[Analysis of empyrical factors for the determination of cardiac output].

With a method by which no recirculation was possible the area of a dilution curve was obtained. On this basis it was searched what percentage represents the forward triangle of the total surface of the curve. The rôle of the V/F of the sampling system on this portion of the curve was studied, surface from which the empirical constants for the estimation of the cardiac output derivates.

Ventilatory response to low levels of CO2.

Ventilation and Pa(CO2), were measured in six subjects after 10-12 min of breathing 1-2% CO2 during hyperoxia and hypoxia. These inspired CO2 concentrations were achieved in two ways: by enriching the inspirate with CO2 and by having the subjects breathe through dead spaces of 100-400 cm3. Breathing through dead space gave the same results as CO2 enrichment of the inspirate when the effect of the dead spaces on mean inspired CO2 was allowed for.

Regional esophageal pressures with lobar obstruction in dogs.

The right lower lobes (RLL) of intact horizontal dogs were obstructed at FRC during spontaneous breathing and artificial ventilation (IPPB). At end inspiration, pressure within the RLL became less than tracheal pressure, and pressure in the lower esophagus declined to a greater extent than in the upper esophagus. Tidal pressure swings in the obstructed RLL were larger than in the esophagus during spontaneous breathing but smaller during IPPB implying that the elastic recoil of the RLL decreased during inspiration at the mediastinal side.

Regional lung function in pleural effusion.

In 6 seated subjects with small unilateral pleural effusion without other radiographic abnormality, we measured regional lung function using xenon-133, comparing the function of the lung on the side with the effusion to the function on the contralateral side. When both lungs were equilibrated with Xe, count rates were lower at the base with the effusion, indicating either collapse or displacement of lung in these regions. Regional lung expansion was measured as fractions of regional total lung capacity: regional functional residual capacity/regional total lung capacity and regional residual volume/regional total lung capacity.

Regional lung function in spontaneous pneumothorax.

Using xenon-133, we measured regional lung volumes in three seated young men with 25 to 40 per cent pneumothorax. There was no gravitational gradient of regional lung expansion in the lung affected by the pneumothorax. There was no gravitational gradient of regional lung expansion in the lung affected by the pneumothorax, whereas an apex-to-base gradient of regional volume was apparent on the contralateral, normal side.

Comparison of the effects of continuous negative external chest pressure and positive end-expiratory pressure on cardiac index in dogs.

Continuous negative external chest pressure was used to increase the functional residual capacity in 6 dogs, and the effects were compared with the effects of increasing functional residual capacity using positive end-expiratory pressure. Cardiac index and mixed venous O2 stauration each decreased from control values during positive end-expiratory pressure, but did not decrease with continuous negative external chest pressure. Continuous negative external chest pressure may provide an alternative to positive end-expiratory pressure for increasing the functional residual capacity of patients in whom the latter causes unacceptable decreases in venous return and cardiac output.

Occlusion pressure responses in asthma and chronic obstructive pulmonary disease.

During CO2 rebreathing we measured ventilation and the pressure generated during the first 0.1 sec of inspiratory effort against a closed airway (P 0.1) in 12 asthmatics during acute exacerbation, 10 normal subjects, and 10 patients with chronic obstructive pulmonary disease.

Depression of hypoxic ventilatory response by nitrous oxide.

Ventilatory responses to CO2 and hypoxia were measured in four normal volunteers breathing 30-50 per cent N2O with and without added inspiratory resistance. CO2 response was measured by a steady-state technique, hypoxic response by a non-steady-state progressive technique. Added inspiratory resistance depressed ventilatory responses to both CO2 and hypoxia.

Effect of meperidine on occlusion pressure responses to hypercapnia and hypoxia with and without external inspiratory resistance.

In 5 normal subjects we measured ventilation and P0.1, the pressure generated by the first 0.1 sec of inspiratory effort against a closed airway, in response to hypercapnia and hypoxia with and without added inspiratory resistance before and after oral meperidine (1.

Diagnosis of obstruction of the upper and central airways.

Patients with obstruction of the upper airways are often treated for long periods of time for other disorders. Correct diagnosis is important since treatment is quite specific. Such patients may present with a characteristic history and findings on physical examination.

Exercise tolerance at 4 and 6 ATA.

Seven normal male subjects performed 5-min bicycle exercise ranging from 50-100% maximum oxygen uptake at 4 ATA and three were also studied at 6 ATA. At all pressures, the subjects breathed 0.2 ATA O2 plus nitrogen.

Pleural pressure with lobar obstruction in dogs.

