provoke cerebral oligaemia in comatose patients after acute head injury?

In 27 comatose patients with acute head injury, 45 paired studies of regional cerebral blood flow (rCBF) were performed before and after hyperventilation. In total 676 regions were studied, and rCBF was calculated as initial slope index using the intracarotid washout technique of 133 Xe. The tests were applied from one day to three weeks after the acute trauma. In total hyperventilation from PaCO2 averaging 4.8 to 3.5 kPa increased the frequency of regions with oligaemia defined CBF less than 20 ml/100 g/min from 5 to 16%. Before hyperventilation oligaemia was observed in 11 of 45 studies (9 of 27 patients); after hyperventilation the frequency increased to 21 studies (15 patients). The frequency of severe oligaemia (CBF less than 15 ml) increased from 0.1 to 3% of all regions, or from 2 to 8 of all studies (from 2 to 9 patients). The increased frequency of oligaemia after hyperventilation was correlated to a poor outcome (dementia, vegetative survival or death), where it was observed in 21% of all regions, in 16 of 26 studies and 11 of 15 patients, whereas the frequency in patients with a good recovery was found to be 7% of all regions and observed in 5 of 19 studies (4 of 12 patients). The high frequency of oligaemia after hyperventilation was associated to a low hemispheric CBF before hyperventilation, but not to the level of PaCO2, the level of intracranial pressure, cerebral perfusion pressure or CSF-pH or lactate.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurologic manifestations of pulmonary disease

Respiratory insufficiency of any cause has significant effects on the nervous system. Headache, mental status changes, papilledema, and numerous motor abnormalities including asterixis are commonly seen. Abnormalities in ventilation and gas exchange result in hypoxia, hypercapnia, and respiratory acidosis, and these, in turn, interfere with cerebral metabolism, increase CBF, and may raise intracranial pressure. Chronic respiratory insufficiency can persist for many months with minimal neurologic symptoms, as numerous compensatory mechanisms, particularly renal, may take effect. Treatment includes restoring adequate ventilation and improving gas exchange and may require tracheal intubation and assisted ventilation. Supplemental oxygen therapy should be carefully monitored, as high rates of flow may suppress the hypoxic drive for respiration and lead to significant carbon dioxide retention. The sleep apnea syndromes are a group of disorders in which abnormal respiratory patterns during sleep result in hypercapnia and hypoxemia. Intermittent obstruction of the upper airway and abnormalities of brainstem respiratory centers cause frequent nocturnal awakenings and apneas in these patients. Treatments vary and include weight loss in obese subjects, respiratory stimulants, tracheostomy, and diaphragmatic pacing. Rapid ascent to high altitudes may result in headache, changes in mental status, papilledema, and other neurologic symptoms in certain individuals: a syndrome known as high-altitude sickness. Hypoxia leading to cerebral edema, nocturnal periodic breathing, and hypobaria produces neurologic symptoms in these individuals. Acetazolamide and dexamethasone may be effective in minimizing symptoms of this disorder. Sustained hyperventilation produces acral and circumoral paresthesias and lightheadedness in anxious individuals and can be maintained by relatively normal ventilatory patterns once established. These symptoms are due to hypophosphatemia and respiratory alkalosis, the latter reducing CBF and causing localized tissue hypoxia. Rebreathing into a paper bag at the first awareness of symptoms is the most effective form of treatment.

Hypoxic hazards of traditional paper bag rebreathing in hyperventilating patients

It is traditional practice to treat acute hyperventilation (thought to be due to anxiety) by having patients rebreathe into a brown paper bag. The author reports three cases in which this treatment, erroneously applied to patients who were hypoxemic or had myocardial ischemia, resulted in death. This clinical experience motivated a study of the effects of paper bag rebreathing in normal volunteers. Subjects deliberately hyperventilated to an average end-tidal CO2 concentration of 21.6 (SD, 3.2) mm Hg and then continued to hyperventilate into a no. 4 Kraft brown paper bag containing the calibrated sensors for a Hewlett-Packard 47210A capnograph and a Teledyne TED 60J digital oxygen monitor. Fourteen men and six women with an average age of 36 years (SD, 6.1) were tested. Results are reported as mm Hg. After 30 seconds of rebreathing, mean change in O2 from room air was -15.9 (SD, 4.6) and mean CO2 was 38.7 (SD, 6.2); at 60 seconds, -20.5 (6.0) and 40.2 (6.4); at 90 seconds -22 (6.8) and 40.5 (6.4); at 120 seconds -23.6 (6.8) and 40.7 (6.5); at 150 seconds -25.1 (1.2) and 41 (7.3); and at 180 seconds -26.6 (8.4) and 41.3 (7.5). A few subjects achieved CO2 levels as high as 50, but many never reached 40. The mean maximal drop in O2 was 26 (8.8); seven subjects had drops in oxygen of 26 mm Hg at three minutes, four had drops of 34 mm Hg, and one had a drop of 42 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of magnesium on anginal attack induced by hyperventilation in patients with variant angina

