James E. Holte

Contribution of Collagen, Elastin, and Smooth Muscle to In Vivo Human Brachial Artery Wall Stress and Elastic Modulus

BACKGROUND The contributions of collagen, elastin, and smooth muscle to arterial mechanical properties in the in vivo human artery are not known. METHODS AND RESULTS We used a recently developed intravascular ultrasound technique to measure total brachial artery wall stress and incremental elastic modulus (Einc) in seven normal human subjects at baseline and after intra-arterial norepinephrine (1.2 micrograms) and nitroglycerin (100 micrograms). Then we applied a modified Maxwell model to estimate the elastic modulus of elastin (EE); the recruitment of collagen fibers supporting wall stress; and the differential contributions of collagen, elastin, and smooth muscle to wall stress and Einc over a wide range of pressure and smooth muscle tone. With this model, EE was 3 x 10(6) dynes/cm2. Collagen fibers were recruited increasingly as transmural arterial pressure increased and reached a value of approximately 5% to 6% at 100 mm Hg under each of the conditions studied. Isobaric smooth muscle contraction resulted in a small decrease in total wall stress and no significant change in total Einc while shifting the predominant element contributing to these mechanical parameters from collagen in parallel with the smooth muscle to collagen in series with the smooth muscle. In contrast, isometric smooth muscle contraction produced large increases in total wall stress (from 0.11 x 10(6) dynes/cm2 after nitroglycerin administration to 1.35 x 10(6) dynes/cm2 after norepinephrine administration) and Einc (from 3.84 x 10(6) dynes/cm2 after nitroglycerin administration to 57.8 x 10(6) dynes/cm2 after norepinephrine administration) entirely as a result of the additional contribution of the smooth muscle and its associated series collagen. CONCLUSIONS This study describes a technique for determining arterial elastic properties and a model that can be used to estimate a number of mechanical parameters of the human brachial artery in vivo. This technique may be useful in studies of the arterial elastic properties of arteries in patients with vascular pathology.

Direct Effects of Smooth Muscle Relaxation and Contraction on In Vivo Human Brachial Artery Elastic Properties

The direct effect of smooth muscle relaxation on arterial elastic properties is controversial. Studies in animals show both a decrease and an increase in elastic modulus. In human subjects, the contribution of smooth muscle to arterial elastic mechanics has been limited by difficulty in separating the direct effects of a vasodilator drug on the arterial wall from the indirect effects due to reduced blood pressure. The purpose of the present study was to assess the direct contribution of vascular smooth muscle to brachial artery elastic mechanics in normal human subjects in vivo. We measured brachial artery compliance and incremental elastic modulus (Einc) in eight normal subjects (age, 22 to 51 years) by using intravascular ultrasound. A 3.5F 30-MHz intravascular ultrasound catheter was placed through a sheath into the brachial artery, and intraarterial pressure, cross-sectional area, and wall thickness were measured simultaneously under baseline conditions and after the administration of intra-arterial nitroglycerin (100 micrograms) and norepinephrine (1.2 micrograms). A pressurized cuff surrounding the brachial artery was inflated to reduce transmural brachial artery pressure. Using this technique, we were able to measure the following arterial characteristics for the first time in human subjects in vivo: (1) the effective unstressed arterial radius and (2) the pressure-area, stress-strain, and pressure-Einc relations over a wide pressure range (0 to 100 mm Hg). Intra-arterial nitroglycerin increased brachial artery area by 22% and intraarterial norepinephrine decreased brachial artery area by 17% at 100 mm Hg transmural pressure (P < .001 versus baseline).(ABSTRACT TRUNCATED AT 250 WORDS)

Initial stability measurement of dental implants placed in different anatomical regions of fresh human cadaver jawbone

