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Biomedical subjects

S H Loring

Publications and source records attributed to S H Loring.

At least 19 recordsLinked to original sources
PubMed2001

Respiratory effects of transient axial acceleration.

Whereas gravity has an inspiratory effect in upright subjects, transient upward acceleration is reported to have an expiratory effect. To explore the respiratory effects of transient axial accelerations, we measured axial acceleration at the head and transrespiratory pressure or airflow in five subjects as they were dropped or lifted on a platform. For the first 100 ms, upward acceleration caused a decrease in mouth pressure and inspiratory flow, and downward acceleration caused the opposite. We also simulated these experimental observations by using a computational model of a passive respiratory system based on anatomical data and normal respiratory characteristics. After 100 ms, respiratory airflow in our subjects became highly variable, no longer varying with acceleration. Electromyograms of thoracic and abdominal respiratory muscles showed bursts of activity beginning 40-125 ms after acceleration, suggesting reflex responses responsible for subsequent flow variability. We conclude that, in relaxed subjects, transient upward axial acceleration causes inspiratory airflow and downward acceleration causes expiratory airflow, but that after ~100 ms, reflex activation of respiratory musculature largely determines airflow.

Acceleration↗
PubMed2001

Interpreting improvement in expiratory flows after lung volume reduction surgery in terms of flow limitation theory.

Spirometry and pulmonary mechanics were measured pre- and postoperatively in 37 patients undergoing bilateral lung volume reduction surgery (LVRS). The relative contributions of changes in compliance (CL), recoil pressures (PTLC), small airway conductance (Gu), and airway closing pressures (Ptm') to changes in expiratory flows were examined with a Taylor series expansion of the Pride- Permutt model of flow limitation. The resulting variational expression, deltaVmax = GudeltaPel + PeldeltaGu - GudeltaPtm' - Ptm'deltaGu - deltaGudeltaPtm', was then used to describe how the peak flow rate (Vmax) depends on preoperative Gu, P TLC, Ptm', and on changes (delta) in these parameters after surgery. After LVRS, both FEV(1) and Vmax increased significantly ( DeltaFEV(1) = 28 +/- 44%; DeltaVmax = 78 +/- 132%), and changes in FEV(1) and Vmax correlated closely (r = 0.74, p < 0.001). Among responders (DeltaFEV(1) > or = 12%; n = 19; DeltaFEV(1) = 60 +/- 38%), PTLC increased (8.8 +/- 2.8 to 12.2 +/- 4.7 cm H2O) and the time constant for expiration (tau = CL/Gu) decreased (2.67 +/- 0.62 to 2.35 +/- 0.55 s), while Ptm', CL, and Gu did not change. GudeltaPel, the change in recoil weighted by preoperative conductance upstream of the flow-limiting site, accounted for 72% of the improvement in Vmax. Among nonresponders ( DeltaFEV(1) = -6 +/- 15%, n = 18), tau increased significantly, contributing to a decline in FEV(1)/FVC ratio. PeldeltaGu decreased (-0.25 +/- 0.68, p = 0.013), accounting for all of the decline in Vmax. This analysis suggests that (1) improvement in expiratory flows after LVRS is largely due to increases in recoil pressure; (2) large improvements in FEV(1) can occur without changes in Gu or Ptm', arguing that LVRS has little effect on airway resistance or closure; and (3) large changes in PTLC can occur without changes in CL, supporting arguments of Fessler and Permutt (Am J Respir Crit Care Med 1998;157:715-722) that "resizing of the lung to chest wall" is the primary mechanism by which LVRS improves lung function.

Female↗
PubMed2001

Comparison of physiological and radiological screening for lung volume reduction surgery.

