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Biomedical subjects

M B Reid

Publications and source records attributed to M B Reid.

At least 73 records · Page 4Linked to original sources
PubMed1989

'Air hunger' arising from increased PCO2 in mechanically ventilated quadriplegics.

A number of investigators have proposed that the sense of respiratory discomfort accompanying hypercapnia depends on respiratory mechanoreceptors which inform the sensory cortex of reflex increases in breathing. To test this hypothesis, we studied subjects whose respiratory muscles were paralyzed, and who were thus unable to increase breathing in response to hypercapnia. We gradually elevated inspired PCO2 in four tracheostomized quadriplegic subjects supported by constant mechanical ventilation. These subjects reported sensations of 'air hunger' (e.g., "short of breath", "air-starved") when end-tidal PCO2 increased 10 Torr (mean) above their resting levels. In a second experiment we used the forced-choice technique to determine the ability of three of these subjects to detect repeated changes of end-tidal PCO2. Two detected 7 Torr changes, the third detected 11 Torr changes. These data suggest that changes in breathing are not necessary to evoke the sense of 'air hunger'. We conclude that the likely mechanisms are (1) projection of chemoreceptor afferent traffic to the sensory cortex, and (2) projection of corollary discharge from brainstem respiratory centers to the sensory cortex.

Adult↗
PubMed1989

Theophylline does not increase maximal tetanic force or diaphragm endurance in vitro.

These experiments tested the capacity of theophylline to improve diaphragm strength (maximal force development) and endurance (maintenance of force output during repeated contractions). Rodent diaphragm strips were mounted at optimal length in oxygenated Krebs-Ringer solution (37 degrees C, pH 7.37). Direct stimuli used supramaximal current density, 0.2-ms pulses, and 250-ms tetanic trains. Theophylline (500 mg/ml) increased force development at low stimulation frequencies but did not increase maximal force [25.7 +/- 0.5 for theophylline vs. 26.0 +/- 0.4 (SE) N/cm2 for control (n = 34)]. During repeated submaximal (25-36 Hz) tetanic contractions, theophylline did not affect endurance. During repeated maximal (160 Hz) tetanic contractions theophylline reduced endurance, accelerating the fall of developed force. Theophylline also inhibited recovery of force after endurance trials ended. We conclude that theophylline does not increase maximal tetanic force and can reduce diaphragm endurance in vitro.

Animals↗
PubMed1989

Diaphragm atrophy and weakness in cortisone-treated rats.

Despite frequent therapeutic use, the potential of corticosteroids to produce respiratory muscle myopathy is unknown. We studied effects of chronic steroid treatment on diaphragm mass and function. Eleven Sprague-Dawley rats were treated with cortisone acetate (100 mg.kg-1.day-1 im) for 10 days. Controls (injected with vehicle) included 11 freely eating rats and 11 animals pair fed to match food intake of cortisone rats. Steroid treatment depressed body weight 30% compared with controls. Mass of diaphragm, gastrocnemius, and extensor digitorum longus showed significant atrophy (30%); heart and soleus were unaffected. Isometric contractile properties of costal diaphragm strips were studied in vitro using direct stimulation. The force-frequency relationship was markedly depressed by steroid treatment, both at low and high frequencies. However, force developed per unit cross-sectional area was similar among all three groups, as were twitch characteristics. When stimulated every minute, forces developed by control strips fell progressively, whereas the forces of cortisone-treated strips remained unchanged. When stimulated every 5 s, the fall in force was not different between groups. We conclude that cortisone weakened the diaphragm by decreasing muscle mass but made the diaphragm more resistant to one form of fatigue in vitro.

Animals↗
PubMed1988

Effects of metabolic blockade on distribution of blood flow to respiratory muscles.

Sublethal inhibition of citrate metabolism in the tricarboxylic acid (TCA) cycle with monofluoroacetate (MFA) has been shown to cause a fivefold increase in myocardial blood flow without any change in cardiac output, blood pressure, or O2 consumption (C. Liang, J. Clin. Invest. 60: 61-69, 1977); however, blood flow did not increase to any organs examined other than the heart, including resting limb skeletal muscle. Preferential inhibition of glycolysis with iodoacetate (IA) failed to cause similar changes in distribution of blood flow. This unique response of myocardium to TCA cycle inhibition suggested a unique metabolic control of cardiac vasodilation. An alternate explanation is that MFA is preferentially concentrated in active muscle. After MFA, tissue citrate accumulates behind the block and the highest levels are reported in the heart and diaphragm, suggesting enhanced blockade or enhanced compensation in these two continuously active muscles. To test the hypothesis that vasodilation in the heart after MFA is not unique and that similar vasodilation will be evoked in active respiratory muscles, we measured blood flow to the myocardium, kidney, diaphragm, intercostals, transverse abdominals, and triceps brachii in anesthetized dogs using radionuclide-labeled microspheres, before and after MFA, and in another set of dogs before and after IA. Before MFA or IA, inspiratory loading significantly increased blood flow to active muscles of breathing in proportion to the added load. After MFA, blood flow to active muscles of breathing as well as to the heart became abnormally elevated with respect to mechanical work, and loading evoked no further increase in blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdominal Muscles↗
PubMed1988

