- Phase contrast mapping MRI measurements of global cerebral blood flow across different perfusion states - A direct comparison with 15O-H2O positron emission tomography using a hybrid PET/MR system. [Journal Article]
- JCJ Cereb Blood Flow Metab 2018 Sep 11; :271678X18798762
- Phase-contrast mapping (PCM) magnetic resonance imaging (MRI) provides easy-access non-invasive quantification of global cerebral blood flow (gCBF) but its accuracy in altered perfusion states is not...
Phase-contrast mapping (PCM) magnetic resonance imaging (MRI) provides easy-access non-invasive quantification of global cerebral blood flow (gCBF) but its accuracy in altered perfusion states is not established. We aimed to compare paired PCM MRI and 15O-H2O positron emission tomography (PET) measurements of gCBF in different perfusion states in a single scanning session. Duplicate combined gCBF PCM-MRI and 15O-H2O PET measurements were performed in the resting condition, during hyperventilation and after acetazolamide administration (post-ACZ) using a 3T hybrid PET/MR system. A total of 62 paired gCBF measurements were acquired in 14 healthy young male volunteers. Average gCBF in resting state measured by PCM-MRI and 15O-H2O PET were 58.5 ± 10.7 and 38.6 ± 5.7 mL/100 g/min, respectively, during hyperventilation 33 ± 8.6 and 24.7 ± 5.8 mL/100 g/min, respectively, and post-ACZ 89.6 ± 27.1 and 57.3 ± 9.6 mL/100 g/min, respectively. On average, gCBF measured by PCM-MRI was 49% higher compared to 15O-H2O PET. A strong correlation between the two methods across all states was observed (R2 = 0.72, p < 0.001). Bland-Altman analysis suggested a perfusion dependent relative bias resulting in higher relative difference at higher CBF values. In conclusion, measurements of gCBF by PCM-MRI in healthy volunteers show a strong correlation with 15O-H2O PET, but are associated with a large and non-linear perfusion-dependent difference.
- Regulation of Regional Cerebral Blood Flow During Graded Reflex-Mediated Sympathetic Activation via Lower Body Negative Pressure. [Journal Article]
- JAJ Appl Physiol (1985) 2018 Sep 06
- The role of the sympathetic nervous system in cerebral blood flow (CBF) regulation remains unclear. Previous studies have primarily measured middle cerebral artery blood velocity to assess CBF. Recen...
The role of the sympathetic nervous system in cerebral blood flow (CBF) regulation remains unclear. Previous studies have primarily measured middle cerebral artery blood velocity to assess CBF. Recently, there has been a transition towards measuring internal carotid artery (ICA) and vertebral artery (VA) blood flow using duplex Doppler ultrasound. Given that the VA supplies autonomic control centers in the brainstem, we hypothesized that graded sympathetic activation via lower body negative pressure (LBNP) would reduce ICA but not VA blood flow. ICA and VA blood flow were measured during two protocols: Protocol-1, low-to-moderate LBNP (-10, -20, -30, -40 Torr) and Protocol-2, moderate-to-high LBNP (-30, -50, -70 Torr). ICA and VA blood flow, diameter, and blood velocity were unaffected up to -40 LBNP. However, -50 and -70 LBNP evoked reductions in ICA and VA blood flow (e.g., -70 LBNP: %∆VA-baseline= -27.6±3.0) that were mediated by decreases in both diameter and velocity (e.g., -70 LBNP: %∆VA-baseline diameter= -7.5±1.9 and %∆VA-baseline velocity= -13.6±1.7), which were comparable between vessels. Since hyperventilation during -70 LBNP reduced PETCO2, this decrease in PETCO2 was matched via voluntary hyperventilation. Reductions in ICA and VA blood flow during hyperventilation alone were significantly smaller than during -70 LBNP and were primarily mediated by decreases in velocity (%∆VA-baseline velocity= -8.6±2.4; %∆VA-baseline diameter= -0.05±0.56). These data demonstrate that both ICA and VA were unaffected by low-to-moderate sympathetic activation, whereas robust reflex-mediated sympatho-excitation caused similar magnitudes of vasoconstriction in both arteries. Thus, contrary to our hypothesis, the ICA was not preferentially vasoconstricted by sympathetic activation.
- Insights into the evolution of polymodal chemoreceptors. [Journal Article]
- AHActa Histochem 2018 Aug 30
- Respiratory chemoreceptors in vertebrates are specialized cells that detect chemical changes in the environment or arterial blood supply and initiate autonomic responses, such as hyperventilation or ...
