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Biomedical subjects

D F Rochester

Publications and source records attributed to D F Rochester.

At least 55 records · Page 3Linked to original sources
PubMed1985

Contractile properties of intercostal muscles and their functional significance.

To have some insight into the functional coupling between the parasternal intercostals (PS) and the diaphragm (DPM), we have examined the isometric contractile properties of bundles from canine PS and DPM muscles. Bundles of external (EXT) and internal (INT) interosseous intercostals were studied for comparison. In addition we have related sonometrically measured length of the intercostals in vivo at supine functional residual capacity (FRC) to in vitro optimal force-producing length (Lo). We found that 1) intercostal twitch speed is significantly faster than DPM, thus displacing their relative force-frequency curve to the right of that of the DPM; 2) the ascending limb of the active length-tension curve of all intercostals lies below the DPM curve; i.e., at 85% Lo, PS force is 46% of maximal force (Po), whereas DPM force is still 87% Po; 3) for any given length change beyond Lo, all intercostals generate greater passive tension than the DPM; 4) Po is greater for the intercostals than the DPM; and 5) at supine FRC, both EXT and INT in dogs are nearly operating at Lo, whereas the PS are operating at a length greater than Lo. We conclude that 1) PS produce less force than DPM during breathing efforts involving low- (10-20 Hz) stimulation frequencies, but they generate more force than DPM when high- (greater than 50 Hz) stimulation frequencies are required; and 2) the pressure-generating ability of the PS is better preserved than that of the DPM with increases in lung volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Changes in heart rate during breathing interrupted by recurrent apneas in humans.

Heart rate varies with breathing patterns, especially in sleep apnea. To assess the effects on heart rate of recurrent apneas interrupting tidal breathing, we studied five normal awake male subjects. These subjects voluntarily changed their breathing pattern from regular tidal breathing to tidal breathing interrupted by breath holding at end expiration. This recurrent apneic breathing pattern did not change mean heart rate but increased its variance significantly. In addition, the variations in heart rate formed a cyclic pattern of oscillation with a mean cycle length identical to both arterial O2 saturation (SaO2) (R = 0.95; P less than 0.01) and ventilation (R = 0.92; P less than 0.01). Cyclic changes in either SaO2 or ventilation reproduced the oscillatory patterns of heart rate seen with tidal breathing interrupted by multiple apneas, but the amplitude of the variance in heart rate was smaller. Finally, preventing the cyclic declines in SaO2 with supplemental O2 did not significantly alter the heart rate changes seen in tidal breathing interrupted by apneas.

Adult↗
PubMed1985

Determinants of maximal inspiratory pressure in chronic obstructive pulmonary disease.

Inspiratory muscle strength in COPD could be reduced either because of mechanical disadvantage consequent to increased lung volume or because respiratory muscles share in generalized muscle weakness. To assess the relative contributions of these factors, we measured maximal inspiratory and expiratory pressures (Pimax, Pemax, cmH2O) at RV and TLC, respectively, in 32 patients with COPD. The TLC, RV, and diaphragm length index at RV (DLI, cm/cm height) were determined roentgenographically and compared with values from 22 normal subjects studied at comparable lung volume. Half the patients with COPD had normal and half had low values of Pemax, but both groups had similar values of TLC, RV, and DLI. In patients with COPD, Pimax correlated (p less than 0.001) with Pemax (r = 0.73) and DLI (r = 0.64). The slope of the Pimax-DLI relationship was essentially the same in both groups of patients with COPD as it was in the normal subjects. However, at any value of DLI, Pimax was in the normal range in patients with normal Pemax, but significantly lower in patients with low Pemax (p less than 0.001). Expressing Pimax as a combined function of Pemax and DLI yielded the highest correlation (r = 0.84, p less than 0.001), with Pemax explaining 46% and DLI explaining 35% of the variance in Plmax not explained by the other variable alone (p less than 0.001). The PaCO2 was elevated in 13 of 18 patients whose Pimax was less than 55 cm H2O, and inversely correlated with Pimax (r = -0.66, p less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

Multivariate analysis of diaphragm EMG power spectral moments.

