Effects of haloperidol on ventilation during isocapnic hypoxia in humans

Respiratory pattern and phrenic and hypoglossal nerve activity during normoxia and hypoxia in 6-OHDA-induced bilateral model of Parkinson's disease

Respiratory disturbances present in Parkinson's disease (PD) are not well understood. Thus, studies in animal models aimed to link brain dopamine (DA) deficits with respiratory impairment are needed. Adult Wistar rats were lesioned with injection of 6-hydroxydopamine (6-OHDA) into the third cerebral ventricle. Two weeks after hypoxic test was performed in whole-body plethysmography chamber, phrenic (PHR) and hypoglossal (HG) nerve activities were recorded in normoxic and hypoxic conditions in anesthetized, vagotomized, paralyzed and mechanically ventilated rats. The effects of activation and blockade of dopaminergic carotid body receptors were investigated during normoxia in anesthetized spontaneously breathing rats. 6-OHDA injection affected resting respiratory pattern in awake animals: an increase in tidal volume and a decrease in respiratory rate had no effect on minute ventilation. Hypoxia magnified the amplitude and minute activity of the PHR and HG nerve of 6-OHDA rats. The ratio of pre-inspiratory to inspiratory HG burst amplitude was reduced in normoxic breathing. Yet, the ratio of pre-inspiratory time to total time of the respiratory cycle was increased during normoxia. 6-OHDA lesion had no impact on DA and domperidone effects on the respiratory pattern, which indicate that peripheral DA receptors are not affected in this model. Analysis of monoamines confirmed substantial striatal depletion of dopamine, serotonin and noradrenaline (NA) and reduction of NA content in the brainstem. In bilateral 6-OHDA model changes in activity of both nerves: HG (linked with increased apnea episodes) and PHR are present. Demonstrated respiratory effects could be related to specific depletion of DA and NA.

Time Domains of the Hypoxic Ventilatory Response and Their Molecular Basis

Ventilatory responses to hypoxia vary widely depending on the pattern and length of hypoxic exposure. Acute, prolonged, or intermittent hypoxic episodes can increase or decrease breathing for seconds to years, both during the hypoxic stimulus, and also after its removal. These myriad effects are the result of a complicated web of molecular interactions that underlie plasticity in the respiratory control reflex circuits and ultimately control the physiology of breathing in hypoxia. Since the time domains of the physiological hypoxic ventilatory response (HVR) were identified, considerable research effort has gone toward elucidating the underlying molecular mechanisms that mediate these varied responses. This research has begun to describe complicated and plastic interactions in the relay circuits between the peripheral chemoreceptors and the ventilatory control circuits within the central nervous system. Intriguingly, many of these molecular pathways seem to share key components between the different time domains, suggesting that varied physiological HVRs are the result of specific modifications to overlapping pathways. This review highlights what has been discovered regarding the cell and molecular level control of the time domains of the HVR, and highlights key areas where further research is required. Understanding the molecular control of ventilation in hypoxia has important implications for basic physiology and is emerging as an important component of several clinical fields. © 2016 American Physiological Society. Compr Physiol 6:1345-1385, 2016.

Hypothyroidism stimulates D2 receptor-mediated breathing in response to acute hypoxia and alters D2 receptors levels in carotid bodies and brain

Hypothyroidism can depress breathing and alter dopamine D2 receptor expression and function. We hypothesized that relative to euthyroid hamsters (EH), hypothyroid hamsters (HH) contain increased D2 receptors in brain regions associated with breathing and carotid bodies (CB), and that stimulation of D2 receptors would decease ventilation more in the HH compared to the EH. Hamsters were treated with vehicle, carmoxirile (peripherally acting D2 receptor agonist), or bromocriptine (central and peripherally acting D2 receptor agonist) and breathing was evaluated during exposure to air, hypoxia, and then air. HH exhibited increased D2 receptor protein levels in the striatum and CB, but decreased levels in the paraventricular hypothalamic nucleus. Relative to vehicle, carmoxirole and bromocriptine stimulated ventilation in the HH during and following exposure to hypoxia. Only bromocriptine depressed ventilation in the EH during and after exposure to hypoxia. Thus, hypothyroidism impacts the expression of D2 receptors in the carotid body, PVN and striatum, and D2 stimulation affects ventilation remarkably differently than in EH.