Respiratory chemoreceptors in vertebrates are specialized cells that detect chemical changes in the environment or arterial blood supply and initiate autonomic responses, such as hyperventilation or changes in heart rate, to improve O2 uptake and delivery to tissues. These chemoreceptors are sensitive to changes in O2, CO2 and/or H+. In fish and mammals, respiratory chemoreceptors may be additionally sensitive to ammonia, hypoglycemia, and numerous other stimuli. Thus, chemoreceptors that affect respiration respond to different types of stimuli (or modalities) and are considered to be "polymodal". This review discusses the polymodal nature of respiratory chemoreceptors in vertebrates with a particular emphasis on chemoreceptors of the carotid body and pulmonary epithelium in mammals, and on neuroepithelial cells in water- and air-breathing fish. A major goal will be to examine the evidence for putative polymodal chemoreceptors in fish within the context of studies on mammalian models, for which polymodal chemoreceptors are well described, in order to improve our understanding of the evolution of polymodal chemoreceptors in vertebrates, and to aid in future studies that aim to identify putative receptors in air- and water-breathing fish.
- Therapeutic hypothermia to reduce intracranial pressure after traumatic brain injury: the Eurotherm3235 RCT. [Clinical Trial]
- HTHealth Technol Assess 2018; 22(45):1-134
- CONCLUSIONS: In participants following TBI and with an ICP of > 20 mmHg, titrated therapeutic hypothermia successfully reduced ICP but led to a higher mortality rate and worse functional outcome.Inability to blind treatment allocation as it was obvious which participants were randomised to the hypothermia group; there was biased recording of SAEs in the hypothermia group. We now believe that more adequately powered clinical trials of common therapies used to reduce ICP, such as hypertonic therapy, barbiturates and hyperventilation, are required to assess their potential benefits and risks to patients.
- Is Acupressure Useful for Alleviating Hyperventilation Syndrome? [Journal Article]
- CJChin J Integr Med 2018 Aug 28
- Mechanisms of exercise limitation in patients with chronic hypersensitivity pneumonitis. [Journal Article]
- EOERJ Open Res 2018; 4(3)
- Small airway and interstitial pulmonary involvements are prominent in chronic hypersensitivity pneumonitis (cHP). However, their roles on exercise limitation and the relationship with functional lung...
Small airway and interstitial pulmonary involvements are prominent in chronic hypersensitivity pneumonitis (cHP). However, their roles on exercise limitation and the relationship with functional lung tests have not been studied in detail. Our aim was to evaluate exercise performance and its determinants in cHP. We evaluated maximal cardiopulmonary exercise testing performance in 28 cHP patients (forced vital capacity 57±17% pred) and 18 healthy controls during cycling. Patients had reduced exercise performance with lower peak oxygen production (16.6 (12.3-19.98) mL·kg-1·min-1versus 25.1 (16.9-32.0), p=0.003), diminished breathing reserve (% maximal voluntary ventilation) (12 (6.4-34.8)% versus 41 (32.7-50.8)%, p<0.001) and hyperventilation (minute ventilation/carbon dioxide production slope 37±5 versus 31±4, p<0.001). All patients presented oxygen desaturation and augmented Borg dyspnoea scores (8 (5-10) versus 4 (1-7), p=0.004). The prevalence of dynamic hyperinflation was found in only 18% of patients. When comparing cHP patients with normal and low peak oxygen production (<84% pred, lower limit of normal), the latter exhibited a higher minute ventilation/carbon dioxide production slope (39±5.0 versus 34±3.6, p=0.004), lower tidal volume (0.84 (0.78-0.90) L versus 1.15 (0.97-1.67) L, p=0.002), and poorer physical functioning score on the Short form-36 health survey. Receiver operating characteristic curve analysis showed that reduced lung volumes (forced vital capacity %, total lung capacity % and diffusing capacity of the lung for carbon dioxide %) were high predictors of poor exercise capacity. Reduced exercise capacity was prevalent in patients because of ventilatory limitation and not due to dynamic hyperinflation. Reduced lung volumes were reliable predictors of lower performance during exercise.
- Hemodynamic Characteristics of Postural Hyperventilation: POTS with Hyperventilation vs Panic vs Voluntary Hyperventilation. [Journal Article]
- JAJ Appl Physiol (1985) 2018 Aug 23
- Upright hyperventilation occurs in approximately 25% of our patients with postural tachycardia syndrome (POTS). Poikilocapnic hyperventilation alone causes tachycardia. Here we examined changes in re...
