Segmental aortic wall stiffness from intravascular ultrasound at normal and subnormal aortic pressure in pigs.

Segmental aortic wall stiffness was calculated from intravascular ultrasound images and intravascular pressures in six pigs at normal and subnormal aortic pressures (21 sequences of pressures and areas before and after boli of intravenous nitroglycerin). The wall stiffness was expressed as the pressure-strain elastic modulus (Ep). The Ep was calculated from the formula: Ep = delta PR delta R-1 (P, pressure; R, radius) in two different ways. First from maximal and minimal values of pressure and area. Second as the slope of linear regression line of delta PR as a function of delta R from 29 simultaneous recorded pressures and images. The average Ep value for all sequences in the different segments was 0.58 +/- 0.55 10(5) Pa (Method 1) and 0.50 +/- 0.40 10(5) Pa (Method 2). Ep increased with the distance from the heart at normal aortic pressures. At subnormal aortic pressures after intravenous nitroglycerin this relationship was not so evident. At subnormal aortic pressures the calculated Ep values were significantly reduced in the lower half of the abdominal aorta. The phase lag, i.e. hysteresis, between pressure and diameter was demonstrated. Our study shows the applicability of intravascular ultrasound as a tool to evaluate arterial wall stiffness.     

Concerted action programme on quality assurance in hospitals in Norway

Below are the results of the assessment phase of a research project conducted in Norway. This project dealt with various quality assurance strategies and their effect on improvement of care with respect to: prophylactic antibiotic use in surgery; preoperative assessment; keeping records and prevention and therapy of bedsores.     

Haemodynamic effects of arterial compliance, total peripheral resistance, and glyceryl trinitrate on regurgitant volume in aortic regurgitation.

STUDY OBJECTIVE--Afterload reduction is known to reduce regurgitant flow in patients with aortic regurgitation. Both arterial compliance and total peripheral resistance are determinants of afterload. The aim of this study was to evaluate the influence of arterial compliance and total peripheral resistance on the regurgitant volume. DESIGN--The values of arterial compliance and total peripheral resistance were assessed during aortic regurgitation at different regurgitant orifice areas in eight pigs before and after a bolus of glyceryl trinitrate. In a computer model the importance of arterial compliance and total peripheral resistance on the regurgitant volume was assessed by keeping each of them constant while the other variable was changed. MEASUREMENTS AND MAIN RESULTS--In both the experimental and computer models a very strong correlation was found between decreased total peripheral resistance and decreased regurgitant volume. Arterial compliance was of hardly any importance. A bolus of glyceryl trinitrate reduced regurgitant volumes and regurgitant fractions significantly. CONCLUSIONS--Total peripheral resistance is an important factor in influencing the regurgitant volumes at a given regurgitant orifice area in aortic regurgitation, while arterial compliance is of less importance. Glyceryl trinitrate effectively reduces the regurgitant volumes by its effect on peripheral resistance.     

Instantaneous cross-sectional flow velocity profiles: a comparative study of two ultrasound Doppler methods applied to an in vitro pulsatile flow model

Two methods based on different techniques for construction of cross-sectional flow velocity profiles from Doppler ultrasound signals were compared: an intraluminal method using pulsed-wave Doppler echocardiography and an extraluminal method using two-dimensional (color) Doppler ultrasound. The methods were applied to an in vitro pulsatile flow model. With the intraluminal method, pulsed Doppler recordings obtained throughout several flow pulses at different positions across a tube were digitized, and cross-sectional flow velocity profiles were obtained by matching the onset of flow velocity at the various positions. With the extraluminal method, cross-sectional flow velocity profiles were obtained by time interpolation between the digital flow velocity data obtained from several flow velocity maps. The first flow velocity map was recorded at onset of flow and the following maps were incrementally delayed with 20 msec from one flow pulse to the next. The time lag caused by the time needed to update each of the flow velocity maps was compensated for by time interpolation between the sequentially recorded flow velocity maps. The cross-sectional flow velocity profiles obtained with the two methods were compared at identical positions within the tube model at equal flow settings and throughout the pulsatile flow periods. At three different flow settings with peak flow velocity of 0.3, 0.5, and 0.7 m/sec, the difference (mean +/- SD) between the obtained velocities were 0.01 +/- 0.04, -0.01 +/- 0.05, and -0.03 +/- 0.07 m/sec, respectively. The findings suggest that cross-sectional flow velocity profiles from pulsatile flow velocity recordings can be obtained equally well with both methods.     

