Hypoxia, hypercapnia, and hypertension: their effects on pulsatile cerebral blood flow

Altered Regional Cerebral Blood Flow of Right Cerebellum Posterior Lobe in Asthmatic Patients With or Without Depressive Symptoms

Background: Asthma is a chronic disease appeared to be associated with depression. But the underpinnings of depression in asthma remain unknown. In order to understand the neural mechanisms of depression in asthma, we used cerebral blood flow (CBF) to probe the difference between depressed asthmatic (DA) and non-depressed asthmatic (NDA) patients. Methods: Eighteen DA patients, 24 NDA patients and 57 healthy controls (HC) received pulsed arterial spin labeling (pASL) scan for measuring CBF, resting-state functional magnetic resonance imaging (rs-fMRI) scan, severity of depression and asthma control assessment, respectively. Results: Compared to NDA, DA patients showed increased regional CBF (rCBF) in the right cerebellum posterior lobe. Compared to HC, DA, and NDA patients all showed significantly decreased rCBF in the right cerebellum posterior lobe. Conclusions: We showed the first evidence of altered rCBF in the right cerebellum posterior lobe in asthma using pASL, which appeared to be involved in the neuropathology in asthma. Clinical Trial Registration: An investigation of therapeutic mechanism in asthmatic patients: based on the results of Group Cognitive Behavioral Therapy (Registration number: ChiCTR-COC-15007442) (http://www.chictr.org.cn/usercenter.aspx).

Impact of COPD exacerbation on cerebral blood flow

We aimed to investigate the impact of chronic obstructive pulmonary disease (COPD) exacerbation on cerebral blood flow (CBF). In 21 COPD patients - in both exacerbation and stable phases -Doppler ultrasonographies of internal carotid artery (ICA) and vertebral artery (VA) were performed. There were significant differences in total, anterior and posterior CBF, ICA and VA flow volumes in exacerbated COPD compared to stable COPD. Total CBF was correlated with cross-sectional areas of left and right ICA, whereas independent predictor of total CBF was cross-sectional area of right ICA. Increased CBF might indicate cerebral autoregulation-mediated vasodilatation to overcome COPD exacerbation induced hypoxia.

Reduction of compartment compliance increases venous flow pulsatility and lowers apparent vascular compliance: Implications for cerebral blood flow hemodynamics

The global compliance of a fixed-volume, incompressible compartment may play a significant role in determining the inherent vascular compliance. For the intracranial compartment, we propose that the free-displacement of the cerebral spinal fluid (CSF) directly relates to cerebral vascular compliance. To test this hypothesis, an in vivo surrogate intracranial compartment was made by enclosing a rabbit's kidney within a rigid, fluid-filled container. Opening/closing a port atop the box modulated the free flow of box fluid (open-box state). We observed that the pulsatility of the renal venous outflow increased in response to hampering the free flow of fluid in-and-out of the container (closed-box state). To associate the observed pulsatility changes with the compliance changes, a parametric method was proposed for the computation of the apparent compliance (C(app)) of the whole renal vascular system. The calculated C(app) for each experiment's closed-box state was favorably compared to a time-domain compliance assessment method at the mean heart rate. In addition, it was revealed that C(app) in the open-box state was greater than that in the closed-box state only when the calculations were performed at frequencies lower than the heart rate and closer to the ventilation rate. These experimental results support the concept that the vessel compliance of vascular systems enclosed within a rigid compartment is a function of the global compartment compliance.

Oxygen-hemoglobin affinity at sea level may predict acute illness at altitude: theory and simulation

Acute mountain sickness carries with it serious health and economic costs. In their pursuit of the mechanisms that produce acute mountain sickness, researchers have overlooked the existence of a possible screening test, a test based on individual variation in cerebral oxygen exchange at sea level. In this paper, I highlight the mathematical link between cerebral oxygen exchange at sea level - this is reflected in the magnitude of the oxygen extraction coefficient - and a change in brain blood flow at altitude; this link has been overlooked. A lower oxygen extraction coefficient at sea level can act - at altitude - to reduce the capacity of the intracranial compartment to accommodate brain swelling, exacerbate increases in cell volume, promote the stimulation of angiogenesis, and further cerebral edema, each of which may contribute to acute mountain sickness. In retrospect, it seems obvious that the initial state of cerebral oxygen exchange will impact the cerebral circulatory response to subsequent hypoxia. This deceptively simple notion offers us an opportunity to identify beforehand those people likely to develop acute mountain sickness when they travel to altitude.

Glaucoma patients demonstrate faulty autoregulation of ocular blood flow during posture change

BACKGROUND/AIMS

Autoregulation of blood flow during posture change is important to ensure consistent organ circulation. The purpose of this study was to compare the change in retrobulbar ocular blood flow in glaucoma patients with normal subjects during supine and upright posture.

METHODS

20 open angle glaucoma patients and 20 normal subjects, similar in age and sex distribution, were evaluated. Blood pressure, intraocular pressure, and retrobulbar blood velocity were tested after 30 minutes of sitting and again after 30 minutes of lying. Retrobulbar haemodynamic measures of peak systolic velocity (PSV), end diastolic velocity (EDV), and resistance index (RI) were obtained in the ophthalmic and central retinal arteries using colour Doppler imaging (CDI).

RESULTS

When changing from the upright to supine posture, normal subjects demonstrated a significant increase in OA EDV (p = 0.016) and significant decrease in OA RI (p = 0.0006) and CRA RI (p = 0.016). Glaucoma patients demonstrated similar changes in OA measures of EDV (p = 0.02) and RI (p = 0.04), but no change in CRA measures.

CONCLUSION

Glaucoma patients exhibit faulty autoregulation of central retinal artery blood flow during posture change.

An improved statistical methodology to estimate and analyze impedances and transfer functions

Estimating the mathematical relationship between pulsatile time series (e.g., pressure and flow) is an effective technique for studying dynamic systems. The frequency-domain relationship between time series, often calculated as an impedance (pressure/flow), is known more generally as a frequency-response or transfer function (output/input). Current statistical methods for transfer function analysis 1) assume erroneously that repeated observations on a subject are independent, 2) have limited statistical value and power, or 3) are restricted to use in single subjects rather than in an entire sample. This paper develops a regression model for transfer function analysis that corrects each of these deficiencies. Spectral densities of the input and output time series and the cross-spectral density between them are first estimated from discrete Fourier transforms and then used to obtain regression estimates of the transfer function. Statistical comparisons of the transfer function estimates use a test statistic that is distributed as chi2. Confidence intervals for amplitude and phase can also be calculated. By correctly modeling repeated observations on each subject, this improved statistical approach to transfer function estimation and analysis permits the simultaneous analysis of data from all subjects in a sample, improves the power of the transfer function model, and has broad relevance to the study of dynamic physiological systems.