Diaphragm Length Research Articles

Diaphragmatic elevation of a patient with chronic obstructive pulmonary disease after left upper lobectomy

Among postoperative pleural space problems after pulmonary resections, it is more difficult and troublesome to manage this space after left upper lobectomy in patients with chronic obstructive pulmonary disease (COPD). We performed a retrospective study focusing on the elevation of ipsilateral hemidiaphragm of the 36 patients with or without COPD after left upper lobectomies, by measuring diaphragmatic dome length (DDL) with a plain posteroanterior roentgenogram. They were divided into two groups: group I (forced expiratory volume in 1 s (FEV1) % predicted < 70%, n = 5); and group II (FEV1) % predicted > or = 70%, n = 31). Of each group, we investigated the trend of both left and right DDLs perioperatively, calculating DDL index (DDL divided by height, DDLI), and also analyzed several perioperative parameters. The trend of left DDLI after surgery was different in the two groups (P=0.012). In group I, left DDLI became larger gradually in proportion to the postoperative weeks, while in group II it became the largest 2 weeks after surgery and decreased gradually. Left DDLI in group I was smaller than that in group II 2 weeks after surgery (P=0.007). We found that the diaphragm of COPD patients does not elongate easily after left upper lobectomy.

Why the kidney glomerulus does not clog: a gel permeation/diffusion hypothesis of renal function.

Current interpretations of kidney function in terms of a coarse filter followed by a fine filter have difficulty explaining why the glomerulus does not clog. I propose, as an alternative, a semiquantitative hypothesis that assumes that the size-selective property of the glomerulus is a consequence of the limited fraction of space in the glomerular basement membrane (a concentrated gel) into which macromolecules can permeate. The glomerular epithelial cell slits and slit diaphragms are assumed to impose substantial resistance to liquid flow across the glomerulus without acting as a molecular sieve. Calculations based on gel behavior show that proteins cross the glomerular basement membrane mainly by diffusion rather than by liquid flow, whereas water crosses entirely by flow. Thus, diffusion provides most of the protein, whereas flow provides the diluent. As a result, the single-nephron glomerular filtration rate (GFR) becomes a prime factor in (inversely) determining the concentration of proteins in early proximal tubular fluid. Because the reabsorption of proteins from the tubules is a saturable process, the gel permeationdiffusion hypothesis readily accounts for the albuminuria observed when single-nephron GFR is substantially reduced by severe pathological decreases in slit diaphragm length, such as occur in minimal-change nephrotic syndrome in humans, in animals treated with puromycin aminonucleoside, or in humans or animals with mutations in the gene coding for nephrin. My hypothesis predicts that albuminuria will ensue, even with a normal kidney, if the single-nephron GFR falls below approximately 50% of normal.

Chest wall kinematic determinants of diaphragm length by optoelectronic plethysmography and ultrasonography.

To estimate diaphragm fiber length from thoracoabdominal configuration, we measured axial motion of the right-sided area of apposition by ultrasonography and volumes displaced by chest wall compartments [pulmonary, abdominal rib cage, and abdomen (Vab)] by optoelectronic plethysmography in four normal men during quiet breathing and incremental exercise without and with expiratory flow limitation. Points at the cephalic area of apposition border were digitized from echo images and mapped into three-dimensional space, and the axial distance from the xyphoidal transverse plane (D(ap)) was measured simultaneously with the volumes. Linear regression analysis between changes (Delta) in D(ap) and the measured volume changes under all conditions showed that 1) DeltaD(ap) was linearly related more to DeltaVab than to changes in pulmonary and abdominal rib cage volumes; and 2) this was highly repeatable between measures. Multiple stepwise regression analysis showed that DeltaVab accounted for 89-96% of the variability of DeltaD(ap), whereas the rib cage compartments added <1%. We conclude that, under conditions of quiet breathing and exercise, with and without expiratory flow limitation, instantaneous DeltaD(ap) can be estimated from DeltaVab.

Diaphragm length during tidal breathing in patients with chronic obstructive pulmonary disease.