Respiratory muscle activity during repeated airflow interruption.

We observed striking differences in respiratory muscle electromyogram activity when active expirations were interrupted in rapid succession, depending on the mode of interruption. When the interruptions were produced at the level of the glottis (utterances, uh-uh-uh-uh, at 5-8 Hz) there were synchronous bursts of activity from expiratory muscles in all three subjects during the periods of no flow and rapid bursts of diaphragmatic activity during the flow phases in one subject. In contrast, when similarly rapid interruptions of active expirations were produced with the tongue on a mouthpiece (utterance, te-te-te-te) or with an external valve, no synchronous bursts were observed. Since all interruptions would have been mechanically similar at expiratory muscular and pulmonary levels, we reasoned that the bursts with glottic interruptions were either programmed centrally or driven reflexly at the laryngeal level.

Electromyography↗
PubMed1987

Pliometric activity of inspiratory muscles: maximal pressure-flow curves.

We tested the hypothesis that inspiratory muscles, like other skeletal muscles, would exert greater force under pliometric conditions (being lengthened while active) than under isometric or miometric (active shortening) conditions. Maximal inspiratory pressure-flow curves of the respiratory system are analogous to the force-velocity curves for isolated muscle (Agostoni and Fenn, J. Appl. Physiol. 15:349-353, 1960). We measured esophageal pressure (Pes) and plethysmographic flow (V) at relaxation volume of the respiratory system in six trained subjects inspiring maximally through graded resistors (miometric), against a closed airway (isometric), and while constant expiratory flows were forced by a reduced pressure source at the airway opening (pliometric). Pes varied inversely with V and this trend continued into the pliometric range. In addition we found that the pressure-flow characteristics of the rib cage and of the abdomen are similar to those for the chest wall as a whole. The mechanical and energetic advantages of muscle activity under pliometric conditions may be available to some inspiratory muscles in both normal and pathological situations.

Adult↗
PubMed1987

Fiber types and fiber diameters in canine respiratory muscles.

In the present study, we measured fiber types and fiber diameters in canine respiratory muscles and examined regional variation within the diaphragm. Samples of eight diaphragm regions, internal intercostals, external intercostals, transversus abdominis, and triceps brachii were removed from eight adult mongrel dogs, frozen, and histochemically processed for standard fiber type and fiber diameter determinations. The respiratory muscles were composed of types I and IIa fibers; no IIb fibers were identified. Fiber composition differed between muscles (P less than 0.0001). Normal type I percent (+/- SE) were: diaphragm 46 +/- 2, external intercostal 85 +/- 6, internal intercostals 48 +/- 3, transversus abdominis 53 +/- 1, and triceps 33 +/- 7. The diaphragm also contained a type I subtype [6 +/- 1% (SE)] previously thought only to occur in developing muscle. Fiber composition varied between diaphragm regions (P less than 0.01). Most notably, left medial crus contained 64% type I fibers. Fiber size also varied systematically among muscles (P less than 0.025) and diaphragm regions (P less than 0.0005). External intercostal fiber diameter was largest (47-50 microns) and diaphragm was smallest (34 microns). Within diaphragm, crural fibers were larger than costal (P less than 0.05). We conclude that there are systematic differences in fiber composition and fiber diameter of the canine respiratory muscles.

Analysis of Variance↗
PubMed1987

Isometric contractile properties of diaphragm strips from alcoholic rats.