To examine whether or not magnesium suppresses coronary spasm, the effect of magnesium infusion on anginal attacks induced by hyperventilation was studied in 20 patients with variant angina. In all patients, anginal attacks associated with ischemic ST segment changes on the electrocardiogram were repeatedly induced by hyperventilation. The study was performed in the early morning successively for 3 days. On days 1 and 3 (control studies), 50 minutes before the hyperventilation test, a 5% glucose solution was infused as a placebo. On day 2 (magnesium study), 50 minutes before the hyperventilation test, magnesium sulfate (0.27 mM/kg body wt) was infused during a 20-minute period. During the control studies, anginal attack was induced by hyperventilation in all 20 patients, whereas during the magnesium study, anginal attack was induced by hyperventilation in only six (30%) of the 20 patients (p less than 0.001 vs. control studies). The changes in arterial blood pH and PCO2 caused by hyperventilation were not significant between the control study and the magnesium study. Mean serum magnesium concentration increased from 2.2 +/- 0.2 to 6.0 +/- 0.5 mg/dl immediately after infusing magnesium and was 4.5 +/- 0.6 mg/dl before the hyperventilation test during the magnesium study. We conclude that magnesium suppresses anginal attacks induced by hyperventilation in patients with variant angina.

Asystole with syncope secondary to hyperventilation in three young athletes

We describe three athletes who had syncope after (case 1) or during (cases 2, 3) hyperventilation. During the episode, ECG showed prolonged sinus arrest. Clinical data and noninvasive investigations were normal and the phenomenon was not reproducible. Electrophysiological study after autonomic blockade allowed a prolonged intrinsic heart rate in case 1, and abnormal corrected sinus node recovery time in cases 1 and 2. During follow-up, symptomatic sinus arrest provoked by deep inspiration occurred in case 3. These cases document prolonged asystole of unknown etiology, secondary to hyperventilation, and probably caused by different vagally-mediated mechanisms.

Interpreting the carboxyhaemoglobin concentration in fetal cord blood

We calculated the fetal-to-maternal carboxyhaemoglobin concentration ratio in 19 mother-infant pairs at the time of term delivery. Mothers, who had a less than 10% drop in their carboxyhaemoglobin concentration during labour, had an average ratio of 1.40 +/- 0.19. For mothers whose carboxyhaemoglobin concentrations dropped by 10% or more during labour, the average fetal-to-maternal carboxyhaemoglobin concentration ratio was 1.83 +/- 0.48. There was a strong correlation (r = 0.82) between the percent change in maternal carboxyhaemoglobin concentration during labour and the fetal-to-maternal carboxyhaemoglobin concentration ratio at the time of delivery. We conclude that increased CO elimination during labour may be accompanied by rapid changes in the maternal carboxyhaemoglobin concentration, leading to a spuriously high fetal-to-maternal carboxyhemoglobin concentration ratio at the time of delivery.

Lactate and hyperventilation substantially attenuate vagal tone in normal volunteers. A possible mechanism of panic provocation?

Many aspects of panic attacks, eg, palpitations, tremor, sweating, and an emotional sense of "fear," have been theorized to arise from sympathetic nervous system activation. However, most studies have not demonstrated clearly increased levels of catecholamines during an attack, which is contrary to this hypothesis. To explore another possible cause for the physiological changes known to occur during a panic attack, we assessed parasympathetic nervous system activity by measuring vagal tone during treatments known to produce panic symptoms: sodium lactate administration and hyperventilation. Our findings showed a marked reduction in vagal tone during both procedures. We postulate that withdrawal of parasympathetic activity may explain some of the physiological changes occurring in panic attacks and be contributing to the origin of panic.

