Muscular weakness and respiratory function.
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Humans↗
Biomedical subjects
P T Macklem
Publications and source records attributed to P T Macklem.
Respiratory muscle dysfunction.
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Diaphragm↗
Relationship between diaphragm length and abdominal dimensions.
We examined the relationship between changes in abdominal cross-sectional area, measured by respiratory inductive plethysmography, and changes in length in the costal and crural parts of the diaphragm, measured by sonomicrometry, in nine supine, anesthetized dogs. During passive inflation, both parts of the diaphragm shortened and abdominal cross-sectional area increased. During passive deflation, both parts of the diaphragm lengthened and abdominal cross-sectional area decreased. We subsequently used the relationship between costal and crural diaphragmatic length, respectively, and abdominal cross-sectional area during passive inflation-deflation to predict the length changes in the costal and crural diaphragm during quiet breathing before and after bilateral phrenicotomy. In the intact animal the inspiratory shortening in the crural diaphragm was almost invariably greater than predicted from the relationship during passive inflation. During inspiration after phrenicotomy the crural diaphragm invariably lengthened, whereas the costal diaphragm often shortened. In general there was a good correlation between the measured and predicted length change for the crural diaphragm (r = 0.72 before and 0.79 after phrenicotomy) and a poor one for the costal diaphragm (r = 0.05 before and 0.19 after phrenicotomy).
Abdomen↗
The effects of parasympathectomy on serotonin-induced bronchoconstriction in the cat.
We studied the contribution of neural influences, in particular, the nonadrenergic, noncholinergic inhibitory system, on the modulation of airway responses to serotonin (5-HT) in the anesthetized and mechanically ventilated cat. Airway responses were assessed by measurement of pulmonary resistance (RL). Parasympathectomy (PS) caused a variable increase in bronchoconstriction in 9 of 10 cats (n = 10) that had received pretreatment intravenously with atropine (3 mg/kg) and propranolol (2 mg/kg); PS performed following pretreatment with phentolamine (2 mg/kg), propranolol, and atropine led to an increase in bronchoconstriction in only 2 of 6 cats. Dose-response curves to aerosolized 5-HT were performed in one group of cats (n = 5) before and 30 min after PS and in control group (n = 6). Both groups of animals were pretreated intravenously with atropine, propranolol, and phentolamine. The concentration of aerosolized 5-HT that was necessary to double pulmonary resistance (ED200RL) was significantly reduced from 0.117 to 0.062 mg/ml (p less than 0.01) by PS, in contrast to control cats in which ED200RL during 2 consecutive dose-response curves (0.076 and 0.087 mg/ml, respectively) did not change significantly. We conclude that there is neural modulation of airway responses to infused 5-HT through an alpha-adrenergic pathway and that an additional inhibitory nonadrenergic, noncholinergic neural influence is demonstrable in the response to aerosolized 5-HT.
Aerosols↗
The clinical relevance of respiratory muscle research. J. Burns Amberson lecture.
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Abdominal Muscles↗
The assessment of diaphragmatic contractility.
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Diaphragm↗
Effects of separate rib cage and abdominal restriction on exercise performance in normal humans.
We assessed the effects of selective restriction of movements of the rib cage (Res,rc) and abdomen (Res,ab) on ventilatory pattern, transdiaphragmatic pressure (Pdi), and electrical activity of the diaphragm (Edi) in five normal subjects exercising at a constant work rate (80% of maximum power output) on a cycle ergometer till exhaustion. Restriction of movements was achieved by an inelastic corset applied tightly around the rib cage or abdomen. Edi was recorded by an esophageal electrode, rectified, and then integrated, and peak values during inspiration were measured. Each subject exercised at the same work rate on 3 days: with Res,rc, with Res,ab, and without restriction (control). Res,rc but not Res,ab reduced exercise time (tlim). Up to tlim, minute ventilation (VE) was similar in all three conditions. At any level of VE, however, Res,rc decreased tidal volume and inspiratory and expiratory time, whereas Res,ab had no effect on the pattern of breathing. Res,ab was associated with higher inspiratory Pdi swings at any level of VE, whereas peak Edi was similar to control. Inspiratory Pdi swings were the same with Res,rc as control, but the peak Edi for a given Pdi was greater with Res,rc (P less than 0.05). During Res,rc the abdominal pressure swings in expiration were greater than with Res,ab and control. We conclude that Res,rc altered the pattern of breathing in normal subjects in high-intensity exercise, decreased diaphragmatic contractility, increased abdominal muscle recruitment in expiration, and reduced tlim. On the other hand, Res,ab had no effect on breathing pattern or tlim but was associated with increased diaphragmatic contractility.
Abdomen↗
Ventilatory muscle function during exercise in air and oxygen in patients with chronic air-flow limitation.