Diaphragm function is compromised in severe chronic obstructive pulmonary disease (COPD) by hyperinflation, but its ability to shorten and contribute to tidal volume is uncertain. We estimated coronal diaphragm length by measuring zone of apposition length with ultrasound and rib cage diameters with magnetometers, in 10 male patients with severe COPD and 10 age- and sex-matched control subjects. Diaphragm length was 20% shorter in patients at residual volume (413 and 536 mm in patients and control subjects, respectively) and FRC (381 and 456 mm, respectively), but was not different at total lung capacity (312 and 336 mm, respectively). Zone of apposition length was reduced 50% at residual volume and FRC in patients, but was larger at a given absolute lung volume than in control subjects. There were no differences in tidal volume (0.8 L), tidal changes in zone of apposition length (20 mm) and diaphragm length (38 and 42 mm), and tidal volume displaced by the diaphragm (0.6 L), even though mean FRC in patients was similar to predicted total lung capacity. Although the diaphragm is shorter at FRC in patients with COPD, its motion and change in length during tidal breathing is similar to that in control subjects.

Effects of Emphysema and Lung Volume Reduction Surgery on Transdiaphragmatic Pressure and Diaphragm Length

To determine the effect of emphysema and lung volume reduction surgery (LVRS) on diaphragm length (Ldi) and its capacity to generate transdiaphragmatic pressure (Pdi). Prospective clinical trial with a parallel group design. Laboratory investigations in normal volunteers recruited by advertisement and in emphysema outpatients being evaluated for elective LVRS. Thirteen normal subjects and 13 emphysema patients matched for age and sex. Six emphysema patients underwent LVRS. Ldi and maximal Pdi during static inspiratory efforts (PdiMax) were measured at three different lung volumes (LVs). Pdi during maximal bilateral phrenic nerve twitch stimulation (PdiTw) was measured at functional residual capacity (FRC). All measurements were repeated at 3, 6, and 12 months postoperatively. Ldi, PdiMax, and PdiTw were lower in emphysema patients than in normal subjects at their respective LVs. PdiMax and PdiTw at FRC returned within the normal range after LVRS in emphysema patients. The relationships between PdiMax and LV or Ldi were shifted respectively to higher LV and shorter Ldi in emphysema patients relative to normal subjects, both before and after LVRS. LVRS effected craniad displacement of the diaphragm but no change in rib cage dimensions. Improvements in dyspnea and quality of life after LVRS correlated with changes in LV and Ldi but not with changes in airway caliber. Adaptive mechanisms, consistent with sarcomere deletion, tend to restore diaphragm strength in emphysema patients at FRC, which are fully expressed after LVRS. Lung remodeling by LVRS may alter pleural surface pressure distribution, causing a sustained change in chest wall shape.

Shape-Memory Micropumps

Motivated by many experimental efforts to develop suitable shape-memory micropumps, we propose a multiscale framework to study the behavior of pressurized films. We use recoverable deflection as a measure to design large stroke micropumps and develop a model to estimate it. We show that the recoverable deflection of a polycrystalline shape-memory film depends on the transformation strain of the underlying martensitic transformation, the texture and especially on the size effects. We find that flat grains are preferable to long grains in columnar films concerning the purpose of large recoverable strain. We also show that common sputtering texture is not ideal for recoverable deflection in both Ti-Ni and Cu-based shape-memory films. It turns out that{100} Cu-based films may have better behavior than Ti-Ni films. We conclude with comparison with experiment. The interest in microelectromechanical system (MEMS) applications has recently motivated many experimental efforts to develop suitable microactuators and micropumps. These devices have a wide range of applications in fields such as drug delivery, inkjet printing and cooling systems of elec- tronic circuits. However, common MEMS-integrated actua- tion scheme has enjoyed limited success in delivering a rea- sonable work output from the extremely small size of devices, and therefore both high stroke and force are the key require- ment for selecting actuating materials. Shape-memory alloys show great promise in this aspect since their work density is significantly higher than that of other types of materials. 26) These alloys are able to recover large strain and are capable of high force, which in turn directly transmit large stoke and high pressure in micropumps. In addition, the disadvantage of low response rate caused by cooling and heating bulk shape- memory alloys can be greatly improved at small scales be- cause of the increase in the surface area to volume ratio. This makes these alloys in the form of thin films ideal for use in MEMS-integrated actuation scheme, and we seek to develop a micromechanical model to understand the behavior of film at an extremely small thickness. In this paper, we propose a framework to study the behavior of pressurized shape-memory thin films with intended appli- cation to large stoke micropumps. Our work was motivated by the recent experiment on the fabrication of SMA actuated micropumps. 16, 17, 26) They have reported that a Ti-Ni microp- ump exhibits the largest work out per cycle per unit volume amongst various common actuator systems. 26) However, the ratio of the deflection to the half-edge length of diaphragm has been observed around several values from 0.04 to 0.12 which only correspond to 0.2%-1.4% small strain. Our the- oretical prediction is around 0.15 which is larger than these experimental observations, and the discrepancy is not com- pletely understood here. We believe there should be a plenty of room to improve this critical ratio to design large stroke mi- cropumps. In particular, we show that {100} Cu-based shape-

