Ventilation/perfusion ratio

About: Ventilation/perfusion ratio is a research topic. Over the lifetime, 2062 publications have been published within this topic receiving 52745 citations.

Oxygen utilization and ventilation during exercise in patients with chronic cardiac failure.

Abstract: Muscular work requires the integration of cardiopulmonary mechanisms for gas exchange and O2 delivery. In patients with chronic cardiac failure, the response of these mechanisms may be impaired, and the pattern of O2 utilization (VO2) and gas exchange during exercise would thus provide an objective assessment of the severity of heart failure. Accordingly, rates of air flow, O2 uptake, CO2 elimination and minute ventilation were determined during progressive treadmill exercise in 62 patients with stable heart failure. Exercise cardiac output, systemic O2 extraction and lactate production were measured directly in 40 patients with heart failure of varying severity. As the severity of heart failure increased from class A to D, there was a progressive decrease in exercise capacity (from 1157 +/- 154 to 373 +/- 157 seconds) and maximum VO2 (23 +/- 3.2 to 8.4 +/- 1.5 ml/min/kg). These decreases corresponded with the reduced maximum cardiac output and stroke volume during exercise. The appearance of anaerobic metabolism (580 +/- 17 to 157 +/- 7 seconds of exercise) and the corresponding anaerobic threshold (17 +/- 0.34 to 7.1 +/- 1.5 ml/min/kg), determined noninvasively, were reproducible and correlated with the rise in mixed venous lactate concentration. No apparent untoward effects were experienced during or after the progressive exercise test. We conclude that the measurement of respiratory gas exchange and air flow during exercise is an objective, reproducible and safe noninvasive method for characterizing cardiac reserve and functional status in patients with chronic cardiac failure.

Physiology of obesity and effects on lung function.

Abstract: In obese people, the presence of adipose tissue around the rib cage and abdomen and in the visceral cavity loads the chest wall and reduces functional residual capacity (FRC). The reduction in FRC and in expiratory reserve volume is detectable, even at a modest increase in weight. However, obesity has little direct effect on airway caliber. Spirometric variables decrease in proportion to lung volumes, but are rarely below the normal range, even in the extremely obese, while reductions in expiratory flows and increases in airway resistance are largely normalized by adjusting for lung volumes. Nevertheless, the reduction in FRC has consequences for other aspects of lung function. A low FRC increases the risk of both expiratory flow limitation and airway closure. Marked reductions in expiratory reserve volume may lead to abnormalities in ventilation distribution, with closure of airways in the dependent zones of the lung and ventilation perfusion inequalities. Greater airway closure during tidal breathing is associated with lower arterial oxygen saturation in some subjects, even though lung CO-diffusing capacity is normal or increased in the obese. Bronchoconstriction has the potential to enhance the effects of obesity on airway closure and thus on ventilation distribution. Thus obesity has effects on lung function that can reduce respiratory well-being, even in the absence of specific respiratory disease, and may also exaggerate the effects of existing airway disease.

Postoperative recovery of pulmonary function.

Abstract: HE POSTOPERATIVE period is frequently asT sociated with clinically important abnormalities of pulmonary function. Following surgery of the abdominal or thoracic cavities, postoperative changes are invariable and severe with recovery of function delayed for days or weeks. This review summarizes the current knowledge about postoperative pulmonary function, emphasizing recent improvements in the understanding of the etiology of postoperative abnormalities, their prevention, and their treatment. Awareness of postoperative pulmonary dysfunction as a major problem is longstanding. Pasteur (I), in 1910, described lobar collapse of the lung after abdominal operations. His speculation about the etiology of the collapse has proved prophetic: “I feel sure that when the true history of postoperative lung complications comes to be written, active collapse of the lung, from deficiency of inspiratory power, will be found to occupy an important position among determining causes.” The role of shallow breathing, without periodic “sighs” in producing hypoxemia (“anoxemia”) was identified by Haldane et al (2) , in 1919. Beecher’s 1932 classic report (3) of reduced lung volumes after laparotomy signaled the start of attempts to quantitate mechanical lung function changes following surgery. Beecher correctly identified the functional residual capacity (FRC) (“subtidal volume”) as “the most significant of all lung volumes (3).” The appvnpriateness of this designation has become more apparent only recently.

Pulmonary Angiography, Ventilation Lung Scanning, and Venography for Clinically Suspected Pulmonary Embolism with Abnormal Perfusion Lung Scan

Abstract: Inherent contradictions in current diagnostic recommendations for pulmonary embolism have created considerable confusion and controversy. To resolve these contradictions, we did a prospective study of ventilation-perfusion scanning, pulmonary angiography, and venography in consecutive patients with clinically suspected pulmonary embolism and abnormal perfusion scans. Ventilation scanning increased the probability of pulmonary embolism in patients with large perfusion defects and ventilation mismatch, but a ventilation-perfusion match was not helpful in ruling out pulmonary embolism. Small perfusion defects with mismatch had neither sufficiently high nor low probability to be of diagnostic value. The observed frequency of proximal vein thrombosis (19% to 51%) and its association with the range of ventilation-perfusion defects have important implications for management of pulmonary embolism. Pulmonary angiography is required in combination with venography in most patients with perfusion abnormalities because the probability of pulmonary embolism is neither sufficiently high nor low to confirm or exclude pulmonary embolism.