PubMed Health⌕ Search

Biomedical subjects

R D Hubmayr

Publications and source records attributed to R D Hubmayr.

61 records · Page 4Linked to original sources
PubMed1987

Regional ventilation during spontaneous breathing and mechanical ventilation in dogs.

We evaluated the effects of the different patterns of chest wall deformation that occur with different body positions and modes of breathing on regional lung deformation and ventilation. Using the parenchymal marker technique, we determined regional lung behavior during mechanical ventilation and spontaneous breathing in five anesthetized recumbent dogs. Regional lung behavior was related to the patterns of diaphragm motion estimated from X-ray projection images obtained at functional residual capacity (FRC) and end inspiration. Our results indicate that 1) in the prone and supine positions, FRC was larger during mechanical ventilation than during spontaneous breathing; 2) there were significant differences in the patterns of diaphragm motion and regional ventilation between mechanical ventilation and spontaneous breathing in both body positions; 3) in the supine position only, there was a vertical gradient in lung volume at FRC; 4) in both positions and for both modes of breathing, regional ventilation was nonlinearly related to changes in lobar and overall lung volumes; and 5) different patterns of diaphragm motion caused different sliding motions and differential rotations of upper and lower lobes. Our results are inconsistent with the classic model of regional ventilation, and we conclude that the distribution of ventilation is determined by a complex interaction of lung and chest wall shapes and by the motion of the lobes relative to each other, all of which help to minimize distortion of the lung parenchyma.

Animals↗
PubMed1987

Evaluation of bronchodilator responsiveness in mechanically ventilated patients.

Airway pressure, flow, and volume were measured before and after administration of aerosolized metaproterenol during controlled mechanical inflation and stepwise deflation of the relaxed respiratory system in 13 mechanically ventilated patients. An increase in passive expiratory flow at constant respiratory system recoil pressure was considered evidence of bronchodilatation. In 10 patients, at a respiratory system recoil pressure of 6 cm H2O (VP6), expiratory flow increased 21 to 500% above prebronchodilator level. In these 10 dynamically hyperinflated patients, an increase in VP6 was associated with a decrease in peak inspiratory pressure (Ppeak) (mean delta = -4.7 cm H2O) and a decrease in intrinsic positive end-expiratory pressure (Peepi) (mean delta = -2.4 cm H2O). The elastance of the respiratory system was not affected by metaproterenol, and the delta Peepi corresponded to a mean decrease in end-expiratory lung volume of 0.20 L. The results are consistent with predictions based on a single-compartment model. When mean expiratory flow is determined only by the tidal volume and expiratory time, a decrease in airway resistance results in a decrease in lung volume at which patients are ventilated. Therefore, the decrease in Ppeak is caused not only by a decrease in the resistive pressure cost but also by a decrease in the elastic pressure cost of inflating the respiratory system. It is emphasized that Ppeak and Peepi provide valuable information about bronchodilator-induced changes in lung function during controlled mechanical ventilation.

Adult↗
PubMed1985

Regional lung strain in dogs during deflation from total lung capacity.

Regional lung distortion during deflation from total lung capacity to functional residual capacity (FRC) in intact supine and prone anesthetized dogs was determined from the displacement of multiple metallic markers embedded in the lung parenchyma. Distortion was expressed as strain (epsilon), which is related to fractional length changes. In the supine position, transverse strain (epsilon yy) was larger than vertical strain (epsilon xx) and cephalocaudal strain (epsilon zz) in the upper lobe. The FRC of the lower lobe was smaller than FRC of the upper lobe and all strains were larger, but epsilon zz increased most and became equal to epsilon yy. In the prone position, epsilon yy was largest in all upper lobes and in three of four lower lobes. Strains and volumes of the upper and lower lobes were similar. The upper and lower lobes rotated slightly around different axes, indicating that interpleural fissures allow additional degrees of freedom for the lungs to conform to the thoracic cavity. In the prone position, there were no consistent gradients of strain or volume. These results indicate that, in determining the regional distribution of FRC in the recumbent dog, in addition to the effect of gravity on the lung, there are important interactions between lung and thoracic cavity shapes.

Animals↗
PubMed1983

Topographical distribution of regional lung volume in anesthetized dogs.

The distribution of regional lung volume during static deflation from total lung capacity to functional residual capacity was determined from the positions of intraparenchymal metallic markers ascertained by a biplane video roentgenographic technique in supine and prone anesthetized dogs. Regional lung volumes were linearly related to overall lung volume so that regional volume could be characterized by a ventilation index (VI), which is the ventilation per alveolus relative to the ventilation of the overall lung. For the supine position, there were vertical and cephalocaudal gradients in VI in both the upper and lower lobes. Mean VI was greater in the lower lobe than in the upper lobe, but VI was less than would be predicted from extrapolation of the upper lobe relationship. For the prone position, there was no consistent gradient in VI in any direction. The magnitude of the gradients in VI and the effects of body position suggest that, in the recumbent dog, the thoracic cavity shape is a more important determinant of regional lung volume than is the effect of gravity on the lung itself.

Anesthesia, General↗
PubMedDate not supplied

Respiratory muscle coordination in acute spinal dogs.

Our objectives were (1) to test whether respiratory muscles of spinal dogs can generate the alternating pattern of activation seen in intact animals and (2) to characterize the responsiveness of spinal rhythms to mechanical ventilation. We recorded the electromyographic activities of inspiratory muscles (diaphragm and parasternal intercostals) and expiratory muscles (triangularis sterni and transversus abdominis) in ten anesthetized dogs before and after transection of the cervical cord at levels C1-C2 (n = 2), C2-C3 (n = 6), and C8 (n = 2). In 9/10 dogs, we observed short lasting (3-4 min) rhythmic ventilatory muscle activity for up to 3 h after transection. Inspiratory and expiratory muscles contracted simultaneously, suggesting an absence of mechanism(s) responsible for reciprocal muscle activation on a spinal level. Five of ten dogs showed tonic rib cage activity during apnea that was phasically modulated during mechanical ventilation. From the absence of alternating inspiratory and expiratory muscle activity in acute spinalized dogs, we conclude that dogs do not have a spinal pattern generator for respiration.

Animals↗
PubMedDate not supplied

Diaphragm dysfunction and respiratory insufficiency after upper abdominal surgery.

This study was designed to determine the contribution of diaphragm dysfunction and pain to respiratory insufficiency after upper abdominal surgery. Respiratory insufficiency and postoperative pain in humans were evaluated by pulse oximetry, pulmonary function tests, and a visual analog scale. Diaphragm shortening in dogs was evaluated with biplane videoroentgenography. In humans, despite reasonable pain control, pulmonary function, as reflected in forced vital capacity (FVC), forced expiratory volume in one second (FEV1) and arterial oxygen saturation (SpO2) were significantly reduced on the first postoperative day. Improved pain control was not associated with improvements in FVC or FEV1. In the dogs, diaphragm shortening and tidal volume were significantly reduced in the immediate postoperative period. Phrenic nerve stimulation immediately after surgery resulted in supramaximal diaphragm shortening, which indicated neither the diaphragm nor phrenic nerves were significantly injured by surgical manipulation. Diaphragm dysfunction has a major role in postoperative pulmonary insufficiency; an afferent-mediated reflex inhibition of the phrenic nerves may be responsible.

Abdomen↗