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Biomedical subjects

D C Shannon

Publications and source records attributed to D C Shannon.

At least 19 recordsLinked to original sources
PubMed1992

Phase delay of pulmonary acoustic transmission from trachea to chest wall.

The frequency-dependent propagation time, or phase delay tau (f), of sonic noise transmission from the trachea to the chest wall was estimated over the 100-600 Hz frequency range using a phase estimation technique from measurements performed on eight healthy subjects. Since tau (f) can be greater than one period of the input signal at frequencies greater than 100 Hz, the unambiguous phase estimate at 100 Hz was used as a starting-point to determine the phase angle H(f) and tau (f) at higher frequencies under the constraint that the spectra did not exhibit large point-to-point discontinuities. The resulting tau (f) range of 0.9-4.1 ms is consistent with sound propagation to the chest wall through both airways and surrounding parenchyma. The frequency and spatial dependence of tau (f) indicates that with increasing frequency more sonic energy travels further into the branching airway structure before coupling into the parenchyma. These results suggest that information concerning distinct regional lung structures may be obtained by probing the system acoustically over selected frequency bands.

Acoustics↗
PubMed1992

Respiratory system stability and abnormal carbon dioxide homeostasis.

We have tested the hypothesis that interactions among eight parameters of the respiratory and cardiovascular systems that determine the loop gain (LG) of the respiratory CO2 feedback control system might account for the degree of stability or instability of breathing patterns in healthy sleeping volunteers as well as in familial dysautonomia (FD) and congenital central hypoventilation syndrome (CCHS) patients. The predictability of cycle duration was tested as well. We measured the values of CO2 sensitivity, CO2 delivery capacity in the circulation, circulation delay, mean lung volume for CO2, and mixed venous PCO2 in 8 FD patients, 2 CCHS patients, and 19 healthy controls. The values of these parameters were used in a mathematical model to compute the LG of the respiratory control system during sleep for each epoch of respiration analyzed. The strength of the ventilatory oscillations (R) was quantified using power density spectra of the ventilation time series. All subjects were studied at inspiratory O2 concentrations (FIO2) of 0.21 and 0.15; CCHS patients and controls were also studied at 0.12 FIO2 to examine the effect of steady-state hypoxia on respiratory system stability. In 2 FD patients, LG was elevated at both levels of FIO2 and periodic breathing was observed; the values of R were elevated. Elevated mixed venous PCO2 and reduced CO2 delivery capacity were chiefly responsible for the abnormally high LG observed. In three healthy volunteers, high LG and unstable patterns were associated with high chemosensitivity. The CCHS patients, however, remained stable even at 0.12 FIO2 because LG remained equivalent to zero due to a lack of chemosensitivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Cellular interstitial pneumonitis in infants. A clinicopathologic study.

Five infants had interstitial pneumonitis with constant histologic findings, which was different from that previously described in children. All the infants presented with tachypnea at birth and persistent disease, both clinically and radiographically, despite treatment. Open-lung biopsy in each case showed a diffuse interstitial thickening due to pale oval and spindle-shaped histiocytes without scarring. This neonatal cellular interstitial pneumonitis differs both clinically and histologically from the usual interstitial pneumonitis, lymphocytic interstitial pneumonitis and desquamative interstitial pneumonitis observed in adults and children. The etiology of this cellular interstitial pneumonitis in neonates is unknown.

Biopsy↗
PubMed1992

Prospective identification of the risk of SIDS.

In the general population, there are a number of epidemiologic and physiologic factors that have been identified as increasing the risk for SIDS. To date, optimum combinations of these factors do not sufficiently discriminate the high-risk infant in order to serve as a basis for prospective screening. In the subsequently born sibling, the risk is only slightly increased, and, again, there are no factors that discriminate the infant at risk of death. Among infants who have sustained an ALTE, there are several identifiable causes or physiologic factors associated with high risk for a repeated event. This article has reviewed the association between risk factors and death in each of these three categories of patients.