Ventilatory muscle function was examined at rest and during exercise on a cycle ergometer in 8 patients with moderate to severe chronic air-flow limitation (FEV1, 32 +/- 4% predicted) in air and in oxygen. The diaphragmatic electromyogram (EMG) was measured using an esophageal electrode. In addition, measurements of esophageal (Pes), gastric (Pga), and transdiaphragmatic (Pdi) pressures and abdominal wall movements were made. Patients exercised to exhaustion at a constant submaximal workload (80% of maximal power output) inspiring air or 40% O2 in random order on separate days. At end-exercise in air, tidal inspiratory Pes swings were 36 +/- 4% of static maximal inspiratory Pes, and inspiratory Pdi swings were 45 +/- 7% of the static maximal Pdi. Arterial oxygen saturation decreased from 91 +/- 2% at rest to 80 +/- 5% at end-exercise in air. During exercise in air, 5 patients demonstrated a persistent and greater than 20% fall in the ratio of high frequency (150 to 350 Hz) to low frequency (20 to 46 Hz) power (H/L) of the diaphragmatic EMG, indicating impending diaphragmatic fatigue, and 2 patients had paradoxical motion of the abdominal wall. Exercise time at the same constant work load increased from 3.0 +/- 0.6 min in air to 6.4 +/- 1.2 min in O2 (p less than 0.005). At the comparable time during exercise in O2 to end-exercise in air, minute ventilation was less by 13% (p less than 0.005), which was entirely attributable to a lower frequency of breathing. Mean inspiratory and expiratory flows and heart rate were all significantly lower.(ABSTRACT TRUNCATED AT 250 WORDS)
Abdomen↗
Mechanics of intercostal space and actions of external and internal intercostal muscles.
It is conventionally considered that because of their fiber orientations, the external intercostal muscles elevate the ribs, whereas the internal interosseous intercostals lower the ribs. The mechanical action of the intercostal muscles, however, has never been studied directly, and the electromyographic observations supporting this conventional thinking must be interpreted with caution. In the present studies, the external and internal interosseous intercostal muscles have been separately stimulated in different interspaces at, above, and below end-expiratory rib cage volume in anesthetized dogs. The axial (cephalo-caudal) displacements of the ribs were measured using linear displacement transducers. The results indicate that when contracting in a single interspace and other muscles are relaxed, both the external and internal intercostals have a net rib elevating action at end-expiratory rib cage volume. This action increases as rib cage volume decreases, but it progressively decreases as rib cage volume increases such that at high rib cage volumes, both the external and internal intercostals lower the ribs. Stimulating the intercostal muscles in three adjacent intercostal spaces simultaneously produced similar directional rib motion results. We conclude that (a) in contrast with the conventional thinking, the external and internal interosseous intercostals acting alone have by and large a similar effect on the ribs into which they insert; (b) this effect is very much dependent on rib cage (lung) volume; and (c) intercostal muscle action is primarily determined by the resistance of the upper ribs to caudad displacement relative to the resistance of the lower ribs to cephalad displacement. The lateral intercostals, however, might be more involved in postural movements than in respiration. Their primary involvement in rotations of the trunk might account for the presence of two differently oriented muscle layers between the ribs.
Animals↗
Respiratory muscle fatigue and ventilatory failure.
In this review emphasis is placed on some major mechanisms involved in inspiratory muscle fatigue. It is certain that respiratory muscle fatigue is a clinical entity, with broad implication in internal medicine. As yet its prevalence is largely unknown. There is reasonable certainty of some of the mechanisms leading to fatigue, for example the effect of loads and circulation. However, the cellular mechanisms, both chemical and electrophysiological, remain obscure. In detecting respiratory muscle fatigue various tests already represent windows from which we can see the malfunction of some mechanisms, unfortunately often not understood. The ideal test to evaluate respiratory muscle fatigue (easy to perform, sensitive, specific, and reliable) has not been developed yet. The clinical identification of respiratory muscle fatigue is still developing, and only tentative guidelines for its treatment can be proposed at this stage. Clearly, much research is required to determine prevalence, establish the diagnosis, and evaluate therapy.
Diaphragm↗
Ventilatory muscles during exercise in air and oxygen in normal men.
To determine whether normal ventilatory muscles fatigue during short-term high-intensity exercise, we measured diaphragmatic electromyogram (EMG, esophageal electrode), and pleural (Ppl), gastric (Pga), and transdiaphragmatic (Pdi) pressures in seven normal young men. On separate days, the subjects performed exercise to exhaustion at a constant work load (80% maximum power output) inspiring air or 40% O2. Before and after exercise, Pdimax and maximum expiratory pressure at the mouth (PEmax) were measured. At 0.5-2 min postexercise, there was a decrease in Pdimax in both air (P less than 0.02) and O2 studies (P less than 0.05). There was some recovery in Pdimax from 2-5 min postexercise in air (P less than 0.05) and complete recovery 2-5 min postexercise in O2. PEmax did not change postexercise. During exercise in air, the EMG predicted diaphragmatic fatigue in five subjects using a 20% fall of the ratio of high-frequency (150-350 Hz) to low-frequency) (20-46 Hz) power (H/L) as the criterion. Further evidence of diaphragmatic fatigue during exercise in air in two subjects was the decrease in end-inspiratory Pdi toward end exercise. There was an increase in exercise time with O2 (P less than 0.05). The improved performance in O2 was associated with a delay in the fall in H/L and the absence of the decrease in end-inspiratory Pdi in those subjects in whom such changes were observed in air.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Mechanical arrangement of costal and crural diaphragms in dogs.
