Influence of cardiac action on gas mixing in closed-chest dogs.

We performed single-breath tests in closed-chest, paralyzed, and anesthetized dogs (6 with bilateral vagotomy and 6 with intact vagi) with the heart beating and during cardiac arrest. Repeated cardiac arrest was achieved by ventricular fibrillation and subsequent defibrillation. Twenty-four single-breath tests per dog were performed in combinations of three inspiratory volumes (VI; 0.2, 0.5, and 0.8 liter) and four postinspiratory pauses (0, 5, 10, and 30 s), either with or without cardiac arrest. The test gas contained four inert relatively insoluble gases (He, Ne, Ar, and SF6) with a sixfold range in diffusivity. Series dead space (VD) decreased with increasing postinspiratory pause, increasing gas diffusivity, or decreasing VI. In vagotomized animals, VD was smaller with the heart beating than during cardiac arrest, but this relationship was reversed in animals with intact vagi. The decrease in VD due to cardiogenic mixing accounted for only 10.8% of the total decrease in VD occurring during a 30-s postinspiratory pause. The slope of phase III decreased with increasing postinspiratory pause except at VI of 0.2 liter. No significant differences were noted in the slope of phase III between experiments performed with the heart beating or arrested. Tracer gas retained in the residual volume after expiration increased with increasing inspiratory pause. Gas retention was greater for He than for SF6 but was not affected by cardiac action. These findings indicate that cardiac action mainly affects the interface between inspired and alveolar gas and has little effect on mixing in the alveolar compartment.

High-frequency oscillation during simulated altitude exposure.

Ventilatory requirements using high-frequency oscillation (HFO) during simulated altitude exposure were investigated in control dogs and animals with oleic acid-induced lung injury. FIO2 values of 0.21 and 1.0 were supplied by bias flow to the normal and injured dogs, respectively. After a control period, animals were exposed to a simulated altitude of 8,000 ft (barometric pressure 564 torr), followed by a second control period at ground level. Both experimental groups had similar values of PaCO2 at ground level and during exposure to reduced barometric pressure. The tidal volume necessary to maintain eucapnia was higher in oleic acid-injured animals compared with the control group; cardiac output and functional residual capacity were lower. The alveolar-arterial oxygen difference was substantially larger in the oleic acid group. Adequate gas exchange can be maintained with HFO during exposure to altitude provided that ventilation and inspired PO2 are not reduced below normobaric levels.

Role of molecular diffusion in conventional and high frequency ventilation.

The influence of molecular diffusion on gas-mixing during conventional mechanical ventilation (CMV) and high frequency ventilation (HFV) was studied by observing the wash-in of six poorly soluble, inert gases in arterial blood. Anesthetized dogs were ventilated either with CMV or HFV. Following a step change in inspired gas composition, the increase in arterial concentrations of hydrogen, helium, methane, ethane, isobutane, and sulfur hexafluoride was determined by gas chromatography. The relative gas diffusivities encompassed a range of almost one order of magnitude. Propane, present in inspired gas during both the control and wash-in phases, served as an internal reference for calculation of blood tracer concentrations. The wash-in of all six inert gases followed a single exponential time course during both CMV and HFV. The rate of wash-in of each gas decreased with increasing molecular weight (MW). The relationship of rate constants to a measure of relative diffusivity (MW-0.5) was significantly different than zero for both types of ventilation. The slope of this relationship was three times larger for CMV than HFV, indicating that molecular diffusion has a greater role in gas mixing during ventilation with large tidal volumes. Diffusion has a minor role in gas mixing during high frequency ventilation with small tidal volumes. Demonstration of the presence of gas separation secondary to molecular diffusion during HFV is enhanced by measuring wash-in, rather than wash-out, of inert gases because gas separation is likely to be obscured as exhaled gases pass through the well-mixed central airways during gas wash-out.

Ventilatory criteria for aeromedical evacuation.

Ventilatory requirements during simulated aeromedical transportation were investigated in normal dogs and animals with oleic acid-induced lung injury. Inspired oxygen fractions of 0.21 and 1.0 were used to ventilate the normal and injured dogs, respectively. Both groups were ventilated with a constant-volume piston ventilator. After a control period, animals were exposed to a simulated altitude of 8,000 ft (barometric pressure 564 mm Hg), followed by a second control period at ground level. Both groups of animals had no change in carbon dioxide production, arterial PCO2 or ventilation during exposure to reduced barometric pressure. Systemic blood pressure, heart rate, cardiac output, and lung volume were all lower in oleic acid-injured animals than controls; the alveolar-arterial oxygen difference was larger in the oleic acid group. With altitude exposure, arterial and mixed venous oxygen tensions were decreased in both groups. Adequate gas exchange can be maintained during exposure to altitude even in animals with abnormal function provided that ventilation is constant and the inspired oxygen fraction is increased to compensate for the reduced barometric pressure.

