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Biomedical subjects

S H Loring

Publications and source records attributed to S H Loring.

At least 37 records · Page 2Linked to original sources
PubMed1991

Influence of posterior cricoarytenoid muscle activity on pressure-flow relationship of the larynx.

We examined the effect of posterior cricoarytenoid (PCA) muscle activity on the pressure-flow (PV) relationship of the larynx in five anesthetized tracheostomized dogs. The PCA activity was recorded using bipolar fine-wire electrodes, expressed as a percentage of the quiet breathing level and altered by mechanical ventilation, changes in lung volume, and chest wall compression. Subglottic pressure was recorded while a constant flow of air was passed through the upper airway. In the absence of PCA activity the PV relationship was alinear and could be described by a power function (P = K0Va, where K0 and a are constants). The slope of the log P-log V plots in the absence of PCA and thyroarytenoid activity was 1.83 +/- 0.02 (SD), whereas with increasing PCA activity it was 1.88 +/- 0.11. An effective hydraulic diameter (DH) was calculated for 20% increments of PCA activity, and in two dogs glottic diameter (Dg) was calculated from glottic area measurements obtained by fiber-optic laryngoscopy. Both DH and Dg increased linearly with increasing PCA activity. Denervation of the cricothyroid muscle had no systematic effect on laryngeal resistance. The results indicate that the PV relationship of the larynx may be described by a power function with a single exponent, the magnitude of which is independent of glottic dilator muscle activity and consistent with orifice flow. However, laryngeal diameter increases linearly with PCA activity in the range studied.

Airway Resistance↗
PubMed1991

Intercostal muscle action inferred from finite-element analysis.

The external and internal intercostal muscles are important respiratory muscles in humans, but their mechanical actions have been controversial. We used finite-element analysis based on anatomic and mechanical measurements in dogs to assess the action of the intercostal and other rib cage muscles in a model of an isolated canine rib cage. When intercostal muscle forces of either the internal or the external layer were applied in a single interspace, they pulled the adjacent ribs together, consistent with published observations in dogs. However, when the forces were applied in all interspaces, the external layer caused an inspiratory motion and the internal layer caused an expiratory motion, consistent with conventional understanding of intercostal muscle actions. Parasternal intercostal, levator costae, and transversus thoracis (triangularis sterni) muscle actions were also simulated. These muscles caused expected movements of the ribs and sternum. We conclude that the actions of intercostal muscles depend on the spatial extent of their activation. Their actions in a single interspace and in multiple interspaces can be observed and explained with three-dimensional finite-element models.

Animals↗
PubMed1990

Determinants of breathing frequency during walking.

Breathing frequency has been shown to depend on metabolic demand, and also to be affected by stepping frequency during walking. To assess the influence of stepping frequency on breathing frequency, we recorded the timing of breathing and stepping in ten naive subjects walking on a treadmill. Five of the subjects showed periods of breathing in rhythm with their stepping (rhythmical entrainment); five subjects never showed rhythmical entrainment. In all subjects, respiratory frequency tended to increase with increases in estimated metabolic rate (EMR) produced by increases in walking speed or treadmill inclination. Breathing frequency was also affected by stepping frequency independent of EMR, both during rhythmical entrainment and in the absence of rhythmical entrainment. The dependence of breathing frequency on stepping frequency may reflect an excitatory influence of voluntary movement on the respiratory center. We conclude that stepping importantly influences breathing frequency during walking whether or not the two are rhythmically linked. Such lability of respiratory frequency probably reflects the small metabolic cost of departure from mechanically optimal frequencies.

Adult↗
PubMed1990

'Air hunger' from increased PCO2 persists after complete neuromuscular block in humans.

The tolerance of totally curarized subjects for prolonged breath hold is viewed by many as evidence that respiratory muscle contraction is essential to generate the sensation of breathlessness. Although conflicting evidence exists, none of it was obtained during total neuromuscular block. We completely paralyzed four normal, unsedated subjects with vecuronium (a non-depolarizing neuromuscular blocker). Subjects were mechanically ventilated with hyperoxic gas mixtures at fixed rate and tidal volume. End-expiratory PCO2 (PETCO2) was varied surreptitiously by changing inspired PCO2. Subjects rated their respiratory discomfort or 'air hunger' every 45 sec. At low PETCO2 (median 35 Torr) they felt little or no air hunger. When PETCO2 was raised (median 44 Torr) all subjects reported severe air hunger. They had reported the same degree of air hunger at essentially the same PETCO2 before paralysis. When questioned afterwards all subjects said the sensation could be described by the terms 'air hunger', 'urge to breathe', and 'shortness of breath', and that is was like breath holding. They reported no fundamental difference in the sensation before and after paralysis. We conclude that respiratory muscle contraction is not important in the genesis of air hunger evoked by hypercapnia.