Physiological and radiological criteria are both used to identify candidates for LVRS. This study compares the predictive value of these screening techniques among patients with homogeneous (Ho) and heterogeneous (He) emphysema. Preoperative inspiratory lung conductance (G(Li)) during spontaneous breathing and quantitative radioisotope V/Q scan (QVQS) results were available for 48 of 50 patients undergoing bilateral LVRS for emphysema. Ho disease (n = 21) was defined by QVQS as an upper/lower perfusion ratio (ULPR) between 0.75 and1.25. G(Li) correlated with 6-mo improvement in FEV(1) (DeltaFEV(1)-6) (r = 0.53, p < 0.001) for the entire cohort, and for patients with both Ho (n = 21, r = 0.56, p = 0.015) and He disease (n = 27, r = 0.46, p = 0.017). ULPR correlated less well with DeltaFEV(1)-6 (n = 48, r = -0.38; p = 0.008) for the cohort, and was significantly correlated with outcomes only in the subgroup of patients with He disease (r = -0.40, p = 0.04). Multivariate regression demonstrated that by combining G(Li) and ULPR criteria, 33% of the DeltaFEV(1)-6 response could be accounted for. We conclude that both physiological and radiological criteria help identify appropriate candidates for LVRS. G(Li) best identifies patients with Ho emphysema who may benefit from surgery, but would be excluded on the basis of strictly radiological criteria. ULPR helps identify patients with He disease that improves with surgery, despite unfavorable G(Li).

Adult↗
PubMed2000

Inhaled albuterol, but not intravenous lidocaine, protects against intubation-induced bronchoconstriction in asthma.

BACKGROUND: The ability of intravenous lidocaine to prevent intubation-induced bronchospasm is unclear. The authors performed a prospective, randomized, double-blind, placebo-controlled trial to test the ability of intravenous lidocaine and inhaled albuterol to attenuate airway reactivity after tracheal intubation in asthmatic patients undergoing general anesthesia. METHODS: Sixty patients were randomized to receive either 1.5 mg/kg intravenous lidocaine or saline, 3 min before tracheal intubation. An additional 50 patients were randomized to receive 4 puffs of inhaled albuterol or placebo 15-20 min before tracheal intubation. Anesthesia was induced with propofol. Immediately after intubation and at 5-min intervals, transpulmonary pressure and airflow were recorded, and lower pulmonary resistance (RL) was calculated. Isoflurane was administered after the initial two measurements to assess reversibility of bronchoconstriction. A bronchoconstrictor response to intubation was defined as RL greater than or equal to 5 cm H2O. l-1. s-1 in the first two measurements after intubation and RL subsequently decreasing by 50% or more after isoflurane. RESULTS: The lidocaine and placebo groups were not different in the peak RL before administration of isoflurane (8.2 cm H2O. l-1. s-1 vs. 7.6 cm H2O. l-1. s-1) or frequency of airway response to intubation (lidocaine 6 of 30 vs. placebo 5 of 27). In contrast, the albuterol group had lower peak RL (5.3 cm H2O. l-1. s-1 vs. 8.9 cm H2O. l-1. s-1; P < 0.05) and a lower frequency of airway response (1 of 25 vs. 8 of 23; P < 0.05) than the placebo group. CONCLUSIONS: Inhaled albuterol blunted airway response to tracheal intubation in asthmatic patients, whereas intravenous lidocaine did not.

Administration, Inhalation↗
PubMed1999

Causes of allograft dysfunction after single lung transplantation for emphysema: extrinsic restriction versus intrinsic obstruction. Brigham and Women's Hospital Lung Transplantation Group.

