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Biomedical subjects

D H Simmons

Publications and source records attributed to D H Simmons.

At least 19 recordsLinked to original sources
PubMed1989

Diaphragmatic contraction during assisted mechanical ventilation.

Indirect evidence from airway pressure recordings in mechanically ventilated patients suggests that the diaphragm exhibits contractile activity beyond that required to trigger a ventilator-assisted breath. We used the diaphragmatic EMG to provide direct evidence of persistent contractile activity and studied the effects of alterations in ventilator-delivered flow rate and tidal volume on the duration of diaphragmatic contraction. The duration of contraction was expressed in terms of inspired volume. During a single breath, diaphragmatic force generation ceases at the point of peak electromyographic activity; hence, the inspired volume at peak EMG is the volume at the diaphragmatic off-switch (Voff). Ventilator-delivered flow rate and tidal volume were varied during assisted (patient-initiated) and controlled (ventilator-initiated) breaths while diaphragmatic EMG and inspired volume were recorded simultaneously in ten patients with a variety of illnesses requiring mechanical ventilation. Spontaneous ventilator-unassisted breaths were also recorded for comparison. We found that (1) during assisted breaths, diaphragmatic activity continued after the ventilator was triggered, (2) Voff was usually close to spontaneous tidal volume, (3) Voff increased significantly as ventilator-delivered flow rate increased, and (4) controlled breaths may also be associated with phasic electromyographic activity. The data have implications for resting patients on assisted ventilation.

Adult↗
PubMed1988

Work of breathing and airway occlusion pressure during assist-mode mechanical ventilation.

We determined the effect of varying ventilator tidal volume (VT) and inspiratory flow (V) on the inspiratory muscle work (WI) during assist-mode mechanical ventilation (AMV) in four healthy subjects. In another four subjects, under constant chemoreceptor input, we determined the responses of neuromuscular output as assessed by the mouth occlusion pressure (P0.1) to alteration in WI. During AMV, the inspiratory external work of breathing is partitioned between WI and ventilator work. With a constant ventilator trigger sensitivity, we calculated WI (joules/L of volume) as the difference between the area subtended by the airway pressure-inspiratory volume curves and the ordinate of the assisted breaths subtracted from that of the controlled breaths at ventilator V of 40, 60 and 80 L/min and ventilator VT of 100, 125 and 150 percent spontaneous breathing VT. At all ventilator settings, WI was less than inspiratory muscle work of spontaneous breathing (SB) and was a function of both ventilator VT and V (p less than 0.05), but ventilator V has more effect on WI. Under isocapnia and hyperoxia, we measured P0.1 and WI during AMV at ventilator VT of 125 percent of spontaneous breathing VT and ventilator V of 60, 80 and 100 L/min. End-expiratory lung volume remained constant. P0.1 during AMV was similar to that of the SB. Although WI decreased with increasing ventilator V, P0.1 did not decrease significantly. We conclude that during AMV, both ventilator V and to a less extent ventilator VT determine W. In healthy subjects changes in WI do not affect P0.1.

Airway Resistance↗
PubMed1988

Complications of gastroesophageal reflux.

An edited summary of an Interdepartmental Conference arranged by the Department of Medicine of the UCLA School of Medicine, Los Angeles. The Director of Conferences is William M. Pardridge, MD, Professor of Medicine. Several specialists have recently recognized that gastrointestinal reflux causes complications resulting in significant disease. It causes discomfort, indigestion, esophagitis, Barrett's esophagus, and carcinoma of the esophagus. Pediatricians attribute many early pulmonary problems, and even some sudden deaths in infants, to the reflux of gastric contents. Otolaryngologists now recognize that many cases of nonbacterial, nonspecific pharyngitis and laryngitis are due to the reflux of gastrc acid secretions. Contact granuloma and cancer of the larynx may, in some instances, be secondary to nocturnal reflux. Thoracic surgeons and pulmonologists believe chronic tracheobronchitis and some cases of pulmonary disease are attributable to recurrent bathing of the respiratory epithelium by aspirated gastric contents. An awareness of the many complications of gastrointestinal reflux should lead to a multidisciplined attack on the factors responsible for these diseases.

Esophageal Diseases↗
PubMed1986

Respiratory drive and timing during assisted ventilation in dogs.