Adult↗
PubMed1990

Speech breathing in individuals with cervical spinal cord injury.

Ten men with cervical spinal cord injury were studied using magnetometers to record surface motions of the chest wall during speech breathing. Individual speech breathing patterns reflected inspiratory and expiratory muscular sparing. Subjects compensated for expiratory muscle impairment by speaking at large lung volumes, presumably to take advantage of the higher recoil pressures available at those volumes. Similarly, subjects used larger lung volumes to increase loudness. Abnormal chest wall behavior was attributed in large part to loss of abdominal muscle function. Because of this, speech breathing in individuals with cervical spinal cord injury may be improved by the use of abdominal binders.

Adult↗
PubMed1990

Total and local impedances of the chest wall up to 10 Hz.

To understand how bical mechanical chest wall (CW) properties are related to those of the CW as a whole, we measured esophageal and gastric pressures, CW volume changes (measured with a head-out body plethysmograph), and anteroposterior and transverse CW diameter changes (measured with magnetometers attached to the surface) during sinusoidal forcing at the mouth (2.5% vital capacity, 0.5-10 Hz) in four healthy subjects. Total CW resistance decreased sharply as frequency rose to 3-4 Hz and remained relatively constant at higher frequencies. Total CW reactance became less negative with increasing frequency but showed no tendency to change sign. Above 2 Hz, diameters measured at different locations changed asynchronously between and within the rib cage and abdomen. "Local pathway impedances" (ratios of esophageal or gastric pressure to a rate of diameter change) showed frequency dependence similar to that of the total CW less than 3 Hz. Local pathway impedances increased during contraction of respiratory muscles acting on the pathway. We conclude that 1) total CW behavior is mainly a reflection of its individual local properties at less than or equal to 3 Hz, 2) local impedances within the rib cage or within the abdomen can change independently in some situations, and 3) asynchronies that develop within the CW during forcing greater than 3 Hz suggest that two compartments may be insufficient to describe CW properties from impedance measurements.

Abdominal Muscles↗
PubMed1990

Abdominal pressure transmission in humans during slow breathing maneuvers.

Pressure transmission within the abdomen was studied in four subjects standing and supine, breathing slowly and performing slow breathing maneuvers. Pressures were measured in the stomach and rectum with air-containing balloon-catheter systems Pga(air) and Prec and in the stomach with a water-filled catheter system Pga(liq). Changes in Pga(air), Pga(liq), and Prec were nearly in phase and linearly related. The changes in Pga(liq) and Prec were nearly equal in all maneuvers, whereas the changes in Pga(air) were systematically greater than those of Pga(liq) and Prec during quiet breathing and relaxation maneuvers in the upright position. During expulsive maneuvers in either posture the abdominal shape and stomach position were relatively constant, and the changes in Pga(air) were nearly equal to those of Pga(liq) and Prec. Discrepancies between changes in Pga(air) and the other pressures were consistent with presumed changes in the height of the gastric air bubble. We conclude that abdominal pressure in humans is essentially hydrostatic during quiet breathing and slow breathing maneuvers.

Abdomen↗
PubMed1990

Relationship between thyroarytenoid activity and laryngeal resistance.

We examined the relationship between subglottic pressure (P), flow (V), and thyroarytenoid (TA) muscle activity in six anesthetized tracheostomized dogs while a constant flow (0.05-1.2 l/s) of warmed humidified air was passed through the upper airway in an expiratory direction. The TA activity was recorded by fine bipolar wire electrodes and was reflexly altered by changes in lung volume and chest wall compression. The integrated muscle activity was expressed as a percentage of a maximal peak integrated TA activity (%max). In the absence of TA activity the pressure-flow relationship was alinear and could be described by a power function. Log-log P-V plots at varying levels of TA activity were linear, with a slope a of 1.84 +/- 0.07 (SD). When TA activity increased, laryngeal resistance increased exponentially. An effective hydraulic diameter was calculated for increments in %max TA and decreased linearly with %max TA. In three dogs the glottic diameter was computed from glottic area measured by fiber-optic laryngoscopy, and it also decreased linearly as TA increased. Sectioning of the external motor branch of the superior laryngeal nerve to the cricothyroid muscle demonstrated no consistent effect on laryngeal resistance over a range of TA activity. The results indicate that laryngeal dimensions decrease linearly with TA activity. However, the P-V relationship of the larynx may be described by a power function, with a single exponent consistent with an orifice flow regimen. Spontaneous activity of the cricothyroid muscle does not measurably influence this relationship.