Efficacy of labral repair,biceps tenodesis,and diagnostic arthroscopy for SLAP Lesions of the shoulder: a randomised controlled trial

Background  

Surgery for type II SLAP (superior labral anterior posterior) lesions of the shoulder is a promising but unproven treatment. The procedures include labral repair or biceps tenodesis. Retrospective cohort studies have suggested that the benefits of tenodesis include pain relief and improved function, and higher patient satisfaction, which was reported in a prospective non-randomised study. There have been no completed randomised controlled trials of surgery for type II SLAP lesions. The aims of this participant and observer blinded randomised placebo-controlled trial are to compare the short-term (6 months) and long-term (2 years) efficacy of labral repair, biceps tenodesis, and placebo (diagnostic arthroscopy) for alleviating pain and improving function for type II SLAP lesions.     

Simple system for analog data transmission from the physiological research laboratory to a digital computer

An unconventional analog-to-digital converter and multiplexer is described. The instrument is based on conversion of the analog signals to time intervals between narrow-width pulses by an encoder unit. The coded analog signals may then be transferred on a single line to a decoder unit and/or stored on a single track of an AM magnetic tape recorder for later processing. The signals are digitized in the decoder unit by measuring the time intervals between the pulses by means of a binary counter driven by a 19.8-MHz oscillator. The decoder is directly communicating with the interface of a digital computer, and a software package has been written for the control of data transmission. The performance of the instrument in our version is: eight separate analog inputs, sampling rate 200 Hz, input voltage −1.6 to 1.6 V, resolution capacity 3.2 V/2¹³, noise ≈0.1%, signal bandwidth de to 50 Hz ac.     

Influence of Moderate Vasoconstriction on the Wave Reflection Properties of the Pulmonary Arterial Bed

Increased transmural pressure in the pulmonary arterial bed may reduce vascular input impedance and reduce hydraulic power linked to pulsatile blood flow. Vascular impedance and pulsatile hydraulic power (Wp) levels of isolated perfused rabbit lungs were compared after similar rises of pulmonary arterial pressure (PAp), induced either by vasoconstriction or by left atrial pressure (LAp) elevation. Resulting Wp levels were significantly smaller after vasoconstriction than LAp elevation. Wp showed a minimum level at physiologic PAp (about 20 cm H₂O) irrespective of the cause of PAp elevation. Pressure pulse wave reflection coefficient (Γ) was calculated for control and test situations, and was found to be approximately doubled after vasoconstriction. Only minor changes in Γ were found after LAP elevation. Accordingly, moderate vasoconstriction (resulting PAp?20 cm H₂O) caused a backward traveling pressure wave of high amplitude, appearing in counter-phase to the forward pressure wave at the input site. The total pressure wave amplitude was thereby markedly lowered, resulting in a reduced Wp level. We assume that this effect of moderate vasoconstriction may be one reason for the existence of vascular smooth muscles in the pulmonary arteries.     

External work and arterial load in canine left ventricular ischaemic failure: evidence of ventricle-load mismatch

Summary. It has been proposed that a normal ventricle and its arterial load constitute a matched system, and that such matching is not present during ventricular failure, i.e., failure represents a state of mismatch between ventricle and arterial load. To investigate this assumption we studied the relationship between external work and load in an equatorial segment of left ventricle (LV) in an intact canine preparation under the hypothesis that the LV works at the peak of the work versus load relationship during control conditions, but is shifted from this peak during LV failure. LV systolic wall force (F) and circumferential segment work (W) were calculated in eight pentobarbital anaesthetized, open-chest dogs from LV pressure (P) and anterior-posterior diameter (D) before and after induction of LV ischaemic failure (50 um microspheres were injected into the left coronary vascular bed). Variations of arterial load were created by acute partial occlusions of the aorta, raising aortic pressure by 45 mm Hg before and 15 mm Hg during failure. Before failure W was unaffected by the variations of arterial load, but W decreased significantly during failure. From the relation between end-systolic F and D, theoretically optimal F (F_opt) corresponding to maximum W was estimated. Before failure the observed F did not differ significantly from F_opt, but the observed F was significantly greater than F_optduring failure. These findings support the notion that ventricular failure represents a state of mismatch between the ventricle and its systolic load.