BACKGROUND: A subset of patients with emphysema who have undergone single lung transplantation (SLT) may subsequently present with dyspnea, worsening airways obstruction, hypoxemia, and progressive chronic native lung hyperinflation. The leading cause of late allograft dysfunction is bronchiolitis obliterans syndrome (BOS). However, extrinsic restriction manifests with a similar clinical presentation and is an additional mechanism to consider. We describe the use of the inspiratory lung resistance (RLi) to distinguish a decline in respiratory status due predominantly to either extrinsic restriction or BOS. METHODS: We studied five patients who underwent SLT for emphysema between 1992 and 1995, in whom the diagnoses of BOS and extrinsic restriction were subsequently entertained. Forced expiratory volume in 1 second (FEV1), RLi, static lung compliance, elastic recoil pressure at total lung capacity (TLC), and the slope of the maximum flow static recoil (MFSR) plot were measured. RESULTS: All patients had severe airflow obstruction, with mean FEV1 0.98 +/- 0.24 liter (26 +/- 5% predicted), elevated static lung compliance, reduced elastic recoil pressure at TLC, and reduced slope of the MFSR plot. Three patients had "low" RLi (9.3-12.8 cm H20/L/sec). Obstruction was attributed predominantly to extrinsic restriction. These patients underwent lung volume reduction surgery (LVRS) on the native lung; improvements in pulmonary mechanics were observed at 6 months. In contrast, two patients had markedly elevated RLi (17.3 and 17.4 cm H2O/L/sec). Obstruction was attributed predominantly to intrinsic airway disease from BOS that was subsequently documented at autopsy. CONCLUSIONS: The RLi appears to be a useful adjunct to the clinical history in distinguishing a decline in respiratory status due predominantly to either BOS or extrinsic restriction in patients who have undergone SLT for emphysema. Determination of the mechanism of allograft dysfunction may allow the selection of an appropriate subset of patients who would benefit from LVRS.

Airway Resistance↗
PubMed1999

Model of functional restriction in chronic obstructive pulmonary disease, transplantation, and lung reduction surgery.

Mechanical interactions between lung and chest wall are important determinants of respiratory function. When chest wall expansion during maximal inhalation generates insufficiently negative pleural pressures, the lungs remain functionally underinflated; this may be termed functional restriction. To explore mechanisms and effects of functional restriction in patients with emphysema, and to predict effects of single lung transplantation and lung volume reduction surgery (LVRS), we used a computational model based on standard physiology and measurements from individual patients. The model's lungs, separated by a compliant mediastinum, exhibit flow limitation according to the equal pressure point approach of Mead and coworkers. Pulmonary elastic recoil pressure is characterized by an exponential equation modified to reflect airway closure. Simulated respiratory maneuvers can be specified by variations in flow or pressure at the airway opening or in respiratory muscle activation. Model simulations successfully mimic recordings from individual patients. Input parameter values may then be altered to predict effects of surgical interventions in these same patients. The model simulations show the following. Single lung transplantation in emphysema can cause functional restriction of the normal transplanted lungs, and larger transplanted lungs may perform less well than smaller ones. LVRS improves lung and chest wall function in emphysema, but not in normal states. Surgical reduction of the native emphysematous lung after single lung transplantation can reduce functional restriction of the transplant and thereby improve its function.

Humans↗
PubMed1998

Relation between preoperative inspiratory lung resistance and the outcome of lung-volume-reduction surgery for emphysema.

BACKGROUND: Surgery to reduce lung volume has recently been reintroduced to alleviate dyspnea and improve exercise tolerance in selected patients with emphysema. A reliable means of identifying patients who are likely to benefit from this surgery is needed. METHODS: We measured lung resistance during inspiration, static recoil pressure at total lung capacity, static lung compliance, expiratory flow rates, and lung volumes in 29 patients with chronic obstructive lung disease before lung-volume-reduction surgery. The changes in the forced expiratory volume in one second (FEV1) six months after surgery were related to the preoperatively determined physiologic measures. A response to surgery was defined as an increase in the FEV1 of at least 0.2 liter and of at least 12 percent above base-line values. RESULTS: Of the 29 patients, 23 had some improvement in FEV1 including 15 who met the criteria for a response to surgery. Among the variables considered, only preoperative lung resistance during inspiration predicted changes in expiratory flow rates after surgery. Inspiratory lung resistance correlated significantly and inversely with improvement in FEV1 after surgery (r=-0.63, P<0.001). A preoperative criterion of an inspiratory resistance of 10 cm of water per liter per second had a sensitivity of 88 percent (14 of 16 patients) and a specificity of 92 percent (12 of 13 patients) in identifying patients who were likely to have a response to surgery. CONCLUSIONS: Preoperative lung resistance during inspiration appears to be a useful measure for selecting patients with emphysema for lung-volume-reduction surgery.

