Biomedical subjects

C M Kenyon

Publications and source records attributed to C M Kenyon.

10 recordsLinked to original sources

PubMed2001

Homeokinesis and short-term variability of human airway caliber.

We hypothesized that short-term variation in airway caliber could be quantified by frequency distributions of respiratory impedance (Zrs) measured at high frequency. We measured Zrs at 6 Hz by forced oscillations during quiet breathing for 15 min in 10 seated asthmatic patients and 6 normal subjects in upright and supine positions before and after methacholine (MCh). We plotted frequency distributions of Zrs and calculated means, skewness, kurtosis, and significance of differences between normal and log-normal frequency distributions. The data were close to, but usually significantly different from, a log-normal frequency distribution. Mean lnZrs in upright and supine positions was significantly less in normal subjects than in asthmatic patients, but not after MCh and MCh in the supine position. The lnZrs SD (a measure of variation), in the upright position and after MCh was significantly less in normal subjects than in asthmatic patients, but not in normal subjects in the supine position and after MCh in the supine position. We conclude that 1) the configuration of the normal tracheobronchial tree is continuously changing and that this change is exaggerated in asthma, 2) in normal lungs, control of airway caliber is homeokinetic, maintaining variation within acceptable limits, 3) normal airway smooth muscle (ASM) when activated and unloaded closely mimics asthmatic ASM, 4) in asthma, generalized airway narrowing results primarily from ASM activation, whereas ASM unloading by increasing shortening velocity allows faster caliber fluctuations, 5) activation moves ASM farther from thermodynamic equilibrium, and 6) asthma may be a low-entropy disease exhibiting not only generalized airway narrowing but also an increased appearance of statistically unlikely airway configurations.

Adolescent↗

PubMed1998

Respiratory ultrasonography of human parasternal intercostal muscle in vivo.

The parasternal intercostal muscle (PS) is phasically active during inspiration, but its mechanical function in humans is poorly understood. The aim of this study was to describe PS motion ultrasonographically during respiration. We used a 7.5-MHz curvilinear phased array transducer to obtain ultrasonograms of the second right and left interspace in the sagittal plane, 2-3 cm lateral to the sternum, in 4 seated subjects (3M, 1F), during tidal breathing and at residual volume (RV), functional residual capacity (FRC) and total lung capacity (TLC). Images were recorded on videotape and off-line, digitized, transferred to a workstation, and traced manually to outline the external and pleural borders of the PS muscle in relation to a rectangle bounded by the second and third ribs. To assess PS shape and motion, we measured inter-rib distance (Lics), PS thickness (Tps), and motion of the midpoint of the muscle relative to the midpoint of the reference rectangle (Mps). We also calculated the average radius of curvature of the external and pleural PS borders (Re, Rp) over the mid 50% of Lics, and 1/Re and 1/Rp. During tidal breathing, Mps moved ventrally by 0.42 +/- 0.06 mm (p = 0.001) against the pleural pressure gradient, and 1/Re and 1/Rp decreased by 1.1 x 10(-2) +/- 1.6 x 10(-3) mm-1 and 8.4 x 10(-3) +/- 1.4 x 10(-3) mm-1, respectively (p < 0.001). Lics and Tps did not change (p > 0.19). We conclude that, during inspiration, the PS moves ventrally and straightens, and lung volume, neural activation and pleural pressure influence PS shape and motion. The findings support an intercostal stabilizing function of the PS and suggest a novel mechanism by which the PS may contribute to the inspiratory fall in pleural pressure.

Adult↗

PubMed1997

Rib cage mechanics during quiet breathing and exercise in humans.

During exercise, large pleural, abdominal, and transdiaphragmatic pressure swings might produce substantial rib cage (RC) distortions. We used a three-compartment chest wall model (J. Appl. Physiol. 72: 1338-1347, 1992) to measure distortions of lung- and diaphragm-apposed RC compartments (RCp and RCa) along with pleural and abdominal pressures in five normal men. RCp and RCa volumes were calculated from three-dimensional locations of 86 markers on the chest wall, and the undistorted (relaxation) RC configuration was measured. Compliances of RCp and RCa measured during phrenic stimulation against a closed airway were 20 and 0%, respectively, of their values during relaxation. There was marked RC distortion. Thus nonuniform distribution of pressures distorts the RC and markedly stiffens it. However, during steady-state ergometer exercise at 0, 30, 50, and 70% of maximum workload, RC distortions were small because of a coordinated action of respiratory muscles, so that net pressures acting on RCp and RCa were nearly the same throughout the respiratory cycle. This maximizes RC compliance and minimizes the work of RC displacement. During quiet breathing, plots of RCa volume vs. abdominal pressure were to the right of the relaxation curve, indicating an expiratory action on RCa. We attribute this to passive stretching of abdominal muscles, which more than counterbalances the insertional component of transdiaphragmatic pressure.