A single derived index of the power spectrum of the diaphragm electromyogram (EMG) has been used in detecting fatigue. Additional information in the EMG could be used to study diaphragm function in other respiratory conditions. Diaphragm EMGs and calculated power spectra at 12 frequencies were measured in normal subjects and patients with severe chronic obstructive pulmonary disease during several respiratory maneuvers both before and after treadmill exercise to dyspnea. The power spectra were characterized by the first five moments. Changes in the EMG were similar when assessed by multivariate analysis of variance of the spectral estimates or of the moments. Factor analysis provided two latent variables that correlated with the first and second moment respectively. The first moment was found to be the most sensitive single discriminant of fatigue and is only slightly improved by adding other information. It is concluded that the first and second moments of the EMG power spectra provide a concise, parsimonious description of the changes in the EMG.

Adult↗
PubMed1984

Effects of thoracic volume and shape on electromechanical coupling in abdominal muscles.

To assess the effects of lung volume and chest wall configuration on electromechanical coupling of the abdominal muscles, we examined the relationship between abdominal muscle pressure ( Pmus ) and electrical activity ( EMGab ) in eight normal subjects during expiratory efforts at lung volumes ranging from functional residual capacity (FRC) to FRC + 2.0 liters. At and above FRC, increases of lung volume did not significantly alter either the Pmus - EMGab relationship or abdominal surface linear dimensions, although expiratory efforts displaced the abdomen inward from its relaxed position. We attribute the constancy of delta Pmus /delta EMG above FRC to the negligible effects of increasing lung volume on abdominal configuration and muscle length. Expiratory efforts performed at lung volumes below FRC resulted in a wider range of abdominal indrawing . Under these conditions the EMGab required to augment Pmus by 30-40 cmH2O increased as the abdomen was displaced inward. This decrease of delta Pmus /delta EMGab appears to reflect muscle shortening, flattening of the abdominal wall, and possibly deformation of the rib cage.

Abdominal Muscles↗
PubMed1984

Compliance of chest wall in obese subjects.

Whereas studies in awake subjects have demonstrated that chest wall compliance (Ccw) is low in obese subjects, the one study performed on paralyzed obese subject found Ccw to be normal. The purpose of this study was to measure Ccw in awake obese subjects with the pulse-flow technique, a method which appears to detect respiratory muscle relaxation. Seven normal males, 14 obese males, and 8 obese females [body mass index (BMI) varied from 20 to 83 kg/m2] were studied in the seated position. Ccw was measured by blowing air at a constant flow into the mouth and lungs for approximately 2 s and calculated by dividing airflow in liters per second by the change in esophageal minus body surface pressure in centimeters of water per second. In normal and obese subjects we found no correlation between BMI and Ccw. We conclude that obesity does not decrease Ccw.

Adult↗
PubMed1984

Acid-fast bacilli in sputum smears of patients with pulmonary tuberculosis. Prevalence and significance of negative smears pretreatment and positive smears post-treatment.

We studied 977 patients with culture-proved pulmonary tuberculosis retrospectively to determine the frequency with which patients were sputum smear negative but culture positive (S-C+) prior to treatment, the frequency with which patients developed the smear positive but culture negative (S+C-) status during treatment, and the implication of these 2 phenomena to the success of treatment. One fourth (25.6%) of the patients were repeatedly S-C+ prior to treatment; the frequency of this phenomenon was inversely proportional to the extent of disease and the presence of cavities. Patients who were S-C+ prior to treatment, and whose organisms were drug-sensitive, had the fastest sputum culture conversion rate. Patients who were S+C+ without far-advanced cavitary disease had a significantly slower conversion rate after 1 month of treatment, and those with far-advanced cavitary disease had the slowest conversion rate. Patients with drug-resistant organisms had slower conversion rates than did their counterparts with drug-sensitive organisms, but in all but 4 of these, sputum smears and cultures ultimately converted to negative. The S+C- phenomenon was observed in 20.4% of patients; its frequency was related to the extent of disease and to treatment regimens that contained rifampin. In all patients who exhibited the S+C- phenomenon, sputum smears converted to negative with continuation of the same treatment regimen.

Adult↗
PubMed1984

Respiratory muscle function in health.