Adult↗
PubMed1997

The elephant's respiratory system: adaptations to gravitational stress.

Elephants have had to adapt to gravitational stresses imposed on their very large respiratory structures. We describe some unusual features of the elephant's respiratory system and speculate on their functional significance. A distensible network of collagen fibers fills the pleural space, loosely connects lung to chest wall but appears not to constrain lung-chest wall movements. Myriad spaces within the network and its rich supply of capillaries suggest effective local sources and sinks for pleural fluid that may replace the gravity-dependent flows of smaller mammals. The lung is partitioned into approximately equal to 1 cm3 parenchymal units by a system of thick, elastic septa that ramify throughout the lung from origins on the lung's elastic external capsule. Parenchymal units suspended upon the elastic septal system protect dependent alveoli from compression, thereby reducing the usual gravitational gradient of lung expansion. Intra-pulmonary airways are devoid of cartilage, instead they appear to derive resistance to collapse from tethering forces of the attached septa.

Adaptation, Physiological↗
PubMed1995

Model for a pump that drives circulation of pleural fluid.

Physical and mathematical models were used to study a mechanism that could maintain the layer of pleural fluid that covers the surface of the lung. The pleural space was modeled as a thin layer of viscous fluid lying between a membrane carrying tension (T), representing the lung, and a rigid wall, representing the chest wall. Flow of the fluid was driven by sliding between the membrane and wall. The physical model consisted of a cylindrical balloon with strings stretched along its surface. When the balloon was inflated inside a vertical circular cylinder containing a viscous fluid, the strings formed narrow vertical channels between broad regions in which the balloon pressed against the outer cylinder. The channels simulated the pleural space in the regions of lobar margins. Oscillatory rotation of the outer cylinder maintained a lubricating layer of fluid between the balloon and the cylinder. The thickness of the fluid layer (h), measured by fluorescence videomicroscopy, was larger for larger fluid viscosity (mu), larger sliding velocity (U), and smaller pressure difference (delta P) between the layer and the channel. A mathematical model of the flow in a horizontal section was analyzed, and numerical solutions were obtained for parameter values of mu, U, delta P, and T that matched those of the physical model. The computed results agreed reasonably well with the experimental results. Scaling laws yield the prediction that h is approximately (T/delta P)(microU/T)2/3. For physiological values of the parameters, the predicted value of h is approximately 10(-3) cm, in good agreement with the observed thickness of the pleural space.

Body Fluids↗
PubMed1995

A simple and reliable method to calibrate respiratory magnetometers and Respitrace.

We present a simple and reliable method to calibrate respiratory magnetometers and Respitrace to infer respiratory volume changes. As in earlier methods, we assume two degrees of freedom in the chest wall and that volume displacement depends linearly on surface motion at the rib cage and abdomen. Because the area of the rib cage is larger, a given motion of its surface produces a greater lung volume change; therefore, the rib cage motion signal is given a larger gain before the two signals are added to estimate volume. In contrast to earlier methods, we use a "standard ratio" to weight relative gains of the rib cage and abdominal signals for all subjects rather than determining a gain ratio for each individual subject. Our procedure does not require subjects to perform the sometimes difficult isovolume maneuvers used in the calibration method of Konno and Mead (J. Appl. Physiol. 22: 407-422, 1967), does not require statistical computation used in the multiple-breath linear regression method, and does not produce the occasional substantial errors in gain ratio that may occur with the other methods. When magnetometers are used, the standard ratio is 4:1 (rib cage-to-abdomen); when Respitrace is used, the standard ratio is 2:1. In 11 subjects, calibration with standard ratios was as accurate as the isovolume and linear regression techniques. Accuracy during normal breathing was nearly always within 10% (median 2%), but occasional large errors occurred with both instruments.