Panic anxiety and hyperventilation in patients with chest pain: a controlled study

We studied the relation between mood disorder and hyperventilation (hypocapnia) before and during exercise treadmill testing in 113 chest pain patients attending a cardiac clinic and 30 healthy controls. In most patients end-tidal PCO2 (PCO2) rose in the normal way on exercise but in a subset of 24 (21 per cent) there was no rise: these patients with initial hyperventilation had significantly higher anxiety scores than those with a normal exercise-induced rise in PCO2. Two of the 24 had ischaemic heart disease and 10 (42 per cent) complained of recent panic anxiety compared with 12 (13 per cent) of the 89 with normal rise in PCO2 (p less than 0.05). Rates of psychiatric morbidity were similar in patients with 'typical' and 'atypical' chest pain. Resting hypocapnia occurred more often in patients with panic anxiety than in either anxious or non-anxious patients without panic. Panic patients also reported more symptoms of breathlessness and hyperventilation-related complaints than those without panic. Our findings confirm the important association between panic and hyperventilation in patients with chest pain. Furthermore, patients with exercise-induced hyperventilation are more likely to have a psychiatric than a cardiac disorder. Early detection and treatment of these patients may reduce the potential morbidity associated with unnecessary invasive investigations.

Acute respiratory failure following pharmacologically induced hyperventilation: an experimental animal study

The pulmonary effects of hyperventilation following infusion of sodium salicylate into the cisterna magna was studied in 16 spontaneously breathing adult sheep. We found a fall in PaO2, a decrease in the static compliance of the respiratory system, abnormal chest roentgenographic films, and grossly abnormal lungs following 3.5 to 13 h of hyperventilation. A control group of 15 sheep (10 sheep similarly injected with sodium salicylate, but then sedated and paralyzed and ventilated at normal tidal volume and respiratory rate on a mechanical ventilator, and 5 sheep infused with saline alone and breathing spontaneously) showed no pulmonary or arterial blood gas abnormalities. We conclude that prolonged hyperventilation under the conditions of this experiment precipitated events that resulted in acute lung injury.

Hyperventilation-induced simultaneous multivessel coronary spasm in patients with variant angina: an echocardiographic and arteriographic study

Left ventricular wall motion abnormalities during an attack of coronary spasm induced by hyperventilation were examined with use of two-dimensional echocardiography in 27 patients with variant angina. Transient abnormal wall motion (asynergy) confined to one coronary artery region was found in 18 of the 27 patients and transient abnormal motion extending over more than one coronary artery region in the remaining 9 patients. Spasm of more than one major coronary artery was demonstrated separately by coronary arteriography during an attack induced by injection of acetylcholine or ergonovine in seven of the nine patients who manifested asynergy in more than one coronary artery region. In one patient, spasm was demonstrated in one major coronary artery, and the other coronary arteries were severely stenosed or occluded organically. In the remaining patient, acetylcholine was not injected into both arteries; however, the attack was sometimes associated with ST segment elevation in the anterior leads and at other times in the inferior leads. Therefore, simultaneous multivessel coronary spasm seems to have occurred in eight of the nine patients who exhibited asynergy in more than one coronary artery region. The 8 patients with simultaneous multivessel coronary spasm had a higher degree and longer duration of ST segment elevation and a higher incidence of arrhythmias during the attack induced by hyperventilation than did the 19 patients with single vessel coronary spasm, and all of them had no significant organic stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperventilation with hypoproteinemia

Hypoproteinemia by itself produces a metabolic alkalosis. It is not clear whether a respiratory compensation (hypercapnia) develops with this alkalosis; patients with liver cirrhosis, most of them with hypoproteinemia, are known to hyperventilate. We studied 23 clinically stable patients with hypoproteinemia, with very low albumin-to-globulin ratios (range 0.4 to 1.1), who had either liver cirrhosis (n = 12) or other medical conditions (n = 11). In both groups, there was marked hypocapnia, accompanied by alkalemia (PaCO2 values (mean +/- SD) 31 +/- 2 and 32 +/- 3 torr; pH (mean +/- SD) 7.45 +/- 0.03 and 7.47 +/- 0.03, for the patients with cirrhosis and those without, respectively). Hypoxemia was not the stimulus provoking hyperventilation. The lowering of PaCO2 was proportional to the reduction of serum albumin and total protein concentrations; no detectable difference was seen between the patients with cirrhosis and those without cirrhosis in this apparent dependence of PaCO2 on the concentration of serum proteins. Many of these clinically stable patients with hypoproteinemia, with or without liver cirrhosis, had appreciable concentrations of unidentified anions in plasma (inappropriately high anion gap). Whatever the nonrespiratory acid-base status of the patients with hypoproteinemia, their pulmonary ventilation (hypocapnia) appeared excessive when compared with subjects (presumably) without proteinemia who had similar nonrespiratory acid-base states. The mechanism responsible for the hyperventilation in hypoproteinemia and the nature of the unidentified anions in this condition are obscure.