Airway Resistance↗
PubMed1990

Chest wall motion of infants during spinal anesthesia.

To test the extent to which diaphragmatic contraction moves the rib cage in awake supine infants during quiet breathing, we studied chest wall motion in seven prematurely born infants before and during spinal anesthesia for inguinal hernia repair. Infants were studied at or around term (postconceptional age 43 +/- 8 wk). Spinal anesthesia produced a sensory block at the T2-T4 level, with concomitant motor block at a slightly lower level. This resulted in the loss of most intercostal muscle activity, whereas diaphragmatic function was preserved. Rib cage and abdominal displacements were measured with respiratory inductance plethysmography before and during spinal anesthesia. During the anesthetic, outward inspiratory rib cage motion decreased in six infants (P less than 0.02, paired t test); four of these developed paradoxical inward movement of the rib cage during inspiration. One infant, the most immature in the group, had inward movement of the rib cage both before and during the anesthetic. Abdominal displacements increased during spinal anesthesia in six of seven infants (P less than 0.05), suggesting an increase in diaphragmatic motion. We conclude that, in the group of infants studied, outward rib cage movement during awake tidal breathing requires active, coordinated intercostal muscle activity that is suppressed by spinal anesthesia.

Anesthesia, Spinal↗
PubMed1989

Chest wall impedance partitioned into rib cage and diaphragm-abdominal pathways.

We measured chest wall "pathway impedances" (ratios of pressure changes to rates of volume displacement at the surface) with esophageal and gastric balloons and inductance plethysmographic belts around the rib cage and abdomen during forced volume oscillations (5% vital capacity, 0.5-4 Hz) at the mouth of five relaxed, seated subjects. Volume displacements of the total chest wall surface, measured by summing the rib cage and abdominal signals, approximated measurements using volume-displacement, body plethysmography over the entire frequency range. Resistance (R) and elastance (E) of the diaphragm-abdomen pathway were several times greater than those of the rib cage pathway, except at the highest frequencies where diaphragm-abdominal E was small. R and E of the diaphragm-abdomen pathway and of the rib cage pathway showed the same frequency dependencies as that of the total chest wall: R decreased markedly as frequency increased, and E (especially in the diaphragm-abdomen) decreased at the highest frequencies. These results suggest that the chest wall can be reasonably modeled, over the frequency range studied, as a system with two major pathways for displacement. Each pathway seems to exhibit behavior that reflects nonlinear, rate-independent dissipation as well as viscoelastic properties. Impedances of these pathways are useful indexes of changes in chest wall mechanical behavior in different situations.

Abdomen↗
PubMed1989

Impedance of the chest wall during sustained respiratory muscle contraction.

We measured total chest wall impedance (Zw), "pathway impedances" of the rib cage (Zrcpath), and diaphragm-abdomen (Zd-apath), and impedance of the belly wall including abdominal contents (Zbw+) in five subjects during sustained expiratory (change in average pleural pressure [Ppl] from relaxation = 10 and 20 cmH2O) and inspiratory (change in Ppl = -10 and -20 cmH2O) muscle contraction, using forced oscillatory techniques (0.5-4 Hz) we have previously reported for relaxation (J. Appl. Physiol. 66: 350-359, 1989). Chest wall configuration and mean lung volume were kept constant. Zw, Zrcpath, Zd-apath, and Zbw+ all increased greatly at each frequency during expiratory muscle contraction; increases were proportional to effort. Zw, Zrcpath, and Zd-apath increased greatly during inspiratory muscle contraction, but Zbw+ did not. Resistances and elastances calculated from each of the impedances showed the same changes during muscle contraction as the corresponding impedances. Each of the resistances decreased as frequency increased, independent of effort; elastances generally increased with frequency. These frequency dependencies were similar to those measured in relaxed or tetanized isolated muscle during sinusoidal stretching (P.M. Rack, J. Physiol. Lond. 183: 1-14, 1966). We conclude that during respiratory muscle contraction 1) chest wall impedance increases, 2) changes in regional chest wall impedances can be somewhat independent, depending on which muscles contract, and 3) increases in chest wall impedance are due, at least in part, to changes in the passive properties of the muscles themselves.