Sarcomeres Are Added in Series to Emphysematous Rat Diaphragm After Lung Volume Reduction Surgery

The diaphragm adapts to its shortened state in experimental emphysema primarily by losing sarcomeres in series, thus reducing its optimal operating length. One would expect improved diaphragmatic function after lung volume reduction surgery (LVRS) only if the muscle can readapt to its elevated, lengthened postoperative position by either adding back sarcomeres or lengthening sarcomeres. We used a model of elastase-induced emphysema in rats to test the hypothesis that sarcomere addition occurs following LVRS. A cohort of emphysematous rats was created by the intratracheal instillation of elastase. Five months after the instillation, one group of rats underwent measurement of in situ costal diaphragm length via laparotomy, the determination of optimal muscle fiber operating length (Lo) on stimulated diaphragm strips in vitro, and the measurement of sarcomere length by electron microscopy on strips fixed at Lo. Another group of rats underwent LVRS or sham sternotomy 5 months after the instillation, and 5 months following the operation these animals underwent the same series of diaphragmatic studies. Lo was significantly greater in rats that underwent LVRS than those that underwent sternotomy (mean [+/- SE] Lo after LVRS, 2.50 +/- 0.08 cm; mean Lo after sternotomy, 2.27 +/- 0.06 cm; p = 0.013). There was no significant difference in sarcomere lengths between the two groups (2.95 +/- 0.04 vs 3.04 +/- 0.04 microm, respectively; p = 0.10). Using Lo as the length basis, the mean sarcomere number was calculated to be 8,712 +/- 192 in animals that had undergone LVRS and 7,144 +/- 249 in animals that had undergone sternotomy (p < 0.001). Sarcomere length is not significantly altered but sarcomeres are added in series following LVRS in this experimental model of emphysema/LVRS. It is likely that this sarcomere addition is a prerequisite to the improvement in inspiratory muscle function that has been observed following LVRS in humans.

Effects of continuous positive airway pressure on diaphragm dimensions in preterm infants.

The use of continuous positive airway pressure (CPAP) in the treatment of a variety of neonatal respiratory conditions is associated with improvement in arterial oxygen saturation, decreased long-term morbidity, and an overall improvement in infant survival. We reasoned that CPAP might change diaphragm length by increasing end-expiratory lung volume (EEV), but the extent to which this occurs has not been assessed. This study was designed to evaluate (1) the extent to which CPAP shortens the diaphragm and (2) the relationship of diaphragm thickness and excursion with arterial oxygen saturation in spontaneously breathing preterm infants. Ultrasonographically (7.5 MHz transducer), diaphragm thickness and diaphragm excursion were measured in 12 stable preterm infants [birth weight 1120+/-225 g (mean+/-SD); study weight 1187+/-400 g; gestational age 29+/-1 week; postnatal age 10+/-8 days, six males and six females] at three levels of CPAP [1-3, 4-6, and 7-9 cm H(2)O (low, medium, and high, respectively)]. Heart rate, respiratory rate, and arterial oxygen saturation were simultaneously recorded. We found that diaphragm thickness and arterial oxygen saturation increased, and diaphragm excursion decreased significantly at higher levels of CPAP (p<0.05). The shortening of the diaphragm at the high levels of CPAP, calculated from the increase in diaphragm thickness, was 36% at EEV and 31% at end-inspiratory volume. We conclude that the improvement in arterial oxygen saturation with CPAP occurred despite the presence of a shorter and a less mobile diaphragm, and that other physiological and mechanical alterations accompanying the application of CPAP offset its negative effects on diaphragm function. We speculate that with excessive CPAP, however, diaphragm dysfunction along with the previously described adverse hemodynamic effects may outweigh its benefits on oxygenation.