Air transportation of patients with acute respiratory failure: theory.

Adult respiratory distress syndrome (ARDS) that results from severe trauma often occurs in remote places, making it necessary to transport the patients to tertiary medical facilities by air. Since these severely hypoxic patients are exposed to additional risk of reduced inspired oxygen tension due to decreased barometric pressure, the feasibility of transportation of these patients was investigated by computer analysis. Mathematical models of pulmonary gas exchange in patients with ARDS were developed to calculate arterial and mixed venous blood tensions while breathing room air and oxygen at sea level, 8,000 ft, and 40,000 ft. Under each condition the following parameters were varied: alveolar ventilation (VA), cardiac output (Q), metabolic rate (VO2), hematocrit (Hcrit), and membrane diffusing capacity for oxygen (DmO2). Most of the gas exchange problems at altitude could be overcome by breathing oxygen as long as cardiac output and hematocrit were adequate. Hypoxemia in ARDS patients will not be greatly affected by the reduced inspired oxygen tensions at altitude in much the same way that hypoxemia in ARDS is poorly responsive to increased inspired oxygen tensions at sea level.

Effectiveness of a new oxygen demand valve in chronic hypoxemia.

The purpose of this study was to compare the efficacy of nasal oxygen delivery by an inspiratory demand valve, which delivers oxygen only during the inspiratory phase, to standard continuous flow oxygen. The inspiratory demand valve attaches to an oxygen source and delivers oxygen after the sensor detects negative pressure through a standard nasal cannula. Seventeen male patients with chronic hypoxemia secondary to COPD were studied under resting conditions. Nine patients with hypoxemia at rest or with exercise were studied using an exercise protocol. Oxygen was delivered at a flow rate which improved the oxygen saturation by 4 percent. Oxygen saturation was measured continuously by an ear oximeter. The results indicate that oxygen saturation was not significantly different for either method of oxygen delivery at rest or during exercise. The time oxygen was delivered was significantly reduced during demand valve use, being 55 percent less at rest and 52 percent less during exercise when compared to continuous oxygen. Further study would be helpful to determine whether the device would reliably deliver oxygen during continuous use and whether it could be adapted to portable systems.

Oxygen-related intrapulmonary shunting in obstructive pulmonary disease.

A simple and previously validated double-indicator technique was used to quantitate shunt in patients with obstructive pulmonary disease at rest, during exercise, and during breathing of 100 percent oxygen. The method avoids several inherent difficulties encountered in previous double-indicator techniques and is independent of the fraction of oxygen in the inspired gas. Sixteen resting patients with mild obstructive pulmonary disease were found to have intrapulmonary shunting less than or equal to 0.7 percent of the cardiac output (mean, 0-3 +/- 0.2 percent [SD]). During submaximal exercise, shunting was also low (mean, 0.3 +/- 0.1 percent of cardiac output). After breathing pure oxygen for 30 minutes, 11 patients had similar results; however, in four patients, breathing 100 percent oxygen caused an increase intrapulmonary shunting to 1 to 6 percent of the cardiac output. It is concluded that some patients with obstructive pulmonary disease develop intrapulmonary shunting in response to breathing oxygen.

Extrinsic allergic alveolitis after Aspergillus fumigatus inhalation. Evidence of a type IV immunologic pathogenesis.

Three weeks after a massive inhalation of mold present on infected oats, a farmer's wife had extrinsic allergic alveolitis. Aspergillus fumigatus was cultured from the moldy oats and from deep bronchial washings obtained at fiberoptic bronchoscopy. Spores and hyphae characteristic of Aspergillus species were demonstrated within granulomas in the pulmonary tissue obtained by transbrochial biopsy. Serum precipitins, delayed (48 hour) cutaneous hypersensitivity and in vitro lymphocyte transformation to A. fumigatus were demonstrated. The findings in this case suggest that a type IV immunologic response and subsequent (lymphocyte-mediated) tissue inflammation may underlie the pathogenesis of this and other forms of hypersensitivity pneumonitis.

Metastatic renal cell carcinoma 24 years after nephrectomy.

Recurrence of renal carcinoma 20 years after primary resection is uncommon. A patient is reported in whom two pulmonary metastases developed 24 years following nephrectomy for renal carcinoma. After a left lower lobectomy and a right pulmonary wedge resection were performed, he survived an additional two years before dying from metastatic disease.