Biomedical subjects
Publications and source records attributed to J Milic-Emili.
In 1966, a paper entitled "Regional distribution of gas in the lung" was published in the Journal of Applied Physiology and became one of the 100 most-cited papers of clinical research from 1961 to 1978. The senior author provides the background and state-of-the art at the time of its publication, and reviews the main findings of the paper and subsequent developments.
BACKGROUND: Proportional assist ventilation (PAV) has been shown to maintain better patient-ventilator synchrony than pressure support ventilation (PSV); however, its clinical advantage regarding invasive ventilation of COPD patients has not been clarified. OBJECTIVES: To compare the effect of PAV and PSV on respiratory parameters of hypercapnic COPD patients with acute respiratory failure (ARF). METHODS: Nine intubated hypercapnic COPD patients were placed on the PAV or PSV mode in random sequence. For each mode, four levels (L1-L4) of support were applied. At each level, blood gases, flow, tidal volume (VT), airway pressure (Paw), esophageal pressure (Pes) (n = 7), patient respiratory rate (fp), ventilator rate (fv), missing efforts (ME = fp - fv) were measured. RESULTS: We found increases in ME with increasing levels of PSV but not with PAV. PO2 and VT increased whereas PCO2 decreased significantly with increasing levels of PSV (p < 0.05). With PAV, PCO2 decreased and VT increased significantly only at L4 whereas PO2 increased from L1 to L4. Runaways were observed at L3 and L4 of PAV. The pressure-time product (PTP) was determined for effective and missing breaths. The mean total PTP per minute (of effective plus missing breaths) was 160 +/- 57 cm H2O/s.min in PSV and 194 +/- 60 cm H2O/s.min in PAV. CONCLUSION: We conclude that in COPD patients with hypercapnic ARF, with increasing support, PSV causes the appearance of ME whereas PAV develops runaway phenomena, due to the different patient-ventilator interaction; however, these do not limit the improvement of blood gases with the application of both methods.
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151 ambulatory male patients with chronic obstructive pulmonary disease have been studied twice, at time intervals ranging from 2 to 36 months (average : 11), to determine the relationships between changes in lung function tests, pattern of breathing and arterial PCO2. This longitudinal analysis confirms the results of cross-sectional studies: variations in PaCO2 seem independent of the evolution of lung function tests (FEV1, VC, FEV1/VC, RV/TLC). Increases in PaCO2 are associated with a decrease in tidal volume and no change in respiratory frequency. These changes in breathing pattern result in a decreased minute ventilation and an increased VD/VT ratio.
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The volume and time components of the breathing cycle together with the mouth occlusion pressure P0.1) were measured in 12 patients with chronic diffuse lung fibrosis (DLF) breathing air and in nine normal subjects matched for age and sex. In addition, static lung elastance was measured in all patients. It was found that in DLF the frequency of breathing (f) and P0.1 were positively correlated with lung elastance, whereas tidal volume (VT) decreased significantly with increasing elastance. Minute ventilation and mean inspiratory flow were independent of lung elastance. The VT and f of DLF reported in this paper and those from other published reports were compared with the VT and f of elastically loaded normal subjects. At equivalent levels of elastance, both DLF and loaded normal subjects show qualitatively similar changes. This data suggests that in DLF patients the inspiratory neuromuscular drive is increased as a function of their elastic load, the increase being sufficient to maintain alveolar ventilation within normal limits.