Doppler characteristics of late-diastolic flow in the left ventricular outflow tract.

This study characterizes the relationship between late-diastolic Doppler detected forward flow in the left ventricular outflow tract and diastolic transmitral flow. Pulsed-wave Doppler interrogation of the left ventricular outflow tract, in a prospective consecutive series (n = 137), revealed the presence of end-diastolic forward flow in 83% of the patients studied. Further quantification of both flow signals was performed in 67 patients. Pulsed-wave mapping demonstrated that peak velocity of the end-diastolic left ventricular outflow tract signal (J wave) was maximal, 2.6 +/- 0.7 cm from the aortic valve anulus, and occurred 48 +/- 34 milliseconds after the peak transmitral atrial velocity flow signal. Peak J velocity ranged from 25 to 118 cm per second and correlated with peak A velocity (r = 0.69, p less than 0.001). Peak J velocity was inversely related to left ventricular end-diastolic dimension (r = -0.53, p less than 0.0001) and left ventricular end-diastolic volume (r = -0.43, p less than 0.004). There was no relationship between J wave velocity and early diastolic filling. We concluded that a late-diastolic forward flow signal is commonly observed in the left ventricular outflow tract. It is a manifestation of transmitral atrial systolic flow in the left ventricular outflow tract and is determined predominantly by peak transmitral atrial velocity and left ventricular size.

Hydrodynamic principles in hydrocephalus: the engineer's perspective.

There have been significant improvements in the prognosis for patients suffering from hydrocephalus stemming from the introduction of the cerebrospinal fluid (CSF) shunt some 40 years ago. Currently, one of the major obstacles to effective shunt treatment is the mismatch between the physiology of the patient and the hydraulics of the shunt system. In order to maintain the proper relationship between CSF and cerebrovascular pressures, the implanted shunt needs to establish normal CSF outflow (absorption) and storage (compliance). Many of today's shunts establish a limited range of normal CSF outflow (absorption) and storage (compliance) once implanted, but a mismatch between CSF and cerebrovascular pressures may exist when the patient changes body position during daily activities. An uncoupling of these pressures creates mechanical strains within cerebral tissues, which are implicated in pathologies related to shunt malfunction. We suggest that re-establishment of normal CSF outflow resistance, which by definition is an indicator of both absorption and compliance, is a fundamental requirement for shunt treatment under most conditions.