Biomedical subjects

G F Dolan

Publications and source records attributed to G F Dolan.

21 records · Page 2Linked to original sources

PubMed1977

Diaphragmatic function during immersion.

Diaphragmatic function during immersion to midneck level was studied in upright mongrel dogs, using constant electrophrenic stimulation. Effectiveness of diaphragmatic contraction was analyzed in terms of inspired volume (VT) (with airways open), and change in intrathoracic pressure (Pmus) (with the respiratory system occluded). Hydrostatic compression of the immersed body decreased functional residual capacity (FRC) to 55% base-line value (FRCO), resulting in a 2.8-fold increase in Pmus. In spite of this Pmus increase, VT often decreased during immersion, averaging only 83% VTO (base-line value in air). Hence, immersion was associated with a marked stiffening of the respiratory system. The Pmus increase during immersion persisted after restoration of FRC to FRCO, and was related to diaphragmatic length being greater in water than in air under condition of iso-lung volume. In all, there were three factors affecting diaphragmatic function during immersion: FRC reduction, change in thoracic configuration, and stiffening of the respiratory system.

Animals↗

PubMed1976

Effect of hyperinflation on inspiratory function of the diaphragm.

The inspiratory efficiency of the diaphragm during unilateral and bilateral phrenic stimulation (UEPS and BEPS) with constant stimulus was studied in seven dogs from FRC to 120% TLC. Alveolar pressures (PAl) were recorded during relaxation, BEPS and UEPS at each lung volume in the closed respiratory system. From the PAl-lung volume curves, tidal volume (VT), and pressure developed by the diaphragm (Pmus) were derived. Results are summarized below. a) Hyperinflation impaired the inspiratory efficiency of the diaphragm which behaved as an expiratory muscle beyond the lung volume of 103.7% TLC (Vinef). b) The diaphragm during UEPS became expiratory at the same Vinef as during (BEPS. C) The VT-lung volume relationship was linear during BEPS, allowing simple quantitation of VT loss with hyperinflation and prediction of Vinef. d) With only one phrenic nerve stimulated, the functional loss is less pronounced in VT than in Pmus, as compared to BEPS, indicating that the respiratory system was more compliant during UEPS than BEPS. This compliance difference from UEPS to BEPS diminished with severe hyperinflation.

Animals↗

PubMed1975

Stability in lobar ventilation distribution during change in thoracic configuration.

Stability in lobar ventilation was examined in dogs during bilateral electrophrenic respiration (BEPR) and positive pressure-assisted ventilation (PPAV). Bilateral prior ligation of the lower and middle lobe pulmonary arteries monitoring of upper lobe ventilation as alveolar minute ventilation (VA), middle and lower lobe ventilation as dead space (VD), and VD/VT ratio, both calculated by the Bohr equation. As documented by chest films, transverse and anteroposterior thoracic diameters during BEPR decreased below FRC values whereas thoracic cephalocaudal dimension greatly increased. During PPAV, all thoracic dimensions increased. Despite these dissimilar regional chest movements, VA, VD, and VD/VT ratio were comparable between PPAV and BEPR under conditions of matched tidal volume and respiratory frequency. Stability in upper lobe ventilation during BEPR was maintained by caudal displacement despite the compression of the rib cage, as documented by tantalum bronchography. Lobar-interdependence appears to be the mechanism transmitting negative pleural pressure developed by the diaphragm to the upper lobes via lower and middle lobe inflation.

Animals↗