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Biomedical subjects

G Volgyesi

Publications and source records attributed to G Volgyesi.

11 recordsLinked to original sources
PubMed1995

Dynamic measurement of tracheal diameter in dogs.

We describe and validate a new minimally invasive method for continuous measurement of tracheal diameter in anesthetized dogs. The method is based on measuring displacement of water into and out of a modified endotracheal tube cuff placed in the trachea. The system was calibrated to allow tracheal diameter to be calculated from known cuff volume. The resolution of the method in measuring changes in tracheal diameter is 0.1 mm over a range of approximately 10-25 mm. The apparatus was tested in five dogs by observing the response of the trachea to four stimuli previously shown to alter tracheal tone: stimulation of nasal mucosa, hyperinflation of the lungs, induction of hypocapnea, and infusion of atropine. The observed changes in tracheal diameter were generally consistent with those of previous studies. The direction and extent of changes in tracheal diameter in response to the test conditions were confirmed by fluoroscopy. We conclude that continuous measurement of volume changes in the cuff reflects corresponding changes in tracheal diameter.

Animals↗
PubMed1995

Increased nitric oxide in exhaled gas as an early marker of lung inflammation in a model of sepsis.

Nitric Oxide (NO) has been implicated in the pathologic vasodilation of sepsis. Because NO can be measured in the exhaled gas of animals and humans, we hypothesized that increases in exhaled NO would occur in a septic model. Using a blinded design, 10 male Sprague-Dawley rats (300 to 400 g) were anesthetized, paralyzed, tracheotomized, and randomized (5/group) to receive an intravenous injection of either lipopolysaccharide (LPS) (Salmonella typhosa, 20 mg/kg) or placebo (equal volume of saline). Thereafter, exhaled gas was collected and measurements of NO concentration were made using chemiluminescence every 20 min for 300 min during ventilation (RR 40 breaths/min, VT 3 ml; PEEP 0, FIO2 0.21). Another group of 10 animals (5 LPS; 5 control) were treated in the same fashion and then killed at 240 min and an arterial blood sample obtained for blood gas and TNF alpha determinations. Pressure volume (PV) curves were constructed and lungs removed, preserved, and submitted for histologic evaluation. LPS-treated rats had lower mean arterial pressures than the control group, p < 0.0001. No significant differences in static lung compliance and PV curves were found in the two groups. TNF alpha levels were greater in the LPS group (1.40 +/- 0.24 ng/ml) versus control group (0.09 +/- 0.04 ng/ml), p < 0.001. By contrast to the control group, exhaled NO concentration rose in all LPS-treated rats at approximately 100 min and at about 160 min reached a plateau that was 6 times greater than control levels (p < 0.0001). There was greater interstitial, airspace, and total lung injury in the LPS group (p = 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Oxidoreductases↗
PubMed1982

Oxygenation during high-frequency ventilation compared with conventional mechanical ventilation in two models of lung injury.

Oxygenation and mean lung volume were investigated during high frequency oscillation (HFO) and conventional mechanical ventilation (CMV) in two models of lung disease and related to the lung mechanics of the lesions. Oleic acid (n = 10) or lung lavage (n = 12) pulmonary injury was induced in a series of rabbits. Each animal was alternately ventilated with HFO (15 Hz sinusoidal wave form) and CMV (flow generator I:E, 1:2; f, 30 breaths/min; VT, 10 to 15 ml/kg) at matched mean airway pressure. Pao2 was measured 5 minutes after onset of ventilation. In the lung lavage model Pao2 was significantly greater during HFO than CMV (Pao2 228 +/- 116 torr vs 71 +/- 42 torr) provided that mean airway pressure was greater than the distinct opening pressure characteristic of this lesion. In the oleic acid model oxygenation was again superior during HFO (Pao2 269 +/- 116 torr vs 110 +/- 83 torr), but only if HFO was preceded by a sustained inflation. Plethysmography in a subset of six rabbits from each group revealed that the improvements in oxygenation were associated with significantly higher mean lung volumes during HFO than CMV (58 +/- 30 ml vs 29 +/- 14 ml lung lavage model, 45 +/- 15 ml vs 30.9 +/- 13 ml on the oleic acid model). The importance of a sustained inflation in rapidly optimizing gas exchange during HFO but not CMV was demonstrated. A sustained inflation resulted in immediate and sustained increases in Pao2 (from 134 +/- 102 torr to 274 +/0 124 torr in the oleic acid model; from 115 +/- 105 torr to 291 +/- 143 torr in the lung lavage model) and mean lung volume (41.8 +/- 11 to 53.8 +/- 9.7 ml in the oleic acid model, 30.9 +/- 7.7 ml to 42.8 +/- 5 ml in the lung lavage model). It is suggested that in these two particular models of lung disease, HFO, when combined with a sustained inflation (to provide opening forces), can more fully exploit the pressure volume hysteresis of unstable lung units than CMV, thereby resulting in the larger mean lung volumes and better oxygenation observed during HFO.

