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Biomedical subjects

N S Arora

Publications and source records attributed to N S Arora.

At least 19 recordsLinked to original sources
PubMed2001

Utility of transesophageal echocardiography for the characterization of cardiovascular anomalies associated with Turner's syndrome.

This case illustrates the complementary value of transesophageal echocardiography to routine transthoracic echocardiography in an asymptomatic adult patient with Turner's syndrome. The combined findings of bicuspid aortic valve, severe aortic dilation, coarctation of the aorta, and type A aortic dissection were clearly delineated by transesophageal echocardiography.

Aortic Dissection↗
PubMed1987

COPD and human diaphragm muscle dimensions.

To assess the effect of COPD on diaphragm muscle dimensions, we measured diaphragm muscle mass, thickness, area, and lengths in 18 COPD patients at necropsy. We compared these results with data obtained from 22 non-COPD patients matched with regard to age, height, weight, and sex distribution. In the COPD patients, diaphragm muscle mass was 213 +/- SD 69 g, thickness was .320 +/- .055 cm, area was 647 +/- 160 cm2, coronal muscle length was 27.8 +/- 4.0 cm and sagittal muscle length was 15.8 +/- 2.8 cm. These values were within +/- 8 percent of the comparable values in the non-COPD patients, with no significant differences. There was no correlation between diaphragm length and lung volume in 13 COPD patients with TLC and ten with RV measurements. We conclude that over the range of lung volume encountered (TLC 135 +/- 28 percent predicted, RV 102 +/- 29 percent predicted TLC), there is no evidence for permanent shortening of the diaphragm.

Adaptation, Physiological↗
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↗
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↗
PubMed1983

Sleep apnea syndrome after poliomyelitis.

We present a case of severe breathing abnormality during sleep in a young man who had had poliomyelitis 20 yr before. His sleep disorder led to respiratory failure and cor pulmonale, which were greatly improved by oxygen therapy. A study of this case and those previously described supports the notion that brainstem damage during acute poliomyelitis is important in the later appearance of sleep-disordered breathing. In addition, such patients usually have mechanical abnormalities involving the thoracic cage and respiratory muscles. These ventilatory restrictions amplify the pathophysiologic effects of abnormal central nervous system control of breathing during sleep, and we suggest that their presence has a key role in the development of sleep apnea syndrome in these patients.

Adult↗
PubMed1982

The pulmonary manifestations of lymphomatoid granulomatosis.

The pulmonary manifestations of 5 biopsy-proved cases of lymphomatoid granulomatosis are discussed. Two patients had diffuse reticulonodular infiltration of the lungs, thought to represent infiltrates of lymphomatoid granulomatosis. Three had nodular densities of varying size and distribution, with radiologically normal intervening lung, and biopsy suggested that these represented infarcts; the actual infiltrates of lymphomatoid granulomatosis were below the limits of resolution of the chest radiograph.

Adult↗
PubMed1982

Respiratory mechanics in supine subjects during progressive partial curarization.

Respiratory mechanics were studied in six supine conscious volunteers during progressive muscle weakness produced by infusion of d-tubocurarine. Partial curarization was carried out to the point of abolishing head lift ability and handgrip strength. At all levels of partial paralysis, expiratory muscle strength was significantly more impaired than inspiratory strength. Despite this, subjects maintained relatively normal maximal expiratory flow rates, whereas inspiratory flows decreased significantly. The diminished inspiratory flows are not fully explained by decreased driving pressures during force inspiration, since inspiratory resistance increased significantly with the decreased flow. Inspiratory flow patterns suggest a variable extrathoracic obstruction most likely due to the absence of normal airway abductor activity during inspiration. Maximal respiratory muscle weakness decreased forced vital capacity by 29% and total lung capacity by 15%. The decreased level of lung inflation did not alter lung elastic recoil. Functional residual capacity was unchanged, but inspiratory capacity decreased by 25% and residual volume increased by 38%. These changes are in accord with predictions based on the decreased muscle strength and normal respiratory system recoil.

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

Stapedius reflex in curarized subjects: an index of neuromuscular weakness.

To examine the validity of the acoustical stapedial reflex (AR) as an index of neuromuscular weakness, the AR was measured along with other indices of muscle strength during administration of d-tubocurarine (dTc) to six healthy subjects. AR decreased immediately after each dTc dose and preceded changes in handgrip strength and respiratory muscle strength, but the peak effects of each dose similarly affected AR and other muscle strength. The findings with electrocutaneous stimulation and effects on growth function of the AR indicate that dTc affects primarily stapedius muscle contraction, the efferent portion of the reflex arc, and does not affect afferent or central portions of the reflex. We therefore conclude that the AR is a valid index of the integrity of neuromuscular transmission which promptly reflects early phase weakness. Unlike other measures of muscle strength, AR testing does not depend on subject cooperation, and involves no discomfort. The test therefore provides a useful means of assessing neuromuscular weakness.

Adult↗
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↗
PubMed1982

The influence of airway obstruction and respiratory muscle strength on maximal voluntary ventilation in lung disease.

To assess the effects of airway conductance (Gaw) and respiratory muscle strength (RMS) on maximal voluntary ventilation (MVV), we studied 8 normal subjects (N), 8 patients with interstitial lung disease (ILD), and 16 with chronic airflow limitation (CAL). In the patients with ILD, RMS explains 83% of the variance in MVV (p less than 0.005), but Gaw explains none. In the patients with CAL, Gaw and RMS explain, respectively, 65 and 34% of the variance in MVV (p less than 0.02). Considering Gaw and RMS together increases the explained variance to 77% (p less than 0.005). In groups CAL and N combined, Gaw and RMS explain 86% of the variance in MVV, with 71% explained by Gaw and 34% by RMS, which the other variable alone failed to explain (p less than 0.005). When the data are normalized for age, sex, height, and lung volume, the influence of %RMS on %MVV is halved, but remains significant (p less than 0.05). We conclude that RMS is a primary determinant of MVV in patients with ILD, and an important determinant in patients with CAL.

Adult↗