Normally both quiet breathing and augmented ventilation during physical exercise are sustained by the inspiratory muscles around the chest wall. Among these, the diaphragm is most important. The inspiratory muscles of the upper airways must also contract to permit inspiration to occur. The expiratory muscles of the chest wall and abdomen do not normally participate in breathing per se, but are critically important for coughing. The strength of respiratory muscle contraction, as estimated from maximum static inspiratory and expiratory pressures, depends on neural drive, the length at which the muscles contract, and the velocity with which they shorten during contraction. The intrinsic strength of the respiratory muscles also depends on whether they are hypertrophied, or atrophied consequent to weight loss. As a result of the structural and biochemical properties of their muscle fibers and their blood supply, normal respiratory muscles have a high level of endurance. However, even well-trained normal subjects may develop inspiratory muscle fatigue if they are subjected to severe inspiratory resistive loads, hypoxia, high levels of physical exercise at normal atmospheric pressure, or work under hyperbaric conditions. The respiratory muscles of normal subjects respond to training. Strength training regimens enhance respiratory muscle but not ventilatory endurance, and vice versa.(ABSTRACT TRUNCATED AT 250 WORDS)

Body Weight↗
PubMed1983

Strychnine poisoning. Recovery from profound lactic acidosis, hyperthermia, and rhabdomyolysis.

Strychnine poisoning results in a predictable and treatable sequence of events involving blockade of the inhibitory neurotransmitter, extensor muscle spasms, seizures, and respiratory paralysis. These spasms may lead to hyperthermia, profound lactic acidosis, and rhabdomyolysis. Acidosis is primarily attributable to lactate, as indicated by the correlation between arterial pH and log of lactic acid concentration (r = -0.878). Interruption of the strychnine blockade is the primary therapy for strychnine poisoning. Phenobarbital in moderate doses should be the first intervention and anesthetic doses should be used if necessary. Suppression of convulsions will permit successful management of the complications of strychnine poisoning. Our patient survived, even though at one point he had a pH of 6.55, a lactate level of 32 mM/liter, a temperature of 43 degrees C, and rhabdomyolysis with an increased creatine phosphokinase level of 359,000 mU/ml (5,983 mumol/s/liter).

Acidosis↗
PubMed1983

Respiratory muscle failure.

The diseases which are commonly complicated by hypercapnic respiratory failure also compromise the respiratory muscles in several ways. Increased work of breathing, mechanical disadvantage, neuromuscular disease, impaired nutritional status, shock, hypoxemia, acidosis, and deficiency of potassium, magnesium, and inorganic phosphorus are the major non-neurologic factors which contribute to respiratory muscle fatigue and failure. Respiratory muscle fatigue has two components. High frequency fatigue occurs rapidly with intense contractile efforts but is usually not severe. It also recovers rapidly with rest. Low frequency fatigue develops more slowly but is severe and requires hours for recovery. Since the spontaneous rate of neural stimulation is predominantly in the low frequency range, this component of fatigue is of particular clinical importance. Fatigue of the inspiratory muscles leads to acute respiratory acidosis, but before carbon dioxide retention occurs, it can be recognized from characteristic symptoms and signs. These include dyspnea which responds to mechanical ventilation, rapid shallow breathing, and asynchronous movements of the chest and abdomen. Inspiratory muscle fatigue must be treated by putting these muscles to rest, by mechanically supporting ventilation. In addition, underlying metabolic nutritional and circulatory abnormalities must be corrected and infection treated. Aminophylline and isoproterenol can restore inspiratory muscle contractility, but controlled clinical trials remain to be done regarding their application in acute and chronic respiratory failure. Inspiratory muscle training improves strength and endurance in patients with obstructive lung disease, cystic fibrosis, and spinal cord injury, but does not always improve physical exercise performance. Again, more work is needed to develop the indications for inspiratory muscle training and to determine the optimum type and duration of the training regimen.

Airway Obstruction↗
PubMed1983

Respiratory muscle and pulmonary function in polymyositis and other proximal myopathies.

We studied 53 patients with proximal myopathy to determine at what level of muscle weakness hypercapnic respiratory failure is likely, and which tests of pulmonary function or respiratory muscle strength would best suggest this development. Respiratory muscle strength was determined from maximal static efforts and in half the patients, both inspiratory and expiratory muscle strengths were less than 50% of normal. In the 37 patients without lung disease respiratory muscle weakness was accompanied by significant decreases in vital capacity, total lung capacity, and maximum voluntary ventilation; by significant increases in residual volume and arterial carbon dioxide tension (PaCO2); and greater likelihood of dependence on ventilators, atelectasis, and pneumonia. Hypercapnia was particularly likely when respiratory muscle strength was less than 30% of normal in uncomplicated myopathy, and when vital capacity was less than 55% of the predicted value in any patient.

Adult↗
PubMed1983

Power spectral analysis of the diaphragm electromyogram.