CO2 response and pattern of breathing in patients with symptomatic hyperventilation, compared to asthmatic and normal subjects

We studied six patients with symptomatic hyperventilation, using new techniques to quantify baseline variability of respiratory variables, and to assess CO2 sensitivity around the control point using a stimulus not detectable by the subject. We compared them with six normal subjects and six patients with mild asthma. Symptomatic hyperventilators had normal mean ventilation and end-tidal carbon dioxide tension (PETCO2) at rest. Asthmatic subjects had higher ventilation and lower PETCO2. Symptomatic hyperventilators had a larger number of sighs and abnormally wide fluctuations in baseline for inspiratory time, expiratory time, and PETCO2. These could not be explained by an abnormal ventilatory response to a transient CO2 input; the transient response near the control point was undoubtedly normal.

Trachea-noise biofeedback in asthma: a comparison of the effect of trachea-noise biofeedback, a bronchodilator, and no treatment on the rate of recovery from exercise- and eucapnic hyperventilation-induced asthma

We review some of the evidence that supports the existence of psychosomatic triggers to bronchospasm in asthmatics, and hypothesize that it may also be possible to consciously reverse bronchospasm using trachea-noise biofeedback. We precipitated significant levels of bronchospasm in 16 asthmatics using exercise or eucapnic-hyperventilation challenges on five occasions, and administered four different treatments and a no-treatment control. The treatments were trachea-noise biofeedback (TNBF), wrong-information TNBF, an inhaled adrenergic bronchodilator, and a placebo inhaler, all given double blind. Half of the subjects had 3 training days in the use of the TNBF device before study. Our results show that TNBF, in the trained subjects only, is associated with a detectable, but not statistically significant, increase in the rate of recovery from bronchospasm over that found with no treatment. We conclude that, although asthmatics seem to have a strong ability to consciously induce bronchospasm, conscious reversal of a full asthma attack using TNBF is limited. Despite contrary conclusions by other investigators, we believe that this study demonstrated little TNBF-assisted recovery from bronchospasm. We suggest that this is because its effect may be inhibited by humoral mechanisms that sustain the attack, but we believe further work is required to support this.

Hyperventilation in the awake state: potentially treatable component of Rett syndrome

Hyperventilation, which occurs in some patients with severe mental handicap, is a prominent feature in the histories of most girls with Rett syndrome but its mechanism and effects have not been established. Respiratory function was therefore studied in 18 patients with Rett syndrome and 23 healthy controls. Ten of the patients (56%), but none of the controls, hyperventilated only when awake, and began doing so after a period of normal breathing without hypoxaemia. After hyperventilation was established it was interspersed with prolonged periods of apnoea (over 19 seconds) accompanied by Valsalva manoeuvres. Hypoxaemia (less than 90%) occurred in 47% of these periods of apnoea and five (50%) of the patients had oxygen saturation values of under 50%. During hyperventilation severe hypocapnia developed in every patient, and recorded arterial pH measurements ranged from 7.47 to 7.60. A further four patients (22%) did not hyperventilate, but had clear histories of hyperventilation when younger. All had frequent apnoeic pauses accompanied by Valsalva manoeuvres. The remaining four girls (22%) neither hyperventilated nor gave a clear history of doing so. Three had occasional apnoeic pauses associated with the Valsalva manoeuvres. All but one of the 18 patients had increased quantities of periodic apnoea compared with the control subjects. The hypocapnic alkalaemia and hypoxaemia resulting from hyperventilation may contribute to the cerebral impairment in Rett syndrome. Since the hyperventilation is 'primary', and not secondary to preceding apnoea, it is potentially treatable. Further studies will determine if treatment is practical and of benefit.

Absence seizure with generalized rhythmic delta activity

In seven children, 5-11 years old, who presented with spells of staring or unresponsiveness, hyperventilation reproduced clinical spells that were accompanied on the EEG by generalized, rhythmic, delta activity. The discharges were usually of abrupt onset, extremely high amplitude, recurrent, and prolonged. One spontaneous staring spell, not provoked by hyperventilation, was also accompanied by generalized rhythmic delta activity. All patients had improvement or complete control of their spells and abolition of the EEG changes with ethosuximide or valproate. Delta activity during hyperventilation in children may not always be benign and may be associated with clinical absence seizures.

Hyperventilation and myocardial infarction

Chest pain that is associated with hyperventilation is often considered to be benign and noncardiac in nature. While not commonly recognized, hyperventilation can provoke coronary vasospasm. We report a man who presented with hyperventilation and developed myocardial infarction. In the setting of hyperventilation, chest pain and ST segment elevation, coronary vasospasm must be considered.