Search PubMed⌕ Search

Biomedical subjects

J Milic-Emili

Publications and source records attributed to J Milic-Emili.

At least 289 records · Page 16Linked to original sources
PubMed1968

Regional distribution of pulmonary ventilation and perfusion in elderly subjects.

Using radioactive xenon, we measured the regional distribution of pulmonary ventilation and blood flow in six normal men, whose ages ranged between 65 and 75 yr. The measurements were made in the standing position. The static volume-pressure relation of the lungs was also measured in five of the subjects. The results indicate that by comparison with normal young men: (a) Blood flow to the upper lung zones was increased, although it still remained predominant in the lower zones. (b) Ventilation distribution during a vital capacity inspiration was similar to that seen in young subjects. (c) In five of the six elderly subjects, however, the distribution of ventilation in the resting tidal volume range was not preferential to the lower zones as it was in young men. This was probably caused by airway closure in the lower lung zones. The elderly subjects thus exhibit during normal tidal volume breathing a ventilation distribution pattern similar to that observed in young subjects when breathing at low lung volumes, i.e., near residual volume. This difference is probably due to the combined effect of the loss in elastic recoil of the lungs observed in the elderly subjects and of a decreased resistance to collapse of the aged airways. These findings suggest that in the elderly subjects there is a significant regional ventilation-perfusion impairment during quiet breathing, which may explain in part the reported increase in alveolar-arterial oxygen difference with advancing age.

Journal Article↗
PubMed1967

Regional distribution of pulmonary ventilation and perfusion in obesity.

Five women and three men, all obese and weighing 95 to 140 kg, were studied by routine pulmonary function tests and by a radioactive xenon technique, while seated upright at rest, to measure the regional ventilation and perfusion distribution in the lung. In four subjects in whom the expiratory reserve volume averaged 49% of predicted normal, the ventilation distribution as measured with (133)xenon was normal. In the remaining four subjects, in whom the expiratory reserve volume was reduced to less than 0.4 L and averaged only 21% of predicted values, the distribution of a normal tidal breath was predominantly to the upper zones. In all subjects the perfusion distribution was predominantly to the lower lung zones but was slightly more uniform than in normal nonobese subjects. During tidal-volume breathing, therefore, in four subjects the ventilation and perfusion distribution was substantially normal, whereas in the remaining four perfusion was maximal in the lower zones, to which ventilation was significantly reduced. These findings show that there may be significant ventilation/perfusion abnormality on a regional basis in obese subjects, this abnormality bearing a close relationship to the reduction in expiratory reserve volume, a finding predictable from recently published data on normal nonobese subjects (1). The abnormalities of ventilation/perfusion relationships that were demonstrated in four of the eight obese subjects could cause a reduction in arterial oxygen tension during resting tidal ventilation.

Adult↗
PubMedDate not supplied

Measurement of respiratory mechanics using the Siemens Servo Ventilator 900C.

The interrupter technique involves measuring the pressure changes at the airway opening during sudden cessation of flow and has been advocated for monitoring respiratory mechanics in artificially ventilated patients. The Siemens Servo Ventilator 900C has the ability to make airway occlusions without interrupting the patient's respiratory support. This study was performed to determine the suitability of the end-inspiratory occlusion facility of the ventilator for interrupter measurements of respiratory resistance and compliance. Measurements were made in a physical model of the respiratory system consisting of two parallel compartments, whose individual resistances and elastances were independently determined. The accuracy of the resistance measurements made using the ventilator were found to be dependent on the inspiratory flow. With an inspiratory flow of 100 ml/s, the resistance of the system could be measured to within 18% of the true value, and the static compliance could be measured to within 26% of the true value. Much of the error in these determinations was due to the finite closure time of the valve in the ventilator, and to the compliance of the gas in the tubing connecting the ventilator with the model. We conclude that the Siemens Servo Ventilator 900C can be used to conveniently obtain estimates of resistance and compliance in ventilated patients.

Airway Resistance↗
PubMedDate not supplied

Noninvasive determination of respiratory mechanics during mechanical ventilation of neonates: a review of current and future techniques.

Study of the mechanical properties of the respiratory system is needed to help provide a better understanding of the pathogenesis of diseases causing respiratory failure. The nature of neonatal intensive care requires that any technique for monitoring respiratory mechanics be simple, noninvasive, and allow continued free access to the neonate. The peak airway pressure developed during volume cycled ventilation reflects the mechanical properties of the respiratory system but cannot distinguish between changes in the flow-resistive or elastic properties. Similarly, dynamic compliance combines both the flow-resistive and elastic components of the respiratory system in a single number and flow-volume loops also reflect both elements. Extracting a single time-constant from the expiratory limb of the latter assumes a single-compartment model for the respiratory system and, as such, does not provide sufficient information to describe frequency dependence of resistance and compliance. Furthermore, flow-volume loops are markedly distorted by the presence of an endotracheal tube, which must be corrected for, before calculating values of resistance and compliance. To provide the information to understand better the physiologic processes and adaptive mechanisms in diseased states causing acute respiratory failure, it is necessary to use a method that is based on a more detailed and realistic model of the respiratory system. Two such techniques that appear to warrant further investigation in ventilated infants are the interrupter technique and the forced-oscillation technique.

Biomechanical Phenomena↗
PubMedDate not supplied

Influence of the viscoelastic properties of the respiratory system on the energetically optimum breathing frequency.

We hypothesized that the viscoelastic properties of the respiratory system should have significant implications for the energetically optimal frequency of breathing, in view of the fact that these properties cause marked dependencies of overall system resistance and elastance on frequency. To test our hypothesis we simulated two models of canine and human respiratory system mechanics during sinusoidal breathing and calculated the inspiratory work (WI) and pressure-time integral (PTI) per minute under both resting and exercise conditions. The two models were a two-compartment viscoelastic model and a single-compartment model. Requiring minute alveolar ventilation to be fixed, we found that both models predicted almost identical optimum breathing frequencies. The calculated PTI was very insensitive to increases in breathing frequency above the optimal frequencies, while WI was found to increase slowly with frequency above its optimum. In contrast, both WI and PTI increased sharply as frequency decreased below their respective optima. A sensitivity analysis showed that the model predictions were very insensitive to the elastance and resistance values chosen to characterize tissue viscoelasticity. We conclude that the WI criterion for choosing the frequency of breathing is compatible with observations in nature, whereas the optimal frequency predictions of the PTI are rather too high. Both criteria allow for a fairly wide margin of choice in frequency above the optimum values without incurring excessive additional energy expenditure. Furthermore, contrary to our expectations, the viscoelastic properties of the respiratory system tissues do not pose a noticeable problem to the respiratory controller in terms of energy expenditure.

Animals↗
PubMedDate not supplied

Inspiratory capacity and exercise tolerance in chronic obstructive pulmonary disease.

During the past half-century, many studies have investigated the correlation of exercise tolerance to routine lung function in patients with obstructive pulmonary disease. In virtually all of these studies, the degree of airway obstruction was assessed in terms of forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC). Because in most studies only a weak correlation was found between exercise tolerance and degree of airway obstruction, it has been concluded that factors other than lung function impairment (eg, deconditioning and peripheral muscle dysfunction) play a predominant role in limiting exercise capacity in patients with chronic airway obstruction. Recent work, however, suggests that in patients with chronic obstructive pulmonary disease, the inspiratory capacity is a more powerful predictor of exercise tolerance than FEV1 and FVC.

Exercise Tolerance↗