Apnea↗
PubMed1990

Does lithium carbonate affect the ion transport abnormality in cystic fibrosis?

Lithium is known to affect several aspects of cellular regulation which may be related to ion channel function in epithelial cells. To determine whether the ion transport abnormality in cystic fibrosis (CF) is affected by lithium with resultant changes in clinical status, 36 CF patients, 12-37 years old, were enrolled in a 14 week, double-blind, placebo-controlled trial. Eighteen patients were randomly assigned to receive lithium carbonate for 10 weeks. At the end of therapy their average serum lithium concentration was 0.56 +/- 0.06 mmol (SEM) per liter. Their sweat chloride concentration fell from 92.1 +/- 4.8 mmol per liter to 87.4 +/- 4.0 mmol per liter after 10 weeks of therapy (P = 0.07) and rose to 94.4 +/- 3.5 mmol per liter 4 weeks after end of therapy (P less than 0.001 compared to results at end of therapy). Their forced vital capacity (FVC) fell from 72 +/- 5.3% of predicted to 66 +/- 5.1% of predicted after 4 weeks of therapy (P less than 0.01), and their forced expiratory volume in one second (FEV1) fell from 56 +/- 5.5% of predicted to 51 +/- 5.5% of predicted after 4 weeks of therapy (P less than 0.01). In a non-blind assessment, performed 19 weeks after the end of therapy, their FVC and FEV1 had risen and were not significantly different from baseline. Sweat chloride, FVC, and FEV1 remained unchanged in the placebo group throughout the period of study.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

Interaction between respiratory and RR interval oscillations at low frequencies.

Oscillations in RR interval between 0.02 and 1.00 cycles per second (Hz) have been related to the action of the autonomic nervous system. Respiration has been shown to influence RR interval at normal breathing frequencies between approximately 0.16 and 0.5 Hz in children and adults--a phenomenon known as respiratory sinus arrhythmia. In this study we investigated the effect of respiration on RR interval in a lower frequency range between 0.02 and 0.12 Hz. Low frequency oscillations in respiration were induced in healthy sleeping adult subjects via the administration of a bolus of CO2 during inhalation. Power spectra of RR interval and respiration were obtained before and after the CO2 pulse, and the frequency content in the low frequency range was quantitatively compared. An increase in the spectral energy in both respiration and RR interval was observed for the group. However, this increase was accounted for by six of 29 epochs. We conclude that respiration (tidal volume) can influence RR interval at frequencies below those usually associated with respiratory sinus arrhythmia. This influence may be mediated through a sympathetic reflex. This result is applicable to the measurement and interpretation of heart rate variability and to autonomic influences of low frequency fluctuations in RR interval.

Adolescent↗
PubMed1990

Supercarbia in children: clinical course and outcome.

Supercarbia (PCO2 greater than or equal to 150 torr) may result in a number of pathophysiologic conditions in experimental models and in humans. We report the clinical course and outcome after supercarbia secondary to hypoventilation in five children. Supercarbia resulted from severe airway obstruction in four children and central hypoventilation in one. Maximal PCO2 values ranged from 155 to 269 torr (mean 206). The time course to development of maximal PCO2 was between 35 min and 2 days. The pH ranged between 6.76 and 7.10 (mean 6.86). No patient was severely hypoxemic (PaO2 less than or equal to 55 torr) during the supercarbia period. Despite very high levels of PCO2 and low pH, the only pathophysiologic change found was temporary depression of neurologic function manifested by stupor or coma. Long-term follow-up of these patients has shown no serious adverse neurologic or developmental effects.

Airway Obstruction↗
PubMed1990

Spectral characteristics of sound transmission in the human respiratory system.

