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Biomedical subjects

A C Bryan

Publications and source records attributed to A C Bryan.

At least 73 records · Page 4Linked to original sources
PubMed1981

Respiratory induction plethysmography (Respitrace): an evaluation of its use in the infant.

Respiratory Induction Plethysmography (RespitraceTM) is a recently described method for noninvasive respiratory monitoring in adults. We report here on its calibration and use in 15 infants. Tidal volume, as measured by this method, was compared with the tidal volume integrated from a pneumotachygraph attached to a tightly fitted face mask. The 2 volumes had a correlation greater than 0.85 (p less than 0.001) with a slope between 0.9 and 1.1. The results were similar in both quiet and rapid eye movement sleep demonstrating that the method can accurately follow paradoxical inward rib cage movement. However, the accuracy decreased at respiratory rates above 80 breaths/min. When the minute ventilation was computed over the same sampling interval by both methods, the mean difference was +0.2 +/- 3.4% (+/- 1 SD) in quiet sleep and +0.8 +/- 4.5% in rapid eye movement sleep. We concluded that this is an accurate method of measuring long-term minute ventilation and tidal volume in small infants, provided that both the calibration procedure and measurements are made in the same posture, and the infant's respiratory rate is less than 80 breaths/min.

Adult↗
PubMed1981

Chest wall mechanics and pattern of breathing during sleep in asthmatic adolescents.

The effect of sleep state on the ventilatory pattern and chest wall mechanics was studied in 8 asthmatic adolescents (mean age +/- SD, 13.6 +/- 1.3 yr) using a respiratory inductive plethysmograph and surface electromyogram (EMG) electrodes. During rapid eye movement (REM) sleep we observed a mean decrease of 43% in intercostal EMG activity. This was associated with paradoxical inward motion of the rib cage to the extent that the rib cage compartment contributed negatively to tidal volume. Accompanying the abnormal chest wall mechanics there was a mean increase of 45 +/- 38% in diaphragmatic EMG activity, as well as a substantial increase in abdominal contribution to tidal volume. However, despite the increased diaphragmatic activity, tidal volume decreased during REM sleep. The abnormal chest wall mechanics during REM sleep were also associated decreased mean inspiratory flow rates and prolongation of the duty cycle (TI/Ttot). The mean maximal decrease in hemoglobin oxygen saturation during sleep compared with that during wakefulness was 3.9%.

Adolescent↗
PubMed1980

Hemoglobin desaturation: its occurrence during sleep in patients with cystic fibrosis.

Sleep studies were performed in 20 clinically stable cystic fibrosis (CF) patients (mean age, 18.2 years) to determine the magnitude of fall in hemoglobin saturation (Sao2) during sleep and to relate these changes to pulmonary function and echocardiographic findings. Five healthy young adults served as controls. In both groups, the maximum fall in Sao2 was seen during rapid eye movement (REM) sleep. The mean maximum fall in the control group during REM sleep was 2.0% (range, 1% to 3%), compared with 7.4% (range, 1% to 23%) in the CF group. Of the 11 patients in whom right ventricular systolic time intervals were obtained, eight of the nine patients with falls in Sao2 greater than 3% during REM sleep had echocardiographic evidence of pulmonary hypertension. Repeated episodes of desaturation during sleep may contribute to the development and progression of cor pulmonale in CF patients.

Adolescent↗
PubMed1980

Ventilation by high-frequency oscillation.

