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Biomedical subjects

Neil R MacIntyre

Publications and source records attributed to Neil R MacIntyre.

24 records · Page 2Linked to original sources
PubMed2002

Intrabreath diffusing capacity of the lung in healthy individuals at rest and during exercise.

BACKGROUND: Traditional approaches to measuring the diffusing capacity of the lung for carbon monoxide (DLCO) treat the lung as a single, well-mixed compartment and produce a single value for DLCO to represent an average diffusing capacity of the lung (DL). Because DL distribution in the lung is inhomogeneous, and changes in the DL in diseased lungs may be regional, measuring regional DL, especially during exercise, may be more sensitive in detecting pulmonary vascular diseases. OBJECTIVES: To characterize regional changes in DL in healthy individuals from rest to exercise, and to provide normal references for future studies in pulmonary vascular disorders. METHODS: We reanalyzed DLCO and phase III CH(4) slopes that were obtained during a slow, single exhalation at rest and during exercise in our extended database of 105 healthy individuals. DLCO profiles between 20% and 80% of exhaled vital capacity (VC) (ie, the intrabreath DLCO) were analyzed by calculating the average DLCO measured at midlung volume (ie, 30 to 45% of exhaled VC [DLCOMLV]) and by fitting the whole curve with a third-order polynomial equation. RESULTS: DLCO decreased nonlinearly by approximately 30%, from 20 to 80% of exhaled VC at rest. DLCO during exercise was greater than that at rest, and the increase was similar at all lung volumes. The CH(4) slopes at rest and during exercise were similar. Prediction equations based on regressions on age, sex, and height were computed for resting and exercise DLCOMLV and the phase III CH(4) slope (an index of ventilation distribution). CONCLUSIONS: Capillary recruitment/dilation during exercise in healthy individuals is a uniform process throughout the lungs. Our analyses provide a database for a noninvasive method that can incorporate exercise to evaluate the volume-dependent distribution of DLCO in lung diseases.

Adult↗
PubMed2002

Setting the frequency-tidal volume pattern.

Alveolar (and thus arterial) P(O2) and P(CO2) clearly depend on minute ventilation. However, we need to balance gas exchange goals against the risk of overstretching, especially of the healthier regions of the lung. The plateau pressure is probably the best easily-obtained marker of the risk of stretch in the lung, and a commonly quoted threshold is 30--35 cm H(2)O, the normal maximum transalveolar pressure at total lung capacity. In establishing the proper balance of stretch versus gas exchange, we need to address what levels of pH and P(aO2) we consider acceptable. There are no good data to guide us on the lowest tolerable pH, but 7.2 is commonly quoted in the literature, and 7.15 was the lower limit of acceptability in the ARDS (acute respiratory distress syndrome) Network trial. P(O2) levels as low as 55 mm Hg may be well tolerated, provided there is reasonable oxygen delivery. In distributing the desired minute volume between respiratory frequency and tidal volume (V(T)), a V(T) of 6 mL/kg ideal body weight has been shown to improve ARDS outcome, compared to 12 mL/kg. Thus, 6 mL/kg should be the "start point." Adjustments upward could be considered the plateau pressure is acceptable, in order to improve gas exchange or comfort. Conversely, downward adjustments should be considered if the plateau pressure is high and the gas exchange is acceptable. Frequency is adjusted for the desired minute ventilation. It must be recognized, however, that as frequency (and minute ventilation) increases, the risk of air trapping and intrinsic positive end-expiratory pressure (PEEP) increases. Just like applied PEEP, intrinsic PEEP increases the baseline pressure and stretch upon which the V(T) is delivered. The end-inspiratory stretch increases accordingly. The shape and duration of the flow pattern may affect gas mixing, recruitment, cardiac function, intrinsic PEEP buildup, and patient comfort. It is also conceivable that certain flow patterns can produce an acceleration injury. Although small clinical trials using physiologic end points espouse certain flow patterns, there are no good outcome data at present supporting any particular approach. Some authors suggest that high-frequency ventilation (HFV) might be considered an "ultimate" lung-protective strategy. HFV creates considerable intrinsic PEEP, which, when coupled with sustained inflation maneuvers, can provide substantial alveolar recruitment. In addition, the small V(T) of HFV prevents excessive end-inspiratory distention. Although considerable clinical data support the use of HFV in pediatric patients at risk for ventilator-induced lung injury, there are few data from adults. Whether HFV will prove valuable in well-designed open lung strategies in the adult population still has to be determined.

Carbon Dioxide↗
PubMed2002

Aerosol delivery through an artificial airway.

For both lung and systemic diseases, aerosol delivery of drugs into the lungs can often offer substantial advantages over other routes of administration. In the intensive care unit, however, the artificial airway can be a substantial barrier to aerosol delivery, so clinicians must pay careful attention to the ventilator pattern, the delivery gas humidity/density, the device characteristics, and the circuit/tube properties. When those are optimized, aerosol delivery from a nebulizer or metered-dose inhaler and through an endotracheal tube can begin to approach that seen in a nonintubated patient. Novel approaches, such as generating the aerosol within the airway, offer the opportunity to greatly increase deposition efficiency and focal drug targeting in intubated patients.

Aerosols↗
PubMedDate not supplied

Marital adjustment among patients with chronic obstructive pulmonary disease who are participating in pulmonary rehabilitation.

BACKGROUND: Marital adjustment has been associated with morbidity and mortality across various chronic diseases but has been largely ignored among patients with chronic obstructive pulmonary disease (COPD). PURPOSE: This study was designed to evaluate the relationship among marital adjustment, quality of life, psychologic functioning, and functional capacity among married patients with COPD who are participating in a 5-week exercise rehabilitation program and their spouses. SAMPLE: A convenience sample of 31 patients with COPD and their partners was included. DESIGN: A prospective 1-group pretest-posttest study was conducted. RESULTS: Marital adjustment scores indicated that patients and partners were, on average, satisfied with their marriages. Patient marital adjustment was associated with patient psychologic well-being, whereas partner marital adjustment was associated with patient physical functioning. In addition, patient and partner perceptions of marital adjustment predicted change in patient functioning after exercise rehabilitation. Patients who entered the program with poor marital adjustment experienced a greater magnitude of improvement in mental health after rehabilitation than did well-adjusted patients. CONCLUSIONS: These findings suggest that marital adjustment is associated with both psychologic well-being and physical functioning among patients with COPD, and that it may predict change among patients with COPD participating in exercise rehabilitation.

Adult↗