STATEMENT OF PROBLEM Initial implant stability has been used as an indicator for future osseointegration and whether an immediate/early loading protocol should be applied. However, differences in initial stability in relation to anatomical regions of jawbone have not been studied extensively because of the risks involved with stability measurements. PURPOSE The purpose of this study was to determine whether initial implant stability varies with anatomical regions of the jawbone. MATERIAL AND METHODS Four pairs of edentulous maxillae and mandibles were retrieved from fresh human cadavers. Six implants (Biomet 3i) per pair were placed in different anatomical regions (maxillary anterior, right and left maxillary posterior, mandibular anterior, right and left mandibular posterior). Immediately after implant placement, initial implant stability was measured with a custom-made resonance frequency analyzer, a commercial resonance frequency analysis device (Osstell), and a mechanical tapping device (Periotest). All implant surgeries and initial stability measurements were performed within 72 hours of death to simulate a clinical setting. Repeated measures ANOVA (alpha=.05) and univariate correlation analyses were used to analyze the data. RESULTS Mandibular implants had significantly higher initial stability than maxillary implants. Posterior maxillary implants were least stable. Stability was less buccolingually than mesiodistally. The measurements from 3 stability measuring devices were strongly associated with each other. CONCLUSIONS Initial implant stability varied among anatomical regions of jawbone. Rank of Periotest value and implant stability quotient (Osstell) had the highest correlation (r=-0.852).

Circadian period of human blood pressure and heart rate in clinical health under ordinary conditions

Putative point-and-interval estimates of the circadian period tau of cardiovascular variables were obtained from 95 clinically healthy nurses who measured their blood pressure and heart rate about every 15 minutes for 48 hours in November or June, using a Colin Medical Instruments ABPM-630 ambulatory monitor. Linear-nonlinear least-squares rhythmometry yields estimates of the circadian period, with a single-component (24-h cosine curve) and a two-component (24- and 12-h cosine curves) model. For systolic blood pressure, in an individualized fashion, analysis based on a single 24-h component allows the determination of the circadian period with 95% confidence limits in all but three of the 95 series. On a population average, 95% confidence intervals bracket anticipated periods of 24 and 12 h; but on an individualized basis, the 95% confidence interval of tau does not cover precisely 24 h in almost 50% of the cases. A reference standard is provided for the assessment by linear-nonlinear rhythmometry of circadian cardiovascular periods under usual conditions of life with a 48-h record.<<ETX>>

Age effects upon the harmonic structure of human blood pressure in clinical health

Ambulatory blood pressure monitoring of 180 clinically healthy adults of both genders is used to investigate and compare ultradian aspects of systolic and diastolic blood pressure as a function of age. Three age categories are considered: 20-40, 40-60, and over 60 years of age. results from least-squares spectra of each data series are further examined by analysis of variance. Gender and age effects are found to characterize the waveform of human blood pressure. These effects can be quantified by spectral analysis and may represent gauges of aging.<<ETX>>

Investigation of non-uniform airflow signal oscillation during high frequency chest compression

BackgroundHigh frequency chest compression (HFCC) is a useful and popular therapy for clearing bronchial airways of excessive or thicker mucus. Our observation of respiratory airflow of a subject during use of HFCC showed the airflow oscillation by HFCC was strongly influenced by the nonlinearity of the respiratory system. We used a computational model-based approach to analyse the respiratory airflow during use of HFCC.MethodsThe computational model, which is based on previous physiological studies and represented by an electrical circuit analogue, was used for simulation of in vivo protocol that shows the nonlinearity of the respiratory system. Besides, airflow was measured during use of HFCC. We compared the simulation results to either the measured data or the previous research, to understand and explain the observations.Results and discussionWe could observe two important phenomena during respiration pertaining to the airflow signal oscillation generated by HFCC. The amplitudes of HFCC airflow signals varied depending on spontaneous airflow signals. We used the simulation results to investigate how the nonlinearity of airway resistance, lung capacitance, and inertance of air characterized the respiratory airflow. The simulation results indicated that lung capacitance or the inertance of air is also not a factor in the non-uniformity of HFCC airflow signals. Although not perfect, our circuit analogue model allows us to effectively simulate the nonlinear characteristics of the respiratory system.ConclusionWe found that the amplitudes of HFCC airflow signals behave as a function of spontaneous airflow signals. This is due to the nonlinearity of the respiratory system, particularly variations in airway resistance.