Anatomic Landmarks To Estimate the Length of the Diaphragm From Chest Radiographs: Effects of Emphysema and Lung Volume Reduction Surgery

To define anatomic landmarks that can be used to predict insertions of the diaphragm on chest radiographs and to estimate diaphragm length. Prospective clinical trial with a parallel group design. Laboratory investigations in normal volunteers recruited by advertisement and in emphysema outpatients being evaluated for elective bilateral lung volume reduction surgery (LVRS). Twenty-six normal subjects classified into young and older age groups, with a third group of 13 emphysema patients matched for age and sex with the older group. Identification and between-group comparisons were made of anatomic landmarks on anteroposterior and lateral chest radiographs obtained at total lung capacity. Predicted landmarks were generated from normal subjects. Within-subject and between-group comparisons were made of diaphragm length index (DLI) based on observed anatomic landmarks (DLIobs) and diaphragm length index based on predicted anatomic landmarks (DLIpred) at functional residual capacity. Anatomic landmarks were not different between the three groups or between male and female subjects, and were not different before and after LVRS in emphysema patients. No difference was found between DLIobs and DLIpred in normal subjects and emphysema patients, but both were smaller in emphysema patients than in normal subjects and increased after LVRS in emphysema patients. This study validates the use of anatomic landmarks to estimate DLI. Using these landmarks simplifies the determination of diaphragmatic lengths and could be a useful tool for the evaluation of the functional capacity of the diaphragm, and possibly as a prognostic indicator of patients who are candidates for LVRS.

Lung volume reduction surgery restores the normal diaphragmatic length-tension relationship in emphysematous rats

Objective: Improved respiratory muscle function is a major effect of a lung volume reduction surgery. We studied length adaptation in rat diaphragmatic muscle in an attempt to elucidate the mechanism by which diaphragmatic function improves after this controversial operation. Methods: We developed a model of elastase-induced emphysema and bilateral volume reduction through median sternotomy in rats. Five months after emphysema induction, maximum exchangeable lung volume was determined in intubated and anesthetized control animals and animals with emphysema. Costal diaphragmatic length was measured in vivo, and the length at which maximal twitch force is generated was determined on muscle strips in vitro. Also 5 months after elastase administration, another cohort underwent volume reduction or sham sternotomy. Five months after the operation, these animals were similarly studied. Results: Lung volume was increased in emphysematous rats versus control rats (50.9 ± 1.7 vs 45.4 ± 1.3 mL, P =.001). Lung volume was decreased in emphysematous animals that had undergone volume reduction versus sham sternotomy (44.7 ± 0.60 vs 49.4 ± 1.0 mL, P =.001). In situ diaphragm length (1.99 ± 0.04 vs 2.24 ± 0.07 cm, P =.001) and the length at which maximal twitch force is generated (2.25 ± 0.06 vs 2.48 ± 0.09 cm, P =.038) were shorter in emphysematous than control animals. After volume reduction, in situ diaphragm length (2.13 ± 0.06 vs 1.83 ± 0.02 cm, P <.001) and the length at which maximal twitch force is generated (2.50 ± 0.08 vs 2.27 ± 0.06 cm, P =.013) were longer than in animals undergoing sham sternotomy. Conclusions: In this experimental model of emphysema and lung volume reduction surgery, emphysema shortens the length at which maximal twitch force is generated and shifts the diaphragmatic length-tension curve to lower lengths; volume reduction returns the length at which maximal twitch force is generated toward normal and shifts the diaphragmatic length-tension curve back to longer lengths. This restoration toward normal physiology may enable the improvement in diaphragmatic function seen after lung volume reduction surgery. The mechanism by which these length adaptations occur merits further investigation. (J Thorac Cardiovasc Surg 2001;121:217-24)

Analytical solutions of sensitivity for pressure microsensors

Pressure microsensors are normally designed in linear operation range. In this study, analytical solutions are presented in order to offer a set of simple equations to designers and researchers to calculate and predict the sensitivity of pressure microsensors. The pressure sensitivity is proportional to the square of the ratio of diaphragm thickness to diaphragm length, but it is inversely proportional to burst pressure. We found that the analytical solutions are in good agreement with simulation by finite element method.

