Short-life radionuclides and regional lung function

Ventilation/Perfusion Relationships and Gas Exchange: Measurement Approaches

Ventilation-perfusion ( V ˙ A / Q ˙ ) matching, the regional matching of the flow of fresh gas to flow of deoxygenated capillary blood, is the most important mechanism affecting the efficiency of pulmonary gas exchange. This article discusses the measurement of V ˙ A / Q ˙ matching with three broad classes of techniques: (i) those based in gas exchange, such as the multiple inert gas elimination technique (MIGET); (ii) those derived from imaging techniques such as single-photon emission computed tomography (SPECT), positron emission tomography (PET), magnetic resonance imaging (MRI), computed tomography (CT), and electrical impedance tomography (EIT); and (iii) fluorescent and radiolabeled microspheres. The focus is on the physiological basis of these techniques that provide quantitative information for research purposes rather than qualitative measurements that are used clinically. The fundamental equations of pulmonary gas exchange are first reviewed to lay the foundation for the gas exchange techniques and some of the imaging applications. The physiological considerations for each of the techniques along with advantages and disadvantages are briefly discussed. © 2020 American Physiological Society. Compr Physiol 10:1155-1205, 2020.

Tomography of regional ventilation and perfusion using krypton 81m in normal subjects and asthmatic patients

Single photon emission computed tomography, a rotating gamma camera, and continuous inhalation or infusion of krypton 81m (half life 13 seconds) were used to measure regional ventilation (V), perfusion (Q), and ventilation-perfusion (V/Q) ratios in five normal subjects in supine, prone, and lateral decubitus postures and in three asthmatic patients (supine posture only) before and after inhalation of 2.5 mg nebulised salbutamol. Vertical and horizontal gradients of V, Q, and V/Q were examined at three levels in each lung in regions of 1.9 cm3 size. In normal subjects V and Q increased along the axis of gravity in all postures and at all levels in the lung except for V in the prone position. Smaller horizontal gradients were found with an increase in V and Q from caudal to cranial--again except in the prone posture, where the gradient was slightly reversed. Constraint to outward motion of the ventral chest and abdominal wall is the most likely explanation for the different behaviour in the prone posture. In chronic asthma the vertical gradients of V and V/Q were the reverse of normal, but the Q gradient was normal. Bronchodilator treatment did not affect the vertical or horizontal gradients significantly, but analysis of individual regions showed that, relatively, V/Q worsened in 42% of them; this was associated in two thirds with an increase in fractional Q. After inhalation of beta agonist local vasodilatation may influence V/Q ratios in some units more than bronchodilatation.

Regional lung ventilation in ankylosing spondylitis

Patients with ankylosing spondylitis (AS) sometimes develop apical lung fibrosis and cavitation. It has been suggested that one causative factor is reduced apical ventilation due to rigidity of the thoracic cage. We measured regional ventilation in 27 patients with AS and 18 normal volunteers. Twelve patients (Group A) had chest expansion greater than 2 cm, twelve (Group B) had chest expansion of 2 cm or less and three (Group C) had apical lung lesions on chest radiographs; patients in Groups A and B had no radiographic lung lesions. Ventilation per unit volume (VE/VA min-1) was calculated from 81Krm washout curves. The ratio of upper zone to lower zone ventilation (VR) was calculated. VR in Group A (0.74 +/- 0.11) and group B (0.75 +/- 0.12) was not significantly different from VR in controls (0.76 +/- 0.08). There was no significant correlation between VR and FVC, FEV1 or maximal chest expansion. In patients with apical fibrosis only the radiographically abnormal areas had reduced ventilation. Patients with AS do not underventilate the upper zones of the lungs except in the presence of radiographically visible fibrosis.

Single-exhalation method for study of lobar and segmental lung function by mass spectrometry in man

A single-exhalation method, based on a modification of the conventional single-breath technique, was applied to study lung function in normal subjects during fiberoptic bronchoscopy. After a single inspiration of a test gas mixture (1% He, 1% C2H2, 0.07% C18O in air), the test gas concentrations were continuously monitored during subsequent slow exhalation, using a respiratory mass spectrometer that sampled either at the lips (Whole-lung test) or, through the bronchoscope, at various sites within the bronchial tree (Regional test). Changes in concentrations of the test gases with time allowed estimation of alveolar ventilation (Va), blood flow (Q), and diffusing capacity (DLCO), per unit accessible lung volume (Va). In the Whole-lung test, both DLCO and Q agreed closely with values obtained in the same subject by a rebreathing method. No differences were observed between the upright and the lateral decubitus positions. In teh Regional test, VA/VA, DLCO/VA and Q/VA were larger in the dependent than in the upper lung, when sampling was from the main bronchi in the lateral decubitus positions. Sampling from lobar bronchi in the upright position revealed an increase from top to bottom in VA/VA, DLCO/CA and Q/VA, this being most marked for Q. These results are compatible with the regional variations that have been shown by radioactive techniques and have been attributed to gravitational forces. The method appears to be suitable for the study of lobar and segmental lung function in patients with lung disease.

Scintigraphic evaluation of regional pulmonary ventilation

Radioactive gases are useful for evaluating pulmonary ventilation because they allow assessment of regional lung function in a physiologic, noninvasive manner. The most widely used radioactive gases are Xe-133, Xe-127, and Kr-81m. These gases provide visual and/or quantitative assessments of regional ventilation or ventilation-perfusion matching in obstructive airways disease, and aid the scintigraphic diagnosis of pulmonary embolism. The precision of ventilation scintigraphy is limited by detector resolution, signal distortion at depth, poor counting statistics, and respiratory motion.