Chronic ethanol consumption alters the structure and function of human respiratory muscle. We have examined its effect on the active and passive mechanical properties of rat diaphragm strips in vitro. We conditioned eight rats using a liquid diet containing ethanol as 36% of calories. Eight control rats were pair-fed an isocaloric, ethanol-free liquid diet. Rats were killed after 23 wk. Two strips from the left hemidiaphragm were suspended in Krebs-Ringers solution at 25 degrees C, equilibrated with 5% CO2-95% O2. Isometric stresses were calculated from force transducer measurements. Strips were stimulated directly at supramaximal voltage. Twitch stress (Pt), measured at optimal length (Lo), was greater in ethanol-conditioned strips: 5.1 vs. 3.8 N/cm2. Times to peak Pt and twitch half-relaxation times were equal. Tetanic stress at Lo (Po) was also greater after ethanol conditioning: 17.2 vs. 12.8 N/cm2. Pt/Po ratios were equal. Expressed as %Po, tetanic stress-stimulation frequency curves and tetanic stress-length curves were identical. Ethanol-conditioned strips were marginally less compliant when passively stretched to lengths between Lo and 130% Lo. We postulate that ethanol may have increased active stress development by reducing intracellular free water.

Alcoholism↗
PubMed1986

Immunohistological demonstration of factors XIIIa and XIIIs in reactive and neoplastic fibroblastic and fibro-histiocytic lesions.

Factor XIII sub-units a and s (XIIIa and XIIIb) have been localized previously in fibroblasts of the liver and in other tissues. An immunoperoxidase technique was used to localize these factors in benign and malignant fibroblastic and fibro-histiocytic lesions. Positive staining was present in cells in almost all of the benign and fibro-histiocytic lesions but was reduced in the malignant group. However, the pattern of staining was not sufficiently consistent to justify the use of the factors XIII as diagnostic markers in soft tissue neoplasia.

Factor XIII↗
PubMed1986

Passive mechanics of upright human chest wall during immersion from hips to neck.

We have determined the mechanical effects of immersion to the neck on the passive chest wall of seated upright humans. Repeated measurements were made at relaxed end expiration on four subjects. Changes in relaxed chest wall configuration were measured using magnetometers. Gastric and esophageal pressures were measured with balloon-tipped catheters in three subjects; from these, transdiaphragmatic pressure was calculated. Transabdominal pressure was estimated using a fluid-filled, open-tipped catheter referenced to the abdomen's exterior vertical surface. We found that immersion progressively reduced mean transabdominal pressure to near zero and that the relaxed abdominal wall was moved inward 3-4 cm. The viscera were displaced upward into the thorax, gastric pressure increased by 20 cmH2O, and transdiaphragmatic pressure decreased by 10-15 cmH2O. This lengthened the diaphragm, elevating the diaphragmatic dome 3-4 cm. Esophageal pressure became progressively more positive throughout immersion, increasing by 8 cmH2O. The relaxed rib cage was elevated and expanded by raising water from hips to lower sternum; this passively shortened the inspiratory intercostals and the accessory muscles of inspiration. Deeper immersion distorted the thorax markedly: the upper rib cage was forced inward while lower rib cage shape was not systematically altered and the rib cage remained elevated. Such distortion may have passively lengthened or shortened the inspiratory muscles of the rib cage, depending on their location. We conclude that the nonuniform forcing produced by immersion provides unique insights into the mechanical characteristics of the abdomen and rib cage, that immersion-induced length changes differ among the inspiratory muscles according to their locations and the depth of immersion, and that such length changes may have implications for patients with inspiratory muscle deficits.

Abdomen↗
PubMed1986

Pulmonary afferent activity during high-frequency ventilation at constant mean lung volume.

We recorded the responses of 21 slowly adapting pulmonary stretch receptors (PSRs) and 8 rapidly adapting pulmonary stretch receptors (RARs) from the vagi of anesthetized open-chest dogs to high-frequency ventilation (HFV) at 15 Hz, at constant mean end-expiratory lung volume, and constant end-tidal PCO2. HFV applied in this way has been shown to prolong expiration. The responses of pulmonary afferents during HFV at constant mean volume have not been described. In the present experiments, receptor discharge during HFV was compared with that during the end-expiratory pause of normal-frequency ventilation. Average PSR discharge increased when HFV was applied, although not all PSRs exhibited increases. RARs were generally silent during normal and high-frequency ventilation at functional residual capacity and above. However, at low lung volumes, RAR discharge increased greatly when HFV was applied. We conclude that PSR discharge is increased during HFV in the absence of increased lung volume and that increases in PSR discharge during HFV are sufficient to explain the reflex that prolongs expiration in dogs.

Adaptation, Physiological↗
PubMed1986

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↗
PubMed1985

High frequency oscillation of the lungs alone lengthens expiration in dogs.