Estimation of diaphragm length in patients with severe chronic obstructive pulmonary disease

In patients with advanced chronic obstructive pulmonary disease (COPD) diaphragm function may be compromised because of reduced muscle fibre length. Diaphragm length (L Di) can be estimated from measurements of transverse diameter of the rib cage (D Rc) and the length of the zone of apposition (L Zapp) in healthy subjects, but this method has not been validated in patients with COPD. Postero-anterior chest radiographs were obtained at total lung capacity (TLC), functional residual capacity (FRC) and residual volume (RV) in nine male patients with severe COPD (mean [S.D.]; FEV 1, 23 [6] %pred.; FRC, 199 [15] %pred.). Radiographs taken at TLC were used to identify the lateral costal insertions of the diaphragm (L Zapp assumed to approach zero at TLC). L Di was measured directly and also estimated from measurements of L Zapp and D Rc using a prediction equation derived from healthy subjects. The estimation of L Di was highly accurate with an intraclass correlation coefficient of 0.93 and 95% CI of ∼±8% of the true value. L Di decreased from 426 (64) mm at RV to 305 (31) mm at TLC. As there were only small and variable changes in D Rc across the lung volume range, most of the L Di changes occurred in the zone of apposition. Additional studies showed that measurements of L Di from PA and lateral radiographs performed at different lung volumes were tightly correlated. These results suggest that non-invasive measurements of L Zapp in the coronal plane (e.g. using ultrasonography) and D Rc (e.g. using magnetometers) can be used to provide an accurate estimate of L Di in COPD patients.

Chest wall hyperinflation during acute bronchoconstriction in asthma.

The mechanics of the chest wall was studied in seven asthmatic patients before and during histamine-induced bronchoconstriction (B). The volume of the chest wall (VCW) was calculated by three-dimensional tracking of 89 chest wall markers. Pleural (Ppl) and gastric (Pga) pressures were simultaneously recorded. VCW was modeled as the sum of the volumes of the pulmonary-apposed rib cage (VRC,p), diaphragm-apposed rib cage (VRC,a), and abdomen (VAB). During B, hyperinflation was due to the increase in end-expiratory volume of the rib cage (0.63 +/- 0.09 L, p < 0.01), whereas change in VAB was inconsistent (0.09 +/- 0.07 L, NS) because of phasic recruitment of abdominal muscles during expiration. Changes in end-expiratory VRC,p and VRC,a were along the rib cage relaxation configuration, indicating that both compartments shared proportionally the hyperinflation. VRC,p-Ppl plot during B was displaced leftward of the relaxation curve, suggesting persistent activity of rib cage inspiratory muscles throughout expiration. Changes in end-expiratory VCW during B did not relate to changes in FEV(1) or time and volume components of the breathing cycle. We concluded that during B in asthmatic patients: (1) rib cage accounts largely for the volume of hyperinflation, whereas abdominal muscle recruitment during expiration limits the increase in VAB; (2) hyperinflation is influenced by sustained postinspiratory activity of the inspiratory muscles; (3) this pattern of respiratory muscle recruitment seems to minimize volume distortion of the rib cage at end-expiration and to preserve diaphragm length despite hyperinflation.

Effect of lung volume reduction surgery on diaphragm length in severe chronic obstructive pulmonary disease.

Lung volume reduction surgery (LVRS) has been suggested as improving respiratory mechanics in patients with severe chronic obstructive pulmonary disease (COPD). We hypothesized that LVRS might lengthen the diaphragm, increase its area of apposition with the chest wall, and thereby improve its mechanical function. To determine the effect of bilateral LVRS on diaphragm length, we measured diaphragm length at TLC, using plain chest roentgenograms (CXRs), in 25 patients (11 males and 14 females) before LVRS and 3 to 6 mo after LVRS. A subgroup of seven patients (reference data) also had diaphragm length measurements made with CXRs, using films made within a year before their presurgical evaluation. Right hemidiaphragm silhouette length (PADL) and the length of the most vertically oriented portion of the right hemidiaphragm muscle (VDML) were measured. Diaphragm dome height was determined from the: (1) distance between the dome and transverse diameter at the manubrium; and (2) highest point of the dome referenced horizontally to the vertebral column. Patients also underwent spirometry, measurements of lung volumes and diffusion capacity, an incremental symptom-limited maximum exercise test, and measurements of 6 min walk distance (6MWD) and transdiaphragmatic pressures during maximum static inspiratory efforts (Pdimax sniff) and bilateral supramaximal electrophrenic twitch stimulation (Pditwitch) both before and 3 mo after LVRS. Patients were 58 +/- 8 yr of age, with severe COPD and hyperinflation (FEV1 = 0.68 +/- 0.23 L, FVC = 2.56 +/- 7.3 L, and TLC = 143 +/- 22% predicted). Following LVRS, PADL increased by 4% (from 13.9 +/- 1.9 cm to 14.5 +/- 1.7 cm; p = 0.02), VDML increased by 44% (from 2.08 +/- 1.5 cm to 3.00 +/- 1.6 cm, p = 0.01), and diaphragm dome height increased by more than 10%. In contrast, diaphragm lengths were similar in subjects with CXRs made before LVRS and within 1 yr before evaluation. The increase in diaphragm length correlated directly with postoperative reductions in TLC and RV, and also with increases in transdiaphragmatic pressure with maximal sniff (Pdimax sniff), maximal oxygen consumption (V O2max), maximal minute ventilation (V Emax), and maximum voluntary ventilation following LVRS. We conclude that LVRS leads to a significant increase in diaphragm length, especially in the area of apposition of the diaphragm with the rib cage. Diaphragm lengthening after LVRS is most likely the result of a reduction in lung volume. Increases in diaphragm length after LVRS correlate with postoperative improvements in diaphragm strength, exercise capacity, and maximum voluntary ventilation.