Abdomen↗

PubMed1997

Human respiratory muscle actions and control during exercise.

We measured pressures and power of diaphragm, rib cage, and abdominal muscles during quiet breathing (QB) and exercise at 0, 30, 50, and 70% maximum workload (Wmax) in five men. By three-dimensional tracking of 86 chest wall markers, we calculated the volumes of lung- and diaphragm-apposed rib cage compartments (Vrc,p and Vrc,a, respectively) and the abdomen (Vab). End-inspiratory lung volume increased with percentage of Wmax as a result of an increase in Vrc,p and Vrc,a. End-expiratory lung volume decreased as a result of a decrease in Vab. DeltaVrc,a/DeltaVab was constant and independent of Wmax. Thus we used DeltaVab/time as an index of diaphragm velocity of shortening. From QB to 70% Wmax, diaphragmatic pressure (Pdi) increased approximately 2-fold, diaphragm velocity of shortening 6.5-fold, and diaphragm workload 13-fold. Abdominal muscle pressure was approximately 0 during QB but was equal to and 180 degrees out of phase with rib cage muscle pressure at all percent Wmax. Rib cage muscle pressure and abdominal muscle pressure were greater than Pdi, but the ratios of these pressures were constant. There was a gradual inspiratory relaxation of abdominal muscles, causing abdominal pressure to fall, which minimized Pdi and decreased the expiratory action of the abdominal muscles on Vrc,a gradually, minimizing rib cage distortions. We conclude that from QB to 0% Wmax there is a switch in respiratory muscle control, with immediate recruitment of rib cage and abdominal muscles. Thereafter, a simple mechanism that increases drive equally to all three muscle groups, with drive to abdominal and rib cage muscles 180 degrees out of phase, allows the diaphragm to contract quasi-isotonically and act as a flow generator, while rib cage and abdominal muscles develop the pressures to displace the rib cage and abdomen, respectively. This acts to equalize the pressures acting on both rib cage compartments, minimizing rib cage distortion.

Abdominal Muscles↗

PubMed1996

Intracellular pressure is a motive force for cell motion in Amoeba proteus.

The cortical filament layer of free-living amoebae contains concentrated actomyosin, suggesting that it can contract and produce an internal hydrostatic pressure. We report here on direct and dynamic intracellular pressure (P(ic)) measurements in Amoeba proteus made using the servo-null technique. In resting apolar A. proteus, P(ic) increased while the cells remained immobile and at apparently constant volume. P(ic) then decreased approximately coincident with pseudopod formation. There was a positive correlation between P(ic) at the onset of movement and the rate of pseudopod formation. These results are the first direct evidence that hydrostatic pressure may be a motive force for cell motion. We postulate that contractile elements in the amoeba's cortical layer contract and increase P(ic) and that this P(ic) is utilized to overcome the viscous flow resistance of the intracellular contents during pseudopod formation.

Amoeba↗

PubMed1996

Procainamide-induced agranulocytosis differs serologically and clinically from procainamide-induced lupus.

Agranulocytosis is a well recognized but uncommon complication of procainamide (PA) therapy, whereas a lupus-like syndrome occurs in approximately 20% of patients treated chronically with PA. In order to gain insight into the immunopathogenic relationships among these conditions, we compared the humoral immune abnormalities in these patient groups as well as in asymptomatic PA-treated patients. A relatively uniform profile of IgM but not IgG autoantibody reactivity with a set of chromatin-related antigens was observed in eight elderly men who developed agranulocytosis after treatment with PA. In contrast PA-induced lupus patients had predominant reactivity with [(H2A-H2B)-DNA] in both IgM and IgG classes. Five of eight patients with agranulocytosis had elevated levels of neutrophil-reactive IgG which appeared to be due to immune complexes based on Fc gamma receptor blocking studies. However, 12 of 15 patients with PA-induced lupus, none of whom had neutropenia, had similar levels of neutrophil-reactive IgG, suggesting that this reactivity was not causally related to agranulocytosis. Agranulocytosis developed after less than 3 months treatment with PA in six of eight patients. This time course was similar to that seen in 77 PA-induced agranulocytosis patients reported in the literature plus 127 patients reported to the U.S. Food and Drug Administration in whom 90% developed agranulocytosis within 3 months of starting PA. In contrast, the mode duration of treatment with PA before lupus-like symptoms develop is 10-12 months. These findings, together with the different profiles of autoantibodies and clinical presentations, suggest that agranulocytosis arises from a different mechanism than that underlying PA-induced lupus.

Aged↗

PubMed1996

Human rib cage distortability.