In 8 anesthetized dogs, during isocapnic hyperoxia we studied the effect of assisted ventilation (AV) on ventilatory drive, inspiratory off-switch volume (Voff) and duration of inspiratory diaphragmatic activity (Tdi). Tidal volumes (Vt) during AV were double spontaneous Vt. Two electrodes were inserted in the diaphragm to obtain the electromyogram (EMG). The index of ventilatory drive was the EMG 0.3--i.e., the amplitude of the moving average EMG 300 ms after the onset of inspiratory activity. AV decreased EMG 0.3 but had no effect on Voff and Tdi. Vagotomy not only abolished the reduction in drive, but may have increased drive during AV.

Animals↗
PubMed1979

Diagnostic value of fiberoptic bronchoscopy in lung cancer presenting as mediastinal mass(es).

The diagnostic yields of prebonchoscopy sputum specimens and fiberoptic bronchoscopy (including brushings, washings, and/or biopsies) were determined in 35 patients who presented primarily with middle or anterior mediastinal and/or paratracheal mass(es) on chest radiographs. The diagnosis was confirmed on histopathology of tissue obtained by needle biopsy, mediastinoscopy, thoracotomy, and/or autopsy. Thirty-one of the patients were found to have primary bronchogenic carcinomas. At bronchoscopy, extrinsic compression of trachea and/or bronchi was visualized in 23 (Group I) and the tracheobronchial tree appeared normal in 12 (Group II). Prebronchoscopy sputa gave a positive yield in only three of the 35 (8%) patients; the yield was similar in both groups of patients. One or more of the bronchoscopic modalities were diagnostic in 69% of Group I patients but were not helpful in Group II patients. The diagnostic yield of brushings, washings, and biopsies in Group I patients was 52%, 61%, and 37%, respectively. The addition of biopsies to washings and/or brushings did not significantly alter the yield. Washings and brushings are recommended as useful, non-invasive procedures in diagnosing middle mediastinal masses with extrinsic compression. Sputum cytology gives a very low yield.

Bronchoscopy↗
PubMed1979

Adult respiratory distress syndrome.

Many causes for the adult respiratory distress syndrome (ARDS) have been reported, all with common pathologic, pathophysiologic and biochemical end results. The final common pathway may involve changes in lung content of a critical enzyme, superoxide dismutase, or alterations in surfactant metabolism, or both. The early assumption that the disorder is partially due to oxygen toxicity from inspired oxygen concentrations greater than 60 percent is consistent with findings of recent biochemical studies. Although the lung normally maintains its alveoli dry, during ARDS increased permeability of small pulmonary vessels results in primary pulmonary edema, in contrast to edema from increased vascular pressure. These data have been obtained mainly in animals; whether they apply to humans with ARDS is not certain. Tissue oxygenation is improved by increasing end-expiratory pressure in an animal model of ARDS, more effectively during spontaneous breathing than during mechanical ventilation. During spontaneous breathing, adverse ventilatory effects were caused by stimulation of pulmonary reflexes.

Humans↗
PubMed1978

Effects of continuous positive airway pressure after oleic acid-induced lung injury in dogs.

The physiologic effects of continuous positive airway pressure (CPAP) of 5,10,15, and 20 cm H2O during spontaneous ventilation were studied in six anesthetized dogs with simulated respiratory distress syndrome (RDS) induced by iv infusion of oleic acid and in three normal controls. After oleic acid, mean PaO2 dropped to 63.6 +/- 3.1 mm Hg while breathing 100% oxygen and mean shunt fraction was 48.3 +/- 3.0%. PaO2 and shunt fraction improved significantly at the two highest levels of CPAP (e.g.,PaO2 271.3 +/- 41.3 mm Hg and shunt fraction 17.8 +/-2.2% at 20 cm H2O CPAP). Mean mixed venous PO2 rose from 37.4 +/- 1.5 mm Hg with no CPAP TO 60.8 +/- 3.1 mm Hg at 20 cm H2O CPAP. Tissue oxygenation appeared to improve during CPAP, since cardiac output, oxygen delivery, and serum lactate were not significantly affected and mixed venous PO2 rose significantly. However, significant hypoventilation occurred at all but the lowest level of CPAP, mean PaCO2 rising from 44.1 +/- 1.8 mm Hg with no CPAP to 77.6 +/-6.8 mm Hg at 20 cm H2O CPAP. The hypoventilation during CPAP is consistent with increased work of breathing due to a combination of decreased lung compliance and increased dead space ventilation due to rapid, shallow breathing.