Upright hyperventilation occurs in approximately 25% of our patients with postural tachycardia syndrome (POTS). Poikilocapnic hyperventilation alone causes tachycardia. Here we examined changes in respiration and hemodynamics comprising cardiac output (CO), systemic vascular resistance (SVR) and blood pressure (BP) measured during head-up tilt (HUT) in 3 groups: patients with POTS and hyperventilation (POTS-HV), patients with Panic Disorder who hyperventilate (Panic), and healthy controls performing voluntary upright hyperpnea (Voluntary-HV). Though all were comparably tachycardic during hyperventilation, POTS-HV manifested hyperpnea, decreased CO, increased SVR and increased BP during HUT; Panic patients showed both hyperpnea and tachypnea, increased CO and increased SVR as BP increased during HUT; and Voluntary-HV were hyperneic by design and had increased CO, decreased SVR, and decreased BP during upright hyperventilation. Mechanisms of hyperventilation and hemodynamic changes differed among POTS-HV, Panic and Voluntary-HV subjects. We hypothesize that the hyperventilation in POTS is caused by a mechanism involving peripheral chemoreflex sensitization by intermittent ischemic hypoxia.
- [Anamnestic headache in patients with cervical artery dissection: clinical characteristics and pathogenetic mechanisms]. [Journal Article]
- ZNZh Nevrol Psikhiatr Im S S Korsakova 2018; 118(7):4-11
- CONCLUSIONS: HPH in patients with CeAD meets criteria of migraine in 15.4% (with aura - 3.1%, without aura - 12.3%), 29.1% patients have nonmigraine HPH. Central mechanisms, namely, the hypersensitivity of the cerebral cortex playing the main role in migraine pathogenesis, are not significant in HPH genesis. The main role appears to have peripheral mechanisms - dysplastic changes in the wall of extra- and intracranial arteries that predispose both to headache and dissection.
- Hypocapnia and mental stress can trigger vicious circles in critically ill patients due to energy imbalance: a hypothesis presented through cardiogenic pulmonary oedema. [Journal Article]
- NHNeuropsychopharmacol Hung 2018; 20(2):65-74
- The pathophysiologic significance of hypocapnia is strongly underestimated both in functional and organic diseases. Alterations of carbon dioxide levels immediately appear in the cytoplasm, causing a...
The pathophysiologic significance of hypocapnia is strongly underestimated both in functional and organic diseases. Alterations of carbon dioxide levels immediately appear in the cytoplasm, causing abrupt pH changes. Compensatory mechanisms develop with latency, so intracellular alkalosis or acidosis can affect metabolism for hours/days. Hyperventilation alkalosis increases metabolic energy/O₂ demand, while ATP production is often reduced due to developing hypophosphatemia. A healthy organism serves the increased energy demand conveniently, as a consequence, the excitability of the corticospinal and neuromuscular systems grows. Functional diseases can occur due to increased membrane Ca2+ transients but tissues remain structurally unchanged. By contrast, a critically ill myocardium cannot satisfy the increased energy demand caused by acute hypocapnia. Vicious circles can occur, with cardiac forward and backward failure; pulmonary wedge pressure increases parallel with the lack of energy which can lead to pulmonary oedema and death. Hypocapnia can generate fatal vicious circles in several critical illnesses. Sympathicotonia and hypocapnia enhance arousal and make biological systems energetically unstable, thus vicious circles almost unavoidably occur. Somatic and psychic processes mutually influence each other, resulting in psychosomatic or somatopsychic disorders. The ability to provide energy supplies can be an important dividing line between organic and functional diseases.
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- Hyperventilation Syndrome and Sustained Hyperchloremia After Kidney Transplant: Time-Sequence Swing of Acid-Base Interpretation. [Case Reports]
- ECExp Clin Transplant 2018 Aug 17
- An interaction between regained renal function in a transplanted kidney and hyperventilation syndrome may interfere with correct diagnosis of acid-base status in patients with preoperative nongap aci...
An interaction between regained renal function in a transplanted kidney and hyperventilation syndrome may interfere with correct diagnosis of acid-base status in patients with preoperative nongap acidosis. Here, we present a patient with glomerular nephritis and hyperchloremia who underwent kidney transplant. Progressively increasing bicarbonate reabsorption by the renal graft, which thereby changed the arterial carbon dioxide tension-to-bicarbonate ratio, resulted in a time-sequence swing of an acid-base interpretation despite persistent mixed respiratory alkalosis due to hyperventilation syndrome and nongap metabolic acidosis due to preexisting hyperchloremia. Specifically, the sequence was mixed primary metabolic acidosis and primary respiratory acidosis immediately after surgery, primary metabolic acidosis and secondary respiratory alkalosis on postoperative days 1 and 2, mixed primary hyperchloremic metabolic acidosis and primary respiratory alkalosis on postoperative day 3, and finally primary respiratory alkalosis and secondary hyperchloremic metabolic acidosis on postoperative day 7. This swing in the acid-base interpretation indicates that the acid-base imbalance described here does not fit the empirical relationship for calculating the expected bicarbonate or carbon dioxide tension value, suggesting that "correct" interpretation of acid-base status may not lead to "correct" diagnosis of acid-base status. It should be remembered that not every acid-base imbalance fits the empirical relationship.