High frequency (15 Hz), low volume (approximately 40 ml) oscillation of the respiratory system lengthens expiration in anesthetized dogs even in the absence of changes in mean expiratory lung volume or blood gases (Banzett et al., 1983). Although vagotomy abolishes this response, we felt it might mask the reflex rather than interrupt the afferent pathway. To ascertain whether pulmonary and airway afferents alone are capable of evoking this reflex, we confined the oscillatory stimulus to the lung by widely opening the chest. The dogs were paralyzed but breathed 'spontaneously' by means of a solenoid valve opened and closed by the phrenic neurogram. End-expiratory lung volume and PCO2 were held constant. All eight dogs that were tested after thoracotomy lengthened expiration during oscillation. Although quantitative comparisons of responses before and after thoracotomy are not entirely reliable, we could see no consistent change in the strength of response with paralysis or with thoracotomy. We conclude that the principal afferent limb of the ventilatory reflex response to oscillation arises in the lungs and intrathoracic airways.

Animals↗
PubMed1985

Reflex compensation of spontaneous breathing when immersion changes diaphragm length.

We measured tidal volume (VT), chest wall dimensions, end-tidal PCO2, and respiratory muscle electromyograms as seated subjects were immersed in water. We studied nine spontaneously breathing subjects; five were uninformed. Raising the water to xiphoid level pushed the abdomen in and expanded the rib cage at end expiration. This increased the diaphragm's operating length, giving it a contractile advantage, and shortened the inspiratory intercostals, giving them a contractile disadvantage. Peak inspiratory activities of both muscle groups decreased; inspiratory time (TI), respiratory frequency (f), and VT were unchanged. The experiments thus demonstrated operational length compensation during immersion and further showed that inspiratory muscle activation is not adjusted locally, according to changes in each muscle's length, but rather that the response is global. Xiphoid-to-shoulder immersion was less easily interpreted, since both rib cage and abdomen were compressed, lengthening both inspiratory muscles. Our subjects continued to maintain VT, f, and TI. Peak inspiratory activities of both muscles were further reduced. We do not attribute the change in inspiratory muscle activation to altered chemical drive or to voluntary response. Rather, the response appears to be a mechanoreceptive reflex that employs afferent information from the lungs or diaphragm to adjust all inspiratory muscle activities.

Diaphragm↗
PubMed1985

Relationship between parasternal intercostal length and rib cage displacement in dogs.

The relationship between parasternal intercostal length and rib cage cross-sectional area was examined in nine supine dogs during passive inflation and during quiet breathing before and after phrenicotomy. Parasternal intercostal length (PSL) was measured with a sonomicrometry technique, and rib cage cross-sectional area (Arc) was measured with a Respitrace coil placed around the middle rib cage. During active inspiration as well as during passive inflation, PSL decreased as Arc increased. However, the relationship between PSL and Arc during active inspiration, whether in the intact or phrenicotomized animal, was almost invariably different from that during passive inflation, so that the same increase in Arc was associated with a greater decrease in PSL in the former than in the latter instance. This difference between passive inflation and active inspiration is probably due to the active contraction of the parasternals during inspiration and the consequent caudal displacement of the sternum. In upright humans, the sternum moves cephalad and not caudad during inspiration, so the relationship between PSL and Arc during active breathing might be similar to that during passive inflation.

Animals↗
PubMed1985

Reflex compensation of voluntary inspiration when immersion changes diaphragm length.

When immersion alters inspiratory muscle operating lengths, spontaneously breathing humans maintain a constant tidal volume by reflex adjustment of inspiratory muscle activation (Reid et al. J. Appl. Physiol. 58: 1136-1142, 1985). We term this the operational length compensation reflex. The present experiment demonstrates that similar adjustments occur during voluntary respiratory maneuvers. Each of seven naive subjects sat in a tank with water at hip level. We trained them to reproduce an inspired volume (+/- 10%) at constant inspiratory duration. They received verbal feedback during training but not during the experiment. We measured surface electromyograms (EMGs) of diaphragm and intercostal muscles and tidal volume. After the subjects were trained, we made repeated measurements of 10 trained breaths with water at the hip and then again after raising water level to the xiphoid (which decreases lung volume and increases operating length of the diaphragm). In 30 of 42 trials there was a substantial fall in peak diaphragm EMG. In 10 trials this was sufficient to prevent any change in tidal volume. Inspiratory flow was more closely regulated than tidal volume. Subjects were not aware of making adjustments in drive.

Adult↗