Animals↗
PubMed1980

Needle tracheostomy: a laboratory study.

Percutaneous needle tracheostomy and transtracheal ventilation continues to be advocated for the management of upper airway obstruction. Recent studies recommend the use of artificial ventilation. However, as apparatus for this is not always available and because there remains some doubt regarding conditions for successful use of needle tracheostomy during spontaneous respiration, we undertook such a study in dogs. Pressure-flow characteristics of short hollow needles 18-10 SWG were first determined. The smallest of these (14 SWG Bardic Intracath) that would deliver flow sufficient (by calculation) to meet the respiratory requirement of 10-13 kg laboratory dogs was selected for further study. Respiration was possible by spontaneous or artificial methods in the presence of complete tracheal occlusion. Little or no deterioration was noted in an hour of such breathing. Artificial ventilation by machine and by hand could considerably lower PaCO2. We conclude that the technique is possible provided appropriate needles are selected and care is given to their method of use.

Airway Obstruction↗
PubMed1979

The consequences of diaphragmatic muscle fatigue in the newborn infant.

We have previously demonstrated that diaphragmatic muscle fatigue can be diagnosed in infants from spectral frequency analysis of the surface diaphragmatic electromyogram. This requires a digital computer, but the analysis takes several days. Spectral frequency changes, however, can be accurately reflected by band pass filtering and expressing the ratio of high-frequency power to low-frequency power. A fall in this ratio of greater than 20% indicates muscle fatigue. Using a simple analog device to obtain this ratio permits the results to be immediately available; we have used this method to study weaning from mechanical ventilators in ten infants. With a successful weaning step there is no significant change in the ratio, whereas an unsuccessful weaning step invariably leads to a decrease in the ratio of greater than 20%, which precedes CO2 retention and clinical deterioration. These data indicate that diaphragmatic muscle fatigue plays an important role in the infant's response to lung disease. Monitoring of the high/low frequency ratio may be helpful in weaning infants from assisted ventilation.

Computers, Analog↗
PubMed1979

Diaphragmatic muscle tone.

It is generally believed that there is a scarcity of muscle spindles in the diaphragm and that there is no tonic activity at end expiration. This conclusion is based mainly on animal studies and the difficulty in differentiating tonic electromyogram activity from noise. We have, however, found a number of muscle spindles in the newborn human diagphragm, concentrated in the region of the central tendon. We also tried to detect tonic activity by decreasing it (by rapid-eye movement (REM) sleep or anesthesia) or increasing it (with abdominal loading). During REM sleep in five infants and five adults, using subcostal electrodes were observed a marked fall in tonic activity (P less than 0.001) compared to non-REM or quiet sleep. We also observed a reduction in diaphragmatic tonic activity with halothane anesthesia (P less than 0.001). With esophageal electrodes in adult subjects, there was a rise in tonic diaphragmatic activity proportional to the amount of abdomina load (P less than 0.001). We conclude that there are muscle spindles in the human diaphragm and that there is tonic activity at end expiration.

Adult↗
PubMed1978

A respiratory jacket for ventilatory measurements in children.

The properties of an air-filled polyurethane-coated nylon jacket for measuring volume parameters were determined on a model and in 13 subjects. There was a linear relationship between jacket pressure on a logarithmic scale and the lung volume change over an operating pressure range of 0.7-6 cmH2O. The magnitude of pressure change was frequency dependent. The magnitude of a calibration signal was reduced by superimposed tidal breathing. For the jacket tested, the calibration signal during tidal breathing was 87% of the calibration during apnea. With these properties established, a calibration technique was devised and tested on 13 infants. Corrected tidal volumes (VT) obtained with the jacket correlated well with those obtained with a pneumotachograph (r = 0.986). At the operating pressures used the jacket caused no significant change in functional residual capacity (FRC), VT, or frequency. The jacket is a reliable technique for measurement of VT and immediate changes in FRC in awake children.

Child, Preschool↗
PubMed1977

Sodium nitroprusside: factors which attenuate its action. Studies with the isolated gracilis muscle of the dog.

In a laboratory preparation of the isolated, acutely denervated, and separately perfused canine gracilis muscle we have made the following observations: 1. At physiological pH, sodium nitroprusside significantly decreases the vascular resistance; 2. At physiological pH, cyanide significantly attenuates the effect of sodium nitroprusside; 3. In an acidaemic milieu, our data suggest that the effect of sodium nitroprusside may be attenuated. We speculate that patients who manifest resistance to the hypotensive effect of sodium nitroprusside may not normally eliminate the cyanide that is released from the biodegradation of sodium nitroprusside. They accumulate free cyanide which interferes with the action of sodium nitroprusside at the receptor level, leading to administration of more nitroprusside and setting in motion a positive feedback vicious cycle. When one is faced with the problem of an abnormal response to sodium nitroprusside in a fit patient, although many factors may be involved, we suggest that the possibility of rising blood cyanide levels and acidosis be given high priority.

Animals↗