Adult↗
PubMed1989

Critical pressures required for generation of forced expiratory wheezes.

Flow limitation (FL) has recently been shown to be a necessary condition for the generation of forced expiratory wheezes (FEW) in normal subjects. The present study was designed to investigate whether it is also a sufficient condition. To do so we studied the effects of varying expiratory effort on generation of FEW. Six normal subjects exhaled with varying force into an orifice in line with a high-impedance suction pump. Esophageal (Pes), airway opening, and transpulmonary (Ptp) pressures were measured alongside flow rate, lung volume, and tracheal lung sounds. In each subject a certain critical degree of effort had to be attained before FEW were generated. This effort, measured as Pes at the onset of wheezes, varied among the subjects (range -11 to 45 cmH2O). Similarly, a minimal Ptp had to be reached for FEW to evolve (mean +/- SD -34 +/- 12 cmH2O, range -18 to -50 cmH2O). These critical Pes and Ptp values were significantly higher than those required for FL. It was concluded that, in addition to the requirement for FL, sufficient levels of effort and negative Ptp must exist before FEW can be generated. By analogy to experimental and theoretical results from studies on flow-induced oscillations in self-supporting collapsible tubes, it was further concluded that these pressures are required to induce flattening of the intrathoracic airways downstream from the choke point. It is this configurational change that causes air speed to become equal to or exceed the critical gas velocity needed to induce oscillations in soft-walled tubes.

Esophagus↗
PubMed1989

Postural changes in spontaneous and evoked regional diaphragmatic activity in dogs.

We addressed the question whether gravity-dependent differences in passive tension and length of the diaphragm are associated with differences in its regional activation. By using intramuscular electrodes, we measured the electromyographic activity of different parts of the diaphragm (Edi) during quiet breathing in several postures in 13 anesthetized mongrel dogs. The Edi of the left and right costal hemi-diaphragm was compared between the left and right lateral decubitus postures, whereas that from the substernal and crural regions was compared between the supine and prone positions. On changing posture, the Edi of the dependent part of the diaphragm decreased in both cases, whereas that of the non-dependent part increased. The results were consistent with reflex modulation of regional diaphragm activation in response to postural changes in local resting length. However, these changes in Edi persisted after bilateral vagotomy, cordotomy (C7-T1) and dorsal rhizotomy of the C5-C7 roots. Compound muscle action potentials, recorded in different regions of the diaphragm and evoked by supramaximal stimulation of the phrenic nerves, were altered with changes in posture in the same direction as Edi. Because the stimuli were supramaximal, these changes reflected systematic changes in the recording conditions with posture, possibly because of a combination of 1) changes in the electrical environment surrounding the intramuscular electrodes and 2) passive changes in muscle length. Our results demonstrate systematic, reproducible, posture-dependent changes in regional Edi that may not be due to different neural drive.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1989

Respiratory mechanics in acute quadriplegia. Lung and chest wall compliance and dimensional changes during respiratory maneuvers.

We measured lung and chest wall compliance as well as rib cage and abdominal dimensions in the supine position in five acute C4-7 quadriplegics. Studies were performed serially from 1 to 12 months after injury. Results were compared with those of control groups of chronic (greater than 1 yr after injury) quadriplegics and normal volunteers. We found that lung compliance was lower in acute and chronic quadriplegics (0.129 +/- 0.023 and 0.176 +/- 0.043 L/mm Hg, respectively) than in normal subjects (0.278 +/- 0.086 L/mm Hg) and that these changes apparently occurred within 1 month of injury. Specific lung compliance appeared to be reduced to a lesser degree, suggesting that the changes in lung compliance were partly due to reduced lung volumes and partly to altered mechanical properties of the lung. During respiratory maneuvers, abdomen and rib cage dimensional changes demonstrated rib cage distortion. This distortion was less severe in chronic than in acute quadriplegics. The improvement in chest wall stability was likely due to increased strength of cervical accessory muscles of respiration and improved coupling of the various rib cage elements in chronic quadriplegics.