Adult↗
PubMed1994

Gravitational and shear-associated pressure gradients in the abdomen.

The abdomen has been variously characterized as a hydrostatic system, in which pressures exhibit a gravitational gradient and pressure fluctuations are spatially uniform, and as a compartment, in which pressure gradients are not simply gravitational and pressure fluctuations differ markedly from place to place. To characterize the pressures acting on the ventral abdominal wall, we used saline-filled catheters and air-filled balloons in anesthetized dogs in various body positions during spontaneous breathing and mechanical ventilation. Pressures were measured in the stomach and at multiple sites next to the abdominal wall. Under most circumstances, measurements next to the abdominal wall exhibited a hydrostatic gravitational gradient of approximately 0.89 cmH2O/cm height and pressure fluctuations were spatially homogeneous. Deviations from this hydrostatic behavior were seen when abdominal pressures were compared with gastric pressures, when measurements were made with a balloon catheter, and when the lower abdomen was constricted with a binder. Analysis of these and previously published data suggests that the abdomen does, at times, behave like a hydraulic system but can deviate from simple hydrostatic behavior to the extent that shape-stable abdominal viscera are deformed.

Abdomen↗
PubMed1993

Lung volume and effectiveness of inspiratory muscles.

We related inspiratory muscle activity to inspiratory pressure generation (Pmus) at different lung volumes in five seated normal subjects. Integrated electromyograms were recorded from diaphragmatic crura (Edi), parasternals (PS), and lateral external intercostals (EI). At 20% increments in the vital capacity (VC) subjects relaxed and then made graded and maximal inspiratory efforts against an occluded airway. At any given level of pressure generation, Edi, PS, and EI increased with increasing lung volume. The Pmus generated at total lung capacity as a fraction of that at a low lung volume (between residual volume and 40% VC) was 0.39 +/- 0.15 (SD) for the diaphragm, 0.20 +/- 0.06 for PS, and 0.22 +/- 0.04 for the lateral EI muscles. Our results indicate a lesser volume dependence of the Pmus-EMG relationship for the diaphragm than for PS and EI muscles. This difference in muscle effectiveness with lung volume may reflect differences in length-tension and/or geometric mechanical advantage between the rib cage muscles and the diaphragm.

Diaphragm↗
PubMed1993

Measurement of gastric and diaphragmatic height during slow breathing maneuvers.

Changes in height of the gastric air bubble can be inferred, in theory, from the difference between gastric pressures measured with water- and air-filled balloon-catheter systems. We describe an apparatus that satisfactorily measures changes in height of gastric balloons in vitro. During slow breathing maneuvers in standing subjects, the apparatus measured changes in height of the balloons in the stomach that were consistent with expected changes in height of the diaphragmatic dome. In four subjects, balloon movements were nearly always less than movements of the costal margin of the diaphragmatic dome observed by ultrasonography; the average ratio of height changes was 0.73. We conclude that changes in height of the diaphragmatic dome can be measured with this method during slow breathing maneuvers in upright subjects.

Abdomen↗
PubMed1992

Action of human respiratory muscles inferred from finite element analysis of rib cage.

The actions of several human respiratory muscles have been inferred from finite element analysis of the rib cage. The human model is based on anatomic and mechanical measurements in dogs and human cadavers. As in an earlier canine model, the external and internal (interosseous) intercostal muscles were found to cause, respectively, inspiratory and expiratory displacements of the rib cage, in agreement with the two-dimensional geometric analysis of Hamberger. When extended to three dimensions, Hamberger's analysis helps explain why muscles at the side of the rib cage produce changes in the anteroposterior diameter, whereas muscles at the front and back of the rib cage cause changes in the transverse diameter.

