Central venous pressure estimation from ultrasound assessment of the jugular venous pulse.

OBJECTIVES: Acquiring central venous pressure (CVP), an important clinical parameter, requires an invasive procedure, which poses risk to patients. The aim of the study was to develop a non-invasive methodology for determining mean-CVP from ultrasound assessment of the jugular venous pulse. METHODS: In thirty-four adult patients (age = 60 ± 12 years; 10 males), CVP was measured using a central venous catheter, with internal jugular vein (IJV) cross-sectional area (CSA) variation along the cardiac beat acquired using ultrasound. The resultant CVP and IJV-CSA signals were synchronized with electrocardiogram (ECG) signals acquired from the patients. Autocorrelation signals were derived from the IJV-CSA signals using algorithms in R (open-source statistical software). The correlation r-values for successive lag intervals were extracted and used to build a linear regression model in which mean-CVP was the response variable and the lagging autocorrelation r-values and mean IJV-CSA, were the predictor variables. The optimum model was identified using the minimum AIC value and validated using 10-fold cross-validation. RESULTS: While the CVP and IJV-CSA signals were poorly correlated (mean r = -0.018, SD = 0.357) due to the IJV-CSA signal lagging behind the CVP signal, their autocorrelation counterparts were highly positively correlated (mean r = 0.725, SD = 0.215). Using the lagging autocorrelation r-values as predictors, mean-CVP was predicted with reasonable accuracy (r2 = 0.612), with a mean-absolute-error of 1.455 cmH2O, which rose to 2.436 cmH2O when cross-validation was performed. CONCLUSIONS: Mean-CVP can be estimated non-invasively by using the lagged autocorrelation r-values of the IJV-CSA signal. This new methodology may have considerable potential as a clinical monitoring and diagnostic tool.

Cerebral Inflow and Outflow Discrepancies in Severe Sudden Sensorineural Hearing Loss.

The aim of this study is to evaluate whether cerebral inflow and outflow abnormalities, assessed by the means of a validated ultrasound model, could be associated with Sudden Sensorineural Hearing Loss (SSNHL). According to Clark, a total of 42 patients affected by severe SSNHL and 19 healthy volunteers matched by gender without any history of sudden hearing impairment have been included in this study. Patients and controls underwent EchocolorDoppler assessment of brain hemodynamics. All subjects affected by SSNHL were also assessed with Auditory Brainstem Responses (ABR) and Magnetic Resonance Imaging (MRI) in order to exclude retrocochlear pathology. The head inflow through the common carotid artery was practically equivalent between groups, but at the level of the carotid bifurcation, the external carotid artery showed a highly significant flow rate in SSNHL 5.4±2 vs 3.9±1.1 ml/s in controls (p=0.01). The brain inflow was similar between patients and controls, but interestingly the flow rate of the vertebral artery was significantly reduced in SSNHL 1.6±0.8 vs 2.8±0.9 ml/s (p=0.01). The brain outflow was found significantly restricted at the level of the jugular outlet 6.6±6 vs 9.9±6 ml/s (p=0.002); consequently, the collateral flow index was significantly increased in SSNHL (p=0.001). The present study shows a discrepant distribution of the brain inflow which seems to penalize the posterior segments of the Willis polygon in patients affected by severe SSNHL. In addition, our study confirms the presence of chronic cerebrospinal venous insufficiency in SSNHL with significant activation of venous collateral circulation.

Ultrasound Monitoring of Jugular Venous Pulse during Space Missions: Proof of Concept.

The jugular venous pulse (JVP) is one of the main parameters of cardiac function and is used by cardiologists in diagnosing heart failure. Its waveform comprises three positive waves (a, c and v) and two negative waves (x and y). Recently, it was found that JVP can be extrapolated from an ultrasound (US) video recording of the internal jugular vein (IJV), suggesting its application in space missions, on which US scanners are already widely used. To date, the feasibility of assessing JVP in microgravity (microG) has not been investigated. To verify the feasibility of JVP assessment in microG, we tested a protocol of self-performed B-mode ultrasound on the International Space Station (ISS). The protocol consisted of a video recording of IJV synchronized with electrocardiogram that produces a cross-sectional area time trace (JVP trace) (in cm2). The scans were acquired in six experimental sessions; two pre-flight (BDC1 and -2), two in space (ISS1 and -2) and two post-flight (Houston PF1, Cologne PF2). We measured the mean and standard deviation of the JVP waves and the phase relationship between such waves and P and T waves on the electrocardiogram. We verified that such parameters had the same accuracy on Earth as they did under microG, and we compared their values. The sensitivity, specificity and accuracy of JVP trace in microgravity are higher than those on Earth. The sequence of (a, c, and v) ascents and (x and y) descents along the cardiac cycle in microG is the same as that on Earth. The cause-and-effect relationship between the P and T waves on the electrocardiogram and a and v waves, respectively, of JVP is also confirmed in microG. Our experiment indicated the feasibility of deriving a JVP trace from a B-mode US examination self-performed by an astronaut in microG.

Clinical Applicability of Assessment of Jugular Flow over the Individual Cardiac Cycle Compared with Current Ultrasound Methodology.

There is growing interest in measuring cerebral venous outflow with ultrasound (US). However, results obtained with the current US Doppler methodology, which uses just a single value of cross-sectional area (CSA) of the vessel, are highly variable and inconclusive. The product of CSA and time-averaged velocity in the case of pulsatile vessels may be a possible source of error, particularly for a pulsatile vein like the internal jugular vein (IJV), where the cardiac pump transmits a sequence of well-established waves along the conduit. We herein propose a novel technique for US IJV flow assessment that accurately accounts for IJV CSA variations during the cardiac cycle. Five subjects were investigated with a high-resolution real-time B-mode video, synchronized with an electrocardiography trace. In this approach, CSA variations representing the pulsatility of the IJV are overlapped with the velocity curve obtained by the usual spectral Doppler trace. The overlap is then phased point by point using the electrocardiography pacemaker. This allows us to experimentally measure the velocity variation in relation to the change in CSA precisely, ultimately enabling calculation of IJV flow. (i) The sequence of CSA variation with respect to the electrocardiography waves corresponds exactly to the jugular venous pulse as measured in physiology. (ii) The methodology permits us to phase the velocity and CSA, which is ultimately what is currently lacking to precisely calculate the flow in the IJV with US. (iii) The time-averaged flow, calculated with the described technique, is very close to that calculated assuming a constant IJV CSA, whereas the time-dependent flow shows differs as much as 40%. (iv) Finally, we tested the accuracy of the technique with a methodology that may allow for universal assessment of the accuracy of each personal US-based evaluation of flow rate.