The Ventilatory Response to Hypoxia in Mammals: Mechanisms, Measurement, and Analysis

The respiratory response to hypoxia in mammals develops from an inhibition of breathing movements in utero into a sustained increase in ventilation in the adult. This ventilatory response to hypoxia (HVR) in mammals is the subject of this review. The period immediately after birth contains a critical time window in which environmental factors can cause long-term changes in the structural and functional properties of the respiratory system, resulting in an altered HVR phenotype. Both neonatal chronic and chronic intermittent hypoxia, but also chronic hyperoxia, can induce such plastic changes, the nature of which depends on the time pattern and duration of the exposure (acute or chronic, episodic or not, etc.). At adult age, exposure to chronic hypoxic paradigms induces adjustments in the HVR that seem reversible when the respiratory system is fully matured. These changes are orchestrated by transcription factors of which hypoxia-inducible factor 1 has been identified as the master regulator. We discuss the mechanisms underlying the HVR and its adaptations to chronic changes in ambient oxygen concentration, with emphasis on the carotid bodies that contain oxygen sensors and initiate the response, and on the contribution of central neurotransmitters and brain stem regions. We also briefly summarize the techniques used in small animals and in humans to measure the HVR and discuss the specific difficulties encountered in its measurement and analysis.

Survey of sedation practices during noninvasive positive-pressure ventilation to treat acute respiratory failure

OBJECTIVES

Noninvasive positive-pressure ventilation (NPPV) is increasingly used in patients with acute respiratory failure, but few data exist regarding current sedation practices during NPPV. We sought to characterize current practices and attitudes regarding sedation during NPPV.

DESIGN

Cross-sectional Web-based survey.

SETTING

Medical institutions.

PARTICIPANTS

Physician members of the American College of Chest Physician's Critical Care Network (n = 2,656) and the European Respiratory Society's Assembly of Critical Care (n = 339).

INTERVENTIONS

Survey.

MEASUREMENTS AND MAIN RESULTS

Of the 790 of 2,985 (27%) of physicians who responded, 15%, 6%, and 28% never used sedation, analgesia, or hand restraints any of the time for NPPV patients, respectively, and the large majority reported using these interventions in < or =25% of patients. Sedation, analgesia, and hand restraints were more commonly used by North Americans than Europeans (41% vs. 24% for sedation, 48% vs. 35% for analgesia, and 27% vs. 16% for hand restraints, all p < .01) and critical care vs. noncritical care physicians (42% vs. 24% for sedation and 50% vs. 34% for analgesia, all p < .01). A benzodiazepine alone was the most preferred (33%), followed by an opioid alone (29%). Europeans were less likely to use a benzodiazepine alone (25% vs. 39%, p < .001) but more likely to use an opioid alone (37% vs. 26%, p < .009). Sedation was usually administered as an intermittent intravenous bolus, outside of a protocol, and was assessed by nurses using clinical end points rather than a sedation scale.

CONCLUSIONS

Most physicians infrequently use sedation and analgesic therapy for NPPV to treat acute respiratory failure, but practices vary widely within and between specialties and geographic regions.

The effect of intracerebroventricular dopamine administration on the respiratory response to hypoxia