In five normal men, we divided the rib cage into lung-apposed [pulmonary rib cage (RCp)] and diaphragm-apposed [abdominal rib cage (RCab)] compartments and calculated their absolute cross-sectional areas (Arc,p and Arc,ab) by anteroposterior and lateral dimensions measured by magnetometry. Distortion was quantified as the displacement of RCp and RCab produced by diaphragmatic twitches away from the relaxed configuration. We measured transdiaphragmatic pressure as the difference between gastric and esophageal pressures. Distortability was expressed as percent distortion per transdiaphragmatic pressure and varied among individuals from 0.02 to 0.23%/cmH2O. The pressure acting to restore the distorted rib cage back to its relaxed shape (Plink) varied from 0.1 to 31.3 cmH2O/%distortion. Distortion correlated positively (r = 0.92) and Plink per percent distortion negatively (r = -0.90) with RCab compliance during the relaxation maneuver (delta Arc, ab/delta gastric pressure). We conclude that rib cage distortability varies widely among normal subjects and is closely linked to RCab compliance.

Abdomen↗

PubMed1996

Chest wall and lung volume estimation by optical reflectance motion analysis.

Estimation of chest wall motion by surface measurements only allows one-dimensional measurements of the chest wall. We have assessed on optical reflectance system (OR), which tracks reflective markers in three dimensions (3-D) for respiratory use. We used 86 (6-mm-diameter) hemispherical reflective markers arranged circumferentially on the chest wall in seven rows between the sternal notch and the anterior superior iliac crest in two normal standing subjects. We calculated the volume of the entire chest wall and compared inspired and expired volumes with volumes obtained by spirometry. Marker positions were recorded by four TV cameras; two were 4 m in front of and two were 4 m behind the subject. The TV signals were sampled at 100 Hz and combined with grid calibration parameters on a personal computer to obtain the 3-D coordinates of the markers. Chest wall surfaces were reconstructed by triangulation through the point data, and chest wall volume was calculated. During tidal breathing and vital capacity maneuvers and during CO2-stimulated hyperpnea, there was a very close correlation of the lung volumes (VL) estimated by spirometry [VL(SP)] and OR [VL(OR)]. Regression equations of VL(OR) (y) vs. VL(SP) (x, BTPS in liters) for the two subjects were given by y = 1.01x-0.01 (r = 0.996) and y = 0.96x + 0.03 (r = 0.997), and by y = 1.04x + 0.25 (r = 0.97) and y = 0.98x + 0.14 (r = 0.95) for the two maneuvers, respectively. We conclude spirometric volumes can be estimated very accurately and directly from chest wall surface markers, and we speculate that OR may be usefully applied to calculations of chest wall shape, regional volumes, and motion analysis.

Humans↗

PubMed1991

Adaptive modeling of the human rib cage in median sternotomy.

This paper describes a limited computer-analyzed kinematic model of the rib cage that can be adapted to individual subjects. Also described is its validation and use in assessing the changes in chest wall shape after coronary artery bypass graft (CABG) surgery in 12 patients. The positions of a small number of anatomic locations on the thoracic spine, ribs, manubrium, and sternum are measured from lateral and posterior-anterior chest radiographs. The computer program puts these two views together removing the magnification and reconstructs any missing points to give a three-dimensional picture of the rib cage to which mathematical models of the bones are scaled. The patients had chest radiographs taken at total lung capacity (TLC) and residual volume (RV) to investigate the source of the restrictive ventilatory defect that follows CABG. The predictions from the model were tested by comparing full-sized computer plots with the actual chest radiographs. The estimates of the bony structures were accurate to +/- 3 degrees for orientations and +/- 6 mm for positions. We found reduced rib motion both "pump-handle" (theta) and "bucket handle" (psi) going from theta, psi left, psi right = 9 degrees, 10 degrees, 14 degrees to 4 degrees, 10 degrees, 9 degrees, respectively, after surgery with P less than 0.025, 0.42, 0.07. The angles were measured from the horizontal and increased caudally. There was also reduction in the range of angles subtended by the arc of the thoracic vertebrae between TLC and RV, which went from 12 degrees to -1 degrees (P less than 0.015). These data explain the fall in lung volumes that follow CABG and provide insight into the contribution made by the ribs and spine in full inspiration and full expiration.

Coronary Artery Bypass↗

PubMed1989

A mathematical analysis for the modelling of trabecular bone.

We present a mathematical analysis of trabecular bone which may be applied to develop dynamic computer simulations of the musculoskeletal system. We have derived an algorithm which can be used to study the genetic limitations within which skeletal articulations may function successfully. We believe that our model will help other workers to advance the understanding of the interplay between genetic and environmental influences in the growth, modelling and degeneration of osseous tissues.

Animals↗