Humans↗
PubMed1992

Effects of series compliance on twitches superimposed on voluntary contractions.

The activation of skeletal muscle during voluntary isometric contraction has been assessed by measuring the increase in force caused by a superimposed maximal shock to the motor nerve (the twitch-interpolation technique). When the muscle is held isometric, the increase in force with stimulation (superimposed twitch force) decreases with increasing voluntary force, and a line fit through the data can be extrapolated to maximal voluntary force at the zero twitch force axis. In a previous paper we questioned the applicability of this technique in situations where a high series compliance allows the muscle to shorten during the superimposed twitch. To explore effects of series compliance, we measured force of the adductor pollicis during voluntary isometric contractions with noncompliant and compliant loading devices. With the compliant loading device, superimposed twitch force was systematically less than with the noncompliant device, and the plot of superimposed twitch force vs. voluntary force was often concave upward, preventing easy extrapolation to maximal voluntary force. These findings are consistent with force-velocity characteristics of muscle and suggest that twitch-interpolation data must be interpreted with caution when the muscle is not held isometric during the superimposed twitch.

Adult↗
PubMed1991

Regional chest wall impedance during nonrespiratory maneuvers.

To assess changes in total and regional chest wall properties during nonrespiratory maneuvers, we measured electromyographic activity of various chest wall muscles, esophageal pressure, and rib cage and abdominal surface displacements in six subjects before and during various static tasks. Subjects were seated at functional residual capacity, and quasi-sinusoidal forcing at the mouth (0.4 Hz, 500 ml) was imposed during the maneuver in the absence of active breathing. Magnitude of total chest wall impedance (magnitude of Zw) increased with effort during all maneuvers; changes in phase were small. Maneuvers involving primarily muscles of the neck and rib cage--holding a 10-kg weight, 10 kg of isometric tension between the arms, and isometric neck flexion--roughly doubled the magnitude of rib cage impedance (magnitude of Zrc) and, to a lesser degree, increased magnitude of diaphragm-abdomen impedance (magnitude of Zd-a). Unilateral and bilateral leg lifts, in addition to increasing magnitude of Zd-a, increased magnitude of Zrc. Passive 90 degrees rotation of the torso caused approximately 25% increases in magnitude of Zrc and magnitude of Zd-a; if the rotation was actively maintained by the trunk muscles, both regional impedances increased over 100%. Increases in magnitude of regional impedance were correlated to increases in regional electromyographic activity; changes in phase were small. Passive restriction of rib cage displacement by strapping increased magnitude of Zrc and magnitude of Zw but not magnitude of Zd-a, whereas abdominal strapping increased magnitude of Zd-a but did not affect magnitude of Zrc or magnitude of Zw.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Dynamic behavior of excised dog rib cage: dependence on muscle.

To assess the contribution of the rib cage to chest wall elastance and hysteresis, we measured force-displacement behavior of the isolated canine rib cage during sinusoidal forcing of the sternum in the midsagittal plane at low frequencies (0.02-2.0 Hz). Elastance of the rib cage was nearly invariant with frequency of forcing from 0.02 to 1.0 Hz and decreased with increasing amplitude. Hysteresis, the width of the force-displacement loop at middisplacement (zero displacement), was nearly constant with frequency below 1.0 Hz and increased with increasing amplitude of forcing. Removal of muscle reduced elastance and hysteresis of the rib cage substantially. The data suggest that the excised dog rib cage shows dynamic behavior similar to that of the intact human rib cage and chest wall and that respiratory muscle is responsible for a major part of the behavior of the passive chest wall. We also calculated the major and minor stiffnesses in the sagittal plane, which differed by a factor of 3-11, and their directions lay close to the dorsoventral and cephalocaudal axes, respectively. Removal of muscle reduced the stiffnesses but did not change their directions. Thus, although respiratory muscles impede motion in the sagittal plane, they do not alter its pattern.

Animals↗