Modeled velocity of airflow in the airways during various respiratory patterns

Our modeling and simulation of the respiratory system with Weibels morphometry shows that the average velocity of expiratory airflow is always greater than the average velocity of inspiratory airflow during tidal breathing when the intervals of inspiration and expiration are same. A nonlinear circuit model was developed comprised with the upper airway, the conducting airways (trachea /spl sim/ terminal bronchioles), and the lumped alveolar space. These compartments are established with known physiologic pulmonary characteristics that are represented by nonlinear resistors and capacitors. In this paper we set up the circuit model reflecting the geometric variation of airways during tidal breathing, and demonstrated computation results for the velocity of airflow along the airways based on 16 different respiratory patterns. The circuit model offers a convenient method that can be used to investigate the velocity of airflow and its interaction with mucus, as well as suggests a basic model for our future research on analyzing airway clearance techniques.

Exact technique for weighting function calculation in 3D cone-beam reconstruction

The exact weighting function in 3D image reconstruction from 2D projections with cone beam geometry is obtained as the volume of intersection of a pyramidal ray with a cubic voxel. This intersection yields a convex polyhedron whose faces are formed by either the side of the pyramid or the voxel face. For each face of a voxel, we maintain a vertex link map. When one of the four pyramidal ray planes clips the voxel, we obtain a new face and a set of new vertices, while updating existing faces and their vertex link maps. Progressively clipping the voxel by the necessary ray planes yields the intersection polyhedron, whose faces and vertices are provided by the face list and its associated vertex link maps. To generate the weight, the volume of the polyhedron is calculated by dividing the polyhedron into tetrahedrons, whose volumes are summed. The exact calculated weights were used to reconstruct 3D vascular images from simulated data using a ROI (region of interest) limited ART (algebraic reconstruction technique). Comparing the results to those obtained from length approximation indicates that more accurate reconstruction could be achieved from the weights calculated with the new method.

Energy Transfer High Frequency Chest Compression

High frequency chest compression (HFCC) supplies a sequence of air pulses to an inflatable vest-like garment that covers the thorax. The pulses produce oscillatory airflow within the lungs of patients with chronic obstructive lung disease (COLD). The energy produced from the machine and transferred from the vest to the patient’s lungs assists in opening airways and increases air volume flow rate to remove mucus for clearance by expectoration or swallowing. Evaluation of relative efficacy for such a system requires an estimate of the pressure and frequency of the vibration energy transferred from vest to body over the operating range of the system. The purpose of this study is to measure the spatial energy distribution of acceleration applied to the vest/chest wall using a 3-D accelerometer. This study is of two waveforms, sinus and triangle, with two different vests, two pulse pressures, and two frequencies to observe the distribution of energy. The results of energy transfer are presented for three protocols: vest on mannequin, vest on control subject and vest on a CF patient. For both a normal subject and a CF patient, volume airflow and pressure at the mouth are reported as an index of energy coupled to the lungs. Our results show significant differences in the both intra-vest and thoracic energy distribution patterns between the machine-vest systems. The products of estimated energy from the normal subject and CF patient vary with machine settings. The premise that all HFCC machines deliver comparable therapy is called into question. Further studies are needed to analyze machine differences and define optimal performance characteristics.

Representations of feed-sideward modulation

To account for phenomena that occur when three or more rhythmic entities interact, called feedsidewards, models from engineering are considered as a possibly useful scaffolding from which to formulate tests of the mechanisms underlying such observations. Rhythms at different organizational levels and cephaloadrenal interactions are discussed. A description of an experiment involving the effects of light on mice is presented. Models for biological and biochemical rhythms are also discussed.<<ETX>>