Acute Disease↗
PubMed1989

Amplitude dependency of regional chest wall resistance and elastance at normal breathing frequencies.

Current methods for measurement of chest wall properties assume that resistance (R) and elastance (E) are independent of the volume breathed. In six healthy subjects relaxed at functional residual capacity, we measured total and regional R and E of the chest wall within the range of normal breathing frequencies (0.2 to 0.6 Hz) and tidal volumes (250 to 750 ml), using volume forcing at the mouth as previously described. With these methods, esophageal and gastric pressures are compared with surface displacements measured with inductance plethysmographic belts to calculate R and E of rib cage and diaphragm-abdomen "pathways." Rib cage R and E were 25 to 30% higher than that of the total chest wall at each frequency and volume, whereas diaphragm-abdomen R and E were at least five times higher. R of the chest wall and each of the pathways decreased by about 70% with increasing frequency and by about 30% with increasing tidal volume. E of the chest wall and each of the pathways also decreased by about 30% with increasing tidal volume but was independent of frequency in this range. These results are consistent with nonlinear, viscoplastic models presented elsewhere. We conclude that: (1) despite the great structural differences between the rib cage and diaphragm-abdomen, each exhibits nonlinear behavior similar to that of the total chest wall; (2) chest wall R and E depend importantly on frequency and tidal volume.

Adult↗
PubMed1989

Diaphragmatic excursion after pleural sclerosis.

Chemical sclerosis of the pleural space is used to prevent recurrence of spontaneous pneumothorax. To test whether sclerosis restricts diaphragmatic excursion, we measured diaphragmatic excursion by ultrasonography in subjects with unilateral pleural sclerosis and compared it with diaphragmatic excursions in normal subjects, in subjects with cystic fibrosis (a diffuse bilateral lung disease), and in those who underwent surgical procedures that obliterate the pleural space. In five subjects with unilateral chemical sclerosis, diaphragmatic excursion was significantly less on the sclerosed side than on the contralateral side (10.7 +/- 1.3 vs 17.3 +/- 1.7 mm, mean +/- SEM; p less than .01). Compared with those of normal subjects, the side-to-side differences in excursion were increased by pulmonary disease (p less than .03) and additionally by unilateral sclerosis (p less than .015). There was no significant difference between diaphragmatic excursions on left and right sides of subjects without history of pleural disease. These data suggest that chemical pleural sclerosis causes a measurable reduction in diaphragmatic excursion on the affected side. The physiologic significance of this effect is not known.

Adolescent↗
PubMed1988

Relative strengths of the chest wall muscles.

We hypothesized that during maximal respiratory efforts involving the simultaneous activation of two or more chest wall muscles (or muscle groups), differences in muscle strength require that the activity of the stronger muscle be submaximal to prevent changes in thoracoabdominal configuration. Furthermore we predicted that maximal respiratory pressures are limited by the strength of the weaker muscle involved. To test these hypotheses, we measured the pleural pressure, abdominal pressure (Pab), and transdiaphragmatic pressure (Pdi) generated during maximal inspiratory, open-glottis and closed-glottis expulsive, and combined inspiratory and expulsive maneuvers in four adults. We then determined the activation of the diaphragm and abdominal muscles during selected maximal respiratory maneuvers, using electromyography and phrenic nerve stimulation. In all subjects, the Pdi generated during maximal inspiratory efforts was significantly lower than the Pdi generated during open-glottis expulsive or combined efforts, suggesting that rib cage, not diaphragm, strength limits maximal inspiratory pressure. Similarly, at high lung volumes, the Pab generated during closed-glottis expulsive efforts was significantly greater than that generated during open-glottis efforts, suggesting that the latter pressure is limited by diaphragm, not abdominal muscle, strength. As predicted, diaphragm activation was submaximal during maximal inspiratory efforts, and abdominal muscle activation was submaximal during open-glottis expulsive efforts at midlung volume. Additionally, assisting the inspiratory muscles of the rib cage with negative body-surface pressure significantly increased maximal inspiratory pressure, whereas loading the rib cage muscles with rib cage compression decreased maximal inspiratory pressure. We conclude that activation of the chest wall muscles during static respiratory efforts is determined by the relative strengths and mechanical advantage of the muscles involved.

Abdominal Muscles↗