Acute hypoxia produces an increase in ventilation. When the hypoxia is sustained, the initial increase in ventilation is followed a decrease in ventilation. The precise mechanism of this decline in ventilation during sustained hypoxia is unknown. Recent studies hypothesized that the accumulation of dopamine in the central nervous system might have a major role in production of hypoxic respiratory depression. The purpose of this study was to examine whether dopamine has an effect on occurance of central ventilatory depression which is seen in acute hypoxia in peripheral chemoreceptors denervated animals. The experiment were conducted in rabbits anesthetized with Na-pentobarbital (25 mg x kg(-1) i.v.). For intracerebroventricular (i.c.v.) injections of dopamine (1 microg) in each animal, canula was placed in left lateral cerebral ventricle by stereotaxic method. Respiratory frequency (f x min(-1)), tidal volume (V(T)) ventilation minute volume (V(E)) and systemic arterial blood pressure (BP) were recorded during air and 3 minutes hypoxic gas mixture (8%O2-92%N2) breathing. I.c.v. administration of dopamine during normoxia decreased V(T), f, V(E) and BP, significantly. When rabbits were injected with an i.c.v. dopamine on hypoxic gas mixture breathing in control animals, there was depression of hypoxic ventilatory responses. After i.c.v. administration of dopamine antagonists haloperidol (0.1 mg) and domperidone (0.07 mg) in chemodenervated rabbits, the significant increases in V(T), V(E) and BP were observed. On the breathing of hypoxic gas mixture of chemodenervated and i.c.v. dopamine antagonists administrated rabbits, hypoxic depression was completely abolished. These results of this study show that accumulation of dopamine in the brain seems to reduce the response of the central control mechanisms to chemoreceptor impulses during normoxia and hypoxia. In conclusion present study suggests important role played by central dopaminergic pathways in the occurence of acute hypoxic ventilatory depression.

Central dopamine modulates anapyrexia but not hyperventilation induced by hypoxia

Hypoxia causes hyperventilation and decreases body temperature (T(b)) and metabolism [O(2) consumption (VO(2))]. Because dopamine (DA) is released centrally in response to peripheral chemoreceptor stimulation, we tested the hypothesis that central DA mediates the ventilatory, thermal, and metabolic responses to hypoxia. Thus we predicted that injection of haloperidol (a DA D(2)-receptor antagonist) into the third ventricle would augment hyperventilation and attenuate the drop in T(b) and VO(2) in conscious rats. We measured ventilation, T(b), and VO(2) before and after intracerebroventricular injection of haloperidol or vehicle (5% DMSO in saline), followed by a 30-min period of hypoxia exposure. Haloperidol did not change T(b) or VO(2) during normoxia; however, breathing frequency was decreased. During hypoxia, haloperidol significantly attenuated the falls in T(b) and VO(2), although hyperventilation persisted. The present study shows that central DA participates in the thermal and metabolic responses to hypoxia without affecting hyperventilation, showing that DA is not a common mediator of this interaction.

Effects of intrathecal morphine on the ventilatory response to hypoxia

BACKGROUND

Intrathecal administration of morphine produces intense analgesia, but it depresses respiration, an effect that can be life-threatening. Whether intrathecal morphine affects the ventilatory response to hypoxia, however, is not known.

METHODS

We randomly assigned 30 men to receive one of three study treatments in a double-blind fashion: intravenous morphine (0.14 mg per kilogram of body weight) with intrathecal placebo; intrathecal morphine (0.3 mg) with intravenous placebo; or intravenous and intrathecal placebo. The selected doses of intravenous and intrathecal morphine produce similar degrees of analgesia. The ventilatory response to hypercapnia, the subsequent response to acute hypoxia during hypercapnic breathing (targeted end-tidal partial pressures of expired oxygen and carbon dioxide, 45 mm Hg), and the plasma levels of morphine and morphine metabolites were measured at base line (before drug administration) and 1, 2, 4, 6, 8, 10, and 12 hours after drug administration.