The amplitude of sound transmission from the mouth to a site overlying the extrathoracic trachea and two sites on the right posterior chest wall over the 100-600 Hz frequency range was measured in eight healthy adult subjects. An acoustic driver and a rigid tube were employed to introduce sound into the mouths of the subjects at resting lung volume, and the transmission measurements were performed using lightweight accelerometers. Similar spectral characteristics of acceleration were observed in all of the subjects showing peaks in the transmission. These characteristics included 1) two regions of increased transmission over the frequency range of the measurements, 2) a decrease in the magnitude of acceleration of the chest wall as compared to the tracheal site of roughly 20 dB at lower frequencies, 3) a strong trend of decreasing acceleration of the chest wall with increasing frequency. These spectra agreed favorably with the predictions of a theoretical model of the acoustical properties of the respiratory system. The model suggests the primary structural determinants of a number of the observed characteristics including the importance of the lung parenchyma in sound attenuation.

Adult↗
PubMed1990

Transfer function of sound transmission in subglottal human respiratory system at low frequencies.

The amplitude of sound transmission from the mouth to a site overlying the extrathoracic trachea and two sites on the posterior chest wall was measured in eight healthy adult male subjects at resting lung volume over the 100- to 600-Hz frequency range. The ratios of the estimated magnitude spectra of transmission of each of the chest wall sites to the tracheal site were determined, with the resulting spectra representing effective transfer functions of transmission in the subglottal system. For the group, the transfer functions exhibited a single peak, which occurred at 143 +/- 13 Hz (mean +/- SD) with a quality factor (Q) of 2.0 +/- 0.2 for the upper chest wall site and at 129 +/- 6 Hz with a Q of 2.2 +/- 0.4 for the lower site. The trend of decreasing spectral energy with increasing frequency was indicated by roll-offs of -10 +/- 4 and -17 +/- 5 dB/octave from 300 to 600 Hz at the two sites, respectively. The fundamental radial mode of a model thoracic cavity, which is a large rigid cylinder filled with lossless lung tissue, provides a good estimate of the observed low-frequency resonance. This agreement suggests that thoracic cavity resonances may have particularly important effects on sound transmission at frequencies below approximately 250 Hz, where the magnitude of parenchymal attenuation appears to be small.

Adult↗
PubMed1989

Rational monitoring of respiratory function during mechanical ventilation of infants and children.

Oxygen and carbon dioxide homeostasis (effective pulmonary gas exchange) requires that lung exchange matches tissue exchange. The movement of gas in and out of the lung is determined by the mechanical properties of the system especially resistance and compliance and the work needed to provide this movement is supplied either by the patient's muscles or by the mechanical ventilator. If the latter is required, its optimal use demands that the user understands the relationship between the mechanical device and the mechanical properties of the patient's respiratory system so that optimal gas exchange can be provided. The following discussion provides the minimum physiological information needed for successful use of a mechanical ventilator and suggests that this requires measurement of at least four parameters: alveolar partial pressure of CO2 (PACO2), arterial oxygen saturation (SaO2), the mechanical RC time constant (RC) and functional residual capacity (FRC).

Carbon Dioxide↗
PubMed1989

A model of acoustic transmission in the respiratory system.

A theoretical model of sound transmission from within the respiratory tract to the chest wall due to the motion of the walls of the large airways was developed. The vocal tract, trachea, and the first five bronchial generations are represented over the frequency range from 100 to 600 Hz by an equivalent acoustic circuit. This circuit allows the estimation of the magnitude of airway wall motion in response to an acoustic perturbation at the mouth. The radiation of sound through the surrounding lung parenchyma is represented as a cylindrical wave in a homogeneous mixture of air bubbles in water. The effect of thermal losses associated with the polytropic compressions and expansions of these bubbles by the acoustic wave is included and the chest wall is represented as a massive boundary to the wave propagation. The model estimates the magnitude of acceleration over the extrathoracic trachea and at three locations on the posterior chest wall in the same vertical plane. The predicted spectral characteristics of transmission are consistent with previous experimental observations. This theoretical approach suggests that the locations of the spectral peaks are a strong function of the geometry and the wall properties of the airways, while the attenuation at higher frequencies is primarily associated with the absorption of sound in the parenchyma.

