Biomedical subjects

K J Sullivan

Publications and source records attributed to K J Sullivan.

21 records · Page 2Linked to original sources

PubMed1987

Age related changes in the rate of stress relaxation within the rat respiratory system.

Stress relaxation within the respiratory system was examined in young rats at different ages, 0-1 day old (GPI), 4-5 days old (GPII) and 30-40 days old (GPIII). Each rat was anesthetized, tracheostomized and placed inside a saline filled plethysmograph with the tracheal cannula projecting through the wall of the plethysmograph. Volume history was standardized by three inflations to a mean transrespiratory system pressure (P) of 20-25 cm H2O, then P was set to zero and lung volume was abruptly increased by rapidly withdrawing fluid from the plethysmograph. Following the volume step, lung volume was maintained constant and changes in P due to stress relaxation were recorded for 30 sec. The rate of stress relaxation was obtained by calculating the slope (R) of the normalized change in P per unit of time on a semi-log plot. GPIII rats exhibited the slowest rate (R = 0.068 +/- 0.004 SD) whereas GPII rats demonstrated the fastest rate (R = 0.092 +/- 0.011 SD). Stress relaxation in GPI was intermediate (R = 0.076 +/- 0.005 SD). Values of dynamic (Cdyn) and static (Cstat) compliance were determined for rats similar in age to the three age groups used to determine R. The difference between Cstat and Cdyn increased with R and was greatest in rats between 0 and 6 days old. We conclude that: (1) stress relaxation within the rat respiratory system at 30-40 days is less than that found in rats during the first week after birth, and (2) changes in the viscoelastic properties of the respiratory system may contribute to age related variation in the difference between Cstat and Cdyn.

Aging↗

PubMed1986

Dynamic lung compliance in newborn and adult cats.

Static (Cstat) and dynamic (Cdyn) lung compliance and lung stress relaxation were examined in isolated lungs of newborn kittens and adult cats. Cstat was determined by increasing volume in increments and recording the corresponding change in pressure; Cdyn was calculated as the ratio of the changes in volume to transpulmonary pressure between points of zero flow at ventilation frequencies between 10 and 110 cycles/min. Lung volume history, end-inflation volume, and end-deflation pressure were maintained constant. At the lowest frequency of ventilation, Cdyn was less than Cstat, the difference being greater in newborns. Between 20 and 100 cycles/min, Cdyn of the newborn lung remained constant, whereas Cdyn of the adult lung decreased after 60 cycles/min. At all frequencies, the rate of stress relaxation, measured as the decay in transpulmonary pressure during maintained inflation, was greater in newborns than in adults. The frequency response of Cdyn in kittens, together with the relatively greater rate of stress relaxation, suggests that viscoelasticity contributes more to the dynamic stiffening of the lung in newborns than in adults. A theoretical treatment of the data based on a linear model of viscoelasticity supports this conclusion.

Animals↗

PubMed1985

Effect of distortion on the mechanical properties of newborn piglet lung.

During breathing the relatively high chest wall-to-lung compliance ratio of the newborn favors distortion of the respiratory system. In this study we have examined the effect of lung deformation, generated by a hydrostatic pleural surface pressure gradient, on the static (Cstat) and dynamic (Cdyn) compliance of the isolated newborn piglet lung. Seven lungs from piglets 2-7 days old have been studied in a saline-filled plethysmograph. Static pressure-volume (PV) curves were obtained by changing the volume a known amount and measuring the corresponding changes in transpulmonary pressure. Dynamic PV curves were obtained by ventilating the lung at a fixed pressure and at 20 cycles/min. These experiments were repeated in an air plethysmograph on the undeformed lung. Lung volume history was standardized prior to each maneuver by three inflations to 20-25 cmH2O. Lung collapse was avoided by applying an end-expiratory load equal to the transpulmonary pressure at functional residual capacity. Cstat was not significantly different between the deformed and undeformed lung (P greater than 0.05). Cdyn was less than Cstat in both cases (P less than 0.025) and was reduced further by deformation (P less than 0.05). We conclude that 1) peripheral airway obstruction or the viscoelastic properties of the piglet lung, or both, decrease Cdyn, and 2) deformation increases the external (PV) respiratory work by further decreasing Cdyn.

Animals↗