We studied the power spectrum of the diaphragm electromyogram (EMG) at frequencies between 31 and 246 Hz in four young normal subjects and five patients with chronic obstructive lung disease (COPD). Diaphragm EMGs were analyzed during spontaneous breathing and maximum inspiratory efforts to determine the effect of signal-to-noise ratio on the power spectrum and if treadmill exercise to dyspnea was associated with diaphragm fatigue. We found that the centroid frequencies of the power spectra (fc) were strongly correlated (r = 0.93) with ratios of power at high frequencies to power at low frequencies (H/L) for all subjects. Of the two indices, H/L had the largest standard deviation expressed as a percentage of the mean. The mean values of both of these decreased significantly after exercise, fc from 100.2 to 97.3 and H/L from 1.07 to 0.97. Signal-to-noise ratios were higher in maximal inspiratory efforts and after exercise in normal subjects and higher in COPD patients. The signal-to-noise ratio was correlated negatively with fc and H/L, indicating that these indices of the shape of the power spectrum are influenced by signal strength and noise levels as well as muscle function. We conclude that the fc and H/L index similar qualities of the power spectrum, that they are partially determined by the signal-to-noise ratio, and that, in some cases, exercise to dyspnea is associated with apparently mild diaphragm fatigue.

Adult↗
PubMed1982

Effect of body weight and muscularity on human diaphragm muscle mass, thickness, and area.

To assess the consequences to the human diaphragm of alterations in body weight and muscularity, we measured the mass, thickness, area, and length of diaphragm muscle at necropsy. Of 33 subjects who were clinically well until sudden death, 27 had sedentary occupations and normal weight (group N), while 6 were nonobese laborers whose average weight was 40% greater than normal (group M). Among 37 patients dying of more prolonged illness, 23 were of normal weight (group W), while 14 weighed 71% of normal (group U). Subjects with obesity, chronic pulmonary disease, or edema were excluded. Disease per se did not significantly affect diaphragm dimensions. However, in group M diaphragm muscle mass, thickness, area, and length were 165, 129, 125, and 117% of normal (P less than 0.005), whereas in group U the corresponding values were 57, 73, 77, and 83% (P less than 0.001). Thus alterations in body weight and muscularity profoundly affect diaphragm muscle mass, causing a nearly threefold variation between muscular normal subjects and underweight patients.

Adolescent↗
PubMed1982

Force-length relationship of the normal human diaphragm.

To characterize the in vivo force-length relation of the human diaphragm, we related pressures during static inspiratory efforts (Pmus and Pdi, respiratory muscle and transdiaphragmatic pressures, respectively) to diaphragm lengths measured on chest X rays from 22 normal subjects. At total lung capacity, the intersection of diaphragm and chest wall contours corresponds to the anatomic junction of diaphragm and chest wall. This point is located by skeletal landmarks to reveal the entire diaphragm contour on films taken at lower lung volumes. To validate the X-ray measurements, corresponding diameters were measured on 32 normal diaphragms at necropsy. After correction for height and diaphragm position, in vivo and necropsy length estimates along the coronal section agreed within 9%. The diaphragm length-lung volume relation is curvilinear, with length increasing primarily in the portion of the diaphragm apposed to the chest wall. As length increases, Pmus and Pdi rise sharply then plateau, generally conforming to force-length behavior of isolated muscle. However, absence of a Pdi peak at presumed diaphragm resting length suggests that Pdi is submaximal during voluntary inspiratory effort.

Adult↗
PubMed1982

Respiratory muscle strength and maximal voluntary ventilation in undernourished patients.

To assess the effect of chronic debilitation on respiratory muscle function, we studied 16 poorly nourished (PN) patients without pulmonary disease, and 16 well-nourished (WN) subjects matched for age and sex. Body weight, vital capacity (VC), maximal voluntary ventilation (MVV), and maximal static inspiratory and expiratory pressures (PImax and PEmax) were measured and expressed as percent predicted. Respiratory muscle strength (RMS) was calculated as (% PImax + % PEmax)2. Body weight was 71% predicted in the PN group and 104% in the WN group. The RMS, MVV, and VC were 37%, 41%, and 63%, respectively, of the values in the WN group (p less than 0.001). The 60% reduction in RMS was shared almost equally among inspiratory and expiratory muscles, and PEmax was linearly related to body weight. Because malnutrition reduces both respiratory muscle strength and MVV, it may well impair respiratory muscle capacity to handle increased ventilatory loads in thoracopulmonary disease.

Adolescent↗