Animals↗
PubMed1989

Breath-by-breath respiratory timing and volume control during periodic breathing.

We examined the control of respiratory pattern during non-rapid-eye-movement sleep-related periodic breathing (PB) in adults, with and without hypoxia. We analyzed 186 cycles of PB from 18 epochs occurring in eight subjects; the mean (+/- SD) cycle duration was 30.8 +/- 8.4 s. Significant oscillations occurred in inspired tidal volume (VT), inspiratory duration (TI), mean inspired flow, inspired minute ventilation, and expiratory duration (TE) (P less than 0.005). For each epoch of PB, moving cross-correlation (MCC) functions were employed to describe the time-dependent intervariable relationships between 1) TI vs. TE, 2) VT vs. TE, and 3) VT vs. breath duration (TT) as synchronization, a strong and consistent intervariable correlation; relative coordination (RC), a weaker interaction characterized by an unstable MCC function oscillating at a subharmonic of the PB frequency; or as independence, with no statistical evidence of interaction. Fourteen epochs showed RC between TI and TE, 11 and 12 of which also showed RC between VT and TE, and VT and TT, respectively. In 4 epochs negative synchronization was exhibited by all three variable pairs. In no case were the oscillations between any pair of variables independent. The modes of coupling between variables were not correlated to O2 saturation, end-tidal CO2 levels, or inspired O2 level. We conclude that during sleep-related PB a nonrandom but weak coupling usually exists between TI and TE, VT and TE, and VT and TT.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1989

Pneumogram recordings in infants resuscitated for apnea of infancy.

Infants who sustained a spell of apnea of infancy during which they were resuscitated have been shown to be at increased risk for sudden infant death syndrome. To determine the value of the pneumogram as a predictor of outcome in this population, the first pneumogram obtained of 51 such infants was analyzed. The infants were grouped on the basis of subsequent outcome during a course of monitoring: group 1--infants who died during a subsequent event; group 2--infants who received resuscitation or vigorous stimulation to terminate a subsequent spell; group 3--infants who survived and did not have a significant subsequent episode. The results for these infants were compared with those of a control group matched for age and sex. A detailed, blinded computer analysis revealed no significant difference in the results of the pneumogram analysis between the three groups. It did not identify the infants in whom apneic spells necessitating resuscitation subsequently developed or those who died. However, when compared with the control group, infants with apnea of infancy had significantly higher mean respiratory rates, heart rates, and tachycardia indexes. It is concluded that, although the first pneumogram does not predict the risk of an adverse outcome in a population of infants with severe apnea of infancy, it does reveal subtle cardiorespiratory differences between study and control infants.

Bradycardia↗
PubMed1988

Bilateral abductor paresis masquerading as asthma.

Rare upper airway lesions may be mistaken for asthma. A 16-year-old Hispanic male athlete presented to our allergy clinic with a 4-month history of wheezing and snoring with hoarseness and progressive fatigue on exertion or during sleep. His mother taped periods of harsh stridor and sleep apnea. There was no family history of vocal cord abnormalities. A year before the onset of symptoms, he suffered injury to his oral cavity with a loss of consciousness during a wrestling match. He denied dysphagia or dysphonia. He failed to respond to bronchodilators, cromolyn, or prednisone therapy during 4 weeks. On referral to our clinic, his physical examination and tape recording were characterized by harsh inspiratory stridor. His pulmonary function tests were significant for peak flow depressed out of proportion to FEV1 with reduced FVC, no response to bronchodilator, and flattened inspiratory loop unresponsive to cough or panting. Fluoroscopy and endoscopy of the upper airway was consistent with "marked bilateral limitation of vocal cord abduction." Sleep study demonstrated desaturation with CO2s in the 60s during sleep. He was started on continuous positive airway pressure, 10 cm at night, with no desaturation or sleep disturbance on follow-up.

Adolescent↗