RESULTS

At base line, the mean (+/-SD) values for the ventilatory response to hypoxia (calculated as the difference between the minute ventilation during the second full minute of hypoxia and the fifth minute of hypercapnic ventilation) were similar in the three groups: 38.3+/-23.2 liters per minute in the placebo group, 33.5+/-16.4 liters per minute in the intravenous-morphine group, and 30.2+/-11.6 liters per minute in the intrathecal-morphine group (P=0.61). The overall ventilatory response to hypoxia (the area under the curve) was significantly lower after either intravenous morphine (20.2+/-10.8 liters per minute) or intrathecal morphine (14.5+/-6.4 liters per minute) than after placebo (36.8+/-19.2 liters per minute) (P=O.003). Twelve hours after treatment, the ventilatory response to hypoxia in the intrathecal-morphine group (19.9+/-8.9 liters per minute), but not in the intravenous-morphine group (30+/-15.8 liters per minute), remained significantly depressed as compared with the response in the placebo group (40.9+/-19.0 liters per minute) (P= 0.02 for intrathecal morphine vs. placebo). Plasma concentrations of morphine and morphine metabolites either were not detectable after intrathecal morphine or were much lower after intrathecal morphine than after intravenous morphine.

CONCLUSIONS

Depression of the ventilatory response to hypoxia after the administration of intrathecal morphine is similar in magnitude to, but longer-lasting than, that after the administration of an equianalgesic dose of intravenous morphine.

Breathing pattern in patients with Parkinson's disease

The improvement in motor performance resulting from levodopa administration in patients with Parkinson's disease (PD) provides the opportunity to investigate ventilatory changes brought about by the disease. The aim of this study has been to investigate these changes in order to specify the mechanisms of the impairment in breathing in PD. Breathing patterns at rest were investigated in 11 patients with idiopathic PD both before (OFF) and after (ON) administration of levodopa at a dose improving their motor performance by at least 30%. Airflow (Fleisch head mounted on a mask), rib cage and abdomen movements (inductance plethysmography) were recorded in the OFF condition 1 h after subjects woke up. Subjects then received levodopa and a new set of recordings was obtained 1 h later, in the ON condition. Breath-by-breath processing of recordings was carried out, and tidal volume (VT), inspiratory (TI) and expiratory (TE) durations were measured. The main finding was a lengthening of TI resulting in a decrease in ventilation and in VT/TI, and an increase in TI/TTOT in the ON compared to the OFF condition. In the ON condition abnormal rib cage-abdomen plots patterns were found in four out of six subjects. A hypothesis on the effect of PD on breathing is proposed on grounds of normal diaphragmatic activity but impaired activity of the other respiratory muscles and more specifically the intercostal muscles.

A new aspect of the carotid body function controlling hypoxic ventilatory decline in humans

Ventilatory response to eucapnic sustained mild hypoxia was measured in one patient with unilateral and three patients with bilateral carotid body (CB) resection (defined UR and BR, respectively). The profile of ventilatory response in UR patient was initially augmented then gradually declined (biphasic pattern) as generally seen in normal subjects although the absolute magnitude was substantially low. On the other hand, biphasic pattern was disappeared in all three BRs. Lack of hypoxic ventilatory decline (HVD) in the late period of sustained hypoxia was in marked contrast to that reported in the anaesthetized and CB-denervated animals whose ventilation was severely depressed lower than the pre-hypoxic control level. In view of recent knowledge that the analogous mild hypoxia in normal animals and humans elicits an useful adaptation to economize energy expenditure with maintaining reversible excitability in control of respiration, BR patients were considered to have lost this ability. We conclude that in awake humans the CB not only stimulates ventilation but also controls the degree of subsequent HVD during sustained hypoxia.

Time domains of the hypoxic ventilatory response

The ventilatory response to hypoxia depends on the pattern and intensity of hypoxic exposure and involves several physiological mechanisms. These mechanisms differ in their effect (facilitation or depression) on different components of ventilation (tidal volume and frequency) and in their time course (seconds to years). Some mechanisms last long enough to affect future ventilatory responses to hypoxia, indicating 'memory' or functional plasticity in the ventilatory control system. A standard terminology is proposed to describe the different time domains of the hypoxic ventilatory response (HVR) and to promote integration of results from different experimental preparations and laboratories. In general, the neurophysiological and neurochemical basis for short time domains of the HVR (seconds and minutes) are understood better than longer time domains (days to years), primarily because short time domains are studied in the laboratory more easily. Understanding the mechanisms for different time domains of the HVR has important implications for both basic and clinical science.