To assess the mechanical arrangement of the costal and crural parts of the diaphragm, we studied changes in diaphragmatic length with piezoelectric crystals in 17 supine anesthetized dogs. During control resting inspiration, the crural part usually shortened more and earlier than the costal part. After phrenicotomy, the crural part always lengthened during inspiration, whereas the costal part shortened or lengthened. These interanimal differences disappeared after opening of the abdomen; the costal part then always lengthened during inspiration. During stimulation of one part, the relaxed nonstimulated part always lengthened. However, when compared with the relationship between length and transdiaphragmatic pressure (Pdi) obtained during passive deflation, the lengthening of the relaxed part during stimulation of either part was small. This difference between predicted and measured Pdi-length relationship decreased in magnitude as lung volume increased above functional residual capacity (FRC) and increased as residual volume was approached. These results indicate that 1) even during quiet breathing the diaphragm in the dog is not a single functional entity; 2) at FRC the costal and crural portions of the diaphragm behave as if they were mechanically arranged partly in parallel and partly in series; and 3) they gradually move into a pure mechanical series arrangement as lung volume increases.
Animals↗
Regional differences in abdominal pressure swings in dogs.
The pressure swings under the costal (Pcos) and crural diaphragms (Pcru) and between the intestinal loops (Pint) were compared with the swings in gastric pressure (Pga) in 13 supine anesthetized dogs. Pcos, Pcru, and Pint were measured with air-filled latex balloons in eight dogs and saline-filled catheters in five. Pga was measured with an air-filled balloon in all dogs. During quiet breathing differences were often present, the directions of which were variable from animal to animal. During mechanical ventilation, all pressures increased, but both Pcos and Pcru increased more than Pga, whereas only a small change was observed in Pint. During bilateral stimulation of the costal diaphragm, Pcos invariably increased more than Pga and Pint, whereas almost no change was observed in Pcru. During bilateral stimulation of the crural diaphragm, Pcru invariably increased more than Pga, Pint, and Pcos. During abdominal muscle stimulation as during external abdominal compression, Pint always increased more than Pcos and Pcru. During lower rib cage compression, Pga, Pcos, and Pcru increased more than Pint. During sternocleidomastoid stimulation, all pressure swings were negative, but the change in Pint was always smaller than in Pcos, Pcru, or Pga. Inhomogeneities observed with balloons and saline-filled catheters were similar. After the abdomen was filled with 2 liters of saline all pressure swings became much more homogeneous.
Abdomen↗
Dyspnea, fatigue, and second wind.
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Diaphragm↗
Inspiratory muscle strength and body composition in patients receiving total parenteral nutrition therapy.
We examined the relationship between inspiratory muscle strength and body composition in 59 patients receiving total parenteral nutrition (TPN). Inspiratory muscle strength was assessed by measuring maximal inspiratory pressure (Pm) after a tidal expiration, with the patient supine and the nose occluded. Body composition was determined by multiple isotope dilution. Body cell mass (BCM) and extracellular mass were estimated by measuring total exchangeable potassium (Ke) and total exchangeable sodium (Nae), respectively; Nae/Ke, an index of the nutritional state, was calculated from these values. The effect of changes in muscle mass was evaluated in 29 of the patients by simultaneous determination of Pm and body composition, prior to and at 2-wk intervals during TPN therapy. The Pm was lower (mean +/- 1 SE:33.5 +/- 2.8 cm H2O) in malnourished patients than in those who were in the normal Nae/Ke range (45.3 +/- 4.8 cm H2O, p less than 0.05). Loss of strength was related to reduction in muscle mass because BCM was also reduced in malnourished patients (15.6 +/- 0.8 kg) when compared to those with normal Nae/Ke (19.3 +/- 0.9 kg), (p less than 0.05), and Pm was positively correlated with BCM (r = 0.27, p less than 0.01). Changes in BCM were accompanied by appropriate changes in Pm during the study period (r = 0.44, p less than 0.01); the majority (21 patients) showed improvement in both BCM and Pm.(ABSTRACT TRUNCATED AT 250 WORDS)
Body Composition↗
The ventilatory pump in exercise.
The response of the ventilatory pump during exercise in health and in patients with COPD is reviewed. The authors' hope is that the pump's response to the stress of exercise will be seen to be efficiently matched to the demands placed on it, even though in disease or under some extreme circumstances in normal subjects it may be stretched to (or beyond) its capacity. From a review of the literature, suggestions are made for directions for future research.
Abdominal Muscles↗