Janneke Gisolf

Human cerebral venous outflow pathway depends on posture and central venous pressure

Internal jugular veins are the major cerebral venous outflow pathway in supine humans. In upright humans the positioning of these veins above heart level causes them to collapse. An alternative cerebral outflow pathway is the vertebral venous plexus. We set out to determine the effect of posture and central venous pressure (CVP) on the distribution of cerebral outflow over the internal jugular veins and the vertebral plexus, using a mathematical model. Input to the model was a data set of beat‐to‐beat cerebral blood flow velocity and CVP measurements in 10 healthy subjects, during baseline rest and a Valsalva manoeuvre in the supine and standing position. The model, consisting of 2 jugular veins, each a chain of 10 units containing nonlinear resistances and capacitors, and a vertebral plexus containing a resistance, showed blood flow mainly through the internal jugular veins in the supine position, but mainly through the vertebral plexus in the upright position. A Valsalva manoeuvre while standing completely re‐opened the jugular veins. Results of ultrasound imaging of the right internal jugular vein cross‐sectional area at the level of the laryngeal prominence in six healthy subjects, before and during a Valsalva manoeuvre in both body positions, correlate highly with model simulation of the jugular cross‐sectional area (R2= 0.97). The results suggest that the cerebral venous flow distribution depends on posture and CVP: in supine humans the internal jugular veins are the primary pathway. The internal jugular veins are collapsed in the standing position and blood is shunted to an alternative venous pathway, but a marked increase in CVP while standing completely re‐opens the jugular veins.

Impact of age on the vasovagal response provoked by sublingual nitroglycerine in routine tilt testing

NTG (nitroglycerine) is used in routine tilt testing to elicit a vasovagal response. In the present study we hypothesized that with increasing age NTG triggers a more gradual BP (blood pressure) decline due to a diminished baroreflex-buffering capacity. The purpose of the present study was to examine the effect of NTG on baroreflex control of BP in patients with distinct age-related vasovagal collapse patterns. The study groups consisted of 29 patients (16-71 years old, 17 females) with clinically suspected VVS (vasovagal syncope) and a positive tilt test. Mean FAP (finger arterial pressure) was monitored continuously (Finapres). Left ventricular SV (stroke volume), CO (cardiac output) and SVR (systemic vascular resistance) were computed from the pressure pulsations (Modelflow). BRS (baroreflex sensitivity) was estimated in the time domain. In the first 3 min after NTG administration, BP was well-maintained in all patients. This implied an adequate arterial resistance response to compensate for steeper reductions in SV and CO with increasing age. HR (heart rate) increased and the BRS decreased after NTG administration. The rate of mean FAP fall leading to presyncope was inversely related to age (r=0.51, P=0.005). Accordingly, patients with a mean FAP fall >1.44 mmHg/s (median) were generally younger compared with patients with a slower mean FAP-fall (30+/-10 years compared with 51+/-17 years; P=0.001). The main determinant of the rate of BP fall on approach of presyncope was the rate of fall in HR (r=0.75, P<0.001). It was concluded that, in older patients, sublingual NTG provokes a more gradual BP decline compared with younger patients. This gradual decline cannot be ascribed to failure of the baroreflex-buffering capacity with increasing age. Age-related differences in the laboratory presentation of a vasovagal episode depend on the magnitude of the underlying bradycardic response.

Limited accuracy of the hyperbaric index, ambulatory blood pressure and sphygmomanometry measurements in predicting gestational hypertension and preeclampsia.

Objective The aim of this study was to validate the hyperbaric index (HBI) for first trimester prediction of preeclampsia and gestational hypertension. Methods Participants were low-risk and high-risk nulliparous women and high-risk multiparous women, and were recruited between April 2004 and June 2006. At a gestational age of 9 weeks (range 8–11 weeks), blood pressure (BP) was measured first by sphygmomanometry and thereafter by ambulatory BP measurement (ABPM) for 48 h. The first 90 low-risk women who had an uneventful pregnancy formed the reference group for calculation of a time-specified tolerance interval with 90% confidence limits. In the validation group, consisting of the remaining women, the HBI was calculated as the time-specified BP excess over this tolerance limit for SBP, DBP and mean arterial pressure. Results The validation group contained 101 women. Fifteen women developed preeclampsia and 13 developed gestational hypertension. For preeclampsia, the maximum HBI had the best predictive capacity with a sensitivity of 73% and a specificity of 86%. However, the difference with standard ABPM measurement or sphygmomanometry was small with a sensitivity between 75 and 73% and a specificity between 86 and 95%. The predictive efficacy for gestational hypertension was poor with all methods (sensitivity between 54 and 77%, specificity between 41 and 78%). Conclusion Standardized sphygmomanometry, ABPM measurement and the HBI calculated from 48-h ABPM had a comparable, restricted predictive efficacy. The high predictive value of HBI as observed in earlier studies could not be reproduced.