Abdominal muscle recruitment and PEEPi during bronchoconstriction in chronic obstructive pulmonary disease.

BACKGROUND: It has been recently shown that, when breathing at rest, many patients with severe chronic obstructive pulmonary disease (COPD) contract abdominal muscles during expiration, and that this contraction is...

Relationship between transdiaphragmatic and mouth twitch pressures at functional residual capacity

The clinical application of transdiaphragmatic twitch pressure (Pdi,tw) response to phrenic nerve stimulation has been hindered by the requirement for placement of oesophageal and gastric balloons. Investigators have reported that mouth twitch pressure (Pmo,tw) estimates Pdi,tw accurately at lung volumes above and below functional residual capacity (FRC). However, it is not known whether Pmo,tw estimates Pdi,tw accurately when stimulation is performed at FRC during relaxed conditions. The aim of this study was to develop a simple method whereby measurements of Pmo could be used to predict oesophageal twitch pressure (Poes,tw) and possibly Pdi,tw at FRC. The study was performed in 11 healthy volunteers during phrenic nerve stimulation. At FRC, 9 of the 11 subjects showed a poor correlation between Pmo,tw and Poes,tw, and between Pmo,tw and Pdi,tw, probably due to varying degrees of glottic closure. Stimulations performed while subjects maintained an inspiratory flow of approximately 50 mL x s(-1), or at the point of reattaining FRC during an inspiration preceded by a limited exhalation, produced good correlations between Pmo,tw and Poes,tw (r=0.97 in both instances) and Pmo,tw and Pdi,tw (r=0.96 and r=0.95, respectively), with a steep slope. The respective slopes for the Pmo,tw Poes,tw relationship were 0.88 and 0.94, and for the Pmo,tw Pdi,tw relationship, 0.59 and 0.54. Unfortunately, these manoeuvres produced a significant increase in transpulmonary pressure (3.6+/-0.6 (SE) and 5.6+/-1.4 cmH2O, respectively), suggesting change in diaphragmatic length. Stimulations delivered while subjects performed an inspiratory effort or during exhalation against a high resistance preceded by a limited inhalation could not be used to predict Poes,tw and Pdi,tw from Pmo,tw. In conclusion, although transdiaphragmatic and oesophageal twitch pressure could be predicted from mouth twitch pressure during some inspiratory manoeuvres mouth twitch pressure was not reliable for the prediction of the oesophageal and transdiaphragmatic twitch pressure at functional residual capacity during relaxed conditions in healthy volunteers.

Diaphragm interference pattern EMG and compound muscle action potentials: effects of chest wall configuration.