The effect of applying a high-frequency small-volume sinusoidal oscillation at the airway was investigated in anesthetized apneic beagle dogs (mean wt 11 kg, mean VDphys 6.6 +/- 0.6 ml/kg). Oscillations generated by a piston in a cylinder were transmitter to the lungs through an uncuffed endotracheal tube (4.5 mm ID, 6.0 mm OD), which allowed a substantial leak back through the vocal cords. A bias flow of fresh gas presented inspired air to the midtracheal level. The minimum distal airway pressure (measured at the end of the endotracheal tube) was maintained between 0 and 2 cmH2O. Peak airway pressures were 4-8 cmH2O. The optimal frequency for CO2 elimination was 15 Hz. Using volumes of 1.9 ml/kg (range 1.7-2.3) at this frequency the mean PaCO2 was 33.1 +/- 0.5 Torr. In four dogs breathing 100% O2 the PaO2 was 594 +/- 9 Torr during spontaneous ventilation and 580 +/- 9 Torr after 5 h of uninterrupted oscillation. In four experiments using room air the PaO2 was 95 +/- 5 Torr during spontaneous respiration and 106 +/- 1 Torr after 5 h of oscillation. In an additional seven studies there was no difference in mean cardiac output between oscillation and conventional mechanical ventilation. This study demonstrates that high-frequency small-volume oscillations can maintain gas exchange for many hours presumably by markedly enhancing the diffusivity of gases in the lung.

Animals↗
PubMed1980

Tonic inspiratory muscle activity as a cause of hyperinflation in histamine-induced asthma.

We studied the change in tonic activity of the inspiratory muscles during acute hyperinflation. Hyperinflation was provoked in two asthmatic and three normal subjects by progressively doubling doses of histamine. Changes in lung volume were determined with magnetometers and with a body plethysmograph. Intercostal muscle activity was recorded with surface electrodes and diaphragmatic activity with esophageal electrodes. Tonic activity was defined as electrical activity in the electromyogram present at end expiration. After histamine the maximal observed increase in plethysmographic thoracic gas volume in the five subjects was 29.8 +/- 6.4% of control (mean +/- SE). Hyperinflation was accompanied by a significant increase in tonic activity of the intercostal muscles (P < 0.01) and the diaphragm (P < 0.01). There was a significant correlation between the increase in thoracic gas volume and the increase in tonic intercostal (r = 0.82, P = 0.003) and diaphragmatic (r = 0.89, P = 0.003) activity. We conclude that histamine-induced hyperinflation is accompanied by persistent inspiratory muscle activity throughout expiration.

Adult↗
PubMed1980

Mechanism of hemoglobin desaturation during rapid-eye-movement sleep in normal subjects and in patients with cystic fibrosis.

To assess the mechanism of the decrease in hemoglobin O2 saturation during rapid-eye-movement sleep, we studied 5 normal subjects 22 to 30 yr of age and 20 patients with cystic fibrosis 9 to 29 yr of age. The largest decrease in arterial O2 saturation, as monitored with an ear oximeter during sleep, occurred during rapid-eye-movement sleep, with a mean +/- SEM decrease of 2 +/- 0.31% in the normal subjects and 7.4 +/- 1.3% in the patients in both groups. Rapid-eye-movement sleep was associated with a significant loss of intercostal and diaphragmatic tonic muscle activity (p < 0.01), as monitored with surface electrodes, and a decrease in the baseline position of the rib cage and abdomen, as recorded by magnetometers (p < 0.01). This suggests a decrease in functional residual capacity, which was accompanied by a consistently lower arterial O2 saturation during rapid-eye-movement sleep. Short periods (< 20 s) of inhibition of phasic respiratory muscle activity during rapid-eye-movement sleep were followed by further decreases in arterial O2 saturation. We conclude that the desaturation during rapid-eye-movement sleep in all subjects was mainly due to a decrease in functional residual capacity, leading to airway closure in the dependent lung regions. The hemoglobin desaturation was further aggravated by transient periods of hypoventilation.

Adolescent↗
PubMed1980

Congenital central hypoventilation and sleep state.

Congenital central hypoventilation (Ondine's curse) is described in an infant with persistant symptoms throughout the first nine months of life. Respiratory control was most severely affected in quiet sleep, although abnormalities were present in rapid eye movement (REM) sleep and while awake. Failure of metabolic control in quiet sleep led to profound hypoventilation. Behavioral or "behavioral-like" inputs in the awake state and REM sleep increased ventilation, but not to expected normal levels. The ventilatory response to inhaled 4% CO2 was markedly depressed in all states.

