Biomedical subjects

R E Hyatt

Publications and source records attributed to R E Hyatt.

At least 91 records · Page 5Linked to original sources

PubMed1976

Total respiratory resistance by forced oscillation in normal subjects.

Total respiratory resistance (Rrs) was studied by the forced oscillation technique at a frequency of 3 cps in 76 normal subjects (36 men, 40 women), ages 21 to 64 years. Slopes (equivalent to specific conductance) assuming a linear relationship with zero intercept between 1/Rrs and thoracic gas volume (TGV) were computed. In women, expiratory slopes were significantly less than inspiratory slopes; moreover, slopes decreased significantly with height and were significantly less in current smokers. For men, there were no consistently significant relationships between slopes and phase, age, height, weight, or smoking habits. Predicted resistance and estimates of the 5th and 95th percentiles of inspiratory, expiratory, and average resistance are presented for all men combined and for currently nonsmoking women. The fact that, in contrast to men, asymptomatic, current women smokers showed an elevation in Rrs when compared to nonsmoking women merits further study.

Adult↗

PubMed1975

Lung volumes and closing capacity with continuous positive airway pressure.

Total lung capacity, vital capacity, residual volume, and functional residual capacity were determined by body plethysmography and the single-breath oxygen (SBO2) test was performed at 0, 5, and 11 cm H20 continuous positive airway pressure in healthy, awake, seated, spontaneously breathing subjects. Mean values for the absolute lung volume at which phase IV of the SBO2 test begins (closing capacity) did not change significantly with continous positive airway pressure at 5 or 11 cm H2O. Mean total lung capacity, functional residual capacity, and residual volume increased significantly, and the mean closing volume, the lung volume above residual volume at which phase IV begins, decreased significantly with 11 cm H20 continuous positive airway pressure; differences at 5 cm H20 were not significant. The slope of the alveolar nitrogen plateau (phase III) obtained during the SBO-2 test did not change with continuous positive airway pressure.

Adult↗

PubMed1975

Positive airway pressure and vertical transpulmonary pressure gradient in man.

Static transpulmonary pressure (Pao-Pes) and the vertical gradient of transpulmonary pressure were determined in five sitting conscious normal subjects at mean airway pressures of 0 (ambient), 11, and 21 cmH2O. All subjects exhibited a nonuniform transpulmonary pressure gradient down the esophagus. The vertical pressure gradient was consistently larger in the lower (8-20cm below esophageal artifact) than in the middle region (0-8cm) of the esophagus. The gradient was not significantly altered by continuous positive airway pressure (11 and 21 cmH2O) or by changes in lung volume (60, 70, and 80% of total lung capacity (TLC)). Continuous positive airway pressure also did not result in a consistent change of the overall static pressure-volume curve of the lung. There was a small but statistically significant increase in TLC with each increase in airway pressure.

Biomechanical Phenomena↗

PubMed1975

Influence of expiratory flow on closing capacity at low expiratory flow rates.

Single-breath oxygen (SBO2) tests at expiratory flow rates of 0.2, 0.5, and 1.01/s were performed by 10 normal subjects in a body plethysmograph. Closing capacity (CC)--the absolute lung volume at which phase IV began--increased significantly with increases in flow. Five subjects were restudied with a 200-ml bolus of 100% N2 inspired from residual volume after N2 washout by breathing 100% O2 and similar results were obtained. An additional five subjects performed SBO2 tests in the standing, supine, and prone positions; closing volume (CV)--the lung volume above residual volume at which phase IV began--also increased with increases of expiratory flow. The observed increase in CC with increasing flow did not appear to result from dependent lung regions reaching some critical "closing volume" at a higher overall lung volume. In normal subjects, the phase IV increase in NI concentration may be caused by the asynchronous onset of flow limitation occurring initially in dependent regions.

Adult↗

PubMed1975

Effect of increased static lung recoil on bronchial dimesions of excised lungs.

We measured bronchial diameters and lengths during static deflation and inflation in eight excised dog lobes before and after static lung recoil (Pst(L)) had been significantly increased by cooling the lobe for 48 h at 4 degrees C and ventilating it for 3 h. In control lobes, bronchial diameters were the same at any volume even though Pst(L) was different during inflation and deflation. These results agree with those of Hughes et al. (J. Appl. Physiol. 32: 25-35, 1972). However, when Pst(L) was increased, diameters at a given volume were significantly increased over control values; diameters at a given pressure were nearly the same as the controls. Therefore, under these conditions, bronchial diameter did not conform to lung volume. The ventilation process appeared to alter the circumferential elastic properties of the bronchi because diameters at all pressures were slightly larger after ventilation. Bronchial length-volume relationships were the same in both control and ventilated lobes. Thus, when Pst(L) was markedly increased, diameter corresponded best to lung recoil and length to lung volume.

Animals↗

PubMed1975

Relationship of air trapping to increased lung recoil pressure induced by chest cage restriction.

Chest cage restriction was produced in 13 normal male subjects. We could not detect trapped air during restriction by comparing lung volumes determined by nitrogen washout with those determined by plethysmography. However, 3 subjects did have definite evidence of trapping because they released small amounts of air (mean, 61 ml) when the restriction was removed. Two subjects had suggestive evidence of trapping. Yet there was no correlation between trapping and the degree of increase in static lung recoil associated with restriction. Seven subjects had chest restriction produced while they were breathing air and again while they were breathing 100 per cent oxygen, in an attempt to reveal the presence of airway closure. In only one subject was oxygen breathing clearly associated with a greater then expected increase in lung recoil after restriction; suggestive changes were seen in 2 other subjects. However, there was no definite correlation between unusual increases in lung recoil induced by restriction while breathing oxygen and the presence of air trapping. We conclude that trapping, hence airway closure, is not required for the increase in static lung recoil that occurs with chest cage restriction.

Adult↗

PubMed1975