The effect of chest wall configuration on the diaphragm electromyogram (EMGdi) was evaluated in five healthy subjects with an esophageal electrode for both interference pattern EMGdi (voluntary contractions) and electrically evoked diaphragm compound muscle action potentials (CMAPs). Diaphragm CMAPs (both unilateral and bilateral) were evaluated for the baseline-to-peak amplitude (Ampl), the time from the onset of the CMAP to first peak (T1), root mean square (RMS), and center frequency (CF) values of the CMAP power spectrum. CF values from the interference pattern EMGdi power spectrum were also calculated. For CMAPs obtained at an electrode position least influenced by variations induced by electrode positioning, Ampl increased with diaphragm shortening from functional residual capacity (FRC) to total lung capacity (TLC) by 101 and 98% (unilateral and bilateral, respectively). Bilateral CMAP RMS values increased 116% from FRC to TLC. CMAP T1 values decreased with diaphragm shortening from FRC to TLC by 1.1 and 2.1 ms for the unilateral and bilateral stimulations, respectively, and CF increased for the bilateral diaphragm CMAPs with diaphragm shortening. CF values from the interference pattern EMGdi did not show any consistent change with chest wall configuration. Thus CF values of the interference pattern EMGdi obtained with an esophageal electrode can be considered reliable for physiological interpretation, at any diaphragm length (if electrode positioning and signal contamination are controlled for), contrary to the diaphragm CMAPs, which are sensitive to changes in chest wall configuration. It is speculated that the different results (over the effects of chest wall configuration on interference pattern EMGdi and diaphragm CMAPs) amy be because of summation properties of the signals and how these influence the EMG power spectrum.

Respiratory muscle length and strength in patients with chronic abdominal distension.

Starling's law (the energy of muscle contraction is proportional to the initial fiber length) has been applied to contraction of inspiratory muscles. Its application to the expiratory muscles is difficult because both maximal length and maximal pressure development occur at total lung capacity (TLC). We hypothesize that decrease of both inspiratory (Pimax) and expiratory (Pemax) muscle strength in chronic ascites (CA) will reflect generalized muscle weakness and stretching of both the diaphragm and abdominal wall as well. To test this hypothesis, we evaluated Pimax and diaphragm length (at functional residual capacity) in 22 patients. Pemax, external oblique and transversus abdominus muscle lengths, and anterior abdominal wall muscle thickness were measured at TLC. We found Pimax (78 +/- 19% predicted), Pemax (61 +/- 17%), and--as an index of general muscle strength--handgrip strength (75 +/- 22%) all to be minimally reduced. Respiratory muscle strength did not correlate with any measurement of inspiratory/expiratory muscle length or thickness. With fluid removal, abdominal muscles shortened; diaphragmatic curvature decreased although diaphragm length was unchanged. Nevertheless, neither Pimax nor Pemax increased. Respiratory muscle strength depends upon generalized muscle strength more so than upon muscle length in CA patients.

Breathing during exercise in dogs--passive or active?

The activation patterns of the costal and crural diaphragm and transversus abdominis muscle and their relationship to esophageal pressure (Pes) changes and footplant were examined in five chronically instrumented dogs which breathed at high frequencies at rest and during exercise. In two tracheostomized dogs, measurements were made of diaphragmatic length via sonomicrometry and of airflow and were related to diaphragmatic electrical activity and Pes. Dogs exhibited either a high-frequency breathing pattern, characterized by Pes changes occurring at 2-6 Hz, or a mixed-frequency breathing pattern, characterized by low-amplitude Pes oscillations (4-6 Hz) superimposed on a slower breathing rate of 0.5-1 Hz. Regardless of the type of breathing pattern elected or of the various breathing-to-stride frequency ratios observed during exercise, decreases in Pes were always associated with phasic electromyographic activity of the costal and crural diaphragm and with phasic diaphragmatic muscle shortening. The transversus abdominis electromyographic activity coincided with an increasing Pes from peak negative values in resting dogs and exhibited both an expiratory and a locomotory modulation during exercise. Although footplant may have contributed to some airflow generation when dogs utilized the mixed-frequency pattern, these data demonstrate that the movement of air into and out of the lungs in stationary or exercising dogs requires phasic neural activation of the diaphragm and other respiratory muscles.

Effects of diaphragm shortening on the mean action potential conduction velocity in canines.

1. The present study was designed to test if the mean muscle fibre action potential conduction velocity (VAPC) in the costal diaphragm changes with muscle length, in spontaneously breathing mongrel dogs. 2. VAPC was determined by the electromyogram (EMG) power spectrum 'dip' method, which is based on the bipolar electrode transfer function. A bipolar EMG electrode with a 20 mm fixed interelectrode distance was sutured to the costal diaphragm in the fibre direction, and in a region with a low density of motor endplates. Diaphragm length was measured with piezoelectric crystals positioned next to the EMG electrode. Seven dogs were vagotomized and spinally anaesthetized in order to increase diaphragmatic shortening, reduce velocity of shortening and abolish possible cross-talk signals from adjacent muscles. 3. Our results showed that VAPC in the canine costal diaphragm was 3.4 m s-1 and was not significantly related to diaphragmatic shortening.