The effects of acute lobar obstruction on pleural surface pressure in supine dogs were examined. The right lower lobes (RLL) were obstructed at FRC in some dogs while in others the left lung and RLL were both obstructed at FRC. At the end of the subsequent inspiration, costal surface pressure was less over the obstructed lobe than over the unobstructed right upper lobe.

Effect of negative abdominal pressure on regional lung volumes in supine dogs.

Using 133Xe we measured regional lung volumes from apex to base in supine dogs during the application of negative abdominal pressure (-50 cm H2O). Changes in rib cage shape were monitored with magnetometers. Negative abdominal pressure caused a decrease of 5% in the cross-sectional area of the upper rib cage and a decrease of 19% in the cross-sectional area of the lower rib cage.

Human lung mechanics during water immersion.

We measured lung volumes, static deflation pressure-volume curves of the lung, maximum expiratory flow-volume curves, and closing capacities in five men standing immersed to the neck in water. FRC was decreased 27%, while other lung volumes did not change significantly. At high lung volumes immersion tended to increase lung elastic recoil while recoil was decreased at low lung volumes, changes compatible with vascular congestion.

Chest wall distortion and regional lung volume distribution in erect humans.

Using 133Xe measured the regional distribution of FRC and of boluses administered at FRC in seated subjects during relaxation, lateral compression of the lower rib cage, and contraction of the inspiratory muscles so that mouth pressure was 50 cmH2O subatmospheric. Lateral compression increased apex-to-base differences of volume and bolus distribution, suggesting an increase of the apex-to-base gradient of pleural surface pressure. Changes in rib cage shape were measured with magnetometers and were qualitatively similar to those associated with increases in apex-to-base difference of pleural surface pressure in animals.

Effect of chest strapping on regional lung function.

We studied lung mechanics and regional lung function in five young men during restrictive chest strapping. The effects on lung mechanics were similar to those noted by others in that lung elastic recoil increased as did maximum expiratory flow at low lung volumes. Chest strapping reduced the maximum expiratory flow observed at a given elastic recoil pressure.

Effects of expiratory threshold loading during steady-state exercise.

Increases in functional residual capacity (FRC) decrease inspiratory muscle efficiency; the present experiments were designed to determine the effect of FRC change on the ventilatory response to exercise. Six well-trained adults were exposed to expiratory threshold loads (ETL) ranging from 5 to 40 cmH2O during steady-state exercise on a bicycle ergometer at 40-95% VO2max. Inspiratory capacity (IC) was measured and changes of IC interpreted as changes of FRC.

The effect of lobar obstruction on regional perfusion in the intact dog.

The effect of acute obstruction of the right lower lobes (RLL) on the relative perfusion of different lung regions was studied using Xenon-133 in anesthetized artificially ventilated supine dogs. When the RLL were obstructed at functional residual capacity (FRC) and the rest of the lung was inflated to a transpulmonary pressure of 10 or 20 cm H2O (1 cm H2O = 94.1 N/m2), relative perfusion increased within 10 s to the obstructed lobes by 59 and 92%, respectively.

Effect of inspiratory resistance of occlusion pressure in hypoxia and hypercapnia.

The authors measured ventilation and the mouth pressure developed during the first 0.1 sec of inspiratory effort against a closed airway (P 0.1) in response to normoxic hypercapnia and normocapnic hypoxia, with and without added inspiratory resistance.

Demonstration of airway closure in man.

After partial equilibration of the lung with a N2O gas mixture absorption of N2O by the pulmonary circulation results in a flow of gas into the lungs during breath holding. A bolus of 133Xe introduced at the mouth at the beginning of the breath hold is carried in by the gas flow and distributed according to regional perfusion. In three subjects, breath holding at FRC, apex-to-base distribution of a 133Xe bolud delivered by N2O absorption (Xecar) was similar to that of a bolus injected intravenously (Xeiv).

The early detection of airway obstruction.

To assess the sensitivity of tests for early, small airway obstruction, we selected 52 cigarette smokers with a ratio of 1-sec forced expiratory volume to forced vital capacity greater than 70 per cent from a smoking cessation clinic. From these subjects, 29 of the 46 tested demonstrated frequency dependence of dynamic compliance, a finding arbitrarily defined as indicative of small airway obstruction in this group. Dynamic compliance was correlated with the British Medical Research Council questionnaire, routine pulmonary function tests, closing volume as a per cent of vital capacity, maximal expiratory flow-volume curves, and flow dependence of distribution of inhaled boluses of xenon-133 (finite difference Xe).