Carbon Dioxide↗
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↗
PubMed1979

Evaluation of the single-breath diffusing capacity in asthma and cystic fibrosis.

To explain why the single-breath carbon monoxide diffusing capacity (Dsb) was, on the average, elevated in 163 asthmatic subjects and 175 patients with cystic fibrosis, we simulated this elevation in ten normal subjects by having them perform the test for Dsb through an inspiratory obstruction. This resulted in an 18 percent increase in Dsb corrected for pulmonary volume. Inhalation of a bronchodilator drug was associated with relief of obstruction and a fall in the corrected Dsb in 31 asthmatic subjects but did not change either the obstruction or the corrected Dsb in 17 patients with cystic fibrosis. We suggest that elevated Dsb in asthma and cystic fibrosis is partly due to maximal inspiration against obstructed airways. This requires abnormally negative intrathoracic pressures, increasing the pulmonary capillary blood volume, and, thereby, increasing the Dsb.

Adolescent↗
PubMed1979

The effects of abdominal loading on rib cage distortion in premature infants.

The action of the diaphragm in inspiration is to decrease intrathoracic pressure and raise abdominal pressure, which elevates the rib cage. In the supine position, the rise in abdominal pressure is smaller because of the lack of abdominal muscle tone. In premature infants the inward pull of the diaphragm on the very compliant ribs causes inward movement on inspiration (ie, distortion) which is exacerbated by the lack of intercostal muscle activity during rapid eye movement (REM) sleep, their predominant state. We raised abdominal pressure by means of an inflatable cuff in 12 newborn infants (gestation 28 to 40 weeks) to try to improve inspiratory coupling of the rib cage and diaphragm. There was no significant change in minute ventilation, indicating no ventilatory impairment. In all studies in which there was distortion, abdominal loading produced a reduction or abolition of distortion (P less than .01). Abdominal loading may be useful in reducing diaphragmatic activity in premature infants.

Abdomen↗
PubMed1978

Exercise ventilatory mechanics at increased ambient pressure.

Transpulmonary pressure, lung volume, and flow rate were recorded in two healthy subjects performing graded exercise between 1 and 10 ATA. At simulated depths greater than 4 ATA, exercise was terminated by severe choking dyspnea at levels of work, oxygen consumption, heart rate, and ventilation significantly lower than during maximum exercise at 1 ATA. Comparison of exercise ventilatory mechanics with corresponding maximum expiratory flow-volume and expiratory isovolume pressure-flow (IVPV) curves demonstrated that the reduced aerobic capacity was associated with expiratory flow limitation. We conclude that dynamic airways compression limited aerobic capacity at these depths by causing a persistent cough making it seem difficult to continue exercise. Analysis of the IVPV curves suggested that maximum expiratory flow was reduced at depth below the rate allowing adequate exercise ventilation because increased gas density raised the resistance downstream from equal pressure points. At each level of sumbaximal exercise, end-expiratory position and alveolar CO2 tension increased with ambient pressure due primarily to the density dependence of airways resistance. In these respects, healthy subjects breathing dense gas resemble patients with obstructive lung disease.

Air Pressure↗
PubMed1978

Effects of respiration on cardiac performance.

The conventional explanation for the fall in left ventricular stroke volume (LVSV) with inspiration is that blood pools in the lungs, thereby decreasing pulmonary venous return. In anesthetized dogs, we have found an increase in left ventricular filling pressure (LVFP) with both constant and increasing lung volume during an inspiratory effort. Transmural aortic diastolic pressure rises as LVSV falls and LVFP rises consistent with the hypothesis that a fall in pleural pressure afterloads the left ventricle. Additionally the increase found in right ventricular filling pressure with inspiration may adversely affect LV performance by decreasing LV compliance and/or contractility. Our findings are incompatible with pooling of blood in the lungs being the primary determinant of the fall in LVSV with inspiration.

Animals↗