Animals↗
PubMed1978

Diagnostic value of fiberoptic bronchoscopy in metastatic pulmonary tumors.

The fiberoptic bronchoscopic procedure (with brushings, washings, and biopsies) was performed and specimens of sputum were obtained before the procedure in 37 patients with cancer metastatic to the lung. Of the 37 patients studied, endobronchial lesions were visualized at bronchoscopic examination in 14 (group 1), and no endobronchial lesion was seen in 23 (group 2). The yield of bronchial brushing and washings was not significantly different in group 1 and 2, whereas examination of sputum obtained before the bronchoscopic procedure and bronchial biopsy in group 1 yielded higher results than the same procedures in group 2. The radiographic findings did not influence the yield with any of the bronchoscopic procedures. The overall positive diagnostic yield from fiberoptic bronchoscopic procedures among these patients was 54 percent (20/37), regardless of their bronchoscopic or radiologic findings.

Biopsy↗
PubMed1977

Effects of hydration and physical therapy on tracheal transport velocity.

A new tracer method for quantitative measurement of tracheal transport velocity (mm per min) in dogs has been described. Using the same technique, the effects of dehydration, rehydration, postural drainage, and chest percussion on tracheal transport velocity were studied. Mean tracheal transport velocity decreased significantly (14.1 +/- 1.4) after dehydration (P less than 0.05) and reverted to normal (19.0 +/- 1.3) with rehydration in 10 dogs. After postural drainage in 7 dogs, mean tracheal transport velocity increased 39.7 +/- 1.78 (SE) per cent (P less than 0.01). After chest percussion in 6 dogs, mean tracheal transport velocity increased 50.9 +/- 1.22 (SE) per cent. With combined postural drainage and chest percussion, mean tracheal transport velocity increased 50.0 +/- 0.32 (SE) per cent. Although maximal improvement occurred after the combined therapy, the changes were not significantly different from those observed with each therapy alone. These therapeutic measures have been used empirically in the past. The present study gives some objective evidence for their beneficial effects in anesthetized dogs.

Animals↗
PubMed1977

A systematic error in the determination of blood PCO2.

An analysis was made of the effect of sodium heparin solution on the determination of arterial blood PCO2, pH, and bicarbonate. Dilution of blood by heparin solution did not affect the pH of blood samples significantly but reduced the measured PCO2 and th calculated bicarbonate and base excess in direct proportion to the amount of dilution. Used in the usual quantities as an anticoagulant, lubricant, and filler of needle and syringe dead space, heparin solution caused a 17 per cent or greater reduction in PCO2 and bicarbonate in approximately 17 per cent of the arterial blood samples currently received for analysis in a university hospital laboratory. Such unrecognized errors could cause misinterpretations of acid-base status. Completely filling the sampling syringe with blood and using a small-gauge needle will reduce the error.

Bicarbonates↗
PubMed1977

Measurement of mucociliary transport velocity in the intact mucosa.

A new method for measuring the velocity of the tracheal mucous transport rate in anesthetized dogs is described. The length of the trachea is determined with the bronchoscope as the distance between the larynx and the lower end of the trachea at the level of the carina. A small volume (0.04 to 0.1 ml) of albumin microspheres 5 mgm to 7 mum in diameter labeled with radioactive 99m technetium or 113m indium is deposited on the mucosal surface at the lower end of the trachea via a catheter placed in the inner channel of a fiberoptic bronchoscope. The movement of the microspheres towards the larynx is visualized and recorded using a scintallation camera (Picker Dyna Camera) with a large field of view (30 cm in diameter) for 30 to 60 minutes, depending upon the time required for the spheres to reach the top of the trachea. Polaroid pictures are made immediately and every minute thereafter until the activity reaches the larynx. The data are also recorded and stored on magnetic tape for subsequent analyses by computer. The length in millimeters divided by the time in minutes gives the transport velocity rate. The mean velocity was found to be 19.2 +/- 1.6 mm/min (+/- SE).

Animals↗